Vertical-transport FET with etched-through source/drain cavity
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Solution Overview
Problem
Conventional vertical-transport field-effect transistors lack a semiconductor material epitaxial structure for the bottom source/drain region that extends completely beneath the semiconductor fin, leading to non-uniform dopant distribution and inefficient carrier transport.
Innovation Solution
A method involving the formation of a semiconductor fin on a sacrificial layer, trench isolation, and removal of the sacrificial layer to create a cavity beneath the fin, allowing for epitaxial growth of a uniformly doped semiconductor material as the bottom source/drain region, which is supported by trench isolation at the fin's end surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial growth is used for bottom source/drain region, then manufacturing process is simple, but dopant distribution is non-uniform and carrier transport efficiency is poor
Solution Approach 1:
The bottom source/drain region is segmented into two distinct parts: a first portion formed by epitaxial growth with uniform dopant distribution, and a second portion formed by selective epitaxial growth. This segmentation allows each portion to serve different functional requirements, with the first portion providing uniform doping and the second portion enabling precise dopant placement beneath the fin.
Solution Approach 2:
Different dopant distribution characteristics are applied to different locations within the bottom source/drain region. The first portion has uniformly distributed dopant concentration throughout its volume, while the second portion has precisely placed doped regions beneath the fin. This local quality differentiation optimizes carrier transport efficiency in each specific area.
2Manufacturing precision
If trench isolation is removed completely, then epitaxial growth can proceed uniformly, but fin support structure is lost
Solution Approach 1:
The trench isolation is selectively removed only from the region where epitaxial growth is desired, while portions of the trench isolation are retained to provide structural support for the fin. This extraction approach allows the epitaxial growth to proceed uniformly in the exposed regions while maintaining necessary mechanical support.
Solution Approach 2:
The trench isolation serves as an intermediary structure that temporarily provides support during fabrication and is then selectively removed to enable epitaxial growth. The remaining trench isolation portions continue to provide support, acting as a mediator between the need for uniform growth and structural integrity.
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 enables a uniformly distributed dopant concentration beneath the fin, enhancing carrier transport efficiency and improving the structure's performance by precisely placing doped regions beneath the vertical channel of the transistor.
Implementation Method 1
the sacrificial layer is removed to form a cavity extending beneath the semiconductor fin
Implementation Method 2
A semiconductor material is formed in the cavity to provide a source/drain region... the first source/drain region is composed of a volume of a semiconductor material having a uniformly-distributed dopant concentration
Data Source
AI summary
Methods of forming a structure for a vertical-transport field-effect transistor and structures for a vertical-transport field-effect transistor. A semiconductor fin is formed on a sacrificial layer, and trench isolation is formed in which the semiconductor fin is embedded. The trench isolation is removed at opposite sidewalls of the semiconductor fin. After the trench isolation is removed at opposite sidewalls of the semiconductor fin, the sacrificial layer is removed to form a cavity extending beneath the semiconductor fin while the semiconductor fin is supported by the trench isolation adjacent to opposite end surfaces of the semiconductor fin. A semiconductor material is formed in the cavity to provide a source/drain region.