Alignment Sensor Asymmetry Correction for Lithography Overlay
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Solution Overview
Problem
Current lithographic apparatuses face challenges in accurately measuring the position of microstructures due to asymmetry in alignment marks, which can lead to overlay errors, especially as feature sizes decrease, and existing metrology tools are not suitable for high-throughput production.
Innovation Solution
A method and apparatus that measure asymmetry-related parameters simultaneously with position measurement using radiation diffraction signals at different wavelengths, polarizations, and spatial frequencies, allowing for correction of position measurements to account for asymmetry influences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing metrology tools are used to measure asymmetry, then measurement accuracy is improved, but throughput is reduced and device compatibility is worsened
Solution Approach 1:
The patent combines asymmetry measurement and position measurement into a single integrated process using the same alignment sensor and radiation beam. The sensor simultaneously captures diffraction signals that contain both position information and asymmetry information, eliminating the need for separate measurement tools and maintaining high throughput while achieving accurate asymmetry measurement.
Solution Approach 2:
The alignment sensor is designed to perform multiple functions: it measures both the position of alignment marks and the asymmetry of microstructures using the same hardware components. By analyzing diffraction signals at different wavelengths, polarizations, and spatial frequencies, the sensor achieves multi-functionality without requiring additional specialized equipment.
2Measurement precision
If asymmetry measurement is performed separately, then measurement accuracy is improved, but device complexity and measurement time increase
Solution Approach 1:
The patent merges asymmetry measurement and position measurement into a single integrated process using the same alignment sensor and radiation beam. The sensor simultaneously captures diffraction signals that contain both position information and asymmetry information, eliminating the need for separate measurement tools and maintaining high throughput while achieving accurate asymmetry measurement.
3Measurement precision
If multiple measurement parameters are captured simultaneously, then measurement accuracy is improved, but signal processing complexity increases
Solution Approach 1:
The patent utilizes variations in radiation parameters (wavelength, polarization, spatial frequency) to extract different measurement information from the same diffraction signals. By analyzing how the signals change with these parameter variations, the system simultaneously determines both position and asymmetry without requiring separate measurement setups, managing complexity through systematic parameter analysis.
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 enables more accurate position measurement and correction for asymmetry, improving overlay precision without reducing the throughput of the alignment system, and can be integrated with existing sensors to enhance measurement accuracy.
Implementation Method 1
measuring a property of a structure on, for example, a substrate, for example an asymmetry-related parameter, the method comprising: (a) illuminating the structure with radiation and detecting radiation diffracted by the structure
Data Source
AI summary
A lithographic apparatus includes a sensor, such as an alignment sensor including a self-referencing interferometer, configured to determine the position of an alignment target including a periodic structure. An illumination optical system focuses radiation of different colors and polarizations into a spot which scans the structure. Multiple position-dependent signals are detected and processed to obtain multiple candidate position measurements. Asymmetry of the structure is calculated by comparing the multiple position-dependent signals. The asymmetry measurement is used to improve accuracy of the position read by the sensor. Additional information on asymmetry may be obtained by an asymmetry sensor receiving a share of positive and negative orders of radiation diffracted by the periodic structure to produce a measurement of asymmetry in the periodic structure.