Lithography Mask Structure Detection via Diffraction Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for detecting lithography mask structures often require stringent optical units and are prone to contamination and signal-noise ratio issues, particularly when using coherent illumination with pellicles, which can lead to inaccurate detection of particles and structure reconstruction.
Innovation Solution
A method and device utilizing diffraction imaging with partially coherent illumination, allowing structure detection without intermediate optical units, and employing iterative Fourier transformation and convolution techniques to improve accuracy, while using absorbers and HDR methods to manage signal-noise ratios and contamination effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent illumination with pellicles is used for structure detection, then measurement precision is improved, but contamination risks increase and signal-noise ratio deteriorates
Solution Approach 1:
The patent removes the pellicle from the optical path between the lithography mask and the detection plane. By extracting this intermediate component, the system eliminates the contamination risks and signal-noise ratio problems associated with pellicles, while maintaining structure detection capability through direct diffraction image recording
Solution Approach 2:
The patent introduces computational processing as an intermediary between light interaction and structure detection. Instead of relying on optical intermediaries like pellicles, the system uses algorithms to process diffraction images and reconstruct mask structures, transferring the detection function from optical to computational domain
2Measurement precision
If intermediate optical units are used in the beam path, then structure detection is enabled, but optical unit demands increase and device complexity increases
Solution Approach 1:
The patent extracts and removes intermediate optical units from the beam path between the lithography mask and detection plane. By eliminating these components, the system reduces device complexity and optical unit demands while maintaining structure detection capability through direct diffraction imaging
Solution Approach 2:
The patent replaces the mechanical/optical system of intermediate units with a computational system. Instead of using physical optical components to detect and process light, the system uses algorithms to analyze diffraction images, substituting mechanical complexity with computational processing
3Device complexity
If single illumination direction is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent employs periodic action by illuminating the lithography mask with light from multiple different directions in sequence. Each illumination direction provides complementary information about the mask structure, and by combining these periodic measurements, the system achieves high measurement precision without requiring complex simultaneous multi-directional illumination
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 reduces the demands on optical units, minimizes contamination risks, and enhances the accuracy of structure detection and reconstruction by leveraging diffraction imaging and advanced signal processing techniques, improving the reliability of lithography mask inspection.
Implementation Method 1
recording a diffraction image of the illuminated portion by spatially resolved detection of a diffraction intensity of the illumination light diffracted from the illuminated portion
Data Source
AI summary
In detecting the structure of a lithography mask, a portion of the lithography mask is firstly illuminated with illumination light of an at least partially coherent light source in the at least one preferred illumination direction. A diffraction image of the illuminated portion is then recorded by spatially resolved detection of a diffraction intensity of the illumination light diffracted from the illuminated portion in a detection plane. The steps of “illuminating” and “recording the diffraction image” are then carried out for further portions of the lithography mask. Between at least two portions of the lithography mask that are thereby detected, there is in each case an overlap region whose surface extent measures at least 5% or more of the smaller of the two portions of the lithography mask. The repetition takes place until the detected portions of the lithography mask completely cover a region of the lithography mask to be detected. The structure of the lithography mask is calculated from the recorded diffraction images of the illuminated portions. A device for carrying out the structure detection method is also specified, which comprises a light source, a spatially-resolving detector and a mask holder. This results in a method and a device for detecting the structure of a lithography mask, in which the demands placed on an optical unit arranged downstream in the beam path from the illumination light of the lithography mask are reduced.