Utilization of Optical Emission Spectroscopy in Characterization of Microwave Plasma

The patterning of electronic materials has been an essential technology in the manufacturing of integrated circuits. This investigation used a TEL Etch System paired with a 2.4 GHz microwave power source and a 30.56 MHz bias power source to create a novel plasma etching system. Critical operating parameters of this system were altered in order to determine their effect on fundamental plasma characteristics. These parameters included pressure within the processing chamber (5-100mTorr) and power from the microwave source (0.4-2kW). The dissociation of chlorine in Cl₂ plasmas was monitored via optical emission spectroscopy (OES) using emission ratios with trace rare gases, specifically the ratios Cl₂/Xe and Cl/Xe were monitored. Using nitrogen plasmas, spectra were analyzed in MATLAB with a simulation to provide the temperature of the plasma gas. It was found that the extent of chlorine dissociation depended on the power delivered to the plasma. The lowest Cl₂ concentration and the highest Cl-atom concentration were seen at the maximum power of 2 kW. Gas temperatures were found to increase with power, reaching up to 1150 K. Also, at higher pressures, higher temperatures were seen for the same power. A ‘dim’ mode of the system was discovered, in which instead of plasma forming near the upper power source, a standing wave formed between the wafer and the upper surface of the reactor. The resulting hysteresis of the system indicated by switching between ‘dim’ and normal operating mode was investigated.