RFP MOSFET Compensating Implant for On-Resistance and Reverse Recovery
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Solution Overview
Problem
State-of-the-art power MOSFETs face challenges in operating efficiently at high speeds due to increased switching power losses and electromagnetic interference, as they struggle to minimize specific on-resistance and switching delays, particularly 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 and enhances doping between the channel and drain, reducing on-resistance while maintaining breakdown voltage and improving body diode reverse recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the doping concentration in the drift region is increased to reduce on-resistance, then the specific on-resistance decreases, but the breakdown voltage deteriorates
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 in a specific region beneath the RFP trench, forming a compensated zone with modified electrical properties. This localized modification allows the drift region to have different effective doping concentrations in different areas, enabling reduced on-resistance in the compensated zone while maintaining adequate breakdown voltage through the undoped or lightly-doped regions.
2Reliability
If the RFP trench depth is increased to improve reverse recovery, then the body diode reverse recovery improves, but the manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by performing the compensating implant before completing the RFP trench formation. The implant is executed through the RFP trench opening at an intermediate stage, allowing the dopants to be introduced into the drift region before the trench is fully etched and filled. This sequencing simplifies the overall fabrication process by combining the implant step with the trench formation process, avoiding the need for separate deep implantation steps after trench completion.
3Loss of energy
If the dopant dose in the compensating implant is increased to enhance doping between channel and drain, then the on-resistance decreases, but the depletion boundary control becomes less precise
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the dopant dose, energy, and implantation angle for the compensating implant. Specific parameter ranges are chosen to achieve the desired balance: the dopant dose is set to provide sufficient doping to reduce on-resistance while the implant energy and angle are controlled to ensure dopants are deposited in the correct spatial region, maintaining precise depletion boundary control. The parameters are tuned based on simulation and experimentation to achieve optimal device performance.
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 reduced on-resistance, increased reliability, and longer operational life, along with reduced electrical stress on dielectric layers and improved reverse recovery characteristics, enabling efficient high-speed operation without compromising breakdown voltage.
Implementation Method 1
The implementation of a compensating implant in the RFP trench of power insulated-gate field effect transistors, which shapes depletion boundaries
Implementation Method 2
recessed field plates, positioned in proximity to and capacitively coupled to said semiconductor material
Implementation Method 3
capacitively coupled to control vertical conduction from a first-conductivity-type source through semiconductor material
Implementation Method 4
diffusions of a second conductivity type lying at least partially beneath said respective second trenches; whereby said diffusions reduce depletion spreading in the OFF state
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.