A method of controlling the capacitance of a thin film transistor liquid crystal display (TFT-LCD) storage capacitor is disclosed. In certain embodiments, the method includes i) forming an undoped amorphous silicon layer on a silicon nitride layer, ii) forming an etching mask on the undoped amorphous silicon layer, and iii) forming two doped amorphous silicon layers on portion of the undoped amorphous silicon layer and the etching mask, the two doped amorphous silicon layers being spaced apart and located on either side of the gate, wherein an etching selectivity ratio of the undpoed and doped amorphous silicon layers over the dielectric layer being not less than about 5.0.