Metrology Method for Overlay Measurement Accuracy
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Solution Overview
Problem
Standard dark field metrology methods provide inaccurate overlay measurements for damaged or highly varied semiconductor metrology targets, as they rely on average pixel intensity, which is unreliable in such cases.
Innovation Solution
A method is developed to select a Region of Interest (ROI) by identifying pixels with similar values in images from metrology tools, using discriminating algorithms to differentiate between invariant and affected pixels, and employing weighted averages for accurate overlay measurement, even in extreme cases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard dark field metrology methods are used to measure overlay, then the measurement process is simple and fast, but the measurement accuracy deteriorates for damaged or highly varied targets
Solution Approach 1:
The patent divides the metrology target into multiple regions and further segments pixels within each region. By identifying and selecting only the invariant pixels that remain consistent across different measurements, the method isolates reliable data points from damaged or varied areas, thereby maintaining measurement accuracy without sacrificing the efficiency of standard dark field metrology
Solution Approach 2:
The patent applies different processing treatments to different regions of the target based on their quality characteristics. Invariant pixels are identified and given weight in the overlay calculation, while affected pixels are excluded or down-weighted. This local differentiation ensures that only high-quality data contributes to the final measurement, resolving the accuracy issue for damaged targets
2Device complexity
If average pixel intensity is used for overlay measurement, then the calculation is simple, but the measurement reliability deteriorates when targets are damaged or highly varied
Solution Approach 1:
The patent performs preliminary analysis of pixel values across multiple measurements before the final overlay calculation. By pre-identifying which pixels are invariant and which are affected, the method prepares a filtered set of reliable data points in advance. This preliminary action ensures that only trustworthy pixels are used in the subsequent weighted average calculation, significantly improving reliability while keeping the actual measurement process efficient
Solution Approach 2:
The patent changes the parameter used for calculation from a simple unweighted average to a weighted average based on pixel invariance. By assigning weights to pixels based on their reliability (invariant pixels receive higher weights), the method transforms the calculation to be more robust against damage and variation, thereby improving measurement reliability without excessive 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 accurate overlay measurement using standard dark field metrology methods, reducing the impact of processing effects and improving measurement reliability for damaged targets.
Implementation Method 1
scatterometry devices direct a beam of radiation onto a target and measure one or more properties of the redirected (e.g., scattered) radiation
Implementation Method 2
A further technique involves having the zeroth order of diffraction (corresponding to a specular reflection) blocked, and only higher orders are processed
Data Source
AI summary
A method provides the steps of receiving an image from a metrology tool, determining individual units of said image and discriminating the units which provide accurate metrology values. The images are obtained by measuring the metrology target at multiple wavelengths. The discrimination between the units, when these units are pixels in said image, is based on calculating a degree of similarity between said units.