Divergent Flow in Chemical Vapor Deposition Reactors

An undesirable flow phenomenon can arise from divergent flow at the entrance region of a chemical vapor deposition (CVD) reactor, leading to uneven and recirculating backflow and correspondingly poor growth uniformity downstream. This phenomenon, recognized only recently in the CVD field, is caused by flow separation at the reactor wall. This type of flow is known as Hamel or Jeffery‐Hamel flow for two‐dimensional planar diverging channels. The onset of Hamel flow depends on gas Reynolds number, reactor divergence angle, and for channel‐type reactors, reactor aspect ratio. The transition from stable flow to Hamel flow was studied experimentally and compared with analytic predictions for idealized geometries. Idealized analytic predictions are shown to be useful for qualitatively interpreting flow behavior, but they are poor guides for quantitative design of CVD reactors of complex entrance geometry. Experimental determination of the maximum allowable divergence angle for a specific flow rate and reactor configuration is required.