Trench-Gate MOSFET Layout for Electric Field Breakdown Control
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Solution Overview
Problem
Conventional trench-gate MOSFETs face dielectric breakdown issues due to electric field concentration at the bottom of the trench, leading to potential carrier injection into the gate insulating film, which compromises the reliability of the device.
Innovation Solution
The semiconductor device incorporates a base-bottom embedded region with a curved surface, separated from the gate-bottom protection region, where the base-bottom embedded region has a deeper bottom surface and a larger curvature radius, effectively mitigating electric field concentration and preventing avalanche breakdown at the gate-bottom protection region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a trench-gate MOSFET structure is used to reduce device area, then the device area is reduced, but electric field concentration occurs at the bottom of the trench leading to dielectric breakdown
Solution Approach 1:
The patent applies local quality by creating a guard ring region with different impurity concentration characteristics than the surrounding regions. Specifically, a p-type guard ring is formed with higher impurity concentration than the adjacent n-type drift region, creating a localized region with different electrical properties that specifically addresses the electric field concentration problem at the trench bottom without affecting the overall device structure
Solution Approach 2:
The guard ring acts as an intermediary region between the high-field trench bottom and the lower-field surrounding areas. This intermediate structure with its specific impurity concentration profile serves as a transition zone that gradually distributes the electric field, preventing sudden field concentration and carrier injection into the gate insulating film
2Ease of manufacture
If the base-bottom embedded region and gate-bottom protection region are formed in the same shape, then manufacturing is simplified, but electric field concentrates at the corners of both regions
Solution Approach 1:
The patent applies asymmetry by forming the guard ring with a different shape than the trench structure. While the trench has vertical sidewalls and a flat bottom, the guard ring is formed with a curved or rounded shape that extends around the trench bottom. This asymmetric configuration ensures that the guard ring corners do not align with the trench corners, preventing simultaneous electric field concentration at both locations
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 design reduces the likelihood of avalanche current flowing into the gate insulating film, enhancing the reliability of the trench-gate MOSFET by concentrating the electric field on the base-bottom embedded region, thus preventing dielectric breakdown and improving breakdown voltage.
Implementation Method 1
the electric field tends to concentrate on the bottom of the trench facing the drain electrode
Implementation Method 2
the p-n junction in the base-bottom embedded region has a higher electric field strength than the p-n junction in the gate-bottom protection region. As a result, carrier injection into the gate insulating film may be prevented by generating the avalanche breakdown in the base-bottom embedded region
Data Source
AI summary
A semiconductor device includes n-type drift layer, n-type current spreading layer having higher impurity concentration than the drift layer, p-type base region provided on top surface, p-type gate-bottom protection region located in the current spreading layer, having first bottom edge portion formed of curved surface, p-type base-bottom embedded region in contact with bottom surface of the base region, having second bottom edge portion formed of curved surface on side surface facing the gate-bottom protection region, being separated from the gate-bottom protection region, and insulated gate electrode structure provided in trench penetrating through the base region to reach the gate-bottom protection region. Bottom surface of the base-bottom embedded region is deeper than bottom surface of the gate-bottom protection region, and minimum value of curvature radius of the first bottom edge portion is larger than minimum value of curvature radius of the second bottom edge portion.