Semiconductor Device With Trench Bottom Insulator
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Solution Overview
Problem
Semiconductor devices with bidirectional Zener diodes in trenches face undesired current increases due to inversion layers forming in the p-type region, leading to increased current flow and potential breakdown issues.
Innovation Solution
Incorporating a bottom wall insulating film with a thickness greater than the side wall insulating film within the trench, and a floating region of the second conductivity type facing the bidirectional Zener diode across the inner wall insulating film, to suppress the inversion of the conductivity type and reduce unwanted current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the p type region faces the n- type epitaxial layer across the gate oxide film in a bidirectional Zener diode structure, then the diode can function bidirectionally, but electrons are drawn to the p type region causing inversion layer formation and undesired current increase
Solution Approach 1:
A bottom wall insulating film is introduced as an intermediary layer between the p type region and the n- type epitaxial layer at the trench bottom. This insulating film prevents direct interaction between the p type region and the epitaxial layer, thereby suppressing the formation of inversion layers and the associated harmful current while preserving the bidirectional Zener diode's protection function.
Solution Approach 2:
The insulating film is applied selectively at the bottom wall of the trench where the p type region contacts the epitaxial layer, rather than uniformly throughout the entire trench structure. This localized application addresses the specific problem of inversion layer formation at the critical interface while maintaining the overall bidirectional diode functionality elsewhere in the structure.
2Reliability
If a bottom wall insulating film is added to suppress inversion, then current control improves, but device structure and manufacturing complexity increase
Solution Approach 1:
The bottom wall insulating film is merged with the existing gate oxide film formation process. Both insulating films are formed using the same oxidation process, eliminating the need for separate fabrication steps and reducing overall manufacturing complexity despite the additional structural element.
Solution Approach 2:
The bottom wall insulating film serves multiple functions: it acts as a physical barrier to prevent inversion layer formation, provides electrical isolation between the p type region and epitaxial layer, and can serve as a foundation for subsequent processing steps. This multi-functionality justifies the added structural element without proportionally increasing complexity.
Data Source
AI summary
A semiconductor device, including a semiconductor layer of a first conductivity type, having a main surface with a diode trench formed therein, an inner wall insulating film, including a side wall insulating film, formed along side walls of the diode trench, and a bottom wall insulating film, formed along a bottom wall of the diode trench and having a thickness greater than a thickness of the side wall insulating film, and a bidirectional Zener diode, formed on the bottom wall insulating film inside the diode trench and having a pair of first conductivity type portions and at least one second conductivity type portion formed between the pair of first conductivity type portions.