Doppler spectroscopic measurements of sheath ion velocities in radio-frequency plasmas
- Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ (United Kingdom)
We have measured the distributions of N{sub 2}{sup +} ion velocity components parallel and perpendicular to the electrode in the sheath of a radio-frequency nitrogen reactive ion etching discharge, using pulsed laser-induced fluorescence. Parallel to the electrode, the ions have throughout a thermal distribution that is found to be consistent with the rotational temperature of 355 K. In the perpendicular direction, we see clearly the acceleration of the ions towards the electrode, and our results agree well with theoretical predictions although an unexpected peak of unaccelerated ions persists. We have also determined the absolute ion concentrations in the sheath, which we have calibrated by analyzing the decay in laser-induced fluorescence in the plasma bulk after discharge extinction. At 20 mTorr, the bulk concentration of 1.0{times}10{sup 10} cm{sup {minus}3} falls to around 2{times}10{sup 8} cm{sup {minus}3} at 2 mm from the electrode. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 496642
- Journal Information:
- Journal of Applied Physics, Vol. 81, Issue 9; Other Information: PBD: May 1997
- Country of Publication:
- United States
- Language:
- English
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