3D-NAND Tungsten Wordline Separation via Segmented Etching
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Solution Overview
Problem
In 3D-NAND semiconductor devices, the etch process for separating tungsten wordlines often results in uneven recesses due to loading effects, leading to variations in wordline formation across the oxide stack layers, which complicates the manufacturing of flash memory applications.
Innovation Solution
A method involving the deposition of a metal, such as tungsten, on a stack of oxide layers to fill gaps and cover the top and sides, followed by oxidation and selective etching to remove the overburden, ensuring uniformity and evenness of the wordlines, with optional use of a TiN barrier layer and controlled temperature and gas exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reactive-ion etch (RIE) process or radical-based etch process is used to remove tungsten from the top/sidewall of the stack, then the tungsten is completely separated and exists only inside of the gap space, but the loading effect of the etch process results in different wordline recess at the top of the stack than at the bottom
Solution Approach 1:
The etch process is divided into multiple sequential steps: a first etch process removes tungsten from the top surface, followed by a second etch process that removes tungsten from the sidewalls. This segmentation allows each etch step to be optimized independently, preventing the loading effect from causing non-uniform wordline recess while maintaining complete separation of tungsten fills.
2Productivity
If the number of oxide stack layers is increased to achieve higher integration, then more cells can be arranged in blocks, but the difference in wordline recess between top and bottom becomes more pronounced
Solution Approach 1:
By segmenting the etch process into top-surface etching followed by sidewall etching, the method maintains uniform wordline recess even as the number of oxide stack layers increases. Each etch step is controlled to work on specific regions, preventing the accumulation of non-uniformity that would occur with a single etch process applied to taller stacks.
Solution Approach 2:
The etch process is made selective to different regions: the first etch process targets the top surface where tungsten overburden exists, while the second etch process targets the sidewalls. This local quality approach ensures that each region is etched appropriately, maintaining uniformity across the entire stack regardless of height.
3Ease of manufacture
If conventional etch processes are used to separate wordlines, then tungsten can be removed from top/sidewall, but the process results in uneven recesses that complicate manufacturing
Solution Approach 1:
The tungsten removal process is segmented into two distinct etch operations: first removing tungsten from the top surface to a controlled depth, then removing tungsten from the sidewalls. This segmentation eliminates the loading effect that causes uneven recesses in conventional single-step etching, while still achieving complete tungsten separation.
Solution Approach 2:
The first etch process performs a preliminary removal of tungsten from the top surface before the second etch process addresses the sidewalls. This preliminary action prepares the structure for the subsequent sidewall etching, ensuring that the final wordline recess is uniform throughout the stack.
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 ensures highly conformal and selective tungsten oxide formation and removal, resulting in uniform tungsten wordlines across the entire oxide stack, improving the uniformity and control of layer thickness, thereby addressing the issue of uneven recesses and enhancing manufacturing efficiency.
Implementation Method 1
The gap space is filled by tungsten using CVD or ALD
Implementation Method 2
The gap space is filled by tungsten using CVD or ALD
Implementation Method 3
The surface of the metal is repeatedly oxidized to form a metal oxide
Implementation Method 4
The metal oxide is etched from the top and sides of the stack leaving the metal in the wordlines
Data Source
AI summary
Methods of wordline separation in semiconductor devices (e.g., 3D-NAND) are described. A metal film is deposited in the wordlines and on the surface of a stack of spaced oxide layers. The metal film is removed by high temperature oxidation and etching of the oxide or low temperature atomic layer etching by oxidizing the surface and etching the oxide in a monolayer fashion. After removal of the metal overburden, the wordlines are filled with the metal film.