Moiré Scatterometry Overlay Wavefront Tilt Correction
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Solution Overview
Problem
Existing scanning overlay metrology techniques are unsuitable for advanced overlay target designs, particularly those with Moiré structures, due to varying grating pitches that cause interference patterns and phase tilts, making accurate overlay measurements challenging.
Innovation Solution
A system and method utilizing a scanning overlay metrology tool that illuminates inverted Moiré structure pairs with mutually coherent beams, captures diffraction orders, and uses a diffractive element to correct wavefront tilts, allowing for accurate overlay measurements by isolating overlapping diffraction orders and removing interference patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If scanning overlay metrology is used to increase measurement efficiency, then productivity is improved, but measurement precision deteriorates due to interference patterns from varying grating pitches
Solution Approach 1:
The patent extracts and removes the harmful interference patterns from the measurement signal by using a reference measurement taken without the Moiré target present. This reference measurement contains the interference patterns caused by the varying grating pitches, which are then subtracted from the actual measurement to isolate the true overlay information.
Solution Approach 2:
The patent introduces a reference measurement as an intermediary element that mediates between the scanning measurement system and the Moiré target. This reference measurement serves as a mediator that captures the systematic interference patterns, allowing them to be separated from the actual overlay signal during data processing.
2Loss of information
If Moiré structures with varying grating pitches are used to encode overlay information, then measurement information is enhanced, but device complexity increases due to interference patterns
Solution Approach 1:
The patent converts the harmful interference patterns generated by the varying grating pitches into a beneficial reference signal. By deliberately measuring the interference patterns in a separate reference measurement, they become a useful tool for correcting the actual overlay measurements rather than remaining as unwanted artifacts.
Solution Approach 2:
The patent performs a preliminary measurement of the interference patterns before taking the actual overlay measurement. This preliminary action captures the systematic errors introduced by the Moiré structure design, allowing them to be compensated for in subsequent measurements through data processing.
3Measurement precision
If inverted Moiré structure pairs with different pitches are illuminated with coherent beams, then diffraction orders can be captured for overlay measurement, but wavefront tilts cause phase errors reducing measurement precision
Solution Approach 1:
The patent uses the reference measurement as feedback to correct the actual overlay measurements. The interference patterns captured in the reference measurement provide feedback information about the systematic errors, which are then used to adjust and correct the phase errors in the actual measurements through subtractive processing.
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
Enables efficient and accurate overlay measurements between layers with Moiré targets by correcting wavefront tilts and isolating relevant diffraction orders, improving measurement precision and throughput in scanning metrology.
Implementation Method 1
an illumination sub-system to illuminate the first and second Moiré structures of one of the one or more inverted Moiré structure pairs with common mutually coherent illumination beam distributions
Implementation Method 2
an objective lens to capture at least +/−1 diffraction orders from the upper and lower gratings of the illuminated one of the one or more inverted Moiré structure pairs as collected light
Implementation Method 3
a first pupil plane includes overlapping pupil-plane distributions of the collected light from the first and second Moiré structures with an interference pattern associated with a relative wavefront tilt
Implementation Method 4
a diffractive element located in the first pupil plane, where one diffraction order of the collected light associated with the first Moiré structure and one diffraction order of the collected light associated with the second Moiré structure overlap at a common overlap region in a field plane
Data Source
AI summary
An overlay metrology system may scan a sample including inverted Moiré structure pairs along a scan direction, include an illumination sub-system to illuminate first and second Moiré structures of one of an inverted Moiré structure pair with common mutually coherent illumination beam distributions, and include an objective lens to capture at least +/−1 diffraction orders from sample, where a first pupil plane includes overlapping distributions of the collected light with an interference pattern associated with relative wavefront tilt. The system may also include a diffractive element in the first pupil plane, where one diffraction order associated with the first Moiré structure and one diffraction order associated with the second Moiré structure overlap at a common overlap region in a field plane, and a collection field stop located in the field plane to pass light in the common overlap region and block remaining light and remove the relative wavefront tilt.