Invention Grant
- Patent Title: Position sensing arrangement and lithographic apparatus including such an arrangement, position sensing method and device manufacturing method
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Application No.: US16069678Application Date: 2017-01-16
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Publication No.: US10317808B2Publication Date: 2019-06-11
- Inventor: Simon Reinald Huisman , Alessandro Polo , Duygu Akbulut , Sebastianus Adrianus Goorden , Arie Jeffrey Den Boef
- Applicant: ASML NETHERLANDS B.V.
- Applicant Address: NL Veldhoven
- Assignee: ASML NETHERLANDS B.V.
- Current Assignee: ASML NETHERLANDS B.V.
- Current Assignee Address: NL Veldhoven
- Agency: Arent Fox LLP
- Priority: EP16151931 20160119
- International Application: PCT/EP2017/050806 WO 20170116
- International Announcement: WO2017/125352 WO 20170727
- Main IPC: G01B11/00
- IPC: G01B11/00 ; G03F9/00 ; G01B9/02 ; G01D5/26

Abstract:
In an alignment sensor of a lithographic apparatus, position sensing radiation is delivered to a target (P1). After reflection or diffraction from the target, position sensing radiation is processed to determine a position of the target. Reference radiation interferes with the position sensing radiation) while a relative phase modulation is applied between the reference radiation and the position sensing radiation. The interfering radiation includes a time-varying component defined by the applied phase modulation. The interfering radiation is delivered to two photodetectors in such a way that each photodetector receives said time-varying component in anti-phase to that received at the other photodetector. A difference signal (i(t)) from said photodetectors contains an amplified, low noise version of said time-varying component. This is used in determining the position of the target. Mode matching enhances interference. Surface scattered radiation is rejected.
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