Super-Junction MOSFET Trench Doping Using Epitaxial p-Columns
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Solution Overview
Problem
Current power MOSFETs face challenges in achieving high cell density and reducing drain-source resistance (RDSON) due to limitations in angled ion implantation methods, which struggle to dope trenches deeply enough with narrow widths and small cell pitches, hindering the development of efficient power conversion devices for low-voltage applications.
Innovation Solution
The use of epitaxial layer deposition and vapor phase deposition techniques to form multi-cell MEMS super-junction MOSFETs, allowing for deeper doping and narrower trench widths, thereby increasing cell density and reducing RDSON by forming p-type columns within narrow trenches, enabling efficient power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If angled ion implantation is used to dope trenches, then doping depth can be achieved, but trench width must be large enough which limits cell density
Solution Approach 1:
The patent replaces the mechanical angled ion implantation process with a chemical vapor deposition (CVD) process. Instead of physically implanting ions at an angle, the invention uses gaseous precursors that diffuse and deposit p-type dopant material conformally on trench sidewalls, eliminating the geometric constraints of angled implantation and enabling deep doping in narrow trenches.
Solution Approach 2:
The invention employs gaseous precursors delivered through a CVD system to deposit dopant material. The gas-phase delivery mechanism allows uniform distribution of dopant precursors throughout the trench structure, enabling consistent doping profiles even in high-aspect-ratio trenches that would be inaccessible to angled ion beams.
2Quantity of substance
If cell density is increased by reducing cell pitch, then RDSON decreases, but doping becomes more difficult with conventional methods
Solution Approach 1:
The patent replaces the mechanical angled ion implantation process with a chemical vapor deposition (CVD) process. Instead of physically implanting ions at an angle, the invention uses gaseous precursors that diffuse and deposit p-type dopant material conformally on trench sidewalls, eliminating the geometric constraints of angled implantation and enabling deep doping in narrow trenches.
Solution Approach 2:
The invention changes the fundamental parameters of the doping process by transitioning from a physical implantation method to a chemical deposition method. This allows control of dopant concentration and distribution through gas flow rates, temperature, and deposition time, providing flexibility to optimize doping for high cell density configurations.
3Area of moving object
If trench width is reduced to increase cell density, then RDSON decreases, but doping depth becomes insufficient with angled ion implantation
Solution Approach 1:
The patent replaces the mechanical angled ion implantation process with a chemical vapor deposition (CVD) process. Instead of physically implanting ions at an angle, the invention uses gaseous precursors that diffuse and deposit p-type dopant material conformally on trench sidewalls, eliminating the geometric constraints of angled implantation and enabling deep doping in narrow trenches.
Solution Approach 2:
The invention transitions from a line-of-sight implantation approach to a three-dimensional conformal deposition process. The CVD method deposits dopant material uniformly on all exposed surfaces of the trench, including sidewalls and bottom, achieving deep and complete doping coverage that angled ion implantation cannot provide in narrow trenches.
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 results in a significant reduction of RDSON to less than 5.0 mohms-cm2 at maximum drain current, enhancing the performance and efficiency of power MOSFETs for low-voltage applications, particularly in portable electrical devices and aerospace systems.
Implementation Method 1
an epitaxial layer is deposited onto a substrate
Implementation Method 2
a first doped semiconductor layer is formed by depositing a p-type dopant onto sidewalls of the trench
Data Source
AI summary
A semiconductor device has a substrate and semiconductor layer formed over the substrate. The semiconductor layer has a first conductivity type. A trench is formed through the semiconductor layer. An epitaxial layer having a second conductivity type is formed over a surface of the semiconductor layer and a side surface of the trench. The epitaxial layer is diffused into the semiconductor layer to form a first column of semiconductor material having the second conductivity type within the semiconductor layer. A first insulating layer is formed over the side surface of the trench. A body region is formed within the semiconductor layer. A source region is formed within the body region. A gate region is formed within the body region. A second insulating layer is formed over the trench. A third insulating layer is formed over the second insulating layer. A conductive layer is formed over the third insulating layer.