WORKPIECE PROCESSING METHOD

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a processing method for processing a workpiece having a plurality of multi-crystal silicon columns embedded in single-crystal silicon so as to expose the heads of the multi-crystal silicon columns.

2. Description of the Related Art

In a semiconductor device manufacture step, the front surface of a generally disklike semiconductor wafer is sectioned by predetermined dividing lines called streets arranged in a lattice-like pattern into a plurality of areas, in which devices such as ICs, LSIs or the like are formed. Then, the semiconductor wafer is cut along the predetermined dividing lines to divide the areas formed with the devices, whereby individual semiconductor chips are manufactured. In order to downsize and sophisticate devices, a module structure is made practicable in which a plurality of semiconductor chips are laminated and the electrodes of the semiconductor chips thus laminated are connected together. In the module structure, through holes (via holes) are formed at respective positions where the electrodes are formed in the semiconductor wafer and conductive material such as multi-crystal silicon, aluminum or the like to be connected to the electrodes is embedded in a columnar manner into the through holes. (See e.g. Japanese Patent Laid-open No. 2003-163323.)

As a processing method for exposing multi-crystal silicon columns in a work piece having a plurality of the multi-crystal silicon columns embedded in a single-crystal silicon, a grinding process using a grinding tool having grinding stones is conceivable. Grinding may be performed using grinding stones with a large grain diameter in order to expose the heads of the multi-crystal silicon columns. In such a case, however, high-precision head-exposure cannot be performed. Even so, if grinding stones with a small grain diameter are used to perform grinding, a problem arises as below. When a multi-crystal silicon portion different in hardness from single-crystal silicon is to be ground, grinding burn or clogging of grinding stones may occur so that the grinding cannot be done.

Incidentally, the head positions of the multi-crystal silicon columns embedded in single-crystal silicon have a variation of approximately 5 μm. Therefore, a removal amount of as small as approximately 5 μm is needed to uniformly expose the heads of the multi-crystal silicon columns to the front surface of the single-crystal silicon. In general, a large removal amount can be handled by forming a rough surface with good biting even by means of a grinding stone having rough grinding grains with a certain level of small diameter and then processing the surface by a grinding stone having grinding grains with a small diameter. However, it is difficult for the grinding method as mentioned above to cope with such a slight removal amount.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a processing method capable of exposing the heads of a plurality of multi-crystal silicon columns embedded in single-crystal silicon with ease and with a high degree of accuracy.

In accordance with an aspect of the present invention, there is provided a method of processing a workpiece having a plurality of multi-crystal silicon columns embedded in single-crystal silicon, including an abrasive step of polishing the single-crystal silicon and the multi-crystal silicon columns by use of an abrasive tool in a dry manner to expose all heads of the multi-crystal silicon columns to a front surface of the single-crystal silicon.

Preferably, the workpiece processing method further includes a grinding step of grinding the single-crystal silicon by use of a grinding tool before the abrasive step.

The processing method according to the present invention includes the abrasive step of concurrently polishing the single-crystal silicon and the plurality of multi-crystal silicon columns in a dry manner by use of the abrasive tool to expose the heads of the multi-crystal silicon columns to the front surface of the single-crystal silicon. Therefore, even if the workpiece contains materials different in hardness from each other, it can uniformly be processed. Thus, the method can provide an effect of exposing the heads of the multi-crystal silicon columns embedded in the single-crystal silicon to the front surface of the single-crystal silicon with ease and with a high degree of accuracy.

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 some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are step diagrams illustrating a processing method according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments for performing a processing method according to the present invention will hereinafter be described with reference to the drawings. The present invention is not limited to the embodiments but can be modified in various ways without departing from the gist of the present invention. FIGS. 1A to 1D are step diagrams illustrating a processing method of an embodiment. A workpiece 10 to be processed is first prepared as illustrated in FIG. 1A. This workpiece 10 has a plurality of multi-crystal silicon columns 12 embedded in single-crystal silicon 11. The head positions of the multi-crystal silicon columns 12 have a variation of h, approximately 5 μm. Therefore, a removal amount of at least 5 μm is needed to uniformly expose the heads of the multi-crystal silicon columns 12.

Referring to FIG. 1B, a grinding step in which only the single-crystal silicon 11 is ground using a grinding tool 20 is performed on such a workpiece 10. The grinding tool 20 is configured such that a plurality of grinding stones 23 are provided on the lower end face of a grinding wheel 22 mounted to a spindle 21 drivingly rotated by a motor not illustrated. The grinding tool 20 and a chuck table (not shown) holding the workpiece 10 are rotated relatively to each other at a given speed to grind the single-crystal silicon 11. A dimension h1 corresponding to a ground amount in this case is controlled to reach a position close to the head of a multi-crystal silicon column 12 located at a highest position in the workpiece 10 as much as possible in a range not reaching the head of this multi-crystal silicon column 12.

The grinding processing by the grinding tool 20 in this grinding step is performed satisfactorily because an object is only the single-crystal silicon 11, which contains no materials different in hardness. The grinding step is performed by being divided into two steps: rough grinding performed by use of grinding stones 23 having rough grinding grains in the most part thereof and finish grinding performed by use of grinding stones 23 having small grinding grains in the last half of the dimension h1. Thus, the processing efficiency of the grinding step (a reduction in processing time) is increased and flatness is enhanced at the time of shift to the next step.

After the grinding step as described above, the single-crystal silicon 11 and the multi-crystal silicon columns 12 are concurrently polished in a dry manner by use of an abrasive tool 30 as illustrated in FIG. 1C. In this way, an abrasive step is performed to expose the heads of the multi-crystal silicon columns 12. The abrasive tool 30 is configured such that an abrasive pad 33 is provided on the full surface of the lower end surface of a polishing wheel 32 mounted to a spindle 31 drivingly rotated by a motor not illustrated. The abrasive pad 33 is composed of felt having a given density or more and a given hardness or more and grinding grains scattered in the felt as disclosed in e.g. Japanese Patent Laid-open No. 2002-283243, etc. The abrasive tool 30 and a chuck table holding the workpiece 10 are rotated relatively to each other at a given speed. Thus, the single-crystal silicon 11 and the multi-crystal silicon columns 12 are concurrently polished in a dry manner. In this case, the processing rate is set slower than that at the time of the grinding step described above. A dimension h2 corresponding to the polishing amount in this case is equal to or greater than the dimension h mentioned above. In the present embodiment, the dimension h2 is set at e.g. approximately 7 μm or more in view of the variations in the dimension h.

The abrasive processing by the abrasive tool 30 in this abrasive step is processing for a portion containing the single-crystal silicon 11 and the multi-crystal silicon columns 12 which are different in hardness from each other. However, since the abrasive processing is dry polishing using the abrasive tool 30, the single-crystal silicon 11 and the multi-crystal silicon columns 12 can uniformly be processed without any problem as illustrated in FIG. 1D. Thus, the heads of the multi-crystal silicon columns 12 embedded into the single-crystal silicon 11 can be exposed with ease and with a high degree of accuracy.

The present invention is not limited to the details of the above described preferred embodiments. 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.