Measurement of complex surface shapes using a spherical wavefront
AssigneeZygo Corporation
InventorsPeter J De Groot, Xavier Colonna De Lega
Life of this patent
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Abstract
Conical surfaces (and other complex surface shapes) can be interferometrically characterized using a locally spherical measurement wavefront (e.g., spherical and aspherical wavefronts). In particular, complex surface shapes are measured relative to a measurement point datum. This is achieved by varying the radius of curvature of a virtual surface corresponding to a theoretical test surface that would reflect a measurement wavefront to produce a constant optical path length difference (e.g., zero OPD) between the measurement and reference wavefronts.
Claims42
An interferometry method for measuring conical surfaces, the method comprising:
- directing a measurement wavefront to reflect from a conical portion of a measurement surface and subsequently overlap with a reference wavefront to form an interference pattern,
- wherein the measurement and reference wavefronts are derived from a common light source and paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a zero optical path length difference between the measurement and reference wavefronts across the interference pattern;
- translating a spherical portion of the optical measurement surface relative to the conical portion of the measurement surface;
- and
- determining information about the conical portion of the measurement surface based on the interference pattern.
An apparatus comprising:
- an interferometer configured to direct a measurement wavefront to reflect from a measurement surface and subsequently overlap with a reference wavefront to form an interference pattern, the measurement and reference wavefronts being derived from a common source,
- wherein the interferometer comprises a beam splitter positioned to direct the measurement and reference wavefronts along different directions and subsequently recombine them, and a spherically shaped reference surface positioned to reflect the reference wavefront back toward the beam splitter,
- wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a zero optical path length difference between the measurement and reference wavefronts across the interference pattern, and
- wherein the spherically shaped reference surface causes the optical measurement surface to have a spherical portion,
- wherein the interferometer further comprises optics to image the spherical portion of the optical measurement surface to an intermediate image plane;
- and
- the apparatus further comprising a translation stage configured to translate the optical measurement surface relative to the measurement surface.
Dependencies are inferred from the claim text.