THE STRESS AND STRENGTH AT THE NECK OF A LARGE-DIAMETER SILICON CRYSTAL DURING GROWTH

Temperature, strength, and stress at the Dash thin neck of large diame ter silicon,crystals during Czochralski growth are analyzed. The combi nation stress from the crystal weight, the meniscus weight, and the su rface tension are calculated for the initial crystal growth stage, inc luding shoulder portion and the first 12.5 cm long of body growth. Two shoulder lengths, 2.5 and 10 cm with three diameter sizes, 200, 250, and 300 mm are calculated. A two-dimensional, axisymmetric heat conduc tion model using a commercially available software, ANSYS(R),(a) is us ed to calculate the temperature distribution in the crystals. The stre ngth of the thin neck is obtained from the relationship between the up per yield strength of silicon and temperature. To maintain a dislocati on-free (DH) lattice structure, the strength of the thin neck must be higher than the combination stress acting upon the thin neck. The resu lts indicated that the neck temperature increases with the crystal dia meter and decreases with the shoulder length. The minimum neck diamete r to maintain a DF structure for a 200 mm crystal is 3.7 mm with a 2.5 cm shoulder and 3.06 mm with a 10 cm shoulder. For a 250 mm crystal, the minimum neck diameter is 4.8 mm with a 2.5 cm shoulder and 4.1 mm with a 10 cm shoulder. For a 300 mm diameter crystal, the minimum neck diameter is 6.1 mm with a 2.5 cm shoulder and 5.2 mm with a 10 cm sho ulder.