Internal stress and microstructure of WNx bilayer films for x-ray masks

In order to obtain the low-stress absorber for the X-ray mask, we have investigated the internal stress and the microstructures of WNx bilayer films with the structure of amorphous/crystalline phases. WNx film goes through a transition from an amorphous phase to a crystalline phase as the N-2 content in the working gas increases. WNx bilayer film was prepared by two-step sputtering with varying N-2 content of 10% for the crystalline phase and 5% for the amorphous phase. Precise stress control of the film was carried out by step annealing in a N-2 atmosphere. We could obtain the internal him stress of less than 10 MPa by step annealing. The WNx bilayer film exhibits a very smooth. surface with roughness of less than 1 nm and a long term stress stability less than of 2 MPa in air.