The flow of gases is parallel to the surface of the wafers. The drop in growth rate with distance can be reduced by tilting the susceptor by about 5°. The goals of m ass transport in gas are to deliver gas uniformly to substrate (uniform films) and to optimize flow for maximum deposition rate. From kinetic theory of gasses, we have seen in previous sections that the dimensions of the system (D) is proportional to . In a CVD system, the pressure is reduced for higher D and higher deposition rate. And the low flow rates produces laminar flow which desirable compared to turbulent flow at high flow rates.

Fig. 3.34 : A laminar flow passing over plate