Silicon Nitride Field Plate MOSFET for Low RDSon and Reverse Blocking
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Solution Overview
Problem
There is a trade-off in the design of power MOSFET devices between their reverse voltage blocking capability and on-state resistance, with existing techniques struggling to simultaneously reduce on-state resistance (RDSon) and maintain high reverse voltage blocking capability.
Innovation Solution
A power transistor device is developed with a polysilicon field plate electrically connected to a crystalline silicon substrate through an interfacial silicon nitride layer, which acts as a diffusion barrier to prevent dopant diffusion and enhance the reverse voltage blocking capability while reducing on-state resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If field plates are placed in trenches in the drift region to improve reverse voltage blocking capability, then reverse voltage blocking capability is improved, but on-state resistance increases
Solution Approach 1:
An interfacial silicon nitride layer is introduced between the polysilicon field plate and the crystalline silicon substrate. This intermediary layer prevents dopant diffusion from the polysilicon into the drift region, thereby maintaining low on-state resistance while allowing the field plate to provide its reverse voltage blocking function through depletion region expansion.
Solution Approach 2:
The invention changes the electrical parameters at the interface between field plate and substrate by introducing the silicon nitride layer. This layer modifies the doping profile and electrical characteristics at the interface, enabling simultaneous achievement of low on-state resistance and high reverse voltage blocking capability through controlled dopant distribution.
2Reliability
If polysilicon field plate is directly connected to crystalline silicon substrate, then electrical connection is established, but dopant diffusion occurs causing crystal defects
Solution Approach 1:
The silicon nitride layer serves as a diffusion barrier intermediary between the polysilicon field plate and crystalline silicon substrate. It maintains electrical connection functionality while preventing harmful dopant diffusion that would compromise crystal structure integrity, thus resolving the contradiction between electrical connectivity and structural stability.
Solution Approach 2:
The invention extracts the dopant diffusion problem from the direct polysilicon-crystalline silicon interface by introducing the silicon nitride barrier layer. This separation removes the harmful interaction while preserving the necessary electrical connection, preventing crystal defects 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
The solution effectively reduces on-state resistance and maintains high reverse voltage blocking capability, improving the performance of power MOSFET devices by preventing dopant outdiffusion and crystal defects, thus enabling better electrical contact and steep pn junction formation.
Implementation Method 1
an interfacial silicon nitride layer that is arranged between the polysilicon of the field plate and the crystalline silicon of the substrate... acts as a diffusion barrier to prevent dopant diffusion
Implementation Method 2
The field plates are electrically connected to a fixed electrical potential, such as gate or source potential in order to allow a depletion region to expand in the drift region
Data Source
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AI summary
In an embodiment, a power transistor device 10, 40, 50, 60 comprises a substrate 11 formed of crystalline silicon and having a first surface 12 and a second surface 13 opposing the first surface 12, a field plate 14 formed of polysilicon that is electrically connected with the substrate 11 and an interfacial silicon nitride layer 15 that is arranged between the polysilicon of the field plate 14 and the crystalline silicon of the substrate 11.