Power MOSFET RFP Trench Doping for Fast Switching Reliability
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Solution Overview
Problem
State-of-the-art power MOSFETs face challenges in operating efficiently at high speeds due to increased capacitances and stored charges, leading to high electromagnetic interference and reduced reliability, especially when switching at frequencies above 1 MHz.
Innovation Solution
The implementation of a compensating implant in the RFP trench of power insulated-gate field effect transistors, which shapes depletion boundaries in the OFF state and enhances doping between the channel and drain, reducing on-resistance and breakdown voltage while minimizing electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the doping concentration in the drift region is increased to reduce on-resistance, then the on-resistance decreases, but the breakdown voltage degrades
Solution Approach 1:
The patent applies local quality by creating a non-uniform doping distribution in the drift region. A compensating implant of opposite polarity dopants is performed to form localized compensated zones beneath the RFP trenches, while leaving other regions with higher doping concentrations. This spatial variation in doping quality allows the drift region to have low on-resistance in most areas while maintaining high breakdown voltage capability in specific localized areas where the compensating implant is present.
2Productivity
If the switching speed is increased to improve operational performance, then the switching efficiency improves, but electromagnetic interference and switching power losses increase
Solution Approach 1:
The patent applies preliminary action by pre-forming compensated zones in the drift region before final device operation. The compensating implant creates regions with balanced doping concentrations that prepare the device to handle switching transitions more cleanly. This preliminary structural preparation reduces the generation of electromagnetic interference and switching power losses during high-speed operation, allowing the device to achieve fast switching speeds without excessive harmful emissions.
3Loss of time
If the RFP trench structure is implemented to reduce switching delays, then the switching performance improves, but electrical stress on dielectric layers increases
Solution Approach 1:
The patent applies parameter changes by modifying the doping concentration parameter in the drift region through the compensating implant. By adjusting the doping levels to create compensated zones, the electrical field distribution is altered, which reduces the electrical stress on the dielectric layers in the RFP trench structure. This parameter modification allows the device to maintain fast switching performance while reducing the harmful electrical stress that would otherwise degrade the dielectric layers.
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 results in improved on-resistance, increased breakdown voltage, reduced electrical stress on dielectric layers, higher reliability, and longer operational life, along with enhanced reverse recovery characteristics of the body diode, effectively addressing the limitations of existing power MOSFETs at high switching speeds.
Implementation Method 1
diffusions of a second conductivity type lying at least partially beneath said respective second trenches
Implementation Method 2
a gate which is positioned in a first trench, and capacitively coupled to control vertical conduction
Implementation Method 3
recessed field plates, positioned in proximity to and capacitively coupled to said semiconductor material
Data Source
AI summary
Improved highly reliable power RFP structures and fabrication and operation processes. The structure includes plurality of localized dopant concentrated zones beneath the trenches of RFPs, either floating or extending and merging with the body layer of the MOSFET or connecting with the source layer through a region of vertical doped region. This local dopant zone decreases the minority carrier injection efficiency of the body diode of the device and alters the electric field distribution during the body diode reverse recovery.