Operational regimes of the saddle field plasma enhanced chemical vapor deposition system

The electrical potential at the substrate surface during the growth of hydrogenated microcrystalline silicon in a direct current saddle field (SF) plasma enhanced chemical vapor deposition (PECVD) system has been previously shown to be a limiting factor for the formation of the microcrystalline phase in the resulting thin films. The authors examine the extension of this concept to large areas under conditions necessary to obtain microcrystalline silicon in a SF-PECVD system-namely the use of hydrogen-diluted silane as a source gas, pressures between 100 and 300 mTorr, and substrate electrical bias between 100 and 250 V. The response of the SF-PECVD system to electrical substrate bias under these conditions is examined in detail, and four regimes of operation are identified, only one of which is useful for the growth of this particular material system. The delineation of these regimes provides new constraints and guidelines for the application of SF-PECVD technology to large-area deposition of thin films sensitive to ion bombardment during growth, such as microcrystalline silicon.