Focus Metrology Pattern with Varying Grating Pitches
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Solution Overview
Problem
Current focus metrology techniques in lithographic processes, particularly in EUV lithography, face challenges such as the need for sub-resolution features and large pitch grating structures, which are difficult to design and optimize, leading to time-consuming target selection procedures and less-than-optimal performance due to process condition changes.
Innovation Solution
A method and apparatus for measuring focus performance using a focus metrology pattern with varying geometric parameters across an array, allowing for measurement at selected subsets of locations, enabling derivation of focus performance without prior target parameter selection and optimizing metrology recipes for subsequent substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sub-resolution features and large pitch grating structures are used for focus metrology, then focus measurement capability is improved, but target design complexity and selection time increase
Solution Approach 1:
The patent changes the geometric parameters of the metrology target by varying the pitch of grating structures across different regions of the array. This allows the same target structure to provide focus measurement capability across multiple pitch values, eliminating the need to select and redesign separate targets for different process conditions.
Solution Approach 2:
The patent creates a universal metrology target that can serve multiple functions and adapt to different process conditions. By incorporating grating structures with varying pitches within a single target array, the same target can be used for focus metrology across different lithographic process conditions, reducing the need for multiple specialized targets.
2Measurement precision
If sub-resolution features and large pitch grating structures are used for focus metrology, then focus measurement capability is improved, but time required for target selection and optimization increases
Solution Approach 1:
The patent performs preliminary action by pre-configuring the metrology target with multiple grating structures of different pitches arranged in an array. This preliminary design ensures that the target is ready to provide focus measurement capability for various process conditions without requiring time-consuming selection and optimization procedures during production.
3Ease of manufacture
If fixed target parameters are used, then target design is simplified, but adaptability to process condition changes decreases
Solution Approach 1:
The patent incorporates a range of pitch values within the metrology target array, allowing the system to adapt to different process conditions by selecting appropriate regions of the array. This maintains relative design simplicity while providing adaptability, as the variation is achieved through systematic parameter changes rather than complex adaptive mechanisms.
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 simplifies focus metrology by eliminating the need for extensive target selection and optimization, providing more efficient and adaptable focus measurement capabilities across various process conditions, improving the consistency and accuracy of focus performance in lithographic processes.
Implementation Method 1
These devices direct a beam of radiation onto a target and measure one or more properties of the scattered radiation—e.g., intensity at a single angle of reflection as a function of wavelength; intensity at one or more wavelengths as a function of reflected angle; or polarization as a function of reflected angle—to obtain a diffraction 'spectrum' from which a property of interest of the target can be determined.
Data Source
AI summary
A lithographic apparatus prints a focus metrology pattern (T) on a substrate, the printed pattern including at least a first array of features (800). Features at any location within the array define a pattern that repeats at in at least a first direction of periodicity (X), while geometric parameters of the repeating pattern (w1, w3) vary over the array. A focus measurement is derived from measurements of the array at a selected subset of locations (ROI). As a result, the geometric parameters upon which the measurement of focus performance is based can be optimized by selection of locations within the array. The need to optimize geometric parameters of a target design on a reticle (MA) is reduced or eliminated. The measured property may be asymmetry, for example, and/or diffraction efficiency. The measured property for all locations may be captured by dark-field imaging, and a subset of locations selected after capture.