Self-Moiré Metrology Targets for Unresolved Device Pitches
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Solution Overview
Problem
On-device overlay metrology is challenging due to unresolved device-like pitches, as modern optical tools struggle to measure these pitches using proxy targets with scales that are not fully process compatible, leading to target asymmetries and low re-scattering efficiency.
Innovation Solution
The use of self-Moiré principle in metrology targets with interlaced lines of elements having different device-like pitches, selected to yield a resolved Moiré pitch, which increases re-scattering efficiency and generates measurable signals for device-like pitches, even when they are unresolved, enabling accurate overlay measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If proxy targets with scales of hundreds of nanometers are used for overlay measurement, then measurement capability is improved, but process compatibility deteriorates and target asymmetries increase
Solution Approach 1:
The patent changes the fundamental parameters of the target design by using device-like pitches (≤100 nm) that match actual device dimensions, rather than traditional proxy target scales. This parameter change enables process compatibility while the Moiré effect mechanism preserves measurement capability through generated resolved pitches.
2Adaptability or versatility
If device-like pitches (≤100 nm) are measured directly, then process compatibility is improved, but measurement precision deteriorates due to unresolved pitches
Solution Approach 1:
The patent introduces an intermediary mechanism—the Moiré effect—where interlaced lines with different pitches act as mediators to convert unresolved device-like pitches into resolved Moiré pitches. This intermediary enables accurate measurement of otherwise unmeasurable small pitches.
Solution Approach 2:
The patent transforms the measurement parameter from direct observation of small pitches (≤100 nm) to observation of Moiré pitches (>400 nm), which are resolved by optical tools. This parameter transformation enables measurement of unresolved pitches through the Moiré effect.
3Ease of manufacture
If traditional grating targets are used, then manufacturing is simplified, but re-scattering efficiency deteriorates leading to low measurement accuracy
Solution Approach 1:
The patent employs a composite target structure combining interlaced lines with different pitches (p1 and p2) within the same target layer. This composite design enhances re-scattering efficiency by creating multiple diffraction orders that interact to produce strong Moiré signals, while remaining manufacturable using standard lithography processes.
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 improves the accuracy of on-device overlay measurements by generating propagating signals from unresolved pitches, allowing for precise measurement of device pitches and reducing target asymmetries, thereby enhancing the effectiveness of scatterometry and imaging metrology.
Implementation Method 1
Using the Moiré principle enables resolving small pitches, as the resolved pitch resulting from mutual re-scattering of diffraction orders between gratings with small unresolvable but close pitches is
Implementation Method 2
mutual re-scattering of diffraction orders between gratings
Data Source
AI summary
Metrology targets and methods are provided, which provide self-Moiré measurements of unresolved target features, i.e., interaction of electromagnetic fields re-scattered off elements within a single target layer provides signals with Moiré pitches that are measurable, although the actual target pitches are unresolved and possibly device-like. Targets comprise cell(s) with interlaced lines of elements having different device-like pitches which are selected to yield resolved Moiré pitch(es). Different target designs are presented for scatterometry and imaging metrology measurements, as well as for critical dimension, dose and focus, and pitch walk measurements—of device-like targets.