Surface morphology of sputter deposited W–Si–N composite coatings characterized by atomic force microscopy

Tungsten–silicon–nitride (W–Si–N) composite coatings on Si(100) substrates were sputter deposited at various silicon target currents, and their surface morphology was studied with scaling analysis and fractal analysis based on atomic force microscopy (AFM). The root-mean-square (rms) roughness σ, roughness exponent α, the correlation length ξ and the average magnitude of the lateral surface slope ρ decrease with the silicon target current, which is caused by the impeding effect of amorphous Si3N4 on the grain growth of W2N and W5Si3. The competition of surface diffusion and shadowing effect together with other processes drives the formation of columnar grains with mould-like tops. The fractal dimensions obtained using power spectrum method and the R/S method are 2.16 ± 0.04 and 2.15 ± 0.01, respectively, and they both increase with the silicon target current.