Ionization Enhanced Solid Phase Epitaxy of Amorphous Silicon with Aluminum Impurities

In this work we measured the functional dependence of the solid phase epitaxial regrowth (SPER) of amorphous silicon on NAI, the concentration of implanted aluminum (p-type). The SPER rates of self-ion amorphized layers in silicon wafers with (100) substrate orientation were measured by in situ high precision, isothermal, cw laser interferometry for temperatures from 470 °C to 550 °C, and concentrations in the range 3×1018 cm−3 ≤NAI≤ 4.7×1020 cm−3 obtained from samples implanted with three different doses.In the concentration range 3×1018 cm−3 ≤NAI≤ 2.3×1019 cm−3, we observed a “compensation effect” in which, with increasing NAI, the SPER rate decreased below the regrowth rate in intrinsic silicon and the activation energy of SPER increased to 2.85 eV, compared to 2.72 eV for intrinsic silicon. In the range 3.3×1019 cm−3 ≤NAI≤ 5.6×1019 cm−3, the regrowth rate increased linearly with NAI as previously observed for SPER in boron, phosphorus, and arsenic implanted samples. However, due to the compensation effect, the aluminum data could not be fit to the normalized equation; V/Vi = 1 + N/Ni, as was done previously for data obtained for boron, phosphorus, and arsenic. The regrowth rate increased nonlinearly to the maximum implanted concentration of 4.7× 1020 cm−3 at which the regrowth rate was more than double the previously observed maximum rate in boron doped silicon. In the high concentration range, the SPER rate enhancement could be fit by a quadratic equation whose curvature was positive as was the case for boron. This contrasts with the negative curvature required to fit the nonlinear dependence of the SPER rate on the concentration of donor impurities such as phosphorus and arsenic.