Site-by-Site Overlay Metrology with Telecentric Focus Alignment
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Solution Overview
Problem
Existing image-based overlay metrology systems face challenges in achieving precise measurements due to alignment errors such as focus, telecentricity, and centering errors, which vary across different overlay targets on a sample, leading to decreased measurement precision and throughput.
Innovation Solution
A site-by-site alignment method that captures multiple alignment images of overlay targets at different focal positions to generate alignment data, adjusting the imaging system to achieve focus, telecentricity, and centering tolerances before taking measurements, using a controller to align the sample within specified tolerances and determine accurate overlay between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single alignment is performed for the entire sample, then the alignment process is simple and fast, but measurement precision decreases due to localized variations of overlay targets
Solution Approach 1:
The patent divides the alignment process into site-by-site segments, performing alignment individually for each overlay target rather than aligning the entire sample once. This segmentation allows each target to be optimized independently, resolving the contradiction between measurement precision and process complexity by making the complexity localized rather than global.
Solution Approach 2:
The patent applies local quality by allowing different alignment parameters (focus, telecentricity, centering) to be optimized specifically for each overlay target location. This ensures that each measurement site has the optimal alignment settings tailored to its local characteristics, thereby improving measurement precision without requiring complex global adjustments.
2Measurement precision
If site-by-site alignment is performed for each overlay target, then measurement precision is improved, but measurement throughput decreases due to additional alignment steps
Solution Approach 1:
The patent performs preliminary alignment actions at each site before measurement, capturing alignment images and adjusting parameters in advance. This preliminary action ensures that when measurement occurs, the system is already optimized for that specific target, thereby maintaining high precision while streamlining the overall process flow.
Solution Approach 2:
The patent implements feedback by capturing alignment images at each site, analyzing them to determine alignment quality, and using this information to adjust alignment parameters before taking measurement images. This closed-loop feedback approach ensures optimal alignment without requiring excessive manual intervention, thereby maintaining throughput while improving precision.
3Measurement precision
If alignment images are captured at multiple focal positions, then alignment accuracy is improved, but measurement time increases
Solution Approach 1:
The patent applies partial action by capturing alignment images at multiple focal positions only when necessary to achieve the required alignment accuracy. The system evaluates the alignment data from these images and performs adjustments only to the extent needed, avoiding unnecessary time consumption while still achieving sufficient alignment accuracy for precise measurements.
Data Source
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AI summary
An overlay metrology tool providing site-by-site alignment includes a controller coupled to a telecentric imaging system. The controller may receive two or more alignment images of an overlay target on a sample captured at two or more focal positions by the imaging system, generate alignment data indicative of an alignment of the overlay target within the imaging system based on the alignment images, set the alignment images as measurement images when the alignment of the overlay target is within selected alignment tolerances, direct the imaging system to adjust the alignment of the overlay target in the imaging system and further receive one or more measurement images from the imaging system when the alignment of the overlay target is outside the selected alignment tolerances, and determine overlay between two or more layers of the sample based on at least one of the measurement images.