DEFECT-GUARDED RAPID THERMAL-PROCESSING

Pattern-induced thermal nonuniformities, arising during rapid thermal processing, are not radially symmetric. So the pattern-induced part of the thermal nonuniformities cannot be reduced by conventional methods such is multiple bank control, circular lamp arrangement, or wafer ro tation. A new approach to the reduction of the transient thermal nonun iformities is described. The approach utilizes a digital control of th e heating power in addition to the pyrometer control. The power absorb ed by the wafer in any time period of processing can be controlled, li mited, or ramped according to a defined recipe. Independent top and bo ttom heater bank control enables step by step changeable asymmetrical heating. These features allow better process design by reduction of an y transient nonuniformities, especially during heating up. The additio nal power cont , together with a new back-radiant silicon ring design allows defect-guarded processing.