Calibration of photoelectromagnetic sensor in a laser source
US9239269B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Jul 14, 2014 |
| Grant date | Jan 19, 2016 |
| Priority date | — |
| Expiry date | Aug 7, 2034 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01J2001/4238
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
In a laser-produced plasma (LPP) extreme ultraviolet (EUV) system, laser pulses are used to produce EUV light. To determine the energy of individual laser pulses, a photoelectromagnetic (PEM) detector is calibrated to a power meter using a calibration coefficient. When measuring a unitary laser beam comprising pulses of a single wavelength, the calibration coefficient is calculated based on a burst of the pulses. A combined laser beam has main pulses of a first wavelength alternating with pre-pulses pulses of a second wavelength. To calculate the energy of the main pulses in the combined laser beam, the calibration coefficient calculated for a unitary laser beam of the main pulses is used. To calculate the energy of the pre-pulses in the combined laser beam, a new calibration coefficient is calculated. When the calculated energy values drift beyond a pre-defined threshold, the calibration coefficients are recalculated.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.