Many types of silicon film are used as materials for the gate electrodes of ultra large scale integration (ULSI) devices. The influence of varying the type of silicon film on local side etch depth and etch rate is investigated using an ECR plasma etching system. Resistivity of silicon films is varied using various impurity concentrations and annealing temperatures. The etch rate of silicon film is confirmed to increase as resistivity decreases in the case of phosphorus doped film. However, the etch rate is constant or decreases to a small extent in the case of boron doped silicon film. In contrast, it is found that the dependence of local side etch depth on resistivity is different to the dependence of etch rate on resistivity. The local side etch depth decreases in the case of phosphorus doped silicon and is almost constant in the case of boron doped silicon as the resistivity decreases. Thus it is found that local side etch depth does not always increase as resistivity of silicon film decreases. The depth of local side etch is influenced by the vertical etch rate, because the ratio of the just etching time to the overetching time is fixed. It is found that the local side etch rate is almost constant in this experiment. Therefore, it is concluded that the difference in local side etch depth is mostly caused by the difference in vertical etch rate.