William D. Partlow

Electron and chemical kinetics in methane rf glow‐discharge deposition plasmas

Experimental measurements and theoretical modeling of methane deposition plasmas have led to the identification of the most likely homogeneous and heterogeneous reaction paths leading to the deposition of amorphous carbon thin films. Experimental measurements of the voltage, current waveforms, mass flow rates, and pressure are used as inputs to the model. The magnitude and flow‐rate dependence of the discharge luminosity, film deposition rates, and downstream mass spectra are compared with the model predictions and used to identify the dominant reaction paths. The model uses Monte Carlo simulation of the electron kinetics to predict the electron impact dissociation and ionization rates. These rates provide input for a plug flow chemical kinetics model.

Ultraviolet Raman spectroscopy characterizes chemical vapor deposition diamond film growth and oxidation

The Raman spectra of diamond and chemical‐vapor‐deposition (CVD) diamond films in the UV have been excited within the diamond band gap at 228.9 nm for the first time. The lack of fluorescence in the UV‐excited Raman spectrum of diamond and CVD diamond films allows Raman spectroscopy to monitor the carbon‐hydrogen (C‐H) stretching vibrations of the nondiamond components of the CVD film as well as the third‐order phonon bands of diamond. The relative intensity of the C‐H stretching bands at ∼2930 cm−1 to the diamond first‐order phonon band at 1332 cm−1 is proportional to the atomic fraction of covalently bound hydrogen in the CVD diamond film. The third‐order phonon band intensity and frequency maxima are very sensitive to the size of the diamond crystallite. Its intensity decreases, and the maximum shifts to lower frequency as the size of the diamond crystallite decreases. It is shown here that UV Raman diamond measurements have significantly greater information content than visible Raman measurements.

Far-UV, visible, and near-IR reflectance spectra of frosts of H2O, CO2, NH3 and SO2

Abstract The reflectance spectra of frosts of several volatiles of interest for comet nuclei and outer-solar-system objects have been measured over the range 0.1–2.5 μm. The spectra of all the frosts have distinctive features which could allow their identification by spectroscopic reflectance remote sensing, especially in the far uv. H 2 O has a minimum at about 0.16 μmand a maximum at 0.13 μm. CO 2 is relatively bright in the far uv, with minima near 0.21, 0.18, and 0.125 μm and maxima at 9, 0.135, and 0.120 μm. NH 3 is bright at wavelengths longer than about 0.21 μm, where the reflectance drops precipitously to a value of only a few percent at shorter wavelenghts. SO 2 has a sharp drop at 0.32 μm and its spectrum remains dark at higher energies, with a minimum at 0.18 μm and a maximum near 0.13 μm. Most of the features in the frosts spectra correspond to bands of absorption lines in the gas phase.

Cathodoluminescence and annealing study of plasma-deposited polycrystalline diamond films

We have measured the cathodoluminescence spectra of microwave plasma‐assisted chemical‐vapor deposited (CVD) polycrystalline diamond films at 77 K over the spectral range of 2300–8000 A. Annealing studies of these spectra have been carried out at 500, 800, 1000, 1200, and 1350 °C. Rich spectra are observed. Many of them are stable up to the highest annealing temperature. Two peaks at 3.188 and 2.638 eV and the 5RL lines are destroyed, while other lines at 3.57 and 3.462 eV appear, after a 1200 °C anneal. The two neighboring peaks at 2.330 and 2.320 eV are probably responsible for the broadness of the often observed peak at 2.328 eV in CVD diamond films. We also compare some of the annealing behavior of the CVD diamond films with those of natural single‐crystal diamond, and conclude that while most of the annealing characteristics of plasma‐deposited diamond films are similar with those which have been reported for single‐crystal natural diamonds, some of the annealing behaviors are different for these two...

Cryogenic cathodoluminescence of plasma‐deposited polycrystalline diamond coatings

The cathodoluminescence spectra of microwave plasma‐deposited polycrystalline diamond films have been measured at liquid‐nitrogen temperatures over the spectral region of 230–800 nm. The diamond coatings had been deposited under several different deposition temperatures and reactant compositions. Measurements on natural type‐IIB diamond crystals were made for comparison. The intrinsic exciton emission bands which fall in the UV just below the band edge were observed, as well as several defect and impurity bands which extend throughout the visible part of the spectrum. SEM micrographs and Raman spectra were obtained for the same set of samples used for the cathodoluminescence measurements. It was found that the diamond‐related cathodoluminescence features were most intense in samples whose Raman spectra exhibited the most intense cubic diamond line at 1332 cm−1 and the least intense graphitic band at about 1500 cm−1.

Diagnostics and modeling of RF discharge dissociation in N/sub 2/O

Measurements were made of the RF discharge dissociation of N/sub 2/O in a parallel-plate reactor by downstream mass spectrometry using a wide range of gas flows and powers at 10 kHz and 13.56 MHz. The results show that the mass 44 signal (N/sub 2/O/sup +/), which is a measure of the amount of undissociated N/sub 2/O, is a function of the discharge input energy per N/sub 2/O molecule (eV/N/sub 2/O). A plug flow, rate equation model of the discharge was used to predict the experimental dissociation rates. A DC Monte Carlo simulation was used to calculate rate coefficients for electron-impact neutral dissociation, ionization, and dissociative ionization. The rate equation model also includes reactions among the dissociation products of N/sub 2/O and species which are synthesized in the discharge, as well as neural and electron-ion recombination at the electrodes. The model predictions identify the major reaction pathways and the sensitivities of the results to the rate coefficient values used. >

Grazing incidence reflectance of SiC films produced by plasma-assisted chemical vapor deposition

The grazing incidence reflectance of silicon carbide films produced by plasma-assisted chemical vapor deposition has been evaluated in the spectral region from 256 to 1216 Å. The results show that reflectivities higher than conventional coatings can be obtained on coatings deposited both on silicon wafers and quartz substrates. Potential application of silicon carbide films for EUV astronomical instruments will be discussed.

Characterization of plasma-deposited and dip-coated films for critical optical applications.

Two types of coatings were evaluated with respect to their suitability for optical applications in which low scattering is required. The plasma-deposition technique produces dense pinhole-free films of refractory materials from a glow discharge plasma at typical substrate temperatures of 200-300 degrees C. Plasma-deposited films of SiO(2) and Si(3)N(4), produced from reactions of SiH(4) with N(2)O and NH(3), respectively, were evaluated in this study. SiO(2) films were also produced from metal-organic precursor solutions using dipping and spinning application techniques followed by pyrolysis at 600 degrees C. Coatings were deposited on the highest quality substrates available, which were characterized prior to deposition so that the effects of the coatings could be separated from those of the substrates. Nomarski microscopy, surface profiling, total integrated scattering, ellipsometry, and photon backscattering techniques were used for characterization. The properties of these coatings and information on how the quality depends on coating conditions are reported in this paper.

Selectively absorbing filters for contrast enhancement of light sources.

A quantitative basis is established for determining the optimum spectral shape of the transmission of optical filters used with information displaying light sources for contrast enhancement. Examples are given for several ideal and practical cases, and performance is evaluated for these.

Cyclohexane-based optical coatings of diamond-like carbon

Protective and anti-reflective optical coatings of diamond-like carbon have been deposited on germanium and silicon substrates from glow discharges of cyclohexane. Films of excellent quality were obtained with high deposition rates using this non-hazardous feed gas. A parametric study was carried out to determine the dependence of the process characteristics and the optical properties of the films on the electrode bias gas pressure and flow. The study determined the contours for film refractive index and deposition rates over the parameter space and also revealed information on the dependence of infrared absorption and film adhesion. Important information on process scaling was determined. A simple dependence of negative self-bias on electrode design was obtained by using electrodes of different sizes. Changes in bias as a result of the coating of grounded reactor surfaces were measured. The effect of feed gas flow on the film and process properties provided insight into the impact of reactant depletion on the deposition process. 258 / SPIE Vol. 1325 Diamond Optics 111(1990)