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2008-021: Calibration Test Surface for Surface Profilometers

Invention: 2008-021

Patent Status: U.S. Patent Number 8,616,044 was issued on December 31, 2013

For technical and licensing related questions, email tcp@bnl.gov.

Summary
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Calibration of the modulation transfer function of surface profilometers with binary pseudorandom test standards: expanding the application range to Fizeau interferometers and electron microscopes.

Describes a test tool that can be used to calibrate surface profilometers. Surface profilometers are basic metrology tools used to characterize high quality optical surfaces with sub Angstrom rms roughness.

Description

Describes a test surface with a number of parallel grooves with uniform depth distributed in a pseudo-random pattern which can be used for calibration of surface profilometers. The invention describes a method of determining instrumental modular transfer function (IMTF).

Benefits

Unlike most conventional test surfaces, these test surfaces have a deterministic white-noise-like character which allows direct determination of the one and two dimensional modular transfer function with a sensitivity uniform over the entire bandwidth of a profilometer. The binary pseudorandom sequences and arrays precisely satisfy the requirements of ease of specification, reproducibility, repeatability, and reasonably low sensitivity to possible fabrication imperfections of the test surface when used as a certified standard. The spectral characteristics of the binary pseudorandom gratings and arrays are mathematically rigorous, reproducible and amenable to simulation.

Applications and Industries

These test surfaces can be used to calibrate stylus profilometers, optical interferometric, atomic force microscopes, scanning probe microscopes, optical, extreme ultraviolet (EUV) and x-ray scatterometers.

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