Lithography Metrology Spatial Light Modulator Asymmetry Correction
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Solution Overview
Problem
Current dark-field metrology techniques for measuring asymmetry and overlay in lithographic processes are limited by low throughput and complexity due to the need to rotate substrates for optimal measurements, which can introduce tool-induced errors and reduce efficiency.
Innovation Solution
A method and apparatus that utilize a spatial light modulator to apply varying optical attenuation to diffracted radiation, allowing for asymmetry measurement without substrate rotation, using calibration measurements to correct for tool-induced errors and enhance sensitivity to performance parameters like focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If substrate rotation is performed to obtain optimal measurement results, then measurement accuracy is improved, but throughput decreases and device complexity increases
Solution Approach 1:
The patent replaces the mechanical substrate rotation system with an optical field rotation approach. Instead of physically rotating the substrate or the entire measurement apparatus, the invention rotates the illumination field and detection angles through controlled beam steering and optical path manipulation. This substitution eliminates mechanical complexity and measurement time associated with substrate rotation while maintaining the ability to capture diffraction orders from multiple angles, thereby improving throughput without sacrificing overlay measurement accuracy.
2Measurement precision
If substrate rotation is performed to obtain optimal measurement results, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The invention replaces mechanical substrate rotation with optical field manipulation. By using controllable illumination fields and beam steering mechanisms, the system achieves the same measurement objectives without requiring mechanical rotation stages or complex positioning systems. This reduces device complexity while maintaining measurement precision for asymmetry and overlay parameters.
Solution Approach 2:
The patent creates a measurement system that can perform multiple functions (measuring overlay, asymmetry, and focus) using a single fixed optical configuration. The versatile optical path design allows the same apparatus to capture diffraction orders from various angles and perform different measurements without requiring additional mechanical components or rotation mechanisms, thereby reducing overall device complexity while maintaining high measurement accuracy.
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 measurement accuracy and throughput by eliminating the need for substrate rotation, reducing tool-induced errors, and enabling direct measurement of parameters such as focus without substrate rotation, while maintaining high precision.
Implementation Method 1
a spatial light modulator which is controlled to apply a varying non-binary optical attenuation over the first and second selected parts of the diffracted radiation prior to forming the first and second images respectively
Implementation Method 2
the first image being formed using a first selected part of diffracted radiation, a second measurement step comprising forming and detecting a second image of the periodic structure while illuminating the structure with a second beam of radiation, the second image being formed using a second selected part of the diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure
Data Source
AI summary
Methods are disclosed for measuring target structures formed by a lithographic process on a substrate. A grating structure within the target is smaller than an illumination spot and field of view of a measurement optical system. The optical system has a first branch leading to a pupil plane imaging sensor and a second branch leading to a substrate plane imaging sensor. A spatial light modulator is arranged in an intermediate pupil plane of the second branch of the optical system. The SLM imparts a programmable pattern of attenuation that may be used to correct for asymmetries between the first and second modes of illumination or imaging. By use of specific target designs and machine-learning processes, the attenuation patterns may also be programmed to act as filter functions, enhancing sensitivity to specific parameters of interest, such as focus.