Sub-angstrom surface metrology with a virtual reference interferometer

Klaus Freischlad

doi:10.1117/12.928975

13 September 2012 Sub-angstrom surface metrology with a virtual reference interferometer

Klaus Freischlad

Proceedings Volume 8493, Interferometry XVI: Techniques and Analysis; 84930B (2012) https://doi.org/10.1117/12.928975
Event: SPIE Optical Engineering + Applications, 2012, San Diego, California, United States

Abstract

Non-contact, 3D optical interferometric profilers provide detailed topography measurements of super-smooth surfaces such as hard disk substrates and super-polished optics. However, the contribution of the interferometer system to the measurement can be significant for surfaces with an RMS roughness of one Angstrom and below. Special care must be taken to minimize random noise as well as to remove the systematic instrument error from the measured data. While the random noise can be addressed by low-noise design and averaging of measurements, the systematic instrument error is more difficult to eliminate. In this paper an interferometer configuration is presented that eliminates the mid to higher spatial frequencies from the reference beam. This configuration is called a virtual-reference interferometer, since there is no physical surface in focus conjugate to the test surface. This provides very smooth systematic instrument errors with essentially no contribution in the mid to high spatial frequencies of surface waviness and roughness. The virtual-reference interferometer has a midsize measurement area of 20x20 mm, is fully compensated for white light, extended source illumination, and enables data acquisition for both phase shifting and coherence scanning modes. Current performance data show a residual systematic tool waviness error of < 0.2 Angstrom RMS, with potential for improvement. Efficient stitching of subaperture measurements accommodates high resolution roughness and waviness maps of test surfaces up to 150 mm x100 mm.

Citation Download Citation

Klaus Freischlad "Sub-angstrom surface metrology with a virtual reference interferometer", Proc. SPIE 8493, Interferometry XVI: Techniques and Analysis, 84930B (13 September 2012); https://doi.org/10.1117/12.928975

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