Czochralski single crystalline silicon@ growth - gives improved yield of defect-free bars due to optimisation of particle distribution, roughness, fracture and pull strength of the polycrystalline grains continuously added

摘要

Si single crystals are grown using a Czochralski method with continuous resupply of granular polycrystalline Si. Granular material properties are optimised as follows: average surface roughness is not more than 0.5 micron, obtd. by cleaning of the granules, pref. using a watery HF soln., the number of granules with a dia. of 2 mm or more is not more than 1000 per 1 kg of material; the average ratio of cavity area to grain area is not more than 3%; the fracture strength KIC is not less than 1.5; the pull strength is not less than 15 kg/mm2; the polysilicon is pref. made by thermal decompsn. of silane or trichlorosilane in a fluid bed reactor. USE/ADVANTAGE - The optimisation of the granular material reduces the number of fracture pieces formed and thereby increases the yield of single crystalline bars without defects. Analysis has shown that fracture occurs due to the thermal shock and that the number of pieces formed depends on size and strength of the grains and number of potential fracture sites. The method is used in the growth of Si crystals, esp. for large, e.g. larger than 6 inch dia., bars.