Nanostructure Transistor Buffer Layer for Dopant Diffusion Control
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Solution Overview
Problem
Dopants from the doped epitaxial material in the source/drain region of nanostructure transistors diffuse into the mesa region, leading to increased electron tunneling, short channel effects, and leakage, which degrade device performance.
Innovation Solution
A buffer layer is formed under the source/drain region with a specific shape and dimensions to prevent dopant diffusion, including a curved top surface and extending over shallow trench isolation regions, fully separating the source/drain region from the mesa region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dopants are introduced into the source/drain region, then electrical conductivity is improved, but dopant diffusion into the mesa region increases short channel effects and leakage
Solution Approach 1:
An undoped epitaxial layer is introduced as an intermediary barrier between the doped source/drain region and the mesa region. This buffer layer physically separates the dopants from the mesa region, preventing diffusion while maintaining the electrical conductivity benefits of doping in the source/drain region. The undoped layer acts as a mediator that blocks harmful dopant migration without interfering with the desired electrical properties.
Solution Approach 2:
The semiconductor structure is segmented into distinct regions: a doped epitaxial layer for the source/drain region, an undoped epitaxial buffer layer as a separation barrier, and the mesa region. This segmentation isolates the dopants to their intended functional area while preventing them from diffusing into adjacent regions, thereby resolving the contradiction between achieving good electrical conductivity and preventing harmful diffusion effects.
2Reliability
If the buffer layer extends over shallow trench isolation regions, then complete separation from mesa region is achieved, but manufacturing complexity increases
Solution Approach 1:
The undoped epitaxial layer serves multiple functions simultaneously: it acts as a dopant diffusion barrier, provides mechanical support for subsequent processing steps, defines the boundary between source/drain and mesa regions, and extends over shallow trench isolation regions to ensure complete separation. By making the buffer layer multi-functional, the design achieves complete separation without proportionally increasing manufacturing complexity, as a single layer performs multiple protective and definitional roles.
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 buffer layer reduces short channel effects, decreases off-current, and minimizes leakage, thereby enhancing the performance of nanostructure transistors.
Implementation Method 1
Dopants from the doped epitaxial material in the source/drain region of nanostructure transistors diffuse into the mesa region
Data Source
AI summary
In some implementations, a buffer layer is formed under a source/drain region of a device. A shape of the buffer layer may include a curved top surface having a height that extends to increase coverage of nanosheets of a fin structure of the device. The shape also includes regions having widths that extend towards shallow trench isolation regions of the device. The shape reduces a likelihood of dopants diffusing from the source/drain region into a mesa region of the fin structure. As a result, a performance of the device may be increased by decreasing short channel effects, decreasing an off-current of the device, and decreasing leakage within the device, among other examples.