JPS6230333A - Method and composition for grinding silicon wafer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a method of polishing silicon wafers and similar materials, and compositions useful for use in the method.

[Prior Art and Problems to be Solved by the Invention] U.S. Pat. No. 3,170,273 discloses that colloidal silica and silica gel are useful as polishing agents for semiconductor crystal surfaces, which are most frequently used in the manufacture of semiconductor devices. show.

The disclosure of this patent is incorporated herein by reference.

The silicon-based abrasives of this patent are particularly suitable for sufficiently polishing the surfaces of silicon crystal wafers, thus making these surfaces suitable for placing epitaxially grown crystal layers.

The particle size of the primary particles of colloidal silica and silica gel in the sols used by the patentee
rticlz 5ize) is 4 to 200 nm. From a commercial point of view, it is preferred to use an aqueous colloidal silica sol with a particle size in the range of 4 to 1100 nm as the abrasive in the method of that patent.

US Pat. No. 4,169,337 discloses a substantial improvement in polishing efficacy over that of US Pat. No. 3,170,273. The disclosure of which is incorporated herein by reference. According to the invention, the secondary particle size is 4 to 200 nm.

The use of either colloidal silica or silica gel, preferably in the range of 4 to 1100 N, in combination with a water-soluble amine as an abrasive agent to effectively polish semiconductor surfaces of conventional types, especially silicon. I understand. The amount of amine relative to silica present in the silica sol or gel may range from 0.5 to 5.0% based on the 5iOz content of the sol or gel. The preferred amount of amine is 1.0-5.0%, most preferably 2.0-4.0%.
It is 0%.

The amine should contain 2 to 8 carbon atoms and preferably has aliphatic character.

U.S. Pat. No. 4,462,188 discloses a further improved aqueous silica composition for polishing silicon wafers. This patent specifically applies to U.S. Pat. No. 41,693.
The polishing agent used for carrying out No. 37 is 0.1 to 5
．． It has been disclosed that substantial improvements can be made when adding 0% by weight, most preferably 2.0 to 4.0% by weight, of water soluble quaternary ammonium salts or bases to such compositions.

In preferred embodiments, the water-soluble quaternary ammonium salt or hydroxide thereof should contain no more than 7 carbon atoms. In a preferred embodiment, it contains one or more alkyl groups, but the chain length should not exceed 2 carbon atoms. Of course, the compound can contain one or more aromatic groups of sufficient length to maintain water solubility. They can contain a nitrogen atom as part of a heterocyclic group, such as the quaternary ammonium salts of morpholine's terrestrial class.

Typical water-soluble quaternary ammonium salts and bases that can be used in the invention of U.S. Pat.
N-dimethylmorpholinium and tetrabutylammonium bromide.

Regarding these materials, tetramethylammonium chloride is preferred.

SUMMARY OF THE INVENTION The present invention includes an improved method for polishing silicon wafers and similar materials, which method is based on the SiO□ content of the sol. Includes the use of a colloidal silica sol or gel in combination with 1-5% by weight of piperazine, or piperazine with a lower alkyl substituent on the nitrogen, as an abrasive. Piperazine can be combined with 0.1-5% by weight of further water-soluble quaternary ammonium salts containing up to 6 carbon atoms or chlorine.

1S Silica Sol A wide variety of aqueous colloidal silicas or gels can be used in the practice of the present invention, as shown herein.

Colloidal silica is preferred. Two such raw materials are
NALCOAG 1050 and NALCO 8G 1 to 6
It is marketed under the name 0. These silica sols and their properties are described below.

NALCOAG 1050 Colloidal Silica (as SiOz) 50% pH 9,
0 Average particle size 16-25 nm Average surface area 120-176 m"/g specific gravity (
20°C (68°F)) 1.39ONa,O
Content 0.4%NALCOAG
1060 Colloidal Silica (as Si02) 50% pH 8,
5 Average particle size 50-70nII + average surface area 40-b specific gravity (20℃ (
68'F)) 1.390 Viscosity (25℃
(77°F)) 0.015Pa -5(15
cP) (max) Besides those sols described above, other silica sols as well as methods for their preparation are disclosed and described in US Pat. No. 3,901,992, which is incorporated herein by reference. Finally, Applicants have proposed using fumed silica in an aqueous medium containing a piperazine compound.
It has been discovered that improved results can be obtained when dispersing silica silica) to obtain silica sols and/or gels.

These amines include not only piperazine itself, but also piperazine containing a lower alkyl substituent on the nitrogen portion of the piperazine molecule. Piperazine with a lower alkyl substituent on the nitrogen can be described as a piperazine having a lower alkyl group containing 1 to 4 carbon atoms. Although the alkyl groups are composed of hydrogen and carbon, they can contain other substituents, such as OH groups, amino groups, and the like.

Piperazines with lower alkyl substituents on the nitrogen that can be used in the practice of this invention are the compounds described below.

N-Aminoethylpiperazine 1,4-bis(3-aminopropyl)piperazine Regarding the above compounds, piperazine is preferred.

The amount of piperazine used, or piperazine with a lower alkyl substituent on the nitrogen, is determined by the amount of SiO contained in the aqueous silica.
Between 0.1 and 5% by weight based on the weight of □. Preferred amounts are 1.0-5%, most preferably 2-4%. U.S. Pat. Nos. 4,169,337 and 4, cited above.
As shown in No. 462,188, the polishing operation is usually carried out in an alkaline pH range of greater than 10. Therefore,
It is necessary to adjust the polishing solution to a pH of about 11 or higher. This can be done with either sodium or potassium bases depending on the particular effect desired to be achieved in the final polishing operation.

Piperazine combined with silica sol for application in wafer polishing offers a number of advantages, as does piperazine combined with fumed silica. Their advantages can be summarized as follows.

A level of 1.2% piperazine requires less colloidal silica than aminoethylethanolamine to provide the same polishing rate.

2. Piperazine in the presence of colloidal silica is
The product does not show discoloration over time.

3. The 2% level of piperazine in the presence of colloidal silica does not require another chemical to kill or inhibit the growth of microorganisms.

4. Polishing silicon wafers requires high pH. The strongly basic piperazine family requires less caustic to adjust p++.

5. Aqueous dispersions of fumed silica in the presence of piperazine can be compared with colloidal silica containing piperazine with the same silica level (2,4%) or with colloidal aminoethylethanolamine with higher silica level (3,2%). +10.6% to +1 to silica
Showing an improvement in polishing rate of 8.2%. For example, 0.22%
of potassium hydroxide and 2.0% piperazine flakes, 30 g of Cabosi
IM-5 (trade name) was dispersed.

A dispersion formulation of fumed silica produced the polishing results described above when 1 part product was diluted with 14 parts water.

〔Example〕

For a detailed description of the invention, U.S. Pat.
Polishing tests were conducted as described and indicated in No. 7. The results of these tests are shown below.

In the tests described below, the compositions of the present invention were compared against commercially available amine-containing silica sol products of the type described in US Pat. No. 4,169,337.

This product is an aqueous colloidal silica sol. It has an average particle size of 50-1100n, is sodium stabilized and contains 50% by weight colloidal silica particles and 2% by weight aminoethylethanolamine. Similar results are obtained with piperazine with added bases other than sodium hydroxide. This commercially available material is hereinafter referred to as Composition 1.

The products used for silicon wafer polishing are summarized below.

Table 6 Polishing rate of composition 1 = 35.6 p m/10 m1n
(1,40 min/]0 m1n) Table 7 Polishing speed of composition 1 = 35.6 μm/m1n (1,40 m1n)
In all of the compositions listed above, unless otherwise specified, the starting silica was the colloidal silica used in Composition 1 diluted to 40% by weight. Furthermore,
Piperazine was used in all of the listed studies.

Table 7 shows the effect of polishing with nitrogen-substituted piperazine. Some of these materials are either less effective than piperazine or cause damage to existing abrasive band materials.

Claims (1)

[Claims] 1. An aqueous colloidal silica sol or gel combined with 0.1 to 5% by weight of piperazine, based on the SiO_2 content of the sol, or piperazine with a lower alkyl substituent on the nitrogen. A method of polishing silicon wafers and similar materials comprising polishing with an abrasive. 2. polishing with an abrasive comprising an aqueous colloidal silica sol or gel combined with 0.1-5% by weight piperazine based on the SiO_2 content of the sol;
A method according to claim 1. 3. Polishing with an abrasive comprising an aqueous colloidal silica sol or gel combined with 0.1-5% by weight of piperazine with lower alkyl substitution on nitrogen based on the SiO_2 content of the sol. 2. The method of claim 1, comprising: 4. Polishing with the polishing agent further combined with 0.1 to 5% by weight of a water-soluble quaternary ammonium salt or base containing up to 6 carbon atoms. Method described. 5. Polishing with the polishing agent further combined with 0.1 to 5% by weight of a water-soluble quaternary ammonium salt or base containing up to 6 carbon atoms. Method described. 6. Polishing with the polishing agent further combined with 0.1 to 5% by weight of a water-soluble quaternary ammonium salt or base containing up to 6 carbon atoms. Method described. 7. A composition useful for polishing silicon wafers and similar materials, comprising an aqueous colloidal silica sol or gel and 0.1 to 5% by weight piperazine based on the SiO content of the sol or gel. A composition consisting of. 8. Primary particle size
an aqueous colloidal dispersion of fumed silica having a size) within the range of 5 to 200 nm;
．． 8. The composition of claim 7 containing 1 to 5.0% by weight of piperazine or piperazine with a lower alkyl substituent on the nitrogen.