JPS62181869A - Polishing of semiconductor wafer - Google Patents

Abstract

PURPOSE:To permit the polishing free from the dispersion of thickness of a wafer by a shortened process by carrying out the surface grinding and polishing for the wafer in the vacuum adsorbed state and press-attaching said wafer onto a polishing plate. CONSTITUTION:A wafer 2 having the minute unevenness on the surface is fixed firmly and in separable ways by the vacuum attraction through a number of vacuum attraction holes 3, onto the surface plate 1 of a surface grinder. In this state, a rotary grindstone 4 is shifted horizontally along the diameter of the wafer 2, and after the back surface of the wafer 2 is ground a buffing surface plate 5 for polishing is attached, and the back surface of the wafer 2 is polished flat. Then, the coating of wax 6 is carried out, and a polishing plate 7 is pressing-attached, and then a vacuum chuck is released to separate the wafer 2 from the surface plate 1 of the surface grinder. Thus, the wafer free from the dispersion of thickness can be polished flat by the shortened process.

Description

[Detailed description of the invention] (g) Technical field The present invention relates to a method for polishing semiconductor wafers.

Semiconductor wafers include GaAs, GaP, InP
, Si 1Ge, etc., is cut into a thin disk shape. In order to perform wafer processing with high precision, the wafer surface must be polished to a mirror surface.

B) Conventional technology A polishing plate with good flatness made of stainless steel, ceramic, etc. is heated to melt the wax, and the wafer is placed on it and pressed from above to attach the wafer to the polishing plate. After this, the wafer surface is lapped or polished.

With this method, the wafer may be curved within the plane. This is because the thickness of the wax is not uniform.

Japanese Patent Application Laid-Open No. 56-164585 (published on December 17, 1981) discloses that in order to solve the problem of non-uniformity in wax thickness, a wafer is first vacuum chucked, then heated,
The company proposes a method in which wax is applied while rotating, a polishing plate is placed on top of the wax, and the polishing plate is attached to the wafer. The wafer is flattened by the plane of the vacuum chuck, and the wax is spin-coated on top of it, so that the wax has a uniform thickness. Therefore, the wax and wafer are fixed on the polishing plate with good flatness.

In either case, only one side of the wafer is lapped.

In this type of single-sided lapping method, the wafers are attached one by one to the polishing plate, so the variation in wafer thickness is reduced by 1.
If it is 0 μm or more, the accuracy of single-sided lapping will be poor. Therefore, a surface grinding or double-sided lapping process was required as a preliminary step.

In addition, when performing surface grinding of a wafer, after the wafer is ground, the wafer is removed from the surface plate, and is adsorbed and attached to the surface plate again. An unevenness or taper of about 8 μm was generated.

These methods have disadvantages in that variations in wafer thickness and unevenness remain, or the process is complicated.

(1) Purpose The first object of the present invention is to provide a method for polishing a wafer without variations in thickness.

A second object of the present invention is to provide a polishing method that can flatten a wafer through a shortened process.

B) Method of the Invention In order to achieve these objects, the present invention involves surface grinding and polishing the wafer while it is vacuum-adsorbed, and then attaching the wafer as it is to a polishing plate.

Surface grinders that vacuum-suction wafers are already on the market. In this method, the wafer is surface ground, and after processing, the wafer is released from suction and cleaned.

However, with this method, the wafer can be made thinner, but damage remains on the shaved surface; wafer accuracy deteriorates if pasted with damage remaining; It has the disadvantage of poor accuracy.

Hereinafter, the present invention will be described in detail with reference to the drawings, and FIGS. 1 to 6 are longitudinal cross-sectional views showing the steps of the present invention.

In FIG. 1, a wafer 2 having projections and depressions is fixed to a surface grinding surface plate 1 by a vacuum chuck.

For this reason, a sufficient number of vacuum suction holes 3 are bored in the portion of the surface grinding surface plate 1 in contact with the wafer 2, and these holes 3 are vacuum-sucked. The surface of the wafer 12 comes into contact with the surface grinding plate 1.

The back side of the wafer is exposed to the outside. Although there are minute irregularities on the surface of the wafer 2, there are only a few voids and there are a sufficient number of vacuum suction holes 3, so the wafer 2 is firmly fixed. It is not fixed with wax like the traditional method.

Therefore, the detachment process is extremely simple. All you have to do is stop the vacuum pump.

Of course, since wax is not used, the protrusions on the wafer surface may be scratched due to mechanical friction or strong contact, but this is not a problem as the surface will be polished later.

In the vacuum chucked state, the surface is ground as shown in FIG. A rotating grinding wheel 4 is moved horizontally along the diameter of the wafer 2 to grind the back surface of the wafer. This also means making the wafers even in thickness. It also has the effect of removing large convex portions.

Next, as shown in FIG. 3, while vacuum chucked, a polishing puff surface plate 5 is applied to the back surface of the wafer 2 to polish it. In this way, the back side of the wafer becomes flat. The fact that the back side is flat is not meaningless.

If there are irregularities on the back surface of the wafer, the wafer is fixed to the polishing plate in a curved state according to the irregularities, so that when the wafer is removed after surface polishing, the irregularities appear on the surface.

Further, if the back surface of the wafer is flat, there is an advantage that when wax is applied later, the wax thickness becomes uniform.

Next, as shown in FIG. 4, wax 6 is applied to the polished back surface of wafer 2. Wafer 2 remains vacuum chucked.

Furthermore, as shown in FIG. 5, a polishing plate 7 is pressed against the back surface of the wafer coated with wax 6. thus,
The back surface of the wafer and the polishing plate 7 are attached.

Release the vacuum chuck. The surface of the wafer 2 is separated from the surface grinding surface plate 1. FIG. 6 shows such a situation. Here, the back surface is flat, and the hooks 6 are also flat. The thickness of Ueno is also the same.

Next, the surface of the wafer 2 is polished according to known means.

(b) Effects (1) The wafer is attracted to the surface grinding plate,
It is processed in parallel (surface grinding and polishing) and attached to the plate while being adsorbed.

Therefore, even if the wafer thickness varies by 10 μm or more, mirror-finished wafers with uniform thickness can be processed without any problem.

(2) Since the back surface is processed to be flat in advance, variations in wax thickness depend on the flatness of the plate. Since the plate is sufficiently flat, the variation in wax thickness can be reduced to 1 to 2 μm.

Therefore, even when a thin wafer is used, for example, a wafer having a thickness of 500 μm or less, the unevenness and taper of the wafer surface are kept to about 3 μm or less.

(3) Processing of the back surface and pasting to the plate are performed in a vacuum chuck state. These steps are performed at the same location, so there is no need for transportation. Since there is no need to transport the wafer, processing time is shortened and the wafer is not contaminated.
There is also less risk of damage.

(4) The process of vacuum chucking on the same surface plate can be easily automated. By automating
It becomes easy to improve thickness accuracy and flatness.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing the state in which the wafer surface is vacuum chucked on a surface grinding plate. FIG. 2 is a sectional view showing a state in which the back surface of the wafer is surface ground. FIG. 3 is a longitudinal cross-sectional view showing a state in which the back surface of the wafer is polished. FIG. 4 is a longitudinal sectional view showing a state in which wax is applied to the back surface of the wafer. FIG. 5 is a longitudinal sectional view showing a state in which a polishing plate is pressed against the back surface of a wafer coated with wax. FIG. 6 is a vertical cross-sectional view of the wafer and polishing plate in a state where the vacuum chuck has been released and the wafer has been removed from the surface grinding surface plate. 1... Surface grinding surface plate 2 -e... Wafer 3... Vacuum suction hole 4... Grinding wheel 5... Puff surface plate for polishing 6... Wafer Sufu...
Polishing plate inventor Takashi Nishiura
Happy Patent Applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] After fixing the front side of the semiconductor wafer to a polishing surface plate using a vacuum chuck, and grinding and polishing the back side of the wafer,
A method for polishing a semiconductor wafer, which comprises applying wax to the back surface of the wafer, pressing a polishing plate to the wax-coated back surface of the wafer, releasing the vacuum chuck, and removing the wafer and polishing plate from the grinding surface plate.