NEGATIVE-ION DENSITIES IN CHLORINE-CONTAINING AND BORON-TRICHLORIDE-CONTAINING INDUCTIVELY-COUPLED PLASMAS

The chlorine negative ion density and the electron density in chlorine - and boron trichloride-containing inductively coupled plasmas were in vestigated experimentally. Measurements were performed in a GEC refere nce cell operated in the inductively coupled mode. The chlorine negati ve ion density was measured as an excess electron density produced by photodetachment of electrons from the negative ions by 266 nm radiatio n from a frequency-quadrupled Nd:YAG laser. Both the excess electron d ensity and the steady-state electron density were measured using a mic rowave interferometer. Various,aas mixtures were investigated includin g pure Cl-2, pure BCl3, combinations of the two, and combinations of t hese gases with N-2 and Ar. Cl- densities up to 4 x10(11) cm(-3) were measured depending on the gas mixture. The ratio of electron density t o Cl- density was ac high as 3 in Cl-2 mixtures, and up to 5 in BCl3 m ixtures. The plasma was probed at lower photon energy (355 nm) to phot odetach electrons from other potential negative ions present in the pl asma: to within the sensitivity of the measurement (1.3x10(8) cm(-3)), no other negative ions such as BClx- or Cl-2(-) ions were detected. S ignificant interactions between Cl-2 and Ar were observed as determine d by changes in the Cl- density. The Cl- density also changed when BCl 3 was added to Cl-2 discharges. Addition of Ar or N-2 to Cl-2 plasmas had little effect on Cl- density, but nitrogen addition had very drama tic effects when added to BCl3, causing a factor of 2 increase the Cl- density. (C) 1997 American Vacuum Society.