Abstract
Silicon nitride films are prepared by a combined high-power impulse/unbalanced magnetron sputtering (HIPIMS/UBMS) deposition technique. Different unbalance coefficients and pulse on/off ratios are applied to improve the optical properties of the silicon nitride films. The refractive indices of the films vary from 2.17 to 2.02 in the wavelength ranges of 400–700 nm, and all the extinction coefficients are smaller than . The Fourier transform infrared spectroscopy and x-ray diffractometry measurements reveal the amorphous structure of the films with extremely low hydrogen content and very low absorption between the near IR and middle IR ranges. Compared to other deposition techniques, films deposited by the combined HIPIMS/UBMS deposition technique possess the highest refractive index, the lowest extinction coefficient, and excellent structural properties. Finally a four-layer coating is deposited on both sides of a silicon substrate. The average transmittance from 3200 to 4800 nm is 99.0%, and the highest transmittance is 99.97% around 4200 nm.
© 2014 Optical Society of America
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