Stepper lenses are tested by the lens manufacturer using various interferometric methods like phase measurement interferometry (PMI), before they are assembled onto the stepper or scanner. Once the system is set up, there are a few methods to study the lens aberrations in-situ using interferometry. The methods currently used are direct ones like direct aerial image measurement (DAIM) or indirect ones in which images of lines and spaces are formed in the photoresist and the aberrations inferred from scanning electron microscope (SEM) images of these. We propose using phase shifting point diffraction interferometry (PSPDI) for the purpose of measuring aberrations in-situ. The method has the advantages of being simple, and of having relaxed coherence length requirements and applicability over a wide wavelength range. We present results from a prototype experiment done on a 436 nm optic on an optical bench using a 442 nm He-Cd laser as source.
Library of Congress Subject Headings
Aberration; Optical measurements; Interferometry; Interferometers; Diffraction patterns
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Venkataraman, P., "Study of aberrations of stepper lenses in-situ using phase shifting point diffraction interferometry" (2002). Thesis. Rochester Institute of Technology. Accessed from
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