JP2001071260A - Wafer holding plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the dispersion depending on an attaching position of a wafer and to improve a yield rate by providing a wafer holding surface with void with a specific area occupation rate and flattening the surface excluding voids. SOLUTION: In a grinding process of a wafer, the wafer 2 is attached to a plate 1 by means of the wax 3, or fixed by vacuum suction. The plate 1 is formed by ceramic such as alumina or the like, a holding surface 1a of the wafer 2 has voids 6 with 5-15% area occupation rate, and the surface excluding voids is a flat surface of below 2 μm of flatness. As the surface is free from projecting parts, and has only recessed part formed by voids 6, the wafer 2 can be prevented from being damaged. Further by putting the wax 3 in the recessed parts of the voids 6, a contact angle is reduced, and the wettability of the wax can be improved, which improves a yield rate of the wafer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate for holding a plate-like body such as a silicon wafer when the body is polished.

[0002]

2. Description of the Related Art Conventionally, when a plate-like body such as a silicon wafer is polished, a plurality of wafers 12 are attached to a holding surface 11a of a plate 11 as shown in FIG. This plate 11 is placed on a lapping machine 14 on which loose abrasive grains 15 are arranged, and the plate 11 and the lapping machine 14 are relatively slid while applying a pressing force F, so that the surface of the wafer 12 is removed. It is designed to be polished.

Further, the plate 11 is formed of ceramics such as alumina, and the holding surface 11a of the wafer 12 is a smooth surface having a flatness of 1 μm or less (see, for example, Japanese Patent Publication No. 60-33624). ).

However, in recent years, the size of the plate 11 has been increased to 500 to 600 mm with the increase in the size of the wafer 12, so that it is necessary to reduce the thickness of the plate 11 in order to reduce the weight. There was a problem that it became easier. On the other hand, a proposal has been made in which the plate 11 is formed of a ceramic having a high Young's modulus, thereby making deformation less likely to occur, increasing the specific rigidity, preventing bending due to its own weight, and reducing the overall weight ( See JP-A-6-270055).

[0005]

By the way, the wafer 12
When the wax 13 is attached to the plate 11 with the wax 13, the wettability of the wax 13
2 greatly affects the flatness. Therefore, conventionally, the surface roughness of the surface of the plate 11 has been roughened in order to improve the wettability, but there has been a problem that the convex portion of the surface irregularities may scratch the wafer.

The holding surface 11a of the plate 11 is processed so that the flatness is 1 μm or less. In practice, as shown in FIG. 3, even if the flatness d is within a predetermined range, It is unavoidable that minute undulations and the like exist on the holding surface 11a.
However, there is also a problem that since the wafer is polished into a undulating shape and becomes a defective product, variation occurs depending on the position where the wafer 12 is attached, and the yield is poor.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a wafer holding plate made of ceramics for holding a wafer during polishing, the wafer holding surface has an area occupancy of 5 to 15%. % Voids, and the surface other than the voids is flat.

Further, the present invention is characterized in that the average diameter of the voids is 3.5 μm or less, and the surface roughness (Ra) of the wafer holding surface including the voids is 0.4 to 2.0 μm. .

That is, according to the present invention, by providing a void in the wafer holding surface, wax enters the concave portion of the void to improve wettability, and since the surface other than the void is a flat surface, it is convex. There is no portion, so that scratching of the wafer can be prevented.

[0010]

Embodiments of the present invention will be described below.

When a plate-like body such as a silicon wafer is polished, a plurality of wafers 2 are adhered to and held by a wax 3 on a holding surface 1a of a plate 1 as shown in FIG. The abrasive grains 5 are placed on the lapping machine 4 on the surface, and the plate 1 and the lapping machine 4 are pressed while applying a pressing force F.
Are relatively slid, so that the surface of the wafer 2 is polished.

In the polishing process of the wafer 2, the wafer 2
Is attached to the plate 1 with wax 3 or fixed by vacuum suction. Wafer 2 for high integration of IC
Is required to be very strict, and accordingly, the flatness of the plate 1 must be strictly suppressed. The flatness at the time of polishing is affected by the pressing force F at the time of polishing and distortion due to temperature change, in addition to the flatness before the wafer 2 is fixed.

Further, as shown in FIG. 1, the plate 1 is formed of ceramics such as alumina,
Of the void 6 having an area occupancy of 5 to 15%
And the surface other than the void 6 is a flat surface having a flatness of 2 μm or less.

As described above, since the holding surface 1a has no convex portion and only the concave portion formed of the void 6, the scratching of the wafer 2 can be prevented. In addition, since the wax 3 enters the concave portion of the void 6, the contact angle is reduced, the wettability of the wax is improved, and the yield of the wafer 2 can be increased.

Here, the area occupancy of the void 6 is 5 to 15
When the void ratio is less than 5%, the surface tension increases, so that the contact angle increases and the wettability deteriorates. On the other hand, when the void ratio exceeds 15%, the contact angle increases, and the wettability also increases. This is because the strength of the plate 1 itself is weakened as well as the strength of the plate 1 becomes unacceptable.

Further, the average diameter of the voids 6 on the holding surface 1a of the plate 1 is set to 3.5 μm or less.
It is preferable that the surface roughness (Ra) containing the silicon wafer be 0.4 to 2.0 μm. This can eliminate minute undulations at the position where the workpiece is attached, and can reduce the variation due to the attachment position. And the like can be polished with extremely high precision and high yield.

The reason why the average diameter of the voids 6 is set to 3.5 μm or less is that if the average diameter of the voids 6 exceeds 3.5 μm, the strength of the plate 1 also decreases.
The reason why the surface roughness (Ra) of the holding surface 1a including the voids 6 is 0.2 to 2.0 μm is that when the surface roughness (Ra) is less than 0.4 μm, the surface tension becomes large, so The corners become larger and the wettability worsens, while 2.0 μm
Is exceeded, the surface shape of the plate 1 is distorted, the flatness cannot be maintained, and the yield of the wafer 2 is reduced.

Various ceramics can be used as the ceramic constituting the plate 1, but alumina ceramics and silicon carbide ceramics are particularly preferable. Here, alumina ceramics means that the content of Al ₂ O ₃ is 99.5% by weight or more, and SiO ₂ ,
Contains CaO, MgO, etc. and has an average crystal particle diameter of 2 to 20 μm
m, preferably 2 to 8 μm.

The silicon carbide-based ceramic is SiC
A sintered body having a content of 95% by weight or more and containing sintering aids such as boron (B), carbon (C), or Al ₂ O ₃ and Y ₂ O ₃ , and having high Young's modulus and high specific rigidity. Not only that, it is also excellent in corrosion resistance and heat conductivity, and is an optimal material for the plate 1.

When manufacturing the plate 1 of the present invention, the above-mentioned raw material powder containing a material which is burned off during firing is formed into a predetermined plate shape and fired. In the sintered body obtained in this manner, the burned-out portion of the material becomes void, and the surface thereof is polished to obtain a sintered body as shown in FIG.
As shown in (1), a void 6 is provided, and other portions can form a flat holding surface 1a.

At this time, the area occupancy of the voids 6 and the average diameter of the voids 6 can be controlled by adjusting the content of the materials to be burned off and the particle size, and these values fall within the above-mentioned ranges. What is necessary is to make it.

In the plate 1 manufactured in this way, voids 6 are present not only in the holding surface 1a but also in the inside. Therefore, the weight can be reduced, and when the holding surface 1a is roughened. By re-polishing, the holding surface 1a having the same void occupancy can be easily obtained.

In the above embodiment, the polishing of the wafer 2 made of silicon or the like has been described. However, the wafer 2 in the present invention is not limited to this, and includes a plate-shaped body made of ceramic, sapphire, glass or the like. However, it goes without saying that the plate 1 of the present invention can also be used for polishing these with high precision.

[0024]

EXPERIMENTAL EXAMPLE 1 Here, a plate 1 was manufactured using ceramics having various void ratios shown in Table 1, and a use test was conducted. Note that, in order to change the area occupancy and the average diameter of the voids, resinous beads were included as a material that would be burned off during firing.

The diameter of each ceramic is 48
A plate 1 having a size of 5 mm and a thickness of 16 mm and having a holding surface 1 a having a flatness of 2 μm as shown in FIG.
After attaching and polishing five silicon wafers each having 6 inches, the flatness and the parallelism of each wafer were inspected, and the ratio (yield) of those falling within a predetermined standard was examined.

The measurement of the area occupation ratio (void ratio) of the voids 6 was performed by the following method. First, an image of the holding surface 1a of the plate 1 is captured by using an optical microscope and a video camera, converted into an analog signal corresponding to the contrast of the image, and the shape is identified and sorted by comparing the analog signal with the reference intensity of shading. Next, after digitizing the image, shape measurement and statistical processing were performed by a computer.

The alumina in Table 1 has an Al ₂ O ₃ content of 99.5% by weight and the average particle diameter is reduced to 2 to 8 μm by reducing the particle diameter of the raw material.

As shown in Table 2, when the area occupation ratio of the voids on the holding surface 1a of the plate 1 is as small as less than 5%, the wafer yield decreases. On the contrary, when the area occupation ratio of the voids exceeded 15%, the strength of the plate 1 was reduced.

On the other hand, the area occupancy of the void is 5 to
In the case of 15%, the contact angle was smaller than that of the conventional product, the wettability was improved, and the yield of the wafer was 80% or more, showing excellent results.

[0030]

[Table 1]

[0031]

[Table 2]

Experimental Example 2 Next, a plate 1 was prepared using alumina A (2%) shown in Table 1.
The same experiment as in Experimental Example 1 above was conducted by changing the average void diameter of the holding surface 1a and the surface roughness (Ra) including the void 6 on the holding surface 1a. The results are as shown in Table 3.

According to Table 3, the average void diameter exceeds 3.5 μm, or the surface roughness is less than 0.4 μm or 2.0 μm.
If it exceeds m, the yield of the wafer 2 is obviously reduced. On the other hand, when the average void diameter is less than 3.5 μm and the surface roughness is in the range of 0.4 to 2.0 μm, the yield can be clearly improved.

[0034]

[Table 3]

[0035]

According to the present invention, in a plate made of ceramics for holding a wafer when it is polished, the wafer holding surface has a void having an area occupancy of 5 to 15% and a surface other than the void. The flat surface makes it possible to improve the wettability of the wax and prevent the wafer from being scratched.

The average diameter of the voids is set to 3.5 μm or less, and the surface roughness (R
By setting a) to 0.4 to 2.0 μm, minute undulations at the position where the workpiece is attached can be eliminated, and variations due to the attaching position can be reduced. It is possible to perform polishing with high yield and high yield.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a wafer holding plate of the present invention.

FIG. 2 is a sectional view of a wafer polishing apparatus using the wafer holding plate of the present invention.

FIG. 3 is a sectional view showing a conventional wafer holding plate.

FIG. 4 is a sectional view of a conventional wafer polishing apparatus using a wafer holding plate.

[Explanation of symbols]

 1, 11: Plate 1a, 11a: Holding surface 2, 12: Wafer 3, 13: Wax 4, 14: Lapping machine 5, 15: Free abrasive 6: Void

Claims (2)

[Claims] 1. A plate made of ceramics for holding when polishing a wafer, wherein the wafer holding surface has voids having an area occupancy of 5 to 15%, and surfaces other than the voids are flat surfaces. A wafer holding plate. 2. The method according to claim 1, wherein the average diameter of the voids is 3.5 μm or less, and the surface roughness (Ra) of the wafer holding surface including the voids is 0.4 to 2.0 μm. 2. The wafer holding plate according to 1.