N, NH, and NH_2 radical densities in a remote Ar-NH_3-SiH_4 plasma and their role in silicon nitride deposition

摘要

The densities of N, NH, and NH_2 radicals in a remote Ar-NH_3-SiH_4 plasma used for high-rate silicon nitride deposition were investigated for different gas mixtures and plasma settings using cavity ringdown absorption spectroscopy and threshold ionization mass spectrometry. For typical deposition conditions, the N, NH, and NH_2 radical densities are on the order of 10~(12) cm~(-3) and the trends with NH_3 flow, SiH_4 flow, and plasma source current are reported. We present a feasible reaction pathway for the production and loss of the NH_x radicals that is consistent with the experimental results. Furthermore, mass spectrometry revealed that the consumption of NH_3 was typically 40%, while it was over 80% for SiH_4. On the basis of the measured N densities we deduced the recombination and sticking coefficient for N radicals on a silicon nitride film. Using this sticking coefficient and reported surface reaction probabilities of NH and NH_2 radicals, we conclude that N and NH_2 radicals are mainly responsible for the N incorporation in the silicon nitride film, while Si atoms are most likely brought to the surface in the form of SiH_x radicals.