AFM Study of Surface Morphology of Aluminum Nitride Thin Films
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(IBAD) method.[3-5] The IBAD method has the advantage of low temperature synthesis owing to the reaction of energetic ions and vaporized metal molecules.[6] In a previous paper, we synthesized AIN thin films at room temperature [3] and reported the influence of the substrate temperature and the kinetic energy of the nitrogen ion beam on the microstructure of the synthesized films.[41 In addition, the present authors have observed the surface morphology of AIN thin films by AFM and showed that the surface of the films synthesized at 473K becomes rough as compared with the films synthesized at room temperature.[5] In the present paper, using the IBAD method, AIN thin films are synthesized on the various substrates with different surface roughness, such as silicon single crystal, soda-lime glass and alumina, at the substrate temperatures of room temperature and 473K. The influence of the substrate roughness and substrate temperature on the surface smoothness of the films is reported. EXPERIMENTAL Nitrogen gas (99.999% pure) and aluminum (99.99% pure) were used as ion source and target respectively. Film synthesis was carried out on the substrates of silicon single crystal (100), soda-lime glass and alumina placed into the load lock in a high vacuum chamber. Two kinds of alumina substrates with different roughness were used; one was as-fired with the average roughness of about 200 nm and the other was obtained by polishing with diamond pastes for a week and the average roughness decreases to about 7 nm. After evacuating the vacuum chamber to about 2.7 x 10-4 Pa, pure nitrogen gas was introduced to the ionization chamber and nitrogen ions were generated by an arc discharge. Then a nitrogen beam was obtained with electric field lenses for focusing and accelerating. The kinetic energy of the nitrogen ions and the deposition rate were kept at 0.5 keV and 0.07 nm/s. Aluminum was evaporated by electron bombardment from a 10 kW electron gum and the evaporation rate was monitored by a quartz sensor. The substrate temperature was kept at room temperature and 473K. The thickness of the synthesized films was measured with a stylus device (Rank Taylor Hobson Ltd.). The crystallography of the films was determined by X-ray diffraction (XRD) using a Cu target (RINT 2500, RIGAKU Co.). The surface morphology was observed by the tapping mode with a NanoScope III (Digital Instruments) equipped with commercial silicon tips. The AFM images were acquired 256 x 256 points per frame, and were corrected by the subtraction of the background slopes. RESULTS AND DISCUSSION Figures 1 (a) and (b) show typical XRD patterns of films synthesized on the silicon single crystal substrate at room temperature and 473K, respectively. The thickness of these films is approximately 300 nm. In both XRD patterns, the
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stronger peak is assigned to the AIN (10-0) and the broad peak is composed of the AIN (00.2) and the AIN (10.1) planes. From these XRD patterns, it is confirmed that polycrystalline AIN thin films are synthesized both at room temperature and
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