SiC Semiconductor Device With Concave Convex Substrate
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Solution Overview
Problem
Wide-gap semiconductor switching devices, such as SiC-IGBTs, face challenges in achieving high performance and reliability due to issues like high built-in voltage, increased internal resistance, curvature of semiconductor wafers, and defects caused by mechanical and heat stress, leading to increased electric power loss and reduced yield.
Innovation Solution
A semiconductor device configuration with parallel-connected bipolar and unipolar transistors, where the unipolar transistor can be driven from near zero voltage, reducing electric power loss and utilizing a thick n-type SiC support substrate to minimize curvature and defects, and employing a punch-through structure to reduce n-drift layer thickness and internal resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If SiC-IGBT is used to achieve high breakdown voltage, then breakdown voltage is improved, but electric power loss increases due to high built-in voltage
Solution Approach 1:
The invention divides the switching device into two parallel transistors: a bipolar transistor (SiC-IGBT) for high breakdown voltage and a unipolar transistor for low voltage operation. This segmentation allows each transistor to operate in its optimal voltage range, reducing overall power loss while maintaining high breakdown capability
Solution Approach 2:
The invention changes the operational parameters by introducing a unipolar transistor that operates at lower voltages (near zero voltage) compared to the bipolar transistor's built-in voltage. This parameter change enables the system to avoid the high voltage drop associated with SiC-IGBT during normal operation, thereby reducing electric power loss
2Manufacturing precision
If thick n-type SiC support substrate is used to minimize curvature, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The invention performs preliminary action by using a thick n-type SiC support substrate from the beginning to prevent wafer curvature and defects during subsequent manufacturing processes. This preliminary structural choice eliminates the need for complex curvature correction steps later in the fabrication process
Solution Approach 2:
The invention extracts the substrate support function from the active device regions by using a dedicated thick n-type SiC support substrate. This separation allows the support substrate to handle mechanical stability requirements independently, simplifying the overall device structure while maintaining manufacturing precision
3Loss of energy
If punch-through structure is used to reduce n-drift layer thickness, then internal resistance is reduced, but breakdown voltage capability is compromised
Solution Approach 1:
The invention segments the voltage handling function: the bipolar transistor with punch-through structure handles high breakdown voltage requirements, while the unipolar transistor handles low voltage switching. This segmentation allows the use of thin n-drift layers in the unipolar transistor (reducing internal resistance) without compromising overall breakdown voltage capability
Solution Approach 2:
The invention creates a composite transistor structure combining bipolar and unipolar transistor types in parallel. This composite approach leverages the high breakdown voltage capability of bipolar transistors and the low internal resistance of unipolar transistors, achieving both objectives simultaneously
Data Source
AI summary
A combined switching device includes a MOSFET disposed in a MOSFET area and IGBTs disposed in IGBT areas of a SiC substrate. The MOSFET and the IGBTs have gate electrodes respectively connected, a source electrode and emitter electrodes respectively connected, and a drain electrode and a collector electrode respectively connected. The MOSFET and the IGBTs are disposed with a common n-buffer layer. A top surface element structure of the MOSFET and top surface element structures of the IGBTs are disposed on the first principal surface side of the SiC substrate. Concave portions and convex portions are disposed on the second principal surface side of the SiC substrate. The MOSFET is disposed at a position corresponding to the convex portion of the SiC substrate. The IGBTs are disposed at positions corresponding to the concave portions of the SiC substrate.