Study of oxygen/TEOS plasmas and thin SiO x films obtained in an helicon diffusion reactor

Abstract

Thin films of silicon dioxide are deposited on Si substrates at ambient temperature in a O 2/TEOS (tetraethoxysilane) helicon diffusion plasma. The plasma source is operated at 5 mTorr (0.7 Pa), 300 W r.f. power. The plasma composition and film properties are studied as functions of the TEOS to oxygen flow rate ratio R, which is varied from 0 to 0.5, at fixed total gas flow rate. The SiO x layers are analyzed by in situ ellipsometry and by ex situ quantitative Fourier Transform Infrared spectroscopy (FTIR). The plasma density, the electron temperature and the concentration of oxygen atoms are measured owing to Langmuir probes and optical emission spectroscopy. At low R the deposition rate is proportional to the TEOS flow rate, while at higher TEOS flow rates it saturates around 110 Å min −1, indicating that the deposition is limited by the availability of oxygen atoms. At very low R ( R≤0.06) good quality SiO 2 films, with low silanol (SiOH) incorporation, are obtained. Correlations between CO and OH emission intensities in the plasma and the quantitative FTIR analysis of the films are investigated.