Inter-relationship of stress and microstructure in BCC and 'beta' tungsten films

In this work, a series of W films are deposited at different deposition rates (0.2, 0.5, and 1.0 nm/s) and pressures (0.27, 0.47, 0.67, and 1.33 Pa). Comparing the residual stresses between different deposition rates, the stress was found to become more tensile at higher depositions rates over the pressure ranges studied. Films deposited at the three highest pressures were tensile in stress, had small grains (-15 to 20 nm), and stabilized the metastable A15 phase often referred to as beta-W. At the lowest pressure, 0.27 Pa, the films were compressive in stress, larger grain sizes (-70 to 90 nm), and primarily stabilized the body centered cubic alpha-W phase. If a W seed layer was grown under either the alpha-W or beta-W growth conditions, the subsequent W layer adopted the phase state of the seed layer, independent of processing conditions and/or grain sizes, suggesting that the phase state is most likely determined in the initial stages of nucleation. The seed layer experiment also suggest that these layers can promote more controlled grain sizes in thicker beta-W films, which has not been observed in previous work. The stress mea-surements are interpreted in terms of a previously developed kinetic model that includes effects of growth ki-netics, microstructural evolution, and energetic particle bombardment.

Automated summary

In this study, a series of W films were deposited at different deposition rates and pressures. The stress of the films was found to increase at higher deposition rates. The films deposited at higher pressures showed tensile stress and stabilized the beta-W phase, while films deposited at lower pressures showed compressive stress and stabilized the alpha-W phase. The phase state of the subsequent W layer was determined by the phase state of the seed layer, indicating that nucleation plays a crucial role.