JPH0811344B2 - Conductive vacuum chuck - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive vacuum chuck, and more particularly to a conductive vacuum chuck suitable for grinding a thin layer represented by a silicon wafer.

[Conventional technology and its problems]

Silicon wafers are widely used as substrates for semiconductor products, and are required to have good surface roughness in addition to high purity and large diameter in accordance with the degree of integration of integrated circuits.

Such good surface roughness is realized by grinding with a grindstone of fine abrasive grains. However, the following points pose a problem in this grinding process. The first point is that the thickness is only 0.4-1
It is to fix the work piece of about mm without deforming it while keeping the flatness good. The second point is to precisely eliminate the deviation of the grindstone and the unevenness of the grindstone, which reduces the grinding efficiency and deteriorates the finished surface. It is to prevent.

Conventionally, a vacuum chuck has been known as a means for fixing a work piece, but since a conventional vacuum chuck has a large opening, it is easy to deform a thin work piece though it has a high suction force.
Good flatness was not obtained.

As a countermeasure, it is possible to use porous ceramics such as white alundum as an adsorption plate. However, this vacuum chuck is not conductive. Therefore, even if it is possible to fix a thin work piece, there is no effect on the sharpening of the grindstone, and there is a problem that the sharpness is reduced in a short time and the finished surface is deteriorated.

The present invention was devised to solve the above problems, and an object of the present invention is to enable thin layer materials typified by silicon wafers to be mirror-finished easily and efficiently. An object of the present invention is to provide a conductive vacuum chuck device of this kind that can effectively realize a dressing grinding method.

[Means for solving the problem]

In order to achieve the above object, the present invention is a base provided with a suction passage, and an adsorption plate made of a breathable metal sintered body is assembled through an insulator having a suction hole communicating with the suction passage. is there.

[Action]

The vacuum chuck of the present invention is fixed to a processing machine by a base, a work piece is arranged on a suction plate, a suction passage is connected to a vacuum pump to suck, and a conductive grindstone is used as a positive electrode and a suction plate by a power supply device. It is energized as a negative electrode. Since the adsorbing plate has an infinite number of minute open pores uniformly distributed, it has an excellent adsorbing power and also has electrical conductivity, so that power is directly supplied to the workpiece. As a result, an electric discharge is generated between the grindstone and the workpiece, an appropriate electric discharge dressing is performed during the grinding, and a good wearing taste is maintained.

〔Example〕

 Embodiments of the present invention will be described below with reference to the accompanying drawings.

1 and 2 show an embodiment of a conductive vacuum chuck device according to the present invention, and FIGS. 3 and 4 show a usage state. Reference numeral 1 denotes a base, which is made of a material having high mechanical strength, has a fixing groove 10 in the lower portion, and is fixed to the table 9 of the processing apparatus. The base 1 is provided with a mounting recess 11 having a required depth at the upper portion.
Further, an air collecting recess 12 concentric therewith is formed, and the air collecting recess 12 communicates with the outer periphery of the base 1 through a suction passage hole 13.

Reference numeral 2 is a disc-shaped insulator made of ceramic or plastic. Concentric grooves 20 are formed on the upper surface, and suction holes 21, 2 reaching the bottom at a required pitch are formed on the bottom of the concentric grooves 20.
One is drilled.

Reference numeral 3 is an adsorption plate made of a breathable metal sintered body, which is made by mixing, molding and sintering metal powder and metal short fibers, and by the sintering fine pores are uniformly distributed on the surface, The open pores penetrate the thickness direction and reach the lower surface. The material, the sintering conditions, and the finishing method of the air-permeable metal sintered body are appropriately selected so as to satisfy the necessary conditions such as air permeability (adsorption force), conductivity, and workability.

Any metal powder may be used as long as it has conductivity. For example, one or two of iron-based powder such as cast iron and pure iron, copper-based powder, and aluminum-based powder.
More than one seed is used. The metal short fibers are a reinforcing material, and iron-based ones such as cast iron, steel and stainless steel are used. The mixing ratio of the metal powder and the metal short fibers is arbitrary, for example 9: 1.
And so on. The insulator 2 is a mounting recess 11 for the base 1.
The suction plate 3 is superposed on the suction plate 3.

Reference numeral 4 denotes a ring-shaped pressing member made of an insulating material such as ceramic or plastic, which has a two-step projecting peripheral portion on the inner diameter side, a flange portion 30 formed on the suction plate 3, and an insulator 2.
It is adapted to engage with the flange portion 22 formed on the.
The pressing member 4 is attached to the upper edge portion of the base 1, and the bolt 5 is screwed in to fix the suction plate 3 and the insulator 2 to the base. A cover 6 is fitted on the outer peripheral surfaces of the base 1 and the pressing member 4. The cover 6 is used to improve the corrosion resistance of the power feeding portion and is also made of an electrically insulating material.

Reference numeral 7 denotes an electrode, which is screwed into the cover 6 and the pressing member 4 as shown in FIG. 2 and has its tip closely contacting the suction plate 3. This electrode is a power supply device for discharging by the cable 18.
Connected with 19.

A suction tube 8 is connected to the suction passage hole 13 via a connector 14, and is connected to a vacuum pump 23.

3 and 4 show a grinding device to which the present invention is applied. The grinding device is fixed to the table 9 by the base 1, and the conductive grindstone 15 is rotatably attached to the upper part by the shaft 16 so that the conductive grindstone 15 can be used. A power supply brush 17 as an electrode is arranged on one side of the power supply device, and is connected to the power supply device 19 by a cable 18 '.

[Operation of Example]

Since the present invention has the above-mentioned structure,
For example, when the silicon wafer W is mirror-finished, the workpiece W is placed on the suction plate 3 and the vacuum pump 23 is driven. Thereby, the suction tube 8, the suction passage hole 13,
Negative pressure acts on the suction plate 3 via the air collecting recess 12, the suction hole 21, and the concentric circular groove 20. Since the adsorbing plate 3 is made of a breathable metal sintered body and innumerable fine open pores are distributed, a uniform suction force is generated on the surface, and even if the workpiece W is thin, it is not deformed. , It is fixed by suction while maintaining good flatness.

In this state, the table 9 and the conductive grindstone 15 are rotated, and the conductive grindstone 15 is pressed against the workpiece W so as to obtain a predetermined cut. As a result, the processed material W is ground. At this time, the table 9 and the conductive grindstone 15 are moved relative to each other to give a feed, and the power supply device 19 is further actuated. The suction plate 3 is made of a metal sintered body, and the electrode 8 supplies the power supply device.
Since it is connected to 19, a weak electric discharge phenomenon occurs at the interface between the conductive grindstone 15 as a positive electrode and the processing material W as a negative electrode, and the electric discharge causes the conductive grindstone 15 to be automatically subjected to in-process dressing at high speed. Done. That is, the discharge melts the base material, removes the abrasive grains with blunt cutting edges, and exposes new abrasive grains. As a result, good sharpness is maintained, and the synergic effect with the adsorption force makes it possible to mirror finish a thin workpiece with high efficiency and accuracy.

At this time, the lower surface of the suction plate 3 is in close contact with the insulating plate 2 and the outer peripheral side is in close contact with the pressing member 4, so that the inside of the chuck has an insulating structure. Therefore, it is electrically insulated from the base 1, and therefore no insulation structure of the processing apparatus including the table 9 is required. The vacuum chuck of the present invention is not limited to the grinding of silicon wafers, but can be applied as a fixing means for processing various other book layer materials.

 Specific examples of the device of the present invention and results of use are shown below.

I. Two types (A, B) of different materials were manufactured as the suction plate. All dimensions were 120 mmφ × 20 mm.

Type A is Fe86wt%, Cu4% as metal powder, Fe as metallic short fiber, Type B is the same as type A as metallic powder, SUS304 is used as metallic short fiber, and the composition is 90% metallic powder respectively.
% And short metal fibers 10 wt%. The sintering conditions for both type A and type B were 1150 ° C. × 1 hour.

After sintering, cutting was performed to make the outer dimensions uniform, the upper surface was ground, and lapped. The finished surface has an average of 10 to 20 μm
The open pores were uniformly distributed. As a result of measuring the adsorption force, the vertical direction is 10.2 kgf for the A type, 24.4 kgf for the B type, 3.4 kgf for the A type in the horizontal direction, 5.8 kgf for the B type. It was found to have a strong adsorption power.

A vacuum chuck was constructed by incorporating a suction plate of type II.A as shown in FIG. 1, and the vacuum chuck was mounted on a rotary surface grinding machine to perform discharge in-process dressing grinding of a silicon wafer.

The grinding wheel is a cast iron bond diamond wheel (200 mmφ,
A cup type, # 1200, concentration degree 75, tooth width 5 mm) was used. The discharge power source was a wire cutting power source, the silicon wafer was 4 inches φ, the thickness was 0.6 mm and 1.0 mm, and 12.03 Ωcm was used.

III. As a result, it was possible to grind silicon wafers of any thickness without any problem, and it was possible to grind to a thickness of about 0.4 mm.

The discharge in-process dressing characteristics for a 0.6 mm thick silicon wafer are shown in FIG.

The grinding conditions at this time are: grinding speed 999m / min, cutting depth 0.
02m / min, discharge condition is pulse width 1μs, rest time 1μ
s, no-load voltage 60V, set current 10A.

It can be seen that the grinding distance continues for a long time with each feed, and a mirror surface with a surface roughness of about 0.10 μm can be obtained with low-speed feed.

〔The invention's effect〕

According to the present invention described above, the thin layer workpiece can be adsorbed and fixed without being deformed, and at the same time, the current can be directly applied, and the structure is simple. Therefore, it is not necessary to modify the processing machine or to take measures against insulation, and the excellent effect that the thin layer material can be processed easily, with high efficiency and high accuracy by the electric discharge in-process dressing is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a conductive vacuum chuck according to the present invention, FIG. 2 is a partially cutaway side view of the same, FIG. 3 is a perspective view showing a state of use of the chuck of the present invention, and FIG. And FIG. 5 is a graph showing machining characteristics when the present invention is used. 1 ... Base, 2 ... Insulator, 3 ... Adsorption plate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/68 P

Claims (3)

[Claims] 1. A conductive body characterized in that a suction plate made of a gas permeable metal sintered body is attached to a base body having a suction passage through an insulator having a suction hole communicating with the suction passage. Vacuum chuck. 2. The adsorption plate according to claim 1, wherein the adsorption plate is made of a composite material obtained by mixing metal powder with short metal fibers, molding and sintering, and having fine open pores on the surface. Conductive vacuum chuck. 3. The conductive vacuum chuck according to claim 1, which is applied to a discharge in-process dressing grinding method in which a conductive grindstone is used as a positive electrode and a work piece is used as a negative electrode to generate a weak discharge.