Role of carbon atoms in the remote plasma deposition of hydrogenated amorphous carbon

Abstract

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's 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 ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The aim of this article is to determine the role of carbon atoms in the growth of hydrogenated amorphous carbon (a-C:H) films by means of an argon/acetylene expanding thermal plasma. Cavity ring down absorption spectroscopy is used to detect metastable carbon atoms by probing the 1s 2 2s 2 2p 3s 1 P 1 ←1s 2 2s 2 2p 2 1 S 0 electronic transition. In addition to absorption measurements, the emission of the same transition is monitored by means of optical emission spectroscopy. These two measurements provide information about the local production of the C atoms and about their reactivity in the gas phase. It will be shown that under growth conditions in an Ar/C 2 H 2 expanding thermal plasma, the metastable carbon density is also representative for the ground state carbon density. From obtained results it is concluded that the carbon atoms react rapidly with acetylene in the gas phase and therefore their contribution to the growth of hard diamond-like a-C:H films can be neglected. Only at low acetylene flows, the condition when soft polymer-like films are deposited, carbon atoms are detected close to the substrate and can possibly contribute to the film growth.

Threshold ionization mass spectrometry of reactive species in remote Ar∕C2H2 expanding thermal plasma

“…9 fully corroborates our conclusion discussed in previous work 19 that the metastable carbon measurements, under Ar/ C 2 H 2 ETP conditions, are also representative of the C ground state. 19 The C 2 maximum density determined by CRDS is 3.5ϫ 10 18 m −3 . ͑The C 2 density calculation from the CRDS data was checked several times.…”

“…9 together with the CRDS measurement of C, CH, and C 2 performed with the laser beam passing 30 mm above the substrate plane. [17][18][19] The relative agreement between TIMS and CRDS measurements is excellent and corroborates that the TIMS measurements under different plasma conditions are comparable.…”

“…͑The C 2 density calculation from the CRDS data was checked several times. In our previous article 19 we mentioned erroneously the maximum C 2 density as being more than ten times smaller͒. Such a high C 2 density seems too be overestimated because it would result, with C 2 sticking probability close to unity, 43 in much faster growth rate than measured.…”

“…41,42 Since the TIMS measures the species densities at the substrate plane, it provides lower values than CRDS measurement in the gas phase. The C density cannot be compared since only the metastable 1s 2 2s 2 2p 2 1 S 0 state 2.52 eV above the ground state was measured by CRDS 19 with the metastable carbon density around 5 ϫ 10 15 m −3 . However, the relative agreement between carbon measurements shown in Fig.…”

“…C, CH, and C 2 radicals have been previously measured using cavity ringdown absorption spectroscopy ͑CRDS͒. [17][18][19] However, the contribution of these radicals to the a-C : H growth ͑radical flux towards the surface multiplied by surface sticking probability͒ appears negligible under the conditions where hard a-C : H films are deposited. This has been attributed to high gas phase reactivity of C, CH, and C 2 with C 2 H 2 , 18 which results in a low density of these radicals close to the substrate.…”