Position sensing arrangement and lithographic apparatus including such an arrangement, position sensing method and device manufacturing method
US10317808B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Jan 16, 2017 |
| Grant date | Jun 11, 2019 |
| Priority date | — |
| Expiry date | Jan 16, 2037 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01D5/266
- WIPO fieldMeasurement
- WIPO sectorInstruments
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.