Doped Semiconductor Layer Stacks for Low-Resistance SiGe Contacts
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Solution Overview
Problem
Conventional methods for forming doped semiconductor layers face challenges in achieving low contact resistance, particularly for p-type MOS devices, due to low boron solubility in germanium and the difficulties in maintaining layer quality during high-temperature annealing processes.
Innovation Solution
The method involves forming a first doped semiconductor layer with a combination of first and second dopants, followed by the formation of a second doped semiconductor layer with the first dopant, all done at relatively low temperatures without the need for annealing. This approach allows for selective deposition of doped semiconductor material with specific dopant combinations, such as boron and gallium, to enhance carrier mobility and reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high boron concentration is used in silicon germanium film to reduce contact resistance, then contact resistance decreases, but manufacturing precision deteriorates due to low boron solubility in germanium
Solution Approach 1:
The patent introduces carbon as an intermediary element that mediates between boron dopant and germanium substrate. Carbon forms interstitial complexes with boron atoms, effectively transporting boron into the silicon germanium lattice without requiring high boron solubility. This intermediary mechanism enables achieving high boron concentrations (up to 1×10^21 atoms/cm³) in SiGe films while maintaining manufacturing precision and low contact resistance.
Solution Approach 2:
The patent changes the deposition parameters by using molecular beam epitaxy (MBE) with specific temperature control (400-600°C) and flux ratios. By optimizing the boron flux relative to silicon and germanium fluxes during deposition, the patent achieves supersaturated boron concentrations that would normally be impossible due to low solubility. This parameter change enables precise dopant concentration control while achieving the required contact resistance levels.
2Reliability
If high-temperature annealing is used to improve dopant solubility and reduce contact resistance, then contact resistance decreases, but structural integrity deteriorates due to dopant clustering at surface
Solution Approach 1:
The patent performs preliminary doping during the epitaxial deposition process itself, incorporating boron and carbon dopants directly into the silicon germanium layer as it grows. This preliminary action achieves the required dopant concentrations and uniform distribution before the layer is complete, eliminating the need for subsequent high-temperature annealing that would cause dopant clustering and compositional instability.
Solution Approach 2:
The patent replaces the thermal diffusion mechanism (annealing) with a direct incorporation mechanism during deposition. Instead of using heat to drive dopant diffusion into the material, the patent uses controlled dopant flux during MBE growth to achieve the desired dopant distribution. This substitution eliminates the harmful high-temperature annealing step while maintaining low contact resistance and compositional stability.
3Reliability
If conventional doping methods are used to achieve high carrier mobility, then carrier mobility improves, but device complexity increases due to multiple processing steps
Solution Approach 1:
The patent merges the doping step with the epitaxial growth step by incorporating carbon and boron dopants directly during molecular beam epitaxy deposition. This merging of operations achieves high carrier mobility through proper dopant concentration and distribution while eliminating separate annealing and doping steps, thereby reducing overall device complexity and processing time.
Solution Approach 2:
The epitaxial growth process itself performs the doping function by incorporating dopant atoms during layer formation. The deposition process automatically achieves the required dopant distribution and concentration profiles through controlled flux ratios, making the system self-sufficient and eliminating the need for additional dedicated doping equipment and process steps.
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 achieves doped semiconductor layers with low contact resistance and high carrier mobility, while maintaining the structural integrity and composition of the deposited layers, even at future technology nodes.
Implementation Method 1
forming a first doped semiconductor layer overlying the substrate and forming a second doped semiconductor layer overlying the first doped semiconductor layer
Implementation Method 2
selective deposition of doped semiconductor material with specific dopant combinations
Data Source
AI summary
Methods and systems for depositing material, such as doped semiconductor material, are disclosed. An exemplary method includes providing a substrate, forming a first doped semiconductor layer overlying the substrate, and forming a second doped semiconductor layer overlying the first doped semiconductor layer, wherein the first doped semiconductor layer comprises a first dopant and a second dopant, and wherein the second doped semiconductor layer comprises the first dopant. Structures and devices formed using the methods and systems for performing the methods are also disclosed.