High Voltage Device With Deep Isolation Layer
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Solution Overview
Problem
High voltage semiconductor devices face challenges in achieving high integration due to the requirement of a field stop area (FSA) under the field oxide layer, which complicates the isolation of neighboring drift regions and increases the area needed, making it difficult to achieve efficient device integration.
Innovation Solution
A high voltage device is fabricated with an isolation layer deeper than the drift regions, eliminating the need for a field stop area by self-aligning the drift regions on the sidewalls of the isolation layer, thereby simplifying the fabrication process and reducing the field region, and using a trench structure with a high density plasma-undoped silicate glass layer for improved filling characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field stop area (FSA) is formed under the field oxide layer to isolate neighboring drift regions, then the isolation between drift regions is improved, but the device area increases and integration density decreases
Solution Approach 1:
The patent transitions from two-dimensional isolation (field oxide layer at the surface) to three-dimensional isolation (isolation layer extending deep into the substrate). By making the isolation layer deeper than the drift region depth, effective isolation is achieved without requiring additional lateral space for field stop areas, thus resolving the contradiction between isolation quality and device area.
2Reliability
If a field stop area (FSA) is formed to separate neighboring drift regions, then the breakdown voltage is maintained, but the fabrication process complexity increases
Solution Approach 1:
The patent extracts and eliminates the field stop area (FSA) from the device structure by implementing deep isolation layers that extend beyond the drift region depth. This removal simplifies the fabrication process by eliminating the need to form and align field stop areas, while the deep isolation layers maintain the necessary breakdown voltage through effective electrical isolation between adjacent drift regions.
3Reliability
If the isolation layer depth is increased beyond the drift region depth, then the isolation effectiveness is improved, but the manufacturing difficulty increases
Solution Approach 1:
The patent applies preliminary action by forming the isolation layer to a depth greater than the drift region depth before drift region formation. This preliminary deep isolation layer serves as a foundation that simplifies subsequent processing steps, as the drift regions can be formed with standard depths without requiring additional field stop area formation, thereby reducing overall manufacturing difficulty despite the initial deeper isolation layer requirement.
Data Source
AI summary
A high voltage device includes drift regions formed in a substrate, an isolation layer formed in the substrate to isolate neighboring drift regions, wherein the isolation layer has a depth greater than that of the drift region, a gate electrode formed over the substrate, and source and drain regions formed in the drift regions on both sides of the gate electrode.