Scatterometer Overlay Error Detection Using 0th Diffraction Order Validation
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Solution Overview
Problem
Existing lithographic techniques often fail to detect overlay errors between gratings that are smaller than the pitch but larger than the bias, leading to undetected errors in the order of 5-20nm, which can result in incorrect measurements.
Innovation Solution
A method using data from the ±1st diffraction orders to measure overlay errors and the 0th diffraction order as an error check, implemented in a scatterometer system that analyzes the intensity of diffraction orders to differentiate between asymmetries with the same overlay error value, thereby identifying false low overlay calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher diffraction orders are analyzed to determine overlay errors, then small overlay errors can be detected, but overlay errors between bias and pitch values can go undetected
Solution Approach 1:
The patent introduces the 0th diffraction order as an intermediary element to validate measurements from higher diffraction orders. By using the 0th order intensity ratio as a reference standard, the system can identify when higher order measurements are unreliable and exclude them from final overlay error calculations, thus preventing false measurements while maintaining detection sensitivity
Solution Approach 2:
The patent implements a feedback mechanism where the 0th diffraction order measurement provides validation feedback for higher diffraction order measurements. When the 0th order intensity ratio falls outside expected ranges, it signals that the higher order measurements should be discarded, creating a self-correcting measurement system that adapts to measurement reliability
2Ease of operation
If asymmetry of diffracted beams is used to determine overlay error, then overlay measurement can be performed, but false low overlay calculations occur when asymmetries have same overlay error value
Solution Approach 1:
The patent makes the 0th diffraction order serve multiple functions: it acts as a reference for validating higher order measurements, provides an independent overlay measurement method, and serves as a quality control checkpoint. This multi-functional use of the 0th order enables the system to both perform measurements and validate their accuracy simultaneously
3Ease of manufacture
If conventional scatterometry methods are used, then measurement process is simple, but overlay errors greater than bias but smaller than pitch cannot be reliably detected
Solution Approach 1:
The patent adds a new dimension to scatterometry by incorporating the 0th diffraction order intensity ratio as an additional measurement parameter. This dimensional addition creates a validation layer that works perpendicular to the traditional higher order measurement approach, enabling the system to detect reliability issues without complicating the fundamental measurement process
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 allows for the accurate detection of overlay errors greater than the bias but smaller than the grating pitch, ensuring reliable measurements by utilizing the intensity difference between the 0th diffraction orders for overlapping gratings with positive and negative biases.
Implementation Method 1
By analysing the characteristics of the reflected radiation it is possible to determine the overlay error OV, between the patterns. Analyzing the characteristics of the higher diffraction orders of the reflected radiation can be used to determine small overlay errors
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
Both the 1st and 0th diffraction orders are detected in a scatterometer. The 1st diffraction orders are used to detect the overlay error. The 0th diffraction order is then used to flag if this is a false overlay error calculation of magnitude greater than the bias but smaller than the pitch of the grating.