Gallium Doped Silicon Germanium via Epitaxial Diffusion
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Solution Overview
Problem
High percentage silicon germanium substrates require high gallium doping for improved semiconductor device performance, but existing methods using boron or in situ doped epitaxial processes result in low solubility and carbon incorporation, which increases resistance and is not viable due to tight device architecture.
Innovation Solution
A method involving the formation of a gallium-doped germanium layer on a high percentage silicon germanium alloy surface layer, with diffusion of gallium into the substrate to create a gallium-doped silicon germanium region, followed by removal of the germanium layer, ensuring no carbon incorporation and achieving high acceptor level doping without dopant-induced end-of-range crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If boron doping is used in high percentage silicon germanium, then the doping process is simple, but the solubility is low and resistance increases
Solution Approach 1:
The patent changes the dopant type from boron to gallium, which has higher solubility in high-Ge SiGe alloys. This parameter change (dopant species) resolves the contradiction by achieving both adequate solubility and low resistance while maintaining process simplicity through established doping techniques.
2Reliability
If in situ doped epitaxial processes are used, then high gallium doping is achieved, but carbon incorporation increases resistance
Solution Approach 1:
The patent separates the doping function from the epitaxial growth process. Instead of using in situ doped epitaxial processes that incorporate carbon, the method deposits a gallium-doped germanium layer and then removes the germanium layer, extracting only the gallium dopant. This resolves the contradiction by achieving high gallium doping while eliminating carbon incorporation.
Solution Approach 2:
The patent uses a gallium-doped germanium layer as an intermediary to transfer gallium dopants to the SiGe surface layer. This intermediary approach allows gallium to be introduced without the carbon that would accompany in situ epitaxial doping, resolving the contradiction between doping effectiveness and carbon avoidance.
3Reliability
If gallium implantation is used, then high gallium doping is achieved, but the tight device architecture prevents viable implementation
Solution Approach 1:
The patent replaces the mechanical implantation process with a chemical deposition and diffusion process. Instead of physically implanting gallium ions through masks and into tight structures, the method deposits a gallium-doped germanium layer that naturally diffuses gallium into the SiGe surface layer during annealing. This substitution resolves the contradiction by achieving high doping concentrations without the geometric constraints of implantation.
4Reliability
If high germanium content channel materials are used, then device performance is improved, but dopant solubility decreases
Solution Approach 1:
The patent changes the dopant species from boron to gallium, which maintains higher solubility even in high-Ge SiGe alloys. This parameter change resolves the contradiction by enabling adequate dopant concentrations in high germanium content materials while preserving the performance benefits of high-Ge channel structures.
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 method effectively provides high gallium doping in silicon germanium alloys without carbon incorporation, enhancing electrical conductivity and reducing resistance, thereby improving the performance of semiconductor devices like FinFETs.
Implementation Method 1
causing diffusion of gallium from the germanium layer into the silicon germanium alloy surface layer
Implementation Method 2
the germanium layer having a higher germanium content and a lower melting point than the silicon germanium alloy surface layer
Data Source
AI summary
A semiconductor structure is provided in which gallium-doped sacrificial epitaxial or polycrystalline germanium layer is formed on a silicon germanium substrate having a high percentage of germanium followed by annealing to diffuse the gallium into the silicon germanium substrate. The germanium layer is selectively removed to expose the surface of a gallium-doped silicon germanium region within the silicon germanium substrate. The process has application to the formation of electrically conductive regions within integrated circuits such as source/drain regions and junctions without the introduction of carbon into such regions.