Multi-gate Transistor with Composite Fin for Leakage Reduction
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Solution Overview
Problem
MOS transistors formed on germanium and III-V compound semiconductors exhibit high drive currents but also suffer from high leakage currents due to low bandgap and high dielectric constants, resulting in low on/off current ratios.
Innovation Solution
A multi-gate transistor design featuring a semiconductor fin with a central fin and sidewall layers of different semiconductor materials, forming a quantum well, with a gate electrode wrapping around the fin and source/drain regions, utilizing high-k dielectric materials and epitaxial growth to reduce leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If MOS transistors are formed on germanium or III-V compound semiconductors to achieve high drive currents, then electron mobility and hole mobility are improved, but leakage currents increase due to low bandgap and high dielectric constants
Solution Approach 1:
The patent employs a composite material structure consisting of a central fin made of high-mobility semiconductor material (germanium or III-V compound) surrounded by sidewall layers of different semiconductor material with higher bandgap. This composite structure allows the central region to provide high carrier mobility for drive current while the sidewall layers provide higher bandgap to suppress band-to-band leakage currents, thus resolving the contradiction between high drive current and low leakage current.
Solution Approach 2:
The patent applies local quality by creating spatial variation in material properties within the fin structure. The central fin region maintains high-mobility material for optimal drive current, while the sidewall regions use materials with higher bandgap specifically to reduce leakage. This localized differentiation of material properties allows each region to optimize for its specific function, resolving the contradiction between speed and harmful leakage effects.
2Power
If high-k dielectric materials are used in gate dielectrics to improve transistor performance, then drive current capability is enhanced, but leakage currents worsen due to high dielectric constants
Solution Approach 1:
The patent changes the material composition parameter of the fin structure by introducing a composite structure with different bandgap materials. This parameter change in the semiconductor region (rather than the dielectric) allows the use of high-k dielectric materials to enhance drive current while the modified semiconductor structure compensates for the increased leakage by providing higher bandgap regions that suppress band-to-band tunneling.
3Speed
If germanium is used instead of silicon to form MOS transistors, then electron mobility and hole mobility are greatly improved, but the oxide solubility in water makes gate dielectric formation difficult
Solution Approach 1:
The patent changes the material parameter by using a composite fin structure where the central high-mobility material (germanium or III-V) is combined with sidewall layers of different semiconductor material. This structural modification allows the device to achieve high mobility while the overall structure enables compatible gate dielectric formation processes, as the sidewall materials can provide surfaces that are more amenable to dielectric deposition and oxidation processes.
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 improves drive currents, reduces leakage currents, and enhances the on-to-off current ratio, achieving better performance in MOS transistors.
Implementation Method 1
The central fin and the semiconductor layer form a quantum well
Implementation Method 2
utilizing high-k dielectric materials
Data Source
AI summary
A multi-gate transistor includes a semiconductor fin over a substrate. The semiconductor fin includes a central fin formed of a first semiconductor material; and a semiconductor layer having a first portion and a second portion on opposite sidewalls of the central fin. The semiconductor layer includes a second semiconductor material different from the first semiconductor material. The multi-gate transistor further includes a gate electrode wrapping around sidewalls of the semiconductor fin; and a source region and a drain region on opposite ends of the semiconductor fin. Each of the central fin and the semiconductor layer extends from the source region to the drain region.