It is known that many processes performed during the manufacture of a semiconductor device require heating of the workpiece. It is most desirable that this heating be uniform across the surface of the workpiece since this will tend to result in a uniform process being performed.
In the prior art, different heating configurations have been proposed to attain relative temperature uniformity. During a typical process, there is a temperature ramping phase where the temperature of the wafer is brought up rapidly to a predetermined level, and a steady state phase where the temperature is maintained at about this level. The temperature non-uniformity has tended to be greater during the ramping phase.
One approach to attaining a uniform temperature is called "zone control". In zone control, a plurality of radiant heating units such as infrared lamps are divided into zones and the lamps in a given zone receive the same power, while lamps in different zones may receive different power, to result in uniform temperature across the wafer. While zone control is advantageous in some applications, it requires complex electronic controls of the power applied to the lamps.
A high temperature, rapid thermal process using flood heating is known. With flood heating, a temperature inversion may be observed wherein the edge of the workpiece is hotter during the ramping phase, while the center of the wafer is hotter during the steady state phase. It has been recognized that this is undesirable in the high temperature environment (e.g. 1150.degree. C.) of rapid thermal processing because the edge to center temperature differences at such process temperature create stresses which can damage the workpiece.