Design elements affecting wafer temperature uniformity in multi-wafer production MBE systems

In this paper we present the results of key experiments that have illuminated our understanding of the interactions between wafers, backing rings, platen and manipulator heater in a 7×6″ multi-wafer production MBE system. We present examples of detailed wafer temperature maps across platens of 6-in diameter GaAs wafers. Results are discussed in terms of a qualitative model that can guide the design of MBE system manipulators, platens and backing rings that will be capable of producing a high degree of temperature uniformity. One of the most important factors is that the backing ring must be of proper width to compensate for heat conducted into the wafer perimeter through contact with the hotter platen. The platen must also be far enough from the radiative heating source, and of low reflectivity, to prevent reflected power from causing localized temperature non-uniformities in the heater. Because of the importance of platen emissivity to the thermal environment of the wafers, users should be aware of unintended changes in emissivity as platens become coated through weeks or months of use.