Optical Distortion Correction via High-Accuracy Reference Measurement
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Solution Overview
Problem
Modern optical measurement systems face significant challenges in correcting distortion errors, particularly in microlithography, where conventional methods struggle to manufacture error-free test structures with measurement accuracy requirements below 1 nm, making precise distortion correction difficult.
Innovation Solution
A method involving a second measurement system with higher accuracy to determine position errors of marks on a sample, which are then used to correct the distortion in the primary measurement system, allowing for improved measurement accuracy by accounting for measurement errors in subsequent measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional distortion correction methods are used, then the measurement system can operate with standard optical components, but the measurement precision deteriorates because distortion errors (e.g., 30 nm) exceed the required measurement accuracy (e.g., < 1 nm)
Solution Approach 1:
The patent introduces a coordinate transformation based on measured mark positions as an intermediary step between the optical measurement system and the ideal reference coordinate system. This transformation mediates the distortion errors by mathematically mapping measured positions to reference positions, enabling correction without requiring physically perfect test structures.
Solution Approach 2:
The patent creates a digital copy of the reference coordinate system through coordinate transformation data. Instead of requiring a physically perfect test structure, the method copies the ideal reference positions into a digital model that can be used for correction, eliminating the need for manufacturing error-free physical test structures.
2Measurement precision
If error-free test structures are manufactured to achieve high measurement accuracy, then measurement precision improves, but the manufacturing complexity and difficulty increase significantly
Solution Approach 1:
The patent replaces the need for physically perfect test structures with a digital copy of reference coordinates obtained through measurement and transformation. This copying approach eliminates the manufacturing complexity of creating error-free physical structures while maintaining the ability to achieve high measurement accuracy through computational correction.
Solution Approach 2:
The patent substitutes the mechanical manufacturing process of creating perfect test structures with a computational coordinate transformation process. Instead of mechanically manufacturing error-free structures, the method uses mathematical transformations to correct positions, replacing mechanical precision requirements with computational processing.
3Measurement precision
If distortion correction is performed using measured mark positions, then measurement accuracy improves, but additional measurement steps and processing time are required
Solution Approach 1:
The patent performs the coordinate transformation and distortion correction in advance, creating correction data that can be applied to subsequent measurements. This preliminary action separates the time-consuming correction process from routine measurements, reducing the time loss for actual measurement tasks.
Solution Approach 2:
The patent establishes a continuous correction process where coordinate transformations are performed once and then continuously applied to multiple measurements. This allows the useful action of measurement to continue without repeated interruption for correction, minimizing time loss while maintaining high accuracy across multiple measurements.
Data Source
AI summary
A method for correcting the distortion of a first imaging optical unit of a first measurement system is provided, wherein the first imaging optical unit has a first measurement accuracy and the method comprises the steps of:a) providing a first sample with first marks,b) measuring the positions of the first marks by use of a second measurement system comprising a second imaging optical unit, which has a second measurement accuracy that is better than the first measurement accuracy,c) establishing on the basis of the positions measured in step b) and predetermined intended positions of the first marks position errors of the first marks on the first sample produced during the manufacture of the first sample,d) measuring the positions of the first marks by use of the first measurement system,e) establishing the measurement error of the first imaging optical unit when determining the position of each first mark on the basis of the positions measured in step d), the position errors established in step c) and the predetermined intended positions of the first marks, andf) taking account of the measurement error established in step e) for correcting the distortion in the case of a further measurement with the first measurement system.