Overlay Metrology Target Fill Factor Modulation for Patterning Compatibility
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Solution Overview
Problem
Overlay metrology structures face a tradeoff between sensitivity and manufacturability, with existing designs often resulting in design rule violations and reduced performance due to optical limitations and lithographic process constraints, particularly in advanced patterning schemes like self-aligned double and quadruple patterning.
Innovation Solution
The solution involves a computer-implemented method for designing metrology targets using fill factor modulation and sub-resolution assist features (SRAF) to create composite periodic structures that maintain compatibility with advanced patterning techniques while enhancing sensitivity and printability, by replacing some target elements with assist elements having different geometric features and optimizing their placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the segmentation size is reduced to meet minimum design rule for manufacturability, then process compatibility is improved, but sensitivity decreases to a level where the sensor cannot extract overlay within reasonable uncertainty
Solution Approach 1:
The target structure is divided into multiple segments with different segmentation sizes. Some segments use larger pitch structures optimized for sensor sensitivity, while other segments use smaller pitch structures meeting minimum design rules for manufacturability. This allows different portions of the target to serve different functions simultaneously.
Solution Approach 2:
Different regions of the metrology target are assigned different local properties - specifically, different segmentation pitches are used in different areas. The target includes both coarse-pitch segments (for sensitivity) and fine-pitch segments (for process compatibility), allowing each region to be optimized for its specific purpose.
2Measurement precision
If large spaces are maintained between segmented structures to comply with optical resolution, then measurement capability is preserved, but process compatibility deteriorates due to impact on target performance and device-to-target similarity
Solution Approach 1:
CMP assist features are introduced as intermediary elements placed within the spaces between segmented structures. These assist features serve as mediators that maintain the necessary optical contrast and resolution while allowing the spaces to be reduced for better process compatibility. The assist features compensate for the reduced spacing by providing additional contrast mechanisms.
3Ease of manufacture
If CMP assist features are introduced to reduce effective spaces, then process compatibility is improved, but contrast is reduced impacting measurement capability
Solution Approach 1:
The target structure employs composite design elements combining different segmentation approaches - some segments maintain larger spaces for contrast, while other segments use CMP assist features for process compatibility. The overall target is a composite structure that integrates both approaches to achieve both measurement capability and manufacturability.
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 fidelity and printability of overlay metrology targets, ensuring they comply with design rules and maintain sufficient sensitivity for accurate overlay extraction within reasonable uncertainty, while reducing the impact of printing issues and scanner aberrations.
Implementation Method 1
a minimum of two diffraction orders are required to be collected by the sensor collection optics
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 2A
AI summary
Metrology targets and target design methods are provided, in which target elements are defined by replacing elements from a periodic pattern having a pitch p, by assist elements having at least one geometric difference from the replaced elements, to form a composite periodic structure that maintains the pitch p as a single pitch. Constructing targets within the bounds of compatibility with advanced multiple patterning techniques improves the fidelity of the targets and fill factor modulation enables adjustment of the targets to produce sufficient metrology sensitivity for extracting the overlay while achieving process compatibility of the targets.