Abstract
We present a novel optical configuration of a phase-shifting interferometer for high-accuracy figure metrology of large dioptric convex spherical surfaces. The conformation and design considerations according to measurement accuracy, practicability, and system errors analysis are described. More in detail, we show the design principle and methods for the crucial parts. Some are expounded upon with examples for thorough understanding. The measurement procedures and the alignment approaches are also described. Finally, a verification experiment is further presented to verify our theoretical design. This system gives full-aperture and high-precision surface testing while maintaining relatively low cost and convenient operation.
Highlights
Modern optical lithography techniques require large ultra-precision lenses
Figure measurements of large convex surfaces are notoriously undesirable because it requires that the clear aperture (CA) and the numerical aperture (NA) of transmission spheres (TS) must be larger than the CA and the NA of the surfaces to be tested
Systematic optical path difference (OPD) error is a combination of an imperfect illumination wavefront, reference surface figure error, imaging aberrations depending on field and pupil, the instrument transfer function (ITF), and so on
Summary
Modern optical lithography techniques require large ultra-precision lenses. Micro-lithographic lenses for the ArF optics generation often have large diameter (200–300 mm) dioptric components. It is common that manufacturers receive requests for optics with a surface roughness of several angstrom rms and overall figure accuracy of better than 1 nm. Figure measurements of large convex surfaces are notoriously undesirable because it requires that the clear aperture (CA) and the numerical aperture (NA) of transmission spheres (TS) must be larger than the CA and the NA of the surfaces to be tested. There are many problems in the design and fabrication of those TS lenses. They are often very bulky, heavy, and expensive. To demonstrate the above situation, we show a 12 inch, 218 mm radius 0.82Fnumber TS lens in Fig. 1 that we have designed
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