Temperature dependence of incorporation processes during heavy boron doping in silicon molecular beam epitaxy

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Abstract
Borondoped layers were grown by siliconmolecular beam epitaxy to establish incorporation processes at temperatures between 900 and 450 °C. For temperatures exceeding 650 °C a surface accumulated phase of boron was formed when doping levels exceeded solid solubility limits. The properties of this surface phase were used to determine solubility limits for boron in silicon. Above 750 °C, the measured equilibrium solubility limit was in the 1019‐cm−3 range in good agreement with previously published annealing data and showing a gradual decrease with decreasing temperature. Below 650 °C, the processes leading to the formation of the surface phase were kinetically limited, manifested by a sharp increase in boronsolubility limit, with completely activated levels above 1 × 1020 cm−3 realized. At intermediate growth temperatures the degree of dopant activation was found to be dependent on growth rate. The stability of fully activated highly‐doped boron layers, grown at low temperatures, to ex situannealing is also discussed.