MOSFET Metal Backgate Work Function Tuning
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Solution Overview
Problem
Existing MOSFET technologies face challenges in adjusting threshold voltage without additional contacts and circuits, as heavily doped semiconductor backgates can only adjust voltage by a limited amount determined by the substrate's conduction and valence band difference, requiring complex fabrication and increased chip area.
Innovation Solution
Implementing a metal backgate with different work function regions created by ion implantation, allowing for independent adjustment of threshold voltages under different transistors or regions, reducing Gate Induced Drain Leakage (GIDL) and Drain Induced Barrier Leakage (DIBL) by tuning work functions during device processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a doped semiconductor backgate is used to adjust threshold voltage, then the threshold voltage can be adjusted within a limited range determined by the conduction and valence band difference, but additional contacts and isolation regions are required which increase fabrication complexity and chip area
Solution Approach 1:
The patent changes the material parameter (work function) of the backgate by using different metal materials or doping concentrations to achieve different threshold voltages. This allows arbitrary threshold voltage adjustment without needing additional contacts or isolation regions, as the work function difference between metal regions inherently provides the voltage difference needed.
Solution Approach 2:
The patent uses metal backgate regions with different work functions to replace the need for separate voltage generation circuits and contacts. The work function difference itself acts as the voltage source, eliminating the need to copy complex voltage generation and routing circuits across the chip.
2Device complexity
If a metal backgate with different work function regions is implemented, then precise control of device threshold voltage is achieved and fabrication is simplified, but additional ion implantation processing steps are required
Solution Approach 1:
The patent combines the threshold voltage adjustment function with the existing metal backgate structure. By integrating the work function adjustment into the backgate formation process itself (through ion implantation or material selection), the patent eliminates the need for separate voltage generation circuits, contacts, and isolation regions, even though it adds ion implantation 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
This approach enables precise control of device threshold voltage, reduces leakage, and simplifies the fabrication process by eliminating the need for additional contacts and circuits, improving overall device performance and power management.
Implementation Method 1
Work function is a material property defined as the energy needed to move an electron from the Fermi level to vacuum. The work function of a material is of interest in MOSFET applications because tuning the work function of a top gate electrode defines the threshold voltage of the MOSFET and influences the transistor performance.
Implementation Method 2
The different metal backgate work function regions are created by implanting the substrate through a mask.
Data Source
AI summary
An SOI substrate, a semiconductor device, and a method of backgate work function tuning. The substrate and the device have a plurality of metal backgate regions wherein at least two regions have different work functions. The method includes forming a mask on a substrate and implanting a metal backgate interposed between a buried oxide and bulk regions of the substrate thereby producing at least two metal backgate regions having different doses of impurity and different work functions. The work function regions can be aligned such that each transistor has different threshold voltage. When a top gate electrode serves as the mask, a metal backgate with a first work function under the channel region and a second work function under the source/drain regions is formed. The implant can be tilted to shift the work function regions relative to the mask.