Scanning Overlay Scatterometry Using Differential Diffraction Signals
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Solution Overview
Problem
Existing overlay metrology systems face challenges with low throughput due to the time required for stage settling and the need for high-sensitivity cameras, and they struggle with printing targets having different pitches.
Innovation Solution
A scanning diffraction-based overlay metrology system that uses an illumination sub-system to generate beams for grating-over-grating structures, collecting only +1 and -1 diffraction orders with separate photodetectors, allowing for differential signal analysis as the sample is scanned, thereby eliminating the need for stage settling and enabling high throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a move and measure (MAM) approach is used with a static sample during measurement, then measurement accuracy can be maintained, but the time required for stage settling reduces throughput
Solution Approach 1:
The system transitions from a static measurement approach to a dynamic scanning approach. The sample is continuously scanned through the measurement field while diffraction signals are collected in real-time, eliminating the need for stage settling while maintaining measurement accuracy through continuous data acquisition during motion
Solution Approach 2:
The measurement process becomes continuous rather than discrete. The sample scans continuously through the measurement field and diffraction signals are collected continuously throughout the scan, eliminating idle settling time and maximizing the utilization of measurement time
2Measurement precision
If image-based scatterometry overlay techniques are used with a high sensitivity camera, then overlay measurement sensitivity is improved, but the cost of the metrology sub-system increases
Solution Approach 1:
The system replaces the mechanical/imaging-based detection system (high sensitivity camera) with an optical diffraction-based detection system using photodetectors. This substitution maintains measurement sensitivity while reducing system cost and complexity by using simpler, more robust photodetector technology
Solution Approach 2:
The measurement approach changes from direct image capture to diffraction order intensity measurement. By measuring the intensities of specific diffraction orders (+1 and -1) and computing their difference, the system achieves high sensitivity overlay measurement without requiring expensive high-sensitivity cameras
3Reliability
If image-based scatterometry overlay techniques requiring two separate measurements per direction are used, then measurement completeness is achieved, but measurement time increases
Solution Approach 1:
The continuous scanning process allows simultaneous collection of diffraction signals for both measurement directions in a single pass, eliminating the need for separate measurements and reducing total measurement time while maintaining complete measurement coverage
Solution Approach 2:
The system merges multiple measurement functions into a single scanning operation. By collecting +1 and -1 diffraction order signals simultaneously during one continuous scan, the system achieves measurement completeness for both directions without requiring separate measurement passes
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
The system achieves high-throughput overlay measurements by scanning samples, reducing measurement time and eliminating the need for high-sensitivity cameras, while allowing for accurate overlay measurements on targets with common pitches.
Implementation Method 1
a first photodetector located in a pupil plane to collect +1-order diffraction from the overlay target, where the first photodetector does not collect 0-order diffraction from the overlay target. In embodiments, the collection sub-system includes a second photodetector located in a pupil plane to collect -1-order diffraction from the overlay target
Data Source
AI summary
An overlay metrology system includes a controller communicatively coupled to a first photodetector and a second photodetector. The controller may be configured to receive one or more signals from the first and second photodetector as an overlay target is scanned. The overlay target may include a plurality of measurement cells, where each measurement cell includes a grating-over-grating structure including a first-layer grating feature on a first layer of a sample and a second-layer grating feature on a second layer of the sample in an overlapping region. The first-layer grating feature and the second-layer grating feature may have a common pitch. The controller may be further configured to determine one or more differential signals between the first photodetector and the second photodetector for each measurement cell of the plurality of measurement cells and determine an overlay measurement based on the determined one or more differential signals.