Focus Metrology Target Design for EUV Lithography
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Solution Overview
Problem
Current focus metrology techniques in lithographic processes, particularly in EUV lithography, face challenges due to the need for sub-resolution features and large grating structures, which contravene design rules and result in weak diffraction efficiency and signal strength, making it difficult to accurately measure focus performance.
Innovation Solution
The method involves simulating a Bossung response with focus-dependent parameters for different structures using computational lithography to select structures for focus monitoring, and deriving focus performance measurements based on metrology data and calibration models, eliminating the need for sub-resolution features and enhancing signal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sub-resolution features and large grating structures are used for focus metrology, then focus measurement capability is improved, but design rules are violated and signal strength is weakened
Solution Approach 1:
The patent changes the physical parameters of the metrology target by using resonant cavity structures with specific geometric configurations (e.g., annular rings, dashed lines, filled shapes) that create strong optical resonance effects. These parameter changes enable the target to produce enhanced diffraction signals without requiring sub-resolution features or large grating structures, thus resolving the contradiction between measurement precision and signal strength
Solution Approach 2:
The patent replaces traditional mechanical/optical diffraction-based focus measurement structures with resonance-based optical cavities. By substituting the measurement mechanism from relying on geometric diffraction patterns to relying on optical resonance phenomena, the system achieves strong signal strength while maintaining compliance with design rules and avoiding sub-resolution features
2Measurement precision
If sub-resolution features are used in patterning device, then focus sensitivity is improved, but design rules are violated
Solution Approach 1:
The patent transforms the metrology target from using sub-resolution features to using resonance cavity structures with dimensions that comply with standard design rules. The resonant cavities are designed with specific geometric parameters (area ratios, spacing, shapes) that enable focus-sensitive measurements while maintaining manufacturability and design rule compliance
Solution Approach 2:
The patent creates resonant cavity structures that copy the essential function of sub-resolution features (focus sensitivity) through a different physical mechanism (optical resonance). The cavities are designed to replicate the focus-dependent optical response needed for metrology while using manufacturable geometric features that obey design rules
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 allows for accurate and efficient focus performance measurement in lithographic processes, improving consistency and resolution without violating design rules, and is adaptable to EUV lithography and other projection-based lithography methods.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation... to obtain a diffraction 'spectrum' from which a property of interest of the target can be determined
Implementation Method 2
Diffraction-based overlay metrology using dark-field imaging of the diffraction orders enables measurement of overlay and other parameters on smaller targets
Data Source
AI summary
Disclosed is a method for selecting a structure for focus monitoring. The method comprises: simulating a Bossung response with focus of a focus dependent parameter, for one or more different structures; and selecting a structure for focus monitoring in a manufacturing process based on the results of said simulating step. The simulating step may be performed using a computational lithography simulation.