EUV Metrology Alignment of Complementary Diffraction Patterns
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Solution Overview
Problem
Metrology devices using EUV measurement radiation and projection optics with low numerical aperture face challenges in accurately aligning diffraction patterns due to significant intensity gradients, leading to loss of information when averaging signals over multiple wavelengths, which reduces sensitivity and makes sub-pixel alignment difficult.
Innovation Solution
A method is introduced to align pairs of complementary diffraction patterns by performing a fine alignment stage that interpolates measured values over a detector area and minimizes residual errors through translation and rotation, allowing for sub-pixel accurate comparison of intensity values across multiple wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If intensity values are averaged over a region of interest to determine intensity asymmetry, then measurement process is simplified, but information contained in diffracted orders is lost and sensitivity decreases
Solution Approach 1:
The patent divides the detector area into multiple discrete pixel elements rather than treating it as a continuous region. Each pixel's intensity value is processed individually, preserving the distinct information from each diffracted order while still enabling systematic analysis through pixel-by-pixel comparison.
Solution Approach 2:
The patent changes the measurement parameter from averaged intensity values to individual pixel intensity values. This parameter transformation allows the system to maintain sensitivity to diffracted order information while still providing a simplified measurement approach through direct pixel comparison between complementary diffraction patterns.
2Measurement precision
If multiple wavelengths are measured to increase sensitivity to parameters of interest, then sensitivity improves, but accurate alignment becomes more difficult due to intensity gradients
Solution Approach 1:
The patent replaces mechanical alignment procedures with an automated computational alignment method. The system uses cross-correlation algorithms to automatically determine sub-pixel shifts between diffraction patterns, eliminating the need for manual mechanical adjustment and enabling precise alignment even with multiple wavelengths present.
Solution Approach 2:
The patent creates a reference diffraction pattern from one wavelength measurement and compares it against diffraction patterns from other wavelengths. This copying and comparison approach enables the system to maintain consistent alignment across multiple wavelengths by referencing the known pattern geometry.
3Measurement precision
If sub-pixel alignment is performed to ensure accurate comparison of intensity values, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical sub-pixel positioning mechanisms with a computational cross-correlation method. The system calculates the optimal shift between diffraction patterns using algorithmic processing of pixel intensity values, achieving sub-pixel alignment accuracy through software rather than hardware complexity.
Solution Approach 2:
The patent implements a self-aligning measurement system where the diffraction patterns themselves provide the alignment information through their inherent geometric relationships. The cross-correlation algorithm automatically determines the relative positioning without requiring external alignment references or complex positioning systems.
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 method enhances the accuracy of parameter measurements, such as overlay, by ensuring precise alignment of diffraction patterns, thereby improving sensitivity and reducing the impact of process-induced structural asymmetry, even with low numerical aperture EUV metrology devices.
Implementation Method 1
detecting a complementary pair of diffraction orders following diffraction of the measurement radiation by the structure
Implementation Method 2
a detector for detecting the measurement radiation scattered by the structure
Data Source
AI summary
A method of aligning a pair of complementary diffraction patterns having a first complementary diffraction pattern and a second complementary diffraction pattern, the pair of complementary diffraction patterns obtained from performance of a metrology process on a structure formed by a lithographic process. The method includes performing at least a fine alignment stage to align the pair of complementary diffraction patterns. The alignment stage includes: interpolating measured values of the first complementary diffraction pattern over at least a portion of a detector area; and minimizing a residual between measured values in the second complementary diffraction pattern and corresponding interpolated values from the interpolation of the first complementary diffraction pattern, by one or both of translation and rotation of the second complementary diffraction pattern.