Sputter deposition and annealing of Ta, $TaSix$ and $TaBx$ composite films and their application in next generation lithography masks

Ta and Ta composites with other elements have been developed as low stress absorbers for x-ray mask technology. These thin films are often produced in small quantities by sputter deposition from targets of pure Ta with chips of the minor elements placed on the target to create the composites. For membrane-mask manufacturing it is important that absorber films have uniform composition, thickness, and low, uniform stress to assure that image size and pattern placement errors are minimal. Since sputtered films containing Ta often have highly compressive stress, several methods have been used to reduce the final stress, including careful control of sputtering conditions, deposition of layered films with different stresses, and thermal annealing. Much data has been reported regarding the effects of thermal annealing of Ta films but less information is available on multiple element films such as $TaSix$ and $TaBx.$ Previous reports on these materials have generally not discussed the behavior of these films under long term, higher volume manufacturing conditions. During the last several years IBM has been engaged in development and fabrication of refractory x-ray membrane masks using Ta composites as absorber materials. Films were sputter deposited from hot isostatically pressed powder targets of Ta, Si, and B using an S-gun magnetron cluster deposition system. This article reports on the deposition and annealing of these films and their application to membrane-mask fabrication in a manufacturing environment. The effects of deposition parameters such as dc power, argon gas pressure, and substrate composition on film stress, composition, and density are discussed. The results of nitrogen annealing on $TaSix$ and $TaBx$ films are presented. Absorber film quality data and its impact on image size, image placement, and defect density of some x-ray masks is presented.