Stress evolution in Mo/Si multilayers for high-reflectivity extreme ultraviolet mirrors

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Abstract
The stress evolution of sputter deposited Mo/Si multilayers of possible application as extreme ultraviolet light mirrors has been investigated by in situ substrate curvature measurements using a multiple parallel laser beam technique. Our preliminary results show well-defined stress modulation concurrent with the deposition of Mo and Si layers in the multilayer structure. Large changes in substrate curvature were measured during the early stages of deposition of the individual layers, with Mo exhibiting apparent tension and Si exhibiting apparent compression. The magnitudes of these curvature changes partially offset each other, resulting in an average compressive stress of −350 MPa in the multilayer. Possible stress generating mechanisms during growth of these multilayers as well as single layer films of Mo and Si will be discussed.