In situ infrared reflection absorption (IRA) spectroscopy was used to investigate materials formed on SiO2 film coated on samples mounted on the inner surface of a process chamber for inductively coupled plasma etching. Aluminum wafers partially covered with photoresist film were etched using BCl3 and Cl-2 plasma generated in a quartz chamber surrounded by a radio frequency (rf) coil. RF bias was applied to the aluminum wafers at the same time. This is the first time that, in order to predict the IRA spectra, the reflectivities of various inorganic multiple layers formed on metal substrates have been calculated using the optical constants of the materials. The experimental spectra for SiO2 film and for the materials formed on it during a 2 mu m deep etching process were well characterized by the calculated spectra of SiO2 film and a B2O3 layer on it, respectively.