Negative ion measurements in ECR plasmas
Summary form only given, as follows. The presence of negative ions can have big effects on the plasma potential, spatial plasma profiles and plasma density. Negative ions also serve as the precursor for particle formation. Significant concentrations of negative ions have already been identified in low power-high pressure capacitively coupled fluorocarbon plasmas. The main goal of this study is to determine what conditions (microwave power, pressure, etc.), if any, give rise to significant negative ion densities in fluorocarbon plasma in an ECR tool. For this purpose, a redesigned omegatron mass spectrometer was employed in an ECR etching plasma, operated at pressures of 0.2-5 mTorr. The modified geometry provides differential pumping with pressures inside the omegatron below the 10/sup -4/ Torr range reducing collisional effects and insulating film deposition, while the neutral pressure in the bulk plasma is in a few mTorr range. The main directions of this experiment are (1) to investigate the geometric effect (collector size, location, etc.) to maximize the resolution of the omegatron and (2) to study the microwave power and neutral pressure dependence for the negative ion species in ECR fluorocarbon etching plasmas. Preliminary results show F/sup -/, F/sub 2//sup -/, CF/sup -/, CF/sub 2//sup -/, CO/sup -/ negative ions in CF/sub 4/, 1000 W ECR plasma. Recent experiments which varied pressure and power are described.