Bonding configuration and density of defects of SiOxHy thin films deposited by the electron cyclotron resonance plasma method

Abstract

The composition, bonding configuration, hydrogen content, and paramagnetic defects of SiOxHy thin films were studied. Films were deposited by the electron cyclotron resonance plasma method at room temperature using SiH4 and O-2 as precursor gases. The film composition was measured by heavy ion elastic recoil detection analysis and energy dispersive x-ray spectroscopy. Suboxide films with compositions ranging from SiO2 to SiH0.38 were obtained. Infrared spectroscopy showed the presence of different Si-O and Si-H vibration modes. The usual estimation of the oxygen to silicon ratio by the wave number of the Si-O-Si stretching band was not accurate for films far from stoichiometry. These off-stoichiometric films also showed a broader Si-O-Si stretching peak than the stoichiometric ones, indicating a higher bonding disorder. The position of the Si-O-Si bending and rocking modes did not depend on the film composition. On the other hand, the peak position of the Si-H modes were found strongly dependent on the Si environment. By single-wavelength ellipsometry at lambda=632.8 nm the refractive index n was found to range between 1.45 (SiO2) and 2.04 (SiO0.06H0.36). Electron spin resonance measurements showed that stoichiometric films presented the well known E' center (.Siequivalent toO(3)) with concentrations in the 10(16)-10(17) cm(-3) range, while for Si-rich films (x<1) the Si dangling bond center (Si-DB, .Siequivalent toSi(3)) was the only detectable defect, with concentrations in the 10(18)-10(19) cm(-3) range. In near-stoichiometric films both E-' and Si-DB centers were found.