Semiconductor Crystal Growth by Vertical Bridgman and Gradient Freezing Processes with Applied Fields

Abstract

Integrated circuits and optoelectronic devices are produced on surfaces of thin wafers sliced from a semiconductor crystal. The performance of the semiconductor is directly related to the uniformity of its composition. The crystal's composition generally changes due to a changing melt composition with segregation coefficient not equal to unity. Therefore, a major objective during the growth of any semiconductor crystal is to minimize the variations of the crystal's dopant or alloy composition. Externally-applied fields such as magnetic and electric fields can be used to provide electromagnetic damping or stirring of the melt motion in order to minimize the dopant or alloy segregation in the melt and thus in the crystal. This research focuses on investigations of various semiconductor crystal growth processes from the melt in the presence of externally-applied fields. These processes are (1) the Bridgman-Stockbarger process in steady magnetic fields, (2) the vertical gradient freezing process using submerged heater growth in steady magnetic and electric fields, (3) the Bridgman process using submerged heater growth in a rotating magnetic field, and (4) the Bridgman process using submerged heater growth in a combination of steady and rotating magnetic fields. Numerical models are developed using a Chebyshev spectral method with Gauss-Lobatto collocation points. These models provide predictions of the temperature, velocity and concentration fields in the melt as well as the dopant or alloy concentration in the entire crystal.