Shielded Gate Trench MOSFET Stepped Epitaxy for Lower On-Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor power devices, such as SGT MOSFETs, face challenges in manufacturing epitaxial layers with graded doping profiles, which affects device performance in terms of specific on-resistance and breakdown voltage.
Innovation Solution
The introduction of a shielded gate trench (SGT) MOSFET with a multiple stepped epitaxial (MSE) structure and multiple edge trenches, along with electric field reducing regions, addresses the manufacturing challenges and improves device performance by reducing specific on-resistance and enhancing breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a graded doped (GD) epitaxial layer with linearly increasing doping concentration is used, then specific on-resistance is reduced and breakdown voltage is improved, but manufacturing difficulty increases significantly
Solution Approach 1:
The epitaxial layer is divided into multiple stepped regions (first stepped region, second stepped region, third stepped region) with different doping concentrations. Instead of a continuous graded profile, the doping concentration changes in discrete steps, making it manufacturable through standard epitaxial growth processes while still achieving the desired electrical characteristics of reduced on-resistance and improved breakdown voltage.
Solution Approach 2:
The doping concentration parameter is changed in discrete steps rather than continuously. The first stepped region has a lower doping concentration, the second stepped region has an intermediate doping concentration, and the third stepped region has a higher doping concentration. This stepwise parameter change achieves the electrical performance benefits of graded doping while maintaining manufacturability.
2Reliability
If multiple stepped epitaxial layers with different doping concentrations are introduced, then specific on-resistance is reduced, but device structure complexity increases
Solution Approach 1:
The device structure is segmented into distinct functional regions: an active area with gate trenches, an oxide charge balance region with the first stepped epitaxial region, and a termination area with the second and third stepped epitaxial regions. Each segment serves a specific function, allowing the complex multi-region structure to be managed and manufactured systematically.
Solution Approach 2:
Different regions of the epitaxial layer are assigned different doping concentrations tailored to their specific functional requirements. The first stepped region near the gate has lower doping for optimal field effect control, while the third stepped region in the termination area has higher doping for improved breakdown characteristics. This local optimization achieves high device performance without requiring uniform complexity throughout the entire structure.
3Reliability
If electric field reducing regions with lower doping concentration are added around gate trench bottoms, then breakdown voltage is improved, but manufacturing steps increase
Solution Approach 1:
The electric field reducing regions are merged with the stepped epitaxial layer structure. The first stepped epitaxial region with its lower doping concentration serves dual functions: it creates the stepped profile for on-resistance reduction and simultaneously forms the electric field reducing regions around the gate trench bottoms. This merging eliminates the need for separate manufacturing steps to create electric field reducing regions, achieving improved breakdown voltage without proportionally increasing process complexity.
Solution Approach 2:
The first stepped epitaxial region performs multiple functions: it establishes the stepped doping profile for on-resistance management, creates electric field reducing regions at the gate trench bottoms for breakdown voltage improvement, and provides a transition zone between the gate area and termination area. This multi-functionality reduces the overall device complexity despite the added performance capabilities.
Data Source
AI summary
The present invention introduces a new shielded gate trench MOSFETs with improved specific on-resistance and avalanche capability structures including an active area and an edge termination area, wherein an epitaxial layer having special multiple stepped epitaxial (MSE) layers in an oxide charge balance (OCB) region, and an edge termination having multiple trench field plates, and electric field reducing regions disposed surrounding bottom of gate trenches with a doping concentration lower than said bottom epitaxial layer of the MSE layers. Moreover, in some preferred embodiment, a multiple stepped oxide structure in the OCB region, and an epitaxial layer in a buffer region below the OCB region with a doping concentration lower than the MSE layers is introduced to further reduce the specific on-resistance and enhance device ruggedness.