Ion Projection Lithography is one promising candidate for a next generation IC technology. Within this field of research one of the most critical aspects is the development of open stencil masks. The stress formation during the mask fabrication process affects the critical dimensions (CD) of the structures to be formed. The stress measurement in the mask blanks is performed by the well known bulging method. The accuracy of the membrane bulging method depends on the correct description of the bulged membrane shape. The accuracy of the method can be improved by including the deviations from spherical approximation by correcting the membrane bulging formula. Additionally, the shape ofthe membrane deformation and the improved bulging formula are compared with FE simulations. The commonly used interferometer technique can not be used to determine the absolute zero point of the membrane (e.g. plane membrane). With the diffraction image technique the zero point is determined by the geometry. Additionally, by bulging of the membrane in two directions, the zero point can be deduced from the anti-symmetry ofthe pressure vs. deflection curve.

Sossna, E.; Kassing, R.; Rangelow, I. W.; Herzinger, C. M.; Tiwald, T. E.; Woollam, John A.; and Wagner, Th., "Thickness analysis of silicon membranes for stencil masks" (2000). Stencil masks are key to charged particle projection lithography, in particular for ion projection lithography. To fulfill pattern printing requirements in the sub-70 nm regime, excellent thickness uniformity and thermal emissivity control are critical parameters for high quality stencil mask fabrication. We propose and demonstrate a technique based on infrared variable angle spectroscopic ellipsometry ͑IR-VASE͒ to measure these parameters with adequate accuracy and precision. The refractive index of the Si membrane was evaluated using a Sellmeier dispersion model combined with a Drude model. Because of its spectral range from 2 to 33 m, the IR-VASE method is sensitive to the thickness of layers as well as to the concentration and profile of Si membrane doping.

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Sossna, E.; Degen, A.; Rangelow, I. W.; Drzik, M.; Hudek, P.; Tiwald, T. E.; and Woollam, John A., "Mechanical, geometrical, and electrical characterization of silicon membranes for open stencil masks" (2001 Silicon membranes are used for stencil masks which are key to charged particle projection lithography, particularly for ion projection lithography, electron beam projection. Quantitative and qualitative determination of the mechanical properties of the true thickness, thickness variations ͑morphology͒, electrical conductivity and stress is critical to the development of next generation lithography. The metrology setup includes high accuracy thickness, refractive index and electrical conductivity measurement based on infrared variable angle spectroscopic ellipsometry, thickness variation characterization based on the Fizeau interferometric scheme and mechanical stress evaluation based on a novel double bulging technique.