SINGLE WAFER PROCESSING IN STAGNATION POINT FLOW CVD REACTOR - PROSPECTS, CONSTRAINTS AND REACTOR DESIGN

A stagnation point chemical vapor deposition (CVD) reactor that obviates substrate rotation can deposit a uniform, thin layer by developing a uniform boundary layer adjacent to the sur-face of deposition in an axially uniform flow. Such a geometry is highly desirable for high throughput, reproducible single wafer processing in electronic industry. It can also operate effectively at atmospheric pressure if its geometrical and operational parameters are optimized. It is shown here that the nature of the gas distributor, optimized diffuser shape inlet with respect to its angle of divergence, diffuser height and its inverted geometry are the key design parameters. The pressure drop across the gas distributor, inlet gas velocity, gas viscosity, width of hydrodynamic boundary layer on the inner walls of the diffuser th at limits the available area for uniform deposition and thermal convection are its important operational parameters. The inverted reactor geometry minimizes the convection related instabilities and helps stabilize the gas flow in the reactor. Analytical expressions are developed to correlate these functional parameters of a stagnation point CVD reactor to its performance in order to develop the reactor design. Finally, the practical aspects including the experimental results of operation of such a CVD reactor design are discussed.