INSITU STRESS MONITORING AND DEPOSITION OF ZERO-STRESS W FOR X-RAY MASKS

We have developed and tested a computer-controlled system for monitoring in situ the stress of tungsten sputter deposited onto x-ray mask membranes. This system allows us to achieve zero stress (i.e., < 5 x 10(7) dyn/cm2) tungsten. The stress is monitored via the resonant frequency of the x-ray mask membrane which changes during deposition due to W stress, mass loading, and temperature rise. Differences in W stress give rise to differences in curvatures of the plot of resonant frequency versus W thickness. This effect can be used to ensure that a film will have stress below 1 x 10(8) dyn/cm2 and can also be the basis of an automated closed-loop, in situ stress control system.