Titanium Silicide Contacts for Thermally Stable SiGe Interfaces
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Solution Overview
Problem
Titanium contacts formed on silicon germanium layers in semiconductor devices are thermally unstable, leading to increased resistance due to void creation and interdiffusion during high-temperature processing steps, which affects transistor performance.
Innovation Solution
A titanium silicide layer is formed by exposing a titanium layer to a silicon precursor like silane at elevated temperatures, reducing interdiffusion and void formation, and a preamorphized silicon germanium surface is used to enhance stability, with multiple titanium silicide layers formed to maintain low resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If titanium contacts are formed on silicon germanium layers, then electrically conductive connections are provided, but resistance increases due to void creation and interdiffusion during high-temperature processing
Solution Approach 1:
The patent applies preliminary action by forming a preamorphized silicon germanium surface layer before depositing the titanium layer. This pre-prepared surface structure prevents interdiffusion and void formation during subsequent high-temperature annealing processes, maintaining low contact resistance while ensuring thermal stability. The preamorphized layer acts as a protective barrier that eliminates the need for post-formation repairs or adjustments.
Solution Approach 2:
The patent employs composite materials by creating a multi-layer structure consisting of the preamorphized silicon germanium surface layer and the titanium contact layer. This composite structure combines the benefits of both materials: the preamorphized silicon germanium provides structural stability and prevents interdiffusion, while the titanium provides electrical conductivity. The interface between these layers is engineered to minimize resistance while maintaining thermal stability during processing.
2Manufacturing precision
If multiple titanium silicide layers are formed, then low resistance is maintained, but process complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the titanium contact structure into multiple thin titanium silicide layers rather than forming a single thick layer. This segmented approach allows for better control of the silicide formation process, ensuring complete reaction without excessive thickness that could lead to void formation. Each thin layer can be properly silicided during annealing, resulting in lower overall resistance while maintaining process control.
Solution Approach 2:
The patent utilizes parameter changes by controlling the thickness, deposition conditions, and annealing parameters of multiple titanium silicide layers. By adjusting these parameters, the process optimizes the formation of low-resistance contacts while managing the complexity of multiple deposition and annealing cycles. The parameters are tuned to ensure that each layer forms correctly without requiring excessive 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
The approach results in thermally stable titanium contacts with unchanged resistance after annealing, reducing voids and maintaining low electrical resistance, thereby improving transistor performance.
Implementation Method 1
A titanium silicide layer is formed by exposing a titanium layer to a silicon precursor like silane at elevated temperatures
Implementation Method 2
thermally stable titanium contacts with unchanged resistance after annealing
Data Source
Figure 1A~1D
Figure 2A~2D
Figure 3
AI summary
The formation of titanium contacts to silicon germanium (SiGe) comprises the formation of a titanium silicide layer in which the silicon for the titanium silicide layer is provided by flowing silane (disilane, trisilane, etc.) over a titanium layer at an elevated temperature. The titanium silicide layer can help limit the amount of titanium and germanium interdiffusion that can occur across the titanium silicide-silicon germanium interface, which can reduce (or eliminate) the formation of voids in the SiGe layer during subsequent anneal and other high-temperature processes. The surface of the SiGe layer upon which the titanium layer is formed can also be preamorphized via boron and germanium implantation to further improve the robustness of the SiGe layer against microvoid development. The resulting titanium contacts are thermally stable in that their resistance remains substantially unchanged after being subjected to downstream annealing and high-temperature processing processes.