Tensile-Strained SiGe Buffer for Germanium Channel Defect Reduction
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Solution Overview
Problem
The direct epitaxial growth of germanium on silicon results in defect formation due to lattice mismatch, degrading the performance of germanium channels in transistor devices.
Innovation Solution
A tensile-strained silicon germanium buffer layer is used, which has a similar lattice constant to germanium, reducing defects and improving the material quality and performance by confining lattice mismatch defects and maintaining high carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct epitaxial growth of germanium on silicon is used, then manufacturing process is simple, but defect density increases due to lattice mismatch
Solution Approach 1:
A tensile-strained silicon germanium buffer layer is introduced as an intermediary between the silicon substrate and the germanium channel. This buffer layer has a lattice constant that is strained to match germanium more closely than silicon, thereby reducing lattice mismatch defects while maintaining a practical epitaxial growth process.
Solution Approach 2:
The lattice constant of the silicon germanium buffer layer is modified through tensile strain to better match the germanium lattice constant. This parameter change reduces the lattice mismatch from 4.2% (silicon-germanium) to a smaller value, significantly reducing defect density in the germanium channel.
2Reliability
If relaxed germanium channel is formed, then carrier mobility is high, but defect density must be very low which is difficult to achieve directly on silicon
Solution Approach 1:
The tensile-strained silicon germanium buffer layer serves as a mediator that enables the formation of high-quality relaxed germanium channels. By providing a lattice-matched interface, it allows germanium to grow with very low defect density, achieving the required quality for high carrier mobility.
Solution Approach 2:
The strain state and lattice constant of the buffer layer are optimized to enable relaxed germanium growth. The tensile strain in the silicon germanium buffer creates a lattice constant that matches relaxed germanium, allowing defect-free channel formation with high carrier mobility.
3Manufacturing precision
If tensile-strained silicon germanium buffer layer is used, then defect density is reduced, but device structure becomes more complex
Solution Approach 1:
The buffer layer composition and strain state are optimized to achieve the desired lattice match. By carefully controlling the silicon germanium composition and applying tensile strain, the buffer layer reduces defects without requiring excessive structural complexity, maintaining manufacturability.
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 use of a tensile-strained silicon germanium buffer layer reduces defects and enhances the performance of germanium channels by providing a defect-free interface and efficient carrier confinement, thereby improving the overall performance of transistor devices.
Implementation Method 1
A buffer layer including tensile-strained silicon germanium (SiGe) on silicon that has a similar lattice constant as germanium
Implementation Method 2
direct epitaxial growth of a non-planar structure (e.g., a fin) of germanium on silicon
Data Source
AI summary
An apparatus including a transistor device including a channel including germanium disposed on a substrate; a buffer layer disposed on the substrate between the channel and the substrate, wherein the buffer layer includes silicon germanium; and a seed layer disposed on the substrate between the buffer layer and the substrate, wherein the seed layer includes germanium. A method including forming seed layer on a silicon substrate, wherein the seed layer includes germanium; forming a buffer layer on the seed layer, wherein the buffer layer includes silicon germanium; and forming a transistor device including a channel on the buffer layer.