Characterization of BCl3/N2 plasmas

Optical emission spectroscopy, quadrupole mass spectrometry, and electron density measurements were used to study the effect of the percentage of N2 on the characteristics of BCl3/N2 plasmas and their resulting etch processes. The etch rate of GaAs increased from 80 Å/min in pure BCl3 to over 1000 Å/min in a 40:60 BCl3:N2 mixture (15 mTorr, 50 W, 20 sccm). The optical emission intensities of both molecular and atomic chlorine exhibited maxima near 30% N2, and an argon actinometer indicated a large increase in argon emission as a function of the increase in N2 percentage. Microwave measurements indicated that the average electron density increased only slightly with an increase in nitrogen percentage up to 60% N2. Mass spectrometric analysis of the plasmas showed that both the dissociation of BCl3 and the production of molecular chlorine were significantly enhanced by the addition of N2. These results suggest that an increase in the electron temperature as a result of electron attachment heating (and possibly energy transfer from N2 metastables) is responsible for the increased dissociation and enhanced production of etch species.