Effect of buoyancy forces and reactor orientation on fluid flow and growth rate uniformity in cold-wall channel CVD reactors

Abstract

Buoyancy forces can effect fluid flow and growth-rate uniformity in chemical vapor deposition (CVD) reactors. A two-dimensional finite element model for mass transfer-controlled CVD in channel reactors was used to determine buoyancy effects on fluid flow and growth rate. Reactor orientation, pressure, and cell spacing between the hot susceptor and the cold opposing wall were studied for metalorganic chemical vapor deposition (MOCVD) of InP from trimethyl indium. Fluid flow in the thermal transition regions at the leading and trailing edges of the susceptor is affected by the ratio of convective to conductive heat transport, represented by the Peclet number for heat transfer Pe T, whether or not buoyancy forces are present. For vertical orientations, fluid flow both over the susceptor and in the thermal transition regions is influenced by the ratio of buoyancy to viscous forces, represented by the ratio of Grashof and Reynolds numbers, Gr/Re. Gas recirculation occurs over the susceptor at high Gr/Re. In horizontal orientations, fluid flow in the thermal transition regions is influenced by the ratio of buoyancy and inertial forces. represented by Gr/Re 2. Gas recirculation in the form of transverse roll waves occurs over both the leading and trailing edges of the susceptor at high Gr/Re 2. Finally, for horizontal orientations with the hot susceptor on the bottom of the reactor, longitudinal roll waves can arise from side wall effects and an instability characterized by the Rayleigh number Ra. Depending on reactor orientation and growth conditions, the presence of buoyancy forces can improve or reduce growth-rate uniformity. Buoyancy effects are reduced by growth at low pressures or design of reactors with small cell spacings.