Underbody Contact for Vertical 3D Memory
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Solution Overview
Problem
As design rules shrink, semiconductor space for fabricating memory devices like DRAM arrays becomes limited, posing challenges in forming effective underbody contacts for horizontal access devices in vertical three-dimensional memory structures, which affects body bias control and access device channel control.
Innovation Solution
The integration of an underbody contact with a digit line and horizontal access devices in vertically stacked memory cells, providing better body bias control and access device channel control through a vertically oriented body contact line, while isolating the digit line to reduce capacitive coupling and dopant diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If design rules are shrunk to increase memory density, then semiconductor space efficiency is improved, but the ability to form effective underbody contacts for horizontal access devices deteriorates
Solution Approach 1:
The patent transitions from planar access devices to vertically stacked three-dimensional memory structures. By stacking multiple memory cell layers vertically, the design achieves higher memory density without further shrinking lateral design rules, thereby maintaining the ability to form effective underbody contacts while increasing productivity.
Solution Approach 2:
The memory structure is divided into multiple stacked layers, each containing memory cells with access devices. This segmentation allows underbody contacts to be formed effectively within each layer while the overall structure achieves high density through vertical stacking, resolving the contradiction between density and contact formation capability.
2Reliability
If underbody contact is integrated with digit line and horizontal access devices, then body bias control and access device channel control are improved, but capacitive coupling between digit line and body contact increases
Solution Approach 1:
An insulating layer is introduced as an intermediary between the digit line and the body contact. This intermediate insulating layer electrically isolates the two conductive elements, eliminating harmful capacitive coupling while allowing both the digit line and underbody contact to maintain their respective functions for signal transmission and body bias control.
Solution Approach 2:
The harmful capacitive coupling effect is extracted and eliminated by separating the digit line and body contact into different electrical domains using the insulating layer. This extraction of the harmful electrical interaction preserves the beneficial body bias control functionality.
3Reliability
If underbody contact is integrated with digit line and horizontal access devices, then access device channel control is improved, but dopant diffusion to source/drain regions increases
Solution Approach 1:
The insulating layer serves as a protective intermediary that physically blocks dopant diffusion pathways between the underbody contact and the source/drain regions. This intermediate barrier maintains effective access device channel control through the underbody contact while preventing harmful dopant contamination of the source/drain regions.
Solution Approach 2:
The potential harmful effect of dopant diffusion is converted into a benefit by using the insulating layer to define precise dopant regions. The insulating layer acts as a dopant diffusion barrier that, while preventing unwanted diffusion, enables more controlled and uniform doping profiles for improved access device performance.
Data Source
AI summary
Systems, methods and apparatus are provided for an array of vertically stacked memory cells having horizontally oriented access devices having a first source/drain region and a second source drain region separated by a channel region, and gates opposing the channel region, vertically oriented access lines coupled to the gates and separated from a channel region by a gate dielectric. The memory cells have horizontally oriented storage nodes coupled to the second source/drain region and horizontally oriented digit lines coupled to the first source/drain regions. An underbody conductive contact of a vertical body contact is formed in direct electrical contact with a body region of one or more of the horizontally oriented access devices and separate from the first source/drain region and the horizontally oriented digit lines by a dielectric.