Wavelength dependence for silicon-wafer temperature measurement by autocorrelation-type frequency-domain low-coherence interferometry

We investigate silicon wafer temperature measurement characteristics based on optical low-coherence interferometry by altering the light source wavelength. Variations in Si wafer optical thickness with temperature are expressed by thermal expansion and the refractive index. The optical characteristics determine the measurement precision and range. In this study, the measurement precision and the measurable temperature range were evaluated for three wavelengths: 1040, 1310, and 1550 nm. The maximum measurable temperature at 1040 nm was the lowest because of signal light absorption caused by fundamental interband absorption. The measurement precision at 1040 nm was the highest at 0.020°C because optical thickness changes per degree C increase with decreasing wavelength.