Controlling the growth of nanocrystalline silicon by tuning negative substrate bias

Application of appropriate dc bias to the substrate has been identified as one of the efficient parameters, beyond the mostly used classical ones, in controlling the growth of nanocrystalline silicon (nC-Si:H) network by plasma CVD of SiH4. The present communication demonstrates that applying negative dc substrate bias at the moderate level the overall nanocrystallinity in the material be enhanced significantly. The nC-Si:H film of ∼70% crystalline volume fraction along with a high σD∼3.1×10–4 S cm–1 and Eσ∼191 meV has been obtained at a low substrate temperature of 200 °C and with a growth rate of ∼8 nm/min from only 1 sccm of the feed gas SiH4, using −75 V dc substrate bias and He as the diluent to the plasma. Besides the extent of crystallinity, the average grain size (ρ) has been demonstrated to be controllable within nano-dimensions, 1< ρ<10 nm, by tuning negative dc substrate bias during plasma processing. The present report comprehensively elaborates the effect of applied negative dc substrate bias on the growth morphology of the nC-Si:H thin films from He-diluted SiH4 plasma, in view of controlling nanocrystallization at low substrate temperature by RF-PCVD, while controlled transmission of energy to the growing surface obtained from metastable and ionic helium (He* and He+) bombardment has been deemed instrumental.