Spectroscopic ellipsometry investigation of microcrystalline fractions in p-type hydrogenated microcrystalline silicon oxide (p-μc-SiOx:H) ultra-thin films

Spectroscopic ellipsometry (SE) was used to characterize the effect of the CO2/SiH4 ratios on the p-type hydrogenated microcrystalline silicon oxide (p-μc-SiOx:H) thin films. The p-μc-SiOx:H thin films were fabricated by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) method on the soda-lime glass substrates. The CO2/SiH4 ratios were varied from 0.0 to 0.5 with constant H2-dilution during the deposition. The p-μc-SiOx:H samples were analyzed for thickness, microstructure, and optical characteristics by SE. The ellipsometric measurements were performed in the range of 0.75-5.5 eV with the incident angle of 50, 60 and 70 degrees. The physical structures were proposed as either the double- and triple-layer models. The optical dispersion was proposed based on Tauc-Lorentz (TL) model in order to extract the information of interest including dielectric dispersion and crystalline fraction. The results from the SE analyses showed that the thin films prepared with pure SiH4 could only be fitted by the triple-layer model, whose effect refractive index was gradually decreased from 3.92 to 2.53 with the increased CO2/SiH4 ratio. With the introduction of the CO2, the obtained films were instead best represented by the double-layer model. The calculated crystalline fractions could be determined from the SE results, which accurately corresponded to those from the Raman spectroscopy and high-resolution transmission electron microscope (HRTEM). In addition, the dielectric dispersion of the thin films was related directly with CO2/SiH4 ratios, but inversely with crystalline fraction with the values of 53 down to 18% with the increased gas mixture ratio.