Radio frequency plasma enhanced chemical vapor deposition
Posted on August, 14 in Thin Film Solar Cells Fabrication, Characterization and Applications
The deposition method most widely used to produce device quality a-Si:H is rf (the excitation frequency of plasma is 13.56 MHz) PECVD. The role of the plasma is to provide a source of energy to dissociate silicon bearing gas, which is usually silane. This is done by collisions with electrons, which originate as secondary electrons in the plasma and build up their energy by acceleration in an electric field. The growth of an a-Si:H film is accomplished by attaching reactive particles of dissociated silane molecules, called radicals, to the surface of the growing film. As the thickness of the a-Si:H film for device applications is around half a micrometer, a-Si:H must be deposited on an appropriate substrate carrier. Some of the energy transferred to silane molecules in the collisions with electrons is radiated as visible light, for which reason the deposition method is also referred to as glow discharge. An important advantage of plasma enhanced CVD deposition is that the deposition temperature of device quality a-Si:H is usually between 200 °C and 250 °C. The low temperature process allows the use of a variety of low cost materials as a substrate, such as glass, stainless steel and flexible plastic foils.