Deposition of microcrystalline silicon with the 'hot wire' technique using fluorinated precursors

Photovoltaic collection of solar energy is a promising renewable energy resource that has been extensively investigated. A thin film material that shows promise for photovoltaics use is microcrystalline silicon muc-Si This material consists of small (∼100--500 Angstrom) crystals possibly contained within an amorphous silicon tissue. The material is much more stable under light exposure than amorphous silicon. There are several issues that need to be addressed before the material can be used in prototype production of PV modules, but the most important is the low deposition rate of the material. Other techniques that have been used to deposit muc-Si are VHF-PECVD, which uses an RF excitation frequency in the 50--100 MHz range, and "Hot-Wire" Chemical Vapor Deposition (HWCVD).;The intent of this study was to examine the deposition of muc-Si films via the HWCVD technique using a fluorinated precursor, with the goal of determining if the presence of fluorine influenced the crystalline fraction of the deposited films, and if so the mechanism by which the fluorinated precursor acted on the growing film. The fluorinated precursor used for this study was silicon tetrafluoride, SiF4. There were five major deposition series covered in this study. (1) Amorphous and microcrystalline silicon films were made via HWCVD and exposed to various hot wire and plasma treatments in an atmosphere of either hydrogen or hydrogen mixed with a small amount (<15%) of SiF4. (2) A series of mucSi depositions made by the HWCVD technique at a lower substrate temperature (<300 C) with the stepwise addition of SiF4. (3) A series of muc-Si depositions made by the HWCVD technique with increasing substrate temperatures up to 430 C and with no SiF4 addition. (4) A series of muc-Si films deposited at a higher substrate temperature (410 C) with the pulsed PECVD technique and no added SiF4. (5) A series of layer-by-layer (LBL) depositions in which the deposition of muC-Si was alternated with a treatment of SiF 4 and H2. (Abstract shortened by UMI.).