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Title: Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond

Abstract

A key aspect of single crystal diamond growth via microwave plasma chemical vapor deposition is in-process control of the local plasma–substrate environment, that is, plasma gas phase concentrations of activated species at the plasma boundary layer near the substrate surface. Emission spectra of the plasma relative to the diamond substrate inside the microwave plasma reactor chamber have been analyzed via optical emission spectroscopy. The spectra of radical species such as CH, C{sub 2}, and H (Balmer series) important for diamond growth were identified and analyzed. The emission intensities of these electronically excited species were found to be more dependent on operating pressure than on microwave power. Plasma gas temperatures were calculated from measurements of the C{sub 2} Swan band (d{sup 3}Π → a{sup 3}Π transition) system. The plasma gas temperature ranges from 2800 to 3400 K depending on the spatial location of the plasma ball, microwave power and operating pressure. Addition of Ar into CH{sub 4}+H{sub 2} plasma input gas mixture has little influence on the Hα, Hβ, and Hγ intensities and single-crystal diamond growth rates.

Authors:
;  [1]
  1. Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 (United States)
Publication Date:
OSTI Identifier:
22479664
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 33; Journal Issue: 6; Other Information: (c) 2015 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BOUNDARY LAYERS; CHEMICAL VAPOR DEPOSITION; DIAMONDS; EMISSION; EMISSION SPECTRA; EMISSION SPECTROSCOPY; MICROWAVE RADIATION; MONOCRYSTALS; PLASMA; SUBSTRATES; TEMPERATURE RANGE 1000-4000 K

Citation Formats

Hemawan, Kadek W., E-mail: khemawan@carnegiescience.edu, and Hemley, Russell J. Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond. United States: N. p., 2015. Web. doi:10.1116/1.4928031.
Hemawan, Kadek W., E-mail: khemawan@carnegiescience.edu, & Hemley, Russell J. Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond. United States. doi:10.1116/1.4928031.
Hemawan, Kadek W., E-mail: khemawan@carnegiescience.edu, and Hemley, Russell J. 2015. "Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond". United States. doi:10.1116/1.4928031.
@article{osti_22479664,
title = {Optical emission diagnostics of plasmas in chemical vapor deposition of single-crystal diamond},
author = {Hemawan, Kadek W., E-mail: khemawan@carnegiescience.edu and Hemley, Russell J.},
abstractNote = {A key aspect of single crystal diamond growth via microwave plasma chemical vapor deposition is in-process control of the local plasma–substrate environment, that is, plasma gas phase concentrations of activated species at the plasma boundary layer near the substrate surface. Emission spectra of the plasma relative to the diamond substrate inside the microwave plasma reactor chamber have been analyzed via optical emission spectroscopy. The spectra of radical species such as CH, C{sub 2}, and H (Balmer series) important for diamond growth were identified and analyzed. The emission intensities of these electronically excited species were found to be more dependent on operating pressure than on microwave power. Plasma gas temperatures were calculated from measurements of the C{sub 2} Swan band (d{sup 3}Π → a{sup 3}Π transition) system. The plasma gas temperature ranges from 2800 to 3400 K depending on the spatial location of the plasma ball, microwave power and operating pressure. Addition of Ar into CH{sub 4}+H{sub 2} plasma input gas mixture has little influence on the Hα, Hβ, and Hγ intensities and single-crystal diamond growth rates.},
doi = {10.1116/1.4928031},
journal = {Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films},
number = 6,
volume = 33,
place = {United States},
year = 2015,
month =
}
  • Here, a key aspect of single crystal diamond growth via microwave plasma chemical vapor deposition is in-process control of the local plasma-substrate environment, that is, plasma gas phase concentrations of activated species at the plasma boundary layer near the substrate surface. Emission spectra of the plasma relative to the diamond substrate inside the microwave plasma reactor chamber have been analyzed via optical emission spectroscopy. The spectra of radical species such as CH, C 2, and H (Balmer series) important for diamond growth were found to be more depndent on operating pressure than on microwave power. Plasma gas temperatures were calculatedmore » from measurements of the C 2 Swan band (d 3Π → a 3Π transition) system. The plasma gas temperature ranges from 2800 to 3400 K depending on the spatial location of the plasma ball, microwave power and operating pressure. Addition of Ar into CH 4 + H 2 plasma input gas mixture has little influence on the Hα, Hβ, and Hγ intensities and single-crystal diamond growth rates.« less
  • Spatially resolved optical emission spectroscopy (OES) has been used to investigate the gas phase chemistry and composition in a microwave activated CH{sub 4}/Ar/H{sub 2} plasma operating at moderate power densities ({approx}30 W cm{sup -3}) and pressures ({<=}175 Torr) during chemical vapor deposition of polycrystalline diamond. Several tracer species are monitored in order to gain information about the plasma. Relative concentrations of ground state H (n=1) atoms have been determined by actinometry, and the validity of this method have been demonstrated for the present experimental conditions. Electronically excited H (n=3 and 4) atoms, Ar (4p) atoms, and C{sub 2} and CHmore » radicals have been studied also, by monitoring their emissions as functions of process parameters (Ar and CH{sub 4} flow rates, input power, and pressure) and of distance above the substrate. These various species exhibit distinctive behaviors, reflecting their different formation mechanisms. Relative trends identified by OES are found to be in very good agreement with those revealed by complementary absolute absorption measurements (using cavity ring down spectroscopy) and with the results of complementary two-dimensional modeling of the plasma chemistry prevailing within this reactor.« less
  • Standard H{sub 2}/CH{sub 4}/B{sub 2}H{sub 6} plasmas (99% of H{sub 2} and 1% of CH{sub 4}, with 0-100 ppm of B{sub 2}H{sub 6} added) used for doped diamond film growth are studied by optical emission spectroscopy in order to gain a better understanding of the influence of boron species on the gas phase chemistry. Only two boron species are detected under our experimental conditions (9/15/23 W cm{sup -3} average microwave power density values), and the emission spectra used for studies reported here are B({sup 2}S{sub 1/2}-{sup 2}P{sub 1/2,3/2}{sup 0}) and BH[A {sup 1}{pi}-X {sup 1}{sigma}{sup +}(0,0)]. Variations of their respectivemore » emission intensities as a function of the ratio B/C, the boron to carbon ratio in the gas mixture, are reported. We confirmed that the plasma parameters (T{sub g}, T{sub e}, and n{sub e}) are not affected by the introduction of diborane, and the number densities of B atoms and BH radical species were estimated from experimental measurements. The results are compared to those obtained from a zero-dimensional chemical kinetic model where two groups of reactions are considered: (1) BH{sub x}+H{r_reversible}BH{sub x-1}+H{sub 2} (x=1-3) by analogy with the well-known equilibrium CH{sub x}+H set of reactions, which occurs, in particular, in diamond deposition reactors; and (2) from conventional organic chemistry, the set of reactions involving boron species: BH{sub x}+C{sub 2}H{sub 2} (x=0-1). The results clearly show that the model based on hydrogen and boron hydrides reactions alone is not consistent with the experimental results, while it is so when taking into account both sets of reactions. Once an upper limit for the boron species number densities has been estimated, axial profiles are calculated on the basis of the plasma model results obtained previously in Laboratoire d'Ingenierie des Materiaux et des Hautes Pressions, and significant differences in trends for different boron species are found. At the plasma-to-substrate boundary, [BH] and [B] drop off in contrast to [BH{sub 2}], which shows little decrease, and [BH{sub 3}], which shows little increase, in this region.« less