SiC Power MISFET With Field Relaxation Layer
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Solution Overview
Problem
The performance of silicon carbide (SiC) power MISFETs is deteriorated by bipolar current due to crystal defects, and integrating a unipolar rectifying element on a separate semiconductor chip increases manufacturing costs and reduces performance per unit area.
Innovation Solution
A semiconductor device with a silicon carbide substrate, a first semiconductor layer, a body region of opposite conductivity type, a gate insulating film, and a field relaxation layer, where the field relaxation layer is shallower than the body region, allowing for a unipolar rectifying element to be integrated within the same chip, reducing manufacturing costs and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a pn type body diode is used as the reflux diode in SiC power MISFET, then both electrons and holes flow to provide rectification function, but bipolar current is generated which expands crystal defects inside the SiC substrate and deteriorates device performance
Solution Approach 1:
The invention introduces a field relaxation layer with specific conductivity type and depth characteristics in a localized region adjacent to the gate electrode. This layer has different electrical properties (conductivity type and depth) from the body region, creating local quality variation that enables unipolar current flow while maintaining the overall rectification function of the device.
Solution Approach 2:
The invention changes the conductivity type parameter by introducing a field relaxation layer with conductivity type opposite to the body region. This parameter change transforms the current conduction mechanism from bipolar (both electrons and holes) to unipolar (only majority carriers), thereby preventing crystal defect expansion while maintaining rectification capability.
2Reliability
If a unipolar rectifying element is formed on another semiconductor chip attached together with the SiC power MISFET chip, then the unipolar rectifying element can prevent bipolar current and crystal defect expansion, but manufacturing cost increases and performance per unit area decreases
Solution Approach 1:
The invention merges the SiC power MISFET and the unipolar rectifying element into a single integrated device structure. The field relaxation layer is formed within the same semiconductor chip as the MISFET, combining the switching function of the MISFET with the rectification function of the unipolar element, thereby eliminating the need for separate chips and reducing manufacturing complexity.
Solution Approach 2:
The invention makes the semiconductor chip universal by enabling it to perform multiple functions: the SiC power MISFET provides switching capability while the integrated field relaxation layer structure provides unipolar rectification capability. This multi-functionality eliminates the need for separate rectifying elements on other chips.
3Reliability
If a unipolar rectifying element is formed on another semiconductor chip attached together with the SiC power MISFET chip, then the unipolar rectifying element can prevent bipolar current and crystal defect expansion, but performance per unit area decreases
Solution Approach 1:
The invention merges the SiC power MISFET and the unipolar rectifying element into a single integrated device structure. The field relaxation layer is formed within the same semiconductor chip as the MISFET, combining the switching function of the MISFET with the rectification function of the unipolar element, thereby eliminating the need for separate chips and reducing manufacturing complexity.
Solution Approach 2:
The invention embeds the unipolar rectifying element structure (field relaxation layer) within the same chip as the main MISFET device. The field relaxation layer is positioned adjacent to the gate electrode and is integrated into the overall device architecture, effectively nesting the rectifying function within the switching device structure.
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 integration of a shallower field relaxation layer within the SiC power MISFET chip prevents bipolar current generation, maintains performance, and reduces manufacturing costs by eliminating the need for a separate rectifying element chip.
Implementation Method 1
a field relaxation layer of the second conductivity type is formed in the first semiconductor layer on the second side surface side of the gate electrode
Implementation Method 2
a body region of a second conductivity type that is opposite to the first conductivity type formed in the first semiconductor layer; a source region of the first conductivity type that is formed in the body region
Data Source
AI summary
Provided is a semiconductor device whose performance is improved. A p type body region is formed in an n type semiconductor layer containing silicon carbide, and a gate electrode is formed on the body region with a gate insulating film interposed therebetween. An n type source region is formed in the body region on a side surface side of the gate electrode, and the body region and a source region are electrically connected to a source electrode. A p type field relaxation layer FRL is formed in the semiconductor layer on the side surface side of the gate electrode, and the source electrode is electrically connected to the field relaxation layer FRL. The field relaxation layer FRL constitutes a part of the JFET 2Q which is a rectifying element, and a depth of the field relaxation layer FRL is shallower than a depth of the body region.