Angled Ion Beam Etching for 3D Memory Layer Access
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Solution Overview
Problem
Conventional methods for fabricating 3D memory devices like VNAND result in complex, less reliable processes due to numerous etch operations and resist trimming, leading to compromised structure quality and increased area occupation, especially when accessing multiple layers.
Innovation Solution
The method involves directing ions at a non-zero angle of incidence to form angled sidewalls in a multilayer device stack, followed by selective etching to create a stepped structure, allowing for convenient access to multiple layers with reduced need for multiple mask operations and lithography steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If vertical reactive ion etching is used to etch layers in a cycle, then one or a few layers can be etched selectively in each cycle, but a large number of etch operations (8, 16, or more) are required for a 64-layer device stack, increasing process complexity
Solution Approach 1:
The patent changes the etching direction from vertical to angled (e.g., 45 degrees), allowing multiple layers to be accessed and etched simultaneously through lateral etching. This dimensional change enables forming pyramidal or tapered structures where a single angled etch operation can expose multiple device layers at different heights, reducing the total number of etch cycles required for deep 3D structures like 64-layer VNAND devices.
2Manufacturing precision
If multiple resist trimming operations are performed between successive etch operations, then mask size can be reduced to access different layers, but the number of mask trimming operations increases proportionally (8, 16, or more), increasing process complexity
Solution Approach 1:
The patent performs preliminary actions by forming the angled sidewalls and pyramidal structures through angled etching before final contact formation. This preliminary structuring allows subsequent planarization and contact operations to be performed more easily, as the angled surfaces provide natural access paths to multiple layers without requiring repeated mask trimming operations.
3Manufacturing precision
If resist trimming is performed on all sides of a square or rectangular resist shape, then the mask element dimensions are reduced uniformly, but the resulting pyramidal structure occupies a large projected area on the substrate, increasing device footprint
Solution Approach 1:
The patent introduces asymmetry by performing angled etching at specific angles (e.g., 45 degrees) rather than uniform trimming on all sides. This creates asymmetric pyramidal or tapered structures where the lateral footprint is reduced compared to symmetric pyramidal structures formed by uniform trimming, while still providing access to multiple layers through the angled sidewalls.
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 simplifies the fabrication of multilayer structures by reducing the number of mask operations and enhancing the reliability of 3D device structures, enabling more compact packing of devices within a given area while maintaining precise control over sidewall angles.
Implementation Method 1
directing first ions along a first direction forming a first non-zero angle of incidence with respect to a normal to a plane of the substrate
Implementation Method 2
etching the second plurality of layers using a first selective etch wherein the first layer type is selectively etched with respect to the second layer type
Data Source
AI summary
A method for fabricating a multilayer structure includes providing a mask on a device stack disposed on the substrate, the device stack comprising a first plurality of layers composed of a first layer type and a second layer type; directing first ions along a first direction forming a first non-zero angle of incidence with respect to a normal to a plane of the substrate, wherein a first sidewall is formed having a sidewall angle forming a first non-zero angle of inclination with respect to the normal, the first sidewall comprising a second plurality of layers from at least a portion of the first plurality of layers and composed of the first layer type and second layer type; and etching the second plurality of layers using a first selective etch wherein the first layer type is selectively etched with respect to the second layer type.