THE ORIGIN OF STRESS IN SPUTTER-DEPOSITED TUNGSTEN FILMS FOR X-RAY MASKS

The mechanism for the cause of stress in a sputter-deposited tungsten (W) film has been clarified. The tensile stress of the film was calculated using the interatomic forces acting on the grain boundary. The average distance of the grain boundary gaps was determined from the measured film density assuming the film had homogeneous size rectangular grains. The calculated and measured stress values were in good agreement in the high working gas pressure region. The difference between these values in the low working gas pressure region has been able to be explained by the compressive stress due to the peening effect of Ar. The low stress in the high pressure region was obtained by large opened grain boundaries which produced low film density. A low film density causes a low x-ray stopping power. The film deposited in the low pressure region is suitable as an x-ray absorber because of its high film density.