Mask Overlay Mark Layout for Diffraction-Based Alignment
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Solution Overview
Problem
The increasing complexity of semiconductor manufacturing due to smaller feature sizes and tighter spacing in advanced process nodes poses challenges in achieving precise mask overlay alignment, leading to misalignment issues that affect integrated circuit performance and yield.
Innovation Solution
The use of mask overlay marks with smaller features and specific pitch combinations that are resolvable by mask making processes but not by metrology or wafer imaging tools, ensuring accurate alignment without printing on the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mask overlay marks with smaller features and specific pitch combinations are used, then mask overlay reliability and repeatability are improved, but the marks become unresolvable by conventional metrology tools
Solution Approach 1:
The patent transitions from using large, easily measurable overlay marks to using arrays of small features where the collective arrangement creates a measurable signal. The individual features are below the resolution limit, but their periodic arrangement in arrays (gratings) creates diffraction patterns that are measurable, effectively moving the measurement from spatial domain to frequency/domain of diffraction orders.
Solution Approach 2:
The patent changes the physical parameters of the overlay mark from large solid features to small periodic features with specific pitch relationships. The pitch is carefully selected to be below the resolution limit of lithography tools (preventing wafer printing) while maintaining measurability through diffraction-based metrology, thus changing the measurement mechanism from direct imaging to optical diffraction analysis.
2Productivity
If smaller feature sizes are used in advanced process nodes, then production efficiency is increased and costs are lowered, but alignment precision deteriorates
Solution Approach 1:
The patent divides the overlay mark into multiple small features arranged in periodic arrays rather than using single large features. This segmentation allows each small feature to be compatible with advanced process node dimensions while the collective array structure provides sufficient signal for precise alignment measurement, resolving the contradiction between small feature size and measurement capability.
Solution Approach 2:
The patent introduces diffraction-based metrology as an intermediary measurement mechanism. Instead of directly imaging small features that are below the resolution limit, the system uses optical diffraction patterns produced by periodic arrays of these small features as an intermediary signal that carries alignment information, enabling precise measurement without requiring the features themselves to be resolvable.
3Manufacturing precision
If overlay marks are made with features smaller than the lithography resolution limit, then the marks are not printed on the wafer, but the marks become undetectable by conventional imaging methods
Solution Approach 1:
The patent moves the detection mechanism from direct spatial imaging to optical diffraction analysis. By arranging small features in periodic arrays, the system transforms the undetectable small features into measurable diffraction patterns, where the measurement occurs in the frequency domain rather than the spatial domain, making sub-resolution features detectable.
Solution Approach 2:
The patent changes the detection parameter from direct feature size measurement to measurement of diffraction pattern characteristics. The periodic arrangement of small features creates specific diffraction orders that can be detected and analyzed, transforming the measurement from detecting individual feature dimensions to detecting the periodicity and position of the feature array through optical diffraction.
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 enhances mask overlay reliability and repeatability, improving the precision of semiconductor fabrication by reducing defects and increasing yield.
Implementation Method 1
a pitch between adjacent two of the plurality of overlay patterns does not exceed the wavelength divided by twice the numerical aperture
Data Source
AI summary
A method includes: generating a designed mask overlay mark associated with an actual mask overlay mark to be formed in a mask; forming the actual mask overlay mark in the mask based on the designed mask overlay mark, the actual mask overlay mark including a plurality of overlay patterns; forming a device feature pattern adjacent to the actual mask overlay mark; forming an alignment of the mask by a mask metrology apparatus including a light source having a wavelength and a numerical aperture, wherein a pitch between adjacent two of the plurality of overlay patterns does not exceed the wavelength divided by twice the numerical aperture; and forming a pattern in a layer of a wafer by transferring the device feature pattern while the mask is under the alignment.