Star Test Polarimetry is a method of inferring polarization information in a single irradiance measurement from the shape of a point spread function [1]. We present the optical design of an image sampling polarimeter that utilizes a stress engineered optical element to image the polarization states of scattered light collected by a lens across a given field. In our scheme, an intermediate image is sampled by a pinhole array and a relay system projects the polarization dependent point spread functions to a CCD. In this way, we show polarization mapping of a sample using a single irradiance image.
Wafer chucks are used in advanced lithography systems to hold and flatten wafers during exposure. To minimize defocus and overlay errors, it is important that the chuck provide sufficient pressure to completely chuck the wafer and remove flatness variations across a broad range of spatial wavelengths. Analytical and finite element models of the clamping process are presented here to understand the range of wafer geometry features that can be fully chucked with different clamping pressures. The analytical model provides a simple relationship to determine the maximum feature amplitude that can be chucked as a function of spatial wavelength and chucking pressure. Three-dimensional finite element simulations are used to examine the chucking of wafers with various geometries, including cases with simulated and measured shapes. The analytical and finite element results both demonstrate that geometry variations with short spatial wavelengths (e.g., high-frequency wafer shape features) present the greatest challenge to achieving complete chucking. The models and results presented here can be used to provide guidance on wafer geometry and chuck designs for advanced exposure tools.
Stress-engineered optical elements have potential applications in snapshot polarimetry, in which a single irradiance
image is used to measure a spatially varying polarization. In this paper, we present star test polarimetry
which is a method of polarization retrieval by analyzing a single frame point spread function. A trigonally
stressed window placed at the pupil plane of an imaging system is used to produce point spread functions which
are then processed to extract the polarization state of the incoming beam under investigation. We outline several
methods which are used to recover the Stokes parameters of a beam of unknown polarization from the irradiance
distribution of its point spread function.
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