JPH0515302B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION 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 ultimate particle size of the colloidal silica and silica gel primary particles of the sol used by the patentee is 4-200 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 100 nm as 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 primary particle size is 4~
200 nm, preferably in the range 4-100 nm, either in colloidal form or silica gel in combination with a water-soluble amine, can be used as an abrasive to effectively polish semiconductor surfaces of conventional types, especially silicon. I found out that it can be polished. The amount of amine on silica present in a silica sol or gel is based on the _SiO2 content of the sol or gel.
It may be in the range of 0.5 to 5.0%. The preferred amount of amine is
1.0-5.0%, most preferably 2.0-4.0%. 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 states that the abrasive used to practice U.S. Pat. It has been disclosed that substantial improvements can be made when added to such compositions. In preferred embodiments, the water-soluble quaternary ammonium salt or quaternary ammonium hydroxide 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 quaternary ammonium salts of morpholine and the like. Typical water-soluble quaternary ammonium salts and quaternary ammonium bases that can be used in the invention of U.S. Pat. morpholinium, 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 comprises: an aqueous colloidal silica sol or silica gel;
An abrasive in the form of a sol containing piperazine or piperazine with a lower alkyl substituent on nitrogen, the weight of the abrasive in the form of a sol containing piperazine or piperazine with a lower alkyl substituent on nitrogen. This includes using as an abrasive abrasives containing 0.1 to 5% by weight based on . The piperazine can be combined with 0.1 to 5% by weight of further water-soluble quaternary ammonium salts or quaternary ammonium chlorides containing up to 6 carbon atoms. Starting Silica Sol A wide range of aqueous colloidal silica sols or silica gels, as shown herein, can be used in the practice of the present invention. Preference is given to using colloidal silica sols. Two such raw materials are NALCOAG
It is commercially available under the names 1050 and NALCOAG 1060. These silica sols and their properties are described below. NALCOAG 1050 Colloidal Silica (as _SiO2 ) 50% PH 9.0 Average particle size 16-25nm Average surface area 120-176m2 ^/ g Specific gravity (20℃ (68〓)) 1.390 Viscosity 0.07Pa・s (70cP) (Max.) _Na2O Content 0.4% NALCOAG 1060 colloidal silica (as _SiO2 ) 50% PH 8.5 Average particle size 50~70nm Average surface area 40~60m2 ^/ g Specific gravity (20℃ (68〓)) 1.390 Viscosity (25℃ (77〓)) 0.015 Pa・s (15 cP) (maximum) In addition to those sols described above, other silica sols as well as their manufacturing methods are covered by US patents.
No. 3901992, which is incorporated herein by reference. Finally, Applicants have discovered that improved results can be obtained when fumed silica is dispersed in an aqueous medium containing a piperazine compound to obtain a silica sol. Fumed silica is a dry process silica that is produced by combustion hydrolysis reaction of volatile silicon compounds in the gas phase and has extremely low adsorbed water. Piperazine or Piperazine with a Lower Alkyl Substituent on the Nitrogen These amines include piperazine itself as well as piperazine containing a lower alkyl substituent on the nitrogen portion of the biperazine 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. can be used to carry out the invention,
Piperazine with a lower alkyl substituent on the nitrogen is the following compound. N-aminoethylpiperazine 1,4-bis(3-aminopropyl)piperazine Regarding the above compounds, piperazine is preferred. The amount of piperazine, or piperazine with a lower alkyl substituent on the nitrogen, used is between 0.1 and 5% by weight, based on the weight of the sol composition containing the piperazine or substituted piperazine and the aqueous silica. . Preferred amounts are 1.0-5%, most preferably 2-4%. As shown in previously cited U.S. Pat.
This is done in the PH area. Therefore, the polishing solution should be about 11 or more
It is necessary to adjust the pH. This can be done with either sodium or potassium bases depending on the particular effect desired to be achieved in the final polishing operation. Advantages of the Invention Piperazine in combination with silica sol for applications in wafer polishing offers a number of advantages, as do piperazine in combination with fumed silica. Their advantages can be summarized as follows. Piperazine at the 12% level requires less colloidal silica than aminoethylethanolamine to provide the same polishing rate. 2 Piperazine in the presence of colloidal silica shows no discoloration of the product over time. 3 Piperazine at the 2% level in the presence of colloidal silica does not require another chemical to kill or inhibit the growth of microorganisms. 4. High pH is required for polishing silicon wafers. The strongly basic piperazine family requires less caustic to adjust the pH. 5 Aqueous dispersions of fumed silica in the presence of piperazine have the same silica level (2.4
%) for piperazine-containing colloidal silica or the silica level is higher (3.2%)
It shows an improvement in polishing rate of +10.6% to +18.2% over colloidal silica containing aminoethylethanolamine. For example, in 67.78 g of water containing 0.22% potassium hydroxide and 2.0% piperazine flakes, 30 g of Cabosil M-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 To illustrate the advantages of the present invention, U.S. Pat.
Polishing tests were conducted as described and shown in No. 4169337. The results of these tests are shown below. In the tests described below, the compositions of the present invention were tested to
Comparisons were made against commercially available silica sol products containing amines. This product is an aqueous colloidal silica sol. It has an average particle size of 50-100 nm, 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.

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Table: In all of the compositions listed above, unless otherwise specified, the starting silica was a 40% by weight dilution of the colloidal silica used in Composition 1. Additionally, piperazine was used in all of the listed tests. 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 polishing pad materials.

Claims (1)

[Claims] 1. Aqueous colloidal silica sol or silica gel;
An abrasive in the form of a sol containing piperazine or piperazine with a lower alkyl substituent on nitrogen, the weight of the abrasive in the form of a sol containing piperazine or piperazine with a lower alkyl substituent on nitrogen. A method for polishing silicon wafers and similar materials, comprising polishing with a material containing 0.1 to 5% by weight based on 2. The method of claim 1, wherein the abrasive in the form of a sol contains 0.1 to 5% by weight of piperazine, based on the weight of the abrasive. 3. The abrasive in the form of a sol contains 0.1 to 5% by weight, based on the weight of the abrasive, of piperazine in which nitrogen has a lower alkyl substituent. The method described in Section 1. 4. The polishing agent in the form of a sol further contains 0.1 to 5% by weight of a water-soluble quaternary ammonium salt or quaternary ammonium base having up to 6 carbon atoms. The method described in any one of paragraphs 1 to 3. 5. A sol composition useful for polishing silicon wafers and similar materials, comprising an aqueous colloidal silica sol or silica gel and containing from 0.1 to 5% by weight of piperazine or nitrogen, based on the weight of the sol composition. A composition comprising piperazine with an alkyl substituent. 6. The composition of claim 5, wherein the aqueous colloidal silica sol is an aqueous colloidal dispersion of fumed silica having a primary particle size in the range of 5 to 200 nm.