Excimer Laser Induced Photolytic Deposition of Aluminum Nitride: Film Growth and Properties
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EXPERIMENT A number of different substrates, namely, GaAs (100), Si (100), fused quartz, and KBr, were used for depositing AIN using LCVD. Details of the substrate cleaning procedures employed have been described elsewhere.' An excimer laser, operating with ArF at a wavelength of 193 nm was used for this experiment. Typical laser repetition rates were 10 or 20 Hz. A 1-m focal length cylindrical lens was used to generate a flat sheet of the laser beam propagating parallel to the substrate and positioned 1-4 mm above it. In the experiments described here, the laser power was controlled to produce a range of incident laser fluences from 0 to 200 mJ/cm 2. TMAA and NH3 were used with partial pressures of 5 mtorr and 35 mtorr, respectively. Argon was used as an inert carrier gas for transporting TMAA. The base pressure in the turbo-pumped deposition system was 5 x 10-8 torr. The total pressure in the system during deposition was less than 200 mtorr. Substrate temperatures of 300-350 K were used; a temperature of 350 K (±5 K) was found to be optimum and well below the onset of thermal decomposition of TMAA. The laser-grown films were characterized for their structure, morphology, and composition using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) Analysis, and Secondary Ion Mass Spectrometry (SIMS). Film thickness was measured using both a spectrophotometric film thickness measurement system, as well as a stylus profilometer. SIMS analyses were performed with an ion microprobe mass analyzer (IMS5f) using a beam of 133 Cs+ ions. The optical absorption at ultraviolet and visible wavelengths as well as mid-infrared absorption of these films were measured. AIN films grown on n-type Si substrates (5-10 92.cm resistivity) were also characterized for their electrical properties with current-voltage (I-V) and capacitance-voltage (C-V) measurements by forming metal-insulatormetal (MIM) and metal-insulator-semiconductor (MIS) structures with aluminum as the top electrode. Details of all these measurements have been described in an earlier paper.' Samples were analyzed by XRD using nickel-filtered copper radiation and a Read thin film camera. Plan view TEM samples were prepared by mechanical grinding of the substrate to a thickness of 100 pm, followed by dimpling from the substrate side with successively finer grits (to 0.05 ptm) until a small perforation was achieved. The sample was then ion milled for several hours from the substrate side, followed by ion milling firom both sides for 15 minutes to clean the film surface. The samples were examined in a Philips Electronics Model EM-400 TEM operated at 80 kV. RESULTS SEM photographs of the films grown on Si(100) and GaAs(100) substrates indicated that the films were smooth and featureless even up to magnifications of 20,000 X. EDX analyses performed on these films (110-150 nm thick) at an incident energy of 5 keV revealed signals due to only AMand N, aside from a signal due to the respective substrate. Fig. 1 shows the EDX data obtained f
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