Effect of plasma-surface interactions on the radial variation of H atom density in a hydrogen radio frequency discharge

The effect of plasma surface interactions on the radial variation of H atom density has been measured in a low pressure pure H2 rf discharge by two-photon (electric quadrupole and magnetic dipole) allowed laser induced fluorescence using a standard reference cell. Measurements were made in the pressure range from 0.5 to 7 Torr and at a rf power of 35 W into the plasma. The influence of different electrode materials on the H atom density close to the electrode surface and in the discharge volume was measured. The data shows that the radial density distribution, under our discharge conditions, is primarily determined by the plasma-surface interactions and not by the discharge current uniformity (or nonuniformity). We have clearly demonstrated the ability of this measurement technique to monitor in situ, plasma induced surface property changes.