Symmetric Unit Cell Overlay Measurement Using Zeroth-Order Diffraction
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Solution Overview
Problem
In the manufacturing of semiconductor devices, there is a challenge in accurately determining and controlling parameters such as overlay and critical dimension (CD) due to increasing complexity and miniaturization, leading to errors that can affect device functionality.
Innovation Solution
A method involving illuminating a substrate with a radiation beam to detect zeroth-order radiation redirected by a unit cell with geometric symmetry, and using a hardware computer system to determine non-nominal overlay values based on optical characteristics, along with processing pupil representations to assess patterning process parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional lithography methods are used for patterning, then manufacturing process can be maintained, but measurement precision and manufacturing precision deteriorate due to increasing miniaturization and process complexity
Solution Approach 1:
The patent uses asymmetric target structures (combining symmetric and asymmetric components) to enhance sensitivity to overlay errors. The asymmetric portion of the target structure produces differential diffraction signals that are highly sensitive to misalignment, enabling precise overlay measurement even as feature sizes decrease and process complexity increases.
Solution Approach 2:
The patent transitions from direct spatial measurement to frequency domain measurement by analyzing diffraction orders. By measuring the intensities of different diffraction orders (frequency components) and processing them through mathematical operations, the system achieves precise overlay measurement without being constrained by direct spatial resolution limits.
2Productivity
If miniaturization is increased to improve device density, then productivity improves, but measurement precision and manufacturing precision worsen due to reduced feature dimensions
Solution Approach 1:
The patent measures overlay and critical dimension by analyzing diffraction intensities in the frequency domain rather than directly measuring physical dimensions. This allows precise measurement of miniaturized features by detecting optical interference patterns that encode dimensional information, enabling accurate measurement even when feature sizes are too small for direct resolution.
Solution Approach 2:
The patent introduces specialized target structures as intermediary elements between the patterning process and measurement system. These targets act as mediators that convert subtle overlay and CD variations into amplified optical signals through diffraction, enabling precise measurement of miniaturized features without directly measuring the features themselves.
3Manufacturing precision
If process complexity is increased to achieve higher accuracy, then manufacturing precision improves, but device complexity increases leading to harder detection and measurement
Solution Approach 1:
The patent divides the measurement process into distinct segments: (1) illuminating the target with radiation, (2) detecting diffraction orders at specific angles, (3) measuring intensities of individual diffraction orders, and (4) processing intensities through mathematical operations. This segmentation simplifies the overall complex measurement system by breaking it into manageable, independent measurement steps that can be implemented with standard optical 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 enables precise measurement and control of overlay and CD, reducing errors and improving the accuracy of the patterning process, thereby enhancing the performance and reliability of semiconductor devices.
Implementation Method 1
illuminating a substrate with a radiation beam such that a beam spot on the substrate is filled with one or more physical instances of a unit cell
Implementation Method 2
detecting primarily zeroth order radiation redirected by the one or more physical instances of the unit cell
Data Source
AI summary
A method of determining overlay of a patterning process, the method including: illuminating a substrate with a radiation beam such that a beam spot on the substrate is filled with one or more physical instances of a unit cell, the unit cell having geometric symmetry at a nominal value of overlay; detecting primarily zeroth order radiation redirected by the one or more physical instances of the unit cell using a detector; and determining, by a hardware computer system, a non-nominal value of overlay of the unit cell from values of an optical characteristic of the detected radiation.