JPS632656A - Wafere polishing method and wafer polishing base plate used for it - Google Patents

Abstract

PURPOSE:To make the polishing rate in a wafer face uniform and obtain a wafer with high flatness by polishing a wafer by the use of a polishing base plate in which the rigidity of the wafer installing part is concentrically and continuously varied from the center toward the outer periphery of said installing part. CONSTITUTION:A stainless disk 12 is installed on a wafer installing part and a hard rubber sheet 10 and a template 11 are stuck on it, and a wafer 3 is fixed to the inside by means of the surface tension of water. And, as the wafer 3 is pressed against a polishing cloth 6, since the rigidity of the installing part is shifted from the center part to the outer periphery, the wafer 3 is slightly deformed and the distribution of contact pressure is the largest at the center part gradually becoming smaller toward the outer periphery, and a polishing rate is the largest at the center gradually becoming lower toward the outer periphery. On the other hand, the wafer 3 is polished in a condition that it is sunk into the elastic polishing cloth 6, and a contacting condition and the feeding condition of a polishing liquid are different between the center part and the periphery part, causing the polishing rate to be larger on the periphery part. And, by combining these two phenomena, the polishing rate in the wafer 3 can be made uniform, 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 method for obtaining wafers with high flatness and a wafer polishing substrate used therein.

(Prior art) Wafers used as IC substrates are made by slicing rod-shaped single crystals (silicon) into rings. However, they cannot be used as they are because of surface irregularities and disordered crystal structures, so the surface is mirror-finished. It needs to be polished until it is in good condition.

The conveyance path of a polishing machine conventionally used for mirror polishing of wafers is shown in cross-sectional views of FIG. 8 and FIG. 1O, both of which show the state during wafer polishing. The wafer 3 is fixed to a highly flat polishing plate 2 made of metal, glass, or ceramic with wax 4 (or a suction pad, etc.), and is pressed against a polishing cloth 6 placed on a surface plate 5, and the polishing liquid is applied to the polishing plate 2. Polishing plate 2 and constant g15 as shown in the figure under supply of 7
is polished by rotating it. FIG. 9 is a bottom view of the polishing plate 2, and numeral 1 in the figure is a wafer mounting section. As can be seen from the figure, four wafers were mounted.

FIG. 10 shows another type of polishing machine, in which a surface plate 5 covered with a polishing cloth is rotated and a wafer polishing plate 2 is rotated by a roller 8 to polish a wafer 3.

In this case as well, the wafer is fixed to the polishing plate with wax, and the hard rubber sheet 1o is pasted on a stainless steel disk as shown in the cross section in FIG. There is a method.

(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. However, according to the above-mentioned conventional polishing machines, even if these precisions are improved, the finished wafer generally has so-called edge sagging near the edges, as shown in Figure 12, and the center is thicker than the periphery. It becomes a wafer. This edge sag depends in particular on the hardness of the polishing cloth; in general, the harder the polishing cloth, the smaller the edge sag can be.

Among the factors that affect the flatness of a wafer, the hardness of the polishing cloth generally tends to increase as the hardness of the polishing cloth increases.

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 furthermore, a deep damage layer is generated on the wafer surface, impairing the crystal integrity of the surface. , which causes defects in the formation of IC patterns, and therefore causes a decrease in chip yield.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems, in which the rigidity of the wafer mounting portion is changed concentrically from the center of the wafer mounting portion toward the outer periphery. A wafer polishing method characterized by polishing a wafer using a polishing substrate, and a method in which a flexible or elastic material is laminated on the surface of a disk in which concentric grooves are formed with a convex portion left in the center of the surface. The present invention provides a wafer polishing substrate characterized by:

(Example) Next, the present invention will be explained according to an illustrated example.
The figure is a sectional view of one embodiment of the present invention.

In the figure, a stainless steel circle 1!112 is attached to the wafer attachment part 14 of the wafer polishing plate 13, a hard rubber sheet 10 and a template 11 are attached to it, and a wafer 3 is fixed inside the template 11 by the surface tension of water. . As shown in the plan view of FIG. 2 (A) and the cross-sectional view of FIG.
2a, and the central portion is a convex portion having a diameter d.

The wafer polishing substrate attached to the wafer polishing plate 13 has a wafer mounting portion 14 whose rigidity changes concentrically and continuously from the center of the mounting portion toward the outer periphery.

FIG. 3 is a cross-sectional view of this wafer polishing substrate 15, showing a state in which a wafer 3 is mounted and a uniform pressure p is applied to the wafer 3 in a plane. The rigidity of the outer periphery of the wafer mounting section changes concentrically and continuously from the center toward the outer periphery due to the bending of the hard rubber sheet 10a. This deflection, that is, the change in rigidity, is the stainless steel circle rIi1
It can be freely controlled by changing the diameter d of the central convex part 2.

When the wafer 3 is mounted on the wafer polishing substrate 15 and pressed against the polishing cloth 6, the wafer 3 is slightly deformed because the rigidity of the wafer mounting portion changes from the center toward the outer periphery, as shown in FIG. Therefore, the contact pressure distribution between the wafer 3 and the polishing cloth 6 is maximum at the center of the wafer, as shown in the graph of FIG.
It becomes smaller towards the outer periphery. Since the polishing rate within the wafer surface is approximately proportional to the contact pressure, it is maximum at the center and decreases toward the outer periphery. Note that the deformation of the wafer 3 shown in FIG. 4 is slight, and the wafer naturally returns to its normal planar shape after polishing.

- On the other hand, the wafer 3 is generally as shown in FIG.

Polishing is performed while submerged in an elastic polishing cloth 6.

Even if the pressing pressure on the wafer 3 is applied uniformly within the wafer surface, the contact state between the wafer 3 and the polishing cloth 6 and the supply state of the polishing liquid differ between the center and the outer periphery of the wafer, so the polishing rate may vary. Generally, as shown in the graph of FIG. 7, it is larger at the periphery than at the center.

The present invention attempts to equalize the polishing rate within the wafer plane by combining the above two phenomena and obtain a wafer with high flatness. By choosing , it is also possible to obtain a concave wafer whose center is thinner than its outer periphery.

Test Example Next, a wafer polishing test was conducted using the wafer polishing substrate 15 of the present invention shown in FIG. 1 in a polishing machine as shown in FIG. The diameter of the wafer 3 used for polishing was 2 inches, the diameter of the constant 515 was 300 mm, and the rotation speed of the constant 115 was 50 rpm.

In test example 1, d of the stainless steel circle 5112 is 39 m.
m, and in Test Example 2, polishing was performed using a material with d of 25 mm. The results are shown in Table 1, and the flatness of the polished wafer was expressed by the unevenness (thickness unevenness) of the surface. For comparison, a test was conducted under the same conditions without using the stainless steel disk 12 (the case shown in FIG. 11).

Table 1 As shown in the results, when a stainless steel disk with d=39 mm was used, a wafer with high flatness was obtained.

(Effects of the Invention) As described above, by using the wafer polishing substrate according to the present invention, wafers with high flatness and stable quality can be obtained.

Furthermore, since this polishing plate has a simple structure, it is easy to manufacture and can be provided at low cost.

[Brief explanation of the drawing]

1 and 3 are cross-sectional views showing a wafer polishing substrate as one embodiment of the present invention and its usage state. 2A and 2B show a bottom view and a sectional view, respectively, of a stainless steel disk used for the wafer polishing substrate of FIG. 1. FIG. 4 is a cross-sectional view of a wafer polished by the method of the present invention, and FIG. 6 is a cross-sectional view of a wafer polished by the conventional method.
The figure is a graph of the contact pressure applied to the wafer and the polishing rate.
Figures 8 and 10 are cross-sectional views of the polishing machine, Figure 9 is a plan view of the polishing plate, Figure 11 is a cross-sectional view of a conventional polishing plate, and Figure 12 is a cross-sectional view of the polishing machine using the conventional polishing plate. FIG. 3 is a cross-sectional view of the resulting polished wafer. Explanation of symbols l...Wafer mounting section 2...Wafer polishing plate 3...Wafer 4...Wax 5...Surface plate
6... Polishing cloth 7... Polishing liquid 8... Roller 9... Wafer polishing plate lO... Hard rubber 11... Template I2.
...Stainless steel disc l...Wafer polishing plate 14--Wafer mounting portion 15...Wafer polishing substrate Fig. 1 Fig. 2 (A) (B) Fig. 3 Fig. 4 Fig. 5
1Figure 7

Claims (1)

[Scope of Claims] 1. Polishing of a wafer, characterized in that the wafer is polished using a polishing substrate in which the rigidity of the wafer mounting part is continuously changed concentrically from the center of the mounting part toward the outer periphery. Method. 2. A wafer polishing substrate characterized in that a flexible or elastic material is laminated on the surface of a disk having concentric grooves with a convex portion left in the center of the surface. 3. The wafer polishing substrate according to claim 2, further comprising a template laminated on a flexible or elastic material.