Sn-Mediated Epitaxial NiGe Contact on Ge Substrate
Solution Overview
Problem
The formation of a germanide layer on a Ge layer results in a polycrystalline structure with low interface flatness, leading to increased contact resistance and reduced on-current in Ge nMOSFETs, due to Fermi level pinning and high interface states.
Innovation Solution
Incorporating a Sn layer at the interface between the Ni and Ge layers, followed by annealing, allows for the epitaxial growth of a single-crystal NiGe layer with high interface flatness, matching lattice planes and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a germanide layer is formed by deposition of metal on Ge layer and annealing, then the germanide can be formed on Ge layer in self-aligning manner, but the germanide becomes polycrystalline with low interface flatness
Solution Approach 1:
A Sn layer is introduced as an intermediary between the metal layer and Ge layer. This Sn layer acts as a mediator that enables epitaxial growth of the metal germanide on the Ge substrate, transforming the polycrystalline deposition process into a single-crystal epitaxial growth process while maintaining self-alignment.
Solution Approach 2:
The structure employs a composite multi-layer configuration consisting of metal layer/Sn layer/Ge layer. This composite structure combines the advantages of each material: the metal provides germanide formation, the Sn layer enables epitaxial growth, and the Ge layer serves as the substrate, achieving both self-alignment and high interface flatness.
2Device complexity
If germanide is formed with low interface flatness, then formation process is simplified, but contact resistance between germanide and Ge increases
Solution Approach 1:
The Sn layer serves as a mediator that facilitates low-resistance contact between the metal germanide and Ge substrate. By enabling epitaxial growth, it creates a high-quality interface with reduced interface states, thereby lowering contact resistance without significantly complicating the formation process.
3Reliability
If interface states are high, then Fermi level pinning is strong, but interface flatness is low
Solution Approach 1:
The Sn layer acts as an intermediary that reduces interface states between the metal germanide and Ge substrate. By enabling epitaxial growth, it creates a cleaner interface with fewer defects and interface states, thereby reducing Fermi level pinning while achieving high interface flatness.
Solution Approach 2:
The introduction of the Sn layer changes the physical and chemical parameters of the interface, including interface state density, crystal structure, and lattice matching. These parameter changes enable simultaneous achievement of low interface states and high interface flatness.
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 approach results in a significant reduction of contact resistance by two to four orders of magnitude and improves the Schottky barrier height, enabling better device performance and compatibility with Ge substrates without causing leakage currents.
Implementation Method 1
the epitaxial growth of a single-crystal NiGe layer with high interface flatness, matching lattice planes
Implementation Method 2
followed by annealing, allows for the epitaxial growth of a single-crystal NiGe layer
Implementation Method 3
followed by annealing, allows for the epitaxial growth of a single-crystal NiGe layer
Data Source
AI summary
According to one embodiment, a semiconductor device includes a semiconductor layer including Ge; and a metal Ge compound region provided in a surface portion of the semiconductor layer. Sn is included in an interface portion between the semiconductor layer and the metal Ge compound region. A lattice plane of the semiconductor layer matches with a lattice plane of the metal Ge compound region.