Modeling of epitaxial silicon growth from the SiH₂Cl₂‐H₂‐HCl system in an rf‐heated pancake reactor

A mathematical model of transport phenomena and epitaxial silicon growth in a pancake chemical vapor deposition reactor is presented for the SiH₂Cl₂‐H₂‐HCl system. Two‐dimensional conservation equations of mass, momentum, energy, and species mass developed in cylindrical coordinates along with appropriate boundary conditions are solved numerically with finite element methods. Streamlines show that the shearing force of the inlet gas flow yields recirculation zones inside the reactor and a separation point on the susceptor. Thermal and concentration boundary layers are seen to develop above the susceptor at pressures between 40 and 150 Torr, and susceptor temperatures between 850 and 1000 °C. When HCl is added to the SiH₂Cl₂‐H₂ system, as it is widely used in the selective epitaxial growth of silicon, the overall growth rate is reduced by silicon substrate etching. It is predicted that growth rates for bulk and selective epitaxy decrease monotonically with increasing HCl/SiH₂Cl₂ or (HCl)²/SiH₂Cl₂ feed flow ratios; also, this model predicts an optimal HCl/SiH₂Cl₂ feed flow ratio at which silicon growth rates on patternless and patterned wafers are equal to each other. The agreement between experimental and predicted growth rate profiles on patternless wafers at different temperatures and flow rates studied is seen to be satisfactory.