Sub-nanometer In-plane Distortion Measurement via Diffraction Grating
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Solution Overview
Problem
Conventional methods for measuring sub-nanometer spatial distortions, particularly in-plane distortions of planar substrates like semiconductor wafers, are inaccurate and prone to noise due to their inability to decouple in-plane from out-of-plane distortions and inefficiencies in optical interference patterns.
Innovation Solution
A measurement system utilizing a transmissive reference diffraction grating and a reflective workpiece diffraction grating, where light is diffracted at oblique angles to form specific beam orders, allowing for the acquisition of in-plane distortion data while minimizing out-of-plane distortion influence and optical noise, using a 1D or 2D grating configuration to simplify interference pattern analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement methods are used for sub-nanometer spatial distortions, then measurement can be performed, but measurement precision deteriorates due to inability to decouple in-plane from out-of-plane distortions
Solution Approach 1:
The patent segments the measurement of spatial distortions by using a diffraction grating to separate in-plane distortion signals from out-of-plane distortion signals. The grating structure divides the optical path into multiple diffraction orders, where specific orders (e.g., +1 and -1) carry in-plane distortion information while being insensitive to out-of-plane distortions, thus enabling precise measurement of in-plane distortions without interference from out-of-plane components.
Solution Approach 2:
The patent introduces a diffraction grating as an intermediary element between the light source and the workpiece. This grating acts as a mediator that modifies the optical interference pattern by diffracting light into specific orders, thereby enabling the decoupling of in-plane and out-of-plane distortion measurements and improving overall measurement precision.
2Measurement precision
If conventional optical interference patterns are used, then distortion data can be acquired, but signal contrast deteriorates and optical noise increases
Solution Approach 1:
The patent extracts the useful in-plane distortion signal from the complex optical interference pattern by selecting specific diffraction orders. By taking out only the +1 and -1 diffraction orders that carry in-plane distortion information and rejecting other orders that contribute to optical noise, the system achieves improved signal contrast and reduced noise in the measurement.
Solution Approach 2:
The patent applies local quality by making the measurement system sensitive to in-plane distortions in specific regions of the optical pattern while being insensitive to out-of-plane distortions. The diffraction grating creates local variations in the optical path that encode in-plane distortion information in specific diffraction orders, allowing selective enhancement of relevant signals while suppressing irrelevant noise.
3Measurement precision
If complex interference pattern analysis is used, then complete distortion data can be obtained, but data processing complexity increases
Solution Approach 1:
The patent extracts only the necessary in-plane distortion information by analyzing specific diffraction orders (+1 and -1) rather than processing the entire complex interference pattern. This extraction approach simplifies data processing while maintaining measurement accuracy, as the selected diffraction orders contain sufficient information about in-plane distortions without requiring analysis of all optical interference components.
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 achieves sub-nanometer accuracy in measuring in-plane distortions with improved signal contrast and reduced complexity in data processing, enabling precise characterization of workpiece shape and distortion changes.
Implementation Method 1
an optically-transparent member having a reference diffraction grating defined on a first surface thereof, the reference diffraction grating configured to diffract light in transmission
Implementation Method 2
a workpiece diffraction grating disposed in mechanical cooperation with the workpiece, the workpiece diffraction grating configured to diffract light in reflection
Implementation Method 3
acquiring a spatial light distribution defined by optical interference between the third and fourth beams with an optical detector to produce data representing the in-plane distortion of the substrate
Data Source
AI summary
A method for measuring a spatial distortion of a target surface (110) of a workpiece (110A). Light is transmitted twice through a reference pattern-generator (104) and impinged upon a workpiece pattern-generator (108). Then, with an optical detector (116), first and second beams formed by the light as a result of interaction with two pattern- generators (104) (106) is acquired to produce a signal characterizing geometry of interference fringes formed at the detector (116) by the first and second beams. Indicia representing at least one of a type and a value of spatial distortion of the target surface (110) is generated and recorded. A system embodying the implementation of the method.