Strained Silicon Layer Formation via Selective Amorphization
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Solution Overview
Problem
Existing methods for forming strained silicon layers often result in a high density of defects in the relaxed SiGe layer, which are transferred to the epitaxial silicon layer, leading to suboptimal performance in transistor devices.
Innovation Solution
A method involving the formation of a strained silicon germanium layer by epitaxial growth over a silicon layer on a substrate, followed by atom implantation to amorphize the silicon and lower SiGe layer, and subsequent annealing to relax and re-crystallize the SiGe layer, creating a strained silicon layer with reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a strained silicon layer is formed by epitaxial growth over a relaxed SiGe layer, then the silicon atoms are stretched beyond their normal inter-atomic distance resulting in a strained silicon layer, but there is a relatively high density of defects in the relaxed SiGe layer which are transferred to the epitaxial silicon layer
Solution Approach 1:
The patent inverts the conventional sequence by first forming a strained SiGe layer over a relaxed silicon layer, then relaxing the SiGe layer through ion implantation and annealing. This inversion allows the silicon layer to be strained by the relaxed SiGe layer, achieving the desired strain while eliminating the defect transfer problem that occurs when growing silicon over relaxed SiGe.
Solution Approach 2:
The patent changes the physical state parameters of the SiGe layer through ion implantation (amorphization) and thermal annealing (recrystallization), transforming it from a strained crystalline state to a relaxed crystalline state. This parameter change enables the overlying silicon layer to maintain strain without inheriting defects from the SiGe layer.
2Reliability
If ion implantation is used to amorphize the silicon and SiGe layers, then defects are reduced in the silicon layer, but the implantation process requires precise control to avoid over-amorphization
Solution Approach 1:
The patent applies local quality by using a mask during ion implantation to selectively amorphize only the SiGe layer and the underlying silicon layer, while leaving the surface portion of the SiGe layer intact. This localized treatment allows precise control over which regions are amorphized and subsequently relaxed, reducing defects in the silicon layer without compromising the overall structure.
3Force
If the SiGe layer thickness is increased to provide sufficient strain, then the strain effect is enhanced, but the layer exceeds the critical thickness below which SiGe grows without defect
Solution Approach 1:
The patent applies preliminary action by first forming the SiGe layer with sufficient thickness to provide the desired strain effect, then subsequently relaxing it through ion implantation and annealing. This preliminary formation allows the layer to exceed the critical thickness for strain generation without immediately introducing defects, and the relaxation step then eliminates those defects while preserving the strain in the silicon layer.
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 results in a high-quality strained silicon layer with low defect density and enhanced stress levels, suitable for high-performance transistor applications, without the need for molecular bonding steps and with simplified, cost-effective processing.
Implementation Method 1
implanting atoms to amorphize the silicon layer and a lower portion of the silicon germanium layer
Implementation Method 2
annealing, to at least partially relax the silicon germanium layer and to re-crystallize the lower portion of the silicon germanium layer and the silicon layer
Implementation Method 3
annealing, to at least partially relax the silicon germanium layer
Data Source
AI summary
The present disclosure concerns a method involving: forming a strained silicon germanium layer by epitaxial growth over a silicon layer disposed on a substrate; implanting atoms to amorphize the silicon layer and a lower portion of the silicon germanium layer, without amorphizing a surface portion of the silicon germanium layer; and annealing, to at least partially relax the silicon germanium layer and to re-crystallize the lower portion of the silicon germanium layer and the silicon layer, so that the silicon layer becomes a strained silicon layer.