Equilibrium Carrier Density and Solubility of Antimony in Silicon

Abstract

The equilibrium solid solubility of antimony in silicon was determined in the range 850°–1300°C by carrier density measurements on polysilicon films doped by ion implantation. Up to 1150°C this property follows very tightly the exponential dependence ne = A exp -(E/RT) with A = (3.81 ± 0.15) x 1021 cm−3 and E = 0.561 ± 0.004 eV. The values at higher temperatures show a smaller increase, the figures at 1200°, 1250°, and 1300°C being 4.4, 4.9, and 5.3 × 1019 cm−3, respectively. The attainment of the two-phase equilibrium was confirmed by carrier profile measurements on isothermally annealed single-crystal specimens doped in a wide range of concentrations, as well as by TEM examinations which detected a high density of particles having the hexagonal structure of antimony. It is shown that the new solubility values, unlike the previous ones, fully comply with the conditions for phase equilibrium. According to this treatment, the values of 0.58 eV and of −2 × 10−4 eV/deg are deduced for the partial molar enthalpy and, respectively, for the excess partial molar entropy of the dopant in silicon relative to the standard liquid state of antimony. © 1989, The Electrochemical Society, Inc. All rights reserved.