JPH0454616B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing colloidal silica used for polishing silicon wafers in the manufacturing process of semiconductor devices. [Technical Background of the Invention] In recent years, in the manufacture of LSIs and VLSIs, polishing agents made of corodal silica have been used in mirror polishing, which is the final finishing step of silicon wafers serving as substrates. By the way, colloidal silica conventionally used for polishing is made by diluting industrial water glass (sodium silicate) with water to give a silica concentration of 2 to 3%.
After removing metal ions such as Na ⁺ through a cation exchange resin, the surfactant and Na ₂ O are
Disperse and stabilize the silica by adding NaOH to a concentration of 0.56%, then heat and concentrate it to a concentration of 10%.
It is manufactured by the method of pre-concentration. [Problems with the background technology] However, since colloidal silica produced by conventional methods contains a large amount of Na ₂ O and also contains large amounts of metals such as Fe, it is difficult to use this as a polishing agent for mirror polishing of wafers. If you do so, the following problems will occur. That is, in the polishing agent
If metal ions such as Na ⁺ ions and Fe ions are included, this polishing agent may cause multiple
When mirror polishing a wafer on which MOSLSI is formed, the metal ions have high mobility in the wafer and oxide film, so a potential difference is created between the gate electrode and the wafer (substrate), resulting in a threshold voltage of Invite fluctuations. In particular, VLSI is 64k bit, 256k bit, 1
megabit, then 4 megabit, MOS
When transistors are miniaturized, fluctuations in threshold voltage due to the metal ions become a serious problem in terms of characteristics. For this reason, very fine (10 to 20 μm) and ultra-high purity colloidal silica suitable for use as a polishing agent is required. [Object of the Invention] The present invention aims to provide a method for producing colloidal silica for polishing which is free of metal ions, has ultra-high purity, and has excellent stability. [Summary of the Invention] The present invention comprises a step of reacting high-purity silica or silicate ester with quaternary ammonium hydroxide to produce a quaternary ammonium silicate, and a step of reacting the quaternary ammonium silicate with a cation exchange resin. A process of removing quaternary ammonium groups by passing through the membrane or electrolyzing using a cation exchange membrane to produce a solution containing silica, and adding quaternary ammonium hydroxide to this solution to reduce the pH to 9. 10 and further adding a dispersant. According to the present invention, quaternary ammonium hydroxide is used as a raw material for producing silicate, and after removing the quaternary ammonium group with a cation exchange resin or the like to produce a solution containing silica, By adding the quaternary ammonium hydroxide as a stabilizer to the produced silica and further dispersing the produced silica by adding a dispersant, it is metal ion-free, ultra-high purity, and stable as described above. Colloidal silica for polishing with excellent properties can be obtained. Furthermore, when wafers are polished using this colloidal silica, mechanical polishing is performed by the silica particles contained therein, and chemical polishing is performed by the added quaternary ammonium hydroxide, which may lead to contamination of the wafers. It is possible to achieve an extremely smooth mirror finish without any scratches. The above-mentioned silicate ester has the general formula Si
(OR) ₄ [However, R in the formula represents an alkyl group having 1 to 4 carbon atoms] can be mentioned. Specific examples include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. It is necessary to use a highly purified silicate ester purified in a purification tower. The above quaternary ammonium hydroxide has the general formula [However, R ₁ to _{R 4} in the formula represent an alkyl group or an alkanol group having 1 to 4 carbon atoms]. Specific examples include tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylethanolammonium hydroxide, triethylethanolammonium hydroxide, and the like. When adding such quaternary ammonium hydroxide in the second step,
The reason why the PH value is limited to the above range is that if it deviates from this range, sufficient stability of silica cannot be achieved. As the cation exchange resin, for example, Diaion SK-1B, SK-102, manufactured by Mitsubishi Kasei Corporation, etc. can be used, and as the cation exchange membrane, for example, Nafion 423, manufactured by DuPont, Inc. can be used. As the dispersant, cationic, anionic, nonionic and amphoteric water-soluble surfactants can be used, but in particular polyoxyethylene nonyl phenyl ether (trade name: Emulgen 910, manufactured by Kao Corporation) can be used.
Nonionic surfactants such as 915) are preferred. It is desirable to add such a water-soluble surfactant in a concentration range of 0.01 to 0.001% in the final colloidal silica state. The reason for this is that if the concentration of the water-soluble surfactant deviates from the above range, the dispersibility of silica particles due to the addition of the surfactant may not be able to be achieved. Note that colloidal silica having a predetermined silica concentration (usually 5 to 20% concentration) is produced by adding quaternary ammonium hydroxide and a dispersant in the above-described method and then heating and concentrating the mixture. [Embodiments of the Invention] Examples of the present invention will be described in detail below. Example 1 First, 152g of purified tetramethoxysilane
(1mol) and 10 of tetramethylammonium hydroxide
After reacting with 600g of % aqueous solution at 60-70℃, the silica concentration was reduced by stripping methanol.
12% Tetramethylammonium Silicate 500
g was produced. Subsequently, this silicate was diluted with pure water to a silica concentration of 35%, and then the tetramethylammonium group was removed through a cation exchange resin to produce a solution with a silica concentration of approximately 3.1%. Next, a 10% aqueous solution of tetramethylammonium hydroxide was added to this solution to adjust the pH to 9.5, and then 1 c.c. of a 1% aqueous solution of polyoxyethylene nonyl phenyl ether was added, and the pH was further adjusted to 60%.
Concentrate under reduced pressure at a temperature of ~70°C until the silica concentration is approx.
10% colloidal silica was produced. Example 2 First, 208g of purified tetramethoxysilane
(1 mol) and 800 g of a 10% aqueous solution of trimethylethanolammonium hydroxide were reacted at 70 to 90°C, and then the ethanol was stripped to produce 650g of trimethylethanolammonium silicate with a silica concentration of 10%. Subsequently, this silicate was diluted with pure water to a silica concentration of 3%, and then trimethylethanolammonium groups were removed through a cation exchange resin to produce a solution with a silica concentration of about 3.1%. Next, a 10% aqueous solution of tetramethylammonium hydroxide was added to this solution to adjust the pH to 9.5, and then 1 c.c. of a 1% aqueous solution of polyoxyethylene nonyl phenyl ether was added, and the pH was further adjusted to 60-70. Colloidal silica with a silica concentration of about 10% was produced by concentrating under reduced pressure at a temperature of .degree. Comparative Example First, industrial water glass (sodium silicate) was diluted with water to have a silica concentration of 2 to 3%, and was passed through a cation exchange membrane to remove metal ions such as Na ⁺ . Next, add surfactant and Na ₂ O to this solution.
After dispersing and stabilizing silica by adding 0.4 to 0.56%, it was heated and concentrated to produce colloidal silica with a silica concentration of about 10%. The physical properties of the colloidal silica produced in Examples 1 and 2 and Comparative Example are shown in Table 1 below, and the results of impurity analysis by flame atomic absorption are shown in Table 2 below.

【table】

[Table] As is clear from Table 2 above, this Example 1,
It can be seen that the colloidal silica obtained in Example 2 contains significantly less metals such as Na and Fe than conventional colloidal silica, and has ultra-high purity. Furthermore, when polishing a silicon wafer on which a plurality of MOSLSIs were fabricated using the colloidal silica of Examples 1 and 2, the back surface of the wafer could be finished to an extremely smooth mirror finish, and the Na No contamination by ⁺ ions, etc., and no fluctuations in threshold voltage were observed. [Effects of the Invention] As detailed above, according to the present invention, colloidal silica for polishing that is free of metal ions, has ultra-high purity, and has excellent stability can be produced, and furthermore, this colloidal silica can be used to manufacture silicon wafers. This polishing has remarkable effects such as being able to achieve an extremely smooth mirror finish without contaminating the wafer.

Claims (1)

[Claims] 1. A step of reacting high-purity silica or silicate ester with quaternary ammonium hydroxide to produce a quaternary ammonium silicate, and passing the quaternary ammonium silicate through a cation exchange resin. A process of removing quaternary ammonium groups by performing electrolysis using watermelon or a cation exchange membrane to produce a solution containing silica, and adding quaternary ammonium hydroxide to this solution to adjust the pH to 9 to 10. 1. A method for producing colloidal silica for polishing, the method comprising the steps of: adjusting the amount of colloidal silica, and further adding a dispersant. 2. Claim 1, characterized in that the silicate ester is represented by the general formula Si(OR) ₄ [wherein R represents an alkyl group having 1 to 4 carbon atoms]. A method for producing colloidal silica for polishing as described in . 3 Quaternary ammonium hydroxide has the general formula [However, R ₁ to _{R 4} in the formula represent an alkyl group or an alkanol group having 1 to 4 carbon atoms]. Method for producing silica. 4. The method for producing colloidal silica for polishing according to claim 1, wherein the dispersant is a water-soluble surfactant.