Calibration of photoelectromagnetic sensor in a laser source

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.

Description

BACKGROUND[0001]1. Field[0002]The present application relates generally to laser systems and, more specifically, to calibration of a photoelectromagnetic sensor in a laser source of a laser produced plasma (LPP) extreme ultraviolet (EUV) system.[0003]2. Related Art[0004]The semiconductor industry continues to develop lithographic technologies which are able to print ever-smaller integrated circuit dimensions. Extreme ultraviolet (“EUV”) light (also sometimes referred to as soft x-rays) is generally defined to be electromagnetic radiation having wavelengths of between 10 and 102 nm. EUV lithography is generally considered to include EUV light at wavelengths in the range of 10-14 nm, and is used to produce extremely small features (e.g., sub-32 nm features) in substrates such as silicon wafers. These systems must be highly reliable and provide cost-effective throughput and reasonable process latitude.[0005]Methods to generate EUV light include, but are not necessarily limited to, conv...

AI Technical Summary

Benefits of technology

The patent describes a system and method for measuring the energy of laser pulses in a laser-produced plasma extreme ultraviolet (EUV) system. The system includes an energy monitor that measures the average power of the laser pulses and the temporal profile of pre-pulses separated from main pulses. The system uses a calibration module to determine the power of the main pulse and the pre-pulse based on a main pulse calibration coefficient and an integral of a voltage signal. The system also includes a single pulse energy calculation (SPEC) module to determine the energy of the pre-pulses and the main pulses based on the pre-pulse calibration coefficient and an integral of a voltage signal. The patent also describes a computer-readable medium with instructions for implementing the system and method. The technical effect of the patent is to provide a reliable and accurate measure of the energy of laser pulses in a LPP-EUV system, which is important for controlling the quality and efficiency of the system.

Problems solved by technology

The instruments, however, may not directly measure certain properties of the laser beam 102 or may be not be calibrated in such a way as to measure the properties of the laser beam 102.

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