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Proceedings Paper

Experiment analysis of freeform testing based on absolute testing method
Author(s): Xin Jia; Fuchao Xu; Tingwen Xing
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Paper Abstract

Requirements for the measurement resolution in the sub-nanometer range have become quite common which includes not only the repeatability or reproducibility but also the absolute measurement accuracy. The freeform lens for wavefront compensating contains some medium spatial frequency terms. The wavefront error of lithographic object lens is very small. One method to reduce the wavefront error of lithographic object lens is to use the freeform lens. The freeform lens for compensation needs more accuracy than the object lens. We can also use freeform lens of sphere or aspheric for compensation. The testing accuracy of sphere and aspheric lens are hard to achieve 1nm. The sphere and aspheric will contain the power term and are hard to find the cat-eye. The ion beam figure system (IBF) is the best polishing machine for nanometer manufacture which will polish the PV of 2um for several weeks even months. Usually we use the PV 200nm lens for compensation. So the freeform for compensation looks like a flat. In this paper we will show the testing experiment of the freeform and the testing problem. The freeform surface is created by 66 Zernike polynomials which are based on the flat lens. The freeform flat is polished by the ion figuring machine of NTG. The environment such as temperature, vibration, humidity is controlled well. The Zygo's interferometer Verifire Ashpere with absolute testing method is used to test the freeform. Position Accuracy is a problem in optical testing and manufacture. The high accuracy testing can’t be determined by one method, we need the different method to compare the result especially these method will contain some defects. The defects of the recently absolute testing method are discussed.

Paper Details

Date Published: 18 August 2014
PDF: 8 pages
Proc. SPIE 9203, Interferometry XVII: Techniques and Analysis, 920315 (18 August 2014); doi: 10.1117/12.2060496
Show Author Affiliations
Xin Jia, Institute of Optics and Electronics (China)
Fuchao Xu, Institute of Optics and Electronics (China)
Tingwen Xing, Institute of Optics and Electronics (China)

Published in SPIE Proceedings Vol. 9203:
Interferometry XVII: Techniques and Analysis
Katherine Creath; Jan Burke; Joanna Schmit, Editor(s)

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