Abstract

In a process for heating, e.g., a semiconductor wafer within a processing chamber, the wafer is exposed to a flux of electromagnetic radiation from lamps energized by alternating electric current. The surface temperature of the wafer is measured, and responsively, the radiation flux is controlled. The temperature measurement procedure includes collecting radiation propagating away from the wafer in a first light-pipe probe, collecting radiation propagating toward the wafer in a second light-pipe probe, and detecting radiation collected in the respective probes. This procedure further involves determining, in the signal received from each probe, a magnitude of a time-varying component resulting from time-variations of the energizing current, and combining at least these magnitudes according to a mathematical expression from which the temperature can be inferred. At least some of the radiation collected by the second probe is collected after reflection from a diffusely reflecting surface. The second probe effectively samples this radiation from an area of the diffusely reflecting surface that subtends a solid angle Ω2 at the wafer surface. The first probe effectively samples radiation from an area of the wafer that subtends a solid angle Ω1 at the first probe. The radiation sampling is carried out such that Ω2 is at least about Ω1.