Temperature Measurement of Si Substrate Using Optical-Fiber-Type Low-Coherence Interferometry Employing Supercontinuum Light

摘要

We have measured the temperature of a Si substrate using an optical low-coherence interferometer employing supercontinuum light (SC). The accuracy of temperature measurement and the minimum measurable thickness of a layer are determined by the maximum resolving power of the optical path length of the medium in low-coherence interferometry, which depends on the coherent length defined by the spectrum profile and the wavelength of the light source. Low-noise, ultraflat, and highly coherent SC, generated using ultrashort laser pulses and optical fibers, was used as a light source. The wavelength dispersion of SC on the Si substrate was compensated by using a silicon mirror as a reference mirror, resulting in shaper interference waveforms of SC at the front and back surfaces of Si substrate than those of the superluminescent diode (SLD) light used as a conventional low-coherence light source. The measurement accuracy of the temperature using SC was improved to be ±0.4 ℃ from ±1.0 ℃ for the case of using the SLD. The temperatures of the Si substrate and SiO_2 thin film were simultaneously measured using SC on an 800-μm-thick Si substrate with an 8.55-μm-thick SiO_2 film. The temperature of the thin film, the thickness of which is several micrometers, was measured using SC and a compensation technique of wavelength dispersion using the silicon reference mirror.