Interference microscope for sub-Angstrom surface roughness measurements

Christopher Saxer; Klaus Freischlad

doi:10.1117/12.500925

30 May 2003 Interference microscope for sub-Angstrom surface roughness measurements

Christopher Saxer, Klaus Freischlad

Proceedings Volume 5144, Optical Measurement Systems for Industrial Inspection III; (2003) https://doi.org/10.1117/12.500925
Event: Optical Metrology, 2003, Munich, Germany

Abstract

Continuing improvements in the fabrication of super-smooth spherical and aspheric optical surfaces for applications such as extreme-ultraviolet lithography have given rise to the need to characterize the surface roughness of these optics to the sub-Angstrom level. Phase-shifting interference microscopes are well suited to acquire high-precision, three-dimensional surface structure rapidly, without contact, and over a wide range of spatial frequencies. This paper describes a new phase-shifting interference microscope by ADE Phase Shift, together with exemplary measurements of Angstrom-level surface roughness. The microscope was designed to measure large diameter (up to 500 mm) convex, concave and aspheric optics. To access all areas of the test surface, samples are placed symmetrically at the center of an R-theta stage. The phase-shifting microscope head pivots in the direction of the translation stage travel by ±20 degrees to match the major component of surface slope, while a second tilt control nulls minor tilt in the orthogonal direction. A 1K by 1K high-resolution, digital camera reduces random noise in the system to below 0.15 Angstrom rms for 16 averaged maps of nulled interferograms. When testing non-planar surfaces, the interference fringes cannot be nulled out, and special care has to be taken to minimize phase-dependent errors, commonly known as fringe print-through. A print-through level of less than 0.2 Angstrom rms has been achieved with a careful opto-mechanical system design in combination with an advanced phase algorithm whose filtering action suppresses higher-order harmonics caused by phase-shifter and detector non-linearity, as well as vibrations.

Citation Download Citation

Christopher Saxer and Klaus Freischlad "Interference microscope for sub-Angstrom surface roughness measurements", Proc. SPIE 5144, Optical Measurement Systems for Industrial Inspection III, (30 May 2003); https://doi.org/10.1117/12.500925

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available