EUV Light Generating Apparatus Thermal Lens Correction
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Solution Overview
Problem
Extreme ultraviolet light generating apparatuses face challenges in maintaining accurate image formation due to focal point shifts caused by thermal lens effects and thermal deformations, which affect the measurement of droplets in the plasma generating region.
Innovation Solution
Incorporating a moving mechanism and stage driving unit to adjust the position of the imaging unit along the optical axis, allowing the control unit to correct the focal point shift based on measured light energy, ensuring the image formation plane matches the imaging surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed imaging system is used to measure droplets in the plasma generating region, then the device structure is simple, but the measurement precision deteriorates due to focal point shifts caused by thermal lens effects and thermal deformations
Solution Approach 1:
The imaging unit is made movable along the optical axis direction through a moving mechanism and stage driving unit, allowing dynamic adjustment of the image formation plane position to track and compensate for focal point shifts caused by thermal effects, thereby maintaining measurement precision without overcomplicating the overall system structure
Solution Approach 2:
The control unit receives information about focal point shifts (from light energy measurement or other sensing) and automatically adjusts the imaging unit position to maintain accurate focus, creating a closed-loop feedback system that corrects thermal drift without requiring manual intervention or system redesign
2Ease of operation
If the image formation plane position is fixed, then the device operation is simple, but the manufacturing precision deteriorates because the image formation plane cannot match the imaging surface when focal points shift
Solution Approach 1:
The image formation plane is made dynamically adjustable through the stage mechanism, allowing it to move along the optical axis to maintain alignment with the imaging surface despite thermal deformations, while the control unit automates the adjustment process to preserve operational simplicity
Solution Approach 2:
The system performs self-correction by automatically adjusting the imaging unit position based on detected focal point shifts, eliminating the need for manual realignment or complex external intervention while maintaining precise alignment between the image formation plane and imaging surface
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 solution enables precise measurement and control of droplet states, even when focal points shift, preventing out-of-focus images and improving the generation efficiency of extreme ultraviolet light.
Implementation Method 1
an LPP (Laser Produced Plasma) type apparatus that employs plasma which is generated by a target substance being irradiated with a laser beam
Implementation Method 2
an image forming optical system provided in the chamber, configured to form an image of the droplet
Implementation Method 3
a stage configured to move at least a portion of the image forming optical system and/or the imaging element in an optical axis direction
Implementation Method 4
a light energy measuring unit configured to measure light energy which is generated when the extreme ultraviolet light is generated
Data Source
AI summary
An extreme ultraviolet light generating apparatus may include: a chamber, within which extreme ultraviolet light is generated from a droplet which is supplied to a predetermined region therein; an image forming optical system that forms an image of the droplet supplied to the predetermined region; an imaging element that captures an image of the formed image; a stage that moves the image forming optical system and/or the imaging element in an optical axis direction of the image forming optical system; a light energy measuring unit that measures light energy which is generated when the extreme ultraviolet light is generated; and a control unit that controls the stage based on a measured value of the light energy measured by the light energy measuring unit such that an image formation plane of the image of the droplet formed by the image forming optical system matches an imaging surface of the imaging element.