Growth rate mass-transfer-limited regime

The diffusion of reactive species within the boundary layer will be the limiting factor in mass transfer limited regime. Applying the laws of diffusion and considering a constant average thickness of the boundary layer, leads to the expression of the growth rate as follows ... 

Heat transfer is an extremely important factor in CVD reactor operation, particularly for LPCVD reactors. These reactors are operated in a regime in which the deposition is primarily controlled by surface reaction processes. Because of the exponential dependence of reaction rates on temperature, even a few degrees of variation in surface temperature can produce unacceptable variations in deposition rates. On the other hand, with atmospheric CVD processes, which are often limited by mass transfer, small susceptor temperature variations have little effect on the growth rate because of the slow variation of the diffusion with temperature. Heat transfer is also a factor in controlling the gas-phase temperature to avoid homogeneous nucleation through premature reactions. At the high temperatures (700-1400 K) of most... 

At high temperatures, the limiting factor is not the surface kinetics but the contribution of matter by the gas phase. The growth rate depends, therefore, on the coefficient hg whose variation with temperature is slow (hg oc T3/2). It is then considered that the growth rate in the regime of mass transfer is proportional to the concentration Cg. 

In the regime limited by the surface kinetics, adding a dopant gas to induce n-type or p-type doping causes an increase in the growth rate. On the contrary, in the regime limited by mass transfer, adding dopants in the reactive gas does not affect the silicon growth rate [16-18]. 

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