A.A. Smolin

Large-area diamond deposition by microwave plasma

Abstract Diamond films of up to 1 mm thickness and of 30 cm2 area have been grown in a 8 kW MW plasma reactor ASTeX PDS-19 using CH4/H2/O2 gas mixtures. Growth rate, film thickness radial profiles, diamond morphology and quality were evaluated in dependence substrate temperature (T=690–900° C), and feed gas composition (CH4/H2=2.5%, O/C=0-0.7). Translucent diamond wafers have been produced without any sign of nondiamond carbon phases. Raman diamond peak being as narrow as 2.5 cm−1. The presence of some impurities (N, H, Si and Al) was detected and analyzed with SIMS and IR optical absorption spectroscopy. An interesting type of diamond growth instability at certain deposition conditions is observed that manifests itself in the form of accelerated growth of selected diamond crystallites of very big lateral size (≈ 1 mm), and of more perfect structure compared to the rest of the film.

D.c. arc plasma deposition of smooth nanocrystalline diamond films

We report on chemical vapour deposition growth of nanocrystalline (grain size 30–50 nm) diamond films of 100 nm to 2 μm thickness in methane-rich mixtures. A d.c. arc discharge in CH4H2Ar gas mixtures with a methane percentage CH4(CH4 + H2) varied from 10% to 100% was used for diamond deposition on Si substrates seeded with ultrafine (5 nm) diamond particles. The films obtained were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray excited Auger electron spectroscopy. Remarkably well-crystallized diamond films were produced even in hydrogen-free gas mixtures. Raman spectra confirmed the nanocrystalline structure of all the films examined. The film hardness measured with a nanoindenter was in the range 70–85 GPa typical for diamond, the highest values corresponding to 100% methane content. The films were very smooth with surface roughness Ra < 20 nm. The essential improvement in surface smoothness was obtained by means of laser-induced disintegration of coalesced seeding particles.

Smoothening of diamond films with an ArF laser

Abstract Polycrystalline diamond films of various microstructures were modified by large-area ArF laser irradiation. The modified film surfaces were characterized employing electron microscopy, mechanical profilometry and optical reflectometry. Laser irradiation was found to smooth the surface finish over a wide range of spatial frequencies covering microroughness imposed by the individual crystallites as well as waviness with periods exceeding the crystal sizes. No smoothening was achieved, however, for chemically non-uniform diamond films. The results can be rationalized in terms of laser-induced surface evaporation. Resistivity measurements revealed the simultaneous formation of a highly stable conductive surface layer upon laser irradiation.

Laser-induced forward transfer of ultra-fine diamond particles for selective deposition of diamond films

Abstract A laser-induced forward transfer (LIFT) technique is used for area-selective prenucleation of Si substrates with ultra-fine diamond powder for subsequent diamond film deposition via a conventional CVD process. The influence of the laser parameters (wavelength, energy density, etc.) on the features of the ablation-deposition process is experimentally studied with the aim of improving the spatial selectivity of diamond patterning.

Photodetectors with CVD diamond films : electrical and photoelectrical properties photoconductive and photodiode structures

Free-standing and silicon-supported diamond films have been used to fabricate photoconductive and photodiode structures for UV light detection. Planar and sandwiched photoconductive structures have been made on microwave plasma-grown free-standing CVD polycrystalline diamond films of 200 μm and 15 μm thicknesses, respectively. A photodiode sandwich structure was obtained on thin (≈2 μm) boron-doped diamond films grown on silicon substrate by hot filament CVD. Parameters of defects in the structures were studied by charge-based deep-level transient spectroscopy (Q-DLTS). Planar photoconductive detectors after annealing in air showed a low dark current < 10 pA and a high spectral discrimination-a 104 higher response to 200 nm than to visible (600 nm) wavelengths. The dark current was < 10 pA. The turn-off time of the device following exposure to light was less then 10 ms. It was found that the annealing in air decreases density of point defects more than order and strongly increases wavelength discrimination. The sandwich photodiodes showed a sharp cut-off in photoresponse at 220 nm with a quantum yield of about 0.3 and a photovoltage in the open circuit regime of up to 1.6 V. Such photodiodes can be used not only for light detection but also for light energy transformation into electrical energy as in a photovoltaic cell.

Fine patterning of diamond films by laser-assisted chemical etching in oxygen

Abstract We report on the use of low power (~2 W) continuous wave Ar+ laser for etching (engraving) of diamond films via a laserinduced local oxidation (burning) reaction. Smooth fine-grained diamond films of about 10 μm thickness have been grown on Mo and Si substrates in a d.c. arc discharge using CH 4 H 2 gas mixtures. The sharply focused laser beam was scanned under computer control over the film surface causing fast diamond oxidation in air or pure O2 atmosphere. The dependence of etch rate on laser power, beam scanning velocity and film quality was examined. Various grooves and holes of a few micrometres in size have been produced with etch rate of tens of micrometres per second.

Thermal conductivity of thin diamond films grown from d.c. discharge

Abstract The in-plane thermal conductivity of thin polycrystalline diamond films produced in a d.c. discharge system has been measured by a contactless technique of transient thermal grating. Diamond films of different qualities but of the same thickness (11 μm) were deposited from CH4/H2 mixtures at methane contents ranging from 2% to 10%. The highest thermal conductivity k = 9.5 W cm−1 K−1 was found for the sample synthesized at the lowest CH4 concentration (2%), the value of k smoothly decreasing to 1.2 W cm−1 K−1 with increasing methane content. The obtained results are in good agreement with previous measurements on similar films performed by the mirage technique. A correlation of thermal conductivity with film morphology and phase content analyzed by SEM and Raman spectroscopy is discussed.

Analysis of intrinsic stress distribution in grains of high quality CVD diamond film by micro-Raman spectroscopy

Micron-scale mapping of intrinsic stress in a free-standing chemical vapor deposition diamond film was performed by analysis of splitting and shift of the Raman diamond line. Stress distribution within individual grains was observed for high quality (line width of 2.8‐3.0 cm -1 ) 600 mm thick free-standing film grown by microwave plasma enhanced chemical vapor deposition. It has been shown that all the variety of the Raman diamond line shapes observed can be presented by a superposition of two symmetric components with narrow widths. In some cases the two components can be completely resolved in succession by polarization analysis. (110)-Oriented crystals reveal anisotropic stress fluctuations up to 9 GPa of both signs (compressive and tensile). For grain sizes of 100‐200 mm high stressed regions of 200‐300 mm 2 area located in the vicinity of edges and grain boundaries have been detected. Possible sources of the high stresses of both signs related to defect and impurity distributions within the grain are discussed.

Tribological properties of smooth diamond films

The friction and wear properties of smooth diamond coatings sliding against a monocrystalline ruby ball were studied using a pin-on-disk tribometer. The smooth diamond film surface was prepared either by (i) deposition of ultrathin nanocrystalline films in the thickness range from 0.2 to 2 μm or by (ii) postgrowth polishing. Excimer laser surface ablation, microwave plasma etching and mechanical lapping with diamond grit were used for postgrowth polishing. A correlation of film surface properties examined with different techniques (atomic force microscopy, Auger electron spectroscopy, Raman spectroscopy, stylus profilometry) and the tribological properties of the diamond films tested was established. The influence of laser-induced surface graphitization on the friction coefficient of laser-polished films was investigated.

Nanocrystalline diamond films: new material for IR optics

Thin nanocrystalline diamond films promising for IR optical applications were grown on Si substrates from methane-hydrogen gas mixture in a DC arc plasma CVD reactor. Three stages for the synthesis of the highly smooth noncrystalline diamond films are important: (i) substrate pretreatment with ultrafine diamond powder, (ii) excimer laser irradiation of seeded substrates, and (iii) two-step deposition process. A correlation between optical properties of the films and growth conditions has been established by means of Raman spectroscopy, spectroscopic ellipsometry and optical transmission spectroscopy techniques. Surface roughness, which was Ra equals 8 - 40 nm for the 1 micrometers thick films, significantly decreased the transmission in the visible because of light scattering, but it had a negligible effect in the IR range. The films are transparent in the IR and have optical constants n equals 2.34-2.36 and k equals 0.005- 0.03. The hydrogen incorporation in the films in amounts up to 1.5% have been deduced from intensity of C-H absorption band around 2900 cm(superscript -1.