Sputter deposition of WNx thin films by helicon-wave-excited argon plasma with N2 seeding

Abstract

—ungsten nitride (WN x ) films were deposited on silicon substrates by nitrogen gas (N 2 ) seeded helicon-wave-excited argon plasma sputtering at various N 2 flow rates (F N2 ), axial distances (Z) and substrate temperatures (T s ). For the substrates without extra heating (289–368 K), increasing F N2 (0–30 sccm) or Z (1.5–6 cm) can both increase the stoichiometry x = [N]/[W], causing a series of crystalline phase evolutions (α-W → β-W → fcc-W 2 N → hexagonal WN). This transition from metallic W to less conductive nitride state, brings about a wide range of the resistivity from 32 to 1941 μΩ-cm. Due to the solid solution hardening effect and the restraint of grain dislocation, the maximum hardness value of 32.2 GPa is obtained when a nanocomposite of β-W and fcc-W 2 N phases is formed. For the substrates with extra heating (Z = 1.5 cm, F N2 = 5 sccm), hexagonal phase WN 0.99 film with high crystallinity has been successfully synthesized at T s = 773 K. Increasing T s from 373 to 873 K, due to the release of the interstitial N atoms and the densification of the structure, the resistivity decreases from 1265 to 952 μΩ-cm and elastic modulus increases slightly from 297 to 329 GPa. The decomposition of the films deposited at various T s starts almost at the same temperature (950 K) followed by two typical N 2 desorption peaks related to the decomposition of W 2 N phase. With increasing T s , the peaks become weaker with a slight shift towards the high temperature region, indicating the improvement of thermal stability. • WN x thin films are deposited by Helicon-wave-excited argon plasma sputtering with N 2 seeding. • Well crystallized hexagonal phase WN films are synthesized. • Structure, composition, morphology, mechanical and electrical properties are investigated. • Films deposited with higher substrate temperature show improved thermal stability.