Structural and electrical properties of SiO_2 films deposited on Si substrates from tetraethoxysilane/oxygen plasmas

摘要

Silicon dioxide films are deposited on silicon substrates from oxygen/tetraethoxysilane (O_2/TEOS) plasmas in a helicon reactor in the 1-10 mTorr range. The influence of the pressure (2 and 5 mTorr) on both the structural and electrical bulk properties of SiO_2 films is investigated. In situ ellipsometry and chemical etching measurements have been performed to evaluate changes in the film macroscopic density. A quantitative infrared analysis in the 3000-3800 cm~(-1) (OH stretching band) range is also carried out to determine the water and isolated SiOH fractions in the oxide. The evolution of the leakage current with the applied bias, measured on metal-oxide-semiconductor capacitors, is related to the structural properties of the films. Lowering the pressure from 5 to 2 mTorr leads to denser films with lower OH content and enhanced bulk electrical properties. Additional current-voltage combined with capacitance/conductance-voltage analyses as well as constant current stress measurements have suggested the presence of hole traps with a high capture cross section (10~(-13) cm~2) in the bulk of the oxide at 5 mTorr. This behavior is not observed at 2 mTorr.