MOLECULAR-BEAM DEPOSITION OF HIGH-QUALITY SILICON-OXIDE DIELECTRIC FILMS

We report a method for depositing clean, uniform and stable SiOx, diel ectric films with high control and reproducibility. The technique uses a molecular or chemical beam epitaxy system (MBE or CBE). The techniq ue offers many advantages over the conventional methods such as load l ock facility, accurate determination of the flux, low background conta mination, in-situ process monitoring tools, and heating, rotation and tilting of the substrate. Rutherford backscattering (RES) shows that t he films deposited without oxygen are stoichiometric, 50% oxygen and 5 0% Si, irrespective of the deposition rate or temperature. Such SiO fi lms have a resistivity of greater than or equal to 10(13) Omega . cm a nd a nominal refractive index of 2 at 632.8 nm. The refractive index c an be reduced by introducing a controlled amount of oxygen into the ch amber to result in SiOx (x = 1-2) films. The SiO films have uniform de nsity and composition, and are free from voids, or any inclusions of d ifferent crystalline or amorphous phases. These SiO films are easy to pattern and their erosion rate is slower than that of SiO2 deposited b y plasma enhanced chemical vapor deposition (PECVD). During 192 h soak in 99 degrees C deionized (DI) water, no moisture absorption was obse rved in SiO films deposited at a rate of 2 Angstrom/s. Even in films d eposited at 11 Angstrom/s, the moisture content after 192 h soak in 99 degrees C DI water was about one third the moisture content of an as- deposited typical PECVD SiO2 film, indicating that the SiO films are h ighly resistant to moisture absorption and the film quality improves w ith reducing deposition rate. The insulating, mechanical and optical p roperties of SiOx films make them suitable for many applications such as surface passivation, mask for processing and facet coating of laser s. The process can be easily integrated with MBE/CBE which would great ly simplify and improve the III-V semiconductor processing. It may als o be possible to deposit such dielectric films by CBE using gaseous co mpound sources.