Low temperatures in RTP

Even though RTP was originally designed for temperatures from 700 to 1200/spl deg/C the processes with lower temperatures gain more and more importance. Steady state temperatures down to 300/spl deg/C makes temperature control from 200/spl deg/C necessary. This processes occur in silicon and in compound semiconductor production. In GaAs production low temperature processes are used for alloying metal to achieve lowest contact resistances. For this applications we used the graphite box supplied for the Mattson SHS2800CS. Together with the special low temperature pyrometer setup. Temperatures can be controlled down to 200/spl deg/C. But the correct temperature profile is not easy to achieve. This is coming from the fact that the wafer can be heated rapidly, but not cooled rapidly. This will lead to a overshoot, 7/spl deg/C in this specific example. To solve this problem a short open loop step was introduced. This method is used in production as a standard now. The alloying of the contacts for HBT and HEMT production using this methods will be presented.