Influence of ignition condition on the growth of silicon thin films using plasma enhanced chemical vapour deposition

The influences of the plasma ignition condition in plasma enhanced chemical vapour deposition (PECVD) on the interfaces and the microstructures of hydrogenated microcrystalline Si (\mu c-Si:H) thin films are investigated. The plasma ignition condition is modified by varying the ratio of SiH_4 to H_2 (R_\rm H). For plasma ignited with a constant gas ratio, the time-resolved optical emission spectroscopy presents a low value of the emission intensity ratio of H\alpha to SiH^* (I_\rm H\alpha /I_\rm SiH^\ast ) at the initial stage, which leads to a thick amorphous incubation layer. For the ignition condition with a profiling R_\rm H, the higher I_\rm H\alpha /I_\rm SiH^\ast values are realized. By optimizing the R_\rm H modulation, a uniform crystallinity along the growth direction and a denser \mu c-Si:H film can be obtained. However, an excessively high I_\rm H\alpha /I_\rm SiH^\ast may damage the interface properties, which is indicated by capacitance--voltage (C--V) measurements. Well controlling the ignition condition is critically important for the applications of Si thin films.