A non-contact temperature measurement of semitransparent silicon wafers with absorption edge wavelength

The temperature dependence on transmittance of a silicon wafer is well known, which is caused by various absorption mechanisms over wide range of spectrum. As the wavelength increases, the photon energy decreases until it becomes smaller than the minimum energy gap in the silicon band structure. At this point there is a rapid drop in absorption, which is often referred to as absorption edge wavelength. The absorption edge shifts to a longer wavelength with increasing temperature because the band gap reduces with increasing temperature. Experiments were carried out from the viewpoints of wavelength (900 ~1700 nm), polarization (p- and s-polarized) and direction (normal to 80deg) for specimens with different resistivity (0.01 ~ 2700 Omegacm). A characteristic curve between absorption edge wavelength and temperature is obtained for all of silicon wafers with different resistivity. The results show that this method is promising for in situ temperature measurements of silicon wafers from room to 1000 K at a wavelength where the wafers are semitransparent. In this paper, an experimental apparatus, measurement results and considerations on advantages and disadvantages of this method are described in detail.