Sub-resolution Dummy Features for Overlay Mark Enhancement
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Solution Overview
Problem
As semiconductor integrated circuits scale down, existing pattern alignment techniques face challenges due to weakening overlay mark signals, leading to imprecise alignment of successive patterned layers during fabrication.
Innovation Solution
The implementation of sub-resolution dummy features in the alignment region, which are smaller than the resolution of alignment detection systems, enhances pattern contrast and maintains satisfactory alignment detection by being undetected by the alignment system, allowing for improved measurement signals and reduced etch loading effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device scaling continues and multiple lithography processes are implemented, then circuit complexity and integration density improve, but overlay mark signals become weaker leading to imprecise alignment
Solution Approach 1:
The patent introduces an intermediary substance (man-made contaminant) that selectively enhances the overlay mark signal without affecting the actual device features. This contaminant acts as a mediator between the lithography process and the alignment detection system, amplifying the weak overlay mark signals to achieve precise alignment measurements while maintaining high integration density through continued device scaling
Solution Approach 2:
The patent changes the physical-chemical parameters of the overlay mark region by introducing specific contaminants that alter the optical or material properties of that region. This parameter change enhances the contrast and detectability of overlay marks without changing the fundamental device structure, thereby improving alignment precision while maintaining productivity gains from scaling
2Measurement precision
If overlay mark features are made larger to improve detection signal strength, then alignment detection improves, but etch loading effects increase
Solution Approach 1:
The contaminant serves as an intermediary that decouples the relationship between overlay mark size and detection signal strength. Instead of increasing feature size to improve detection, the contaminant enhances the signal from smaller features by modifying their interaction with the detection system, thereby avoiding etch loading effects while maintaining measurement precision
Solution Approach 2:
The patent applies local quality enhancement by selectively placing contaminants only in the overlay mark regions rather than uniformly across the entire wafer. This localized modification improves detection accuracy in specific areas without affecting the overall etch loading balance across the substrate, as the contaminant enhancement is confined to small, targeted locations
Data Source
AI summary
Methods and apparatuses for alignment are disclosed. An exemplary method includes providing a substrate having a device region and an alignment region; forming a first material layer over the substrate; forming a device feature and a dummy feature in the first material layer, wherein the device feature is formed in the device region and the dummy feature is formed in the alignment region; forming a second material layer over the first material layer; and forming an alignment feature in the second material layer, the alignment feature being disposed over the dummy feature in the alignment region. The device feature has a first dimension and the dummy feature has a second dimension, the second dimension being less than a resolution of an alignment mark detector.