Dynamic Optical Array Illumination Control for Aberration Compensation
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Solution Overview
Problem
Optical lithography faces challenges in achieving diffraction-limited performance due to optical aberrations and imperfections in illumination and collection optics, which affect overlay metrology accuracy in semiconductor manufacturing.
Innovation Solution
The use of dynamic optical array devices, such as micro-mirror arrays, in both pupil and field conjugate planes within the illumination optics to control and optimize the spatial and angular distribution of light, allowing for intentional aberration compensation to match the collection optics' flaws, thereby enhancing illumination quality and reducing overall system errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard illumination optics are used, then the system is simple and cost-effective, but optical aberrations and imperfections degrade illumination quality and reduce overlay metrology accuracy
Solution Approach 1:
A spatial light modulator is introduced as an intermediary device in the illumination path to dynamically correct optical aberrations. The SLM acts as a mediator between the imperfect illumination optics and the measurement system, applying computationally calculated phase and amplitude corrections to compensate for optical imperfections, thereby improving overlay metrology accuracy without requiring complete redesign of the illumination optics
Solution Approach 2:
The system dynamically changes the optical parameters (phase and amplitude) of the illumination light using the spatial light modulator. By computationally calculating the optimal illumination conditions and applying them through the SLM, the system adapts illumination parameters to compensate for optical aberrations, improving measurement precision while maintaining relatively simple hardware
2Illumination intensity
If diffusers are used to improve illumination, then illumination quality is enhanced, but control over illumination characteristics is lost due to their random nature
Solution Approach 1:
The spatial light modulator provides dynamic control over illumination characteristics, allowing real-time adjustment of phase and amplitude parameters. Unlike static diffusers, the SLM can be programmatically controlled to create specific illumination patterns and correct aberrations, maintaining both high illumination quality and precise control through software-driven operation
Solution Approach 2:
The system employs computational feedback to determine the optimal illumination conditions. By calculating the required phase and amplitude corrections based on the optical system's characteristics and measurement requirements, the SLM is dynamically configured to provide both high-quality illumination and precise control, eliminating the randomness inherent in diffuser-based approaches
3Reliability
If high-quality optics are used to achieve diffraction-limited performance, then illumination quality improves, but system cost and complexity increase
Solution Approach 1:
The system accepts the presence of optical imperfections and aberrations rather than attempting to eliminate them through expensive high-quality optics. Instead, it computationally characterizes these imperfections and uses the spatial light modulator to apply corrective phase and amplitude modifications, converting the harm of optical imperfections into a manageable parameter that can be corrected through computation, thereby achieving diffraction-limited performance with simpler, lower-cost optics
Solution Approach 2:
The system replaces the mechanical/optical approach of using high-precision optics with a computational approach. Rather than relying on mechanically perfect optical components, the system uses computational algorithms to determine correction parameters and applies them through the spatial light modulator, substituting mechanical precision with computational correction to achieve the same illumination quality at lower cost and complexity
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 the delivery of a diffraction-limited, aberration-free illumination spot, improving overlay metrology accuracy and enabling the use of optics of reduced quality while optimizing illumination for various applications, thus enhancing the precision and cost-effectiveness of optical systems.
Implementation Method 1
a first dynamic optical array device located in a pupil conjugate of the illumination optics is adjusted to compensate for a spatial distribution of aberrations
Implementation Method 2
a second dynamic optical array device located in a field conjugate of the illumination optics is adjusted to compensate for an angular distribution of aberrations
Data Source
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AI summary
An optical system may include an objective, a source of illumination, an illumination system having illumination optics configured to direct the illumination onto the objective, and at least two dynamic optical array devices located at a pupil conjugate plane and a field conjugate plane, respectively in the illumination optics. The dynamic optical array devices are configured to control one or more properties of illumination coupled from the illumination system to the objective.