Resonant Amplitude Grating Mark for Lithography Alignment
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Solution Overview
Problem
Conventional alignment and overlay targets in lithographic processes are sensitive to process-induced deformations, leading to inaccuracies in alignment and overlay error measurements due to asymmetries and depth variations, which complicates the reproduction of small features in sub-micron semiconductor devices.
Innovation Solution
A method involving alignment and overlay marks with periodic structures having specific refractive index and length configurations that scatter radiation mainly by excitation of a waveguiding mode, reducing sensitivity to asymmetries and depth variations, allowing for accurate alignment and measurement using a single wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional alignment marks with phase gratings are used, then alignment measurements can be performed, but the marks are sensitive to process-induced deformations causing asymmetries and depth variations that lead to alignment errors
Solution Approach 1:
The patent changes the fundamental optical parameter of the alignment mark from phase modulation to amplitude modulation. The periodic structure is designed to scatter radiation primarily through amplitude variations rather than phase variations, making the mark insensitive to depth variations and process-induced asymmetries that affect phase-based marks. This parameter change resolves the contradiction by maintaining measurement precision while eliminating sensitivity to process deformations.
Solution Approach 2:
The patent applies different local qualities to different portions of the periodic structure. The unit cell is divided into first and second portions with different scattering characteristics, where the first portion has a first effective refractive index and the second portion has a second effective refractive index. This local differentiation creates amplitude-based scattering that is robust against process variations while maintaining high measurement precision.
2Measurement precision
If multiple wavelengths are used to compensate for mark asymmetries, then measurement accuracy can be improved, but the device complexity and process time increase
Solution Approach 1:
The patent employs a single wavelength radiation source instead of multiple wavelengths, significantly simplifying the measurement system. The amplitude-based periodic structure provides robust measurements at one wavelength, eliminating the need for complex multi-wavelength configurations. This reduces device complexity and process time while maintaining high measurement precision through the inherent robustness of amplitude-based scattering.
3Manufacturing precision
If tight control loops are applied to control lithographic apparatus stability, then pattern reproduction accuracy improves, but the process complexity and manufacturing difficulty increase
Solution Approach 1:
The patent incorporates alignment marks with amplitude-based periodic structures directly into the substrate or patterning device during manufacturing, before the lithographic process begins. These pre-configured marks provide robust reference features that simplify the alignment process and reduce the need for complex tight control loops during operation, thereby maintaining high manufacturing precision while reducing operational complexity.
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
The solution provides accurate and robust alignment and overlay measurements, reducing Alignment Position Deviation (APD) to sub-angstrom levels, enabling higher precision in feature reproduction and tolerance to process fluctuations, and simplifying the manufacturing process with insensitive marks for wafer-to-wafer error correction.
Implementation Method 1
scattering occurs mainly by excitation of a waveguiding mode in the periodic structure
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 the mark. The scattering is mainly by coupling of the incident radiation to a waveguiding mode in the periodic structure. 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 essentially equals an integer multiple of a wavelength present in 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 selected from 0.30 to 0.49 of the wavelength present in the spectrum of the radiation.