Influence of internal stress and layer thickness on the formation of hydrogen induced thin film blisters in Mo/Si multilayers

A Mo/Si multilayer film may blister under hydrogen exposure. In this paper, we investigate the impact of intrinsic stress on blister formation in multilayers by varying the Si thickness between 3.4-11 nm and changing the hydrogen ion exposure conditions. Increasing the thickness of a-Si is found to introduce a higher average compressive stress in the multilayer film. Measurements of the average film stress before and after hydrogen exposure did not reveal a correlation between stress relaxation and the observation of surface blisters. Comparing the experimentally observed blister size distribution to that predicted by elastic models of blistering due to pressure, and thin film buckling showed that increasing hydrogen pressure under the blister cap is the main cause of the observed blisters. It is also shown that hydrogen diffusion plays an essential role in the blister formation process as sufficient hydrogen is required to pressurize the blister.