Measurement and modeling of a diamond deposition reactor: Hydrogen atom and electron number densities in an Ar∕H2 arc jet discharge

Abstract

Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: A combination of experiment ͓optical emission and cavity ring-down spectroscopy ͑CRDS͒ of electronically excited H atoms͔ and two-dimensional ͑2D͒ modeling has enabled a uniquely detailed characterization of the key properties of the Ar/ H 2 plasma within a ഛ10-kW, twin-nozzle dc arc jet reactor. The modeling provides a detailed description of the initial conditions in the primary torch head and of the subsequent expansion of the plasma into the lower pressure reactor chamber, where it forms a cylindrical plume of activated gas comprising mainly of Ar, Ar + , H, ArH + , and free electrons. Subsequent reactions lead to the formation of H 2 and electronically excited atoms, including H͑n =2͒ and H͑n =3͒ that radiate photons, giving the plume its characteristic intense emission. The modeling successfully reproduces the measured spatial distributions of H͑n Ͼ 1͒ atoms, and their variation with H 2 flow rate, F H 2 0 . Computed H͑n =2͒ number densities show near-quantitative agreement with CRDS measurements of H͑n =2͒ absorption via the Balmer-␤ transition, successfully capturing the observed decrease in H͑n =2͒ density with increased F H 2 0 . Stark broadening of the Balmer-␤ transition depends upon the local electron density in close proximity to the H͑n =2͒ atoms. The modeling reveals that, at low F H 2 0 , the maxima in the electron and H͑n =2͒ atom distributions occur in different spatial regions of the plume; direct analysis of the Stark broadening of the Balmer-␤ line would thus lead to an underestimate of the peak electron density. The present study highlights the necessity of careful interco...

Cavity Ring-Down Spectroscopy Measurement of H(n=2) Density in Mesoplasma for Fast-Rate Silicon Epitaxy

“…This density is higher than that reported for a cascade dc-arc jet plasma expanding under pres-sures 0.07-0.75 Torr 19) and for a high-density helicon-wave plasma operating at 0.05 Torr; 23) indeed, it is as high as that reported for a dc-arc jet plasma expanding under a pressure of 50 Torr. 12,13) This H(n ¼ 2) density is even comparable to the density of the ground state H(n ¼ 1) in a plasma generated by an ultrahigh frequency power at 500 MHz operated at 0.1-0.2 Torr. 24) In the mesoplasma, the Ar/H 2 gas in the core plasma can be dissociated completely and a large number of Ar þ ions can exist.…”

“…The number density of H(n ¼ 2), N Hðn¼2Þ , can be determined from the absorption cross-section, , and the decay rate constant, ðÞ, if the H(n ¼ 2) atoms are uniformly distributed along the absorption path length, d; that is: 12) N Hðn¼2Þ…”

Reevaluation of the mechanism for ultrananocrystalline diamond deposition from Ar∕CH4∕H2 gas mixtures

“…Typical values of plasma parameters obtained from this model are as follows: E / N ϳ 6.5-8.5ϫ 10 −17 V −1 cm 2 , T e ϳ 2.4-3 eV for a 1% CH 4 /2% H 2 / 97% Ar mixture at 100 Torr, and E / N ϳ 25-30ϫ 10 −17 V −1 cm 2 , T e ϳ 1.3-1.5 eV for a 1% CH 4 /H 2 mixture at 20 Torr. Established plasma-chemical mechanisms ͑ϳ35 species and ϳ300 reactions for H/C/Ar mixtures͒ [21][22][23] together with the electron temperature dependence of the electron collision processes are used in the 2D model of the microwave reactor. The incorporation of nine gas-surface reactions, involving the H abstraction to form surface sites, and the subsequent reactions of these sites with H and hydrocarbon radicals serve to alter significantly the gas composition close to the surface.…”

Measurement and modeling of Ar∕H2∕CH4 arc jet discharge chemical vapor deposition reactors II: Modeling of the spatial dependence of expanded plasma parameters and species number densities

“…Phases ͑I͒ and ͑II͒ for an argon-hydrogen plasma have been fully described in our preceding paper 7 and are only briefly summarized here. The first two phases of the model address the activation within the primary nozzle of an Ar/ H 2 feedstock gas flow and the expansion of the resultant, partially ionized mixture into the reaction chamber.…”