3D NAND Source Contact Formation Using Backside ACS Etching
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Solution Overview
Problem
The challenge in fabricating three-dimensional (3D) NAND flash memory is the difficulty in forming source contacts to channel layers without damaging the channel layers on the sidewalls of channel holes, which can lead to pinholes and reliability issues.
Innovation Solution
A method is described for forming a 3D memory device by sequentially depositing a first etch-stop layer, a second etch-stop layer, and an alternating dielectric stack on a substrate. Channel holes are formed through the stack, and memory films and channel layers are disposed on the sidewalls. The substrate is removed, and the etch-stop layers are selectively etched to expose portions of the channel layers, allowing for the formation of an array common source (ACS) on the backside of the second etch-stop layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If memory films are removed from the bottom of channel holes to form source contacts, then source contact formation is achieved, but channel layers on sidewalls are damaged causing pinholes
Solution Approach 1:
The patent divides the etch-stop function into two separate layers: a first etch-stop layer (silicon oxide) that protects the substrate and a second etch-stop layer (polycrystalline silicon) that protects the channel layers. This segmentation allows selective removal of memory films without damaging channel layers, as each etch-stop layer is designed to protect specific structures during different etching steps.
Solution Approach 2:
The patent introduces etch-stop layers as intermediary protective structures between the memory films and the structures that need protection (substrate and channel layers). These intermediary layers enable the etching process to remove memory films while stopping before damaging the channel layers, thus preventing pinhole formation.
2Ease of operation
If the substrate is removed to access channel layers, then source contact access is improved, but structural support is reduced
Solution Approach 1:
The patent performs preliminary actions by forming both etch-stop layers and the alternating dielectric stack before removing the substrate. This ensures that the protective structure is in place before the substrate removal process, allowing safe access to channel layers while maintaining structural integrity through the retained etch-stop and dielectric layers.
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 method enables the formation of reliable source contacts to the channel layers without damaging the channel layers on the sidewalls, thereby improving the yield and reliability of the 3D NAND flash memory devices.
Implementation Method 1
removing the substrate and stopping on the first etch-stop layer includes removing the substrate by a wet etch
Implementation Method 2
removing the first etch-stop layer and the exposed portions of the memory films includes removing the first etch-stop layer and the exposed portions of the memory films by a wet etch
Data Source
AI summary
The present disclosure provides a method for forming a three-dimensional (3D) memory device. The method includes disposing an alternating dielectric stack over a substrate, wherein the alternating dielectric stack includes first dielectric layers and second dielectric layers alternatingly stacked on the substrate. The method also includes forming a channel structure penetrating through the alternating dielectric stack and extending into the substrate, wherein the channel structure includes a channel layer disposed on a sidewall of a memory film. The method further includes removing the substrate and a portion of the memory film that extends into the substrate to expose a portion of the channel layer; and disposing an array common source (ACS) on the exposed portion of the channel layer.