Vertical FET Trench Layout for Short-Circuit Current Limiting
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Solution Overview
Problem
Existing vertical field-effect transistor structures are sensitive to process variations and have insufficient current limitation, leading to short circuits and increased production costs due to precise distance requirements between shielding regions.
Innovation Solution
The design features trenches of different depths with shielding regions only at the bottom of the first trenches, reducing sensitivity to process variations and allowing less precise distance control, while the second trenches have a thicker dielectric layer and no shielding regions, effectively limiting short-circuit current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shielding regions are formed at the bottom of all trenches with uniform depth, then current limitation is achieved, but the structure becomes highly sensitive to process variations requiring precise distance control
Solution Approach 1:
The patent divides the trench structure into two distinct types: first trenches with shielding regions at the bottom, and second trenches without shielding regions. This segmentation allows the shielding regions to be spatially separated, reducing their mutual interaction and sensitivity to distance variations while maintaining effective current limitation through the JFET mechanism formed by the shielding regions and channel zone.
Solution Approach 2:
The patent applies different configurations to different locations: first trenches have shielding regions formed at their bottoms, while second trenches have no shielding regions. This local differentiation allows the structure to achieve current limitation where needed (at first trench bottoms) while reducing sensitivity to process variations by eliminating the precise distance control requirement between shielding regions.
2Reliability
If precise distance between shielding regions is maintained, then short-circuit current is limited, but production costs increase due to stringent process requirements
Solution Approach 1:
By segmenting the trench structure into first and second trenches with different characteristics, the patent reduces the need for precise distance control between shielding regions. The shielding regions are located only at the bottoms of first trenches, and their interaction with second trenches is minimized, allowing less stringent manufacturing tolerances and lower production costs.
Solution Approach 2:
The patent extracts the shielding region formation from all trenches and applies it selectively only to first trenches. This extraction eliminates the need to control distances between shielding regions in second trenches, simplifying the manufacturing process and reducing costs while maintaining effective current limitation through the JFET mechanism.
3Ease of manufacture
If uniform trench depth is used for all trenches, then manufacturing is simplified, but sensitivity to process variations increases
Solution Approach 1:
The patent introduces asymmetry in trench depths: first trenches have a specific depth suitable for forming shielding regions at their bottoms, while second trenches have a different depth that is optimized for their function without shielding regions. This asymmetric design reduces sensitivity to process variations by allowing each trench type to be independently optimized for its specific function.
Solution Approach 2:
Different trench depths are applied locally to different trench types: first trenches are deeper to accommodate shielding region formation, while second trenches are shallower or differently shaped. This local optimization allows each trench type to perform its specific function effectively while reducing overall sensitivity to manufacturing process variations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the sensitivity to process variations, prevents complete short circuits, and lowers production costs by allowing less precise adherence to intermediate distance requirements, while maintaining effective current limitation and expanding the applications of vertical field-effect transistor structures.
Implementation Method 1
each of the gate electrodes located in the second trenches (18b) can also comprise a first partial electrode (24a) and a second partial electrode (24b), wherein the first partial electrode (24a) is located on a side of the associated second partial electrode (24b) oriented toward the trench bottom (20b) of the relevant second trench (18b), and an intermediate volume between the first partial electrode (24a) and the associated second partial electrode (24b) is filled with the at least one insulation dielectric (26)
Implementation Method 2
vertical field-effect transistor structures in which a JFET forms between the shielding regions of a vertical field-effect transistor structure according to the present invention, which JFET limits a current through the channel zone of the vertical field-effect transistor structure in the event of a short circuit
Data Source
AI summary
A vertical field-effect transistor structure including a semiconductor body having a drift zone having a first doping of a first doping type, multiple first trenches, and multiple second trenches. The first trenches have at most a first trench depth, and the second trenches have at least a second trench depth. The second trench depth is at least 50 nm longer than the first trench depth. The structure includes a shielding region adjacent to each trench bottom of the first trenches, which has a second doping of a second doping type, and at least one gate electrode in each of the first and second trenches, which is electrically insulated at least from the adjacent trench bottom and trench side wall. Each region adjacent to the trench bottoms of the second trenches has exclusively the first doping of the drift zone and is free from the second doping.