In-Situ Doped Nanosheet Transistor Gradient Channel
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Solution Overview
Problem
Existing semiconductor fabrication methods struggle to achieve a gradient doping concentration and threshold voltage (Vt) level along the channel regions of nanosheet transistors, particularly in non-planar architectures like FinFETs and gate-all-around nanosheet FETs, due to difficulties in controlling dopant implantation in thin nanosheets.
Innovation Solution
The method involves an in-situ doping process using epitaxial growth to create a gradient doping concentration by forming a doped region with a higher dopant concentration on the source-side of the channel, which is then diffused into the undoped channel regions, achieving a gradient Vt level by controlling the dopant distribution across the channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional dopant implantation methods are used in non-planar nanosheet architectures, then device density and performance are improved, but control of dopant distribution and gradient doping concentration becomes difficult
Solution Approach 1:
The patent applies preliminary action by forming the desired dopant concentration gradient directly during the epitaxial growth process itself, rather than attempting to implant dopants afterward. The gradient doping is built into the nanosheet structure during its creation, with dopants incorporated at different concentrations at different positions along the channel as the nanosheet grows. This eliminates the need for subsequent complex implantation steps and provides precise control over dopant distribution from the outset.
Solution Approach 2:
The patent replaces the mechanical dopant implantation process with a chemical epitaxial growth process. Instead of physically shooting dopant ions into the nanosheet structure, dopants are incorporated chemically during the epitaxial growth of the nanosheet material. This substitution allows for better control over dopant placement and concentration gradients, as the chemical process can be precisely controlled through gas flow rates, temperatures, and precursor ratios during growth.
2Ease of manufacture
If uniform doping is applied across the channel region, then fabrication simplicity is maintained, but carrier mobility and device performance are reduced due to lack of steep potential distribution
Solution Approach 1:
The patent applies local quality by creating different dopant concentrations at different locations along the nanosheet channel. The source-side region has a higher dopant concentration than the drain-side region, creating a non-uniform doping profile. This local variation in dopant concentration produces the steep potential distribution needed near the source to enhance carrier mobility and improve device performance, while still maintaining a relatively simple epitaxial growth fabrication process.
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 the creation of transistors with a controlled gradient doping concentration and Vt level, enhancing carrier mobility and device performance by maintaining a steep potential distribution near the source-side of the channel, thus improving the electrical characteristics of nanosheet transistors.
Implementation Method 1
Dopants are provided in the source-side nanosheet region by incorporating an in-situ doping process into a process used to form the source-side nanosheet region
Implementation Method 2
a doping concentration in the source-side nanosheet region is greater than a doping concentration of the drain-side nanosheet region
Data Source
AI summary
Embodiments of the invention are directed to a method of performing fabrication operations to form a transistor. The fabrication operations include forming a nanosheet having a first nanosheet sidewall and a second nanosheet sidewall. The nanosheet is communicatively coupled to a source region at the first nanosheet sidewall. The nanosheet is communicatively coupled to a drain region at the second nanosheet sidewall. The nanosheet further includes a source-side nanosheet region that includes the first nanosheet sidewall. The nanosheet further includes a drain-side nanosheet region that includes the second nanosheet sidewall. Dopants are provided in the source-side nanosheet region using an in-situ doping process, wherein a doping concentration in the source-side nanosheet region is greater than a doping concentration of the drain-side nanosheet region.