EUV Source Borescope Inspection for Tin Debris Monitoring
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Solution Overview
Problem
The deposition of tin debris in the EUV radiation source of extreme ultraviolet lithography systems reduces the intensity and direction of generated EUV radiation, necessitating a method to monitor and determine when cleaning is required to maintain efficiency.
Innovation Solution
An observation system with a borescope and camera assembly, attached to an extendible lead screw assembly, is used to acquire images of the chamber interior, allowing analysis of tin debris accumulation and determining if cleaning thresholds are exceeded, with the system capable of extending beyond a blocking shield to image the IF cap region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blocking shield is placed in the chamber to prevent laser beam escape, then laser safety is improved, but the ability to image the IF cap region is blocked
Solution Approach 1:
The chamber is segmented into two functional zones: a laser generation zone with the blocking shield for safety, and an imaging zone at the IF cap region that can be accessed by the borescope. This spatial segmentation allows the blocking shield to remain in place for laser safety while the extendible borescope can image the IF cap region without being blocked.
2Difficulty of detecting and measuring
If the borescope is extended beyond the blocking shield to image the IF cap region, then imaging capability is improved, but the system complexity increases
Solution Approach 1:
The extendible borescope assembly acts as an intermediary device that bridges the gap between the blocked viewing area and the imaging camera. It allows the camera to capture images of the IF cap region through the opening without requiring the blocking shield to be removed or modified, thus maintaining laser safety while enabling imaging.
3Productivity
If tin debris accumulates on the collector mirror, then EUV radiation intensity decreases, but cleaning operations require system shutdown and disassembly
Solution Approach 1:
The imaging system enables preliminary monitoring of tin debris accumulation on the collector mirror and in the IF cap region before cleaning is required. By detecting debris levels in advance through regular imaging, the system allows for planned cleaning operations rather than emergency shutdowns, improving operational efficiency and reducing the frequency of disassembly.
4Measurement precision
If the borescope camera is positioned to image the IF cap region, then monitoring accuracy is improved, but the device requires extension mechanisms increasing complexity
Solution Approach 1:
The borescope assembly incorporates dynamic extension capability through a lead screw mechanism, allowing the camera to move from a retracted position to an extended position where it can image the IF cap region. This dynamic positioning enables the camera to achieve optimal imaging angles and distances for accurate monitoring while maintaining a compact configuration when not in use.
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
Enables accurate monitoring of tin debris accumulation, ensuring timely cleaning to maintain EUV radiation intensity and direction, thereby improving the overall efficiency of the EUV radiation source.
Implementation Method 1
a high-power laser beam is focused on small droplet targets of metal, such as tin, to form a highly ionized plasma that generates EUV radiation with a peak maximum emission at 13.5 nm
Implementation Method 2
acquire images of the chamber interior, allowing analysis of tin debris accumulation
Data Source
AI summary
A method of inspecting an extreme ultraviolet (EUV) radiation source includes, in an idle mode, inserting a borescope mounted on a fixture through a first opening into a chamber of the EUV radiation source. The borescope includes a connection cable attached at a first end to a camera. The EUV radiation source includes an excitation laser that generates a light beam that is configured to focus onto tin droplets to generate EUV radiation inside the chamber of the EUV radiation source. The method further includes extending the extendible section, in a direction toward the second opening of the EUV radiation source, to move the camera beyond the blocking shield, and acquiring one or more images from a region beyond the blocking shield. The method also includes analyzing the one or more acquired images to determine an amount of tin debris deposited inside the chamber of the EUV radiation source.