Transport phenomena in vertical reactors for metalorganic vapor phase epitaxy: I. Effects of heat transfer characteristics, reactor geometry, and operating conditions

Abstract

Effects of operating conditions, reactor geometry, and heat transfer characteristics on flow patterns and growth rate uniformity in vertical, axisymmetric reactors for metalorganic vapor phase epitaxy (MOVPE) are described. Finite element solutions of two- and three-dimensional models of transport phenomena in vertical MOVPE reactors identify regions of inlet flow rates, susceptor rotations, and pressures where flow recirculations due to natural convection are minimized and good deposition rate uniformity is achieved. Particular attention is placed on understanding the influence of reactor geometry and heat transfer characteristics on flow fields and film thickness variations. The numerical computations demonstrate that modifications in the orientation of the reactor, the inlet size and its distance from the susceptor as well as the shape of the reactor enclosure can be used effectively to optimize reactor performance. Baffles can also be used advantageously to improve uniformity in existing reactor enclosures but at the expense of more complex flow patterns. The simulations underscore the importance of including accurate heat transfer treatments in MOVPE models by illustrating that different flow fields result from the commonly used thermal boundary conditions and a detailed heat transfer model. The model predictions are shown to be in good agreement with experimentally observed flow fields, wall temperatures and growth rates for GaAs. Nonlinear transport phenomena lead to the existence of multiple steady flows for the same operating parameters as well as the breaking of axisymmetry and development of fully three-dimensional flow patterns. An example of a non-axisymmetric flow field is given and the assumption of axisymmetry in models of vertical reactors is discussed.