Composite Insulator Structure for Memory Transistors
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Solution Overview
Problem
Current memory technologies face challenges in efficiently forming non-volatile and volatile transistors with improved channel tunneling and reduced interface trap density, particularly in the context of elevationally-extending strings of memory cells.
Innovation Solution
The formation of transistors with a specific structure involving alternating tiers of conductive and insulative materials, where a second insulating material with lower oxygen diffusivity and higher shear strength is used adjacent to the channel material, along with a charge-blocking region and charge-storage material, to enhance programmability and reduce interface traps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional insulating materials are used in transistor formation, then manufacturing is simplified, but interface trap density increases and channel tunneling efficiency decreases
Solution Approach 1:
The patent employs a composite insulating material structure consisting of multiple layers with different properties. Specifically, it uses a first insulating material layer (such as silicon oxide) combined with a second insulating material layer (such as silicon nitride or silicon oxynitride), where each layer serves distinct functions: the first layer provides good interface characteristics with the channel, while the second layer provides superior oxygen barrier properties and mechanical strength, thereby reducing interface trap density without excessive complexity
Solution Approach 2:
The patent applies different insulating materials at different locations within the transistor structure based on local requirements. The first insulating material is positioned adjacent to the channel region where low interface trap density is critical, while the second insulating material is positioned where oxygen diffusion blocking is most important. This localized optimization resolves the contradiction by matching material properties to specific functional needs
2Reliability
If oxygen diffusion is not blocked effectively, then manufacturing is simpler, but interface trap density increases reducing transistor reliability
Solution Approach 1:
The patent uses a composite insulating material system where the second insulating material layer (such as silicon nitride or silicon oxynitride) provides superior oxygen diffusion blocking properties compared to conventional single-layer insulators. This multi-layer composite structure achieves effective oxygen blocking to prevent interface trap formation while maintaining compatibility with existing manufacturing processes
Solution Approach 2:
The insulating material layers serve as intermediary barriers between the channel region and the environment where oxygen diffusion could cause damage. The second insulating material acts as a specific intermediary layer dedicated to oxygen blocking, protecting the channel-interface from oxygen-induced trap formation without requiring complete process redesign
3Productivity
If channel tunneling efficiency is improved, then memory cell performance increases, but interface trap density may increase causing reliability issues
Solution Approach 1:
The patent optimizes the interface quality locally at the channel-insulator boundary by using a first insulating material that forms a low-trap-density interface, while simultaneously using a second insulating material that provides oxygen blocking. This local optimization at the critical interface region enables high tunneling efficiency without the reliability penalty of increased interface traps
Solution Approach 2:
The composite insulating material structure enables simultaneous optimization of interface quality and oxygen blocking. The first insulating material layer provides excellent interface characteristics for efficient channel tunneling, while the second insulating material layer provides oxygen diffusion blocking to prevent interface degradation, thereby achieving both high performance and reliability
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 results in improved string current, channel tunneling, and reduced interface trap density, leading to more efficient memory cell operation and enhanced performance in memory arrays.
Implementation Method 1
A second insulating material of different composition from that of the first insulating material is adjacent the second side of the first insulating material... lower oxygen diffusivity than the first material
Implementation Method 2
The amorphous channel material having the insulator material there-adjacent is subjected to a temperature at or above the crystallization temperature to transform the amorphous channel material into crystalline channel material
Data Source
AI summary
A transistor comprises channel material having first and second opposing sides. A gate is on the first side of the channel material and a gate insulator is between the gate and the channel material. A first insulating material has first and second opposing sides, with the first side being adjacent the second side of the channel material. A second insulating material of different composition from that of the first insulating material is adjacent the second side of the first insulating material. The second insulating material has at least one of (a), (b), and (c), where, (a): lower oxygen diffusivity than the first material, (b): net positive charge, and (c): at least two times greater shear strength than the first material. In some embodiments, an array of elevationally-extending strings of memory cells comprises such transistors. Other embodiments, including method, are disclosed.