Effect of a temperature gradient on arsenic diffusion in silicon

Abstract

The effect of a temperature gradient on arsenic diffusion was investigated. Arsenic-implanted silicon wafers were subjected to temperature gradients in the order of 100°C cm −1 in a rapid thermal anneal apparatus. No measurable differences were observed in the arsenic profiles by changing the direction of the temperature gradient in the low dose (1×10 14 cm −2 ) Si(111) and Si(100). There was also no measurable difference in the arsenic profiles for the high dose (6×10 15 cm −2 ) Si(100) due to temperature gradients. However, in the high dose Si(111) arsenic penetrated deeper on the cold side. The difference in arsenic penetration on the cold and hot sides of the sample was in the order of 10–15 nm for a 10–90s anneal. The Soret effect contribution to the isothermal diffusion was estimated by solving the diffusion equation. The calculations agree well with measured results for the low and high dose Si(100). However, there is disagreement for the high dose Si(111). It is proposed that the defect-enhanced Soret effect, which couples arsenic diffusion flux to the heat flux in the highly disordered crystal, may cause the observed temperature gradient dependence in arsenic penetration.