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

We report a method for depositing clean, uniform and stable SiOx, dielectric films with high control and reproducibility. The technique uses a molecular or chemical beam epitaxy system (MBE or CBE). The technique offers many advantages over the conventional methods such as load lock facility, accurate determination of the flux, low background contamination, in-situ process monitoring tools, and heating, rotation and tilting of the substrate. Rutherford backscattering (RES) shows that the films deposited without oxygen are stoichiometric, 50% oxygen and 50% Si, irrespective of the deposition rate or temperature. Such SiO films have a resistivity of greater than or equal to 10(13) Omega . cm and a nominal refractive index of 2 at 632.8 nm. The refractive index can be reduced by introducing a controlled amount of oxygen into the chamber to result in SiOx (x = 1-2) films. The SiO films have uniform density and composition, and are free from voids, or any inclusions of different crystalline or amorphous phases. These SiO films are easy to pattern and their erosion rate is slower than that of SiO2 deposited by plasma enhanced chemical vapor deposition (PECVD). During 192 h soak in 99 degrees C deionized (DI) water, no moisture absorption was observed in SiO films deposited at a rate of 2 Angstrom/s. Even in films deposited 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 highly resistant to moisture absorption and the film quality improves with reducing deposition rate. The insulating, mechanical and optical properties of SiOx films make them suitable for many applications such as surface passivation, mask for processing and facet coating of lasers. The process can be easily integrated with MBE/CBE which would greatly simplify and improve the III-V semiconductor processing. It may also be possible to deposit such dielectric films by CBE using gaseous compound sources.