JPH0494122A - Double side abrasion of thin plate - Google Patents

Abstract

PURPOSE:To enable grinding to reduce irregularities of wafer thickness and to make the thickness uniform by setting a processing object in a round hole of a carrier for holding the processing object, by setting a thin board whose shape is the same as that of a cut-out part in the cut-out part whose round hole is not filled, and by grinding both sides. CONSTITUTION:For example, a thin board 6 having the same share as a cut-out part is set in the cut-out part formed for an OF line 5 of a wafer to fill a round hole and to eliminate a clearance of the cut-out part. Thereby, the wafer is uniformly pressurized by upper and lower surface plates and grinding powders hardly collect in the cut-out part, thereby enabling uniform grinding and realizing uniform thickness. The spacer 6 is formed of the same material as a carrier 2 such as epoxy resin and made to the same thickness as the carrier. Then, the round hole of the carrier is filled and a clearance is eliminated, a pressure is uniformly applied all over the carrier, and grinding powders does not collect. Further uniform grinding can be realized in this way.

Description

[Detailed Description of the Invention] [Summary] Regarding the improvement of a method for polishing thin plates such as semiconductor wafers and electronic material substrates, the present invention aims to reduce variations in wafer thickness and polish the wafer so that the thickness is uniform. A workpiece consisting of a circular thin plate with a notch (e.g. a semiconductor wafer)
In a polishing method in which both surfaces are polished while holding the workpiece in a carrier, the workpiece is fitted into a perfect circular hole in the carrier that holds the workpiece, and at the same time, the notch is inserted into the notch portion where the perfect circular hole is not filled. The feature is that a thin plate of the same shape as the part is inserted and both sides are polished.

[Industrial Application Field 1] The present invention relates to an improvement in a method for double-sided polishing of thin plates such as semiconductor wafers and electronic material substrates.

For example, in semiconductor devices such as LSI, many microscopic elements are formed on the surface of a semiconductor wafer (hereinafter referred to as a wafer), but the degree of integration is increasing year by year, and on the other hand, wafers are becoming larger and larger due to rationalization. It has a caliber.

Therefore, it is becoming increasingly difficult to maintain or improve manufacturing yield and quality because a large number of fine elements must be formed on a large-diameter wafer, and the present invention relates to uniformity of wafer thickness, which is the basis for this.

[Prior Art] For example, a silicon wafer is made into a cylindrical single crystal ingot by a pulling method or a zone melting method, and this ingot is cut into wafers by slicing with a high-speed rotating internal blade. . After this rough wafer is lapped to make it a flat rough surface, the wafer periphery is beveled;
Then, the wafer is polished to remove processing distortions and defects on the wafer surface, and is finished into a wafer with a mirror surface on which semiconductor elements can be formed.

The present invention relates to a method of lapping or polishing both sides of such a rough wafer. Conventionally, single-sided polishing was the mainstream, but recently, due to the demand for improved processing accuracy, double-sided polishing has become widely used. FIG. 4 shows a schematic perspective view of such a wafer polishing apparatus for double-sided polishing, in which symbol 1 is a wafer, 2 is a carrier that holds the wafer, and 3 is a drive unit, and the wafer is inserted into the four holes of the carrier 2. Insert 1,
While the carrier 2 is rotated by the gear around the drive unit 3, the carrier 2 itself also rotates, and both sides of the wafer are polished by such planetary motion. Although not shown, the gear 2 holding the wafer 1 is held between and pressed by two surface plates (tables) covered with an abrasive cloth made of polyurethane-impregnated polyester nonwoven fabric, etc., and these two surface plates are also They also rotate in opposite directions. By rotating the wafer in this manner and polishing the wafer while dropping the etching liquid in which fine powder is suspended, the wafer is polished uniformly. This polishing method is called mechanochemical polishing, and polishing progresses through the synergistic effect of mechanical polishing using fine powder (powder with a diameter of 0.05 μm) and chemical polishing using an etching solution such as alkali. .

The following FIG. 5 shows a plan view of a conventional carrier holding a wafer, where l is the wafer, 2 is the carrier, and 4 is a gear. The thickness of the carrier 2 is often about 273 times the thickness of the wafer 1 after polishing. For example, for a silicon wafer with a diameter of 150 mmφ and a thickness of 620 μm, a carrier with a thickness of about 430 μm is used.
The material of the carrier is, for example, epoxy resin.

As shown in the figure, the wafer 1 has a regular notch C.
The straight line 5 is called the orientation flat line (OF line) and is an important line that indicates the crystal orientation. This OF line 5 is created by measuring the crystal orientation of a single crystal ingot and grinding it.

[Problem to be solved by the invention]

By the way, the reason why both sides are polished using the above-mentioned wafer polishing equipment is to make the thickness of the wafer uniform with high precision. There is a problem in that the wafer has a notch, which makes it difficult to make the thickness of the wafer uniform.

Figure 2(b) shows a conventional wafer iso-thickness diagram after polishing, and this figure illustrates the thickness change of a wafer with a diameter of 6 inches (diameter 150 mm) and a thickness of 620 tIm. is an isogene line, and the isogene spacing is 0.1μ
It's at m. As can be seen from this figure, in the conventional polishing method, the wafer is formed into a tapered shape with the thickness being the thinnest at the OF line 5. This is because due to the notch, the pressure applied to the wafer surface is not uniform and the pressure is distributed, and moreover, polishing powder accumulates in the gap between the notches and polishing progresses around the area. it is conceivable that.

This figure 2 illustrates one wafer, but
FIG. 3(b) is a diagram showing the distribution of conventional TTV values measured on a large number of wafers.
ckness Variation) is an evaluation value representing the difference between the thickest part and the thinnest part within the wafer.

The horizontal axis is the TTV value (μm), and the vertical axis is the ratio (%) of the number of occupied wafers to all wafers. %. It goes without saying that the smaller the TTV value, the better, but it is desirable that the TTV value be at least 1 μm or less for most wafers.

The present invention proposes a double-sided polishing method aimed at reducing such problems, reducing variations in wafer thickness, and polishing the wafer to make the thickness uniform.

[For production]

That is, for example, a thin plate having the same shape as the notch is fitted into a notch formed for the OF line of the wafer to fill the circular hole and eliminate the gap between the notches.

In this way, the wafer is uniformly pressed by the upper and lower surface plates, and polishing powder is less likely to accumulate in the notch, so that the wafer is polished evenly and has a uniform thickness.

[Means to solve the problem]

The purpose of this polishing method is to polish both sides of a workpiece (for example, a semiconductor wafer) made of a circular thin plate having a notch by holding it on a carrier. Inserting things and at the same time,
This is achieved by a polishing method in which a thin plate having the same shape as the notch is fitted into the notch where the perfect circular hole is not filled, and both sides are polished.

〔Example〕

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 shows a plan view of a carrier holding a wafer according to the present invention, and the same parts as in FIG. 5 are given the same symbols. It is. This spacer 6 is made of the same material as the carrier 2, for example, epoxy resin, and has the same thickness as the carrier. By doing so, the perfect circular hole in the carrier is filled, there is no gap, the pressure on the entire carrier becomes uniform, and polishing powder is not accumulated, so that uniform layer polishing can be performed.

FIGS. 2(a) and 2(b) show wafer iso-thickness diagrams after polishing; FIG. 2(a) is an iso-thickness diagram of the wafer after polishing according to the present invention, and FIG. FIG. 3 is an isopic diagram of a wafer after conventional polishing. The lines in the figure are iso-thickness lines, and the iso-line spacing is 0.1 μm.The wafer according to the present invention tends to be slightly thicker in the center, but it is similar to wafers polished by conventional methods. There is no tapered shape in which the thickness of the OF line 5 is reduced.

3(a) and 3(b) are TTV distribution charts after polishing, where (a) is a distribution diagram of a large number of wafers after polishing according to the present invention, and FIG. 3(b) is a distribution chart of a large number of wafers after conventional polishing. It is a distribution map of wafers. The horizontal axis is the TTV value (μm)2 The vertical axis is the ratio (%) of the number of occupied wafers to all wafers.After polishing using the conventional method, the average TTV value is 1.21μm, and the ratio of wafers with a TTV value of 1μm or less is However, after polishing according to the present invention, the average T T V 4M was about 0.42%.
80 um, the ratio of wafers with a TTV value of 1 μm or less is 92%, and the goal of having most wafers with a TTV value of 1 μm or less has been almost achieved. ), a silicon wafer with a thickness of 620 μm.

The above example is an example in which both sides are polished, but the polishing amount is as small as about 25 μm on one side. On the other hand, polishing by lapping, which is a pre-process, results in a thick polishing amount of about 50 μm on one side, and even greater effects can be obtained by applying the present invention to this double-sided lapping method.

It goes without saying that the present invention can also be applied to electronic material substrates such as quartz substrates used as oscillators and other substrates (for example, lithium niobate (LiNbO3)).

[Effects of the Invention] As is clear from the above explanation, according to the double-sided polishing method according to the present invention, it is possible to make the thickness of the thin plate uniform, improving the yield of semiconductor devices and electronics, and improving the quality. There are some things that make a significant contribution to the

[Brief explanation of the drawing]

Fig. 1 is a plan view of the rear holding a wafer according to the present invention, Fig. 2(a), (■) is a wafer iso-thickness diagram after polishing, and Fig. 3
Figures (a) and (b) are TTV distribution diagrams after polishing, Figure 4 is a schematic perspective view of a wafer polishing apparatus, and Figure 5 is a plan view of a conventional carrier holding a wafer. In the figure, 1 is a wafer (workpiece), 2 is a carrier, 3 is a drive unit, 4 is a gear,
Reference numeral 5 indicates an OF line, and 6 indicates a spacer (a thin plate having the same shape as the notch).

Claims (2)

[Claims] (1) In a polishing method in which a workpiece consisting of a circular thin plate having a notch is held in a carrier and polished on both sides, the workpiece is fitted into a circular hole in the carrier that holds the workpiece, and at the same time A method for polishing both sides of a thin plate, characterized in that a thin plate having the same shape as the notch is fitted into the notch where the circular hole is not filled, and both sides are polished. (2) The method for double-sided polishing of a thin plate according to claim (1), wherein the workpiece is a semiconductor wafer.