Membrane-mask distortion correction: Analytical and experimental results

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 shallo w, fine-period fiducial grid, made by interference lithography. After patte rning 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. U sing an analytical technique we developed, the stress distribution that cau sed the distortion is calculated from the HPSI measurements using a rapid a lgorithm. To correct the distortion we follow the proposal of Feldman [J. V ac. Sci. Technol. B 17, 3407 (1999)] and apply a heat distribution such tha t 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 ex perimental results which support its feasibility. (C) 2000 American Vacuum Society. [S0734-211X(00)01906-5].