Metal-Induced Localized Etching for High Stack 3D NAND
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Solution Overview
Problem
Conventional methods for fabricating high-stack NAND devices face challenges such as increased tensile stress leading to substrate warping, difficulty in achieving vertical and uniform hole profiles, and irregular hole shapes due to non-volatile plasma polymer deposition, which affect charge storage and data retention.
Innovation Solution
A metal-induced localized etching (MILE) process is used to etch high aspect ratio holes with uniform width and vertical sidewalls in stacks with 60 or more layers, employing a metal block to catalyze the dissolution of stack layers with a wet etch solution like hydrogen peroxide and hydrofluoric acid, allowing for the formation of monolithic three-dimensional NAND strings with vertical semiconductor channels and controlled gate electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching methods are used to etch high aspect ratio holes in stacks with 60 or more layers, then the etching process can be performed, but the hole profiles become irregular and non-vertical due to non-volatile plasma polymer deposition
Solution Approach 1:
The patent replaces conventional plasma-based mechanical etching with a chemical dissolution process using wet etch solutions (such as hydrogen peroxide and hydrofluoric acid). This chemical approach eliminates plasma polymer deposition that causes irregular hole profiles, enabling vertical sidewalls and uniform cross-sections in high aspect ratio holes through catalytic metal-induced localized etching
Solution Approach 2:
The patent changes the etching mechanism from plasma-based physical/chemical removal to liquid-based chemical dissolution. By transitioning to wet etch solutions and controlling parameters such as solution composition, temperature, and exposure time, the process achieves uniform hole profiles with vertical sidewalls that maintain consistent dimensions throughout the stack depth
2Quantity of substance
If the stack height is increased to achieve higher density NAND devices, then storage capacity increases, but tensile stress increases leading to substrate warping
Solution Approach 1:
The patent introduces a metal block as an intermediary catalyst in the wet etching process. This metal block enables controlled localized etching that proceeds uniformly through the stack, reducing differential stress accumulation. The catalytic metal block facilitates consistent material removal without the lateral stress buildup that occurs in conventional plasma etching of high stacks
3Ease of manufacture
If conventional etching methods are used, then the etching process is simpler, but the hole shapes become irregular affecting charge storage and data retention
Solution Approach 1:
The patent uses a metal block as a catalytic intermediary that directs and controls the wet etching process. The metal block enables uniform dissolution of stack layers while maintaining vertical sidewalls and consistent hole cross-sections. This approach preserves manufacturing simplicity while dramatically improving hole shape consistency through the catalytic action of the metal block
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 MILE process enables the creation of NAND strings with vertical sidewalls and uniform cross-sections, reducing tensile stress and improving data retention by maintaining consistent hole shapes, thereby enhancing the scalability and reliability of high-stack NAND devices.
Implementation Method 1
employing a metal block to catalyze the dissolution of stack layers with a wet etch solution like hydrogen peroxide and hydrofluoric acid
Implementation Method 2
etching process using a wet etch solution comprising hydrogen peroxide and hydrofluoric acid
Data Source
AI summary
A method of making a monolithic three dimensional NAND device includes forming a stack of alternating layers of a first material and a second material different from the first material over a substrate, forming a mask layer over the stack and patterning the mask layer to form at least on opening in the mask layer to expose a top layer of the stack. The method also includes forming a metal block in the at least one opening in the mask layer, etching the stack by metal induced localized etch using the metal block in the at least one opening in the mask layer to form at least one opening in the stack and forming at least one layer of the NAND device in the at least one opening.