Although rapid thermal processing (RTP) has existed for a number of years, difficulties associated with pyrometric temperature measurement and control have prevented RTP's widespread acceptance in manufacturing. We show that nominal process-associated film thickness variations drastically reduce the wafer-to-wafer process repeatability using pyrometry. These thickness variations lead to large changes in wafer emissivity producing temperature errors of as much as +/- 100 K. The result is reduced process capability which limits the utility of RTP in manufacturing. This paper contrasts pyrometric temperature feedback with power control (PC). The data indicate that PC results in significant reduction of wafer-to-wafer temperature fluctuations, to better than +/- 5 K. The improvement is due to minimal sensitivity of PC to dielectric-film-induced wafer emissivity fluctuations. Therefore, PC can be used without the need for back-side strip, allowing seamless integration into semiconductor processing. We also present a theoretical basis for power control and discuss the limitations and boundary conditions governing the technique.
James S. Nakos,
"Seamless application of rapid thermal processing in manufacturing", Proc. SPIE 1804, Rapid Thermal and Laser Processing, (16 March 1993); doi: 10.1117/12.142666; https://doi.org/10.1117/12.142666