For the homogeneous reaction:

We found that

The first reaction is in equilibrium

Case A:  Small Consumption of SIH2

In many cases a very thin film of the material is deposited (a few molecular layers) and as a result very little SiH2 is consumed. For example if SiH4 dissociates to form 1 mole SiH2 and 1 mole of H2 at equilibrium and then 0.01 mole of SiH2 is consumed in the deposition, then for all practical purposes   (i.e., 0.99  » 1.0). Consequently,

Case B:  Significant Consumption of SIH2
One the other hand if significant amounts of SiH2 are consumed, we can still obtain   from the equilibrium relationship. However   and we must include   in the rate law

which is the same as Eqn. below (S10-12) on p666.


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