Thermomigration of aluminum-rich liquid droplets in silicon

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Abstract
Aluminum‐rich liquid droplets migrating in a thermal gradient in the 〈111〉 direction in silicon form flattened triangular platelets bounded by (111) planes and leave behind p‐type trails in n‐type silicon. The droplet migration rate decreases with decreasing droplet size because of processes at the solid‐liquid interface. Above 700°C the migration rate is an Arrhenius function of temperature and is consistent with a liquid diffusion coefficient D=4×10−3 exp(−[7.1 kcal/mole °K]/RT) cm2/sec. Below 700°C, an aluminum‐oxygen interaction causes a large decrease in droplet velcotiy. Droplet migration up a temperature gradient in the Al–Si system generates a hydrostatic tension in the droplet liquid which exceeds the yield stress of silicon after the droplet has traveled 7°C. On cooling a sample and solidifying a droplet, a large positive pressure is produced in the solidified droplet which causes yielding or cracking in the surrounding silicon matrix.

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