Laser-induced fluorescence measurements of transverse ion temperature in an electron cyclotron resonance plasma

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Abstract
Laser-induced fluorescence has been used to measure the Doppler profile of a transition in N+2 [the R18 component of the X2∑+g(ν = 0)⇒B2∑+u(ν = 0) band] in a pure N2 electron cyclotron resonance (ECR) plasma. The transverse ion temperature (Ti⊥) was determined from the measured width of the Doppler broadened transition. The measurements were made on axis, 41 cm downstream (‖B‖∼170 G) from the first electron cyclotron resonance. We found Ti⊥ decreased from 0.25 to 0.12 eV as the corresponding downstream neutral pressure increased from 0.5 to 4.0 mTorr. These results have important implications for the use of ECR devices for plasma etching, since Ti⊥ may determine the ultimate limit to the anisotropy of the etch.