Redeposition-free of silicon etching by CF4 microwave plasma in a medium vacuum process regime

This work presents a redeposition-free process to etch silicon by CF4 plasma in a modified microwave oven reactor operated in a medium vacuum process regime (25 to 1 x 10(-3) Torr) that only uses a mechanical pump which is introduced at a lower cost compared to the ICP etching system. In order to achieve the capability of the etching process provided by this system, experimental trials were conducted by varying the microwave power in the range of 360-1200 W, gas flow rate 30-90 mL/min and bias voltage at the substrate holder-100 V to -300 V. Plasma species present in the discharge were also monitored by optical emission spectroscopy (OES) for a better understanding of the mechanism of the etching process. The etched sidewalls were observed by scanning electron microscope (SEM), the etched roughness was measured by atomic force microscope (AFM) and the etched depths were measured by a stylus profiling technique.