Defocus-Based Aperture Calibration for Optical Detection Systems
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Solution Overview
Problem
Existing exposure apparatuses face challenges in maintaining accurate pupil position adjustments in the illumination and imaging systems over an operation period without using costly encoders, which can fluctuate the refractive index and require restricted tools and time for adjustment.
Innovation Solution
A calibration method for a detection system that adjusts the positions of apertures in the illumination and imaging systems based on defocus characteristics, using a plurality of apertures with different openings, and performs position adjustments to return to a reference position, allowing self-contained calibration without encoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an encoder is used to store and maintain the pupil position adjustment, then the position accuracy can be maintained over operation periods, but the cost increases and the encoder generates heat that fluctuates the refractive index of air
Solution Approach 1:
The invention extracts and removes the encoder component from the system. Instead of using an encoder to store and maintain pupil position adjustment, the patent uses a computational method that calculates the optimal aperture stop position based on measured image quality metrics, thereby eliminating the harmful heat generation and refractive index fluctuations associated with encoders while maintaining position accuracy
Solution Approach 2:
The invention replaces the mechanical encoder-based position storage system with an optical measurement and computational calculation system. By measuring image quality metrics (such as modulation transfer function or contrast) and computationally determining the optimal aperture stop position, the system substitutes the mechanical encoder with a non-contact, heat-free optical and computational approach
2Ease of operation
If traditional adjustment techniques are used on the user site, then the pupil position can be adjusted, but the tools and time required for adjustment are largely restricted
Solution Approach 1:
The invention enables the exposure apparatus to perform self-calibration and self-adjustment of the aperture stop position without requiring external tools or expert intervention. The system automatically measures image quality metrics, computes the optimal position, and adjusts the aperture stop itself, thereby eliminating the need for restricted adjustment tools and reducing adjustment time significantly
Solution Approach 2:
The invention implements a feedback mechanism where the system continuously or periodically measures the actual image quality (using MTF, contrast, or other metrics) and uses this feedback to computationally determine and adjust the aperture stop position. This closed-loop feedback system enables rapid, accurate adjustment without requiring extensive manual calibration tools or time
3Measurement precision
If the aperture stop position is adjusted frequently to maintain accuracy, then the positioning accuracy is improved, but the operation time and complexity increase
Solution Approach 1:
The invention changes the approach from mechanical position tracking (using encoders) to optical parameter measurement (using image quality metrics such as MTF, contrast, or sharpness). By measuring these optical parameters and computationally deriving the optimal aperture stop position, the system achieves high positioning accuracy with simpler, more integrated calibration procedures that do not require complex external tools or frequent manual interventions
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 and efficient recalibration of the detection system, maintaining high positioning accuracy for improved overlay accuracy in semiconductor manufacturing, reducing reliance on costly encoders and minimizing mechanical fluctuations.
Implementation Method 1
an illumination system for illuminating a detection target (for example, a mark) formed on a substrate with detection (observation) light
Implementation Method 2
an imaging system for detecting an image of the detection target by concentrating light from the detection target
Implementation Method 3
forming an image of light from the detection target on a photoelectric conversion element
Data Source
AI summary
A calibration method of a detection system including an illumination system configured to illuminate a detection target, and an imaging system configured to form an image of light from the detection target on a photoelectric conversion element, the method including obtaining, for each of at least two combinations of first apertures in the illumination system and second apertures in the imaging system, each of which is formed by selecting one first aperture and one second aperture from the plurality of first apertures and the plurality of second apertures, a defocus characteristic indicating a shift amount of the image on the photoelectric conversion element with respect to a defocus amount of the detection target in a state in which each of the first aperture and the second aperture is positioned in a first position shifted from a reference position.