Overlay Error Metrology Method for Lithographic Substrates
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Solution Overview
Problem
Current metrology solutions for overlay errors in lithographic processes are limited by measurement errors caused by target structural asymmetry, which can lead to inaccurate alignment of patterns in different layers, resulting in issues like short circuits and reduced fabrication yield.
Innovation Solution
A method to determine overlay error by obtaining an apparent overlay error and systematically removing errors caused by factors other than misalignment, using diffraction orders to correct for asymmetry and improve measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology methods are used to measure overlay error, then measurement can be performed, but measurement precision deteriorates due to target structural asymmetry causing systematic errors
Solution Approach 1:
The patent extracts and removes the systematic error component from the apparent overlay error measurement. By separating the true overlay error from the asymmetry-induced systematic error, the method achieves more accurate and reliable measurements. The systematic error is identified and subtracted from the apparent error to obtain the corrected overlay error value.
Solution Approach 2:
The patent implements a feedback mechanism where the measured apparent overlay error is used to calculate and remove the systematic error component. The corrected overlay error then feeds back into the alignment process, enabling iterative refinement of measurement accuracy and compensating for target structural asymmetries.
2Manufacturing precision
If alignment targets are used to align substrates, then alignment can be achieved, but measurement precision deteriorates due to asymmetry in target structures
Solution Approach 1:
The patent extracts the systematic error component that arises from target structural asymmetry and removes it from the measurement. This separation allows the true alignment precision to be determined without the contaminating effect of target asymmetry, thereby improving both measurement precision and manufacturing precision.
Solution Approach 2:
The patent changes the parameter being measured from the apparent overlay error (which includes systematic errors) to the corrected overlay error (which has had the systematic error removed). This parameter transformation enables more precise alignment by accounting for target structural asymmetries.
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 enhances the accuracy and reliability of overlay error measurements, reducing the impact of structural asymmetry and improving the alignment of patterns in different layers, thereby increasing fabrication yield and reducing device failures.
Implementation Method 1
a measurement beam B is directed onto a target structure T on the substrate W to provide diffraction orders
Data Source
AI summary
A method to determine an overlay error between a first structure and a second structure, wherein the first structure and second structures are on different layers on a substrate and are imaged onto the substrate by a lithographic process, the method comprising: obtaining an apparent overlay error; obtaining a systematic error caused by a factor other than misalignment of the first and second structures; and determining the overlay error by removing the systematic error from the apparent overlay error. The method may alternatively comprise obtaining apparent characteristics of diffraction orders of diffraction by an overlapping portion of the first and second structures; obtaining corrected characteristics of the diffraction orders; determining the overlay error from the corrected characteristics; and adjusting a characteristic of the lithographic process based on the overlay error.