TRANSPORT OF NEUTRAL RADICALS IN CF4/O2 MICROWAVE DOWNSTREAM PLASMAS

摘要

Optical and mass spectrometric diagnostics were employed for investigating the transport of neutral radicals in CF4/O2 microwave downstream plasmas. Fluorine atom densities were measured both in the plasma source and in the downstream region, using Ar actinometry; a small if electrode was set in the downstream region to establish local discharges for optical emission spectroscopy. Moreover, the densities of feed gases (CF4 and O2) and products (SiF4 and F2) were measured in the downstream region by mass spectrometry. The transport efficiency of F atoms from the plasma to the downstream region was quite low (=1 %) for a pure CF4 discharge, and increased significantly with increasing percentage of O2 added. Mass spectrometric measurements indicated that a large amount of F atoms are consumed during their transport to the downstream region through erosion of quartz discharge tube walls as well as surface recombination; both densities of SiF4 and F2 in the downstream region were typically -10-30% of the total gas density.