Metrology Apparatus Using Single First-Order Beam for Overlay
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Solution Overview
Problem
Conventional scatterometers face challenges in accurately measuring smaller targets due to reduced throughput and increased space requirements, as well as aberrations influencing measurement results in dark field metrology.
Innovation Solution
A metrology apparatus and method that simultaneously illuminates and images multiple targets on a substrate using an illumination beam and objective lens, collecting radiation diffracted by the targets to form images with one first-order diffracted beam, allowing for separate target identification and correction for optical aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dark field metrology is used to measure smaller targets, then measurement accuracy is improved, but throughput is reduced and space requirements increase
Solution Approach 1:
The patent combines multiple measurement functions into a single optical path by using a beam splitter to simultaneously direct light to multiple detectors. This allows measurement of both the zeroth-order reflected light (for surface topology) and first-order diffracted light (for overlay) in parallel, thereby improving throughput while maintaining measurement accuracy for small targets
2Measurement precision
If dark field metrology is used to measure smaller targets, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent designs the optical system to perform multiple measurement functions using a unified optical path. The same objective lens and beam splitter assembly handle both zeroth-order and first-order light collection, reducing the need for separate measurement systems and simplifying the overall device complexity while maintaining high measurement accuracy
3Measurement precision
If multiple pairs of differently biased gratings are used for accurate overlay determination, then measurement accuracy is improved, but space requirements increase
Solution Approach 1:
The patent segments the overlay measurement process by using a beam splitter to separate the optical path into two channels: one for measuring zeroth-order reflected light and another for measuring first-order diffracted light. This allows accurate overlay determination using a single grating pair rather than multiple pairs, thereby reducing the space required on the substrate while maintaining measurement accuracy
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 more accurate and efficient measurement of smaller targets with improved throughput and reduced space requirements, while compensating for optical aberrations to enhance measurement accuracy.
Implementation Method 1
The objective lens is configured to direct the measurement beam of radiation onto the targets on the substrate and to collect radiation diffracted by the targets
Data Source
AI summary
A metrology apparatus is arranged to illuminate a plurality of targets with an off-axis illumination mode. Images of the targets are obtained using only one first order diffracted beam. Where the target is a composite grating, overlay measurements can be obtained from the intensities of the images of the different gratings. Overlay measurements can be corrected for errors caused by variations in the position of the gratings in an image field.