Temperature dependencies of hydrogen-induced blistering of thin film multilayers

We report on the influence of sample temperature on the development of hydrogen-induced blisters in Mo/Si thin-film multilayers. In general, the areal number density of blisters decreases with increasing exposure temperature, whereas individual blister size increases with exposure temperatures up to ∼200 °C but decreases thereafter. Comparison as a function of sample temperature is made between exposures to a flux containing both hydrogen ions and neutrals and one containing only neutrals. In the case of the neutral-only flux, blistering is observed for exposure temperatures ≥90 °C. The inclusion of ions promotes blister formation at <90 °C, while retarding their growth at higher temperatures. In general, ion-induced effects become less evident with increasing exposure temperature. At 200 °C, the main effect discernable is reduced blister size as compared with the equivalent neutral-only exposure. The temperature during exposure is a much stronger determinant of the blistering outcome than either pre- or post-annealing of the sample. The trends observed for neutral-only exposures are attributed to competing effects of defect density thermal equilibration and H-atom induced modification of the Si layers. Energetic ions modify the blistering via (temperature dependent) enhancement of H-mobility and re-crystallization of amorphous Si.