Advances in diamond film growth have prompted us to study the interfaces involved in this process: the interface with the substrate, and the growth interface with the ambient hydrocarbon vapor. Carbon chemistry lies at the heart of the properties of both interfaces, and much of the relevant chemistry is not well understood. We report here the energies involved in some idealized chemical processes that may be important in the growth process. Results (Schottky barriers, interface energies) for diamond/metal interfaces are also reported, and the especially unusual diamond/nickel results we have recently obtained are discussed in some detail.

A new technique has been developed to grow semiconductor grade diamond substrates with dimensions comparable to those of currently available Si wafers. Previously, the synthetic single crystal diamond that could be grown measured only a few millimeters across, compared with single crystal Si substrates which typically are 10 to 15 cm in diameter. In the technique described, an array of features is first etched in a Si substrate. The shape of the features matches that of inexpensive, synthetic faceted diamond seeds. A diamond mosaic is then formed by allowing the diamond seeds to settle out of a slurry onto the substrate, where they become fixed and oriented in the etched features. For the experiments reported, the mosaic consists of seeds ∼ 100 μm across on 100 μm centers. A mosaic film is obtained by chemical vapor deposition of homoepitaxial diamond until the individual seeds grow together. Although these films contain low angle (<1°) grain boundaries, smooth, continuous diamond films have been obtained with electronic properties substantially better than those of polycrystalline diamond films and equivalent to those of homoepitaxial single crystal diamond films. The influence of growth conditions and seeding procedures on the crystallographic and electronic properties of these mosaic diamond films is discussed.

A low pressure chemical vapor deposition technique using water-alcohol vapors has been developed for the deposition of polycrystalline diamond films and homoepitaxial diamond films. The technique uses a low pressure (0.50 – 1.00 Torr) rf-induction plasma to effectively dissociate the water vapor into atomic hydrogen and OH. Alcohol vapors admitted into the chamber with the water vapor provide the carbon balance to produce diamond growth. At 1.00 Torr, high quality diamond growth occurs with a gas phase concentration of water approximately equal to 47% for methanol, 66% for ethanol, and 83% for isopropanol. A reduction in the critical power necessary to magnetically couple to the plasma gas is achieved through the addition of acetic acid to the water.alcohol solution. The lower input power allows lower temperature diamond growth. Currently, diamond depositions using water:methanol:acetic-acid are occurring as low as 300 ° C with only about 500 W power input to the 50 mm diameter plasma tube.

We have applied an electron cyclotron resonance technique to deposit diamond thin films on various substrates under remote plasma, low temperature (600°C) and low pressure (60 mTorr) conditions. Diamond films were grown on different substrates (silicon, molybdenum) with varying concentrations of precursor gases (methanol and water). A positive substrate bias (50 to 60 V) was found to be essential for the growth of diamond films onto substrates positioned 16 cm below the ECR plasma. The films were characterized by Raman, X-ray diffraction and scanning electron microscopy for microstructure, phase purity and chemical bonding characteristics. The effect of various processing parameters including gas pressure, gas composition, substrate temperature and bias have also been analyzed.

Polycrystalline diamond films were synthesized both by using an open atmosphere combustion flame, and also using a combustion flame in an enclosed chamber. By operating the pre-mixed oxy-acetylene torch in a chamber, we were able to vary the atmosphere around the flame in a controlled manner and study the effects on the diamond films. Varying the atmosphere around the flame is of interest to control the incorporation of unwanted gases, such as room air, and to obtain finer control over the flame properties. We report on the properties of films grown in the open atmosphere and in the chamber with oxygen and argon.

We have constructed a novel, sequential DC glow and hot filament CVD reactor, to study the influence of single parameters on the deposition of diamond thin films. This reactor is capable of growing diamond films, with independent excitation of hydrogen and methane. This is achieved by the sequential exposure of the substrate to spatially separated, chemically independent, plasma regions of hydrogen, and methane in helium. The substrate is mounted on a rotating plate above the gas sources at a variable distance, typically 0.5 – 2 mm. The plate is radiantly heated from behind to a desired temperature up to 1300 K. Using the sequential deposition chamber we have been able to deposit good quality diamond up to 8% methane in helium, without the presence of oxygen, by separating a source of atomic hydrogen and a source of methane. These experiments show that methane and atomic hydrogen do not need to be present simultaneously to grow diamond. Our results further indicate that the primary critical parameter for both quality and growth rate, in hot filament deposition of diamond, is the concentration of atomic hydrogen in the system.

Diamond thin films were grown on a scratched silicon crystal surface by a novel CVD technique. The heated substrate, mounted on a rotating platform, was exposed to a bombardment of sputtered carbon atoms, from a graphite target in a helium plasma, and subsequently bombarded by atomic hydrogen generated by a hot tungsten filament. The resulting diamond films were characterized by Raman spectroscopy and SEM. The SEM images indicate highly faceted diamond crystals and the Raman spectra show a single narrow peak characteristic of pure diamond with no graphitic component. The effective growth rate is about 0.5 microns per hour of exposure time. The novel sequential CVD reactor is described and possible growth mechanisms are discussed.

Rudder et al. [1] observed heavy (>109 cm-2) diamond nucleation on unscratched Si wafers overlaid with carbon fibers during CVD growth. We demonstrate that the nucleation occurs on the edges of etch pits and carbon-rich particles resulting from reaction between the fibers and the substrate. Both the etch pits and the particles satisfy what we consider to be two necessary conditions for ‘spontaneous’ nucleation; a carbon-saturated surface and high energy sites (unsatisfied valencies) at edges and steps.

The growth of CVD diamond onto iron based substrates is complicated by preferential soot formation and carbon diffusion into the substrate, leading to poor quality films and poor adhesion. One strategy to overcome these problems is the use of thin film barrier layers between the Fe substrate and the growing diamond film. The present investigation reports the growth of diamond films on Fe substrates coated with thin films of TiN. The effectiveness of the TiN layers in inhibiting C diffusion into the Fe substrate was investigated by Auger measurements of the C distribution within the TiN layer, through the interface and into the substrate both before and after diamond deposition.

The results show that a layer of TiN only 250Å thick is sufficient to inhibit soot formation and C diffusion into the Fe bulk, as well as providing nucleation sites for CVD diamond growth.

Diamond crystals have been selectively grown on the apex of anisotropically chemically etched silicon pyramids. A novel process sequence is developed which exposes patterned sharp apex of silicon pyramids surrounded by thermally grown silicon dioxide to a high pressure microwave plasma-assisted chemical vapor deposition (HPMACVD) process where the reactant feed gases are methane and hydrogen. Nucleation rate of diamond is very high on the sharp edge of a silicon mesa structure or an apex of a silicon pyramid as anticipated. Selective growth of diamond particles on the apex of silicon pyramids fabricated using various approaches were analyzed by scanning electron microscopy.

We have analyzed the non-equilibrium thermal effects of pulsed nanosecond lasers on carbon-implanted copper substrates. The thermal effects of pulsed nanosecond lasers were simulated by numerically solving the heat flow equation and taking into account the phase changes which occur at the surface of the irradiated solid. Intense pulsed laser irradiation induces rapid heating at the near surface resulting in melting, followed by rapid quenching of the melt phase. The effect of laser variables (energy density, etc.) on the maximum melt depth, melt-in and solidification velocities and transient temperature profiles have been computed. Maximum melt depths and the surface temperatures were found to increase approximately in a linear manner with pulse energy density. Extremely high average solidification velocities (20–45 m/sec) were calculated which may give rise to solute trapping and other non-equilibrium segregation effects. The change in laser-irradiated characteristics of copper substrates as a result of carbon-ion implantation is also discussed.

Present state of the work devoted to the control of properties of diamond is analyzed, with emphasis on the results obtained in USSR, including the data on ion implantation and several types of devices. Future possibilities of the work with single crystals, films and diamond ceramics are discussed and typical difficulties indicated.

High resolution cathodoluminescence (CL) spectroscopy and imaging have been performed in transmission electron microscopy (TEM) to analyze defects and impurities in polycrystalline diamond films grown by chemical vapor deposition (CVD) using a variety of gas mixtures, and oxyacetylene combustion flame synthesis (CFS). The combination of CL and TEM allows a direct correlation of film microstructure with the electronic structure due to defects. The CL was found to be very nonuniformly distributed on a submicron scale reflecting different spatial distributions of N, B and Si impurities and their correlations with microstructure. Band A CL due to closely-spaced donor-acceptor (D-A) pairs was correlated with dislocations in both CVD-grown and CFS material whereas band A from widely-separated D-A pairs was uniformly distributed in the films. CL from several different N-related point-type defects was observed and found to depend on the growth gases used, although no correlation with microstructure has been observed so far. A di-Si interstitial impurity, believed to arise from the Si substrate and reactor walls, was not correlated with any microstructure but varied greatly in concentration from grain to grain and from film to Film. In addition, both highly faulted and defect-free grains were found to emit no visible CL due to mid gap states.

Diamond (111) surfaces with the dehydrogenerated 2×1 reconstruction have been exposed to a beam of atomic fluorine at 300 K. The uptake of fluorine, as measured using X-ray photoelectron spectroscopy, is quite efficient and saturates at a coverage of less than a monolayer. Low energy electron diffraction patterns indicate that fluorine termination of the diamond surface produces a lxi bulk-like reconstruction in contrast to the disordered surface produced on the (100) surface.

Undoped and boron-doped diamond epitaxial films were deposited on diamond(001) substrate by micro-wave plasma assisted chemical vapor deposition and their surfaces were studied by scanning tunneling microscopy in air. An atomic order resolution was confirmed for the observation.

For the undoped epitaxial films, which showed 2×1 and 1×2 RHEED patterns, dimer type reconstruction was observed and it was considered that the growth occurs through the dimer row extension. In the case of B-doped films, the dimer reconstruction was also observed. However, 2×2 structure due to the absence of dimer was partially observed.

The effect of boron concentration and methane concentration during epitaxial growth on the surface morphology were also studied. The morphology observed by STM became flatter, as the concentration of B-doping and methane concentration, during growth, increased.

Auger spectroscopy is used to determine the bonding states of carbon in the interfacial region between silicon and PECVD diamond films. SiC and sp2-hybridized carbon are observed. We suggest a possible growth sequence for diamond films to account for the interfacial layer.

We report an essentially complete characterization of energies and relaxation processes of the lowest seven electronic states of the N-V (nitrogen-vacancy) center in diamond using several different nonlinear laser spectroscopie techniques. We have also applied ultrafast optical techniques to measure dielectric properties of CVD and bulk diamond in the 0.3–1.6 THz range for the first time.

We have studied the electrical properties of boron doped composite films that consist of diamond and amorphous carbon. These films were deposited by hot filament chemical vapor deposition at a relatively high carbon/hydrogen ratio. The mixture of trimethyl borate vapor, and methane served as a source gas. The composite films had much smoother surfaces than polycrystalline diamond films.

The surface morphology and average roughness were determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Raman spectroscopy and x-ray diffraction were used to analyze the structure of the films.

A composite film grown with 4% methane in hydrogen had a higher resistivity than a well faceted diamond film grown at 0.5% methane. In contrast to hydrogenated amorphous carbon films which have a lower resistivity after thermal annealing, the resistivities of composite films increased by a factor of two to ten after 3 hours annealing at 600°C.

Raman scattering and photoluminescence spectroscopies have been used to characterize polycrystalline diamond films deposited on molybdenum substrates by laminar and turbulent premixed oxygen-acetylene flames in air. Samples deposited under laminar flame conditions are characterized by a high degree of incorporation of nitrogen-vacancy complexes. However, samples deposited with a turbulent flame show a significant decrease in the concentration of these defects and a reduction of the amorphous carbon film component.

We describe the applicability of oxygen based Electron Cyclotron Resonance (ECR) etching of diamond for the purpose of fabricating electronic test structures and recessed gate field effect transistors. Boron doped homoepitaxial diamond films grown in a microwave assisted CVD reactor were used for this study. Etch rates from 8 nm/min up to 0.5 μm/min. were achieved depending on etch parameters.