Trench Gate Shielding Structure for Oxide Breakdown Control
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Solution Overview
Problem
Power semiconductor devices face premature oxide breakdown due to high electric fields, particularly at the corners of gate trenches, leading to device failure, and existing doping methods like ion implantation cause lattice damage and uneven dopant concentration.
Innovation Solution
Incorporating a bottom shielding structure and support shielding structures of a different conductivity type under and alongside the gate trench, with varying material, depth, and dopant concentration to reduce electric fields and enhance protection of the gate insulating layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion implantation is used to dope shielding structures, then dopant concentration can be controlled, but lattice damage and uneven dopant concentration occur
Solution Approach 1:
The patent changes the doping method from ion implantation to in-situ doping during epitaxial growth. This parameter change eliminates lattice damage caused by ion implantation while maintaining precise dopant concentration control through process parameters such as temperature, pressure, and gas flow rates during the epitaxial growth of the shielding structures
Solution Approach 2:
The patent replaces the mechanical ion implantation process with a chemical vapor deposition-based in-situ doping method during epitaxial growth. This substitution eliminates the mechanical damage inherent in ion implantation while achieving uniform dopant distribution through controlled chemical reactions during the growth process
2Reliability
If gate trenches are used in power semiconductor devices, then device performance is enhanced, but oxide breakdown occurs at trench corners due to high electric fields
Solution Approach 1:
The patent applies preliminary anti-action by forming shielding structures with opposite conductivity type before the gate trench is etched. These pre-formed shielding structures (n-type in p-type substrate or p-type in n-type substrate) create opposing electric fields that counteract the high electric field concentration at the trench corners, preventing oxide breakdown before it occurs
Solution Approach 2:
The patent introduces shielding structures as intermediary elements between the gate trench and the substrate. These intermediary structures act as electric field mediators, redistributing and reducing the electric field intensity at critical locations (trench corners) while maintaining the performance benefits of the gate trench structure
3Reliability
If shielding structures are formed closer to gate trench sidewalls, then electric field reduction is improved, but manufacturing precision decreases due to doping diffusion
Solution Approach 1:
The patent performs preliminary action by forming the shielding structures before etching the gate trenches. This sequence allows the shielding structures to be precisely positioned at predetermined distances from where the trench sidewalls will be formed, avoiding dopant diffusion issues that would occur if doping happened after trench formation. The spacing is controlled during the epitaxial growth stage with high precision
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 solution effectively reduces avalanche breakdown and enhances the reliability and ruggedness of power semiconductor devices by providing a lower resistance current path and improved electric field distribution.
Implementation Method 1
The support shielding structures laterally spaced apart from the gate trench sidewalls provide improved electric field distribution and reduce avalanche breakdown
Implementation Method 2
The shielding structures may be formed by any suitable doping process, for example, by in-situ doping, ion implantation, or diffusion
Data Source
AI summary
A power semiconductor device includes a semiconductor layer structure comprising a drift region of a first conductivity type, and a gate trench extending into the drift region. The gate trench includes sidewalls and a bottom surface therebetween. A bottom shielding structure of a second conductivity type is provided under the bottom surface of the gate trench. First and second support shielding structures of the second conductivity type extend into the drift region on opposing sides of the gate trench and are spaced apart from the sidewalls thereof. A material composition, distance of extension into the drift region relative to a surface of the semiconductor layer structure, and/or dopant concentration of the bottom shielding structure may be different from that of the first and second support shielding structures. Related devices and fabrication methods are also discussed.