A method and apparatus for processing a semiconductor substrate is described. The apparatus is a process chamber having an optically transparent upper dome and lower dome. Vacuum is maintained in the process chamber during processing. The upper dome is thermally controlled by flowing a thermal control fluid along the upper dome outside the processing region. Thermal lamps are positioned proximate the lower dome, and thermal sensors are disposed among the lamps. The lamps are powered in zones, and a controller adjusts power to the lamp zones based on data received from the thermal sensors.