Submicron thickness calibration of vapor‐deposited SiO2 films by infrared spectroscopy

Infrared transmission spectra of a series of SiO2 films vapor deposited on silicon from SiH4 and O2 at 450 °C have been studied as a function of film thickness in the submicron range from 1000 to 9000 A. Absorbances of band maxima observed in the frequency range 250–1400 cm−1 are shown to obey the Lambert‐Bouguer's law in both as‐deposited and heat‐treated (800–1200 °C) materials. Apparent absorption coefficients calculated for the transmission mimima at 1060, 800, and 450 cm−1 are 2.5 ± 0.1 × 104, 0.24 ± 0.02 × 104, and 0.74 ± 0.02 × 104 cm−1 for as‐deposited films and 3.4 ± 0.1 × 104, 0.34 ± 0.02 × 104, and 1.06 ± 0.02 × 104 cm−1 for heat‐treated films, respectively. The thickness of SiO2 films as‐deposited at 450 °C as well as heat treated to 800 °C and above can be determined nondestructively using the present absorbance data.