Germanium Concentration Gradient in SiGe Channel Transistors
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Solution Overview
Problem
Silicon-germanium channel transistors face increased leakage current due to band-to-band tunneling (BTBT) in the off-state, despite enhanced carrier mobility, necessitating methods to reduce leakage while maintaining high mobility.
Innovation Solution
A semiconductor device design featuring an active layer with a high germanium concentration channel region and a lightly doped drain (LDD) region with a lower germanium concentration, where the LDD region is formed adjacent to the channel, and a gate structure with a high-k dielectric layer and silicon oxide layer to reduce BTBT and leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a silicon-germanium channel is used to enhance carrier mobility, then carrier mobility is improved, but leakage current in off-state increases due to band-to-band tunneling
Solution Approach 1:
The active layer is designed with non-uniform germanium concentration distribution, where the channel region has high germanium concentration for high carrier mobility, while the drain region has lower germanium concentration to reduce band-to-band tunneling and leakage current. This local differentiation of material composition resolves the contradiction between mobility enhancement and leakage reduction.
Solution Approach 2:
The germanium concentration parameter is varied spatially within the active layer. By changing the germanium concentration from high in the channel to low in the drain region, the patent achieves both high carrier mobility in the channel and reduced leakage current at the drain, effectively resolving the technical contradiction.
2Speed
If a high germanium concentration is used in the channel region to maintain high mobility, then carrier mobility is maintained, but band-to-band tunneling increases causing higher leakage
Solution Approach 1:
Different regions of the active layer are assigned different germanium concentrations tailored to their specific functions. The channel region maintains high germanium concentration for high mobility, while the drain region uses lower germanium concentration to suppress band-to-band tunneling, thus resolving the contradiction locally in each region.
Solution Approach 2:
The active layer is segmented into functionally distinct regions with different germanium concentrations. The channel portion is separated from the drain portion by creating a gradient or abrupt change in germanium concentration, allowing each segment to optimize its performance for its specific function without compromising the other.
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 design achieves reduced leakage current in the off-state while maintaining high carrier mobility, enhancing the operational speed and efficiency of the transistor.
Implementation Method 1
a silicon-germanium channel has a band gap less than that of a silicon channel and, thus, a leakage current in an off-state may increase due to band to band tunneling (BTBT)
Implementation Method 2
Silicon-germanium channel regions have been used to enhance the mobility of carriers
Data Source
AI summary
Semiconductor devices are provided including an active layer, a gate structure, a spacer, and a source/drain layer. The active layer is on the substrate and includes germanium. The active layer includes a first region having a first germanium concentration, and a second region on both sides of the first region. The second region has a top surface getting higher from a first portion of the second region adjacent to the first region toward a second portion of the second region far from the first region, and has a second germanium concentration less than the first germanium concentration. The gate structure is formed on the first region of the active layer. The spacer is formed on the second region of the active layer, and contacts a sidewall of the gate structure. The source/drain layer is adjacent to the second region of the active layer.