US Patent No. 9,170,498

LITHOGRAPHIC APPARATUS AND A METHOD FOR DETERMINING A POLARIZATION PROPERTY OF A PROJECTION SYSTEM USING AN ADJUSTABLE POLARIZER AND INTERFEROMETRIC SENSOR


Patent No. 9,170,498
Issue Date October 27, 2015
Title Lithographic Apparatus And A Method For Determining A Polarization Property Of A Projection System Using An Adjustable Polarizer And Interferometric Sensor
Inventorship Marcus Adrianus Van De Kerkhof, Helmond (NL)
Wilhelmus Petrus De Boeij, Veldhoven (NL)
Hendrikus Robertus Marie Van Greevenbroek, Eindhoven (NL)
Martijn Gerard Dominique Wehrens, Waalre (NL)
Haico Victor Kok, Eindhoven (NL)
Wilhelmus Jacobus Maria Rooijakkers, Eindhoven (NL)
Tammo Uitterdijk, De Bilt (NL)
Assignee ASML Netherlands B.V., Veldhoven (NL)

Claim of US Patent No. 9,170,498

1. A method for determining a polarization property of a lithographic apparatus, comprising:
measuring one or more wavefronts of a radiation beam from a source module using an interferometric sensor, wherein:
the source module is disposed at a level of a patterning device in the apparatus and comprises a lens and a polarizing component,
the source module does not include the patterning device,
the lens is configured to collimate the radiation beam before it passes through the polarizing component,
the interferometric sensor comprises a diffractive element disposed at a level of a substrate in the apparatus and a detector
spaced apart from the diffractive element, and

the diffractive element is arranged to provide shearing interferometry between at least two wavefronts mutually displaced
in a direction of shear; and

determining, from the wavefront measurements, information on polarization affecting properties of a projection system of the
lithographic apparatus.