SiC Vertical MOSFET Body Structure for Threshold Voltage Control
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Solution Overview
Problem
Existing silicon carbide MOSFET devices face issues such as high process variability in switch-on threshold voltages, high leakage currents, and rapid degradation due to high electric fields, which are exacerbated by high-energy dopant ion implantation causing lattice defects and straggling, leading to performance degradation and reduced lifespan.
Innovation Solution
The MOSFET device employs a structure with deep and superficial body regions of varying doping levels and widths, formed using low-energy dopant ion implantation, reducing lateral straggling and enabling a lower pitch design, thus improving threshold voltage control and reducing electric field concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-energy dopant ion implantation is used to form body regions, then doping depth can be achieved, but lateral straggling increases causing high process variability in threshold voltages
Solution Approach 1:
The body region formation is segmented into two separate implantation steps: first forming a deep body region with high-energy ions to achieve the required doping depth, then forming a superficial body region with low-energy ions to define the precise lateral boundaries. This segmentation eliminates lateral straggling in the critical superficial region while still achieving the necessary deep doping penetration.
Solution Approach 2:
The deep body region is formed first as a preliminary action before forming the superficial body region. This preliminary deep doping provides the foundation for subsequent threshold voltage adjustment through the superficial implantation, allowing better overall control of the final threshold voltage while minimizing lateral straggling effects.
2Reliability
If high-energy dopant ion implantation is used, then doping depth is achieved, but lattice defects increase causing rapid degradation
Solution Approach 1:
The implantation process is segmented into two energy levels: high-energy implantation for deep body region formation (affecting only the lower portion of the structure), and low-energy implantation for superficial body region formation. This segmentation ensures that the critical superficial region near the surface experiences minimal lattice damage, reducing degradation while still achieving the required deep doping penetration through the first step.
Solution Approach 2:
Different implantation energies are applied to different depth zones: high-energy ions are used specifically for the deep body region where deep penetration is required, while low-energy ions are used for the superficial region where minimal damage is critical. This local differentiation of implantation quality optimizes both deep doping effectiveness and surface region integrity.
3Manufacturing precision
If larger pitch is used to reduce lateral straggling effects, then manufacturing precision improves, but cell density decreases
Solution Approach 1:
The body region formation is segmented into deep and superficial components formed by separate implantation steps. This allows the superficial region to be precisely defined with narrow lateral dimensions using low-energy implantation, enabling smaller pitch without suffering from lateral straggling. The deep region provides the necessary doping depth while the superficial region defines the precise lateral boundaries for high-density integration.
Solution Approach 2:
The implantation energy parameter is changed between two distinct steps: high energy for deep penetration and low energy for precise lateral definition. This parameter variation allows the superficial body region to be formed with minimal lateral straggling, enabling reduced pitch and higher cell density while maintaining manufacturing precision for threshold voltage control.
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 a MOSFET device with lower process variability, higher cell density, reduced on-state resistance, and extended lifespan by minimizing lattice defects and electric field-induced degradation.
Implementation Method 1
forming, in a silicon carbide work body having a first type of conductivity and a face, a superficial body region of a second type of conductivity... forming a source region, of the first type of conductivity, in the superficial body region... forming, in the work body, a deep body region of the second type of conductivity
Data Source
AI summary
A vertical conduction MOSFET device includes a body of silicon carbide, which has a first type of conductivity and a face. A superficial body region of a second type of conductivity has a first doping level and extends into the body to a first depth, and has a first width. A source region of the first type of conductivity extends into the superficial body region to a second depth, and has a second width. The second depth is smaller than the first depth and the second width is smaller than the first width. A deep body region of the second type of conductivity has a second doping level and extends into the body, at a distance from the face of the body and in direct electrical contact with the superficial body region, and the second doping level is higher than the first doping level.