Germanium MISFET Channel Structure for Short Channel Effect Suppression
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Solution Overview
Problem
Semiconductor devices with MISFETs using germanium channels face increased short channel effects due to germanium's higher dielectric constant, leading to deteriorated carrier mobility and reduced drive current, especially when impurity concentration is increased to suppress these effects.
Innovation Solution
A semiconductor device structure is implemented with multiple layers of different dielectric constants, where the germanium layer is formed with a thickness of 3-40 nm to suppress short channel effects without compromising drive current, using a silicon germanium layer as an intermediate layer to reduce distortion and dislocation, and a gate insulating film to optimize carrier distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If germanium is used as the channel material to increase carrier mobility, then carrier mobility is improved, but short channel effect is intensified due to higher dielectric constant
Solution Approach 1:
The patent changes the physical parameters of the channel structure by controlling the germanium layer thickness to 3-40 nm and adjusting impurity concentration to 1×10^19 to 1×10^21 atoms/cm³. These parameter changes optimize the balance between utilizing germanium's high carrier mobility while suppressing the short channel effect that is intensified by germanium's higher dielectric constant.
Solution Approach 2:
The patent employs a composite structure combining silicon substrate with a germanium layer formed thereon. This composite material approach allows the device to benefit from both silicon's mechanical stability and germanium's high carrier mobility, while the specific thickness control of the germanium layer mitigates the adverse short channel effect.
2Reliability
If impurity concentration in the channel is increased to suppress short channel effect, then short channel effect is suppressed, but carrier mobility deteriorates
Solution Approach 1:
The patent optimizes the impurity concentration parameter within the specific range of 1×10^19 to 1×10^21 atoms/cm³. This parameter optimization achieves sufficient suppression of the short channel effect while maintaining carrier mobility within acceptable ranges, resolving the trade-off between reliability and speed.
3Power
If germanium layer thickness is increased to utilize high mobility, then drive current is improved, but short channel effect is intensified
Solution Approach 1:
The patent establishes an optimal thickness range of 3-40 nm for the germanium layer. This parameter optimization allows the device to充分利用 germanium's high carrier mobility for improved drive current while preventing the intensification of short channel effect that would occur with thicker layers.
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 structure effectively suppresses short channel effects and maintains high drive current by utilizing germanium's high mobility while minimizing the impact of its high dielectric constant, with the silicon germanium layer contributing to improved performance by reducing the S-value and enhancing carrier mobility.
Implementation Method 1
a gate insulating film which covers the semiconductor region
Implementation Method 2
a semiconductor region including two or more semiconductor layers of different dielectric constants
Data Source
AI summary
To suppress short channel effects and obtain a high driving current by means of a semiconductor device having an MISFET wherein a material having high mobility and high dielectric constant, such as germanium, is used for a channel. A p-type well is formed on a surface of a p-type silicon substrate. A silicon germanium layer having a dielectric constant higher than that of the p-type silicon substrate is formed to have a thickness of 30 nm or less on the p-type well. Then, on the silicon germanium layer, a germanium layer having a dielectric constant higher than that of the silicon germanium layer is formed to have a thickness of 3-40 nm by epitaxial growing. The germanium layer is permitted to be a channel region; and a gate insulating film, a gate electrode, a side wall insulating film, an n-type impurity diffusion region and a silicide layer are formed.