Overlay Error Measurement Using Correlation Profiles
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Solution Overview
Problem
Conventional overlay error measuring devices face challenges in achieving high precision when measuring dimensions between patterns across layers, especially when the lower layer pattern is obscured by a thin film, leading to insufficient signal quantity and difficulty in securing accurate measurements.
Innovation Solution
An overlay error measuring device that uses a charged particle beam to extract signal waveforms, processes them to find correlations, and measures dimensions using correlation profiles, allowing for precise measurements even with weak signal quantities from lower layers by discriminating between different luminance levels and using symmetry profiles for center of gravity detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a charged particle beam device is used to measure overlay error, then measurement precision is improved, but signal quantity from the lower layer becomes insufficient when a thin film is present
Solution Approach 1:
The signal waveform is segmented into multiple portions based on luminance thresholds. The extraction portion is identified by comparing signal intensity at different positions, and only the relevant segment containing the lower layer pattern information is used for correlation calculation. This segmentation allows the system to isolate useful signal portions from the weak lower layer signal even in the presence of a thin film.
Solution Approach 2:
The system dynamically adjusts the threshold value for signal extraction based on the measured signal waveform characteristics. By changing the threshold parameter adaptively, the system optimizes the extraction of lower layer pattern information from the weak signal, improving measurement precision without requiring increased signal quantity.
2Measurement precision
If conventional edge detection methods are used for each layer, then measurement process complexity increases, but measurement precision may be compromised when lower layer signal is weak
Solution Approach 1:
The system merges the detection of upper and lower layer patterns into a single correlation-based measurement process. Instead of separately detecting edges for each layer and then calculating dimensions, the system performs correlation calculation between the extracted signal waveform and a reference waveform, automatically determining the dimension between layers in one integrated step.
Solution Approach 2:
The correlation profile serves as an intermediary that bridges the upper and lower layer pattern information. By calculating the correlation between the extracted signal waveform and reference waveform, the system generates a correlation profile from which the dimension can be directly obtained, avoiding the need for separate edge detection operations on each layer.
3Reliability
If the lower layer pattern is disposed under a thin film, then overlay error measurement becomes more difficult, but the need for accurate measurement remains critical for semiconductor manufacturing
Solution Approach 1:
The system performs preliminary extraction of the signal waveform portion containing lower layer pattern information before conducting the correlation calculation. By pre-identifying and extracting the relevant signal segment based on luminance characteristics, the system prepares the optimal input data for correlation analysis, ensuring reliable measurement even when the lower layer is obscured by a thin film.
Solution Approach 2:
The system replaces traditional mechanical or optical edge detection methods with a signal processing-based correlation approach. Instead of physically or optically isolating and detecting edges of patterns under thin films, the system uses electronic signal waveform analysis and correlation calculation to determine dimensional information, achieving reliable measurement where conventional methods fail.
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
Enables stable and precise overlay error measurement by accurately detecting center of gravity positions even from weak signals, improving measurement precision and simplifying the measurement process without requiring edge detection for each layer.
Implementation Method 1
An image obtained by a charged particle beam device is formed on the basis of detection of electrons or ions emitted from a sample
Data Source
AI summary
The purpose of the present invention is to provide an overlay error measuring device which measures an overlay error with high accuracy even when a lower layer pattern is disposed under a thin film and a sufficient signal amount cannot be ensured. The present invention proposes an overlay error measuring device provided with an arithmetic processing unit for measuring a pattern formed on a sample on the basis of a signal waveform obtained by a charged particle beam device. The arithmetic processing unit finds a correlation with the signal waveform using a partial waveform obtained on the basis of partial extraction of the signal waveform, forms a correlation profile indicating the correlation, and measures an overlay error using the correlation profile.