Multi-layer Overlay Metrology Target with Rotational Symmetry
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Solution Overview
Problem
Current overlay metrology systems face limitations in accurately measuring alignment between multiple layers in semiconductor processing due to the need for separate pattern elements for X- and Y-overlay measurements and potential issues with contrast levels in measurement structures.
Innovation Solution
A multi-layer overlay target with target structures invariant to 180-degree rotation and pattern elements with individual 180-degree rotational symmetry, allowing for simultaneous X- and Y-overlay measurements using a single image grab, and an apparatus with structured illumination and cross-polarization for contrast enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate pattern elements are used for X- and Y-overlay measurements, then measurement capability in both directions is achieved, but device complexity and measurement time increase
Solution Approach 1:
The patent combines X-overlay and Y-overlay measurement capabilities into a single pattern element structure. The target structure includes multiple pattern elements (e.g., four quadrants) that can simultaneously provide measurement information for both orthogonal directions, eliminating the need for separate dedicated pattern elements for each measurement direction.
Solution Approach 2:
The pattern element design makes each element universal by enabling it to serve multiple measurement functions. The same pattern element can be used for both X-overlay and Y-overlay measurements through appropriate image analysis algorithms, making the metrology system more versatile and efficient.
2Measurement precision
If multiple target structures are used for comprehensive overlay measurement, then measurement accuracy is improved, but contrast levels and image quality deteriorate
Solution Approach 1:
The patent applies local quality by optimizing the contrast properties of specific regions within the target structure. Different areas of the target are designed with appropriate pattern densities and geometries to ensure sufficient contrast for measurement while maintaining the overall multi-directional measurement capability. The pattern elements are locally optimized rather than uniformly designed.
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 improved accuracy in overlay metrology by allowing simultaneous measurement of alignment errors in multiple directions and enhances contrast levels in measurement structures, reducing measurement time and compatibility with existing metrology tools.
Implementation Method 1
a first polarizer configured to polarize at least a portion of light emanating from the illumination source; a second polarizer configured to analyze at least a portion of light reflected from the surface of the one or more specimens
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A multi-layer overlay target for use in imaging based metrology is disclosed. The overlay target includes a plurality of target structures including three or more target structures, each target structure including a set of two or more pattern elements, wherein the target structures are configured to share a common center of symmetry upon alignment of the target structures, each target structure being invariant to N degree rotation about the common center of symmetry, wherein N is equal to or greater than 180 degrees, wherein each of the two or more pattern elements has an individual center of symmetry, wherein each of the two or more pattern elements of each target structure is invariant to M degree rotation about the individual center of symmetry, wherein M is equal to or greater than 180 degrees.