EUV Spectral Measurement for In-Band and OOB Light Control
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Solution Overview
Problem
EUV tools face challenges in maintaining high throughput and image quality due to the presence of out-of-band (OOB) photons, which are not effectively filtered by the multilayer stack-based EUV reflective optics and can degrade actinic image quality.
Innovation Solution
The implementation of a system that includes a beam-narrowing aperture and a band-selection filter, along with in-situ spectral characterization using a grating and sensor, allows for the selective filtering and characterization of OOB light, thereby mitigating its impact on image quality and maintaining high throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If OOB light is filtered using additional filtering elements, then image quality is improved, but EUV photon loss increases and throughput is reduced
Solution Approach 1:
The patent implements a feedback mechanism by using a spectral analyzer to measure the actual OOB light content in the optical path, then using this information to dynamically adjust imaging parameters or apply computational corrections. This allows the system to maintain high image quality without requiring aggressive physical filtering that would block valuable EUV photons, thereby preserving throughput.
Solution Approach 2:
The patent introduces a spectral analyzer as an intermediary device that characterizes the OOB light spectrum without blocking the main EUV beam. This intermediary provides information about the harmful OOB photons, enabling the system to compensate for their effects through computational methods while keeping the filtering elements open for maximum EUV transmission.
2Productivity
If OOB light is allowed to propagate, then throughput is maintained, but image quality degrades due to artifacts
Solution Approach 1:
The spectral analyzer provides real-time feedback on the OOB light spectrum, which is then used to dynamically adjust imaging parameters or apply computational corrections during image processing. This feedback loop allows the system to maintain high throughput by keeping filtering elements open while compensating for OOB artifacts through information-driven adjustments.
Solution Approach 2:
The patent converts the harmful effect of OOB light into a beneficial measurement opportunity. By using the OOB photons that would otherwise be harmful to calibrate and characterize the optical system's spectral response, the system gains valuable information about its own performance, which can then be used to correct images and improve overall system understanding without blocking the OOB light.
3Reliability
If filters are used to suppress OOB light, then spectral purity is improved, but EUV transmission is reduced
Solution Approach 1:
The spectral analyzer provides continuous feedback on the actual spectral content, allowing the system to determine when OOB suppression is truly necessary. This feedback mechanism enables the system to maintain filters in a more open state than traditional approaches, maximizing EUV transmission while only applying suppression when and where actually needed based on real-time spectral measurements.
Solution Approach 2:
The system uses its own spectral measurements to determine its own filtering requirements, rather than relying on fixed, conservative filtering settings. The spectral analyzer enables the optical system to self-diagnose and self-adjust its filtering needs, allowing it to operate with higher EUV transmission while maintaining adequate spectral purity through intelligent, measurement-based control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate characterization of OOB light, allowing EUV tools to operate with high throughput while maintaining defect sensitivity and printability predictions, thus improving overall system performance and diagnostic capabilities.
Implementation Method 1
a grating to spectrally disperse the light from the substrate
Implementation Method 2
a band-selection filter to filter out the OOB light or the EUV IB light
Implementation Method 3
a sensor to detect the light from the substrate as relayed by the imaging optics and spectrally dispersed by the grating
Data Source
AI summary
A substrate is mounted on a chuck in a chamber of an EUV tool. An illumination aperture in the chamber provides a beam of light to illuminate the substrate on the chuck. The beam of light includes extreme ultraviolet (EUV) in-band (IB) light and out-of-band (OOB) light. The OOB light has longer wavelengths than the EUV IB light. A beam-narrowing aperture in the chamber, which is switchable into and out of a path for the beam of light, selectively narrows the beam of light to illuminate the substrate. A band-selection filter filters out the OOB light or the EUV IB light. Imaging optics in the chamber relay light from the substrate to an imaging plane. A grating spectrally disperses the light from the substrate. A sensor detects the light from the substrate as relayed by the imaging optics and spectrally dispersed by the grating.