Semiconductor Device Isolation Trenches Prevent Parasitic Transistor
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Solution Overview
Problem
In semiconductor devices, the P-type cell peripheral junction region and P-type floating region are prone to joining, leading to unstable collector current characteristics due to process accuracy dependencies and potential parasitic PNP transistor formation, causing oscillations around the threshold.
Innovation Solution
A semiconductor device design featuring a region isolation trench structure and an outer isolation trench structure that intervene between the main junction region and the floating region, ensuring reliable isolation and preventing undesired contact between them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the P-type cell peripheral junction region and P-type floating region are positioned close to each other, then device area is reduced, but the regions are liable to join together causing unstable operation
Solution Approach 1:
The device structure is segmented by introducing an n-type buffer region between the P-type cell peripheral junction region and the P-type floating region. This segmentation physically separates the two P-type regions that would otherwise be in direct contact, preventing their joining while maintaining compact device dimensions.
Solution Approach 2:
An n-type buffer region is introduced as an intermediary layer between the two P-type regions. This intermediary region acts as a barrier that prevents the P-type cell peripheral junction region and P-type floating region from joining together, thereby eliminating the parasitic PNP transistor formation while maintaining close positioning for area efficiency.
2Manufacturing precision
If the spacing between P-type cell peripheral junction region and P-type floating region is small, then manufacturing precision requirements are reduced, but parasitic PNP transistor formation is more likely
Solution Approach 1:
The n-type buffer region serves as a protective intermediary that eliminates the harmful parasitic PNP transistor effect. By placing this intermediary region between the two P-type regions, the design makes the structure insensitive to small variations in spacing, as the n-type buffer prevents direct P-type to P-type contact regardless of the exact distance.
Solution Approach 2:
The potential harm of close spacing (which could cause P-type region joining and parasitic transistor formation) is converted into a benefit by introducing the n-type buffer region. This buffer region transforms the close-spacing configuration from a harmful scenario into a safe one, allowing compact design without the risk of parasitic effects.
3Device complexity
If the P-type cell peripheral junction region and P-type floating region are opposed across a small spacing, then device complexity is reduced, but collector current characteristic stability deteriorates
Solution Approach 1:
The simple opposed structure is segmented by inserting the n-type buffer region, creating a three-region sequence (P-type cell peripheral junction region - n-type buffer region - P-type floating region). This segmentation maintains structural simplicity while fundamentally improving the stability of collector current characteristics by preventing parasitic transistor formation.
Data Source
AI summary
A semiconductor device includes: a semiconductor layer of a first conductivity type having a first main surface and a second main surface; an active region defined in a surface layer of the first main surface; an outer region defined outside the active region in the surface layer; and a main junction region of a second conductivity type provided in the outer region as surrounding the active region. The semiconductor device includes: a floating region of the second conductivity type provided in an electrically floating state in the active region; a region isolation trench structure which isolates the floating region in the surface layer; an outer isolation trench structure disposed in spaced relation from the region isolation trench structure to define the main junction region outward thereof; and an intervening region disposed between the region isolation trench structure and the outer isolation trench structure.