Properties of reactively sputtered W–Si–N films

Abstract

Recently, it has been found that ternary nitrides of the type Me–Si–N (Me=Ti, Zr, Ta, W, etc.) containing a low (≤10 at.%) amount of Si can form nanocomposites with enhanced hardness. However, there is insufficient knowledge on properties of these nitride films with a high content of Si. This article reports on the d.c. reactive magnetron sputter deposition of W–Si–N films with a high (≥20 at.%) content of Si and their physical and mechanical properties. Films were characterized by XRD, EDX, microhardness, elastic recovery, resistance to plastic deformation, macrostress σ and thermogravimetry. On the basis of a systematic investigation of the properties of reactively sputtered W–Si–N films it was found that (1) according to the elemental composition, which can be controlled by a variation of the partial pressure of nitrogen ( p N2), W–Si–N films are nanocomposites composed of a mixture of different phases, either WSi 2+W+Si 3N 4 or Si 3N 4+WN x , when produced at low and high values of p N2, respectively; (2) the 4 to 5 μm thick W–Si–N films produced at high values of p N2 exhibit (i) an amorphous structure, (ii) the highest (≈35 GPa) hardness and (iii) a relatively low (≈−1.6 GPa) compressive macrostress σ, (3) the maximum hardness H max does not depend on the energy density E bi delivered to the growing film by bombarding ions but the value of E bi must be higher than a minimum energy E bimin≈0.1 MJ/cm 3, (4) H and σ of the hardest W–Si–N film do not depend on (i) the film thickness h up to 15 μm and (ii) the deposition temperature T s up to 500 °C and (5) the oxidation resistance is achieved up to approximately 800 °C. Special attention is devoted to correlations between the film hardness and the content of Si 3N 4 in the film. The W–Si–N films with a higher content of Si and a higher N/Si ratio exhibit a higher H. Correlations between the hardness H, effective Young's modulus E*= E/(1− ν 2), elastic recovery W e and the ratio H 3/ E *2 are also given (here ν is the Poisson's ratio). The main conclusion resulting from this work is a finding that the high (≥60 vol.%) content of Si 3N 4 in the W–Si–N film is not a sufficient condition to achieve the oxidation resistance exceeding 1000 °C. The thermal stability of individual phases from which the Si based (Me–Si–N) nitride film is composed must be ensured too.