Coherent Scatterometry for Sub-Wavelength Alignment Mark Metrology
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Solution Overview
Problem
Current alignment mark technologies struggle to measure smaller marks due to low signal-to-noise ratios and are difficult to integrate within the device structure, leading to inaccuracies and space inefficiencies in lithographic processes.
Innovation Solution
Employing Coherent Fourier Scatterometry (CFS) to measure ultra-small alignment marks smaller than the wavelength, utilizing coherent illumination and balanced detection to enhance signal-to-noise ratio and enable accurate alignment without additional surface enhancements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional alignment mark technologies are used, then measurement capability is limited by signal-to-noise ratio, but reducing mark size further improves space efficiency and integration within device structure
Solution Approach 1:
The patent changes the illumination parameters from incoherent or partially coherent light to coherent light, and changes the detection parameters by implementing balanced detection between reference and signal beams. This parameter transformation enables the measurement system to achieve sufficient signal-to-noise ratio even when measuring ultra-small alignment marks that are smaller than the illumination wavelength, thereby resolving the contradiction between small mark size and measurement accuracy
Solution Approach 2:
The patent replaces conventional direct imaging measurement methods with coherent scatterometry based on optical interference and diffraction principles. By substituting the mechanical/optical imaging approach with a wave-based interference measurement approach, the system can extract precise position information from scattered light patterns of sub-wavelength marks, overcoming the diffraction limit and enabling accurate measurement of ultra-small alignment marks
2Area of stationary object
If alignment marks are made smaller to fit within device structure, then space efficiency improves, but signal-to-noise ratio deteriorates making measurement difficult
Solution Approach 1:
The patent introduces a reference beam as an intermediary element that interferes with the scattered signal beam from the alignment mark. This reference beam carries coherent light that, when combined with the weak scattered signal, creates an interference pattern that amplifies the detectable signal. The reference beam acts as a mediator that transforms the undetectably weak scattered light from sub-wavelength marks into a measurable interference signal, thereby enabling detection of ultra-small alignment marks without requiring larger mark sizes
3Measurement precision
If conventional incoherent illumination is used, then setup complexity is low, but measurement precision of sub-wavelength marks is insufficient
Solution Approach 1:
The patent implements a measurement system where coherent illumination and balanced detection work together as a universal platform capable of measuring alignment marks of any size, including sub-wavelength marks. The coherent light source and interferometric detection setup create a multi-functional system that can simultaneously provide high precision measurement, work with various mark geometries, and achieve sufficient signal-to-noise ratio without requiring additional surface enhancements or complex mark structures, thereby justifying the increased system complexity through universal measurement capability
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
CFS allows precise alignment with improved signal-to-noise ratio, reducing mark size to match product features, minimizing space usage, and enhancing alignment accuracy by detecting smaller alignment marks within the device structure.
Implementation Method 1
capturing the scattered radiation scattered from the alignment mark as a result of said illumination step
Implementation Method 2
Employing Coherent Fourier Scatterometry (CFS) to measure ultra-small alignment marks smaller than the wavelength, utilizing coherent illumination
Implementation Method 3
determining at least one position value for said alignment mark from an angularly resolved representation of said scattered radiation
Data Source
AI summary
Disclosed is a method for measuring alignment on an alignment mark, and associated apparatuses. The method comprises illuminating the alignment mark with illumination comprising at least one wavelength; capturing the scattered radiation scattered from the alignment mark as a result of said illumination step, and determining at least one position value for said alignment mark from an angularly resolved representation of said scattered radiation, wherein said alignment mark, or a feature thereof, is smaller than said at least one wavelength in at least one dimension of a substrate plane.