Liquid phase epitaxy of silicon: an experimental and numerical parametric study

Abstract

A combined experimental and computational study of LPE growth of silicon from a tin-silicon solution is performed to investigate the effect of varying strengths of solutal convection. The LPE experiments and computer simulations are performed in a “sandwich” growth cell, and the characteristic Rayleigh number is varied by changing the spacing between upper and lower substrates. The time-dependent simulations, which take into account convective and diffusive transport as well as limited rate interface kinetics, predict, as expected, that stronger convection results in growth rate enhancement, particularly for the top substrate. The predicted growth thicknesses are found to be in excellent agreement with the measured values for both substrates over a range of substrate spacings (2 to 8 mm). More surprisingly, the simulations reveal that enhanced convective transport does not necessarily result in rougher substrate surfaces. In fact, the smoothest substrate is predicted for the largest spacing investigated (8 mm). Further analysis shows that this is due to a change in the convection regime. For the lower inter-substrate spacings the convection cells and concentration patterns are quasi-stationary and results in localized mass transfer maxima and minima throughout the growth process. Enhanced convection in this regime results in an increasingly wavier top substrate. With further increases in the inter-substrate spacing (> 4 mm), however, solutal convection becomes not only more intense but also increasingly more chaotic. The high and low concentration gradient regions associated with the local growth rate maxima and minima move continuously, resulting in much more uniform time-averaged growth rates and hence flatter upper substrates. These findings are consistent with experimental profiles obtained with a profilometer.