Power MOSFETs with Embedded Dielectric Trenches
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Solution Overview
Problem
High voltage power devices like MOSFETs face challenges in minimizing conduction power loss due to limitations in scaling and increasing cell density, which results in higher specific on-resistance and parasitic capacitances, making it difficult to achieve low Rsp and efficient energy handling.
Innovation Solution
The introduction of buried or embedded dielectric layers with permanent charges and the use of trench fill layers formed by Selective Epitaxial Growth or Semi-Insulating-Poly-Silicon, which provide additional current paths and reduce specific on-resistance by forming inversion layers along the interfaces, thereby enhancing current conduction and reducing parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cell pitch is reduced to increase packing density, then specific on-resistance decreases, but parasitic capacitances increase
Solution Approach 1:
The patent transitions from planar surface charges to vertically extending buried dielectric layers with permanent charges throughout the drift region depth. This three-dimensional charge distribution creates inversion layers along the entire interface, providing additional current conduction paths without increasing lateral cell pitch, thereby reducing Rsp while avoiding increased parasitic capacitances.
Solution Approach 2:
The patent uses composite structures combining semiconductor drift region material with embedded dielectric layers containing permanent charges. This composite architecture creates distinct functional zones: the dielectric layers provide charge balancing and form inversion channels, while the surrounding semiconductor material maintains bulk conduction, achieving low Rsp without proportionally increasing parasitic capacitances.
2Reliability
If trench depth increases to improve charge balancing, then breakdown voltage is maintained, but manufacturing difficulty increases
Solution Approach 1:
The patent provides for partial filling of deep trenches with dielectric material, where the dielectric layer extends to a depth sufficient to provide the required charge balancing effect, but does not necessarily fill the entire trench depth. This selective partial filling achieves the necessary charge balancing for breakdown voltage while reducing the manufacturing complexity of completely filling very deep trenches.
3Loss of energy
If permanent charge is introduced in trenches, then drift region resistance is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent introduces permanent charges into the dielectric layers during the trench formation and filling process, before the device is fully assembled and operational. This preliminary charge introduction eliminates the need for separate charge implantation steps later, simplifying the overall manufacturing process while achieving the desired reduction in drift region resistance through inversion layer formation.
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 leads to reduced specific on-resistance, improved energy efficiency, faster switching speed, and lower heat dissipation, while also reducing the cost for given performance parameters.
Implementation Method 1
The permanent charge also forms an induced drift region by forming an inversion layer along the interface between the oxide and the P-type layer
Implementation Method 2
Positive permanent charge 124 is present near the trench sidewalls, and provides improved charge balancing when the epitaxial layer 112 is depleted under reverse bias
Data Source
AI summary
Power devices using refilled trenches with permanent charge at or near their sidewalls. These trenches extend vertically into a drift region.