Jwam John Gielen

Plasma beam deposited amorphous hydrogenated carbon: Improved film quality at higher growth rate

High quality diamondlike a‐C:H has been deposited, at low ion bombardment energies, from an expanding thermal argon/acetylene plasma at high growth rate. It is observed that quality improvement, in terms of hardness, is equivalent to maximization of the refractive index. The highest refractive indices are obtained when the admixed acetylene flow and the argon ion flux emanating from the plasma source are comparable in magnitude, which suggests critical loading. This also indicates that the acetylene has to be dissociated only once. Combination with the observed quality behavior at higher deposition rates suggests that there is one preferred hydrocarbon radical for deposition, probably C2H.

Effect of substrate conditions on the plasma beam deposition of amorphous hydrogenated carbon

A study on the effect of substrate conditions was performed for the plasma beam deposition of amorphous hydrogenated carbon ( a -C:H) from an expanding thermal argon/acetylene plasma on glass and crystalline silicon. A new substrate holder was designed, which allows the control of the substrate temperature independent of the plasma settings with an accuracy of 2 K. This is obtained via a combination of a good control of the holder’s yoke temperature and the injection of helium gas between thermally ill connected parts of the substrate holder system. It is demonstrated that the substrate temperature influences both the a -C:H material quality and the deposition rate. The deposition rate and substrate temperature are presented as the two parameters which determine the material quality. In situ studies prove that the deposition process is constant in time and that thermally activated etching processes are unlikely to contribute significantly during deposition. Preliminary experiments with an additional substrate bias reveal that an energetic ion bombardment of the growingfilm surface does not influence the deposition process. A tentative deposition model is proposed based on the creation and destruction of active sites, which depend on the particle fluxes towards the substrate and the substrate temperature. This model allows the qualitative explanation of the observed deposition results.

Quality improvement of plasma-beam-deposited amorphous hydrogenated carbon with higher growth rate

An improved plasma beam deposition set-up, based on an expanding thermal plasma, is presented. Amorphous hydrogenated carbon films have been deposited on glass and crystalline silicon, under variation of the arc current and admixed acetylene flow. The films have been analysed ex situ with infrared absorption spectroscopy, broadband visible light transmission and nano-indentation measurements. These techniques reveal the growth rate, refractive index, bonded C - H density, optical bandgap and hardness. The growth rate and refractive index are found to increase with decreasing arc current and increasing acetylene flow admixture. The quality of the films in terms of refractive index and hardness increases with increasing growth rate and inverse energy coefficient, whereas the bonded hydrogen concentration and optical bandgap then decrease. From comparison of the growth rate dependency with the inverse energy coefficient dependency, we conclude that the growth rate is the preferred parameter in terms of which to describe the film properties because it is directly related to the plasma composition.

Deposition of a-Si:H and a-C:H using an expanding thermal arc plasma

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, for a-Si:H and for a-C:H, are possible without loss of quality.

Deposition of amorphous carbon layers from C2H2 and CF4 with an expanding thermal arc plasma beam set-up

Amorphous fluorohydrogenated carbon layers are deposited on silicon and glass substrates using an expanding thermal arc plasma, burning on argon with a fixed flow (3 standard cm3 s- ‘) of acetylene and a varying flow (O-2.9 standard cm3 s- ‘) of tetrafluoromethane. The layers deposited are analyzed in situ by means of ellipsometry and ex situ by means of Fourier transform infrared spectroscopy, transmission of visible light, scanning electron microscopy and atomic force microscopy. It is found that the growth rate of the layers is independent of the CF, flow added to the plasma. No dramatic variation in the refractive index, extinction coefficient and optical bandgap is observed with changing CF, flow. The molecular bonding structure is influenced by the addition of CF,, suggesting that the layers are modified by the addition of CF,.

The role of hydrogen during plasma beam deposition of amorphous thin films

Abstract The influence of wall-associated H 2 molecules and other hydrogen-containing monomers on the degree of ionization in the expanding thermal plasma used for the fast plasma beam deposition of amorphous hydrogenated carbon (a-C:H) and amorphous hydrogenated silicon (a-Si:H) was determined. Deposition models are discussed with emphasis on the specific role of the ion during deposition. The connection between the role of atomic hydrogen and the degree of ionization in the plasma beam deposition of a-C:H and a-Si:H is addressed.

Fast deposition of thin amorphous films using an expanding thermal plasma

The basic elements of expanding plasma beam deposition are explained. The principle of dissociation is discussed and illustrated for an Ar/CzH2 plasma. Recent results on high quality aC:H deposition are discussed. It is demonstrated that quality is not connected to growth rate. Moreover for a-C:H it is shown that quality improves with increasing growth rate.

Influence of the addition of CF4 on the deposition of a-C:H layers using the expanding thermal plasma technique

Abstract Applying an expanding cascaded arc thermal plasma beam deposition technique, amorphous fluorohydrogenated carbon (a-C:H,F) layers were deposited from acetylene (C 2 H 2 ) and tetrafluoromethane (CF 4 ). Deposition of the layers was monitored in situ by HeNe ellipsometry and the layers were analyzed ex situ by Fourier transform IR spectroscopy. It is found that the growth rate of the layers is independent of the addition of the CF 4 precursor. However, the structure of the layers is influenced by the addition of CF 4 . It is found that the extinction coefficient decreases with increasing CF 4 flow. The composition of the layers is changed with respect to the bonding types in the layers. The addition of CF 4 leads to incorporation of F in the layers and also to the appearance of sp 2 CH bonds, which implies modification of the layers by CF 4 .

Fast deposition of a-C:H and a-Si:H using an expanding thermal plasma beam

Summary form only given. A fast deposition method, utilizing a thermal plasma which expands into a vacuum vessel, has been used to deposit amorphous hydrogenated silicon and carbon layers (a-Si:H and a-C:H, respectively). The deposited layers are produced by admixing silane and methane (or acetylene) to the argon carrier plasma. In contrast to the conventional plasma enhanced chemical vapour deposition where the deposition is diffusion limited, in this deposition device the deposition mechanism is flow determined. As a result, the deposition rates are large, typically 100 nm/s for a-C:H and 10 nm/s for a-Si:H. The a-Si:H layers are deposited on crystaline silicon and Corning glass substrates, and the a-C:H layers are deposited on either steel, zinc or silicon substrates.