Microwave Plasma-Activated Chemical Vapor Deposition of Nitrogen-Doped Diamond. I. N₂/H₂ and NH₃/H₂ Plasmas

Abstract

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(X(3)Σ(-), 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(A(3)Π) radicals, and N2(C(3)Πu) 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(A(3)Σ(+)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.

Spatially Resolved Optical Emission and Modeling Studies of Microwave-Activated Hydrogen Plasmas Operating under Conditions Relevant for Diamond Chemical Vapor Deposition

“…show an approximate 1/p decrease (in both the radial and axial directions). The present calculations confirm the main effects of varying p and P revealed and described in the earlier studies (that did not involve direct calculation of the electromagnetic fields) 60,67 but also…”

“…That the employed rate coefficient (k 3 = 10 −9 cm 3 s −1 ) returns an H(n = 2) column density in the plasma core, {H(n = 2)} ~ 4×10 8 cm −2 , in good accord with the value measured in our cavity ring down spectroscopy absorption studies of dilute N 2 in H 2 plasmas operating under very similar process conditions, 60 provides further (albeit indirect) indication of the necessity of the fast collisional quenching (3). Lacking alternative information, we assume the same values for the rate coefficients k 12 and k 4 , while k 13 was derived from experimental data.…”

What [plasma used for growing] diamond can shine like flame?

“…For typical process pressures, p >100 Torr, Tgas becomes sufficient for thermal dissociation of H2 to be the main route to producing H atoms. 63,67,71,74 The primary ionization mechanism also depends on the process conditions. Direct EI ionization of H2 (1), the sets of reactions (2) and (3) H2 + e  H2 + + 2e (1)…”

“…71 Reactions of CH radicals (and C atoms) with N2 are further N atom sources in the case of H/C/N plasmas, wherein reactions between NHx (x = 0-3) and CHx (x = 0-3) radicals then provide the route to forming HCN (which, like C2H2, is a stable species in the hot region). 57,61 Notwithstanding, N2 still constitutes ~99.5% of the total nitrogen in the core of a MW activated H/C/N plasma operating under our base conditions of p and P. Less than 0.25% of the input N2 is converted to HCN and the relative abundances of N-containing species that might plausibly be considered reactive at the growing diamond surface (e.g.…”

Investigation of bonded hydrogen defects in nanocrystalline diamond films grown with nitrogen/methane/hydrogen plasma at high power conditions

“…Then we briefly discuss the "invisible" impact of high microwave power on diamond growth and H incorporation through intermediate process such as gas phase chemistry and substrate surface chemistry based on some literature work through computer simulation of microwave plasma of CH 4 /H 2 and with N 2 [5,[40][41][42]. In the present study, the amount of hydrogen and methane was kept constant at 4% CH 4 /H 2 , with increasing power from 3.0 to 4.0 kW, the density of both H atom and CH 3 radical should increase significantly due to much higher gas temperature (above 3200 K).…”