Lithography Mask Position Error Measurement via Magnified Imaging
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Solution Overview
Problem
Existing methods for measuring relative local position errors in objects exposed section by section, such as lithography masks or wafers, are complex and costly, making it difficult to determine small errors accurately without intrafield distortion calibration.
Innovation Solution
A method and device that image a larger region of the object in magnified fashion, detect position errors of measurement marks, correct for errors caused by imaging and detection, and derive the relative local position error using high-pass filtering and averaging, allowing for accurate determination without precise object positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intrafield distortion calibration is performed to determine small position errors accurately, then measurement precision is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent segments the measurement process into two distinct parts: (1) capturing a magnified image of the entire exposure region containing multiple sections, and (2) processing the image data to extract position errors. By separating the imaging function from the calibration function, the system avoids the need for complex intrafield distortion calibration while maintaining high measurement precision through image-based analysis
Solution Approach 2:
The patent uses an optical copy (magnified image) of the exposure region to perform measurements. Instead of directly measuring the actual position errors on the object, the system creates a magnified visual copy and analyzes position errors from this image representation. This copying approach simplifies the measurement process and eliminates the need for complex calibration procedures
2Measurement precision
If multiple recordings are taken to improve measurement accuracy, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent transitions from a temporal approach (multiple sequential recordings) to a spatial approach (single magnified image capturing the entire region). By imaging the complete exposure field at once with magnification, the system extracts position information from the spatial distribution of features in the single image, eliminating the need for multiple time-consuming recordings
3Measurement precision
If high magnification imaging is used to detect small position errors, then measurement precision is improved, but errors caused by magnified imaging and detection increase
Solution Approach 1:
The patent employs a feedback mechanism where the magnified image is processed to identify position errors, and this information is used to correct for imaging and detection errors. The system uses the detected position data to calculate and compensate for systematic errors introduced by magnification, thereby improving overall measurement accuracy
Solution Approach 2:
The patent converts the harmful effect of magnification-induced errors into a beneficial measurement tool. By deliberately using magnified imaging that introduces measurable errors, the system can calculate these errors and use them to determine the actual position offsets. The magnification errors become a reference for calibrating the measurement system
Data Source
AI summary
A method for measuring the relative local position error of one of the sections of an object that is exposed section by section, in particular of a lithography mask or of a wafer, is provided, each exposed section having a plurality of measurement marks, wherein a) a region of the object which is larger than the one section is imaged in magnified fashion and is detected as an image, b) position errors of the measurement marks contained in the detected image are determined on the basis of the detected image, c) corrected position errors are derived by position error components which are caused by the magnified imaging and detection being extracted from the determined position errors of the measurement marks, d) the relative local position error of the one section is derived on the basis of the corrected position errors of the measurement marks.