Overlay Mark Layout for Accurate 3D Stack Alignment
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Solution Overview
Problem
Conventional 3D electronic devices face significant overlay errors and yield loss due to transparent stacks and imperfections in high aspect ratio features, leading to inaccurate alignment and registration of multiple decks, especially in memory devices.
Innovation Solution
Positioning overlay marks in the upper portion of the stack with reflective or opaque materials to enhance optical contrast, blocking radiation from lower portions and improving alignment accuracy during lithography processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional transparent stacks are used in 3D electronic devices, then the device structure can be formed with high aspect ratio features, but overlay errors increase and alignment accuracy deteriorates due to poor optical contrast
Solution Approach 1:
The patent applies local quality by making only the overlay mark region opaque while keeping the rest of the stack transparent. This is achieved by forming an opaque material layer selectively at the overlay mark location, allowing the overlay marks to provide strong optical contrast for alignment without affecting the transparency needed for observing HAR feature formation in other regions.
Solution Approach 2:
The patent introduces an intermediary opaque material layer between the transparent stack materials and the detection system. This intermediary layer at the overlay mark position enhances the optical signal for alignment detection, acting as a mediator that improves contrast without requiring the entire stack to be opaque.
2Manufacturing precision
If high aspect ratio features are formed in transparent stacks, then device integration density increases, but overlay errors increase due to imperfections in HAR features affecting alignment signals
Solution Approach 1:
The patent extracts the overlay mark function from the HAR features themselves and creates separate dedicated overlay mark structures. By forming distinct opaque overlay marks in the upper portion of the stack, the alignment detection is separated from the HAR feature formation process, preventing imperfections in HAR features from affecting alignment signal accuracy.
3Measurement precision
If overlay marks are positioned throughout the entire stack, then alignment detection is possible, but optical signal from lower portions with imperfections contaminates the alignment measurement
Solution Approach 1:
The patent applies local quality by concentrating the opaque material layer specifically at the overlay mark region in the upper portion of the stack, while leaving other regions transparent. This localized opacity ensures that only light reflected from the upper portion overlay marks is detected, eliminating contamination from imperfections in lower portions of the stack.
4Ease of manufacture
If transparent materials are used for the stack, then the structure can be formed, but additional processing is required to enable overlay-topography transfer when opaque sacrificial hardmasks are used
Solution Approach 1:
The patent applies local quality by making only the overlay mark region opaque while keeping the sacrificial hardmask and other stack materials transparent. This selective opacity eliminates the need for additional processing to transfer overlay topography, as the opaque overlay marks directly provide the necessary optical contrast for alignment detection throughout the fabrication process.
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 stable and accurate overlay alignment, reducing errors and yield loss by enhancing optical signal detection from the upper portion of the stack, enabling tight tolerances and improved fabrication of high aspect ratio features.
Implementation Method 1
The overlay marks are detected by the metrology system, which is used by a lithography system to align the subsequently-formed decks over the initial deck... When the radiation (e.g., a detection signal from the metrology system) is reflected by the overlay alignment marks, the imperfections in the overlay alignment marks cause an alignment signal arising from a bulk volume (e.g., lower portion and middle portion) of the stack to differ from the alignment signal arising from an upper portion of the stack
Data Source
AI summary
An electronic device comprising a multideck structure including a base stack of materials and one or more stacks of materials on the base stack of materials, at least one high aspect ratio feature in an array region in the base stack of materials and in the one or more stacks of materials, and overlay marks including an optical contrast material in or on only an upper portion of the base stack of materials in an overlay mark region of the electronic device is disclosed. The overlay mark region is laterally adjacent to the array region and the overlay marks are adjacent to at least one additional high aspect ratio feature in the base stack of materials. Additional electronic devices and memory devices are disclosed.