Real-time optical thermometry during semiconductor processing

The optical techniques used to monitor the temperature of wafers during semiconductor processing are surveyed. The physical principles underlying each method are described. Applications of each optical diagnostic are presented, along with the strengths and weaknesses of the probe. Most of these optical diagnostics have been implemented in research reactors to monitor wafer temperature during one or several types of thin-film processing, such as molecular beam epitaxy, rapid thermal processing, and plasma etching. Pyrometry is the workhorse of noninvasive optical probes of temperature, although it needs supporting models and optical measurements to improve accuracy. Other optical thermometric wafer diagnostics are very promising and are being developed intensively, particularly reflection interferometry, transmission spectroscopy, and various interferometry methods that directly measure the thermal expansion of the wafer.