Effects of process variables on properties and composition of a-Si:C:H films
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W.A. Lanford Department of Physics, State University of New York at Albany, Albany, New York 12222
S.V. Babu Center for Advanced Materials Processing, Box 5705, Clarkson University, Potsdam, New York 13699 (Received 24 April 2002; accepted 17 October 2002)
Physical properties of a-Si:C:H films, including composition, optical constants, microhardness, and surface energy, were investigated. A factorial experimental design was employed to establish the effects of plasma-assisted chemical vapor deposition parameters on the physical properties of the films. The dynamics of the plasma deposition process are discussed in relation to the interactions observed among the process variables and the effects of the variables on the physical properties of the films.
I. INTRODUCTION
The composition and structure of amorphous carbon and a-Si:C films have been the subject of much study and speculation.1– 4 Having no long-range order, amorphous films cannot be characterized by standard x-ray or electron diffraction techniques. In many amorphous carbon films there is the added complication of hydrogen incorporation. Hydrogen is incorporated into the a-C:H films in both bonded and unbonded forms in large quantities3,4 during deposition. This hydrogen can have a very significant effect on the physical properties of the film.5,6 Analysis for hydrogen content is difficult with most characterization techniques, particularly when the hydrogen is unbonded. One method that has been successful in measuring the hydrogen content (both bonded and unbonded) of a-C:H and related films is nuclear reaction analysis (NRA).7–9 In the NRA method, N15 ions bombard the sample and induce nuclear reactions with hydrogen. By measurement of the nuclear reaction yield versus beam energy, the hydrogen concentration can be obtained as a function of depth. In this investigation, NRA in combination with Rutherford back-scattering spectrometry (RBS) is used to determine the composition of a-Si:C:H films. The optical properties of a-Si:C:H films have been of considerable interest10–13 due to their application in window layers, light-emitting diodes, and other electronic
devices.14,15 Optical transparency in some of these films, combined with excellent mechanical properties,11,16 has also led to their use as protective coatings on optical glass. To create a-Si:C:H films with optical properties tailored to different applications, a thorough understanding of how deposition conditions affect optical properties is needed. The dependence of the optical properties of these films on the deposition conditions can be extremely complex.13,17–19 In this investigation, compositional, optical, and mechanical characterization were combined with a twolevel factorial experimental design20 to present a more complete picture of how deposition conditions affect the growth of a-Si:C:H films. II. EXPERIMENTAL A. Film deposition
Silicon-containing diamondlike carbon (DLC) films were deposited by plasma-assisted chemical vapor deposition (PACVD) on 〈001〉-silicon wafers from a combina
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