Superjunction Transistor Trench Barrier for Doping Control
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Solution Overview
Problem
Conventional VDMOSFETs with super junction structures face limitations in reducing specific on-state resistance due to high dopant concentration and thickness of the n-type drift doped region, and the multi-epitaxy technology used for fabrication is costly and complex, making it difficult to miniaturize the devices.
Innovation Solution
A semiconductor device with a vertical super junction structure is fabricated by growing an epitaxial layer on a substrate, forming trenches with a barrier region at the bottom to prevent dopant penetration, and using a dielectric material and polysilicon gates to create a doped region with a uniform conductivity type, which reduces recoil effects and enhances doping uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the dopant concentration of the n-type drift doped region is increased to reduce specific on-state resistance, then the on-state resistance improves, but the breakdown voltage decreases
Solution Approach 1:
The drift region is segmented into multiple regions with different doping concentrations: a first doped region with higher dopant concentration adjacent to the body region, and a second doped region with lower dopant concentration adjacent to the drain region. This segmentation allows the device to achieve low on-state resistance through the highly doped first region while maintaining high breakdown voltage through the lightly doped second region, thus resolving the contradiction between these two parameters.
Solution Approach 2:
Different regions of the drift doped region are assigned different doping concentrations according to their specific functional requirements. The first doped region near the body has high dopant concentration to reduce contact resistance and improve on-state characteristics, while the second doped region near the drain has low dopant concentration to sustain high electric fields and maintain breakdown voltage. This local quality differentiation resolves the contradiction by optimizing each region for its specific purpose.
2Manufacturing precision
If multi-epitaxy technology is used to create super junction structure, then the doping uniformity improves, but the fabrication complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the need for complex multi-epitaxy processes by using a single epitaxial growth step to form the entire drift region. The different doping concentrations in the first and second doped regions are achieved through selective dopant implantation or diffusion after the single epitaxial growth, rather than requiring multiple epitaxial growth cycles. This extraction of the multi-epitaxy requirement simplifies the fabrication process while maintaining doping uniformity control.
Solution Approach 2:
The drift region is formed in advance through a single epitaxial growth process with uniform doping, and then subsequent selective dopant implantation or diffusion creates the different doping concentration regions. This preliminary formation of the uniformly doped drift region through simple epitaxial growth, followed by selective modification, achieves the desired doping profile without requiring complex multi-epitaxy 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 approach results in semiconductor devices with low specific on-state resistance (<25 mΩ·cm2) and high breakdown voltage (>700 V), overcoming the limitations of conventional technologies by achieving uniform doping profiles and reducing fabrication costs.
Implementation Method 1
A barrier region is formed at a bottom of the trench. A doped region of a second conductivity type is formed in the epitaxial layer and surrounds sidewalls of the trench, wherein the barrier region prevents a dopant used for forming the doped region from reaching the epitaxial layer under the barrier region.
Implementation Method 2
A doped region of a second conductivity type is formed in the epitaxial layer and surrounds sidewalls of the trench
Implementation Method 3
growing an epitaxial layer on a substrate, wherein the epitaxial layer and the substrate have a first conductivity type
Data Source
AI summary
A method for fabricating a semiconductor device is provided. An epitaxial layer is grown on a substrate, wherein the epitaxial layer and the substrate have a first conductivity type. A trench is formed in the epitaxial layer. A barrier region is formed at a bottom of the trench. A doped region of a second conductivity type is formed in the epitaxial layer and surrounds sidewalls of the trench, wherein the barrier region prevents a dopant used for forming the doped region from reaching the epitaxial layer under the barrier region. The trench is filled with a dielectric material. A pair of polysilicon gates is formed on the epitaxial layer and on both sides of the trench.