JPH0831779A - Polishing method for compound semiconductor substrate - Google Patents

Abstract

PURPOSE:To make it possible to obtain a substrate having a mirror surface with good surface roughness without haze by preventing the residue of an oxide film on the surface of substrate when polishing mirror surface. CONSTITUTION:In polishing and finishing the surface of a compound semiconductor substrate such as plate-shaped GaAs to mirror surface by supplying a polishing solution and rubbing the surface with polishing cloth, the polishing solution is made of an aqueous solution containing sodium hydroxide and a chloratebased salt selected from hypochlorite, chlorite, chlorate and perchlorate such as NaClO as the main components, and its pH is higher than 10 but lower than 11.5. Therefore, the polishing solution itself possesses a dissolving action for oxide film, and the substrate surface can be processed to a mirror surface having good surface roughness without haze, so that a device having good characteristics can be obtained by using said substrate and also an improve yield can be expected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a compound semiconductor substrate, and more particularly to a technique useful when applied to mirror-polishing of a gallium arsenide (GaAs) substrate (wafer).

[0002]

2. Description of the Related Art In a compound semiconductor, which is attracting attention as a substrate material for light-emitting devices, high-speed arithmetic devices, etc., particularly a substrate made of GaAs, it has been conventionally required to make a mirror surface of the substrate by rubbing it with a polishing cloth. Although a polishing liquid containing a chlorine-based oxidizer and having a pH of about 9 (weakly alkaline) is widely used, the polishing liquid itself has almost no action of dissolving an oxide film formed on the substrate surface during polishing. Therefore, there is a drawback in that haze may remain on the surface of the substrate or the surface roughness may be deteriorated by the oxide film, which may lead to deterioration of characteristics of a device formed using the substrate.

Therefore, in order to eliminate the above drawbacks, GaAs
Several proposals have been made for a substrate polishing liquid. For example, Japanese Examined Patent Publication No. 55-28417 discloses NaClO.
A polishing liquid prepared by mixing an aqueous solution of (sodium hypochlorite) and an aqueous solution of Na ₂ CO ₃ (sodium carbonate) is disclosed. Further, in this publication, a solution obtained by mixing NaOH (sodium hydroxide) into a NaClO aqueous solution is
It has been pointed out that it is not suitable for forming a featureless surface of GaAs.

On the contrary, H. Hartnagel et al.
l of Materials Science 8 (1973, 1061-1)
(063 page), a polishing solution prepared by diluting a standard solution containing 1N NaClO in a 0.1N (normality) NaOH aqueous solution by 40 times (the inventors prepared a solution having the same composition and measured it). However, the pH was 11.5.)
It was reported that the surface of the substrate was like a mirror surface when using.

Further, Kasai et al. Of Saitama University have published a collection of papers of the spring conference of the Seiki Society of Japan in 1985 (287-288).
Page) introduces a polishing liquid in which KOH (potassium hydroxide) is mixed in a NaClO aqueous solution.

[0006]

However, when the present inventors made an additional test, the above Japanese Patent Publication No. 55-284.
With respect to the polishing liquid described in Japanese Patent Publication No. 17, the polishing process does not proceed because something like a passivation film is formed on the substrate surface, while the polishing liquid reported by Kasai et al. A large number of fine pits (holes) were generated and the mirror surface could not be obtained. Further, in the polishing liquid proposed by H. Hartnagel et al., The action of dissolving the substrate becomes stronger as the pH becomes higher. Therefore, if the substrate has crystal defects or scratches at a pH of 11.5 or higher, that portion should be removed. However, there is a disadvantage that pits are easily dissolved and pits are easily generated after polishing, or scratches are likely to remain.

The present invention has been made in view of the above circumstances and has a mirror surface having no haze and good surface roughness by preventing the oxide film from remaining on the substrate surface during mirror polishing. It is an object of the present invention to provide a method for polishing a compound semiconductor substrate that can obtain a substrate.

[0008]

In order to achieve the above object, the present inventors prevent the formation of an oxide film by allowing the polishing liquid itself to dissolve the oxide film on the substrate surface. It is thought that the oxide film can be removed or the oxide film can be completely removed. For example, a polishing liquid containing a chlorine-based oxidizing agent as a main component, which is generally used in the mirror polishing of GaAs substrates, was examined. As a result, they have found that if the pH of the polishing liquid is adjusted to 10 or more and less than 11.5 by adding NaOH, no oxide film can be seen on the surface of the substrate after polishing.

The present invention has been made on the basis of the above findings, and the invention according to claim 1 is to polish a flat plate compound semiconductor substrate by rubbing it with a polishing cloth while supplying a polishing liquid. In finishing the surface to a mirror surface, the polishing liquid contains a chloric acid salt selected from hypochlorite, chlorite, chlorate and perchlorate and sodium hydroxide as main components. Aqueous solution and pH of 1
It is characterized by being 0 or more and less than 11.5. In this invention, for example, as in the invention of claim 2, the hypochlorite is sodium hypochlorite, and in the invention of claim 3, the compound semiconductor is gallium arsenide. Is.

Here, the proper range of the pH of the polishing liquid is determined based on the experiments by the present inventors, but if the pH does not reach the above lower limit, the haze on the surface of the GaAs substrate even after polishing And a black oxide film that causes deterioration of the surface roughness remains, while if the above upper limit is exceeded, p
Since the action of dissolving the substrate becomes stronger as H becomes higher, if the substrate has crystal defects or scratches at a pH of 11.5 or higher, that portion is selectively dissolved and pits easily occur after polishing. Or, it is not preferable because scratches are likely to remain.

[0011]

According to the above means, a chloric acid-based salt selected from hypochlorite, chlorite, chlorate and perchlorate is used as a polishing liquid when mirror polishing a compound semiconductor substrate. Since an aqueous solution containing, as a main component, and sodium hydroxide and having a pH of 10 or more and less than 11.5 is used, the action of dissolving the oxide film of the polishing liquid itself prevents the formation of an oxide film on the substrate surface, or Makes it possible to completely remove the oxide film from the substrate surface, and the substrate surface can be processed into a mirror surface having good surface roughness and no haze. Then, a device having good characteristics can be manufactured using the substrate, and improvement in yield is expected.

[0012]

EXAMPLES The features of the present invention will be clarified below with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited to the following Examples. In each of Examples and Comparative Examples, as a mirror polishing device, one surface of the substrate was pressed against a polishing cloth, and the polishing cloth and the substrate surface were supplied with a relative movement while supplying a relative motion to the one surface. A conventional single-sided polishing machine for processing the surface into a mirror surface was used. In addition, in each example, a disk-shaped Ga
Using As substrate, the processing pressure to press the substrate is 100
Although g / cm ^{2 was used} and the supply amount of the polishing liquid was 0.5 liters per minute, these are appropriately selected depending on the size of the substrate, the number of processed substrates, the time required for the processing, and the like.

(Example 1 and Example 2) In Example 1,
The concentration of NaClO and NaOH is 0.1N each
(Available chlorine amount: 3.5 g / l) and 0.025 N (1 g
/ L) and a polishing solution having a pH of 10.0 was used. In Example 2, the concentrations of NaClO and NaOH are 0.1 N and 0.05 N (2 g / l), respectively, and pH 1
The polishing liquid of 1.4 was used. In Example 1 and Example 2,
In both cases, a mirror-polished surface was obtained. For each of the mirror surfaces of Examples 1 and 2, Surfscan 450 manufactured by Tencor Co., Ltd.
The haze was measured by 0, and the surface roughness was measured by AFM (atomic force microscope).

(Comparative Example 1 and Comparative Example 2) In Comparative Example 1,
A polishing solution having a NaClO concentration of 0.1 N and a pH of 8.9 was used, but NaOH was not added to this polishing solution. In Comparative Example 1, it was also visually confirmed that the scratches, which are presumed to be caused by the contact with the polishing cloth, remained on the polishing surface. Further, when the haze and the surface roughness were measured in the same manner as in each of the above Examples, it was significantly inferior to the above Examples 1 and 2. In Comparative Example 2, NaClO and Na
The concentration of OH is 0.1N and 0.5N (20g
/ L), and a polishing liquid having a pH of 13.0 was used, but many pits were generated on the polishing surface, and a mirror surface could not be obtained.

From the above Examples 1 and 2 and Comparative Examples 1 and 2, pH was 10 or more by adding NaOH to NaClO.
It was confirmed that by using a polishing liquid adjusted to be less than 1.5, a mirror surface having good surface roughness and no haze can be obtained. Then, it is expected that a device having excellent characteristics can be obtained and the yield can be improved by forming the device on the mirror surface.

Although NaClO was used as the chloric acid salt in the above examples, the polishing liquid itself has the action of dissolving the oxide film at a pH of 10 or more and less than 11.5 due to the addition of NaOH. If there is Ca (Cl
O) ₂ (calcium hypochlorite) and other hypochlorites,
Chlorates such as NaClO ₃ (sodium chlorate) and N
perchlorate such as aClO ₄ (sodium perchlorate),
Chlorite may be used.

Further, in the above-mentioned embodiment, the mirror-polishing process of the GaAs substrate is explained, but the present invention is also effective for the mirror-polishing process of the compound semiconductor substrate other than GaAs such as InP.

[0018]

According to the method of polishing a compound semiconductor substrate according to the present invention, a flat plate-shaped compound semiconductor substrate such as gallium arsenide is rubbed with a polishing cloth while being supplied with a polishing liquid to polish the substrate. In finishing the surface of the to a mirror surface, the polishing liquid, a hypochlorite salt such as sodium hypochlorite, chlorite salt, chlorate salt selected from chlorate and perchlorate and water Since it is an aqueous solution containing sodium oxide as a main component, and the pH is adjusted to 10 or more and less than 11.5, the polishing liquid itself has a dissolving effect on the oxide film, thereby forming an oxide film on the substrate surface. It is possible to prevent or completely remove the oxide film from the substrate surface, and the substrate surface can be processed into a mirror surface having good surface roughness and no haze. Then, a device having good characteristics can be manufactured using the substrate, and improvement in yield is expected.

Claims (3)

[Claims] 1. A flat compound semiconductor substrate is rubbed with a polishing cloth while being supplied with a polishing liquid to polish the surface of the substrate to a mirror surface, and the polishing liquid is hypochlorite, An aqueous solution containing a chloric acid salt selected from chlorite, chlorate, and perchlorate as main components and sodium hydroxide, and having a pH of 10 or more and 11.5.
A method for polishing a compound semiconductor substrate, wherein 2. The method for polishing a compound semiconductor substrate according to claim 1, wherein the hypochlorite is sodium hypochlorite. 3. The method for polishing a compound semiconductor substrate according to claim 1, wherein the compound semiconductor is gallium arsenide.