Asymmetric Grating Measurement via Azimuthal Scatterometry
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Solution Overview
Problem
Conventional optical scatterometry methods struggle to accurately measure asymmetric properties of semiconductor device structures due to high correlation between similar critical dimension parameters, leading to inaccurate measurements of features like trapezoid grating wall angles and spacer widths.
Innovation Solution
The method involves measuring signals at different azimuth angles or angles of incidence and calculating the difference between them to determine asymmetric structural parameters, such as sidewall angles, using a regression approach that includes differential signals to reduce parameter correlation and increase sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical scatterometry methods are used to measure symmetric structures, then measurement is straightforward, but they fail to accurately determine asymmetric properties due to high correlation between similar parameters
Solution Approach 1:
The measurement process is segmented into multiple distinct steps: measuring at first azimuth angle, measuring at second azimuth angle, calculating differences, and determining asymmetric parameters. This segmentation allows each step to focus on specific aspects of the measurement, improving accuracy for asymmetric structures while managing complexity through systematic progression.
Solution Approach 2:
The invention introduces azimuth angle as an additional dimensional parameter for measurement. By measuring at multiple azimuth angles (first and second angles) rather than a single angle, the method captures asymmetric properties that cannot be detected by conventional single-angle measurements, thereby improving measurement precision for asymmetric structures.
2Measurement precision
If multiple diffraction orders are selected in RCWA, then simulation accuracy improves, but computation time increases nonlinearly
Solution Approach 1:
The invention uses differential signals obtained from measurements at multiple azimuth angles to isolate asymmetric parameter information. This partial action approach focuses computational effort on extracting specific asymmetric properties rather than computing all parameters with high precision, thereby reducing overall computation time while maintaining accuracy for the parameters of interest.
Solution Approach 2:
The method changes the measurement parameters by introducing azimuth angle variation. Instead of relying solely on increasing the number of diffraction orders to improve accuracy, the invention transforms the problem by measuring at different azimuth angles and using differential calculations, which improves asymmetric parameter accuracy without the nonlinear computation time penalty.
3Manufacturing precision
If asymmetric structures are measured using conventional methods, then measurement process is simple, but parameter correlation leads to inaccurate determination of features like wall angles and spacer widths
Solution Approach 1:
The invention explicitly exploits asymmetry by measuring at multiple azimuth angles and calculating differential signals. The differential measurement approach is specifically designed to isolate asymmetric parameter information, breaking the correlation between similar parameters that plagues conventional symmetric measurement methods. This allows accurate determination of asymmetric features like unequal wall angles or spacer widths.
Solution Approach 2:
The differential signal calculated from measurements at different azimuth angles serves as an intermediary that isolates asymmetric parameter information. This intermediary quantity removes the correlation between similar parameters by focusing on the asymmetric components, making it easier to accurately determine critical dimensions of asymmetric features.
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 improves the accuracy of critical dimension measurements by breaking the correlation between similar parameters, enabling more precise determination of asymmetric features in semiconductor devices, such as trapezoid grating structures with varying wall angles or spacer widths.
Implementation Method 1
measuring, for a grating structure, a first signal and a second, different, signal obtained by optical scatterometry
Implementation Method 2
RCWA and similar algorithms have been widely used for the study and design of diffraction structures
Data Source
AI summary
Methods of determining asymmetric properties of structures are described. A method includes measuring, for a grating structure, a first signal and a second, different, signal obtained by optical scatterometry. A difference between the first signal and the second signal is then determined. An asymmetric structural parameter of the grating structure is determined based on a calculation using the first signal, the second signal, and the difference.