G. Sánchez

Internal stress and strain in heavily boron-doped diamond films grown by microwave plasma and hot filament chemical vapor deposition

The internal stress and strain in boron‐doped diamond films grown by microwave plasma chemical vapor deposition (MWCVD) and hot filament CVD (HFCVD) were studied as a function of boron concentration. The total stress (thermal+intrinsic) was tensile, and the stress and strain increased with boron concentration. The stress and the strain measured in HFCVD samples were greater than those of MWCVD samples at the same boron concentration. The intrinsic tensile stress, 0.84 GPa, calculated by the grain boundary relaxation model, was in good agreement with the experimental value when the boron concentration in the films was below 0.3 at.%. At boron concentrations above 0.3 at.%, the tensile stress was mainly caused by high defect density, and induced by a node‐blocked sliding effect at the grain boundary.

Pulsed laser deposition of diamond from graphite targets

Diamond crystals of 1 μm mean size were grown on (100) silicon substrates by ArF (193 nm) laser ablation of graphite in a hydrogen atmosphere with a laser power density of 1.3×108 W/cm2 at relatively low substrate temperature (450 °C). Raman spectroscopy analysis confirmed the diamond cubic structure of the crystals by the presence of a sharp peak at 1332 cm−1. When a KrF (248 nm) laser was used instead of the ArF no diamond phases were detected in the deposited films and the Raman spectra showed only the two bands centered at 1340 and 1600 cm−1 characteristic of amorphous carbon. The results demonstrated that the laser wavelength is a determinant parameter in the growth of diamond by laser ablation of graphite.

Synthesis of cubic aluminum nitride by carbothermal nitridation reaction

Abstract Cubic aluminum nitride (AlN) was synthesized by the carbothermal nitridation reaction of aluminum oxide (Al 2 O 3 ). The effects of Al 2 O 3 particle size, reaction temperature and reaction time on the synthesis of cubic AlN were investigated, and the reaction mechanism was also analyzed. The results showed that cubic AlN could be formed at a lower temperature with fine Al 2 O 3 powder than with coarse Al 2 O 3 powder. The cubic AlN may be the product of Al 23 O 27 N 5 synthesized from Al 2 O 3 and hexagonal AlN, and transforms into hexagonal AlN at temperatures above 1800°C.

Diamond and diamond-like carbon films

Abstract Polycrystalline diamond films are grown from low pressure gas mixtures, the deposition techniques are Microwave Plasma Chemical Vapour Deposition and Hot filament Chemical Vapour Deposition, in both techniques the deposition temperature is close to 900°C. The film growth process is strongly dominated by the initial nucleation stage, after this stage, the film grows at a rate of one micron per hour. The carbon atoms in the diamond film are fully fourfold (sp 3 ) co-ordinated and the film properties are close to those of single crystalline diamond: extremely hard, resistant and transparent from UV to IR. Diamond-like carbon (DLC) films are amorphous and contain a variable amount of hydrogen in their structure, the carbon atoms are partially threefold (sp 2 ) co-ordinated. Films are obtained at temperatures below 250°C and deposited on almost any substrate. Film composition, structure and functional properties are strongly dependent on the level of ionic bombardment of the film during growth. DLC films are very hard, have a low friction coefficient and good wear resistance, are chemically inert and are transparent in the IR.

Nucleation and initial growth of bias-assisted HFCVD diamond on boron nitride films

Abstract Diamond was grown on boron nitride thin films deposited on silicon substrates. The effects of substrate biasing on the nucleation and growth of diamond were studied. Boron nitride (BN) films were obtained by rf plasma CVD. FT-IR analysis of the BN films revealed a hexagonal structure and a high transparency. The diamond deposition process was carried out in a bias-assisted hot filament reactor. Both positive and negative biases relative to the filament were applied to BN-coated Si substrates. The density and morphology of the diamond crystallites in the early stages of the nucleation were studied by scanning electron microscopy. We found that negative substrate biases higher than 200 V greatly increased the nucleation density of diamond, reaching a maximum of 1010 cm−2 for −250 V. After the nucleation stage, continuous diamond films were grown under standard deposition conditions and Raman analysis revealed the high quality of the diamond films.

Atomic force microscopy observation of the first stages of diamond growth on silicon

Abstract The first stages of diamond growth on scratched silicon substrates were studied by atomic force microscopy (AFM). Samples were obtained by both hot filament and microwave plasma CVD methods at short deposition times prior to coalescence. It was observed that, after an incubation time, diamond nanocrystals nucleated onto the scratches produced by diamond paste polishing. The Raman spectra of the crystals showed different bands associated with several carbon phases. Simultaneous with diamond growth, we detected an etching effect of the silicon surface attributed to the atomic hydrogen present in the activated gas.

Growth of diamond by laser ablation of graphite

Thin film growth by laser ablation deposition has been established as a useful method for obtaining films of novel materials on different substrates. The high energy of the emitted particles in the ablation process could be used to obtain diamond thin films at relatively low substrate temperatures. We tried this technique to grow carbon films with a high amount of diamond phases from a pyrolytic graphite target. The laser is an excimer laser (ArF, λ = 193 nm) focused at a fluence of 3 J cm−2 and operating at 5 Hz repetition rate. The films were grown on (100) silicon substrates at 450 °C. The films were deposited under (a) vacuum conditions, (b) 1 mbar of hydrogen or (c) 1 mbar of helium to determine the influence of a gas atmosphere in the growth process. Scanning electron microscopy demonstrated the growth of diamond on silicon substrates with crystals as big as 20 μm. Raman spectroscopy studies of the films showed the peak at 1332 cm−1 characteristic of the diamond structure, even for vacuum deposition conditions.

Piezoresistivity of p-type heteroepitaxial diamond films on Si(100)

Abstract The piezoresistive effect of p-type heteroepitaxial diamond films was investigated. The films were grown by microwave plasma chemical vapor deposition and in situ boron doping was performed by cold ion implantation and rapid thermal annealing. The strain gauge was made by ion etching in an oxygen plasma. The gauge factor for the heteroepitaxial p-type diamond films at 100 microstrain was found to be 1200 at room temperature and was 980 even at 200 C, greatly exceeding that of polycrystalline diamond films. The gauge factor did not change after pure acid treatment for up to 8 h, and little variation was found under ion irradiation.

Nucleation of diamond on silicon by biased HFCVD: A comparative study

Abstract The first stages of diamond deposition on pristine silicon by the bias assisted hot filament CVD technique were studied. Two different experimental setups were used to clarify the role played by negative bias in the nucleation process. In the first setup, a negative bias was applied directly to the substrate. For negative biases in the 300 V range, a great increase of the nucleation density was found, with values up to 10 10 cm −2 , which was six orders of magnitude higher than that obtained when no bias was used to assist the process. AES and Raman analyses revealed that the material formed under such biasing conditions was basically a mixture of diamond and sp 2 carbon. In the second setup, a negatively biased diamond coated tungsten electrode was placed between the filament and the substrate. In this case, diamond formation was detected by AES and Raman measurements even for very short bias times. Bias voltages higher than 300 V markedly enhanced diamond nucleation density, although this enhancement was not as notable as in the first setup. In both cases, XPS and AES studies detected the presence of SiC as a result of bias treatment.

Growth of diamond films on boron nitride thin films by bias-assisted hot filament chemical vapor deposition

We report the growth of continuous diamond thin films by bias-assisted hot filament chemical vapor deposition onto hexagonal boron nitride films prepared by plasma chemical vapor deposition on silicon substrates. Negative substrate biasing during the early stages of diamond growth greatly increased the nucleation density. Values of 1010 cm−2 were achieved at −250 V for bias times as short as 25 min. After the nucleation stage, high quality polycrystalline continuous diamond films, as revealed by scanning electron microscopy and Raman analysis, were grown under standard hot filament deposition conditions.