Plasma-induced Chemical Vapor Deposition Research Articles

Internal friction studies of nanocomposite superhard nc-TiN/a-Si 3N 4 and nc-(Ti 1− xAl x)N/a-Si 3N 4 films

Elastic and anelastic properties of TiN/a-Si 3N 4 and (Ti 1− x Al x )N/a-Si 3N 4 superhard nanocomposite (nc) films prepared by plasma-induced chemical vapor deposition (PCVD), magnetron sputtering and vacuum arc deposition (physical vapor deposition, PVD) have been investigated by mechanical spectroscopy. One internal friction peak with relaxational nature was observed at temperatures around 230–280 °C and frequencies about 100 Hz for as-deposited films prepared by PVD, while no peak was detected in the films prepared by PCVD whose hardness was as high as 50 GPa. A comparison of a series of samples indicates that the peak is higher for films with lower hardness. The activation energy and the pre-exponential factor of the relaxation time are deduced as 0.7–1.0 eV and 10 −10 to 10 −12 s, respectively. The intensity of this peak decreases with increasing annealing temperature. After annealing at 600–750 °C, this peak disappears and Young's modulus increases, in agreement with the increase in the hardness upon the annealing reported earlier. This internal friction peak is suggested to be associated with a thermally activated relaxation process within the interfaces that were not fully developed during the PVD process.

Comparative study of the tribological behaviour of superhard nanocomposite coatings nc-TiN/a-Si 3N 4 with TiN

Superhard nanocomposite nc-TiN/a-Si 3N 4 coatings were prepared by reactive magnetron sputtering (RMS) and pulsed dc plasma-induced chemical vapour deposition (PCVD) on stainless steel substrates. The tribological behaviour of these coatings at room and elevated temperature was compared with that of TiN coatings deposited by RMS and PCVD. The results show that the superhard nanocomposite nc-TiN/a-Si 3N 4 coatings have a somewhat higher friction coefficient of 0.55–0.7 at room temperature that decreases to about 0.4–0.5 at 550 °C. However, the friction coefficient of pure TiN coatings is 0.6 at room temperature and increases to 0.7 after a sliding distance of 0.1 km at 550 °C.

All-dry siloxane based resist system: Plasmainduced chemical vapor deposition and reactive ion etch development

We investigated and demonstrated the plasma induced chemical vapor deposition and reactive ion etch development of highly silicon enriched resist layers. There is no need for post deposition silicon enrichment. Deposition and development have been performed in conventional parallel plate reactors. The resist is sensitive to deep-UV and electron beam exposure with 150 mJ/cm 2 (193 nm) and 150 μC/cm 2 (20 keV) photospeed respectively. Depending on the development parameters the exposure characteristic can be reversed from negative to positive. Possible applications range from top imaging layer in a bilayer resist system to a stand alone layer in selective etch processes which also use selectivity to SiO 2 .

Large-area boron carbide protective coatings for controlled thermonuclear research prepared byin situ plasma CVD

Impurity release from the first wall and components facing the hot plasma in Tokamak devices for controlled fusion research and the concomitant pollution of the plasma lead to enhanced energy losses and deuterium-tritium luel dilution. Both these effects can prevent reaching the ignition conditions. The recently developed technique for large areain situ deposition of boron carbide protective coatings by means of plasma-induced chemical vapor deposition enables one to significantly improve the purity of the fusion plasma. The prospects of approaching the scientific break-even in the large machines of the Tokarnak type has been increased.

Surface processes and rate-determining steps in plasma-induced chemical vapour deposition: Titanium nitride, boron carbide and silicon

Several recently developed plasma chemical vapour deposition (CVD) processes, including the low temperature deposition of high quality TiN and large area in situ CVD of boron carbide protective coatings, are discussed. A detailed insight into the reaction mechanism and the rate-determining steps has been obtained for the deposition of amorphous and crystalline silicon. Particular attention is devoted to the processes taking place at the surface of the growing film.

Optical time-domain reflectometry (OTDR) of diameter modulations in single mode fibers

The influence of several types of diameter variations on the attenuation and on the optical time-domain reflectometry (OTDR) traces of specially prepared depressed cladding SM (single-mode) fibers is experimentally investigated. Depressed-cladding SM fibers have been prepared by the low-pressure plasma-induced chemical vapor deposition (PCVD) process. The core consists of GeO/sub 2/-doped SiO/sub 2/ and the cladding region of fluorine-doped silica. During drawing, the diameter of the fiber is controlled within +or-0.3 mu m for slow perturbations by adjusting the drawing speed (Anritsu M501A). Variations of the core diameter have been accomplished by changing the set point of the fiber diameter control. Core diameter changes give rise to steps or deviations in slope of the OTDR power trace of about 0.3 dB/ mu m. No indication of additional attenuation due to axial fiber parameter variations has been found up to core diameter changes of 12 mu m/m, despite severe distortions of the OTDR traces. >

Refractive index of doped and undoped PCVD bulk silica

The wavelength dependence of the refractive index of GeO 2 and GeO 2 F -doped PCVD (plasma induced chemical vapor deposition) silica was measured with an overall accuracy of ± 6 × 10 −5. A model has been developed for predicting the refractive index in the binary glass systems GeO 2 SiO 2 and F SiO 2 and the ternary glass system GeO 2 / F / SiO 2. Refractive index and dispersion characteristics are presented as a function of the dopand concentrations for concentration levels relevant for optical telecommunication fibers. Comparing the material dispersion of PCVD silica with data from samples prepared by alternative methods reveals significant differences. Independent of the dopand species, the dispersion of PCVD-silica at a given wavelength is higher than for silica samples investigated in the literature resulting in a shift of the zero dispersion wavelengths to lower values. The use of the PCVD- specific material properties improves the agreement of the theoretical calculated and the measured dispersion characteristics of PCVD fibers.

Development of plasma CVD and feasibility study of boron carbide in-situ coatings for tokamaks

The in-situ, plasma-induced chemical vapour deposition and materials properties of boron-carbon coatings have been optimized for their application as renewable coatings of the first wall in tokamak devices. Recently, such coatings were successfully applied in TEXTOR.

Thermal expansion coefficients of doped and undoped silica prepared by means of PCVD

The thermal expansion coefficient of silica prepared by means of low-pressure plasma-induced chemical vapour deposition has been investigated in the temperature range 20 to 750° C. Undoped, fluorine-doped (up to 5wt%), germanium-doped (up to 14 wt%), as well as F/GeO2-codoped samples were measured and compared to NBS standard silica samples. Fluorine-doped silica shows a lower thermal expansion coefficient than the NBS standard. A surprising hysteresis effect in the measured expansion curves was found. Its concentration dependence and annealing is discussed.

Stress in optical waveguides 1: Preforms

The intrinsic stress properties of GeO2- and F-doped optical fiber preforms have been investigated in detail. The materials were prepared by low-pressure plasma-induced chemical vapor deposition (PCVD), and the dopant concentrations cover the range normally used in optical fiber manufacture (+1% > Δ > −1%). Homogeneously doped preform regions exhibit a constant stress level. This level is exclusively dependent on dopant concentrations. In GeO2-doped silica the stress increases linearly with the dopant concentration. For F-doped silica, however, this dependency is strongly nonlinear. A negative stress difference between undoped PCVD material and the substrate tube material can be explained by the reduced thermal expansion coefficient of PCVD-SiO2 caused by chlorine incorporated during the deposition step. The experiments agree excellently with theoretical predictions based on thermal expansion data.

Dispersion-flattened single-mode fibers prepared with PCVD: Performance, limitations, design optimization

The first test on the reproducibility of the preparation of dispersion-flattened single-mode (DFSM) fibers is reported in this paper. Dispersion of less than 2 ps/(nm . km) between 1.32 and 1.6μm was achieved for a set of 15 fibers (31 km), with identical diameter prepared by means of the low pressure plasma-induced chemical vapor deposition (PVCD) process. Investigations on the influence of the substrate tube geometry, the "rod-in-tube" technique, and refractive index distortions on dispersion are presented. CAD optimized index profiles are discussed.

Optical thin films obtained by plasma-induced chemical vapor deposition

A plasma-aided deposition technique was used to prepare thin oxide coatings by the reaction of volatile chlorides with oxygen. A 13.56 MHz r.f. supply was connected to a circular electrode on which the substrates were supported. A glow discharge was set up at pressures between 5 and 100 m Torr, and a self-bias on the electrode of between − 100 and − 1000 V (depending on input power and pressure) creates ion-plating conditions. GeCl 4, SiCl 4, TiCl 4 and SnCl 4 were used to prepare the corresponding dioxides. The deposition conditions (pressure, bias, gas ratios and treatment time) were varied and the resultant films examined in terms of thickness (and coating rate) and their respective indices. The films were generally smooth and highly transparent and were deposited at rates of tens of nanometres per minute. TiO 2 and SiO 2 were produced with refractive index values of 2.2 and 1.45 respectively at rates of 50 nm min −1; these rates were found to be relatively insensitive to the gas pressure and r.f. bias. In 2O 3 films were similarly prepared from trimethyl indium vapour and O 2. These films could be electrically conducting. In contrast with earlier published work on reactive plasma deposition of oxide films, this work was carried out at ambient temperatures.

Film preparation using plasma or ion activation

It has been well established that reactive layer growth can be enhanced by using plasma or ion activation. The capabilities of these techniques are discussed in connection with results obtained for the following film deposition processes: (1) the formation of silicon layers by plasma-induced chemical vapour deposition (CVD) from SiCl 4H 2; (2) the synthesis of Si x N y H z coatings by plasma-induced CVD from SiNH 3; (3) the preparation of hard and transparent (diamond-like) carbon films by the condensation of ionized organic species.