Laser Physical Vapor Deposition of Si_3N_4 and SiC, and Film Formation Mechanism(Materials, Metallurgy & Weldability)

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This paper describes the characteristics and formation mechanisms of laser physical vapor deposition (LPVD) films, which were produced on Ti or other metallic substrates from SiC or Si_3N_4 targets with a wide range of chamber pressures and substrate temperatures by using a cw Nd: YAG laser as a heat source for evaporation. Flat, smooth, dense, amorphous LPVD films with small particles were formed from any target. In the case of Si_3N_4 many crystalline Si_3N_4 particles of 1 to 15μm size of globular or granular shapes and metallic Si particles of about 5μm size of hemispherical shape were mainly observed in the films from porous high-purity and dense lower-purity targets, respectively. Such particles result from Si_3N_4 fractions or Si liquid ejected as spatter from the target. The N content in the amorphous film was reduced greatly in comparison with the original one in the target, probably because the laser-irradiated part of Si_3N_4 target was decomposed into Si and N, and N was easily pumped out as N_2 gas. Hard films of Hk=8〜12GPa were made from both Si_3N_4 targets at the substrate temperature of 723〜923K under the pressure of 0.02〜1Pa. In the case of SiC, small granular particles of less than 5μm were seen in the film. Much harder SiC films of Hk=10〜36GPa were produced at 623〜873K under high vacuum of about 0.03Pa. The scratch test showed an exfoliation load of more than 4N for any substrate, and the fracture took place in the LPVD film on Ti, Ta and Type 304 substrates although the fracture occurred along the interface between the film and the substrate in the case of W. These suggest that the adhesion of the LPVD film was better in the former case than in the latter case. TEM observation of films or clusters formed on the Carbon film revealed that evaporated atoms might be deposited directly as a dense amorphous film under high vacuum of 0.01Pa. On the other hand, at pressures of approximately 1Pa or more, clusters or ultrafine particles must be at first formed on the substrate and then transformed into the film due to the thermal effect of the heated substrate.
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Laser Physical Vapor Deposition of Si_3N_4 and SiC, and Film Formation Mechanism(Materials, Metallurgy & Weldability)

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