Wafer Temperature Measurement in RTP

Abstract

Wafer temperature measurement has long been thought of as the key, if not the only hurdle to the implementation of rapid thermal processing, RTP. This belief may not be true, however it is believed by a substantial percentage of the participants in the industry. I would contend that wafer temperature uniformity and repeatability are the key barriers to widening the application of RTP [1 – 3]. As an example, physical vapor deposition, PVD is in widely spread use throughout the world with no direct wafer temperature measurement. The PVD systems sold today are both uniform and repeatable enough to perform their processing requirements. Unlike RTP the PVD equipment is good enough today without direct wafer temperature measurement. As process requirements improve PVD like RTP will indeed need in-situ wafer temperature measurement. RTP equipment by its very nature usually requires real-time wafer temperature measurement. If a production reactor could be built that heated the wafers uniformly to the same temperature repeatedly without any temperature measurement that reactor would find widely spread acceptance in production. A wide range of different measurement and control methods are in production today, including open-loop power control [1,4]. As process requirements tighten (± 3°C) satisfactory process results will be possible only with real time wafer temperature measurement and closed loop-control.