We report a combined experimental/modeling study of microwave activated dilute N2/H2 and NH3/H2 plasmas as a precursor to diagnosis of the CH4/N2/H2 plasmas used for the chemical vapor deposition (CVD) of N-doped diamond. Absolute column densities of H(n = 2) atoms and NH(X3Σ–, v = 0) radicals have been determined by cavity ring down spectroscopy, as a function of height (z) above a molybdenum substrate and of the plasma process conditions, i.e., total gas pressure p, input power P,
and the nitrogen/hydrogen atom ratio in the source gas. Optical
emission spectroscopy has been used to investigate variations in the
relative number densities of H(n = 3) atoms, NH(A3Π) radicals, and N2(C3Πu) molecules as functions of the same process conditions. These experimental data are complemented by 2-D (r, z)
coupled kinetic and transport modeling for the same process conditions,
which consider variations in both the overall chemistry and plasma
parameters, including the electron (Te) and gas (T) temperatures, the electron density (ne), and the plasma power density (Q).
Comparisons between experiment and theory allow refinement of prior
understanding of N/H plasma-chemical reactivity, and its variation with
process conditions and with location within the CVD reactor, and serve
to highlight the essential role of metastable N2(A3Σ+u) molecules (formed by electron impact excitation) and their hitherto underappreciated reactivity with H atoms, in converting N2 process gas into reactive NHx (x = 0–3) radical species.