ALD Sidewall Process for Non-Volatile Memory Dielectric Integrity
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Solution Overview
Problem
The existing non-volatile semiconductor memory technologies, such as EEPROM and flash memories, face challenges in reducing the size of memory cells while avoiding the Bird's Beak Effect, which occurs during sidewall oxidation, leading to increased dielectric thickness and capacitive interference.
Innovation Solution
The use of Atomic Layer Deposition (ALD) to deposit oxide and nitride sidewall layers, including configurations like oxide-nitride-oxide (ONO) and nitride-oxide-nitride-oxide-nitride (NONON), prevents the Bird's Beak Effect by controlling the dielectric structure between the floating gate and control gate, and the implant process is strategically performed to create source/drain regions and offset the implant from the stack edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxidation process is used to grow oxide sidewall during transistor sidewall formation, then sidewall protection is achieved, but Bird's Beak Effect occurs causing dielectric corner oxidation
Solution Approach 1:
The patent applies preliminary action by depositing the oxide-nitride-oxide dielectric structure before the sidewall oxidation process. The nitride layer is deposited in advance to serve as a diffusion barrier that prevents oxygen from reaching and oxidizing the dielectric corners during the subsequent sidewall oxidation process, thereby preventing the Bird's Beak Effect before it can occur.
Solution Approach 2:
The nitride layer acts as an intermediary barrier between the oxide dielectric and the oxidizing environment. This intermediate nitride layer prevents direct interaction between oxygen and the dielectric corners during sidewall formation, blocking the harmful oxidation effect while allowing the sidewall oxidation process to proceed for transistor fabrication.
2Manufacturing precision
If outer nitride layers are added to ONO dielectric to create NONON structure, then Bird's Beak Effect is prevented, but dielectric thickness increases
Solution Approach 1:
The patent applies local quality by placing the nitride barrier layer specifically at the corners and interfaces where oxidation would occur, rather than uniformly thickening the entire dielectric structure. The oxide-nitride-oxide configuration provides localized protection at critical areas while maintaining overall dielectric thickness optimization for memory cell size.
Solution Approach 2:
The patent uses composite materials by combining oxide and nitride layers in an oxide-nitride-oxide (ONO) structure. This composite dielectric provides both the electrical insulation properties of oxide and the oxidation barrier properties of nitride, achieving Bird's Beak prevention without requiring excessive overall thickness compared to a purely nitride-based structure.
3Manufacturing precision
If dielectric thickness is increased to prevent oxidation, then Bird's Beak Effect is avoided, but memory cell size increases
Solution Approach 1:
The patent changes the material composition parameter of the dielectric structure by introducing nitride layers with high oxidation barrier properties. This material parameter change allows for thinner overall dielectric thickness while achieving the same oxidation prevention effect that would require much thicker oxide-only structures, thereby reducing memory cell area.
4Reliability
If thicker dielectric is used to prevent oxidation, then dielectric integrity is maintained, but capacitive coupling between floating gates increases
Solution Approach 1:
The patent applies local quality by concentrating the nitride barrier material at critical interfaces where oxidation would compromise dielectric integrity, rather than uniformly increasing dielectric thickness throughout. This localized barrier approach maintains dielectric integrity at thin sections while minimizing overall capacitance between floating gates.
Solution Approach 2:
The oxide-nitride-oxide composite structure provides dielectric integrity through the nitride barrier layers at interfaces while the thinner oxide sections reduce capacitive coupling. The composite structure achieves both reliability and reduced interference by optimizing material distribution rather than uniform thickness increase.
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 effectively prevents the Bird's Beak Effect, maintaining the integrity of the dielectric structure, reducing memory cell size, and minimizing capacitive interference, thereby enhancing memory cell density and storage capacity.
Implementation Method 1
the stack of multiple layers is etched to form word lines and the etch is continued to separate the floating gate material layer strips into individual floating gates. An implant (or other) process is used to create source/drain regions. A sidewall process is used that prevents a Bird's Beak Effect from occurring in the dielectric between the floating gate and the control gate during the side wall fabrication by using ALD to deposit oxide and nitride sidewall layers
Implementation Method 2
during the creation of sidewalls for a transistor, an oxidation process can be used to grow an oxide sidewall
Implementation Method 3
outer nitride layers have been added to the ONO dielectric to create NONON (nitride-oxide-nitride-oxide-nitride) because nitride is a good barrier to diffusion and, therefore, prevents oxidation
Data Source
AI summary
Non-volatile storage elements (or other device) are created. One embodiment includes creating floating gate stacks comprising a floating gate, a control gate and a dielectric between the floating gate and the control gate. One example of a suitable dielectric includes a first layer of oxide, a layer of nitride and a second layer of oxide, all three of which are deposited using Atomic Layer Deposition (or other process). An implant (or other) process is used to create source/drain regions. ALD is used to deposit oxide and nitride for sidewalls.