Patent ID: 9261800
Filing Date: 2016-02-16
CPC Classification: G01B,G03F,H01J

Claim Text:
1. Method of pre-aligning an L-shaped interferometer module for use in an exposure tool comprising a frame provided with first mounting surfaces and a mirror for reflecting an interferometer beam, wherein said interferometer module comprises an interferometer head for emitting an interferometer beam and a further interferometer head for emitting a further beam perpendicular to said interferometer beam, wherein said first and second interferometer head are arranged on different legs of said L-shaped interferometer module for emitting their respective interferometer beam towards each other, wherein said module is connected to second mounting surfaces for cooperative engagement with said first mounting surfaces, said method comprising the steps of: aligning the orientation of said module relative to said second mounting surfaces outside of said exposure tool, wherein said orientation of said module relative to said second mounting surfaces is aligned based on a pre-determined orientation of said first mounting surfaces relative to said mirror, wherein said predetermined orientation comprises an angular orientation and a positional orientation of said first mounting surfaces relative to said mirror; aligning the orientation of said further interferometer head relative to said second mounting surfaces outside of said exposure tool based on said pre-determined orientation of said first mounting surfaces relative to said mirror, wherein the orientations of said interferometer head and said further interferometer head are adjusted such that said beams emitted by said interferometer head and said further interferometer head are inclined at a pre-determined angle of 90 degrees to each other.