Advanced metrology for integration into manufacture of high-resolution x-ray gratings

Optical manufacturing technologies can only be as accurate, reliable, and efficient as the metrology techniques used to calibrate and guide the fabrication process and evaluate the results. The development of metrology capabilities has not kept pace with the need for increasingly high-resolution variable-line-spacing (VLS) x-ray gratings for high-intensity coherent x-ray light sources. Thus, innovation in metrology is necessary for progress in grating manufacturing. We propose to develop next-generation metrology technology, with higher accuracy and dynamic range than is currently available, suitable for integration into VLS x-ray grating fabrication processes, from a technique based on stitching together interferometric microscope measurements of the grating surface. The accuracy of the stitching technique will be enhanced by the development of test samples, algorithms, and software to characterize and deconvolve the measuring instrument response, reducing blurring, geometrical distortion, and other sources of systematic error. In Phase I, the efficacy of data stitching in concert with instrument response deconvolution and geometrical aberration correction will be demonstrated for metrology of VLS x-ray diffraction gratings. Oversampled and overlapping measurements of gratings will be made with an interferometric microscope. Specialized binary pseudorandom array test samples will be developed, manufactured, and used to determine the instrumental transfer function and geometrical aberrations of the microscope. Software will be developed to correct the data for the measured instrument response and then perform the stitching procedure. In Phase II, we will focus on integrating our methodology into x-ray grating manufacturing. Phase II work will also concern more sophisticated analytical models for fitting the surface topography of x-ray beamline optics. Such models are critically needed to accurately forecast beamline performance and correctly specify optics for fabrication.