EUV Plasma Position Detection Using Dual Optical Systems
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Solution Overview
Problem
In mask defect inspection using extreme ultraviolet (EUV) light, the position of the plasma bright spot can fluctuate, causing illumination deviations from the inspection region, which necessitates accurate detection and correction of the plasma position shift.
Innovation Solution
A position detection apparatus and method that utilize a first optical system and a second optical system, along with position detectors, to focus and detect EUV light and other wavelength components, enabling the detection of plasma position changes in multiple directions and correcting the optical axis of the EUV light optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a light source of laser produced plasma (LPP) scheme is used to generate EUV light, then EUV light can be generated for mask inspection, but the position of the plasma bright spot fluctuates causing illumination deviation from the inspection region
Solution Approach 1:
The patent implements a feedback mechanism where the position of the plasma bright spot is continuously monitored using optical systems that detect light emitted from the plasma. The detected position information is fed back to control systems that adjust the relative positions of the laser beam and target, or adjust the illumination optical system, to maintain the plasma bright spot at the desired position for stable critical illumination of the inspection region.
Solution Approach 2:
The patent replaces direct mechanical positioning mechanisms with optical detection and control systems. Instead of mechanically stabilizing the plasma position through precision mechanical stages, the system uses optical fields to detect plasma position and converts this information into control signals for actuators that adjust the optical paths or target positions, substituting mechanical stability requirements with optical measurement and active control.
2Reliability
If the position of the plasma bright spot changes, then the illumination deviates from the inspection region, but implementing position detection and correction systems increases device complexity
Solution Approach 1:
The patent makes the optical detection system multi-functional by using the same optical paths and detectors to serve both the EUV light collection function and the plasma position detection function. The optical systems are configured to simultaneously extract EUV light for inspection and detect visible or UV light from the plasma for position monitoring, allowing one system to perform multiple functions and reducing overall device complexity.
Solution Approach 2:
The patent introduces optical intermediaries such as dichroic mirrors, beam splitters, and wavelength-selective filters that allow the detection system to extract position information from the plasma light without interfering with the EUV light path. These intermediary optical elements enable the separation and routing of different wavelength components, allowing position detection to occur alongside EUV light collection without requiring completely separate systems.
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
Improves the detection accuracy of the plasma position, ensuring stable illumination and maintaining inspection precision by accurately tracking and correcting plasma position shifts.
Implementation Method 1
plasma generated by causing the condenser lens to focus laser light on a target
Implementation Method 2
focus laser light on a target to generate plasma
Implementation Method 3
light including the first light and second light generated along with EUV light from plasma
Implementation Method 4
EUV light from plasma generated by causing the condenser lens to focus laser light on a target
Implementation Method 5
a first optical system configured to focus first light by a condenser lens
Implementation Method 6
a second optical system configured to focus the second light, a second position detector that detects the second light focused by the second optical system
Data Source
AI summary
A position detection apparatus according to the present disclosure includes a first optical system configured to focus, among light including first light and second light generated along with EUV light from plasma generated by causing a condenser lens to focus laser light on a target, the first light by the condenser lens, a first position detector configured to detect the first light focused by the first optical system, a second optical system configured to focus the second light, a second position detector configured to detect the second light focused by the second optical system, and a position detection processing unit configured to detect change of a position of the plasma from change of a spot of the first light and change of the spot of the second light.