EUV Inspection System with Modular Sensor Array and Catadioptric Optics
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Solution Overview
Problem
Current EUV mask inspection systems face challenges with low resolution and inadequate field of view, inefficient EUV photon generation, and inadequate sensitivity for features at 13 nm, requiring a high magnification and large field of view inspection system with a cost-effective EUV source that minimizes power consumption and debris effects.
Innovation Solution
The proposed inspection system includes a high brightness laser-pumped EUV plasma source with a double aperture component for pupil shaping, a modular array of sensor modules, and an optic configuration with multiple mirrors providing magnification and correcting keystone distortion, along with a detector subsystem for efficient EUV mask and wafer inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional transmissive microscopes with moderate NA are used for mask inspection, then the system provides sufficient sensitivity for deep UV mask defect detection, but the resolution and field of view are inadequate for EUV patterned mask inspection
Solution Approach 1:
The patent changes the wavelength parameter from deep UV to EUV (13.4 nm) to achieve the required resolution for smaller features. It also implements a reflective optical system instead of transmissive, and uses a catadioptric design combining mirrors and lenses to achieve both high resolution and large field of view simultaneously, resolving the contradiction between measurement precision and manufacturing precision
Solution Approach 2:
The inspection system is divided into multiple independent modules including illumination subsystem, detection subsystem, and processing subsystem. Each module can be optimized independently for its specific function while contributing to the overall system performance, allowing high resolution imaging with large field of view without compromising defect detection sensitivity
2Illumination intensity
If high average power EUV sources are used to provide sufficient brightness for inspection, then the etendue requirements are met, but power consumption increases significantly
Solution Approach 1:
The patent uses pulsed laser operation to generate EUV radiation from plasma, where high peak power is achieved during short pulses rather than continuous operation. This periodic action provides sufficient EUV brightness for inspection while reducing average power consumption and heat load on the system
Solution Approach 2:
The patent replaces conventional mechanical EUV source designs with a laser-produced plasma source, where optical energy from lasers is converted to EUV radiation through plasma generation. This substitution achieves high brightness with lower overall power consumption and reduced material degradation compared to traditional approaches
3Length of stationary object
If coherent deep UV illumination sources are used for mask inspection, then the system provides sufficient magnification for defect detection, but the sensitivity is inadequate for EUV masks with 13 nm features
Solution Approach 1:
The patent changes the illumination wavelength from deep UV (193 nm, 257 nm) to EUV (13.4 nm) to match the feature size of modern masks. This parameter change enables direct imaging of 13 nm features with adequate sensitivity, as the shorter wavelength provides the necessary resolution without requiring extreme magnification that would compromise field of view
4Area of stationary object
If a large field of view is implemented for EUV mask inspection, then cost-effective inspection is achieved, but the resolution decreases for detecting small defects
Solution Approach 1:
The patent implements a catadioptric optical system where different regions of the optical path have different functions - mirrors provide bulk magnification and field of view, while specialized lens elements at critical locations provide resolution enhancement. This local optimization of optical quality allows simultaneous achievement of large field of view and high resolution for defect detection
Solution Approach 2:
The patent uses a reflective optical system with multiple optical paths and dimensions to achieve high magnification (100X or greater) while maintaining a large field of view. By adding dimensional complexity to the optical design rather than simply increasing magnification in one dimension, the system resolves the trade-off between field of view and resolution
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
The system achieves high magnification and large field of view for EUV patterned masks and wafers, providing adequate sensitivity and cost-effectiveness with reduced power consumption and debris effects, enabling efficient EUV mask inspection.
Implementation Method 1
a high brightness laser-pumped EUV plasma source
Implementation Method 2
laser-pumped EUV plasma source
Implementation Method 3
an optic configuration with multiple mirrors providing magnification and correcting keystone distortion
Implementation Method 4
a detector subsystem for efficient EUV mask and wafer inspection
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
Inspection of EUV patterned masks, blank masks, and patterned wafers generated by EUV patterned masks requires high magnification and a large field of view at the image plane. An EUV inspection system can include a light source directed to an inspected surface, a detector for detecting light deflected from the inspected surface, and an optic configuration for directing the light from the inspected surface to the detector. In particular, the detector can include a plurality of sensor modules. Additionally, the optic configuration can include a plurality of mirrors that provide magnification of at least 100X within an optical path less than 5 meters long. In one embodiment, the optical path is approximately 2-3 meters long.