Surface roughness and structural aspects of anodic and cathodic plasma deposited a-Si:H at low temperature

Surface topography and structural properties of a-Si:H thin films, deposited at 75 °C by plasma-enhanced chemical vapor deposition (PECVD) have been examined using argon/helium/silane feedstock under different substrate bias and gas-dilution conditions. Notable differences in the surface roughness evolution are shown for films deposited in ‘cathodic’ versus ‘anodic’ mode – where the substrate is placed on the powered and grounded electrode, respectively – with rare-gas dilution type playing a minor role. By suitable choice of processing parameters including the aforementioned RF mode, we can modify and control the surface morphology from very rough to mirror-smooth. Our rough films deposited in anodic mode do not follow conventional growth evolution models, but instead are believed to include additional surface growth mechanisms, that could consist of shadowing instability and re-emission. Cathodic mode films processed from argon and helium feedstock both produced smooth films but exhibited different levels of coating stress and structural disorder with higher compressive stress and more network disorder associated with the argon case.