Improvement of pyrometric sensing in rapid thermal processing via adaptive cancellation of lamplight interference

Abstract

Rapid thermal processing (RTP) is an emerging and promising technology in semiconductor manufacturing that provides numerous advantages over traditional batch processing. A central problem in RTP technology is the precise control of wafer temperature. However, the inability to accurately measure wafer temperatures during processing has thus far proved a major obstacle to the effectiveness of temperature control strategies. Pyrometry, the most commonly encountered temperature-sensing technique used in RTP, suffers from large bias due to uncertainty in the emissivity of silicon wafers. Texas Instruments has recently proposed an innovative technique that overcomes the problem of emissivity uncetainty. However, the new technique suffers from interference of lamplight that is the heating source in RTP. This paper proposes a system-theoretic approach to greatly mitigate the lamplight interference. An on-line adaptive cancellation technique is adopted to estimate time-varying gains. Experimental results of the proposed method are described.