Why a separate pretreatment chamber is designed when the linear buffer chamber already has filaments for wafer degassing? What are the differences between these two chambers in terms of their purpose?
Among the standard surface coating methods, MBE has probably the highest demands when it comes to vacuum quality. Therefore even the smallest contaminants you can imagine may be fatal for your processes and for that reason it is considered reasonable to keep everything as separated as possible.
Of course I don't know your setup but I would imagine that one of the chambers is meant to be used for the removal of coarse residuals and one is used for the fine finish - and from the arrangement, i.e. which one is closer to the deposition chamber, you should be able to tell which one is for what.
Loading chamber is designed to clean cassette and platen at moderate temperatures, when cassette is moved to outgassing chamber it doesn't contaminate it. Prebake step helps keep outgassing chamber clean.
It follows :
a) Adsorbed contamination that is already existing on the wafers, is desorbed in the process of 'degassing' at high temperature. As a result, vacuum level is degraded and it is taken care by pumps in Pre-treatment chamber.
b) Thus, it fulfills the prime interest to keep the main growth chamber free of any contamination.
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