Amorphous SiO2 films have been deposited onto the Si substrate, without heating, using sputtering-type electron cyclotron resonance (ECR) microwave plasma. In situ Fourier transform P-polarized infrared reflection absorption spectroscopy (ISFT-PIRRAS) has been used to study the properties of a-SiO2/Si interface. The results from ISFT-PIRRAS monitoring indicated that the interface stress led to significant distortion in the local structure, which resulted in the broadening of a transverse optical mode (TO3) located at 1050 cm(-1). The interface stress decreased with increased film thickness. In addition, the longitudinal optical phonon mode (LO3, located at 1223 cm(-1)) related to TO3 mode was observed due to Berreman effect [B. Harbecke, Appl. Phys. A: Solids Surf. 38 (1985) 263]. This phonon mode is very sensitive to SiO2 film thickness, which enables it to be used to detect and characterize ultra thin SiO2 film. When the film thickness is over 30 nm, a nonlinear dependence of the intensity of LO3 mode on film thickness was observed. However, the TO3 mode has a near linear dependence on film thickness. Thus, it is more accurate and suitable to detect thick film by monitoring TO3 mode intensity.