US 5,898,501 AGranted

Apparatus and methods for measuring wavefront aberrations of a microlithography projection lens

AssigneeNikon Corporation

InventorsJun Suzuki, Takashi Gemma, Yutaka Ichihara

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Abstract

Apparatus and methods are disclosed for measuring wavefront aberrations microlithography projection lenses such as i-line or excimer laser projection lenses. The apparatus comprises an argon-ion laser irradiating a Fizeau surface that reflects reference light and transmits test light. The test light is reflected by a spherical reflecting surface to pass twice through the test lens and the Fizeau surface, to interfere with the reference light. A piezoelectric element changes the fringes slightly. An image-pickup device receives the interference fringes and outputs data to a processor that calculates corresponding wavefront aberrations of the test lens. For testing an i-line lens, the argon laser can be a single-mode, 363.8 nm laser. For testing a lens used with a KrF excimer laser, the argon laser can emit second-harmonic light at 248.25 nm.

Claims23

Dependent claims

A wavefront aberration-measuring apparatus for measuring wavefront aberrations of an exposure projection lens for an exposure device for microlithography, the exposure projection lens being selected as a test lens to be observed with the apparatus, the apparatus comprising:

(a) a reference surface,
(b) a laser light source arranged to provide reference light to the reference surface and test light to the test lens;
(c) a spherical reflective surface arranged to reflect the test light, that has passed through the test lens in a first direction back through the test lens in a second direction, opposite the first direction;
(d) an image-pickup device arranged to receive reference light from the reference surface and test light from the test lens, returning from the test lens in the second direction, such that interference fringes are formed by the reference light and test light at the image-pickup device and are sensed by the image-pickup device;
(e) an interference-fringe scanner arranged to scan the interference fringes sensed by the image-pickup device by altering a phase relationship between the test light and the reference light at the image-pickup device;
and
(f) a processor arranged to receive information from the image-pickup device to calculate wavefront aberrations of the test lens based on the scanned interference fringes sensed by the image-pickup device.

4 more elements

Dependencies are inferred from the claim text.