The quartz crucible currently in use usually has an inner and outer structure, the inner side is a transparent layer with fewer bubbles, and the outer side is a non-transparent layer with more bubbles. The main function of the outer bubble layer is to make the heat transfer more uniform.
The bubbles grow and merge with the high temperature process, which may cause the inner layer of quartz to peel off. In addition, amorphous quartz crucibles crystallize at high temperatures to form a stable crystalline state of cristobalite.
In the flow scouring of molten silicon, the crystal cristobalite peels off into the melt, and then flows to the crystal growth front, which is easy to cause the silicon single crystal to lose its single crystal structure, which is commonly known as the long crystal breakage.
It has been found that a compound coated with a layer of barium ions on the inner wall of a quartz crucible can promote the crystallization of the inner layer of the quartz crucible. In the "Technical Specification for the Production of Quartz Crucible for the Growth of Monocrystalline Silicon for Electronic Special Materials" (local standard of Hebei Province), the main coating raw materials are indicated: barium hydroxide, barium carbonate; Reagent purity 9999%。
Some analysts believe that the doping of BAC3 can promote the formation of tiny and dense cristobalite crystals on the inner wall of the crucible, and the dense inner wall crystal layer is not easy to be washed and peeled off by the silicon melt, and the tiny particles are easier to melt in the high-temperature melt even if they are peeled. Due to the extremely small coefficient of barium in silicon, about 225*10-8, so a trace amount of barium-doped will not affect the lifetime of monocrystalline silicon with few tons.
In addition, the barium hydroxide coating on the surface of the crucible was made more firmly by using the study of the reaction mechanism of the crucible coating to reduce the erosion of the silica liquid on the crucible surface and improve the service life of the quartz crucible.
Barium coating process. The production of barium coating is the core process of coated crucible production, which can ensure the formation of a uniform crystallization layer during the use of crucible and improve the crystal growth performance of crucible. The barium hydroxide powder is dissolved in water, the crucible is put into the barium applicator, and the barium hydroxide is evenly sprayed on the inner surface of the crucible. Barium hydroxide is very easy to react with CO2 in the air to produce BaCO3, and the coating on the surface of the crucible is BaCO3. There is no BA ion production in the process of barium coating, but the BA(OH)2 solution and BACO3 precipitation are highly toxic substances that are harmful to the human body, and the operation process needs to be protected.
Research status of quartz crucible coatings.
In order to elucidate the effect of BA doping in quartz crucibles for the growth of Zzoral silicon crystals, Xinming Huang et al. studied the reaction between Si melt and Ba-doped quartz glass by in-situ observation and differential scanning calorimetry, and found that when the concentration of BA in quartz glass was higher than 30 ppm, Ba doping completely inhibited the generation of brown rings.
Mo Yu et al. studied two kinds of quartz crucibles with different inner coatings, one is a crucible (SQC) with an inner layer of high-purity synthetic quartz sand, and the other is a crucible (NQC) of natural quartz sand coated with an ionic solution of alkaline earth metal barium. After the long-term growth of large-diameter (350 mm) single crystals using two quartz crucibles, the surface morphology of the two quartz crucibles was observed by metallurgical microscope, and the roughness was tested by a roughness tester, and the metal concentration of the grown crystals was measured by ICP-MS. The results show that the use of NQC has an impact on the dislocation-free growth and quality of single crystals due to the presence of more impurity particles into the silicon melt, and the use of SQC can reduce this phenomenon.
Hansen et al. proposed an ionic solution coated with alkaline earth metal (such as Ba) in the crucible, which can improve the crucible quality and facilitate the growth of single crystals.
Tomzig et al. discuss the difficulties of growing 300 mm high-quality single crystals, mentioning that the use of endosynthetic quartz crucibles may provide a higher lifetime. At present, the crucible of inner barium quartz is widely used for the growth of single crystals with small diameters, while synthetic crucibles are widely used by foreign manufacturers for the growth of large single crystals. Due to the slow development of large-size single crystal growth technology in China, it is difficult to prepare large-size synthetic quartz crucibles, and there are few in-depth studies on synthetic quartz crucibles.
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The 2nd Anhui International Quartz Industry Conference and Exhibition 2024.