Kn Rosser

Examination of the effects of nitrogen on the CVD diamond growth mechanism using in situ molecular beam mass spectrometry

Abstract Molecular beam mass spectrometry (MBMS) has been used to obtain quantitative measurements of the composition of the gas-phase species prevalent during diamond hot filament CVD using a variety of nitrogen-containing source gas mixtures. The ratio of C:N in the feedstock was maintained at 1:1, and the gas mixtures used were 0.5% each of CH 3 NH 2 and HCN in H 2 , and 0.5% CH 4 in H 2 with added NH 3 and N 2 at 0.5 and 0.25% respectively. The deposition rate and resulting film quality at optimum growth temperatures depend critically on the origin of carbon-containing species. At the relevant process temperatures, most of the gas-phase carbon exists in the form of unreactive HCN (∼70–90%) for all precursor gas mixtures (except CH 4 /N 2 ), with very little C 2 H 2 detected. As a result, poor quality diamond films were deposited at rates of less than 0.1 μm h −1 . For CH 4 /N 2 mixtures, however, equal amounts of HCN and C 2 H 2 were detected, and well-faceted diamond films were produced at higher deposition rates (∼0.45 μm h −1 ). These observations are explained in terms of the effects that nitrogen, and its resulting reaction products (NH 3 , HCN, CH 3 NH 2 , etc.), have on the gas-phase chemistry occurring during the CVD process. In particular, we suggest that N 2 can act as a catalyst for the destruction of H atoms, which in turn leads to significant changes in the gas-phase chemistry.

Gas-phase composition measurements during chlorine assisted chemical vapor deposition of diamond: A molecular beam mass spectrometric study

We have constructed a molecular beam mass spectrometer designed specifically to sample gases from a diamond chemical vapor deposition ~CVD! process chamber thereby enabling characterization of the gas-phase CVD environment. With this in situ diagnostic technique we have obtained quantitative measurements of the composition of the gas-phase species as a function of filament temperature for a variety of C/H/Cl gas mixtures. The precursor mixtures used were 1% of a chloromethane (CH 42n Cl n , n51-4! in hydrogen and 1% CH 4 in hydrogen with added Cl 2 varying from 1% to 4%. At filament temperatures optimum for diamond growth (2300°C! the relative CH4/C2H2/C2H4 product distribution measured in the gas mixture is remarkably similar to that established when CH4 is the carbon precursor species. At these filament temperatures almost all the chlorine is reduced to HCl, its concentration being proportional to the Cl fraction in the source gas, regardless of the form of the chlorine in the source gas mixture. Compositional analysis of the as-grown diamond films indicated that no chlorine was present in the bulk of the films, though trace amounts of chlorine were detected on the film surface. From these observations we surmise that chlorine atoms are involved in the gas-surface reactions which produce active growth sites on the diamond surface.

Investigation of the addition of nitrogen-containing gases to a hot filament diamond chemical vapour deposition reactor

Abstract We have investigated the effect that addition of various nitrogen-containing gases, such as ammonia, methylamine and HCN, has on the composition of the films deposited in a standard hot filament diamond chemical vapour deposition reactor. Total process gas concentration (C + N) was maintained at 1% in H 2 throughout the experiments. When using a feedstock of methane and ammonia, we generally find that for methane-rich mixtures diamond films are formed; for ammonia-rich mixtures, silicon nitride is formed by reaction of the ammonia with the Si substrate; for approximately equal ratios of CH 4 to NH 3 , little film deposition occurs. Other gases, such as CH 3 NH 2 and HCN, behave similarly to 1:1 mixtures of CH 4 and NH 3 . Results are explained in terms of a simple chemical model of the gas phase chemistry and surface interactions.

In situ plasma diagnostics of the chemistry behind sulfur doping of CVD diamond films

Microwave plasma enhanced chemical vapour deposition (CVD) has been used to grow sulfur doped diamond films using a 1% CH yH gas mixture with various levels of H S addition (100–5000 ppm), upon undoped Si substrates.X-Ray photoelectron 42 2 spectroscopy has shown that S is incorporated into the diamond at number densities (F0.2%) that are directly proportional to the H S concentration in the gas phase.Four-point probe measurements showed the resistivity of these S-doped films to be a 2 factor of three lower than undoped diamond grown under similar conditions.Sulfur containing diamond film was also obtained using a 0.5% CS yH gas mixture, although the high resistivity of the sample indicated that the sulfur had been incorporated into 22 the diamond lattice in a different manner compared with the H S grown samples.Molecular beam mass spectrometry has been 2 2 plasma region as a result of gas phase reactions.Additional measurements from a 1% CS yH plasma gave similar species mole 22 fractions except that no CS was detected.These results suggest that CS may be the first step toward C–S bond formation in the film and thereby a pathway allowing S incorporation into diamond.Optical emission spectroscopy has shown the presence of S 2 in both gas mixtures, consistent with the observed deposition of sulfur on the cool chamber walls. 2002 Elsevier Science B.V. All rights reserved.

In-situ mass spectrometric study of the gas phase species involved in CVD of diamond as a function of filament temperature

Abstract We have used a molecular beam mass spectrometer to obtain quantitative measurements of the composition of the gas-phase species during the chemical vapour deposition (CVD) of diamond films as a function of filament temperature for a variety of different hydrocarbon precursor gases. For filament temperatures near to, and above, the optimum for diamond growth (ca. 2400 K), we find that the relative concentrations of the various stable hydrocarbon species (CH 4 , C 2 H 2 and C 2 H 4 ) present in the gas mixture, and the way that these concentrations vary with temperature, are remarkably insensitive to the particular choice of hydrocarbon feedstock gas.

CVD diamond coated fibres

Abstract Diamond-coated fibres have been fabricated using hot filament chemical vapour deposition (CVD) and tested for mechanical stiffness. The fibres coated include small (

Sub-doppler spectroscopy of the C′ v2 = 2 Rydberg level of ND3 at vacuum ultraviolet energies

A pulsed dye laser amplifier for cw lasers has been constructed. By frequency doubling the output pulses, and using counter-propagated beams with 2 + 1 multiphoton ionisation detection, very high resolution spectroscopic studies of atomic and molecular states lying at vacuum ultraviolet energies have become possible. The effective VUV two-photon bandwidth was determined from a sub-Doppler 6s7s 1S0−6s2 1S0 excitation spectrum of mercury vapour, and found to be 275 MHz (0.009 cm−1) fwhm. The 220 band in the C′1A′1X1A1 Rydberg transition of ND3 shows very narrow sub-Doppler linewidths, of which the narrowest, with J = K = 0, has a deconvoluted homogeneous width of 350 MHz in our experiment, corresponding to a lifetime of 0.45 ns. The general trend of an increase in linewidth with rotational excitation is consistent with rovibronic coupling to the continuum of the A1A″2 state. In addition, a number of apparently random level shifts and anomalously weakened lines is attributed to a perturbation, most probably by the overlapping and more severely predissociated v 2 = 8 level of the B 1E″ state, acting as an additional doorway to the dissociative A state levels.

Molecular beam mass spectrometry studies of the gas-phase chemistry occurring during microwave plasma assisted chemical vapour deposition of diamond

A molecular beam mass spectrometer has been used for in-situ studies of the gas-phase composition during microwave plasma chemical vapour deposition of diamond, in a way that decouples the gas-phase reactions from those occurring near the substrate surface. The system has been used to examine the plasma composition for a variety of hydrocarbon precursor-in-H 2 feedstock gas mixtures. Stable hydrocarbon species, and the methyl radical signal, were recorded and calibrated to give mole fractions of all the carbon-containing species present at detectable levels. The plasma composition has been studied with varying chemical vapour deposition process parameters such as applied microwave power, and concentration of hydrocarbon in the feed gas. Molecular beam mass spectrometry has also been used to determine the plasma gas temperature, yielding results in good agreement with non-invasive methods.

Diamond deposition in a DC-arc Jet CVD system: investigations of the effects of nitrogen addition

Abstract Studies of the chemical vapour deposition of diamond films at growth rates >100 μm h −1 with a 10-kW DC-arc jet system are described. Additions of small amounts of N 2 to the standard CH 4 /H 2 /Ar feedstock gas results in strong CN(B→X) emission, and quenches C 2 (d→a) and H α emissions from the plasma. Species selective, spatially resolved optical emission measurements have enabled derivation of the longitudinal and lateral variation of emitting C 2 , CN radicals and H ( n =3) atoms within the plasma jet. Scanning electron microscopy and laser Raman analyses indicate that N 2 additions also degrade both the growth rate and quality of the deposited diamond film; the latter technique also provides some evidence for nitrogen inclusion within the films.

Gas-phase concentration measurements and diamond film composition from chlorine assisted CVD

Abstract Molecular beam mass spectrometry has been used to obtain quantitative measurements of the composition of the gas-phase species prevailing during diamond chemical vapour deposition (CVD) using a variety of chlorine containing source gases. Gas mixtures used were 1% of a chlorinated methane (CH4 −n,Cln,n = 1 − 4) in H2 and 1% CH4 in H2 with added chlorine varying from 1%–4%. At filament temperatures optimum for diamond growth (≈2300 °C) the relative concentrations of the various hydrocarbon species (CH4, C2H2, C2H4) in the gas mixture are remarkably similar to those measured when the carbon precursor species is CH4. At these filament temperatures almost all the chlorine is reduced to HCl, its concentration being proportional to the chlorine fraction in the source gas, regardless of the form of the chlorine in the input mixture. Auger electron spectroscopy analysis of the as-grown diamond films indicated that no chlorine was present in the bulk of the films, though trace amounts of chlorine were detected on the film surface. These observations are consistent with the supposition that chlorine atoms are involved in the gas-surface reactions which produce active growth sites on the diamond surface.