DRESSING APPARATUS, DRESSING METHOD, AND METHOD OF MANUFACTURING DEVICE CHIPS

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an apparatus for and a method of dressing grindstones, and a method of manufacturing device chips using the dressing apparatus and method.

Description of the Related Art

Device chips that incorporate devices such as integrated circuits (ICs) are indispensable components in various electronic appliances such as cellular phones and personal computers, for example. The device chips are fabricated according to a sequence of steps of thinning down a semiconductor wafer with a plurality of devices constructed in a face side thereof and then dividing the semiconductor wafer to separate areas thereof that include the respective devices.

A semiconductor wafer as a workpiece is thinned down by a grinding apparatus, for example. The grinding apparatus thins down the workpiece by grinding its reverse side that is free of devices. The grinding apparatus includes a chuck table for holding the workpiece with its face side facing downwardly toward the chuck table and a vertical spindle on which a grinding wheel having grindstones is mounted. The grinding wheel is of an annular shape with the grindstones attached to its lower surface. The spindle has a lower end to which the grinding wheel is fixed and is rotatable about its central axis in unison with the grinding wheel.

Each of the grindstones secured to the grinding wheel is made of abrasive grains bound together by a bonding material. The bonding material includes a vitrified bond containing air bubbles or a resin bond, for example. The abrasive grains that are made of diamond or cubic boron nitride are dispersed in the bonding material, making up the grindstone.

The grinding apparatus thins down the workpiece, i.e., the semiconductor wafer, as follows.

The workpiece is placed on an upper surface of the chuck table that acts as a holding surface. The workpiece is held on the chuck table such that the face side of the workpiece where the devices are present faces downwardly toward the holding surface of the chuck table. In other words, the workpiece is held on the chuck table with its reverse side free of the devices being exposed upwardly.

The grinding wheel with the grindstones attached to its lower surface is positioned above the workpiece whose reverse side faces upwardly. The grinding wheel mounted on the spindle and the chuck table holding the workpiece start to rotate about their respective vertical axes. While the grinding wheel and the chuck table are rotating, the chuck table and the spindle are moved vertically toward each other. The grindstones on the lower surface of the rotating grinding wheel and the reverse side of the workpiece on the holding surface of the chuck table come into abrasive contact with each other, whereupon the abrasive grains exposed on lower surfaces of the grindstones grind the reverse side of the workpiece.

The abrasive grains continuously grind the reverse side of the workpiece while the chuck table and the spindle are moving vertically toward each other, thereby removing a layer of the reverse side of the workpiece and hence thinning down the workpiece by the predetermined thickness.

The grinding step as it goes on produces swarf from the workpiece and the grindstones, and the swarf is deposited on the grinding surfaces of the grindstones, tending to load the grindstones. In order for the grindstones to grind the workpiece without fail, some of the abrasive grains are required to be exposed from the bonding material on the grinding surfaces of the grindstones that contact the workpiece. The swarf deposited on the grinding surfaces is likely to be stuck between the exposed abrasive grains and makes the abrasive grains less exposed than they should. In addition, as the grindstones repeatedly grind workpieces, the abrasive grains exposed on the grinding surfaces of the grindstones are worn off or dulled over time.

For eliminating loading and dulling of the grindstones to recover their grinding capability, it is customary to scrape the grinding surfaces of the grindstones at appropriate timings to sharpen the grindstones for better grinding. Such a step is referred to as dressing (see, for example, JP 2021-121464A).

Although the grinding capability of grindstones mounted on the lower surface of a grinding wheel can be recovered by replacing the grinding wheel with another grinding wheel, the grinding surfaces of the grindstones on the replacing grinding wheel may have their positions or heights varied among themselves. In a case where the grinding surfaces of the grindstones vary in position, a dressing step is effective to align the positions of the grinding surfaces with each other.

The grindstones are dressed as follows. First, a dresser board is positioned below the grinding wheel mounted on the spindle. The dresser board is similar in nature to grindstones in that it includes abrasive grains that are hard enough to grind at least the bonding material of the grindstones, for example.

Then, while the dresser board and the grinding wheel are rotating respectively about their central axes, the dresser board and the spindle are vertically brought toward each other to bring the grinding surfaces of the grindstones and the upper surface of the dresser board into abrasive contact with each other. When the grindstones and the dresser board slide abrasively against each other, the upper surface of the dresser board is ground by the abrasive grains that are exposed on the grinding surfaces of the grindstones and the grinding surfaces of the grindstones are ground by the abrasive grains that are exposed on the upper surface of the dresser board.

SUMMARY OF THE INVENTION

During the dressing step described above, it is desirable to appropriately control the relative movement of the dresser board and the grindstones in vertical directions, i.e., directions transverse to the directions along which the grindstones and the dresser board slide abrasively against each other, and the loads applied to the dresser board and the grindstones.

While the dresser board is dressing the grindstones, the dresser board and the grindstones are required to be pressed against each other under suitable forces. If the forces are too weak or the dresser board and the grindstones are not held in contact with each other, then the dresser board is unable to dress the grindstones smoothly. If the forces are too strong, then the dresser board and the grindstones are likely to be worn too much and consumed too early.

When the dresser board starts to dress the grindstones, it is necessary to move the dresser board and the grindstones closely toward each other. If the relative speed at which the dresser board and the grindstones move relatively to each other is too small, then it takes a long period of time to start dressing the grindstones, possibly adversely affecting the productivity, i.e., efficiency with which to dress the grindstones with the dresser board. On the other hand, if the relative speed is too large, then the dresser board and the grindstones are liable to impinge upon each other.

It is therefore an object of the present invention to provide a dressing apparatus, a dressing method, and a method of manufacturing device chips that are capable of appropriately controlling loads applied between a dresser board and grindstones at the time the dresser board and the grindstones move relatively to each other in directions transverse to the plane along which the grindstones and the dresser board slide abrasively against each other, i.e., at the time the dresser board dresses the grindstones.

In accordance with an aspect of the present invention, there is provided a dressing apparatus for dressing grindstones that grinds a workpiece by causing the grindstones and a dresser board to slide abrasively against each other, the dressing apparatus including a board holder for holding the dresser board, a moving mechanism for moving the board holder and the grindstones relatively to each other in a direction transverse to a plane along which the grindstones abrasively slide against the dresser board, and a measuring instrument for detecting a load applied to the dresser board.

In accordance with the aspect of the invention, preferably, the moving mechanism includes a mechanism for moving the board holder with respect to the grindstones, and the dressing apparatus further includes a measurement reference marker disposed in a path along which the dresser board is to be moved by the moving mechanism.

In accordance with the aspect of the invention, preferably, the moving mechanism includes an actuator for moving the board holder with respect to the grindstones, and the dressing apparatus further includes a guide for limiting movement of the board holder in directions transverse to the directions in which the actuator moves the board holder.

In accordance with the aspect of the invention, preferably, the dressing apparatus further includes a workpiece holder for holding the workpiece and a grinding actuator on which there is mounted a grinding wheel rotatable about its central axis, the grindstones being mounted on the grinding wheel, in which the grinding wheel is rotated to rotate the grindstones and the grinding actuator is operated to bring the grindstones into contact with the workpiece held by the workpiece holder thereby to grind the workpiece, and the grinding wheel is rotated to rotate the grindstones and the grinding actuator is operated to bring the grindstones into contact with the dresser board held by the board holder thereby to dress the grindstones.

In accordance with the aspect of the invention, preferably, the grinding wheel is rotated to rotate the grindstones and the grinding actuator is operated to bring the grindstones into contact with the dresser board thereby to dress the grindstones irrespectively of whether the grindstones are not grinding the workpiece or the grindstones are grinding the workpiece held by the workpiece holder.

In accordance with the aspect of the invention, the dressing apparatus further includes a liquid supply nozzle for supplying a liquid to the dresser board held by the board holder.

In accordance with the aspect of the invention, the dressing apparatus further a cleaning nozzle for supplying a fluid to the grindstones, in which the grinding wheel, the workpiece holder, and the board holder are disposed such that a path followed by the grindstones rotated by the grinding wheel when the grinding wheel is rotated overlaps a portion of the workpiece held by the workpiece holder and overlaps a portion of the dresser board held by the board holder as viewed in a direction transverse to a plane along which the grindstones are rotated, and the cleaning nozzle is disposed to supply the fluid at a position out of contact with the workpiece held by the workpiece holder and the dresser board held by the board holder on the path followed by the grindstones as viewed in the direction transverse to the plane along which the grindstones are rotated.

In accordance with another aspect of the present invention, there is provided a dressing method of dressing grindstones for grinding a workpiece, using a dressing apparatus including a board holder for holding a dresser board, in which the dressing apparatus causes the dresser board held by the board holder and the grindstones to slide abrasively against each other, the dressing method including dressing the grindstones, using the dressing apparatus by measuring a load applied to the dresser board and pressing the board holder and the grindstones against each other in a direction transverse to a plane along which the grindstones and the dresser board slide abrasively against each other such that the measured load applied to the dresser board has a value falling within a predetermined numerical range.

In accordance with the other aspect of the present invention, the dressing apparatus further includes a moving mechanism for moving the board holder with respect to the grindstones in the direction transverse to the plane along which the grindstones and the dresser board slide abrasively against each other, and a measurement reference marker disposed in a path followed by the dresser board when the board holder is moved by the moving mechanism, and the dressing method further includes moving the board holder by the moving mechanism and recording information about a position of the board holder at the time the dresser board held by the board holder and the measurement reference marker contact each other, and controlling the distance that the board holder is moved by the moving mechanism on the basis of the recorded information about the position of the board holder.

In accordance with the other aspect of the present invention, the dressing apparatus further includes a moving mechanism for moving the board holder with respect to the grindstones in the direction transverse to the plane along which the grindstones and the dresser board slide abrasively against each other, and the dressing method further includes moving the board holder by the moving mechanism and recording information about the position of the board holder at the time the board holder or the dresser board held by the board holder and the grindstones contact each other, and controlling the distance that the board holder is moved by the moving mechanism on the basis of the recorded information about the position of the board holder.

In accordance with the other aspect of the present invention, the grindstones are dressed by using the dressing apparatus by either bringing the dresser board into contact with the grindstones while the grinding stones are grinding the workpiece or by bringing the dresser board into contact with the grindstones while the grinding stones are not grinding the workpiece.

In accordance with a further aspect of the present invention, there is provided a method of manufacturing device chips by dividing a workpiece, including dressing grindstones for grinding a workpiece, using a dressing apparatus including a board holder for holding a dresser board, in which the dressing apparatus causes the dresser board held by the board holder and the grindstones to slide abrasively against each other, grinding the workpiece by the grindstones dressed by using the dressing apparatus or grinding the workpiece by the grindstones while simultaneously the grindstones are being dressed by using the dressing apparatus, and after the workpiece is ground, dividing the workpiece into device chips, in which the grindstones are dressed by using the dressing apparatus by measuring a load applied to the dresser board, and pressing the board holder and the grindstones against each other in a direction transverse to a plane along which the grindstones and the dresser board slide abrasively against each other such that the measured load applied to the dresser board has a value falling within a predetermined numerical range.

In accordance with the further aspect of the present invention, the workpiece is divided along division initiating points formed in the workpiece into the device chips.

With the dressing apparatus, the dressing method, and the method of manufacturing device chips according to the respective aspects of the invention, it is possible to appropriately control the load applied between the dresser board and the grindstones when the dresser board and the grindstones are moved relatively to each other in the direction transverse to the plane along which the dresser board and the grindstones slide abrasively against each other to dress the grindstones or when the grindstones are dressed by the dresser board by measuring the load applied to the dresser board.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly in block form, schematically illustrating a central portion of a dressing apparatus according to an embodiment of the present invention;

FIG. 2 is a perspective view schematically illustrating a dressing assembly of the dressing apparatus;

FIG. 3 is a front elevational view of the dressing assembly illustrated in FIG. 2;

FIG. 4 is a sectional side-elevational view taken along line IV-IV of FIG. 3;

FIG. 5 is an enlarged fragmentary cross-sectional view, partly in elevation, of a central portion of a moving mechanism of the dressing assembly illustrated in FIG. 2;

FIG. 6 is a front elevational view, partly in cross section, illustrating a positional relation between a grindstone handler, a workpiece handler, and the dressing assembly;

FIG. 7 is a plan view illustrating the positional relation between the grindstone handler, the workpiece handler, and the dressing assembly;

FIG. 8 is a flowchart of a processing sequence of a dressing method and a method of manufacturing device chips according to the embodiment;

FIG. 9 is a side elevational view schematically illustrating the positional relation between the grindstone handler, the workpiece handler, and the dressing assembly in a board thickness detecting step;

FIG. 10 is a side elevational view schematically illustrating the positional relation between the grindstone handler, the workpiece handler, and the dressing assembly in a grindstone thickness detecting step; and

FIG. 11 is a side elevational view, partly in cross section, schematically illustrating a dividing step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A dressing apparatus, a dressing method, and a method of manufacturing device chips according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. First, the dressing apparatus will be described below. The dressing apparatus according to the present embodiment is combined as a dressing function with a grinding apparatus, or stated otherwise, functions as a part of a grinding apparatus that dresses grindstones of the grinding apparatus. According to the present invention, however, the dressing apparatus may be separate from and independent of a grinding apparatus that includes grindstones to be dressed by the dressing apparatus.

FIG. 1 schematically illustrates, in perspective view, partly in block form, a central portion of the dressing apparatus. FIGS. 2 through 4 schematically illustrate, respectively in perspective, front elevation, and sectional side elevation, a dressing assembly of the dressing apparatus illustrated in FIG. 1. In FIG. 4, some components including a power transmitting belt 36 and guides 42 are omitted from illustration for the sake of brevity.

As illustrated in FIG. 1, the dressing apparatus 2 includes a grindstone handler 4, a workpiece handler 6, and a dressing assembly 8.

The grindstone handler 4 includes a spindle 10 as a grinding actuator and a moving mechanism 12 for moving the spindle 10 in vertical directions or Z-directions.

The spindle 10 includes a substantially cylindrical member extending along its central axis in vertical directions or Z-directions and rotatable about the central axis. The spindle 10 has a lower end on which a grinding wheel 14 is mounted. The grinding wheel 14 is securely attached to the lower end of the spindle 10 in axial alignment with the spindle 10. When the spindle 10 is rotated about its vertical central axis by an electric motor, not depicted, coupled to the spindle 10, the grinding wheel 14 is also rotated in unison with the spindle 10 in a horizontal plane or an XY-plane about a central axis thereof aligned with the vertical central axis of the spindle 10.

The terms “vertical” and “horizontal” used herein mean not only strictly vertical and horizontal, but also substantially vertical and horizontal, covering slight deviations such as inclinations and curvatures from strictly vertical and horizontal directions. The vertical directions and the horizontal plane are also referred to as “Z-directions” and “XY-plane” respectively herein.

The grinding wheel 14 refers to a disk-shaped component with a plurality of grindstones 16 attached thereto. The grindstones 16 are arranged in an annular array on a lower surface of the grinding wheel 14. The grinding wheel 14 is mounted on the lower end of the spindle 10 such that the lower surface of the grinding wheel 14 on which the grindstones 16 are disposed face downwardly.

The moving mechanism 12 includes a mechanism for moving the grindstones 16 and a workpiece 18 to be ground thereby relatively to each other in vertical directions or Z-directions transverse to the plane along which the grindstones 16 and the workpiece 18 slide abrasively against each other at the time the grindstones 16 grind the workpiece 18. The moving mechanism 12 also functions as a mechanism for moving the grindstones 16 and a dresser board 24 for dressing the grindstones 16 relatively to each other in vertical directions or Z-directions transverse to the plane along which the grindstones 16 and the dresser board 24 slide abrasively against each other at the time the grindstones 16 are dressed by the dresser board 24.

The moving mechanism 12 includes a ball screw, not depicted, extending in vertical directions and a stepping motor, not depicted, for rotating the ball screw about its vertical central axis. When the stepping motor is energized, it rotates the ball screw to move the spindle 10 upwardly or downwardly in the vertical directions. According to the present invention, the moving mechanism 12 is not restricted to the structural details described above, but may be any of various mechanisms for moving the spindle 10, i.e., the grinding actuator, vertically.

According to the present embodiment, the moving mechanism for moving the grindstones 16 and the workpiece 18 relatively to each other in vertical directions or Z-directions is illustrated as a mechanism for moving the spindle 10, i.e., the grindstones 16, toward and away from the workpiece 18. Alternatively, or additionally, the moving mechanism may include a mechanism for moving the workpiece 18 toward and away from the spindle 10.

According to the present embodiment, furthermore, the moving mechanism for moving the grindstones 16 and the dresser board 24 relatively to each other in vertical directions or Z-directions includes, in addition to the moving mechanism 12 for moving the grindstones 16, i.e., the spindle 10, a moving mechanism 30 (see FIG. 2) for moving the dresser board 24 in the dressing assembly 8. The structure and function of the moving mechanism 30 will be described in detail later.

As illustrated in FIG. 1, the workpiece handler 6 includes a chuck table 20 as a workpiece holder for holding the workpiece 18 and a support table 22 that supports the chuck table 20 thereon.

The workpiece 18 includes, for example, a disk-shaped wafer made of a semiconductor material such as silicon. However, the workpiece 18 is not limited to any particular materials, shapes, structures, sizes, kinds, and uses. For example, the workpiece 18 may include a wafer made of GaAs, InP, GaN, or SiC, glass, ceramic, resin, or metal. Moreover, the workpiece 18 may include an object other than a wafer, e.g., any of various objects that can be ground by the grindstones 16.

The chuck table 20 as the workpiece holder has an upper surface as a holding surface 20a for holding the workpiece 18 by attracting the lower surface of the workpiece 18 under suction. The chuck table 20 houses therein a mechanism, not depicted, for developing a negative pressure between the holding surface 20a and the object thereon to attract the lower surface of the workpiece 18 under suction.

The support table 22 includes a rotary table with the chuck table 20 mounted on an upper surface thereof. The support table 22 is rotatable about an axis along vertical directions or Z-directions. The support table 22 may additionally be movable upwardly and downwardly along vertical directions or Z-directions.

The chuck table 20 is disposed on the support table 22 at a position offset from the axis about which the support table 22 is rotatable. In other words, when the support table 22 is rotated, the chuck table 20 is angularly moved in a horizontal plane, i.e., an XY-plane, with respect to the spindle 10 and the grinding wheel 14 of the grindstone handler 4.

The chuck table 20 is rotatably supported on the support table 22 for rotation about its central axis along vertical directions or Z-directions.

As illustrated in FIGS. 1 through 4, the dressing assembly 8 includes a chuck table 26 as a board holder for holding the dresser board 24, a support table 28 that supports the chuck table 26 thereon, the moving mechanism 30 for moving the chuck table 26 and the support table 28 along vertical directions, i.e., Z-directions, with respect to the grinding wheel 14 and the grindstones 16, and an auxiliary support 38 that supports the support table 28 thereon.

The support table 28 refers to a table that is supported by the auxiliary support 38 and that is movable upwardly and downwardly along vertical directions, i.e., Z-axis directions. According to the illustrated embodiment, the support table 28 is in the form of a plate lying along a horizontal plane, i.e., an XY-plane. The auxiliary support 38 and the moving mechanism 30 will be described in detail later.

The chuck table 26 as the board holder includes a main portion protruding upwardly from the support table 28 and having an upper surface as a holding surface 26a. A seal unit 32 is disposed on a lower side of the support table 28 that is opposite the chuck table 26 across the plane of the support table 28. The seal unit 32 interconnects the chuck table 26 and an external negative pressure source, not depicted, for developing and applying a negative pressure to an object such as the dresser board 24 placed on the holding surface 26a of the chuck table 26.

The seal unit 32 includes a nonrotatable lower structure and a rotatable upper structure rotatably coupled to the nonrotatable lower structure for rotation about its central axis along vertical directions. The chuck table 26 is coupled to an upper portion of the rotatable upper structure, so that the chuck table 26 will be rotated about its central axis with respect to the support table 28 when the rotatable upper structure is rotated about its central axis.

The seal unit 32 has a fluid channel, not depicted, defined therein that is fluidly connected to the inside of the chuck table 26. The fluid channel extends through the nonrotatable lower structure and the rotatable upper structure. The fluid channel extends through the junction between the nonrotatable lower structure and the rotatable upper structure via a joint including a magnetic fluid and an O-ring, not depicted, that keep the fluid channel hermetically sealed at the junction while allowing the rotatable upper structure to rotate with respect to the nonrotatable lower structure.

The fluid channel in the nonrotatable lower structure has a lower end of the seal unit 32 connected through a tube to the external negative pressure source, not depicted. A positive pressure source, not depicted, is also fluidly connected to the tube via a valve.

The negative pressure source includes an ejector, for example, whereas the positive pressure source includes a mechanism for supplying compressed air, for example. The valve operates to fluidly connect the fluid channel in the seal unit 32 selectively to the negative pressure source and the positive pressure source.

When the fluid channel in the seal unit 32 is fluidly connected to the negative pressure source by the valve, the negative pressure from the negative pressure source is applied to the inside of the chuck table 26, attracting the dresser board 24 under suction to the holding surface 26a. When the fluid channel in the seal unit 32 is fluidly connected to the positive pressure source by the valve, the compressed air from the positive pressure source is supplied to the inside of the chuck table 26, blowing air from the holding surface 26a to dislodge the dresser board 24 easily from the chuck table 26.

The main portion of the chuck table 26 that protrudes upwardly from the support table 28 and has the holding surface 26a is rotatable about its central axis along vertical directions with respect to the support table 28. A servomotor 34 is disposed on the lower side of the support table 28 as a rotary actuator for rotating the main portion of the chuck table 26.

The servomotor 34 and the chuck table 26, i.e., the upper portion of the rotatable upper structure, are operatively connected to each other by an endless belt 36 as a rotary power transmitting member beneath the support table 28. When the servomotor 34 is energized, it generates rotary power that is transmitted through the endless belt 36 to the chuck table 26, rotating the chuck table 26 together with the dresser board 24 held on the holding surface 26a.

A foundation base 40 as a bottom plate of the dressing assembly 8 is positioned below the support table 28. The foundation base 40 is in the form of a plate lying along a horizontal plane, i.e., an XY-plane and is placed on a floor within the dressing apparatus 2 to provide a structural basis for the dressing assembly 8.

The moving mechanism 30 and the auxiliary support 38, each extending along vertical directions or Z-directions, are disposed between and attached to the support table 28 and the foundation base 40 that are disposed respectively in upper and lower positions. The support table 28 and the foundation base 40 are coupled to each other by the moving mechanism 30 and the auxiliary support 38.

The auxiliary support 38 includes a fluid pressure cylinder such as an air cylinder, for example. The auxiliary support 38 can be selectively extended and contracted in vertical directions by the pressure of a fluid supplied thereto to apply loads in the vertical directions to objects coupled to respective opposite ends thereof in the vertical directions, i.e., the support table 28 and the foundation base 40.

The auxiliary support 38 as the fluid pressure cylinder is disposed between and attached to the support table 28 and the foundation base 40 while being extendible and contractible in the vertical directions. The moving mechanism 30 also includes a fluid pressure cylinder such as an air cylinder, for example.

The moving mechanism 30 can be selectively extended and contracted in vertical directions by the pressure of a fluid supplied thereto to apply loads in the vertical directions to objects coupled to respective opposite ends thereof in the vertical directions, i.e., the support table 28 and the foundation base 40.

The moving mechanism 30 as the fluid pressure cylinder is disposed between and attached to the support table 28 and the foundation base 40 while being extendible and contractible in the vertical directions.

The auxiliary support 38 as the fluid pressure cylinder is extendible and contractible on its own and is also extendible and contractible by the moving mechanism 30 as it is extended and contracted. In addition, the auxiliary support 38 is controlled to apply loads that are commensurate with the weights of the support table 28 and various devices and components supported on the support table 28, i.e., the chuck table 26, the seal unit 32, the servomotor 34, the endless belt 36, sheaths 42a of guides 42 and guide pins 30g, a presser 30h, and a load sensor 30b of the moving mechanism 30, to be described later, upwardly to the support table 28.

The weights of the support table 28 and various devices and components supported on the support table 28 referred to above will hereinafter be referred to simply as “the weight of the support table 28.”

The load to be applied to the support table 28 to support the devices and components, i.e., the weight of the support table 28, vary depending on the dresser board 24 held on the chuck table 26 and inclination of the support table 28. The load applied upwardly from the auxiliary support 38 as the fluid pressure cylinder to the support table 28 may not necessarily be in strict agreement with the weight of the support table 28. The auxiliary support 38 as the fluid pressure cylinder is enough to be able to bear most of the weight of the support table 28.

A plurality of guides 42 are disposed below the support table 28 for keeping the postures of the chuck table 26 and the support table 28 while the support table 28 are being vertically moved and supported by the moving mechanism 30 and the auxiliary support 38. According to the present embodiment, the dressing assembly 8 includes a total of two guides 42 positioned one on each side of the auxiliary support 38.

Each of the guides 42 includes a sheath 42a and a post 42b. The sheath 42a includes a tubular member extending downwardly from the lower surface of the support table 28 and has an open lower end. The post 42b includes a rod-shaped member extending upwardly from the foundation base 40 below the support table 28 and an upper portion movably inserted in the sheath 42a. The cross-sectional shape and dimensions of the sheath 42a along a horizontal plane or XY-plane are substantially the same as the cross-sectional shape and dimensions of the post 42b along a horizontal plane or XY-plane. The sheath 42a and the post 42b are telescopically slidable with respect to each other in vertical directions or z-directions, but are essentially not movable with respect to each other along the horizontal plane or XY-plane.

The sheath 42a is fixed to the support table 28 and the post 42b is fixed to the foundation base 40. The sheath 42a and the post 42b that are thus essentially immovable with respect to each other along the horizontal plane or XY-plane restrain each other from moving along the horizontal plane or XY-plane, thereby limiting the movement of the chuck table 26 in directions along the XY-plane transverse to the directions along the Z-direction in which the chuck table 26 is movable by the moving mechanism 30.

In the dressing assembly 8 including the above mechanisms, the weight of the support table 28 is borne mainly by the auxiliary support 38 as the fluid pressure cylinder. The point where the load is applied from the auxiliary support 38 to the support table 28 is not necessarily aligned with the center of gravity of the support table 28 under its own weight. However, even though the support table 28 tends to be inclined by a moment produced by the deviation of the load applied to the support table 28 from the center of gravity of the support table 28, since the support table 28 is restrained from moving in a direction transverse to the Z-directions by the guides 42, the support table 28 is kept in a posture along the horizontal plane, i.e., the XY-plane.

Moreover, inasmuch as the auxiliary support 38 is extended and contracted by the moving mechanism 30 as it is extended and contracted, the auxiliary support 38 applies a substantially constant load to the support table 28 at any height irrespectively of how much the moving mechanism 30 is extended and contracted. When the moving mechanism 30 and the auxiliary support 38 are extended and contracted, variations in the loads applied from the moving mechanism 30 and the auxiliary support 38 to the support table 28 are liable to produce a moment tending to incline the support table 28. Nevertheless, the guides 42 are effective to keep the support table 28 in the same posture.

The auxiliary support 38 may have any specific structural details as long as they allow the support table 28 to move along vertical directions, i.e., Z-directions, and urge the support table 28 to move under appropriate forces in a vertical direction, i.e., a Z-direction, away from the foundation base 40. For example, the auxiliary support 38 may include a mechanism including a helical spring rather than a fluid pressure cylinder. However, the auxiliary support 38 should preferably include a fluid pressure cylinder as it is able to adjust the entire length of the auxiliary support 38 and also the load applicable by the auxiliary support 38.

The guides 42 are not limited to the illustrated structural details. Each of the guides 42 may include a mechanism including a vertical through hole defined in the support table 28 and a vertical columnar member fixed to the foundation base 40 and extending through the vertical through hole in the support table 28. Alternatively, each of the guides 42 may include a mechanism including a wall or a frame extending around the entire edges of the support table 28. Further alternatively, it is theoretically possible to limit the support table 28 against inclination or movement under magnetic forces or resilient forces from resilient members such as springs, for example.

Structural details of the moving mechanism 30 will be described below. FIG. 5 illustrates a central portion of the moving mechanism 30 in enlarged fragmentary cross section, partly in elevation. As illustrated in FIG. 5, the moving mechanism 30 includes an actuator 30a that is extendible and contractible along vertical directions or Z-directions to move the chuck table 26 and the support table 28 with respect to the grindstones 16 (see FIG. 1) and a load sensor 30b as a measuring instrument for detecting a load applied to the dresser board 24 held on the chuck table 26.

The actuator 30a includes a mechanism extendible and contractible along vertical directions or Z-directions transverse to a plane along which the grindstones 16 abrasively slide against the dresser board 24 to generate urging forces along the vertical directions or the Z-directions. The mechanism may include any of various mechanisms including an electromagnetic mechanism, a fluid pressure mechanism, or a rack-and-pinion mechanism, for example, that may be powered by a power source such as an electric motor, if necessary.

The load sensor 30b includes a load cell, for example, mounted on the lower surface of the support table 28. When an object such as a presser 30h to be described later is brought from below into contact with the load sensor 30b, the load sensor 30b detects the load applied from the object and inputs a signal representing the detected load to a controller 50 (see FIG. 1) to be described later.

The load sensor 30b essentially acts as a sensor for detecting the load applied to the dresser board 24 held on the chuck table 26. According to the present embodiment, the load sensor 30b detects the load as a load applied from the actuator 30a to the support table 28.

The actuator 30a includes a hollow cylindrical main body 30c and a rod 30d having a portion slidably inserted in the main body 30c. The portion of the rod 30d is telescopically inserted into the main body 30c through an upper end thereof along its central axis and is slidable axially in directions into and out of the main body 30c under electromagnetic forces or fluid pressures, so that the actuator 30a is extendible and contractible as a whole longitudinally along its central axis.

The main body 30c of the actuator 30a has a lower end remote from the upper end through which the rod 30d is inserted, the lower end being mounted on the foundation base 40. The rod 30d includes an upper distal end portion 30e extending upwardly away from the main body 30c. The actuator 30a is disposed between and attached to the support table 28 and the foundation base 40 with the distal end portion 30e is axially oriented toward the support table 28 positioned above the actuator 30a. The load sensor 30d on the support table 28 is aligned with an axial extension of the distal end portion 30e of the rod 30d.

The distal end portion 30e of the rod 30d may be arranged such that it can be brought into direct contact with the load sensor 30b when the actuator 30a is extended. According to the present embodiment, however, a damper 30f is provided between the rod 30d and the load sensor 30b to prevent the rod 30d from coming into direct contact with the load sensor 30b.

The damper 30f will be described in specific detail below. The damper 30f includes a plurality of guide pins 30g, a presser 30h, and a resilient urging member 30h.

The guide pins 30g protrude downwardly from the lower surface of the support table 28 around the load sensor 30b on the lower surface of the support table 28. The presser 30h is supported on the guide pins 30g.

The presser 30h is in the form of a plate supported at a position below the load sensor 30b and above the distal end portion 30e of the rod 30d in a posture lying along a horizontal plane or XY-plane. The presser 30h has a central upward protrusion on an upper surface thereof. When the actuator 30a is extended, as described later, the central upward protrusion is brought into contact with the load sensor 30b.

The presser 30h has a plurality of vertically through holes defined in a peripheral portion thereof and aligned respectively with the guide pins 30g. The presser 30h is positioned such that the guide pins 30g extend vertically through the respective vertically through holes in the presser 30h. The guide pins 30g that extend downwardly from the support table 28 have respective heads on their lower ends that are positioned beneath the presser 30h. The heads are larger in diameter than the other portions of the guide pins 30g. When the presser 30h is not raised by the rod 30d of the actuator 30a, i.e., is in the solid-line position in FIG. 5, the presser 30h rides on the heads of the guide pins 30g and hence is suspended from the heads of the guide pins 30g.

A spacer 30i protrudes downwardly from a central lower surface of the presser 30h. The spacer 30i includes a tubular member housing therein the distal end portion 30e of the rod 30d and surrounding the distal end portion 30e as viewed in plan, i.e., as viewed along vertical directions or Z-directions. The distal end portion 30e of the rod 30d is inserted from below into the spacer 30i through an opening defined in a lower end of the spacer 30i.

The resilient urging member 30h is disposed between the spacer 30i and the rod 30d for normally urging the presser 30h and the rod 30d to move apart from each other in vertical directions or Z-directions along which the actuator 30a is extendible and contractible.

According to the present embodiment, the resilient urging member 30h includes a helical spring though it may be another structure depending on the structure of the actuator 30a. According to the present embodiment, the distal end portion 30e of the actuator 30a is smaller in diameter than the other portion of the rod 30d. The distal end portion 30e will hereinafter be also referred to as a “smaller-diameter portion.” The helical spring as the resilient urging member 30h is disposed around the distal end portion 30e as the smaller-diameter portion.

The distal end portion 30e has an upper end portion positioned in the spacer 30i. The resilient urging member 30h has an upper end held against the lower end of the spacer 30i and a lower end held against a radial step between the distal end portion 30e as the smaller-end portion and the other portion of the rod 30d.

The damper 30f that is thus interposed between the rod 30d and the load sensor 30b. When the actuator 30a is to raise the support table 28, the actuator 30a applies a force through the resilient urging member 30h and the presser 30h.

The dressing assembly 8 includes the auxiliary support 38, i.e., the fluid pressure cylinder, that supports the support table 28 on the foundation base 40. The weight of the support table 28 is borne mainly by the auxiliary support 38 in the form of the fluid pressure cylinder. When the actuator 30a of the moving mechanism 30 is contracted, the distal end portion 30e of the rod 30d is sufficiently spaced downwardly from the lower surface of the support table 28 and hence the load sensor 30b mounted thereon.

At this time, the presser 30h included in the damper 30f is suspended from the lower surface of the support table 28 by the guide pins 30g, as indicated by the solid lines in FIG. 5.

As the actuator 30a is then extended, the rod 30d is pushed upwardly to cause the distal end portion 30e to support the presser 30h thereon through the resilient urging member 30h and to lift the presser 30h longitudinally along the guide pins 30g until the central upward protrusion of the presser 30h is brought into contact with the load sensor 30b.

Upon continued extension of the actuator 30a, the rod 30d applies an upward thrust to the load sensor 30b and the support table 28 through the resilient urging member 30h and the presser 30h. The load sensor 30b now detects the load applied from the rod 30d.

The dressing assembly 8 further includes a measurement reference marker 44 (see FIGS. 3 and 4) for detecting the position of the chuck table 26 as the board holder that has been moved along vertical directions or Z-directions by the moving mechanism 30. According to the present embodiment, the measurement reference marker 44 includes a rod-shaped member having a proximal end attached to the foundation base 40 and a portion that extends upwardly from the foundation base 40 above a position higher than the support table 28 and that is bent in overhanging relation to the holding surface 26a of the chuck table 26 on the support table 28.

The overhanging portion of the measurement reference marker 44 has a distal end in a position above the chuck table 26 on a path to be followed by the dresser board 24 held on the holding surface 26a at the time the chuck table 26 is moved along vertical directions or Z-directions. The position is also located on a path to be followed by the holding surface 26a of the chuck table 26 at the time the chuck table 26 is moved along vertical directions or Z-directions.

Since the distal end of the measurement reference marker 44 is located in the position referred to above, when the moving mechanism 30 elevates the support table 28 and the chuck table 26, the holding surface 26a of the chuck table 26 or the dresser board 24 held on the holding surface 26a comes into contact with the distal end of the measurement reference marker 44 at the position.

The portion of the measurement reference marker 44 that is positioned above the chuck table 26 is disposed in a position not overlapping the grinding wheel 14 and the grindstones 16 as viewed in plan, i.e., as viewed along vertical directions or Z-directions, in order to prevent itself from presenting an obstacle to a dressing step to be described later. Alternatively, the measurement reference marker 44 may be made movable or removed so that it can be retracted away from the paths of the chuck table 26 and the dresser board 24, if necessary.

The measurement reference marker 44 is not limited to the illustrated structural details, but may have any of various other structural details. The measurement reference marker 44 may have at least a portion that is positioned on the path to be followed by the dresser board 24 on the holding surface 26a at the time the chuck table 26 is moved along vertical directions or Z-directions and that is fixed in position along vertical directions or Z-directions to a component secured to the foundation base 40, e.g., the main body 30c of the actuator 30a that remains stationary when the actuator 30a is extended or contracted, or a housing of the dressing apparatus 2 in which the dressing assembly 8 is installed.

The dressing assembly 8 further includes a liquid supply nozzle 46 (see FIGS. 3 and 4) for supplying a dressing liquid such as water, for example, to the grindstones 16 and the dresser board 24 that are abrasively sliding against each other when the grindstones 16 are dressed by the dresser board 24. According to the present embodiment, the liquid supply nozzle 46 has an outlet port positioned above the chuck table 26 as the board holder. When the grindstones 16 are dressed by the dresser board 24, the liquid supply nozzle 46 supplies the dressing liquid through the outlet port to the grindstones 16 and the dresser board 24.

The measurement reference marker 44 and the liquid supply nozzle 46 are omitted from illustration in FIGS. 1 and 2.

FIGS. 6 and 7 illustrate, by way of example, the layout of a nozzle similar in function to the liquid supply nozzle 46, i.e., a cleaning nozzle 48. FIGS. 6 and 7 illustrate, respectively, in front elevation, partly in cross section, and plan a positional relation between the grindstone handler 4, the workpiece handler 6, and the dressing assembly 8, in the dressing apparatus 2 illustrated in FIG. 1.

In the dressing apparatus 2 according to the present embodiment, the grindstone handler 4 and the dressing assembly 8, and the chuck table 20 of the workpiece handler 6 are in a positional relation illustrated in FIGS. 6 and 7 upon rotation of the support table 22 of the workpiece handler 6. In the illustrated positional relation, the rotation of the support table 22 of the workpiece handler 6 allows the chuck table 20 as the workpiece holder on the support table 22 and the chuck table 26 as the board holder on the support table 28 of the dressing assembly 8 to be located closely to each other.

Since the chuck tables 20 and 26 are located closely to each other, as illustrated in FIG. 7, the grinding wheel 14 may be positioned such that the circular path followed by the grindstones 16 attached to the grinding wheel 14 of the grindstone handler 4 has a portion overlapping the chuck table 20 as the workpiece holder and another portion overlapping the chuck table 26 as the board holder, as viewed in plan.

More specifically, the grinding wheel 14, the chuck table 20, and the chuck table 26 are disposed relatively to each other such that the circular path followed by the grindstones 16 that rotate in unison with the grinding wheel 14 overlaps a portion of the workpiece 18 held on the chuck table 20 and also a portion of the dresser board 24 held on the chuck table 26.

With the above positional relation, some of the grindstones 16 on the grinding wheel 14 are brought into contact with the workpiece 18 on the chuck table 20 and some of grindstones 16 are brought into contact with the dresser board 24 on the chuck table 26, so that the grindstones 16 can grind the workpiece 18 and can be dressed by the dresser board 24 at the same time when the grinding wheel 14 is rotated. At this time, the chuck tables 20 and 26 are rotated to rotate the workpiece 18 and the dresser board 24 held respectively on the holding surfaces 20a and 26a about their central axes along vertical directions or Z-directions.

Providing the grindstones 16 grind the workpiece 18 and are dressed by the dresser board 24 simultaneously, according to the examples illustrated in FIGS. 6 and 7, the cleaning nozzle 48 that supplies a cleaning fluid such as water or air, for example, to the grindstones 16 is disposed to supply the fluid to a position on the circular path followed by the grindstones 16, not overlapping the workpiece 18 on the chuck table 20 and the dresser board 24 on the chuck table 26 as viewed in plan.

The cleaning nozzle 48 has an outlet port for ejecting the cleaning fluid to the grindstones 16 at the position referred to above. When the cleaning nozzle 48 supplies the cleaning fluid to the position on the circular path followed by the rotating grindstones 16, the grindstones 16 are cleaned by the ejected cleaning fluid at the position not overlapping the workpiece 18 and the dresser board 24.

Alternatively, the chuck table 20 may be retracted away from the grindstones 16, and the grinding wheel 14 may be rotated while the grindstones 16 are held in abrasive contact with only the dresser board 24 on the chuck table 26, so that the grindstones 16 may be only dressed without grinding the workpiece 18 on the chuck table 20.

According to the present embodiment, therefore, the dressing apparatus 2 is capable of adjusting a positional relation between the grindstone handler 4, the workpiece handler 6, and the dressing assembly 8 to dress the grindstones 16 with the dresser board 24 by bringing the dresser board 24 into abrasive contact with the grindstones 16 rotated by the grinding wheel 14 irrespectively of whether the workpiece 18 on the chuck table 20 is not being ground by the grindstones 16 or is being ground by the grindstones 16.

As illustrated in FIG. 1, the dressing apparatus 2 is electrically connected to a controller 50 that controls various components of the dressing apparatus 2.

The controller 50 includes an operating unit 50a for performing various processing operations required to actuate the dressing apparatus 2 and a storage unit 50b for storing various pieces of information such as data and programs used to actuate the dressing apparatus 2. The operating unit 50a includes a processor such as a central processing unit (CPU), for example. The storage unit 50b includes memories such as a read only memory (ROM) and a random access memory (RAM), for example.

The controller 50 also includes a communication unit 50c that electrically communicates with various components of the dressing apparatus 2 and inputs control signals to those components. Specifically, the communication unit 50c inputs various control signals to the grindstone handler 4, the workpiece handler 6, and the dressing assembly 8 via wired or wireless links.

The controller 50 controls operations, to be described below, of the dressing apparatus 2 according to the programs stored in the storage unit 50b and executed by the operating unit 50a. The controller 50 may also control operations other than those described below.

Grindstone Handler 4

• • Rotation of the grinding wheel 14
  • Movement along vertical directions of the spindle 10, the grinding wheel 14, and the grindstones 16 by the moving mechanism 12

Workpiece Handler 6

• • Rotation of the support table 22
  • Rotation of the chuck table 20
  • Attraction of the workpiece 18 under suction by the chuck table 20

Dressing Assembly 8

• • Extension and contraction of the actuator 30a of the moving mechanism 30 and adjustment of the load applied thereby
  • Extension and contraction of the auxiliary support 38 and adjustment of the load applied thereby
  • Rotation of the chuck table 26, i.e., operation of the servomotor 34 as the rotary actuator
  • Attraction of the dresser board 24 under suction by the chuck table 26
  • Supply of the dressing liquid from the liquid supply nozzle 46.
  • Supply of the cleaning fluid from the cleaning nozzle 48

An input and output unit 50d is electrically connected to the controller 50. The input and output unit 50d includes user interfaces such as a keyboard and a monitor display, for example. An operator who operates the dressing apparatus 2 enters operating instructions to the input and output unit 50d to enable the controller 50 to operate the components of the dressing apparatus 2.

An operation sequence of dressing and grinding steps performed by the dressing assembly 8 and the dressing apparatus 2 including the dressing assembly 8 will be described below with reference to FIGS. 8 through 10. FIG. 8 is a flowchart of a processing sequence of a dressing method and a method of manufacturing device chips according to the embodiment. FIGS. 9 and 10 schematically illustrate, in side elevation, the positional relation between the grindstone handler 4, the workpiece handler 6, and the dressing assembly 8 respectively in a board thickness detecting step and a grindstone thickness detecting step of the operation sequence illustrated in FIG. 8.

The grindstones 16 are dressed by bringing the grindstones 16 and the dresser board 24 into contact with each other and causing them to abrasively slide against each other. For dressing the grindstones 16 with the dressing apparatus 2 and the dressing assembly 8, it is necessary to adjust the distance between the grindstones 16 and the dresser board 24 and bring them into contact with each other in distance adjusting step S20 of the operation sequence illustrated in FIG. 8. The operation sequence illustrated in FIG. 8 includes board thickness detecting step S10 for acquiring information to be used in distance adjusting step S20.

In board thickness detecting step S10, the actuator 30a of the moving mechanism 30 is energized to move the chuck table 26 as the board holder upwardly in a vertical direction, and information about the position of the chuck table 26 at the time the dresser board 24 on the chuck table 26 and the distal end of the measurement reference marker 44 contact each other is recorded.

More specifically, as indicated by the solid lines in FIG. 9, the chuck table 26 is retracted downwardly by contracting the actuator 30a (see FIG. 5) of the moving mechanism 30, and the dresser board 24 is placed on the holding surface 26a of the chuck table 26. With the dresser board 24 on the holding surface 26a, the negative pressure source, not depicted, fluidly connected to the seal unit 32 (see FIG. 3) is actuated to generate and apply a negative pressure to the inside of the chuck table 26, enabling the holding surface 26a to attract the dresser board 24 under suction thereto.

Then, the actuator 30a is extended to lift the chuck table 26 as indicated by an arrow in FIG. 9. At this time, the distal end of the measurement reference marker 44 has been positioned above the chuck table 26, and the moving mechanism 12 (see FIG. 1) has retracted the grinding wheel 14 upwardly to a position in which the cutting edges, i.e., lower ends, of the grindstones 16 are positioned above a lower surface of the distal end of the measurement reference marker 44.

As the actuator 30a is continuously extended, as indicated by the broken lines, the dresser board 24 held on the holding surface 26a of the chuck table 26 comes into contact with the measurement reference marker 44. The contact of the dresser board 24 with the measurement reference marker 44 is detected as a load by the load sensor 30b (see FIG. 5) or a change in a load value detected by the load sensor 30b.

As described above, most of the weight of the support table 28 is borne by the auxiliary support 38. Since the auxiliary support 38 is extended and contracted by the moving mechanism 30 as it is extended and contracted by the actuator 30a, the load detected by the load sensor 30b is zero or of an extremely small value until the dresser board 24 contacts the measurement reference marker 44.

When the dresser board 24 contacts the measurement reference marker 44, the measurement reference marker 44 obstructs upward movement of the support table 28. As the actuator 30a is further extended, the presser 30h suspended from the lower surface of the support table 28 by the guide pins 30g is pushed upwardly by the distal end portion 30e of the rod 30d and brought into contact with the load sensor 30b (see FIG. 5).

The value of the load detected by the load sensor 30b varies when the load sensor 30b is contacted by the presser 30h. Inasmuch as the detected value of the load is input from the load sensor 30b to the controller 50 (see FIG. 1), the controller 50 grasps the contact of the presser 30h with the load sensor 30b as a change in the value of the load detected by the load sensor 30b.

At this time, the controller 50 records information about the position of the chuck table 26. “The information about the position of the chuck table 26” refers to information representing the position of the chuck table 26 along vertical directions or related information by which the position of the chuck table 26 along vertical directions can be grasped.

Specifically, “the information about the position of the chuck table 26” may be represented by a numerical value indicating the position of the chuck table 26 along vertical directions or the position of the support table 28 on which the chuck table 26 is mounted with respect to the foundation base 40 or the floor within the dressing apparatus 2, or a length by which the actuator 30a or the auxiliary support 38 is extended at the time or a controlling variable for extending the actuator 30a or the auxiliary support 38. Further alternatively, the thickness of the dresser board 24 to be calculated by a step described below may represent “the information about the position of the chuck table 26 at the time the dresser board 24 on the chuck table 26 and the distal end of the measurement reference marker 44 contact each other.”

Before or after the support table 28 with the dresser board 24 held on the chuck table 26 is lifted to bring the dresser board 24 into contact with the measurement reference marker 44 as described above, the support table 28 with the dresser board 24 not held on the chuck table 26 is lifted to bring the holding surface 26a into contact with the measurement reference marker 44, and the position along the Z-directions of the support table 28 or the chuck table 26 or the length by which the actuator 30a or the auxiliary support 38 is extended at the time is recorded. Then, the thickness of the dresser board 24 can be grasped by comparing the data representing the recorded position and length with the recorded “information about the position of the chuck table 26 at the time the dresser board 24 on the chuck table 26 and the distal end of the measurement reference marker 44 contact each other.”

Specifically, the difference calculated between the positions along the Z-directions of the chuck table 26 that have been recorded in both instances represents the thickness of the dresser board 24.

According to the present embodiment, the auxiliary support 38 as the fluid pressure cylinder is provided in addition to the moving mechanism 30 for supporting the support table 28, so that almost no load is applied between the moving mechanism 30 and the support table 28 until the chuck table 26 or the dresser board 24 held on the chuck table 26 contacts an upper object.

This arrangement offers the following advantage. In board thickness detecting step S10 and grindstone thickness detecting step S70 to be described later, the time at which the dresser board 24 or the chuck table 26 contacts the measurement reference marker 44 and the grindstones 16 can be grasped as the time at which the value of the load detected by the load sensor 30b varies from zero or nearly zero to a large positive value. Consequently, the contacts between the dresser board 24 or the chuck table 26 and the measurement reference marker 44 and the grindstones 16 can be detected highly accurately.

Moreover, during most of the periods of time during board thickness detecting step S10, grindstone thickness detecting step S70, and movement adjusting step S20, there is essentially no load is applied to the moving mechanism 30. During dressing step S30, the moving mechanism 30 is not required to bear the weight of the support table 28 and the actuator 30a may produce a load enough to press the dresser board 24 against the grindstones 16. Therefore, the mechanism of the actuator 30a, which may include an electric motor, may be a small-size, lower-output device.

The auxiliary support 38 may be dispensed with and the contacts referred to above may be detected in the same manner as described above. According to such a modification, the weight of the support table 28 is borne in its entirety by the moving mechanism 30. In the actuator 30a of the moving mechanism 30, the distal end portion 30e of the rod 30d is kept at all times in direct contact with the load sensor 30b.

According to the modification, when grindstone thickness detecting step S70 starts to be carried out, the load that is commensurate with the weight of the support table 28 is detected by the load sensor 30b. When the dresser board 24 contacts the measurement reference marker 44, the detected value of the load increases, so that the load sensor 30b can detect the contact.

Thereafter, on the basis of the information about the position of the chuck table 26 that has been recorded in board thickness detecting step S10, distance adjusting step S20 is carried out to control the distance that the chuck table 26 is moved by the moving mechanism 30.

For dressing the grindstones 16, the cutting edges, i.e., lower ends, of the grindstones 16 are held in contact with the upper surface of the dresser board 24 on the chuck table 26. In order to prevent the grindstones 16 and the dresser board 24 from impinging upon each other or from undergoing excessive forces therebetween upon contacting each other, it is necessary for the grindstones 16 and the dresser board 24 to avoid moving toward each other at a high speed before they contact each other. On the other hand, if the grindstones 16 and the dresser board 24 move toward each other at a low speed from widely spaced positions, then the dressing step tends to take too much time, possibly adversely affecting the efficiency with which to dress the grindstones 16.

For moving the grindstones 16 and the dresser board 24 closely to each other, it is effective to move them at a high speed up to positions that are sufficiently close to, but slightly spaced from, each other, and then move them at a low speed toward each other from the sufficiently close positions.

The movement at the low speed is occasionally called “air cutting.” Specifically, when two objects, e.g., the grindstones 16 and the dresser board 24, are moved into contact with each other, they are moved first at a relatively high speed while they are relatively far from each other and then at a relatively low speed while they are relatively close to each other. For the sake of convenience, the movement at the relatively low speed is referred to as “air-cutting movement” and the movement at the relatively high speed is referred to as “previous movement.”

The time at which the previous movement switches to the air-cutting movement or the distance between the two objects at that time may be determined as “the time or distance at which the objects are as close to each other as possible but are free from an unexpected collision” on the basis of measurement errors and accuracies of movement of various components.

For determining the time or distance as described above, it is effective to use the information about the thickness of the dresser board 24 held on the chuck table 26. If the position of the cutting edges or lower ends of the grindstones 16 in the Z-directions has been grasped and in addition the thickness of the dresser board 24, i.e., the distance between the holding surface 26a of the chuck table 26 and the upper surface of the dresser board 24, has been grasped, then it is possible to recognize how much the chuck table 26 is to be moved before the holding surface 26a of the chuck table 26 and the upper surface of the dresser board 24 contact each other.

According to the present embodiment in which the chuck table 26 with the dresser board 24 held thereon is moved along the Z-directions, “the information about the thickness of the dresser board 24” is equivalent to “the information about the position of the chuck table 26” that has been recorded in board thickness detecting step S10. In distance adjusting step S20, therefore, the movement of the chuck table 26 by the moving mechanism 30 is controlled by using the information about the position of the chuck table 26 that has been recorded in board thickness detecting step S10.

For example, as illustrated in FIG. 10, the moving mechanism 12 (see FIG. 1) of the grindstone handler 4 moves the grinding wheel 14 along the Z-direction to a position where the grindstones 16 can be dressed, i.e., lowers the grinding wheel 14 toward the chuck table 26 of the dressing assembly 8 positioned below.

Then, the actuator 30a (see FIG. 5) of the moving mechanism 30 of the dressing assembly 8 is extended to elevate the chuck table 26 as indicated by an arrow in FIG. 10 to bring the dresser board 24 closely to and into contact with the grindstones 16. While the chuck table 26 is thus being moved, the time at which to switch from the previous movement to the air-cutting movement is adjusted on the basis of the information recorded in board thickness detecting step S10.

When the dresser board 24 on the chuck table 26 contacts the grindstones 16 as indicated by the broken lines in FIG. 10, dressing step S30 starts to be carried out. In dressing step S30, the actuator 30a (see FIG. 5) is extended to apply a load from below to the support table 28 to press the dresser board 24 against the grindstones 16 positioned over the dresser board 24, and the grinding wheel 14 and the chuck table 26 are rotated about their respective central axes along the Z-directions.

The dresser board 24 held on the chuck table 26 and the grindstones 16 are rotated while in abrasive sliding contact with each other, dressing the grindstones 16. At this time, the liquid supply nozzle 46 (see FIGS. 3 and 4) supplies the dressing liquid to the dresser board 24 to assist in dressing the grindstones 16.

During dressing step S30, measuring step S40 and load adjusting step S50 are carried out.

In measuring step S40, the load applied to the dresser board 24 is continuously measured. The value of the applied load is detected by the load sensor 30b (see FIG. 5).

In load adjusting step S50, the load output from the actuator 30a is adjusted on the basis of the value of the load measured in measuring step S40. Specifically, the chuck table 26 and the grindstones 16 are pressed against each other along the Z-directions transverse to the plane along which the grindstones 16 and the dresser board 24 slide abrasively against each other, so that the value of the load detected by the load sensor 30b falls within a predetermined numerical range.

In the dressing assembly 8 according to the present embodiment, consequently, the dresser board 24 dresses the grindstones 16 while the load applied between the grindstones 16 and the dresser board 24 is being adjusted to an appropriate value.

Moreover, at the same time that the dresser board 24 dresses the grindstones 16, the grindstones 16 grind the workpiece 18 in grinding step S60. In grinding step S60, specifically, the workpiece 18 is held on the holding surface 20a of the chuck table 20 of the workpiece handler 6, and the support table 22 is turned to position the chuck table 20 that is holding the workpiece 18 below the grinding wheel 14. In other words, the grinding wheel 14 of the grindstone handler 4, the chuck table 20 of the workpiece handler 6, and the chuck table 26 of the dressing assembly 8 are brought into the positional relation illustrated in FIGS. 6 and 7.

Then, the grinding wheel 14 and the chuck tables 20 and 26 are rotated about their respective central axes along the Z-directions while the workpiece 18 on the chuck table 20 and the dresser board 24 on the chuck table 26 are being held against the lower ends of the grindstones 16 attached to the lower surface of the grinding wheel 14. In this manner, grinding step S60 is carried out simultaneously with dressing step S30. At this time, the cleaning nozzle 48 (see FIG. 7) ejects the cleaning fluid to the grindstones 16.

The more the workpiece 18 is ground, the thinner the workpiece 18 becomes and the lower the surface of the workpiece 18 ground by the grindstones 16 drops. The grinding wheel 14 with the grindstones 16 abrasively contacting the upper surface of the workpiece 18 to grind the workpiece 18 is moved downwardly toward the chuck table 20 by the moving mechanism 30 of the grindstone handler 4.

When the grindstones 16 are dressed by the dresser board 24 at the same time that they grind the workpiece 18, the movement of the ground surface of the workpiece 18, i.e., the plane along which the grindstones 16 and the workpiece 18 abrasively slide against each other, is equivalent to the movement of the dressed surfaces of the grindstones 16, i.e., the plane along which the grindstones 16 and the dresser board 24 abrasively slide against each other. As the dressed surfaces of the grindstones 16 are lowered, therefore, the actuator 30a of the moving mechanism 30 may be contracted as much, moving the dresser board 24 and the chuck table 26 downwardly.

However, the distance along the Z-directions that the ground surface of the workpiece 18 is lowered in one dressing cycle is very small. According to the present embodiment, the movement of the dressed surfaces of the grindstones 16 as they are dressed at the same time that they grind the workpiece 18 is absorbed by the resilient urging member 30h of the damper 30f. In other words, the actuator 30a is not contracted, but the helical spring as the resilient urging member 30h is compressed to allow the support table 28 to be lowered.

Since the resilient urging member 30h is compressed, it increases the pressing force acting between the grindstones 16 and the dresser board 24. However, because the distance that the ground surface of the workpiece 18 is lowered in one dressing cycle is very small, as described above, the distance that the resilient urging member 30h is compressed is also very small, and hence the increase in the pressing force acting between the grindstones 16 and the dresser board 24 is negligibly small.

In a case where the position of the chuck table 26 along the Z-directions is to be adjusted for a small distance by the actuator 30a, the actuator 30a is required to be extended or contracted with high accuracy. According to the present embodiment, however, the resilient urging member 30h is provided to take up the downward movement of the support table 28. Therefore, the grindstones 16 can continuously be dressed appropriately while allowing the dressed surfaces to move downwardly without the need for accurate control over the actuator 30a.

During dressing step S30, the chuck table 20 of the workpiece handler 6 may be retracted downwardly away from the grinding wheel 14, so that the grindstones 16 do not grind the workpiece 18, but are dressed by the dresser board 24. In other words, dressing step S30 may be carried out by keeping the dresser board 24 in abrasive contact with the grindstones 16 as they are grinding the workpiece 18 or by keeping the dresser board 24 in abrasive contact with the grindstones 16 as they are not grinding the workpiece 18.

Alternatively, while the workpiece 18 is being kept in abrasive contact with the grindstones 16, the dresser board 24 may not be kept in abrasive contact with the grindstones 16, so that the grindstones 16 grind the workpiece 18, but are not dressed by the dresser board 24.

In a step similar to board thickness detecting step S10 described above, a value relative to the thickness of the grindstones 16, i.e., the distance from the lower surface of the grinding wheel 14 to the lower ends of the grindstones 16, may be measured in grindstone thickness detecting step S70, and the measured value may be used in distance adjusting step S20.

In grindstone thickness detecting step S70, specifically, the moving mechanism 30 moves the chuck table 26 as the board holder along the Z-directions and information about the position of the chuck table 26 at the time when the chuck table 26 or the dresser board 24 held thereon contacts the grindstones 16 is recorded.

Specific details of grindstone thickness detecting step S70 are essentially identical to those of board thickness detecting step S10 except that the grindstones 16 rather than the measurement reference marker 44 are to be contacted by the chuck table 26 as it moves.

Alternatively, the same step as grindstone thickness detecting step S70 may be carried out without the dresser board 24 being held on the chuck table 26, and information about the position of the chuck table 26 at the time when the chuck table 26 as the board holder contacts the grindstones 16, rather than the information about the position of the chuck table 26 at the time when the dresser board 24 and the grindstones 16 contact each other, may be recorded.

Grindstone thickness detecting step S70 is carried out according to a sequence described below, for example, before or after grinding step S60 is repeated or a grinding step (steps S40 through S60) at the same time as dressing step S30 is repeated.

First, after dressing and grinding steps S30 through S60 have been carried out in a first cycle or immediately after the grinding wheel 14 has been replaced with a new one, grindstone thickness detecting step S70 is carried out in a first cycle.

The actuator 30a of the moving mechanism 30 is compressed and the dresser board 24 is held on the holding surface 26a of the chuck table 26. The grinding wheel 14 is placed along the Z-directions at a position where the grindstones 16 can grind the workpiece 18.

Then, the actuator 30a is extended until the dresser board 24 on the chuck table 26 contacts the lower ends of the grindstones 16. The load sensor 30b detects a load and the controller 50 records information about the position of the chuck table 26 at this time.

Then, dressing and grinding steps S30 through S60 are carried out again in a second cycle, after which grindstone thickness detecting step S70 is carried out again in a second cycle in the same manner as described above. The position of the grinding wheel 14 along the Z-directions remains the same in the first and second cycles of grindstone thickness detecting step S70.

The information about the position of the chuck table 26 that has been recorded in the first cycle of grindstone thickness detecting step S70 and the information about the position of the chuck table 26 that has been recorded in the second cycle of grindstone thickness detecting step S70 are compared with each other to recognize the amounts of wear of the grindstones 16 and the dresser board 24 in the first cycle of dressing and grinding steps S30 through S60. The recognized amounts of wear can be used in determining the time to switch from the previous movement and the air-cutting movement in distance adjusting step S20 to be carried out prior to dressing step S30, for example.

Specifically, providing the first cycle of dressing and grinding steps S30 through S60 and then the second cycle of dressing and grinding steps S30 through S60 are to be carried out, if the grinding wheel 14 is to remain in the same position along the Z-directions in the first and second cycles of dressing and grinding steps S30 through S60, the position of the chuck table 26 on which the grindstones 16 and the dresser board 24 contact each other is higher in distance adjusting step S20 prior to the second cycle of dressing and grinding steps S30 through S60 than in distance adjusting step S20 prior to the first cycle of dressing and grinding steps S30 through S60 by the sum of the amounts of wear of the grindstones 16 and the dresser board 24.

Each time dressing and grinding steps S30 through S60 is repeated by using the same grindstones 16 and the same dresser board 24, the time at which to switch from the previous movement to the air-cutting movement in distance adjusting step S20 prior to dressing and grinding steps S30 through S60 should be delayed by a period of time commensurate with the amount of wear grasped in grindstone thickness detecting step S70.

Alternatively, the thickness of the grindstones 16 may be measured in grindstone thickness detecting step S70, for example. For measuring the thickness of the grindstones 16 in grindstone thickness detecting step S70, with the grindstones 16 not mounted on the grinding wheel 14, the chuck table 26 or the dresser board 24 held thereon is brought into contact with the grinding wheel 14, and the information about the position of the chuck table 26 at that time is recorded in the same manner as described above.

Then, with the grindstones 16 mounted on the grinding wheel 14, the chuck table 26 or the dresser board 24 held thereon is brought into contact with the grinding wheel 14, and the information about the position of the chuck table 26 at that time is recorded in the same manner as described above. The thickness of the grindstones 16 can then be calculated by comparing the information acquired at both times.

After the grindstones 16 have been dressed and then the workpiece 18 has been ground by the dressed grindstones 16 or after the grindstones 16 have been dressed and the workpiece 18 has been ground by the dressed grindstones 16 at the same time, the workpiece 18, e.g., a semiconductor wafer, is divided into individual device chips in dividing step S80. FIG. 11 schematically illustrates, in side elevation, partly in cross section, dividing step S80 as a stage in the method of manufacturing device chips according to the present embodiment. The workpiece 18 will hereinafter be described as a wafer 18.

In dividing step S80, a laser processing apparatus 52 illustrated in FIG. 11, for example, is used to apply a laser beam to the wafer 18 to divide the wafer 18.

The laser processing apparatus 52 includes a laser beam applying unit 54 for applying the laser beam to the wafer 18 and a holding mechanism 56 for holding the wafer 18.

The laser beam applying unit 54 includes a laser oscillator, not depicted, for emitting the laser beam and an optical system including optical elements such as a condensing lens and a mirror, not depicted, for focusing the laser beam and applying the focused laser beam to the wafer 18 held by the holding mechanism 56.

The holding mechanism 56 includes a chuck table, for example, for holding the wafer 18 as the workpiece under suction thereon. The holding mechanism has an upper surface as a holding surface 56a for holding the wafer 18 thereon. The holding surface 56a is supplied with a negative pressure from a suction source, not depicted, to hold the wafer 18 under suction thereon. The holding mechanism 56 has a lower portion coupled to a rotating mechanism, not depicted, for rotating the holding mechanism 56 about its central axis along the vertical directions.

According to the present embodiment, the wafer 18 is handled in the form of a frame unit in which the wafer 18 is attached to an annular frame by an adhesive tape. The frame unit including the wafer 18 is held on the holding surface 56a of the holding mechanism 56. The laser beam applying unit 54 applies the laser beam, which has a wavelength absorbable by the material of the wafer 18, to the wafer 18. The condensing lens included in the laser beam applying unit 54 focuses the laser beam and applies the focused laser beam to the wafer 18 such that the laser beam has a focused spot at a desired position in or on the wafer 18.

While the laser beam is being applied to the wafer 18, the holding mechanism 56 and the laser beam applying unit 54 are moved relatively to each other along the holding surface 56a to ablate the wafer 18 along a grid of projected dicing lines established on the wafer 18. When the wafer 18 is ablated by the laser beam, the wafer 18 is divided along the projected dicing lines into individual device chips.

In dividing step S80, specifically, the laser beam may be applied to the wafer 18 to form a plurality of grooves in the wafer 18 along the projected dicing lines and then external forces may be applied to the wafer 18 to divide the wafer 18 along the grooves. Alternatively, the laser beam may be applied to the wafer 18 to form modified layers in the wafer 18 along the projected dicing lines and then external forces may be applied to the wafer 18 to divide the wafer 18 along the modified layers. The grooves or the modified layers formed in the wafer 18 function as division initiating points where the wafer 18 can be divided into device chips.

Division initiating points may be formed in the wafer 18 anytime before dividing step S80. For example, division initiating points may be formed in the wafer 18 after grinding step S50 or grinding step S60 may be performed on the wafer 18 where division initiating points have been formed in advance.

Alternatively, dividing step S80 may be carried out by using a cutting apparatus that includes a cutting unit and a holding mechanism.

The cutting unit includes a spindle with a cutting blade mounted thereon and a housing in which the spindle is rotatably supported. The cutting blade includes an annular base and an annular cutting edge attached to the annular base and extending along an outer circumferential portion of the annular base.

The spindle is of a cylindrical shape having an axial end that supports a blade mounter with the cutting blade mounted thereon and an opposite end coupled to a rotary actuator such as an electric motor, for example. The spindle is housed in the housing and has a horizontal axis about which the spindle is rotatable by the rotary actuator. When the rotary actuator is energized, it rotates the spindle about its horizontal axis and also the cutting blade in unison.

For cutting the wafer 18 held by the holding mechanism, the cutting blade is rotated in unison with the spindle and cuts into the wafer 18. While the cutting blade is cutting into the wafer 18, the cutting unit and the holding mechanism are moved relatively to each other to divide the wafer 18 along the projected dicing lines. Alternatively, the cutting blade forms cut grooves in the wafer 18 along the projected dicing lines, after which external forces are applied to the wafer 18 to divide the wafer 18 along the cut grooves.

According to another dividing step, grooves are formed in a face side of the wafer 18 by a laser ablation step or a cutting step, after which a reverse side of the wafer 18 that is opposite the face side is ground to thin down the wafer 18 until the grooves formed in the wafer 18 are exposed on the reverse side thereof, thereby dividing the wafer 18. According to a further alternative step, a wafer 18 with grooves or modified layers formed therein may be thinned down by grinding and additionally divided along the grooves or modified layers as division initiating points by external forces applied when the wafer 18 is ground. If any one of these steps is used to divide the wafer 18, the dividing step and the grinding step are simultaneously carried out.

At the time of fabricating device chips from the wafer 18, other steps such as an ultraviolet irradiation step and a film growth step may also be carried out on the wafer 18 before or after the wafer 18 is divided.

The processing sequence illustrated in FIG. 8 is illustrative only, the illustrated steps may be switched around and omitted, other steps may be added, and details of the steps may be changed. For example, a board thickness detecting step S10 and a grindstone thickness detecting step S70 may be carried out at desired times other than those described above. In FIG. 8, dividing step S80 is illustrated as being carried out after grindstone thickness detecting step S70. However, a dividing step may be carried out prior to or concurrent with a grindstone thickness detecting step. As described above, a dividing step may be carried out simultaneously with a grinding step.

In FIG. 8, at least part of the operation of the actuator 30a as it is extended or contracted in board thickness detecting step S10 and grindstone thickness detecting step S70, the adjustment of the pressing force produced by the actuator 30a in load adjusting step S50, the setting of a speed at which the chuck table 26 moves in distance adjusting step S20, and the setting of a position and time to start the air-cutting movement may be carried out by operating instructions entered by the operator to the input and output unit 50d or may be automatically carried out by the controller 50.

If the controller 50 performs the above processing details, then the controller 50 stores the information about the position of the chuck table 26 acquired in board thickness detecting step S10 and grindstone thickness detecting step S70 in the storage unit 50b, and the operating unit 50a sets a position and time to start the air-cutting movement in distance adjusting step S20. While adjusting the operation and output power of various components on the basis of the stored data, the controller 50 sends control signals to the components through the communication unit 50c to perform distance adjusting step S20, dressing step S30, and load adjusting step S50.

The structural and methodical details of the present embodiment are not restrictive, but may be changed or modified without departing from the scope of the invention.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.