MOSFET Back Gate Threshold Voltage Control
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Solution Overview
Problem
MOSFETs face challenges in adjusting threshold voltage without increasing channel doping concentration, which affects performance and power consumption, especially as devices scale down and short channel effects become prominent.
Innovation Solution
Incorporating a back gate and counter doped region in the semiconductor substrate, where the back gate's doping type is opposite to the counter doped region, allowing for adjustment of the threshold voltage through applied bias voltage and ion implantation techniques, facilitating a controlled doping profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the doping concentration in the channel region is increased to raise the threshold voltage, then the threshold voltage is improved, but the carrier mobility drops and device performance degrades
Solution Approach 1:
The invention segments the doping function by introducing a separate back gate structure that can independently control the threshold voltage without requiring increased channel doping. The back gate acts as an independent control element that segments the threshold voltage adjustment function from the channel doping concentration, allowing each to be optimized separately.
Solution Approach 2:
The back gate serves as an intermediary element between the control circuitry and the channel region. By applying voltage to the back gate, the threshold voltage is adjusted through this intermediary structure rather than directly through channel doping, enabling precise control without the harmful effects of high doping concentrations.
2Productivity
If the channel length is reduced to improve integration level, then the integration density is improved, but short channel effects arise and threshold voltage control becomes difficult
Solution Approach 1:
The invention adds another dimension to threshold voltage control by introducing the back gate, which controls the channel from the substrate side (vertical dimension) in addition to the front gate control from the top. This dual-gate control mechanism allows effective threshold voltage management even when the channel length is reduced for higher integration.
Solution Approach 2:
The back gate enables dynamic parameter changes in the threshold voltage by applying different voltages to the back gate electrode. This allows the threshold voltage to be adjusted as a variable parameter rather than being fixed by the doping profile, which is critical for maintaining control as channel length decreases.
3Reliability
If channel doping is increased to suppress short channel effects, then the threshold voltage is raised, but ions neutralize source/drain region ions and device resistance increases
Solution Approach 1:
The invention segments the function of suppressing short channel effects from the function of setting threshold voltage. The back gate handles the suppression of short channel effects through electric field control, while the channel doping can be kept at optimal levels for low resistance, eliminating the need to use high doping solely for short channel effect suppression.
Solution Approach 2:
The invention replaces the mechanical/chemical approach of using high doping concentrations to suppress short channel effects with an electric field-based approach using the back gate voltage. This substitution allows suppression of short channel effects without the harmful neutralization of source/drain ions that occurs with high channel doping.
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 approach enables adjustable threshold voltage without degrading device performance, effectively managing short channel effects and optimizing power consumption in MOSFETs.
Implementation Method 1
When a bias voltage is applied to the back gate and the counter doped region, the resultant electric field is applied to the channel region through the buried insulating layer
Implementation Method 2
performing a first ion implantation to form a back gate in the semiconductor substrate... performing a third ion implantation through the gate opening to form a counter doped region in the back gate
Data Source
AI summary
The present disclosure discloses a MOSFET and a method for manufacturing the same, wherein the MOSFET comprises: an SOI wafer comprising a semiconductor substrate, a buried insulating layer, and a semiconductor layer, the buried insulating layer being disposed on the semiconductor substrate, and the semiconductor layer being disposed on the buried insulating layer; a gate stack disposed on the semiconductor layer; a source region and a drain region embedded in the semiconductor layer and disposed on both sides of the gate stack; and a channel region embedded in the semiconductor layer and sandwiched between the source region and the drain region, wherein the MOSFET further comprises a back gate and a counter doped region, and wherein the back gate is embedded in the semiconductor substrate, the counter doped region is disposed under the channel region and embedded in the back gate, and the back gate has a doping type opposite to that of the counter doped region. The MOSFET can adjust a threshold voltage by changing the doping type of the back gate.