Effects of grain size and plasma-induced modification of the dielectric on the mobility and stability of bottom gate microcrystalline silicon TFTs

Mobility and stability in bottom-gate microcrystalline silicon TFTs with the active layer deposited at 200°C by PECVD from SiF₄/Ar/H ₂ mixtures have been studied. For fixed deposition conditions, the plasma treatment of the silicon nitride appears to be the key parameter which allows control of the density of sticking sites and thus achievement of lateral growth. This leads to large columns and improved mobility of the TFTs. However, the reduction of the density of sticking sites also favors the damage of the silicon nitride and eventually leads to deterioration of the stability of the devices.