POLISHING SURFACE DRESSING METHOD AND METHOD OF MANUFACTURING SUBSTRATE

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2024-167389 filed with the Japan Patent Office on Sep. 26, 2024, the entire content of which is hereby incorporated by reference.

BACKGROUND ART

1. Technical Field

The present invention relates to a polishing surface dressing method of dressing a polishing surface of a polishing pad configured to polish a workpiece such a wafer, and also relates to a method of manufacturing a substrate including the polishing surface dressing method.

2. Related Art

For example, in a process of manufacturing semiconductor devices such as ICs and LSI circuits, a wafer is thinned to have a predetermined thickness by grinding the back surface of the wafer, in order to reduce the size and weight of the semiconductor device. This grinding of the wafer is performed by pressing a grinding stone onto the back surface (an upper surface in a processing state) of the wafer while rotating the grinding stone at high speed. As the back surface of the wafer is ground by such a grinding method, grinding marks remain on the back surface (ground surface) of the wafer. Such grinding marks may decrease the bending strength of the wafer.

Under these circumstances, the grinding marks are removed by polishing the back surface (ground surface) of the wafer by a polishing pad of a polishing apparatus. As the polishing apparatus, for example, an apparatus configured to perform chemical mechanical polishing (CMP) has been known. This apparatus poshes a wafer by pressing a polishing pad larger in diameter than the wafer onto the wafer while supplying slurry that is polishing liquid to a polished area of the wafer, where the wafer makes contact with the rotating polishing pad. In this polishing apparatus, the rotating polishing pad is pressed onto the entire upper surface of the wafer with a predetermined force, in a state in which the rotational axial center of the polishing pad and the rotational axial center of the wafer are deviated from each other in a direction parallel to the polishing surface of the polishing pad. As a result, the entire upper surface of the wafer is polished.

In such a wafer polishing process, the polishing surface of the polishing pad is, for example, regularly dressed by a dressing mechanism. However, when a wafer having been ground in a grinding process that is executed before the polishing process is irregular in thickness, it is difficult to uniformize the thickness of the wafer even if the wafer is polished in the subsequent polishing process.

Due to this, in a grinding and polishing apparatus proposed in Japanese Unexamined Patent Publication No. 2015-223636, the thickness distribution in the radial direction of a workpiece such as a wafer is measured by a thickness measurer, before polishing. Thereafter, in accordance with the measured thickness distribution in the radial direction of the workpiece, the dressing amount of dressing the polishing pad by the dressing mechanism is adjusted. In this way, the workpiece is polished to be uniform in thickness.

SUMMARY

However, in the grinding and polishing apparatus proposed in Japanese Unexamined Patent Publication No. 2015-223636, dressing conditions of the polishing surface are changed solely based on the thickness distribution of the workpiece, without measuring the shape of the polishing surface of the polishing pad. Due to this, the polishing surface may be excessively ground, or the shape of the polishing surface may not be sufficiently adjusted by the dressing. Furthermore, in the grinding and polishing apparatus, the distribution of the thickness in the radial direction of the workpiece must be measured before the polishing surface of the polishing pad is dressed. An unnecessary time is therefore needed before the polishing surface of the polishing pad is dressed.

When the workpiece is a wafer, a film deposition process of depositing a film such as an epitaxial film onto the surface of the polished wafer is executed after polishing. The polished wafer is required to be variously shaped to meet the requirement of this process. When a wafer is polished, because the entire surface of the polishing pad is brought into contact with the wafer, it is necessary to change the shape of the polishing surface of the polishing pad in accordance with the required shape of the wafer.

For the reason above, traditionally, in order to polish a wafer to have a desired shape, a surface pressure measurer is pressed onto the polishing surface of the polishing pad to measure the shape of the polishing surface before dressing. Subsequently, in accordance with the measured shape of the polishing surface, the polishing surface is dressed.

The traditional dressing method, however, requires the measurement of the shape of the polishing surface of the polishing pad by the surface pressure measurer before the polishing surface is dressed. This is disadvantageous in that the dressing of the polishing surface is time consuming and inefficient.

The present invention has been done to solve the problem above. An object of the present invention is to provide a polishing surface dressing method by which a wafer with a desired shape can be efficiently obtained by polishing because a polishing surface of a polishing pad is dressed in a short time.

To achieve the above-described object, a polishing surface dressing method (present polishing surface dressing method) according to an aspect of the present invention comprises dressing a polishing surface of a polishing pad of a polishing apparatus by a dressing section of a dressing mechanism, the polishing apparatus including: a holding table which is rotatable and holds a workpiece; the polishing pad which is rotatable and has the polishing surface provided to oppose a holding surface of the holding table; the dressing mechanism which is configured to make contact with the polishing surface and dress the polishing surface; a first direction movement mechanism which is configured to move the dressing section of the dressing mechanism in a first direction that is orthogonal to the polishing surface; a second direction movement mechanism which is configured to move at least one of the dressing section or the polishing pad in a second direction parallel to the polishing surface; and a displacement measuring unit which is configured to measure a displacement amount in the first direction of the dressing section, the dressing the polishing surface by the dressing section including: a dressing step of dressing the polishing surface by moving the dressing section along the polishing surface by the second direction movement mechanism while causing the dressing section to be in contact with the polishing surface by the first direction movement mechanism; a polishing surface shape measuring step of measuring the shape of the polishing surface based on the displacement amount in the first direction and a movement position in the second direction of the dressing section that is in contact with the polishing surface; a determination step of determining appropriateness of the shape of the polishing surface measured in the polishing surface shape measuring step; and a condition change step of changing a contact condition in which the dressing section makes contact with the polishing surface in the dressing step, when the shape of the polishing surface is determined to be “No Good”, the dressing step being performed based on the contact condition changed in the condition change step.

According to the present polishing surface dressing method, in the dressing step, the dressing section that is in contact with the polishing surface of the polishing pad is moved horizontally so that the polishing pad is dressed. Simultaneously, in the polishing surface shape measuring step, the shape of the polishing surface is measured based on the displacement amount in the first direction of the dressing section measured by the displacement measuring unit and the movement position in the second direction of the dressing section. To put it differently, the dressing of the polishing surface of the polishing pad and the measurement of the shape of the polishing pad are simultaneously done. The time required for determining appropriateness of the shape of the dressed polishing surface is therefore shortened.

When the shape of the polishing surface of the polishing pad after the dressing is “Good”, a workpiece with a desired shape can be efficiently obtained by carrying out polishing of the workpiece in the subsequent step by using the polishing pad whose polishing surface has been dressed. When the shape of the polishing surface of the polishing pad after the dressing is “No Good”, the measured shape of the polishing surface of the polishing pad is fed back. The contact condition in which the dressing section of the dressing mechanism makes contact with the polishing pad is changed based on the shape of the polishing surface having been fed back, and the polishing surface of the polishing pad is dressed again. It is therefore possible to obtain the workpiece with the desired shape by polishing the workpiece by using the polishing pad whose polishing surface has been dressed again.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken side view of an important part of a polishing apparatus, which shows a dressing step and a polishing surface shape measuring step of a polishing surface dressing method of an embodiment of the present invention.

FIG. 2 is a broken side view of the important part of the polishing apparatus, which shows a polishing step of a method of manufacturing a substrate including the polishing surface dressing method of the embodiment of the present invention.

FIG. 3 is a flowchart showing a flow of steps of the polishing surface dressing method of the embodiment of the present invention and a method of manufacturing a wafer including the polishing surface dressing method.

FIG. 4 is a flowchart showing processing steps of the polishing surface dressing method of the embodiment of the present invention and a method of manufacturing a wafer including the polishing surface dressing method.

FIG. 5 relates to the polishing surface dressing method of the embodiment of the present invention, and shows three patterns of the shape of the polishing pad and the shape of the wafer after polishing, when the shape of the wafer before the polishing is flat.

FIG. 6 relates to the polishing surface dressing method of the embodiment of the present invention, and shows three patterns of the shape of the polishing pad and the shape of the wafer after polishing, when the shape of the wafer before the polishing is convex.

FIG. 7 relates to the polishing surface dressing method of the embodiment of the present invention, and shows three patterns of the shape of the polishing pad and the shape of the wafer after polishing, when the shape of the wafer before the polishing is concave.

DETAILED DESCRIPTION

In the following detailed description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

The following describes an embodiment of the present invention with reference to attached drawings.

Structure of Polishing Apparatus

To begin with, the structure of a polishing apparatus 1 configured to perform a polishing surface dressing method of the present embodiment is described. Hereinafter, an X-axis direction indicated by an arrow in each of FIG. 1 and FIG. 2 (i.e., a second direction parallel to a later-described polishing surface 25a of a polishing pad 25) is referred to as “horizontal direction”, and a Z-axis direction (i.e., a first direction orthogonal to the later-described polishing surface 25a of the polishing pad 25) is referred to as “up-down direction”.

The polishing apparatus 1 shown in FIG. 1 and FIG. 2 is an apparatus configured to polish an upper surface of a wafer W (see FIG. 2) which is a thin circular plate and is a workpiece. This polishing apparatus 1 includes, as main components, a holding table 10 which holds the wafer W, a polishing unit 20 which is configured to polish the wafer W held by the holding table 10, an elevation mechanism 30 which is a first direction movement mechanism configured to move up and down the polishing unit 20 along the up-down direction (first direction), a slurry supply unit 40 which is configured to supply slurry to between a polishing pad 25 of a polishing unit 20 and the wafer W, a dressing mechanism 50 (see FIG. 1) which is configured to dress the polishing surface 25a of the polishing pad 25, a horizontal movement mechanism 60 which is a second direction movement mechanism configured to move the dressing mechanism 50 along the horizontal direction (second direction), a displacement measuring unit 70 which is configured to measure a displacement amount in the up-down direction (first direction) of a dressing section 51 (see FIG. 1) of the dressing mechanism 50, and a controller 80 configured to control each component.

The wafer W is made of a monocrystalline silicon base material. On a front surface of the wafer W which faces down in the state shown in FIG. 2, plural unillustrated devices are formed. These devices are protected by an unillustrated protection tape which is pasted onto the front surface of the wafer W. The front surface (lower surface in FIG. 2) of the wafer W is held by the holding table 10, and the back surface (upper surface in FIG. 2) of the wafer W is polished by the polishing unit 20. Examples of the material of the wafer W include gallium arsenide (GaAs), silicon carbide (SiC), and ceramic, in addition to silicon (Si).

The following describes the main components of the polishing apparatus 1, i.e., the holding table 10, the polishing unit 20, the elevation mechanism 30, the slurry supply unit 40, the dressing mechanism 50, the horizontal movement mechanism 60, the displacement measuring unit 70, and the controller 80 in order.

Holding Table

As shown in FIG. 2, the holding table 10 includes a frame 10A and a base 10B, which are upper and lower members each being disc-shaped, and a disc-shaped porous member 11. The frame 10A and the base 10B are made of, for example, stainless steel (SUS), and are connected with each other so as to be integrated. The porous member 11 is embedded in a circular recess 10a that is formed at a central part of the frame 10A. The porous member 11 is made of porous ceramic, etc. An upper surface of the porous member 11, which is exposed to the frame 10A, constitutes a holding surface 11a that sucks and holds the disc-shaped wafer W. This porous member 11 is selectively connected to an unillustrated suction source such as a vacuum pump and an ejector.

To a rotational shaft 12 which extends vertically downward from a central part of the holding table 10, a motor 13 constituting a rotational driving source and an encoder 14 configured to detect the number of rotations and rotation direction of the motor 13 are connected. As the rotational shaft 12 is rotationally driven by the motor 13 in a direction indicated by an arrow in the drawing, the holding table 10 and the wafer supported thereby rotate about a vertical rotational axial center CL2 at a predetermined speed in the same direction. The motor 13 and the encoder 14 are electrically connected to the controller 80. The controller 80 is configured to receive a detection signal detected by the encoder 14 and control the rotation of the motor 13 based on the received detection signal.

Polishing Unit

The polishing unit 20 includes a vertical spindle 22 which is rotationally driven in a direction indicated by an arrow in the drawing at a predetermined speed by a spindle motor 21 functioning as a rotational driving source, a disc-shaped platen 24 which is attached to the lower end of the spindle 22 via a cylindrical connector 23, and a disc-shaped polishing pad 25 which is detachably attached to the lower surface of the platen 24. The platen 24 is made of aluminum alloy, etc. The polishing pad 25 attached to the platen 24 is, for example, a non-woven fabric or a polyurethane foam including abrasive grain made of, for example, silica, diamond, or alumina. To the spindle motor 21, an encoder 26 configured to detect the number of rotations of the spindle motor 21 is attached. This encoder 26 is electrically connected to the controller 80. The controller 80 is configured to control the rotation of the spindle motor 21 based on a detection signal sent from the encoder 26.

As shown in FIG. 2, the polishing pad 25 has an area that is sufficient to cover from above the wafer W held by the holding surface 11a of the holding table 10. To be more specific, the outer diameter of the polishing pad 25 is arranged to be larger than the outer diameter of the wafer W. The polishing pad 25 is rotationally driven at a predetermined speed in a direction indicated by an arrow in the figure, about a vertical rotational axial center CL1 that is eccentric in the horizontal direction from the center of the wafer W by ε indicated in the figure. The holding table 10 and the wafer W held thereby are rotationally driven at a predetermined speed in a direction indicated by an arrow in the figure (in the same direction as the rotational direction of the polishing pad 25) about a vertical rotational axial center CL2 which is offset in the horizontal direction from the rotational axial center CL1 of the polishing pad 25 by ε.

Elevation Mechanism

The elevation mechanism 30 is a mechanism configured to move up and down the polishing unit 20 in the up-down direction (first direction), and is constituted by a known ball screw mechanism. In this regard, although not illustrated, the ball screw mechanism is composed of members such as a rotatable ball screw that is vertically provided, a motor that is a rotational driving source configured to rotate the ball screw forward and reverse, a nut member attached to an elevation plate that holds the polishing unit 20, and a vertical guide rail that guides the up-down movement of the elevation plate. Into the nut member, the ball screw is inserted and screwed.

With this arrangement, as the motor is activated and the ball screw is rotated forward or reverse, the nut member screwed with the ball screw move up or down along the guide rail, together with the elevation plate. As a result, the polishing unit 20 held by the elevation plate moves up or down along the up-down direction (first direction).

Slurry Supply Unit

The slurry supply unit 40 is configured to supply slurry to a contact portion (polished area) of the wafer W where the wafer W makes contact with the polishing pad 25, while the wafer W is polished. The slurry supply unit 40 includes a slurry supply source 41. A pipe 42 extending from the slurry supply source 41 is connected to a supply path 43 that is a circular hole. This supply path 43 is vertically formed to pass through the center of each of the spindle 22, the connector 23, the platen 24, and the polishing pad 25 of the polishing unit 20. The pipe 42 is provided with an electromagnetic shut-off valve V. The slurry is, for example, acidic solution with dissolved permanganate, or alkaline solution with dissolved sodium hydroxide or potassium hydroxide.

Dressing Mechanism

As shown in FIG. 1, the dressing mechanism 50 includes a disc-shaped dressing section 51. The dressing section 51 is configured to rotate in a direction indicated by an arrow in the drawing, while being in contact with the polishing surface 25a of the polishing pad 25. This dressing section 51 includes a metal base 51a and a grinding stone 51b that is electrodeposited to the base 51a and includes abrasive grain made of diamond, etc.

The dressing section 51 is attached to the upper end of an output shaft (motor shaft) 53a. This output shaft 53a extends vertically upward from a motor 53 that is a rotational driving source provided above a supporting plate 52. The motor 53 is provided with an encoder 54 that is configured to detect the number of rotations and the rotation direction of the motor 53. The motor 53 and the encoder 54 are electrically connected to a later-described dressing section rotation controller 83 provided in the controller 80.

In the dressing mechanism 50, an air cylinder 56 constituting an elevation mechanism configured to move up and down the dressing section 51 in the up-down direction is provided on a horizontal supporting base 55. To the upper end of a piston rod 56a that extends vertically upward from the air cylinder 56 and is capable of moving up and down, the supporting plate 52 is attached together with the motor 53, the encoder 54, and the dressing section 51.

The air cylinder 56 includes a cylinder 56A, an unillustrated piston which is fitted into the cylinder 56A to be movable up and down, and a piston rod 56a which extends upward from the piston and penetrates the cylinder 56A. As compressed air is supplied to and discharged from unillustrated upper and lower chambers above and below the piston in the cylinder 56A, the unillustrated piston and the piston rod 56a move up and down. As the piston rod 56a moves up and down, the dressing section 51 moves up and down. The elevation mechanism configured to move up and down the dressing section 51 may be formed of a hydraulic cylinder or a ball screw mechanism, for example.

The air cylinder 56 constituting the elevation mechanism configured to move up and down the dressing section 51 is electrically connected to a later-described dressing section pressing force controller 85 provided in the controller 80. The pressure in the upper chamber or the lower chamber formed in the cylinder 56A is detected by an unillustrated pressure sensor and a detection signal is sent to the dressing section pressing force controller 85 of the controller 80. Accordingly, the dressing section pressing force controller 85 controls the pressing force of the dressing section 51 by which the polishing surface 25a of the polishing pad 25 is pressed, by adjusting the pressure in the upper chamber or the lower chamber in the cylinder 56A by controlling an unillustrated pressure regulator.

Horizontal Movement Mechanism

The horizontal movement mechanism 60 shown in FIG. 1 constitutes a second direction movement mechanism configured to move the dressing mechanism 50, i.e., the dressing section 51 in the horizontal direction (second direction). Being similar to the elevation mechanism 30, the horizontal movement mechanism 60 is constituted by a ball screw mechanism. That is to say, although not illustrated, the ball screw mechanism constituting the horizontal movement mechanism 60 is composed of members such as a rotatable ball screw that is horizontally provided, a motor that is a rotational driving source configured to rotate the ball screw forward and reverse, a nut member attached to the supporting base 55, and a horizontal guide rail that guides horizontal movement of the dressing mechanism 50. Into the nut member, the ball screw is inserted and screwed.

With this arrangement, as the motor of the ball screw mechanism is activated and the ball screw is rotated forward or reverse, the nut member into which the ball screw is screwed moves horizontally along the guide rail, together with the dressing mechanism 50. As a result, the dressing section 51 of the dressing mechanism 50 moves along the horizontal direction (second direction). The horizontal movement mechanism 60 is electrically connected to a later-described dressing section moving speed controller 84 provided in the controller 80. An unillustrated encoder configured to detect the number of rotations and the rotation direction of an unillustrated motor which is a driving source of the horizontal movement mechanism 60 is also electrically connected to the controller 80. With this arrangement, when a detection signal is sent from the encoder to the controller 80, the controller 80 calculates the position in the horizontal direction of the dressing section 51 of the dressing mechanism 50. Furthermore, the calculated position in the horizontal direction of the dressing section 51 is stored in a later-described storage 81 of the controller 80.

Displacement Measuring Unit

The displacement measuring unit 70 is configured to optically measure a displacement amount in the up-down direction (first direction) of the dressing section 51 in a contactless manner, when the dressing section 51 of the dressing mechanism 50 is moving in the horizontal direction (second direction) while being in contact with the polishing surface 25a of the polishing pad 25 and dressing the polishing surface 25a. In the present embodiment, the displacement measuring unit 70 is constituted by a laser displacement meter. This displacement measuring unit 70 is provided on the supporting base 55 of the dressing mechanism 50. Above the displacement measuring unit 70, an arm-shaped reference member 71 which extends horizontally from the supporting plate 52 of the dressing mechanism 50 is provided. The reference member 71 is made of a material with high light reflectance.

This displacement measuring unit 70 emits laser light vertically upward. This laser light is reflected on the lower surface of the reference member 71, returns to the displacement measuring unit 70, and is received by the displacement measuring unit 70. By performing spectroscopic analysis of optical interference of the laser light, the displacement measuring unit 70 measures the displacement amount in the up-down direction of the dressing section 51 of the dressing mechanism 50. The measured displacement amount of the dressing section 51 is sent to the storage 81 of the controller 80 and is stored in the storage 81.

Controller

The controller 80 includes members such as a CPU (Central Processing Unit) configured to perform computation based on a control program and the storage 81 such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

In the present embodiment, as described below, a contact condition in which the dressing section 51 makes contact with the polishing surface 25a of the polishing pad 25 is changed in a condition change step. To change the contact condition, the following parameters are used in the present embodiment.

• • 1) Rotation speed of the polishing pad 25
  • 2) Rotation speed of the dressing section 51
  • 3) Moving speed of the dressing section 51
  • 4) Pressing force of the dressing section 51

Under these circumstances, the controller 80 is provided with a pad rotation controller 82 configured to control the rotation speed of the polishing pad 25, the dressing section rotation controller 83 configured to control the rotation speed of the dressing section 51, the dressing section moving speed controller 84 configured to control the moving speed of the dressing section, and the dressing section pressing force controller 85 configured to control the pressing force of pressing the dressing section 51 onto the polishing pad 25. The control of the rotation speed of the polishing pad 25 by the pad rotation controller 82, the control of the rotation speed of the dressing section 51 by the dressing section rotation controller 83, the control of the moving speed of the dressing section 51 by the dressing section moving speed controller 84, and the control of the pressing force of pressing the dressing section 51 onto the polishing pad 25 by the dressing section pressing force controller 85 will be detailed later.

Polishing Surface Dressing Method

With reference to FIG. 3 to FIG. 7, the following describes a polishing surface dressing method of the present embodiment and a method of manufacturing a wafer including the polishing surface dressing method, which are executed by the polishing apparatus 1 structured as described above. It is noted that the wafer is an example of a substrate, and the method of manufacturing the wafer is an example of a method of manufacturing a substrate.

To begin with, the polishing surface dressing method of the present embodiment and the method of manufacturing the wafer including the polishing surface dressing method are outlined with reference to FIG. 3. In this polishing surface dressing method, a dressing step and a polishing surface shape measuring step are simultaneously performed. The polishing surface dressing method includes a dressing step, a polishing surface shape measuring step, a determination step, and a condition change step in a flowchart shown in FIG. 3. The method of manufacturing the wafer includes a polishing step in addition to the steps of the polishing surface dressing method.

In the dressing step, as shown in FIG. 1, the polishing surface 25a is dressed by the dressing section 51 in such a way that the dressing section 51 of the dressing mechanism 50 is moved up by the air cylinder 56 to make contact with the polishing surface 25a of the polishing pad 25, and in this state the dressing section 51 is horizontally moved along the polishing surface 25a of the polishing pad 25 by the horizontal movement mechanism 60. In the polishing surface shape measuring step, the shape of the polishing surface 25a of the polishing pad 25 is measured based on a displacement amount in the up-down direction (first direction) and a movement position in the horizontal direction of the dressing section 51 that is in contact with the polishing surface 25a of the polishing pad 25 in the dressing step. The displacement amount in the up-down direction of the dressing section 51 is optically measured by the displacement measuring unit 70 in a contactless manner. The position (movement position) in the horizontal direction of the dressing section 51 is calculated based on the number of rotations and the rotation direction of the unillustrated motor serving as the driving source of the horizontal movement mechanism 60, which are detected by the unillustrated encoder.

In this way, while the polishing surface 25a of the polishing pad 25 is dressed by the dressing section 51 of the dressing mechanism 50 in the above-described dressing step, the shape of the polishing surface 25a of the polishing pad 25 after the dressing is measured in the polishing surface shape measuring step. Thereafter, based on a desired shape of the wafer W after polishing, the appropriateness (“Good” or “Not Good (NG)”) of the shape of the polishing surface 25a of the polishing pad 25 after the dressing is determined in the subsequent determination step.

In this determination step, when the shape of the polishing surface 25a of the polishing pad 25 after the dressing is “Good”, the process proceeds to the subsequent polishing step, and the wafer W is polished by simply using the polishing pad 25 which has been dressed and measured in shape. On the other hand, when the shape of the polishing surface 25a of the polishing pad 25 after the dressing is “No Good (NG)”, the shape of the polishing surface 25a of the polishing pad 25, which has been measured in the polishing surface shape measuring step, is fed back. Subsequently, in the condition change step, the contact condition in which the dressing section 51 makes contact with the polishing surface 25a is changed based on the shape of the polishing surface 25a measured in the polishing surface shape measuring step. Thereafter, the dressing and the measurement of the shape of the polishing surface 25a of the polishing pad 25 are repeated in such a way that the process of (the dressing step+the polishing surface shape step)→(the determination step) is repeated until the shape of the polishing surface 25a of the polishing pad 25 becomes “Good”. The change of the contact condition in which the dressing section 51 makes contact with the polishing surface 25a of the polishing pad 25 will be detailed later.

Now, the following details the polishing surface dressing method and the method of manufacturing the wafer (substrate) including the polishing surface dressing method of the present embodiment with reference to a flowchart shown in FIG. 4. The polishing surface dressing method includes steps S1 to S8 and S11 shown in FIG. 4. The method of manufacturing the wafer includes a step a S9 in addition to the steps S1 to S8 and S11.

When the dressing mechanism 50 dresses the polishing pad 25, as the dressing mechanism 50 shown in FIG. 1 is moved in the horizontal direction (second direction) by the horizontal movement mechanism 60, the dressing section 51 of the dressing mechanism 50 is moved to a position at an outer circumferential part of the polishing pad 25, which is an initial position indicated by solid lines in FIG. 1 (step S1 in FIG. 4). Thereafter, the air cylinder 56 of the dressing mechanism 50 is driven so that the dressing section 51 moves up (step S2 in FIG. 4), and whether the dressing section 51 has made contact with the polishing surface 25a of the polishing pad 25 is determined (step S3 in FIG. 4). The polishing surface 25a of the polishing pad 25 may be made contact with the dressing section 51 of the dressing mechanism 50 by moving down the polishing pad 25 by driving the elevation mechanism 30 of the polishing unit 20.

When the dressing section 51 of the dressing mechanism 50 makes contact with the polishing surface 25a of the polishing pad 25 (step S3: Yes), the dressing step (see FIG. 3) is executed and the polishing surface 25a of the polishing pad 25 is dressed by the dressing section 51 of the dressing mechanism 50. At the same time, the polishing surface shape measuring step (see FIG. 3) is executed so that the shape of the polishing surface 25a is measured (step S4 in FIG. 4). When the dressing section 51 is not in contact with the polishing surface 25a of the polishing pad 25 (step S3: No), the steps S2→S3 are repeated until the dressing section 51 makes contact with the polishing surface 25a of the polishing pad 25.

In the dressing step, as shown in FIG. 1, the spindle motor 21 of the polishing unit 20 is activated and the polishing pad 25 rotates about the rotational axial center CL1 at a predetermined speed in the direction indicated by the arrow in the figure. Simultaneously, the motor 53 of the dressing mechanism 50 is activated and the dressing section 51 rotates at a predetermined speed in the direction indicated by the arrow in the figure (in the same direction as the rotation direction of the polishing pad 25). Furthermore, the dressing section 51 is horizontally moved by the horizontal movement mechanism 60 in a direction indicated by the figure (rightward in FIG. 1) from the initial position indicated by the solid lines in FIG. 1 to a position indicated by chain lines (i.e., the central position of the polishing pad 25). As a result of this, the polishing surface 25a of the polishing pad 25 is dressed by the dressing section 51 of the dressing mechanism 50. At the same time, the shape of the polishing surface 25a of the polishing pad 25 is measured and the dressing amount of dressing the polishing pad 25 by the dressing section 51 is accumulated (step S4 in FIG. 4).

In the measurement of the shape of the polishing surface 25a of the polishing pad 25 in the polishing surface shape measuring step, the shape of the polishing surface 25a is measured by (i) obtaining (calculating) the position (movement position) in the horizontal direction (second direction) of the dressing section 51 of the dressing mechanism 50 moving in the horizontal direction while being in contact with the polishing surface 25a and (ii) measuring the displacement amount in the up-down direction (first direction) of the dressing section 51 at each position in the horizontal direction by the displacement measuring unit 70. In this regard, the position in the horizontal direction of the dressing section 51 is calculated in such a way that the number of rotations of an unillustrated motor provided in the horizontal movement mechanism 60 is measured by an unillustrated encoder. The position in the horizontal direction of the dressing section 51 and the displacement amount in the up-down direction at each position are sent to the storage 81 of the controller 80 and are serially stored in the storage 81.

Concurrently with the dressing step and the polishing surface shape measuring step, a dressing amount measurement step is executed. This dressing amount measurement step includes accumulation of the dressing amount of the polishing pad 25 in the dressing step, determination of whether the accumulated value of the dressing amount is less than a predetermined set value, and issuing of an alarm when the accumulated value of the dressing amount has reached the set value (steps S4, S5, and S11 in FIG. 4).

To put it differently, when the dressing amount of the polishing pad 25 in the dressing of the polishing surface 25a of the polishing pad 25 by the dressing section 51 is accumulated, whether the accumulated dressing amount is less than a predetermined set value (i.e., whether the accumulated value of the dressing amount has reached the durability life of the polishing pad 25) is determined (step S5 of FIG. 4). When the accumulated value of the dressing amount is less than the set value (step S5: Yes), i.e., when the polishing pad 25 has not reached the durability life, whether the dressing of the polishing surface 25a of the polishing pad 25 has been finished is determined (step S6 in FIG. 4). When the accumulated value of the dressing amount of the polishing pad 25 has reached the set value (step S5: No), it is determined that the polishing pad 25 has reached the durability life, an alarm notifying this information is issued (step S11 in FIG. 4), and the dressing and the measurement of the shape of the polishing surface 25a of the polishing pad 25 are finished (step S10 in FIG. 4). In this case, the polishing pad 25 is replaced with new one.

The dressing section 51 of the dressing mechanism 50 is moved by the horizontal movement mechanism 60 from the initial position indicated by the solid lines in FIG. 1 to a final position indicated by chain lines (the central position of the polishing pad 25), while dressing the polishing surface 25a of the polishing pad 25. As a result, the dressing and the measurement of the shape of the polishing surface 25a of the polishing pad 25 are finished (step S6: Yes). Thereafter, the air cylinder 56 of the dressing mechanism 50 is driven so that the dressing section 51 moves down, and the dressing section 51 is separated from the polishing surface 25a of the polishing pad 25 (step S7 in FIG. 4). Subsequently, whether the shape of the polishing surface 25a of the polishing pad 25, which has been dressed, is good or not is determined (step S8 in FIG. 4).

When the shape of the dressed polishing surface 25a of the polishing pad 25 is good (step S8 in FIG. 4: Yes), the process proceeds to the polishing step (see FIG. 3) and a polishing process of polishing the wafer W is executed (step S9 in FIG. 4).

That is to say, in the polishing process of polishing the wafer W, as shown in FIG. 2, the wafer W is sucked and held by the holding surface 11a of the holding table 10. To be more specific, when the wafer W is placed on the holding surface 11a of the holding table 10, the porous member 11 of the holding table 10 is connected to an unillustrated suction source. As a result, the porous member 11 is vacuum-sucked by the suction source and hence negative pressure is generated in the porous member 11. Due to this negative pressure, the wafer W is sucked by and held on the holding surface 11a of the holding table 10. At this stage, the vertical rotational axial center CL2 passing through the center of the holding table 10 is offset in the horizontal direction (second direction) by ε shown in the figure from the vertical rotational axial center CL1 passing through the center of the polishing pad 25.

When the wafer W is sucked by and held on the holding surface 11a of the holding table 10 as described above, the spindle motor 21 of the polishing unit 20 is activated and the polishing pad 25 is rotationally driven about the rotational axial center CL1 at a predetermined speed in the direction indicated by the arrow in the figure. Furthermore, the motor 13 is activated, and the holding table 10 and the wafer W held thereby are rotationally driven about the rotational axial center CL2 at a predetermined speed in the direction indicated by the arrow in the figure (in the same direction as the rotation direction of the polishing pad 25).

In the above-described state in which the wafer W and the polishing pad 25 rotate in the directions shown in the figure, the elevation mechanism 30 is driven to move down the polishing pad 25 in a −Z-axis direction. As a result of this, the polishing surface 25a of the polishing pad 25 makes contact with the entire upper surface (back surface) of the wafer W. Simultaneously, the shut-off valve V of the slurry supply unit 40 is opened. As a result, the slurry is supplied from the slurry supply source 41 to a contact portion (polished portion) of the wafer W where the wafer W makes contact with the polishing pad 25, through the supply path 43 that is a circular hole and is vertically formed to pass through the center of each of the pipe 42, the spindle 22, the connector 23, the platen 24, and the polishing pad 25. Consequently, the entire upper surface of the wafer W is chemically and mechanically polished by the polishing pad 25, with the supply of the slurry. As a result, the grinding marks remaining on the upper surface of the wafer W are removed and the bending strength of the wafer W is improved. In this way, when the shape of the polishing surface 25a of the polishing pad 25 after the dressing is good (step S8: Yes), the upper surface of the wafer W is polished by the polishing pad 25 and the series of the steps is finished (step S10 in FIG. 4).

On the other hand, when the shape of the polishing surface 25a of the polishing pad 25 after the dressing is “No Good (NG)” (step S8: No), the contact condition in which the dressing section 51 of the dressing mechanism 50 makes contact with the polishing pad 25 is changed (step S12 in FIG. 4). In this regard, as parameters for changing the contact condition in which the dressing section 51 makes contact with the polishing pad 25, the present embodiment employs the above-described four parameters, i.e., the rotation speed of the polishing pad 25, the rotation speed of the dressing section 51, the moving speed of the dressing section 51, and the pressing force of the dressing section 51. After the contact condition in which the dressing section 51 makes contact with the polishing pad 25 is changed by controlling at least one of these parameters, the polishing surface 25a of the polishing pad 25 is dressed again (steps S1 to S8 in FIG. 4).

The rotation speed of the polishing pad 25 is changed by the pad rotation controller 82 provided in the controller 80. That is to say, when the rotation speed of the spindle motor 21 detected by the encoder 26, i.e., the rotation speed of the polishing pad 25 is sent to the pad rotation controller 82 of the controller 80, the pad rotation controller 82 controls the rotation speed of the spindle motor 21 so that the rotation speed of the polishing pad 25 is set at an appropriate value. To be more specific, the higher the rotation speed of the polishing pad 25 is, the larger the dressing amount of the polishing surface 25a of the polishing pad 25 is.

The rotation speed of the dressing section 51 of the dressing mechanism 50 is changed by the dressing section rotation controller 83 provided in the controller 80. That is to say, when the rotation speed of the motor 53 detected by the encoder 54, i.e., the rotation speed of the dressing section 51 is sent to the dressing section rotation controller 83 of the controller 80, the dressing section rotation controller 83 controls the rotation speed of the motor 53 so that the rotation speed of the dressing section 51 is set at an appropriate value. To be more specific, the higher the rotation speed of the dressing section 51 is, the larger the dressing amount of the polishing surface 25a of the polishing pad 25 is.

The moving speed of the dressing section 51 in the horizontal direction (second direction) is changed by the dressing section moving speed controller 84 provided in the controller 80. That is to say, when the rotation speed of an unillustrated motor detected by an unillustrated encoder provided in the horizontal movement mechanism 60 is sent to the dressing section moving speed controller 84 of the controller 80, the dressing section moving speed controller 84 controls the rotation speed of the motor so that the moving speed of the dressing section 51 is set at an appropriate value. To be more specific, the higher the moving speed of the dressing section 51 is, the smaller the dressing amount of the polishing surface 25a of the polishing pad 25 is. On the contrary, the lower the moving speed of the dressing section 51 is, the larger the dressing amount of the polishing surface 25a of the polishing pad 25 is.

The pressing force of the dressing section 51 is changed by the dressing section pressing force controller 85 provided in the controller 80. That is to say, the pressure in an unillustrated lower chamber in the air cylinder 56 of the dressing mechanism 50 is sent to the dressing section pressing force controller 85 of the controller 80, and the dressing section pressing force controller 85 calculates the pressing force with which the dressing section 51 presses the polishing pad 25. The dressing section pressing force controller 85 controls the pressure in the lower chamber of the air cylinder 56 so that the pressing force of the dressing section 51 is set at an appropriate value. To be more specific, the larger the pressing force of the dressing section 51 is, the larger the dressing amount of the polishing surface 25a of the polishing pad 25 is. On the contrary, the smaller the pressing force of the dressing section 51 is, the smaller the dressing amount of the polishing surface 25a of the polishing pad 25 is.

In this way, at least one of the four parameters, i.e., the rotation speed of the polishing pad 25, the rotation speed of the dressing section 51, the moving speed of the dressing section 51, and the pressing force of the dressing section 51, is controlled. Consequently, the contact condition in which the dressing section 51 makes contact with the polishing pad 25 is changed (step S12 in FIG. 4). Thereafter, the steps S1 to S8 shown in FIG. 4 are repeated and the polishing surface 25a of the polishing pad 25 is dressed again. This re-dressing of the polishing surface 25a of the polishing pad 25 is repeated until the shape of the polishing surface 25a of the polishing pad 25 after the dressing is evaluated as “Good”.

The shape of the wafer W before polishing (after grinding) is, for example, 1) flat (even thickness), 2) convex with a thick central portion, or 3) concave with a thin central portion. Various shapes that the wafer W after the polishing is required to have and shapes of the polishing surface 25a of the polishing pad 25 corresponding to the respective shapes of the wafer W after the polishing, when the shape of the wafer W before the polishing is one of the above-described 1) to 3), are shown as patterns 1 to 3 in each of FIG. 5, FIG. 6, and FIG. 7. The shape of the wafer after the polishing (before the grinding) is obtained by measuring the thickness of the wafer W at plural parts along the radial direction of the wafer W.

1) When Shape of Wafer W Before Polishing Is Flat:

As shown by the pattern 1 in FIG. 5, when the shape of the wafer W before the polishing is flat and the required shape of the wafer W after the polishing is convex with a thick central portion, the polishing surface 25a of the polishing pad 25 is dressed so that the central portion is thick and convex and the intermediate portion in the radial direction is thin and concave.

When the required shape of the wafer W after the polishing is flat as in the pattern 2, the polishing surface 25a of the polishing pad 25 is dressed to be flat and even in thickness.

When the required shape of the wafer W after the polishing is concave with a thin central portion as in the pattern 3, the polishing surface 25a of the polishing pad 25 is dressed so that the central portion is thin and concave and the intermediate portion in the radial direction is thick and convex.

2) When Shape of Wafer W Before Polishing Is Convex:

As shown by the pattern 1 in FIG. 6, when the shape of the wafer W before the polishing is convex and the required shape of the wafer W after the polishing is convex with a thick central portion, the polishing surface 25a of the polishing pad 25 is dressed so that the central portion is thick and convex and the intermediate portion in the radial direction is thin and concave.

When, as in the pattern 2, the required shape of the wafer W after the polishing is convex but is gentler than the shape in the pattern 1, the polishing surface 25a of the polishing pad 25 is dressed to be flat and even in thickness.

When the required shape of the wafer W after the polishing is flat as in the pattern 3, the polishing surface 25a of the polishing pad 25 is dressed so that the central portion is thin and concave and the intermediate portion in the radial direction is thick and convex.

3) When Shape of Wafer W Before Polishing Is Concave:

As shown by the pattern 1 in FIG. 7, when the shape of the wafer W before the polishing is concave and the required shape of the wafer W after the polishing is flat, the polishing surface 25a of the polishing pad 25 is dressed so that the central portion is thick and convex and the intermediate portion in the radial direction is thin and concave.

When the required shape of the wafer W after the polishing is concave as in the pattern 2, the polishing surface 25a of the polishing pad 25 is dressed to be flat and even in thickness.

When, as in the pattern 3, the required shape of the wafer W after the polishing is concave and deeper in concavity than the shape of the pattern 2, the polishing surface 25a of the polishing pad 25 is dressed so that the central portion is concave and thin whereas the intermedial portion in the radial direction is convex and thick.

As clarified above, according to the method of dressing the polishing pad 25 of the present embodiment, in the dressing step, the dressing section 51 that is in contact with the polishing surface 25a of the polishing pad 25 is moved horizontally so that the polishing surface 25a is dressed. Simultaneously, in the polishing surface shape measuring step, the shape of the polishing surface 25a is measured based on the displacement amount in the up-down direction (first direction) of the dressing section 51 measured by the displacement measuring unit 70 and the movement position in the horizontal direction (second direction) of the dressing section 51. To put it differently, the dressing of the polishing surface 25a of the polishing pad 25 and the measurement of the shape of the polishing surface 25a are simultaneously done. The time required for determining appropriateness of the shape of the dressed polishing surface 25a is therefore shortened.

When the shape of the polishing surface 25a of the polishing pad 25 after the dressing is “Good”, the polishing of the wafer W, which is the subsequent step, is performed by using the polishing pad 25 whose polishing surface 25a has been dressed. It is therefore possible to efficiently obtain the wafer W with a desired shape, by the polishing. When the shape of the polishing surface 25a of the polishing pad 25 after the dressing is “No Good”, the measured shape of the polishing surface 25a of the polishing pad 25 is fed back. The contact condition in which the dressing section 51 of the dressing mechanism 50 makes contact with the polishing pad 25 is changed based on the shape of the polishing surface 25a having been fed back, and the polishing surface 25a of the polishing pad 25 is dressed again. It is therefore possible to obtain the wafer W with the desired shape by polishing the wafer W by using the polishing pad 25 whose polishing surface 25a has been dressed again.

The embodiment described above presupposes that the workpiece is a wafer. In this regard, the present embodiment is similarly applicable to a method of dressing a polishing pad by which a workpiece different from a wafer is polished.

Furthermore, in the embodiment above, the dressing of the polishing surface 25a of the polishing pad 25 in the dressing step is performed by moving the dressing section 51 of the dressing mechanism 50 in the horizontal direction. In this regard, it is possible to employ an arrangement in which the polishing surface 25a of the polishing pad 25 is dressed while either the polishing pad 25 is moved or both the dressing section 51 and the polishing pad 25 are moved.

The application of the present invention is not limited to the embodiment described above, and various variations are of course possible within the scope of the claims and the technical ideas described in the specification and drawings.

The foregoing detailed description has been presented for the purposes of illustration and description. Many modifications and variations are possible in light of the above teaching. It is not intended to be exhaustive or to limit the subject matter described herein to the precise form disclosed. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims appended hereto.