Effect of He content on microstructure, mechanical properties and He thermal desorption behavior of W film fabricated by RF magnetron sputtering

In order to study the effect of He content on microstructure, mechanical properties and He thermal desorption behavior of W film, He-charged W films on Si substrates were fabricated by a radio frequency (RF) magnetron sputtering device in different He/Ar mixture gases. The deposited W films had a typical columnar structure, and the grain size of W films decreased as He/Ar ratio increased by means of the observation of scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis confirmed that W films had a typical bcc structure, and the introduced He atoms can refine grain size and increase the lattice strain. TEM analysis showed that large numbers of He bubbles can be formed in W films, as well as the size and density of these He bubbles increased with the increase of the He/Ar ratio. The shape of He bubbles trapped by different sites also had some differences. Thermal desorption spectra (TDS) revealed that He content increased with He/Ar ratio increasing and different types of He atoms could be introduced into W films. The hardness value measured by nanoindentation tests increased with He/Ar ratio increasing, which demonstrated that nano-sized He bubbles could strengthen W films.