Superimposed Grating Overlay Target for Lithography
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Solution Overview
Problem
Existing lithographic scatterometers require a significant area on the substrate to determine overlay error, which is undesirable due to space constraints in device manufacturing.
Innovation Solution
A substrate with superimposed patterns having different periodicities in orthogonal directions, allowing for spatial distinction of diffraction patterns, enabling efficient measurement of overlay error without interference between patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple superimposed gratings are used to determine overlay error, then measurement capability is improved, but the area occupied on the substrate increases
Solution Approach 1:
The patent applies dimensionality change by using gratings with different orientations (first set in one direction, second set in another direction) and different periodicities. This allows the diffraction patterns from each grating set to be spatially separated in the diffraction pattern image, enabling independent measurement of overlay errors for each grating set without requiring separate physical areas on the substrate.
Solution Approach 2:
The patent segments the measurement function by creating distinct grating sets with different characteristics (orientation and periodicity). Each grating set can be independently analyzed through its unique diffraction pattern, allowing simultaneous measurement of multiple overlay errors in a single compact target area on the substrate.
2Loss of information
If multiple superimposed patterns are used for measurement, then measurement information increases, but diffraction pattern interference occurs
Solution Approach 1:
The patent applies local quality by assigning different local characteristics to different grating sets - specifically different orientations and different periodicities. This creates distinct diffraction pattern signatures for each grating set, allowing the measurement system to locally identify and analyze each pattern type separately, thus preventing interference while maintaining rich measurement information.
Solution Approach 2:
The patent changes physical parameters of the gratings - specifically the orientation angle and periodicity - to create distinguishable diffraction patterns. By varying these parameters across different grating sets, each set produces a unique diffraction signature that can be independently detected and analyzed, eliminating cross-interference while preserving comprehensive measurement data.
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 reduces the area required for overlay error measurement by allowing for the selective detection of diffraction orders from each pattern set, minimizing crosstalk and optimizing substrate usage.
Implementation Method 1
the diffraction patterns of at least one order corresponding to each of the first and second pluralities of superimposed patterns are spatially distinguishable from each other
Data Source
AI summary
A second set of superimposed gratings are superposed over a first set of superimposed gratings. The second set of gratings have a different periodicity from the first set of gratings or a different orientation. Consequently the first order diffraction pattern from the second set of superimposed gratings can be distinguished from the first order diffraction pattern from the first set of superimposed gratings.