Self-consistent microwave field and plasma discharge simulations for a moderate pressure hydrogen discharge reactor

Abstract

A self-consistent two-dimensional model of the electromagnetic field and the plasma in a hydrogen discharge system has been developed and tested in comparison to experimental measurements. The reactor studied is a 25 cm diameter resonant cavity structure operating at 2.45 GHz with a silica belljar of 10 cm diameter and 17 cm height contained within the microwave cavity. The inside of the belljar where the discharge occurs contains a substrate holder of 5 cm diameter that is used to hold substrates for diamond deposition. The electromagnetic field model solves for the microwave fields using a finite difference time-domain solution of Maxwell’s equations. The plasma model is a three energy mode (gas, molecular vibration, and electron) and nine species (H2, H, H(n=2), H(n=3), H+, H2+, H3+, H−, electron) model which accounts for non-Boltzmann electron distribution function and has 35 reactions. Simulated characteristics of the reactor in two dimensions include gas temperature, electron temperature, electron density, atomic hydrogen molar fraction, microwave power absorption, and microwave fields. Comparisons of the model are made with close agreement to several experimental measurements including coherent anti-Stokes Raman Spectroscopy measurement of H2 temperature versus position above the substrate, Doppler broadening optical emission spectroscopy (OES) measurements of H temperature versus pressure, actinometry measurements of the relative H atom concentration, Hα OES intensity measurements versus position, and microwave electric field measurements. The parameter range studied includes pressures of 2500–11 000 Pa, microwave powers of 300–2000 W, and three vertical positions of the substrate holder.

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)…”

Modeling of the microdischarges in plasma addressed liquid crystal displays

“…It has been suggested that these high vibrational levels are populated mainly through radiative decay of higher singlet electronic states excited by energetic electrons. 32,36,41 Since the exact vibrational distribution resulting from these processes is unknown, the effective rate coefficient for reaction ͑I-18͒ is no more than a rough estimate. The rate coefficient of reaction ͑I-17͒ is taken to be proportional to the excitation rates of H 2 (C 1 ⌸ u ) and H 2 (B 1 ⌺ u ϩ ); 36,41 the proportionality constant, however, is only a conjecture.…”

Reduction of Copper Oxide by Low-Temperature Hydrogen Plasma

“…In order to get a perspective on the effect of operating parameters on conversion of hydrogen gas to its plasma state and its impact on the reduction process, a mention about average microwave power density (MWPD) is warranted [27,28]. The average power density is regulated through careful monitoring of microwave power and pressure.…”