Trench Isolation Structure With Air Gap for Higher Withstand Voltage
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Solution Overview
Problem
Current semiconductor devices face challenges in effectively reducing electric field concentration and preventing crystal defects in trench isolation structures, which can lead to reduced withstand voltage and device reliability.
Innovation Solution
The semiconductor device employs a trench structure with a buried conductor and insulating films formed across air gaps, which reduces electric field concentration and prevents stress accumulation in insulating films, thereby enhancing withstand voltage and preventing crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench isolation structure is formed with insulating film covering the trench side surface and polysilicon buried in the trench, then region isolation is achieved, but electric field concentration occurs and crystal defects may form in the insulating film
Solution Approach 1:
An air gap is introduced as an intermediary layer between the insulating film and the polysilicon buried conductor. This air gap acts as a stress-relief medium that prevents stress transfer from the polysilicon to the insulating film, thereby eliminating the root cause of crystal defect formation while maintaining the electrical isolation function of the trench structure
Solution Approach 2:
The physical and mechanical properties of the trench structure are changed by replacing the traditional continuous insulating film configuration with one that includes an air gap. This parameter change (introducing void space) fundamentally alters the stress distribution characteristics, preventing stress accumulation in the insulating film that would otherwise lead to crystal defects
2Ease of manufacture
If the insulating film is formed directly on the trench side surface without air gaps, then manufacturing process is simpler, but stress accumulates in the insulating film causing crystal defects
Solution Approach 1:
The air gap serves as a mediator that decouples the stress fields between the polysilicon and the insulating film. By introducing this intermediate layer, the manufacturing process maintains simplicity while achieving superior insulating film quality through stress elimination, preventing crystal defect formation
3Reliability
If polysilicon is buried in the trench to provide electrical connection, then electrical connectivity is improved, but stress is transferred to the insulating film causing crystal defects
Solution Approach 1:
The air gap functions as a stress-isolating intermediary that allows the polysilicon to maintain its electrical connectivity function while preventing mechanical stress transfer to the insulating film. This mediator layer preserves the electrical performance benefits of polysilicon burial while eliminating the detrimental stress effects
Solution Approach 2:
The trench structure is segmented into distinct functional zones: the polysilicon region for electrical connection, the air gap region for stress isolation, and the insulating film region for electrical isolation. This segmentation allows each component to perform its intended function without interfering negatively with others
Data Source
AI summary
A semiconductor device includes a semiconductor chip that has a first principal surface and a second principal surface located on a side opposite to a side of the first principal surface and an element isolation portion that is formed on the side of the first principal surface of the semiconductor chip and that demarcates an active region. The element isolation portion includes a trench formed on the side of the first principal surface of the semiconductor chip, a first insulating film formed on a side surface of the trench, a second insulating film formed inside the trench inwardly from the first insulating film with an air gap between the first insulating film and the second insulating film, and a buried conductor that is covered by the second insulating film and that is connected to the semiconductor chip at a bottom portion of the trench.