REAL-TIME DETERMINATION OF PLASMA ETCH-RATE SELECTIVITY

Real-time etch-rate selectivity of thin transparent films is determine d within seconds by an in situ two-colour laser interferometer. Two-po int laser reflectrometry is used to determine the etch rates and etch selectivity of unpatterned polysilicon and SiO2 films. The state of a magnetically confined inductively coupled plasma tool used in the expe riments, including rf power to the antenna and the wafer stage, gas pr essure and flow rates, is computer controlled and monitored. The depen dence of the etch selectivity on tool state parameters is characterize d in real time by varying the tool state and monitoring the etch rate of the films. The etch rate measurements have been combined with densi ty characterization of the etch radicals in the discharge. The time-de pendent density of atomic chlorine during the process is obtained by t emporal optical-emission actinometry combined with in-line mass spectr ometry from a pressure calibrated residual gas analyser. The etch sele ctivity of polysilicon to SiO2 in a chlorine discharge, determined by a simultaneous etch of both films, differs from the etch-rate ratios o f the films when they are etched separately. It is suggested that this difference is due to the presence of oxygen in the polysilicon etch p rocess when the two films are etched simultaneously.