Selective Tungsten Etch for 3D NAND Gapfill
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Solution Overview
Problem
Current methods for filling tungsten in 3D-NAND structures, particularly in buried wordlines, face challenges due to the loading effect of etch processes, resulting in uneven wordline recesses and inadequate gapfill, especially as oxide stack layers increase.
Innovation Solution
A method involving depositing a metal layer on a substrate with features, oxidizing it to form a metal oxide layer, and selectively etching the metal oxide layer using a combination of high or low temperature oxidation and halide etchant processes to achieve conformal tungsten oxide films and controlled tungsten removal, facilitating improved gapfill and wordline separation without plasma use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etch processes (RIE or radical-based etch) are used to remove tungsten from top/sidewall, then tungsten separation is achieved, but uneven wordline recess occurs due to loading effect
Solution Approach 1:
The patent changes the chemical parameters of the etch process by using a halide-based etchant (such as WF6, WCl6, or WBr6) instead of conventional RIE or radical-based etchants. This parameter change enables selective etching of tungsten oxide while leaving metallic tungsten unaffected, thereby eliminating the loading effect that causes uneven wordline recess and achieving uniform gapfill across multi-tier VNAND structures
Solution Approach 2:
The patent introduces an intermediary oxidation step that converts metallic tungsten to tungsten oxide before etching. This intermediary transformation allows the etch process to selectively remove only the oxidized portions (from top/sidewall) while preserving the metallic tungsten in the gap space, thereby achieving clean separation without the loading effect that plagues direct etching methods
2Manufacturing precision
If deposition-etch cyclic techniques are used to improve gapfill, then tungsten deposition uniformity is enhanced, but process complexity increases with no effective cyclic process available
Solution Approach 1:
The patent applies preliminary oxidation to convert the deposited tungsten to tungsten oxide before the etch step. This preliminary action ensures that the subsequent etch process can selectively remove excess tungsten from top/sidewall regions while preserving the gapfill tungsten, achieving effective cyclic deposition-etch processing with controlled and simplified process steps
3Manufacturing precision
If tungsten is deposited to fill gap space and separate wordlines, then wordline isolation is achieved, but contact resistance increases due to native oxide formation
Solution Approach 1:
Instead of attempting to prevent oxide formation during deposition, the patent inverts the approach by intentionally allowing oxidation to occur and then using selective etching to remove the oxide from contact regions. This inversion strategy effectively eliminates contact resistance issues while maintaining wordline separation, as the halide-based etchant selectively removes tungsten oxide without affecting metallic tungsten
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 enables uniform tungsten film deposition from top to bottom of oxide stacks, improves contact resistance by removing native oxide, and provides a controlled etching process for better gapfill in 3D-NAND structures, addressing the unevenness and inefficiencies of existing methods.
Implementation Method 1
oxidizing the metal to a first depth for form a metal oxide layer on the metal layer
Implementation Method 2
etching the metal oxide layer to selectively remove the metal oxide layer
Data Source
AI summary
Methods of dep-etch in semiconductor devices (e.g. V-NAND) are described. A metal layer is deposited in a feature. The metal layer is removed by low temperature atomic layer etching by oxidizing the surface of the metal layer and etching the oxide in a layer-by-layer fashion. After removal of the metal layer, the features are filled with a metal.