SiC Trench Layout With Protective Regions for Gate Oxide Reliability
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Solution Overview
Problem
Silicon carbide semiconductor devices with trench gates face challenges in preventing breakdown of the gate insulating film due to electric field concentration at trench ends, particularly when a Schottky barrier diode region is not evenly distributed, which compromises the reliability of the device.
Innovation Solution
The silicon carbide semiconductor device incorporates a Schottky barrier diode region interposed in the transistor region, with a drift layer extending over both regions, and includes first and second protective regions with higher impurity concentrations to relax electric fields and prevent breakdown, ensuring a sufficient area for the Schottky barrier diode and enhancing the reliability of the gate insulating film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky barrier diode region is inserted between trenches to prevent excessive increase of trench-to-trench distance, then electric field concentration at trench ends is reduced, but the area available for the Schottky barrier diode region is limited
Solution Approach 1:
The patent applies local quality by creating a protective region with different impurity concentration (higher doping) specifically at the trench end portions where electric field concentration occurs. This localized modification of material properties relaxes the electric field at critical points without affecting the overall trench arrangement or requiring excessive spacing between trenches, thereby maintaining both reliability and area efficiency.
2Area of stationary object
If the Schottky barrier diode region is arranged adjacent to trench end portions, then the trench-to-trench distance in the arrangement direction is not excessively increased, but electric field concentration at trench end portions causes gate insulating film breakdown
Solution Approach 1:
The patent addresses this contradiction by modifying the local quality of the semiconductor material at trench end portions through increased impurity concentration. This creates a protective region that specifically mitigates electric field concentration at the problematic trench ends, allowing dense trench arrangements to coexist with reliable gate insulating films.
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 electric field concentration at trench ends, thereby increasing the reliability of the gate insulating film and allowing for a higher Schottky current while maintaining a dense trench arrangement without excessive trench-to-trench distance.
Implementation Method 1
The drift layer extends over the transistor region and the Schottky barrier diode region... is made of silicon carbide and has a first conductivity type
Implementation Method 2
a first protective region... and a second protective region... to relax electric fields and prevent breakdown
Data Source
AI summary
A drift layer is made of silicon carbide and has a first conductivity type. At least one trench has a first side surface facing a Schottky barrier diode region, and a second side surface extending in a transistor region and contacting a source region, a body region, and the drift layer. A first protective region is provided under the at least one trench, has a second conductivity type, and is higher in impurity concentration of the second conductivity type than the body region. A second protective region extends from the first protective region, reaches at least one of the first side surface and an end region of the second side surface continuous with the first side surface, has an uppermost portion shallower than a lowermost portion of the body region, and is higher in impurity concentration of the second conductivity type than the body region.