VACUUM ULTRAVIOLET-RADIATION DAMAGE IN ELECTRON-CYCLOTRON RESONANCE AND REACTIVE ION ETCH PLASMAS

A comparative study of vacuum ultraviolet radiation damage has been carried out in an electron cyclotron resonance (ECR) and reactive ion etching (RIE) hybrid chamber. The damage was measured by changes in the density of interface states, the midgap capacitance-voltage shifts, and from photo I-V gate voltage shifts in metal-oxide semiconductor (MOS) capacitors before and after plasma exposure. The results suggest that the damage found in the samples exposed to either ECR or RIE plasmas appears in the form of neutral electron traps in the bulk of the SiO2 film and "slow" interface states. The positive charge found in the exposed samples results from the filling and emptying of these slow interface states and not from trapped holes. Electron trap densities are found to be in the low to mid 10(12) cm-2 range for all plasma-exposed samples. Even after a standard post-metalization anneal (PMA), the density of electron traps is only reduced by approximately a factor of 2 and appears relatively independent of the type of the plasma exposure. The density of the slow interface states is found to be in the high 10(11) cm-2 range and in the low 10(10) cm-2 range, for the ECR plasma samples, before and after the PMA, respectively. The RIE exposed slow state density was initially congruent-to 2 x 10(12) cm-2 and reduced to 2 x 11(11) cm-2 after the PMA, an order of magnitude higher than that of the ECR-plasma exposed samples.