Deep Trench Isolation Structure for Higher Breakdown Voltage
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Solution Overview
Problem
Current semiconductor devices with Deep Trench Isolation (DTI) structures face challenges in maintaining high breakdown voltage due to electric field concentration at the side walls of isolation trenches, which can lead to breakdown of the inner insulating film and reduced device reliability.
Innovation Solution
Incorporating a second isolation conductor sandwiched between the first isolation conductor and the buried region, with a unique trench structure and insulating film configuration that includes a central convex portion and side concave portions, helps distribute the electric field and prevent insulating film destruction, thereby enhancing the breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DTI structure with insulating film and polysilicon is used for element isolation, then isolation effectiveness is improved, but electric field concentration occurs at the side walls leading to breakdown voltage reduction
Solution Approach 1:
The patent segments the single isolation conductor into multiple conductors arranged in an array within the isolation trench. This segmentation distributes the electric field across multiple conductors rather than concentrating it at the side walls, thereby reducing electric field concentration while maintaining effective isolation between elements.
Solution Approach 2:
The patent introduces an intermediary conductive structure (the array of conductors) between the insulating film and the high-concentration impurity region. This intermediary structure modifies the electric field distribution pattern, preventing direct concentration at the insulating film side walls while maintaining the isolation function.
2Reliability
If polysilicon is buried in the trench with insulating film to achieve electrical connection, then electrical connectivity is improved, but breakdown voltage decreases due to side wall electric field concentration
Solution Approach 1:
The single buried polysilicon conductor is segmented into multiple conductors arranged in an array. This segmentation distributes the electrical connection function across multiple conductors while simultaneously distributing the electric field, preventing concentration at any single location and thereby maintaining breakdown voltage.
Solution Approach 2:
The patent transitions from a single-point or single-line electrical connection to a distributed array of conductors across the trench width. This dimensional change from concentrated to distributed connectivity maintains electrical function while altering the electric field distribution pattern to prevent breakdown.
3Device complexity
If a simple trench structure with insulating film is used, then manufacturing complexity is reduced, but electric field distribution is poor leading to insulating film breakdown
Solution Approach 1:
The patent adds segmented conductive elements to the trench structure. While this increases structural complexity, the segmentation enables proper electric field distribution that prevents insulating film breakdown, thereby improving reliability. The added complexity is justified by the critical improvement in film integrity.
Solution Approach 2:
The patent creates a composite structure combining insulating film and multiple conductive elements within the trench. This composite configuration allows the insulating film to function effectively by providing both isolation and a controlled electric field environment, preventing film breakdown while maintaining structural integrity.
Data Source
AI summary
A semiconductor device includes: a semiconductor chip including first and second main surfaces; and an element isolation portion partitioning a device region at the first main surface. The element isolation portion includes: a first isolation trench formed at the first main surface; an isolation insulating film at an inner wall of the first isolation trench; and an isolation conductor buried in the first isolation trench via the isolation insulating film. The isolation conductor includes: a first isolation conductor formed at a central portion of the first isolation trench; and a second isolation conductor formed at a side of the first isolation conductor with an inner insulating film interposed therebetween. The second isolation conductor includes an inner wall in contact with the inner insulating film and an outer wall, wherein a top of the second isolation conductor includes an inclined wall inclined downward from the outer wall toward the inner wall.