INSITU PROCESS EVALUATION DURING HYDROGEN PLASMA-ETCHING OF A-SI-H FILMS BY MICROWAVE DETECTED TRANSIENT PHOTOCONDUCTIVITY MEASUREMENTS

During removal of amorphous silicon films deposited on crystalline sil icon substrates by dry etching in a hydrogen plasma the kinetics of mo bile excess charge carriers have been followed by measuring the change of the microwave reflection after laser pulse illumination. Following the amplitude of the measured transient signals the thickness of the remaining amorphous silicon film can be determined and the decay in th e nanosecond time range yields information about the defect density of the substrate surface. The impact of the plasma process on the surfac e recombination is shown and a criterion for endpoint detection is giv en in the case of a-Si:H removal from crystalline silicon covered with a SiO2 layer.