R.E. Clausing

Textures and morphologies of chemical vapor deposited (CVD) diamond

Abstract The textures, surface morphologies, structural perfection, and properties of diamond films grown by activated chemical vapor deposition (CVD) vary greatly with the growth conditions. The evolution of two commonly observed polycrystalline morphologies, which give rise to 〈110〉 textures, will be described as well as the development of four films grown to produce 〈100〉, 〈111〉 and “near 〈100〉” textures with various combinations of growth facets. These films were grown to test models of texture development. Films free of twins, microtwins, and stacking faults are deposited when only {100} facets are permitted to grow. In polycrystalline materials, special conditions must be met to avoid the formation of planar defects at the peripheries of individual crystallites. The planar defects grow from {111} or mixed microfaceted surfaces. Twinning plays an important role in the growth of {111} faceted surfaces. The films have been characterized with Raman spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical methods.

Measurement of crystalline strain and orientation in diamond films grown by chemical vapor deposition

We have used x-ray diffraction to characterize diamond films grown in three characteristic morphologies by chemical vapor deposition. Each morphology has a fiber texture about the growth direction; we report the crystal axis aligned in this direction for each morphology. In all cases the average lattice constant agrees with that of bulk diamond; we report the range of strain in each sample.

Electron microscopy of the growth features and crystal structures of filament assisted CVD diamond films

Abstract Scanning and transmission electron microscopy (SEM and TEM) have been used to examine the topographic and internal features of diamond films grown by the hot filament assisted chemical vapor deposition method. Films were grown under conditions chosen to provide three distinctly different diamond microstructures. One of these film structures is virtually free of stacking faults and twins within the grains. This paper relates internal and external growth features to each other, to Raman spectra and to the growth conditions. The growth features are discussed in terms of growth mechanisms.

X-ray and optical characterization of three growth morphologies of CVD diamond films

Abstract Using X-ray texture measurements and optical goniometry, we have determined the texture and facet orientation of diamond films grown by CVD with three distinct morphologies. The first morphology has { 111} and {100} facets and a texture which is attributed to preferential growth as the result of rapid nucleation of atomic layers at {111} twin boundaries. The second morphology has {100} facets and a texture which may be due to the influence of surface diffusion on growth competition. The third morphology has {111} facets and a texture which is attributed to competition of uniformly growing grains.

The role of H2O in enhancing hot filament assisted diamond growth at low temperatures

The addition of a small amount of oxygen to a hot filament assisted chemical vapor deposition reactor allows diamond to be deposited at significantly lower filament and substrate temperatures. Scanning electron microscopy and Raman spectroscopy are used to compare films grown with and without oxygen addition as a function of substrate temperature at high and low filament temperatures. Oxygen addition is found to favor growth of high quality diamond at low substrate temperatures (<600 °C). The amount of nondiamond carbon is reduced and the clarity and smoothness of facets improves dramatically under these conditions. Equilibrium calculations and residual gas analysis indicate there is H2O in the gas above the substrate during these depositions. The correlation between the dramatic reduction in the nondiamond carbon content of the films and the increased H2O levels near the substrate at low temperatures leads to the conclusion that H2O plays an important role in facilitating deposition at lower temperatures...

Effect of surface defects on CVD diamond nucleation on 6H SiC

Abstract The thin SiC layer often observed between a Si substrate and a diamond film has led to the belief that the formation of this SiC layer precedes diamond nucleation. However, the nucleation of diamond on a clean, undamaged SiC surface is difficult. Some of the defects introduced by abrading the surface of many substrate materials with diamond powder before deposition appear to serve as nucleation sites. Atomic-scale defects (vacancies, interstitials) and impurities can be introduced by ion implantation. Single-crystal 6H SiC with the external face composed of Si or C were implanted with silicon (150 keV) and carbon (55 keV) ions at fluences between 2 × 10 14 ions cm −2 and 2 × 10 15 ions cm −2 . Nucleation did not occur on as-received or implanted samples. Abrasion with diamond powder using an ultrasonic cleaner bath caused profuse nucleation on all samples. It was found that nucleation density on abraded samples decreased when implanted with increasing fluence of ions. Fluences of 2 × 10 14 Si + ions cm −2 (150 keV) and 4 × 10 14 C + ions cm −2 (55 keV) did not effect the nucleation of diamond on silicon carbide. However, a fluence of 2 × 10 15 Si + ions cm −2 completely suppresses the nucleation of diamond. Rutherford backscattering spectrometry/channeling studies on the high-fluence-implanted silicon carbide sample showed the presence of an amorphous surface layer suggesting that CVD diamond does not nucleate on amorphous SiC.

Crystallite geometry of hot filament chemical vapor deposited diamond

Abstract Diamond crystallites and thin films were grown on (100) Si using CH 4 , CO and H 2 gases flowing over a heated tungsten filament. The relative sizes of the {100} and {111} facets were used to characterize the growth rate ratio along these two crystal directions. The ratio depended upon the composition of the feed gases as well as the filament temperature. These results were discussed in terms of developing a specific texture in polycrystalline diamond and in terms, of adsorption mechanisms which could explain the dependence.

Surface-sensitive characterization of diamond by ionization electron energy loss spectroscopy

Abstract Ionization loss spectroscopy has been performed on diamond deposited by chemical vapor deposition and on graphite by use of conventional Auger equipment (backscattering geometry). The results are compared with reported data on natural diamond and on graphite. Polycrystalline chemical-vapor-deposited diamond exhibits a spectrum similar to that of natural, single-crystal diamond. Reference is also made to ionization loss spectroscopy in the transmission electron microscope and to near-edge, X-ray absorption fine structure measurements. The prominent features of the measured spectra are correlated with π and σ bonding. The applied method is sensitive to π bonding as well as being surface sensitive and, therefore, is particularly suited to check the deviation from perfect diamond bonding at the surface.

Growth Mechanisms of CVD Diamond Films Determined by a Novel TEM Technique

Abstract A novel transmission electron microscopy (TEM) technique is introduced for studying thick as-grown CVD diamond films. For a texture consisting of 2-3 μm-diam grains with (001) and {111} facets, we have found that the core volume bounded by the (001) top facet and orthogonal {110} (i.e., the volume shadowed by the (001) top) is free from microtwins and stacking faults, but may contain a few dislocations. The remaining volume around the core, bounded by {111} facets, is filled with microtwins. The formation of microtwins in CVD diamond is associated with growth on {111}. For a texture with only (001) and near {110} facets, the film is free from microtwins but contains more dislocations. A (001) twin-free column model is described to summarize all these observations.

Control of Texture and Defect Structure for Hot-Filament-Assisted CVD Diamond Films

The morphology of diamond films grown by activated chemical vapor deposition, (CVD), varies greatly depending on the deposition conditions [1–6]. Small changes in the deposition conditions can cause major changes in the film morphology and crystal perfection. Areas a few millimeters apart in a film may be quite different unless considerable care is taken to ensure uniform deposition conditions. Because the properties of diamond films are strongly dependent upon the crystallite size, orientation, and perfection, it is important to understand the way in which growth conditions affect the film structure in order to design and optimize films for specific applications.