SiC Buffer Layer Doping Profile for Voltage Blocking Reliability
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Solution Overview
Problem
There is a need to improve the tradeoff between voltage blocking capability and reliability in silicon carbide (SiC) semiconductor devices, particularly in insulated gate field effect transistors (IGFETs) and insulated gate bipolar transistors (IGBTs), as shrinking device geometries to reduce costs challenges the increase in voltage blocking capability due to process-related stress incorporation.
Innovation Solution
A silicon carbide semiconductor device with a buffer layer featuring a specific doping concentration profile, including valley, plateau, and transition portions, where the doping concentration varies by less than 20% and the transition portion extent ranges from 1% to 30% of the valley portion, reducing intrinsic stress and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If device geometries are shrunk to reduce costs, then manufacturing cost decreases, but voltage blocking capability deteriorates
Solution Approach 1:
The buffer layer is designed with a non-uniform doping concentration profile featuring valley portions (lower doping) and plateau portions (higher doping). This local variation in doping quality allows different regions to serve different functions: valley portions reduce stress while plateau portions maintain voltage blocking capability, resolving the contradiction between cost reduction through geometry shrinking and maintaining electrical performance.
Solution Approach 2:
The invention changes the doping concentration parameter throughout the buffer layer by creating a profile with varying doping levels (valley and plateau portions). This parameter variation enables the buffer layer to simultaneously achieve stress reduction (improving reliability) and maintain adequate doping levels for voltage blocking, allowing device geometries to be shrunk without sacrificing voltage blocking capability.
2Strength
If doping level and thickness of deposited layers are increased to improve voltage blocking capability, then voltage blocking capability improves, but process-related stress incorporation increases, deteriorating reliability
Solution Approach 1:
The buffer layer employs local quality variation through valley portions (lower doping) and plateau portions (higher doping). The valley portions reduce intrinsic stress to improve reliability, while the plateau portions maintain sufficient doping levels to support voltage blocking capability, thus resolving the contradiction between improving voltage blocking and maintaining reliability.
Solution Approach 2:
The buffer layer is segmented into multiple regions with different doping characteristics (valley portions and plateau portions). This segmentation allows the structure to simultaneously achieve stress reduction in valley regions and voltage blocking in plateau regions, eliminating the need to uniformly increase doping level and thickness which would otherwise cause excessive stress and reduce reliability.
3Productivity
If device geometries are shrunk to increase device functionalities per unit area, then device functionalities per unit area increase, but process-related stress incorporation increases, deteriorating reliability
Solution Approach 1:
The buffer layer's non-uniform doping profile with valley portions (lower doping) and plateau portions (higher doping) enables stress management in shrunk device geometries. The valley portions reduce intrinsic stress that would otherwise accumulate in high-density device configurations, allowing increased device functionalities per unit area while maintaining reliability.
Data Source
AI summary
A silicon carbide (SiC) semiconductor device is proposed. The SiC semiconductor device includes a buffer layer of a first conductivity type and a drift layer of the first conductivity type arranged, along a vertical direction, on the buffer layer. A vertical profile of a doping concentration of the buffer layer includes at least a first valley portion, a first plateau portion and a first transition portion extending from the first valley portion to the first plateau portion. The doping concentration of each of the first valley portion or the first plateau portion varies by less than 20 %. A vertical extent of the first transition portion ranges from 1 % to 30 % of a vertical extent of the first valley portion.