Precision measurements of the effect of implanted boron on silicon solid phase epitaxial regrowth

Abstract

The epitaxial recrystallization rates of self-ion amorphitized layers in silicon wafers with 〈100〉 substrate orientation were measured by in situ, high precision, isothermal cw laser interferometry. With this one-sample technique the changes produced by implanted boron impurity concentrations (NB) in the activation energy Ea and preexponential V0 of solid phase epitaxy were measured for concentrations in the range 5 × 1018 cm−3 < NB < 3 × 1020 cm−3 and for temperatures from 450 to 550°C. The differential changes in Ea produced were measured to within ± 23 meV when systematic errors were eliminated. Changes in activation energy and entropy [Ea and log (V0)] were found to be linearly correlated for all concentrations. This observation is consistent with the idea that electronically active impurities alter regrowth velocities by reducing the critical temperature for disordering at some of the interfacial sites at which elementary reconstructive processes are driven by thermal fluctuations. For small Nn, the critical temperature of the impurity-modified reconstruction is estimated at 1200K, approximately 200 K below the melting temperature of amorphous silicon. The Ea decreased exponentially with NB to a concentration Ninfl, larger than the estimated equilibrium solubility limit, where there was an inflection point in the V vs NB curve. The Ea increased for values of NB larger than Ninfl, showing that the differential increase in V for higher concentrations was due to a differential increase in the activation entropy. A change in the correlation between Ea and log (V0) at Ninfl indicated that larger NB produced an additional reduction of the critical temperature of the reconstruction. For small NB, the data support a simple Fermi level shifting model for the “electronic effect” of impurities on SPE (solid phase epitaxial) regrowth.