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The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl (SiH 3 ) radical whereas the ion-electron induced dissociation mechanism leads to SiH x (xϽ3) radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals SiH x (xϽ3) with silane. Almost independent of the plasma conditions used, approximately one H 2 is produced per consumed SiH 4 molecule. Disilane production is observed which roughly scales with the remaining silane density. Possible production mechanisms for both observations are discussed.

The properties of hydrogenated amorphous silicon (a-Si:H) deposited at very high growth rates (6–80 nm/s) by means of a remote Ar–H2–SiH4 plasma have been investigated as a function of the H2 flow in the Ar–H2 operated plasma source. Both the structural and optoelectronic properties of the films improve with increasing H2 flow, and a-Si:H suitable for the application in solar cells has been obtained at deposition rates of 10 nm/s for high H2 flows and a substrate temperature of 400 °C. The “optimized” material has a hole drift mobility which is about a factor of 10 higher than for standard a-Si:H. The electron drift mobility, however, is slightly lower than for standard a-Si:H. Furthermore, preliminary results on solar cells with intrinsic a-Si:H deposited at 7 nm/s are presented. Relating the film properties to the SiH4 dissociation reactions reveals that optimum film quality is obtained for conditions where H from the plasma source governs SiH4 dissociation and where SiH3 contributes dominantly to film growth. Conditions where ion-induced dissociation reactions of SiH4 prevail and where the contribution of SiH3 to film growth is much smaller lead to inferior film properties. A large contribution of very reactive (poly)silane radicals is suggested as the reason for this inferior film quality. Furthermore, a comparison with film properties and process conditions of other a-Si:H deposition techniques is presented.

Fourier transform infrared spectrometry, visual transmission spectroscopy, and in situ ellipsometry have been performed on plasma beam deposited (PBD) amorphous hydrogenated silicon layers. From these measurements refractive index at infrared wavelengths and at 632.8 nm, the optical band gap and the hydrogen content of the layers have been determined. The hydrogen concentration of the layers varies between ∼9 and 25 at. %. It was found that the refractive index decreases more with hydrogen concentration in the layer than predicted by theoretical calculations assuming tetrahedral structures. The band gap of the material remains constant at ∼1.72 eV for the range of hydrogen contents measured. The resonance frequency of the SiH stretching mode (around 2000 cm−1) increases with increased hydrogen content. This is additional evidence to support the assumption that clustered SiH (SiH on voids) does not have its stretching mode near the 2100 cm−1 SiH2 peak. From the results presented it is concluded that PBD layers show behavior similar to plasma enhanced chemical vapor deposition layers with respect to the hydrogen content in the layers.

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The surface reaction probability ␤ in a remote Ar-H 2 -SiH 4 plasma used for high growth rate deposition of hydrogenated amorphous silicon ͑a-Si:H͒ has been investigated by a technique proposed by D. A. Doughty et al. ͓J. Appl. Phys. 67, 6220 ͑1990͔͒. Reactive species from the plasma are trapped in a well, created by two substrates with a small slit in the upper substrate. The distribution of amount of film deposited on both substrates yields information on the compound value of the surface reaction probability, which depends on the species entering the well. The surface reaction probability decreases from a value within the range of 0.45-0.50 in a highly dissociated plasma to 0.33Ϯ0.05 in a plasma with ϳ12% SiH 4 depletion. This corresponds to a shift from a plasma with a significant production of silane radicals with a high ͑surface͒ reactivity (SiH x ,xϽ3) to a plasma where SiH 3 is dominant. This has also been corroborated by Monte Carlo simulations. The decrease in surface reaction probability is in line with an improving a-Si:H film quality. Furthermore, the influence of the substrate temperature has been investigated.

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Abstract. This paper deals with the deposition of a-C:H and a-Si:H using the expanding thermal arc technique. The method is compared with other deposition techniques. The basics of the technique are explained and recent results on the deposition of high-quality a-C:H and a-Si:H are discussed. It is shown that high rates, 7 nm s −1 for a-Si:H and 50 nm s −1 for a-C:H, are possible without loss of quality.