Surface modification process of quartz glass crucible

#The present invention relates to a surface modification process of a quartz glass crucible and to a surface modified quartz glass crucible which is used in the process of pulling up silicon single crystal used for a semiconductor etc. from molten silicon.

#As one of the causes that a dislocation is formed in silicon single crystal in the pulling method, it has been known that cristobalite formed on the inside surface of the quartz glass crucible is released into the molten silicon. As a countermeasure to this, a process is known in which an alkaline earth metal is coated on an inside surface of the crucible to act as a crystallization promoter. The metal forms a cristobalite layer on the inside surface of the crucible at an early stage of pulling up (e.g. U.S. Pat. No. 5,976,247, Japanese Patent No. 3,100,836). In these inventions, a barium hydroxide solution is coated on the surface of the quartz glass crucible and the coated barium hydroxide reacts with carbon dioxide in air to form barium carbonate on the surface of the crucible. The barium carbonate is weakly adhered on the surface of the crucible by drying and is used as a crystallization promoter.

#However, quartz glass crucibles surface-treated by conventional methods have the following problems and improvements are desired. That is, (A) since the barium carbonate powder on the quartz glass crucible is not fixed with any binder, the adhesion strength of the powder is very weak so that the powder is easily abraded and falls off when contacted by persons and instruments. Such abrasion occurs in the production process of the crucibles, such as product inspection, conveyance, and insertion to a carrying case, etc. It also occurs in the user's process, where the quartz glass crucible is set on a carbon susceptor in the crystal puller. As a result, its adhesion state becomes non-uniform and spot-like. Furthermore, there is also a possibility that worker health is negatively affected because barium carbonate powder is scattered when the carrying case is opened. (B) Since the adhesion strength of powder is very weak, nucleation efficiency as a crystallization promoter is low, and so the amount of barium carbonate required becomes excessive. (C) If the crucible is washed, the barium carbonate powder adhered on the surface of the crucible is washed away. It is then impossible to wash the crucible after the adhesion of the barium carbonate powder, even if some contaminants adhere on the surface of the crucible.

#Two kinds of a partial hydrolyzate of alkoxysilane oligomer of (I) and (II) were prepared at the mixing ratios of raw materials and the reaction conditions, shown in Table 1.

#(2-1) 13.8 g of 2-ethylhexanoic barium (C7H15COO)2Ba was dissolved in a mixed solvent of 60 g of iso-amyl alcohol and 26.2 g of iso-amyl acetate to make a 5 weight % solution, which was calculated as BaO. Next, 20 g and 50 g of the partial hydrolyzates of alkoxysilane oligomer shown in Table 1 (I), were added and mixed with 20 g, 40 g, and 50 g of the solutions respectively. Furthermore, in the liquid A and the liquid B, 1-butanol was added to adjust the concentrations. Then, the silica sol liquids of A, B, and C shown in Table 2 were prepared.

#(2-2) 24.0 g of 2-ethylbutyric barium (C5H11COO)2Ba was dissolved in a mixed solvent of 70 g of 1-butanol and 6 g of acetylacetone, and refluxed to make 10 weight % solution, which was calculated as BaO. Next, 40 g and 80 g of the partial hydrolyzates of alkoxysilane oligomer shown in Table 1 (II) were added to mix with 20 g and 50 g of the solutions respectively. Furthermore, in the liquid D, iso-amyl alcohol was added to adjust the concentration. Then, the silica sol liquids D and E shown in Table 2 were prepared.