High-pressure hydrogen annealing for resistivity reduction of ultrathin tungsten electrodes

High-pressure H₂ annealing was employed to reduce the resistivity of ultrathin W films (11 −35 nm) grown by chemical vapor deposition, a thickness regime that is largely affected by grain boundary scattering. When compared with N₂ annealing, a significant decrease in resistivity was induced by H₂ annealing with increasing temperatures from 300 °C to 500 °C, and this effect was pronounced when the pressure was increased to 5 bar. Various characterization methods were utilized to identify the possible origins of the observed resistivity reduction in ultrathin W films, including the reduction of impurity contents and surface oxides, phase change, surface smoothing, and grain growth. Although the facile reduction of surface oxides by H₂ annealing could contribute somewhat to the resistivity reduction with increasing temperature, the pressure effect could not be explained. Instead, a greater increase in grain size for H₂ annealing compared to N₂ annealing was identified under increasing temperature and pressure via X-ray diffraction analyses, suggesting H₂-accelerated grain growth.