CALIBRATION OF PHOTOELECTROMAGNETIC SENSOR IN A LASER SOURCE

摘要

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.

主权项

1. A system comprising:
an energy monitor within a laser source of a laser-produced plasma (LPP) extreme ultraviolet (EUV) system, the energy monitor configured to measure laser pulses having a same wavelength and occurring in a burst, the energy monitor comprising:
a power meter configured to measure an average power of the laser pulses over a defined period of time, anda photoelectomagentic (PEM) detector configured to provide a first voltage signal indicative of a temporal profile of the burst of the laser pulses over at least a portion of the defined period of time; a calibration module configured to determine a calibration coefficient based on the average power and the first voltage signal, the calibration coefficient being a ratio of an energy of the burst of the laser pulses determined from the average power and an integral of the first voltage signal; and a single pulse energy calculation (SPEC) module configured to determine an energy of a subsequent pulse of the series of the laser pulses based on the calibration coefficient and a pulse integral of a second voltage signal provided by the PEM detector indicating a temporal profile of the subsequent pulse.