Membrane-mask distortion correction: Analytical and experimental results

Abstract

We describe a strategy for eliminating distortion in x-ray masks. Prior to patterning the x-ray absorber, the mask membrane is patterned with a shallow, fine-period fiducial grid, made by interference lithography. After patterning the absorber, the grid is measured using a holographic-phase-shifting interferometer (HPSI) to determine the distortion, i.e., the distribution of displacements from the original grid caused by stress in the absorber. Using an analytical technique we developed, the stress distribution that caused the distortion is calculated from the HPSI measurements using a rapid algorithm. To correct the distortion we follow the proposal of Feldman [J. Vac. Sci. Technol. B 17, 3407 (1999)] and apply a heat distribution such that taking into account thermal diffusion and heat loss the resulting thermal expansion produces a compensating stress distribution. This adaptive x-ray mask should enable real-time distortion correction. We show first-stage experimental results which support its feasibility.