Multi-Gate Device Diffusion Stop Layer to Reduce Leakage
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Solution Overview
Problem
Conventional multi-gate transistor structures, such as FinFETs and MBC transistors, face challenges in reducing leakage, capacitance, and resistance, which are not adequately addressed by existing designs.
Innovation Solution
The introduction of a diffusion stop layer with a higher germanium content than the outer epitaxial layer, formed through conformal deposition and selective etching, to control dopant diffusion and reduce parasitic capacitance, combined with epitaxial layers to enhance carrier mobility and prevent dopant out-diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-gate transistor structures are used to improve gate control, then gate-channel coupling is increased, but parasitic capacitance increases
Solution Approach 1:
The source/drain structure is segmented into multiple epitaxial layers with different germanium contents. The outer epitaxial layer has lower germanium content while the inner epitaxial layer has higher germanium content, creating distinct functional zones that reduce parasitic capacitance while maintaining gate control
Solution Approach 2:
Different regions of the source/drain structure are assigned different material compositions. The outer region uses lower germanium content material to reduce capacitance, while the inner region uses higher germanium content material to maintain electrical performance and carrier mobility
2Reliability
If conventional multi-gate transistor structures are used, then device performance is improved, but leakage current is not sufficiently reduced
Solution Approach 1:
The germanium content parameter is varied across different epitaxial layers to optimize device performance. By controlling the germanium concentration gradient between outer and inner layers, the patent achieves better carrier mobility while reducing leakage current through improved band structure
3Productivity
If source/drain structures are scaled down, then production efficiency is increased, but dopant diffusion control becomes more difficult
Solution Approach 1:
The outer epitaxial layer acts as an intermediary barrier between the doping region and the channel. This intermediate layer with controlled germanium content regulates dopant diffusion, preventing excessive dopant migration while enabling efficient production through standardized fabrication processes
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 diffusion stop layer effectively reduces leakage and parasitic capacitance while improving device performance by controlling dopant diffusion and enhancing carrier mobility, thus addressing the limitations of conventional multi-gate transistor structures.
Implementation Method 1
a diffusion stop layer with a higher germanium content than the outer epitaxial layer, formed through conformal deposition and selective etching, to control dopant diffusion
Implementation Method 2
combined with epitaxial layers to enhance carrier mobility and prevent dopant out-diffusion
Data Source
AI summary
Methods and semiconductor structures are provided. A method according to the present disclosure includes depositing a top epitaxial layer over a substrate, forming a fin structure from the top epitaxial layer and a portion of the substrate, recessing a source/drain region of the fin structure to form a source/drain recess, conformally depositing a semiconductor layer over surfaces of the source/drain recess, etching back the semiconductor layer to form a diffusion stop layer over a bottom surface of the source/drain recess, depositing a first epitaxial layer over the diffusion stop layer and sidewalls source/drain recess, depositing a second epitaxial layer over the first epitaxial layer, and depositing a third epitaxial layer over the second epitaxial layer. A germanium concentration of the diffusion stop layer is greater than a germanium concentration of the top epitaxial layer or a germanium concentration of the first epitaxial layer.