Optical Properties in Mid-Infrared Range of Silicon Oxide Thin Films with Different Stoichiometries

SiO_x thin films were prepared using magnetron sputtering with different O₂ flow rates on a silicon substrate. The samples were characterized using Fourier transform infrared spectroscopy in transmission and reflection, covering a spectral range of 5 to 25 μm. By employing a multilayer model, the values of the complex refractive index that best fit the experimental transmission and reflection results were optimized using the Brendel-Bormann oscillator model. The results demonstrate the significance of selecting an appropriate range of O₂ flow rates to modify the SiO_x stoichiometry, as well as how the refractive index values can be altered between those of Si and SiO₂ in the mid-infrared range.