Grating Talbot Effect Focal Plane Detection in Photolithography
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Solution Overview
Problem
Current methods for detecting the focal plane in photolithography machines suffer from low accuracy and poor anti-interference capabilities, failing to meet the high precision and efficiency requirements, especially with the enhancement of resolution and enlargement of exposure fields.
Innovation Solution
A method utilizing the Grating Talbot Effect, involving a system with a light source, beam collimator, 4f optical system, diffraction grating, and CCD detector, measures focal plane accuracy by analyzing the period and phase changes in Talbot self-images formed when the silicon wafer is in focus or defocused, allowing for precise detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CCD or PSD sensor methods are used for focal plane detection, then the measuring system is simple and easy to operate, but the measurement accuracy is low and cannot meet high-precision photolithography requirements
Solution Approach 1:
The patent introduces a diffraction grating as an intermediary element between the light source and detector. The grating converts focal plane position information into spatial frequency information through diffraction, enabling high-precision measurement. The grating equation d*sin(θ) = n*λ establishes a direct relationship between diffraction angle and wavelength, allowing accurate focal plane detection through spectral analysis.
Solution Approach 2:
The patent replaces conventional mechanical scanning methods with an optical field-based detection approach. Instead of physically moving the detector or sample to measure focal plane, the system uses optical diffraction patterns to encode focal position information, which is then decoded through image processing algorithms.
2Measurement precision
If moiré fringe detection method is used, then detection accuracy is improved, but the system has weak anti-interference capability and higher environmental requirements
Solution Approach 1:
The patent changes the detection parameter from spatial domain (moiré fringe patterns) to frequency domain (diffraction spectrum). By analyzing the spatial frequency distribution of diffraction orders, the system achieves robust focal plane detection that is insensitive to environmental disturbances such as vibration and thermal fluctuations.
Solution Approach 2:
The patent performs preliminary calibration by establishing the relationship between diffraction pattern characteristics and focal plane position before actual measurement. This pre-established calibration model enables rapid, accurate detection without requiring complex real-time environmental compensation.
3Area of stationary object
If multipoint measurement by array of slots is used, then coverage of exposure visual field is improved, but algorithm optimization is needed to improve measurement accuracy
Solution Approach 1:
The patent divides the diffraction pattern into multiple discrete diffraction orders, each carrying independent focal plane information. By analyzing the positions and intensities of individual diffraction orders separately and then combining the results, the system achieves both wide field coverage and high measurement precision.
Solution Approach 2:
The patent transforms the two-dimensional spatial measurement problem into a three-dimensional measurement by incorporating spectral information. The diffraction pattern provides both spatial position and frequency information, enabling simultaneous measurement of focal plane position and tilt across the exposure field.
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 provides a high-precision focal plane detection with improved anti-interference capabilities and efficiency, meeting the demands of advanced photolithography machines by using a common Ronchi grating and 4f optical system.
Implementation Method 1
a detection technique based on moiré fringe of a grating is applied to measurements for detecting focal plane in a projection photolithography system
Implementation Method 2
a diffraction grating, and a CCD detector
Data Source
AI summary
The present disclosure relates to a method for detecting focal plane based on a grating Talbot effect, the function of which is to detect position of a silicon wafer in a photolithography machine in real time so as to implement an adjustment of leveling and foal plane of the silicon wafer in a high resolution. The detection system utilizes a phase change of “self-image” generated by a grating Talbot effect caused by defocusing of the silicon wafer, so as to accomplish the detecting for focal plane of the silicon wafer in the photolithography machine in a high resolution: if the silicon wafer is at a focal plane, the imaged wavefront by the grating is a planar wavefront; and when the silicon wafer is defocused, the imaged wavefront is a spherical wavefront. Such a detection system has a simple structure, a higher anti-interference capability and a perfect adaption of the process.