Trench Field Plate Structure for Reliable Power Transistors
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Solution Overview
Problem
Existing power electronic transistors, such as silicon CoolMOS and IGBTs, face challenges in reliability due to limitations in the design of their trench and mesa structures, which affect their performance and durability.
Innovation Solution
A transistor device with a semiconductor substrate featuring elongate active trenches and mesas, where a field plate and gate electrode are positioned, with specific dimensions and insulation layers to enhance reliability, and a method for forming a field plate using sequential etch processes to optimize the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate electrode is positioned directly above the field plate with uniform insulation, then the manufacturing process is simpler, but the electrical insulation and mechanical stability are insufficient
Solution Approach 1:
The patent applies local quality by varying the insulation layer thickness at different locations beneath the gate electrode. The insulation layer has a first thickness in a first region and a second thickness in a second region, creating locally optimized electrical insulation and mechanical support where needed most, thereby improving reliability without requiring complete structural redesign
Solution Approach 2:
The patent introduces dimensional variation by creating a non-uniform insulation layer profile with different thicknesses in different regions. This transforms a previously two-dimensional uniform insulation structure into a three-dimensional graded structure, enabling improved electrical insulation and mechanical stability through vertical dimension control
2Reliability
If standard trench widths are used, then the manufacturing process is simpler, but the device performance and reliability are limited
Solution Approach 1:
The patent applies parameter changes by optimizing the trench width to specific ranges (1400-1900 nm) and adjusting the aspect ratio within defined ranges. These parameter optimizations improve device performance and reliability by enhancing charge compensation and electrical characteristics, while the sequential etching process makes achieving these precise parameters more manageable
3Reliability
If the field plate depth is not controlled precisely, then the fabrication process is less complex, but the charge compensation effectiveness is reduced
Solution Approach 1:
The patent applies preliminary action by using a sequential etching process where the first etch process creates the initial trench structure and the second etch process precisely defines the final field plate depth. This staged approach allows for better control of the field plate depth parameter, ensuring charge compensation effectiveness while managing fabrication complexity through progressive refinement
Data Source
AI summary
A transistor device includes a semiconductor substrate having a first major surface, a cell field and an edge termination region laterally surrounding the cell field. The cell field includes: elongate active trenches that extend from the first major surface into the semiconductor substrate, a field plate and a gate electrode being positioned in each elongate active trench, the gate electrode being arranged above and electrically insulated from the field plate; and elongate mesas, each elongate mesa being formed between neighbouring elongate active trenches, the elongate mesas comprising a drift region, a body region on the drift region and a source region on the body region.