Negative ion measurements in ECR plasmas

Summary form only given, as follows. An omegatron mass analyzer was modified and employed in detecting negative ions in an Electron Cyclotron Resonance (ECR) etching plasma, operating at a pressure of 0.3/spl sim/10 mTorr. Plasma is permitted to flow through a biased aperture along the magnetic field and an end plate is biased negatively. The negative ions emerging from the aperture encounter transverse RF electric fields applied inside the omegatron chamber, while most positive ions are collected at the end plate. Peaks in the collected current, transverse to the magnetic field occur as a result of cyclotron resonance. The polarity of the peaks depends on the charge of the ion species. The redesigned omegatron mass spectrometer includes differential pumping which can make the inside pressure of the omegatron below the 10/sup -4/ Torr range reducing the effect of collision within the omegatron. Preliminary results show H/sup +/, H/sub 2//sup +/, H/sub 3//sup +/, H/sup -/ and H/sub 2//sup -/ in hydrogen, O/sup +/, O/sub 2//sup +/, O/sup -/ and O/sub 2//sup -/ in oxygen, F/sup -/ and NF/sup -/ in NF/sub 3/ ECR plasmas. Recent experiments with CF/sub 4/ and NF/sub 3/ plasmas are described.