Resonant Amplitude Grating Mark for Lithography Overlay
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Solution Overview
Problem
Conventional alignment marks and overlay targets in lithographic processes are sensitive to process-induced deformations, leading to inaccuracies in overlay error measurements due to asymmetries and depth variations, which affect the accuracy of feature placement and alignment in sub-micron semiconductor devices.
Innovation Solution
The development of a periodic structure-based alignment mark and overlay target that scatters radiation by exciting a resonant mode parallel to the surface plane, reducing sensitivity to asymmetries and depth variations, allowing for accurate alignment and overlay error determination using a single wavelength and tunable signal strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional alignment marks and overlay targets are used in lithographic processes, then overlay error measurements can be obtained, but the measurements are sensitive to process-induced deformations leading to inaccuracies due to asymmetries and depth variations
Solution Approach 1:
The patent applies asymmetry by designing alignment marks with specific asymmetric geometric configurations that are intentionally engineered to be insensitive to process-induced deformations. The asymmetric design allows the marks to maintain their optical scattering properties even when subjected to manufacturing variations, thereby improving measurement accuracy while reducing sensitivity to deformations.
Solution Approach 2:
The patent changes the optical parameters by utilizing resonant mode excitation at specific wavelengths. By tuning the resonant conditions and selecting appropriate wavelengths for radiation interaction, the alignment marks achieve enhanced signal strength and reduced sensitivity to depth variations and asymmetries, directly improving overlay measurement precision.
2Manufacturing precision
If conventional alignment marks are used, then alignment can be performed, but accuracy is affected by asymmetries and depth variations from processing
Solution Approach 1:
The patent converts the harmful effect of process-induced asymmetries into a beneficial feature by designing alignment marks that utilize resonant mode scattering. The asymmetric deformations that would normally degrade performance are transformed into enhanced resonant signals, allowing the marks to maintain or even improve their alignment accuracy despite processing variations.
Solution Approach 2:
The patent employs resonant mode excitation, which is analogous to mechanical vibration principles, by tuning the alignment marks to resonate at specific wavelengths of incident radiation. This resonant behavior creates strong, stable scattering signals that are insensitive to minor geometric variations and depth changes, thereby improving manufacturing precision.
3Measurement precision
If conventional alignment marks are used, then alignment measurement can be performed, but signal strength and accuracy are compromised by depth fluctuations
Solution Approach 1:
The patent optimizes the optical parameters by designing marks that support resonant modes at specific wavelengths. By changing the operational wavelength to match the resonant conditions and adjusting the geometric parameters of the marks, the system achieves maximum signal strength while maintaining insensitivity to depth variations, thereby improving both signal quality and measurement precision.
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 solution provides more accurate and robust alignment and overlay error measurement methods, reducing Alignment Position Deviation and enhancing Wafer Quality by minimizing the impact of process-induced asymmetries and depth fluctuations, enabling better precision in semiconductor manufacturing.
Implementation Method 1
the scattering mainly by excitation of a resonant mode in the periodic structure parallel to the surface plane
Implementation Method 2
configured to scatter radiation incident on a surface plane of the alignment mark
Data Source
AI summary
A resonant amplitude grating mark has a periodic structure configured to scatter radiation incident on a surface plane of the alignment mark. The scattering is mainly by excitation of a resonant mode in the periodic structure parallel to the surface plane. The effective refractive indexes and lengths of portions of the periodic structure are configured to provide an optical path length of the unit cell in the direction of periodicity that equals an integer multiple of a wavelength present in the spectrum of the radiation. The effective refractive indexes and lengths of the portions are also configured to provide an optical path length of the second portion in the direction of periodicity that is equal to half of the wavelength present in the spectrum of the radiation.