a$)$ Develop a model to predict the diffusion$-$limited flux of arsine to the surface of the

wafer. State all your assumptions.

b$)$ Estimate the initial deposition rate of arsenic $($in g min ${?}^{-1})$ onto the surface of a $15cm$

diameter silicon wafer if $D_{\text{A}\text{s}\text{H}3,H2}=221c{m}^2{s}^{-1}.$

The process operates at a pressure of $300Pa$ and a temperature of $600C.$ In many CVD

reactors, the gas phase over the thin film is not mixed. Furthermore, at $600C$ the surface

reaction is very fast. Consequently, the molecular diffusion of $As{H}_3$ vapour to the surface of

the wafer can be assumed to control the rate of $A{s}_{(s)}$ formation.

A mixture of arsine and hydrogen gas continuously flows into the reactor at a molar ratio

of $4$:$1H_2$:$As{H}_3.$ A diffuser $6cm$ above the wafer provides a quiescent gas space over the

growing As$($s$)$ film.