3D Memory Control Gate Staircase Contacts for Word Line Isolation
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Solution Overview
Problem
Planar memory cell technologies face challenges in scaling due to increased costs and complexity as feature sizes approach limits, necessitating a transition to three-dimensional (3D) memory architectures to enhance memory density.
Innovation Solution
A method for forming a 3D memory device involves creating a staircase structure with alternating dielectric and sacrificial layers, followed by etching and deposition processes to form cavities and conductive layers, with an etch stop layer and insulating layers to facilitate contact formation, enabling efficient word line and control gate structure creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If planar memory cells are scaled to smaller sizes to increase density, then memory density improves, but fabrication complexity and cost increase significantly
Solution Approach 1:
The patent transitions from planar (2D) memory cell architecture to three-dimensional (3D) memory architecture by stacking multiple memory layers vertically. This dimensional change allows continued density improvement without further scaling lateral features, thereby avoiding the fabrication complexity and cost associated with extreme miniaturization of planar cells.
Solution Approach 2:
The memory device is divided into multiple stacked layers, each containing memory cells. This segmentation allows the overall memory capacity to be distributed across several layers, achieving high density while maintaining manageable fabrication processes for each individual layer.
2Quantity of substance
If etching processes are used to form staircase structures in 3D memory, then memory density increases, but etching variations cause shorts between adjacent word lines
Solution Approach 1:
A mandrel structure is introduced as an intermediary element during the etching process. The mandrel serves as a physical barrier and reference structure that helps maintain consistent etch depths and prevents etching variations from causing shorts between adjacent word lines. The mandrel is temporarily present during fabrication and is removed after serving its protective function.
Solution Approach 2:
The mandrel structure is formed in advance before the critical etching steps that create the staircase structure. This preliminary action establishes a reference framework that guides subsequent etching processes, ensuring uniform word line formation and preventing shorts before they can occur.
3Ease of manufacture
If conventional contact structures are formed in 3D memory, then fabrication is simplified, but etching variations lead to electrical shorts between adjacent word lines
Solution Approach 1:
The mandrel acts as an intermediary structure that enables conventional-looking fabrication steps to produce reliable results. By providing a physical reference and barrier during etching, the mandrel ensures that simple fabrication processes do not compromise electrical isolation between word lines, thus maintaining both ease of manufacture and reliability.
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 allows for the formation of reliable word line and control gate structures in 3D memory devices, reducing etching variations and preventing shorts between adjacent word lines, thereby improving memory density and device performance.
Implementation Method 1
oxidizing a portion of the etch stop layer through the plurality of openings
Data Source
AI summary
A method for forming a three-dimensional memory device can include forming a staircase structure. An alternating layer stack is disposed and etched to form steps. A continuous layer disposed on the staircase structure continuously extends over the steps. An insulating layer is disposed on the continuous layer and a slit is formed extending through the staircase structure. The slit exposes sidewalls of the continuous layer and the steps. The sacrificial layer is removed and a cavity is formed in place of the continuous layer. An etch stop layer is disposed in the cavity and continuously extends over the steps. Openings are formed through the insulating layer and expose a portion of a lateral surface of the etch stop layer. The openings are extended through the etch stop layer to expose a lateral surface of each step of the steps. Contacts are formed in the openings.