Trench MOS Gate Structure for High Breakdown Voltage
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Solution Overview
Problem
The existing trench MOS barrier Schottky (TMBS) diode structures face challenges in achieving high breakdown voltage due to electric field localization at the edge termination trench, making it difficult to manufacture and resulting in lower breakdown voltage compared to the Schottky junction section, and the edge termination trench with a field plate structure is hard to process and limits breakdown voltage enhancement.
Innovation Solution
A method of manufacturing a semiconductor device with a trench MOS gate structure that includes forming active section trenches and ring-shaped edge termination trenches, depositing conductive material, and using chemical mechanical polishing to expose the semiconductor substrate, allowing for a thicker insulator film in the edge termination trench to sustain a stronger electric field and improve breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional planar SBD structure with p-type guard ring is used, then the manufacturing process is simple, but the reverse recovery time is elongated and high-speed operation is prevented
Solution Approach 1:
The device is divided into two distinct functional regions: active section trenches for current conduction and ring-shaped edge termination trenches for electric field management. This segmentation allows the guard ring function to be separated from the main current path, enabling high-speed operation while maintaining manufacturing simplicity through simultaneous formation of both trench types
Solution Approach 2:
A n-type semiconductor layer is introduced as an intermediary between the p-type semiconductor substrate and the Schottky junction. This intermediate layer enables the guard ring to function as a Schottky barrier rather than a pn-diode, preventing minority carrier accumulation and reducing reverse recovery time while maintaining ease of manufacture
2Reliability
If a trench MOS gate structure is used to relax electric field strength, then the breakdown voltage is improved, but the edge termination trench with field plate structure is hard to process
Solution Approach 1:
The active section trenches and ring-shaped edge termination trenches are formed simultaneously in a single etching process step. This merging of formation steps simplifies manufacturing by eliminating sequential processing of different trench types, reducing overall processing difficulty while maintaining the breakdown voltage improvements provided by the trench MOS gate structure
Solution Approach 2:
The ring-shaped edge termination trenches serve multiple functions: they provide electric field relaxation through the MOS gate structure, act as a guard ring for voltage breakdown prevention, and define the active area boundary. This multi-functionality reduces the need for additional specialized structures, simplifying the overall manufacturing process while achieving high breakdown voltage
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 method effectively relaxes electric field strength near the Schottky junction, enhances the breakdown voltage, and stabilizes the manufacturing process by balancing electric field distribution and increasing the breakdown voltage beyond the active section.
Implementation Method 1
polishing the oxide film with a chemical mechanical polishing apparatus for exposing the semiconductor substrate to the surface of the mesa region and for exposing the electrically conductive material to the opening of the active section trench
Implementation Method 2
allowing for a thicker insulator film in the edge termination trench to sustain a stronger electric field and improve breakdown voltage
Data Source
AI summary
A method of manufacturing a semiconductor device is disclosed. The method includes forming a first trench and a second trench in an n-type substrate surface, the first trenches being spaced apart from each other, the second trench surrounding the first trenches, the second trench being wider than the first trench. The method also includes forming a gate oxide film on the inner surfaces of the first and second trenches, and depositing an electrically conductive material to the thickness a half or more as large as the first trench width. The method further includes removing the electrically conductive material using the gate oxide film as a stopper layer, forming an insulator film thicker than the gate oxide film, and polishing the insulator film by CMP for exposing the n-type substrate and the electrically conductive material in the first trench.