Nucleation reactant addition rate effect

Goals To demonstrate the effect of seeding point and addition of reactant on nucleation and filtration rate... 

Since the interposition of a barrier layer diminishes the effective contact between reactants, the nucleation step in solid + solid reactions is Usually completed very rapidly at temperatures conveniently used in studies of the bulk reaction and, accordingly, the rate processes are often deceleratory throughout. In addition to the progressive diminution in rate... 

The problem of assuring uniform depositions on many wafers closely spaced in a long uniform tube was solved when operation of the reactor at low pressure was considered.22 Normally, in an atmospheric pressure cold wall CVD system, the reactant gas is heavily diluted in N2 in order to reduce gas phase nucleation. At the pressures used for low pressure CVD (0.5-1.0 Torr), this is less of a problem so less diluent is needed. The net effect then is that deposition rates only fall by a factor of five. However, as many as 100 wafers can be processed in such a reactor at one time (see Figure 26), and this more than compensates for the lower deposition rate. In addition, due to the low pressure, diffusion occurs at high rates and the deposition tends to be controlled by the surface temperature. Given the very uniform temperatures available in a diffusion furnace, the deposition uniformity tends to be excellent in such a system. 

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