JPS632655A - Wafer polishing plate - Google Patents

Abstract

PURPOSE:To make the polishing rate in a wafer face constant and obtain a wafer with high flatness by making the surface condition of a wafer installing part a concentric, linear or nonlinear slope from the center of the installing part to the outer periphery. CONSTITUTION:A wafer 3 is fixed to a wafer installing part 1 whose surface condition is a concentric, liner or nonlinear slope from the center to the outer periphery, with a wax 4 and, as a wafer polishing plate 2 is pressed against a surface plate 5, the center part is pressed against the polishing cloth 6 harder than the outer periphery part, and the distribution of contact pressure is the largest at the center, gradually becoming smaller toward the outer periphery. Therefore, the polishing rate is the largest at the center gradually becoming lower toward the outer periphery. On the other hand, since the polishing cloth 6 has elasticity and as the wafer 3 is in a little inwardly recessed state, there is difference in the contacting condition and the polishing-liquid feeding condition between the center part and the periphery part and, in general, the polishing rate is larger on the periphery part. And, by combining these two phenomena, the polishing rate in the wafer 3 face can be made constant, obtaining a wafer 3 with high flatness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wafer polishing plate. More specifically, the present invention relates to a wafer polishing plate that produces wafers with excellent flatness.

(Prior art) It is generally made by slicing a wafer-shaped semiconductor crystal (such as silicon) used for IC substrates into a disk shape with a thickness of about 5004 m. Since a disturbed surface layer remains and is unusable, the surface must be polished starting with a coarse abrasive until it finally reaches a mirror-like state. The wafer is then sent to an IC manufacturing process, where a large number of identical ICs are regularly arranged on the surface, and each IC is then cut into chips of several mm square to form products. At this time, the so-called chip yield (ratio of good products) has important meaning both technically and economically, and in order to make this as high as possible, various quality requirements are made for polished wafers, and especially for High surface flatness is required.

Conventionally, mirror polishing of wafers is usually performed using a polishing machine as shown in FIG. That is, a polishing plate 2 made of metal, glass, or ceramic with high flatness
The wafer 3 is fixed on the surface of the wafer 3 with wax 4 (or a suction bat), the polishing plate 2 is pressed onto the surface plate 5 on which the polishing cloth 6 is placed, and the polishing plate 2 and the polishing plate 2 are A method is used in which the wafers 3 are polished by rotating the disks 5 on their own axis as shown in FIG.

In the single-sided polishing machine shown, four
Two polishing plates are arranged, and four wafers are mounted on each polishing plate.

The polishing machine of FIG. 7 produces a wafer shown in cross section in FIG.

(Problem to be solved by the invention) The flatness of a polished wafer mainly depends on the flatness of the polishing plate, wafer mounting accuracy, polishing conditions (pushing pressure, rotational speed of the surface plate and polishing plate, etc.) , is affected by the hardness of the polishing cloth, etc., but even if these precisions are improved, the finished wafer will generally have so-called edge sagging near the edges, as shown in Figure 8, and the center will be distorted by the periphery. The wafer is thicker than that. This edge sag is particularly influenced by the hardness of the polishing cloth, and generally the harder the polishing cloth, the smaller the edge sag can be.

Regarding the hardness of the polishing cloth among the factors that influence the flatness of the wafer, if the hardness of the polishing cloth is increased to -W, the flatness tends to increase. However, in mirror polishing, if the hardness of the polishing cloth is increased too much, the holding power of the polishing liquid decreases, resulting in uneven polishing, and a deep damage layer is generated on the surface of the sea urchin, which impairs the crystalline integrity of the surface. This causes defects in the formation of IC patterns, and therefore causes a decrease in chip yield.

(Means for Solving the Problems) The inventors of the present invention have conducted intensive research on a method for improving the shortcomings of conventional polishing machines and obtaining polished wafers with excellent flatness without edge droop or damaged layers. As a result, it was discovered that the object could be satisfied by modifying the surface shape of the wafer mounting portion of the wafer polishing plate, and based on this knowledge, the present invention was accomplished.

That is, the present invention provides a wafer polishing plate characterized in that the surface of the wafer mounting portion is a concentric linear or nonlinear inclined surface from the center of the mounting portion toward the outer periphery.

(Example) Next, the present invention will be explained in detail according to the illustrated example.
FIG. 1 is a bottom view of one embodiment of the present invention, and FIG. 2 is a sectional view taken along the line A-A in FIG. showing a wafer
As shown in Figure @2, the surface of the wafer mounting part 1 is concentric from the center to the outer periphery so that the cross section is convex, and
It has a shape that changes continuously.

The dimensions of the wafer mounting portion of the wafer polishing plate of the present invention are appropriately selected depending on the size of the wafer to be polished, but -
Generally, the height of the convex part of the wafer mounting part is 1 relative to the diameter of the wafer.
150,000 to 11,500 is preferred.

The wafer is attached to the polishing plate in exactly the same manner as in the conventional method.

Using this wafer polishing plate, wafer polishing is performed using an ordinary surface plate having a polishing cloth as shown in FIG.

(Function) In a polishing machine equipped with the wafer polishing plate 2 of the present invention, the wafer 3 is fixed to the wafer mounting part 1 with wax 4, and the wafer polishing plate 2 is fixed at a fixed position 511.
5, the contact state between the wafer 3 and the polishing cloth 6 is as shown in FIG. 3 (cross-sectional view), with the center being pressed more strongly against the polishing cloth 6 than the outer periphery, and therefore the contact pressure distribution is as shown in FIG. As shown in the graph, it is maximum at the center of the wafer and decreases toward the outer periphery. Since the - side polishing rate is almost proportional to the contact pressure, the in-plane polishing rate is almost the same as the contact pressure distribution, and is maximum at the center of the wafer and decreases toward the outer periphery.

In addition, in FIG. 3, the wafer is in a pressed state, and when it is removed from the wafer mounting portion l, the wafer 3 naturally returns to its normal flat thin plate shape.

- On the other hand, since the polishing cloth 6 has elasticity, the wafer 3 is
Usually, as shown in FIG. 5 (cross-sectional view), the wafer is polished by being slightly sunk in the polishing cloth 6 due to the pressing pressure and being subjected to the rotational forces of the surface plate 5 and the wafer polishing plate 2, respectively. Therefore, even if the pressing pressure is constant on the inner surface of the wafer 3, the contact state between the wafer 3 and the polishing cloth 6 and the supply state of the polishing liquid 7 will differ between the center and the outer periphery of the wafer 3. In general, the polishing rate is higher at the periphery than at the center of the wafer, as shown in the graph of FIG.

In the present invention, by combining these two phenomena, the polishing rate within the wafer surface is kept constant and a wafer with high flatness is obtained.

Note that by arbitrarily combining the effects of these two phenomena, a concave wafer in which the center is thinner than the outer periphery can be obtained.

(Effects of the Invention) By using the wafer polishing plate of the present invention, wafers with excellent flatness can be produced without producing edge sagging or damaged layers, which have been problems in the past.
High quality wafers can be obtained.

[Brief explanation of drawings]

1 and 2 are a bottom view and a sectional view of one embodiment of the wafer polishing plate of the present invention, and FIG. 3 is a sectional view and a sectional view showing the state of polishing by the wafer polishing plate of the present invention FIG. 5 is a sectional view showing how a wafer is pressed by a conventional polishing plate. FIG. 4 is a graph showing the pressure distribution on a wafer when the polishing plate of the present invention is used. FIG. 6 is a graph showing the wafer polishing rate. FIG. 7 shows a polishing machine using a conventional wafer polishing plate, and FIG. 8 is a sectional view of a polished wafer obtained by this conventional polishing machine. Explanation of symbols l...Wafer mounting section 2...Wafer polishing plate 3...Wafer 4...Wax 5...Surface plate
6...Kenfu cloth 7...polishing liquid

Claims (1)

[Claims] A wafer polishing plate characterized in that the surface of the wafer mounting portion is a concentric linear or non-linear inclined surface from the center of the mounting portion toward the outer periphery.