Spectroscopic diagnostics and modeling of Ar/H{sub 2}/CH{sub 4} microwave discharges used for nanocrystalline diamond deposition

Journal Article · Wed Dec 01 04:00:00 EST 2004 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1814174· OSTI ID:20658112

Lombardi, G; Hassouni, K; Benedic, F; Mohasseb, F; Roepcke, J; Gicquel, A ^[1]

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1. Laboratoire d'Ingenierie des Materiaux et des Hautes Pressions, UPR 1311 CNRS, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France)

In this paper Ar/H{sub 2}/CH{sub 4} microwave discharges used for nanocrystalline diamond chemical vapor deposition in a bell-jar cavity reactor were characterized by both experimental and modeling investigations. Discharges containing 1% CH{sub 4} and H{sub 2} percentages ranging between 2% and 7% were analyzed as a function of the input microwave power under a pressure of 200 mbar. Emission spectroscopy and broadband absorption spectroscopy were carried out in the UV-visible spectral range in order to estimate the gas temperature and the C{sub 2} density within the plasma. Infrared tunable diode laser absorption spectroscopy was achieved in order to measure the mole fractions of carbon-containing species such as CH{sub 4}, C{sub 2}H{sub 2}, and C{sub 2}H{sub 6}. A thermochemical model was developed and used in order to estimate the discharge composition, the gas temperature, and the average electron energy in the frame of a quasihomogeneous plasma assumption. Experiments and calculations yielded consistent results with respect to plasma temperature and composition. A relatively high gas temperature ranging between 3000 and 4000 K is found for the investigated discharge conditions. The C{sub 2} density estimated from both experiments and modeling are quite high compared with what is generally reported in the literature for the same kind of plasma system. It ranges between 10{sup 13} and 10{sup 14} cm{sup -3} in the investigated power range. Infrared absorption measurements and model predictions indicate quite low densities of methane and acetylene, while the atomic carbon density calculated by the model ranges between 10{sup 13} and 10{sup 15} cm{sup -3}. The methane and hydrogen introduced in the feed gas are subject to a strong dissociation, which results in a surprisingly high H-atom population with mole fraction ranging between 0.04 and 0.16. Result analysis shows that the power coupling efficiency would range between 70% and 90%, which may at least explain the relatively high values obtained, as compared with those reported in the literature for similar discharges, for gas temperature and C{sub 2} population. The high H-atom densities obtained in this work would indicate that growing nanocrystalline diamond films would experience a very high etching. Simulation results also confirm that sp species would play a key role in the surface chemistry that governs the diamond growth.

• OSTI ID: 20658112
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 11 Vol. 96; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABSORPTION SPECTROSCOPY
ACETYLENE
ARGON
CHEMICAL VAPOR DEPOSITION
DIAMONDS
ELECTRON TEMPERATURE
EMISSION SPECTROSCOPY
ETHANE
HIGH-FREQUENCY DISCHARGES
HYDROGEN
INFRARED SPECTRA
ION TEMPERATURE
METHANE
NANOSTRUCTURES
PLASMA
PLASMA DENSITY
PLASMA DIAGNOSTICS
PLASMA SIMULATION
ULTRAVIOLET SPECTRA
VISIBLE SPECTRA