Self-Aligned Metal Compound Sidewall Spacers for NAND Control Gates
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Solution Overview
Problem
The etching process in NAND memory device fabrication generates tungsten oxide whiskers and surface diffusion byproducts, leading to contamination and decreased performance, particularly in devices with metal control gates like tungsten.
Innovation Solution
The formation of self-aligned metal compound sidewall spacers, such as metal silicide spacers, on the control gates acts as a diffusion barrier during etching, preventing tungsten oxide whiskers and etch byproducts, and improving the integrity of the NAND memory stacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If metal control gates (tungsten) are used in NAND strings, then device performance and storage capacity are improved, but tungsten oxide whiskers and surface diffusion byproducts are generated during etching, causing contamination and decreased reliability
Solution Approach 1:
A sidewall spacer layer is introduced as an intermediary material between the metal control gate and the etching environment. This spacer layer acts as a protective mediator that prevents direct interaction between the etchant and the tungsten control gate, thereby preventing tungsten oxide whisker formation and surface diffusion while allowing the metal control gate to maintain its high performance benefits
Solution Approach 2:
The sidewall spacer layer is formed in advance before the etching process to preemptively prevent the generation of tungsten oxide whiskers and surface diffusion byproducts. By establishing this protective barrier beforehand, the harmful effects are prevented from occurring in the first place, rather than attempting to remove or mitigate them after formation
2Ease of manufacture
If conventional etching processes are used without protection, then manufacturing simplicity is maintained, but contamination from tungsten oxide whiskers and etch byproducts increases, reducing manufacturing precision
Solution Approach 1:
The sidewall spacer layer serves as an intermediary protective element that is integrated into the existing fabrication process flow. While it adds one additional formation step, it prevents the need for complex contamination removal procedures later, ultimately maintaining ease of manufacture while significantly improving etching precision by preventing whisker formation and byproduct contamination
3Device complexity
If no sidewall protection is provided during etching, then device complexity is minimized, but structural integrity of control gates deteriorates due to surface diffusion and whisker formation
Solution Approach 1:
The sidewall spacer layer acts as a protective intermediary that preserves the structural integrity of the metal control gate during etching. By preventing direct exposure to etchants, it stops surface diffusion and whisker formation that would otherwise compromise the control gate's composition and structure, with the spacer being a simple additive rather than a complex structural modification
Solution Approach 2:
The sidewall spacer layer is formed in advance to preemptively protect the control gate structure before etching occurs. This preliminary protective action prevents degradation of the control gate integrity during subsequent processing steps, ensuring the metal control gate maintains its structural stability throughout fabrication
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 use of metal compound spacers effectively reduces contamination and enhances the endurance and performance of NAND devices by preventing tungsten oxide whiskers and surface diffusion, maintaining the structural integrity and reliability of the memory stacks.
Implementation Method 1
The etching process in NAND memory device fabrication generates tungsten oxide whiskers and surface diffusion byproducts
Implementation Method 2
reacting a first material with exposed sidewalls of the plurality of control gates to form self aligned metal-first material compound sidewall spacers
Data Source
AI summary
A method of making a NAND string includes forming a tunnel dielectric over a semiconductor channel, forming a charge storage layer over the tunnel dielectric, forming a blocking dielectric over the charge storage layer, and forming a control gate layer over the blocking dielectric. The method also includes patterning the control gate layer to form a plurality of control gates separated by trenches, and reacting a first material with exposed sidewalls of the plurality of control gates to form self aligned metal-first material compound sidewall spacers on the exposed sidewalls of the plurality of control gates.