JPH02208931A - Polishing process for compound semiconductor substrate - Google Patents

Abstract

PURPOSE:To enhance the flatness by a method wherein the surface pressure exceeding specified value is applied on substrates to polish the surface in recessed shape and then the secondary polishing process is performed using a soft abrasive cloth. CONSTITUTION:During the primary polishing process, a polishing solution 5 containing abrasive grain and a hard abrasive cloth 2 are used while the surface pressure exceeding 100g/cm<2> is applied on wafers 4 to polish the surface in recessed shape. Next, during the secondary polishing process, the polishing solution 5 containing no abrasive grain and the abrasive cloth 2 with a foaming layer are used to polish the plane in flat shape. In the said processes, the polishing amount in the wafer 4 peripheral parts is decreased by the abrasive grain in the primary polishing while the polishing amount in the central part is increased so that the wafer 4 surface may be polished in recessed shape. At this time, the polishing amount in the peripheral parts is controlled by the surface pressure in anticipation of the sag during the secondary polishing process. Through these procedures, the wafer 4 peripheral parts, even if excessively polished in the secondary polishing process, can be flattened.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for polishing a compound semiconductor substrate after lapping, in order to remove a processed strain layer on the surface of the substrate and obtain a distortion-free mirror surface. In particular, the present invention relates to improved primary polishing of secondary polishing.

[Conventional technology] For polishing compound semiconductor substrates (hereinafter referred to as wafers),
(2) There is no polishing damage left on the wafer surface; (2) The wafer is required to have an even and flat thickness and a mirror surface without distortion.

The wafer polishing method adopted to meet this requirement is to first achieve uniform flatness and thickness by lapping, and then to remove damage caused by lapping by polishing to obtain a mirror surface without distortion.

FIG. 2 shows an example of a single-sided polishing apparatus for polishing wafers.

A plurality of wafers 4 are attached to a top plate 3 called a mount plate with wax 6. Top plate 3
is designed to rotate (in the direction of the arrow). wafer 4,
4 is a polishing surface plate l that rotates (in the direction of the arrow) with polishing cloth 2 stretched on it.
to press against. Pressing against the polishing surface plate l is performed by a pressure cylinder 7. Polishing liquid 5 from the center of the polishing surface plate L
The wafers 4 are polished by rotating the polishing surface plate 1 and the top plate 3 while supplying the wafers.

The polishing work using this polishing device is performed twice: primary and secondary. In the primary polishing, in order to maintain flatness, a polishing liquid 5 containing abrasive grains and a relatively hard polishing cloth 2 made of non-woven fabric are used. In addition, in the secondary polishing, in order to remove the slight damage remaining on the primary polished surface and to finish the surface to a mirror surface without minute irregularities, a polishing liquid 5 consisting of a chemical liquid that does not contain abrasive grains and a foam layer are used. A relatively soft polishing cloth 2 is used.

By the way, compound semiconductors have lower mechanical strength than Si. For example, in the case of GaAs, the hardness is less than half that of Si, and it is brittle and easily damaged. For this reason, the primary polishing in which abrasive grains are added to the polishing liquid 5 is performed at a relatively low surface pressure.

Therefore, as shown in Figure 3, in the primary polishing, a flat surface finished by lapping can be maintained (Figure 3 (
a)).

However, because secondary polishing uses a chemical solution without abrasive grains and a soft polishing cloth with a foam layer, differences in pressure distribution tend to occur within the wafer surface (particularly in the peripheral area where pressure tends to be high). As the polishing progresses, so-called "peripheral sagging" 8 occurs (FIG. 3(b)).

It is said that the reason why the pressure in the peripheral area tends to increase during secondary polishing is that because the polishing cloth is soft, the polishing cloth may wrap around the wafer or the wafer may dig into the polishing cloth.

As a result of peripheral sag occurring in the secondary polishing, the flatness of the surface of the sea urchin deteriorates.

The TTV (total total thickness variation), which is a measure of flatness, was as high as 2 to 4 μm in conventional products.

[Problems to be Solved by the Invention] As described above, in the conventional polishing method in which a relatively low surface pressure is applied in the primary polishing, even if the flatness obtained by lapping can be maintained in the primary polishing, In the secondary polishing, the wafer was not polished uniformly and sag occurred in the peripheral area, making it impossible to obtain a wafer with high flatness.

The purpose of the present invention is to overcome the above-mentioned drawbacks of the prior art,
An object of the present invention is to provide a method for polishing a compound semiconductor substrate in which even if excessive polishing occurs in the peripheral area during secondary polishing, the wafer surface is not affected by the excessive polishing and a high degree of flatness can be obtained.

[Means for Solving the Problems] The compound semiconductor substrate polishing method of the present invention is performed after lapping to make the flatness and thickness uniform, and removes the processing strain layer on the wafer surface caused by lapping, and reduces the strain. Polysilling is performed in two stages to obtain a mirror-like surface.The first step uses a hard non-woven fabric and a polishing solution containing abrasive grains, and the second step uses a soft polishing cloth and a chemical polishing solution. In the polishing method that causes sag in the peripheral area due to polishing, 100g of
By applying a surface pressure of /am'' or more, the wafer surface is polished into a concave shape, taking into account the sag in the peripheral area formed during secondary polishing, and the wafer is finally flattened. be.

[Function] The present invention focuses on the fact that when the wafer surface pressure is increased during polishing, the wafer surface becomes concave, and in anticipation of the peripheral sagging that is inevitable in the secondary polishing, the wafer surface is flattened in the primary polishing. This is done by intentionally polishing the surface into a concave shape.

The mechanism by which the wafer surface becomes concave when the wafer surface pressure is increased during primary polishing is not clearly understood, but it is thought that the abrasive grains become mischievous because the polishing cloth is hard.

When a surface pressure of log/cm2 or more is applied to the substrate during primary polishing, the amount of polishing at the periphery of the wafer is small due to the action of abrasive grains, and the amount of polishing at the center is large, resulting in a concave surface shape of the wafer. Polished. The amount of polishing in the peripheral area takes into account the sagging of the peripheral area during secondary polishing. Therefore, blood pressure is also adjusted accordingly. Wafer surface pressure 10
Even if the pressure is 0 g/an' or more, it is within a pressure range that does not cause damage or damage to the wafer.

When the wafer surface is polished into a concave shape in the primary polishing, 2
Even if excessive polishing occurs in the periphery during the next polishing, the periphery of the wafer will not sag because the periphery is made thicker to account for this amount of polishing.

Therefore, the final stage of polishing flattens the wafer surface.

[Example] An embodiment of the present invention will be described below.

The single-sided polishing apparatus used in this embodiment is exactly the same as the apparatus shown in FIG. 2, and therefore its description will be omitted.

Polishing is performed after lapping to equalize flatness and thickness, and is performed in two stages to remove the processing strain layer on the Uninow surface and obtain a distortion-free mirror surface.

In the primary polishing, a hard nonwoven fabric is used as the polishing cloth 2 that is adhered to the polishing platen l, and the polishing liquid 5 contains abrasive grains. The pressure of the pressure cylinder 7 is controlled and the wafer 4 is coated with 100g/
The polishing surface plate 1 and the top plate 3 are rotated by applying a surface pressure of 1 cm" or more, and the wafer 4 is polished into a concave shape while taking into account the sag in the peripheral area formed by the secondary polishing.

In the secondary polishing, a polishing cloth having a soft foam layer is used as the polishing cloth 2, and a chemical liquid containing no abrasive grains is used as the polishing liquid 5. Then, when the polishing surface plate l and the top plate 3 are rotated to perform secondary polishing, the wafer 4 is polished into a concave shape in the primary polishing, so even if excessive polishing occurs in the peripheral area in the secondary polishing. Since the peripheral portion is made thick in consideration of this amount of polishing, the peripheral portion of the wafer 4 does not sag.

Therefore, the wafer surface is finally planarized.

As described above, according to this embodiment, a large pressure equal to or greater than log/am' is applied to the wafer 4 in the primary polishing to reduce the amount of polishing in the peripheral area, so that overpolishing occurs in the secondary polishing. However, the difference in the amount of in-plane polishing is covered, and therefore, the flatness of the surface of the sea urchin obtained by lapping will not be deteriorated by polishing.

In addition, in the above-mentioned example, a case was described in which a nonwoven fabric was used as the primary polishing cloth and a cloth with a foam layer was used as the secondary polishing cloth, but the present invention is not limited to this. It is also possible to use a relatively soft and viscoelastic polishing cloth, etc., as a secondary polishing cloth.

Now, a specific example of polishing a GaAs wafer using the above-mentioned apparatus will be described.

A Ga wafer with a diameter of 2 inches and a thickness of 550 μm was manufactured by the LEC method ('TFI, body-sealing pulling method).
An As wafer was used.

First, after lapping to make the flatness and thickness uniform, etching is performed to remove the warpage caused by processing strain caused by lapping, and the etching is polished to a thickness of 430 μm.
Ten wafers 4 were adhered to the ceramic top plate 3 of 00xx with wax 6.

As mentioned above, in the primary polishing, a polishing liquid 5 containing abrasive grains and a non-woven polishing cloth 2 are used, and a surface pressure of 150 is applied to the wafer 4.
g/cm” and then polished to 20 μm.
A concave surface shape of 1 to 2 μm as shown in Figure (a) was obtained.

Next, in secondary polishing, 10 μm polishing was performed using a polishing liquid 5 that did not contain abrasive grains and a polishing cloth 2 that had a foam layer, and a flat planar shape as shown in FIG. 1(b) was obtained. .

When the wafer 4 was removed from the apparatus, cleaned, and then measured for flatness, the TTV was 1 to 2 μm, which was higher than the conventional 2 to 2 μm.
4 μm could be significantly improved.

Further, after cleaning the wafer, the wafer surface was observed under a spotlight, and no particular scratches were found.

In this way, according to the present embodiment, a mirror-finished wafer with high precision can be obtained, and therefore, it is possible to sufficiently meet requirements for pattern miniaturization, which is becoming increasingly demanding in wafer processes.

[Effects of the Invention] According to the present invention, the surface of the substrate is polished into a concave shape by applying a surface pressure of 100g7cm or more to the substrate, so even if excessive polishing occurs at the periphery during secondary polishing, the surface of the substrate remains unchanged. A substrate with extremely high flatness can be obtained without being affected by excessive polishing.

[Brief explanation of the drawing]

FIG. 1 shows primary polishing obtained by an embodiment of the compound semiconductor substrate polishing method according to the present invention. An explanatory diagram showing the wafer surface shape in secondary polishing, FIG. 2 is a front view of an example of a conventional single-sided polishing apparatus which is also used in the polishing method of the present invention, and FIG. 3 is a diagram showing the wafer surface shape obtained by the conventional method.
FIG. 4 is an explanatory diagram showing the wafer surface shape of secondary polishing. 2 is a surface plate, 2 is a polishing cloth, 4 is a wafer as a compound semiconductor substrate, 5 is a polishing liquid, 7 is a pressure cylinder that applies surface pressure to the substrate, and 8 is a sag generated around the wafer. (a) Surface area of 1&resink 0m (b) Surface height of 2 missing parts resink

Claims (1)

[Claims] A polishing method that obtains a distortion-free mirror surface on the substrate surface by pressing a compound semiconductor substrate against a polishing cloth provided on a rotating surface plate with a predetermined surface pressure. In a method for polishing a compound semiconductor substrate, the peripheral part of the substrate surface is excessively polished when polishing using a soft polishing cloth and a chemical polishing liquid in secondary polishing, using a polishing cloth and a polishing liquid containing abrasive grains. In the first polishing described above, the substrate is pressed with a surface pressure of 100 g/cm^2 or more to allow for excessive polishing of the peripheral area that will occur in the second polishing, and the substrate surface is polished into a concave shape, and finally the substrate is polished. A method for polishing a compound semiconductor substrate, characterized by flattening the substrate.