Vertical Transistor Body Contact Layout for Floating Body Relief
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Solution Overview
Problem
Floating body effects in vertical access transistors of DRAM memory cells lead to degraded charge retention and power distribution issues, necessitating the development of architectures and methods to alleviate these problems.
Innovation Solution
Integrated assemblies with vertically-displaced source/drain regions and body contact regions adjacent to them, featuring insulative posts and layers formed through trench and bowl region etching and filling with insulative material, which provide a reference voltage to prevent floating body effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If vertical access transistors are used to occupy smaller footprint, then integration density is improved, but floating body effects occur leading to degraded charge retention and power distribution problems
Solution Approach 1:
The semiconductor structure is segmented into multiple regions: a first region with a first conductivity type and a second region with a second conductivity type. This segmentation allows the body contact to be electrically coupled to a specific region, thereby eliminating floating body effects while maintaining the vertical transistor's compact footprint.
Solution Approach 2:
An intermediary structure (insulative material layer) is introduced between the body contact and the source/drain regions. This intermediary allows selective electrical coupling of the body contact to the channel region while providing isolation where needed, resolving the floating body problem without increasing footprint.
2Productivity
If vertical access transistors are used to achieve higher integration, then device density is improved, but floating body effects cause power distribution problems
Solution Approach 1:
The structure is divided into conductive type regions that can be selectively coupled to power distribution networks. The first and second conductivity type regions are segmented such that one region receives the reference voltage through the body contact, enabling proper power distribution across the high-density integrated array.
3Reliability
If body contact is formed adjacent to source/drain regions, then floating body effects are alleviated, but manufacturing complexity increases due to additional etching and filling steps
Solution Approach 1:
The bowl-shaped etch regions serve multiple functions: they define the body contact location, provide isolation through insulative material filling, and establish the reference voltage connection. This multi-functionality reduces the need for separate processing steps while achieving reliable floating body effect mitigation.
Solution Approach 2:
The etching process parameters are changed to create bowl-shaped regions instead of traditional planar trenches. This parameter change in the etch profile allows the insulative material to be strategically positioned to alleviate floating body effects while integrating smoothly with existing fabrication flows.
4Reliability
If insulative material is filled in bowl regions to form posts and layers, then body contact isolation is improved, but manufacturing precision requirements increase
Solution Approach 1:
The use of bowl-shaped (curved) etch regions instead of planar trenches provides geometric tolerance that relaxes manufacturing precision requirements. The curved geometry naturally accommodates variations in etch depth and insulative material filling, while still achieving the required body contact isolation and electrical coupling.
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
The solution effectively alleviates floating body effects, improving charge retention and power distribution across memory arrays by providing a stable reference voltage to the body regions of transistors, enhancing the performance and reliability of memory devices.
Implementation Method 1
trenches into a mass of semiconductor material, and formation of bowl regions along bottoms of the trenches
Implementation Method 2
The trenches and bowl regions are filled with insulative material to form insulative posts within the trenches and to form an insulative layer (or floor) from the insulative material in the bowl regions
Data Source
AI summary
Some embodiments include an integrated assembly having a semiconductor-containing structure with a body region vertically between an upper region and a lower region. The upper region includes a first source/drain region. The lower region is split into two legs which are both joined to the body region. One of the legs includes a second source/drain region and the other of the legs includes a body contact region. The first and second source/drain regions are of a first conductivity type, and the body contact region is of a second conductivity type which is opposite to the first conductivity type. An insulative material is adjacent to the body region. A conductive gate is adjacent to the insulative material. A transistor includes the semiconductor-containing structure, the conductive gate and the insulative material. Some embodiments include methods of forming integrated assemblies.