SiC Schottky Diode Edge Termination via Sloped P-Type Epitaxy
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Solution Overview
Problem
Silicon carbide Schottky diodes face significant perimeter leakage due to negative charge accumulation at the edge of the Schottky contact, leading to high electric fields and reduced blocking voltages, which is exacerbated by the need for expensive and damaging ion implantation techniques for edge termination structures, and the introduction of minority carriers during forward bias.
Innovation Solution
The use of a P-type epitaxial layer grown on top of the N-type SiC layer with a sloped edge created by plasma etching, eliminating the need for ion implantation and preventing hole injection by forming a Schottky contact instead of an Ohmic contact with the P-type epitaxial ring, thereby reducing perimeter leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ion implantation is used to create P-type ring for edge termination, then perimeter leakage is reduced, but manufacturing cost increases and crystal damage occurs
Solution Approach 1:
The invention changes the doping method from ion implantation to in-situ doped epitaxial growth. This parameter change in the manufacturing process eliminates the need for high-energy ion bombardment and subsequent high-temperature annealing, thereby reducing manufacturing complexity and cost while avoiding crystal damage. The P-type ring is formed during the epitaxial growth process itself, with dopants incorporated directly into the crystal lattice.
Solution Approach 2:
The invention replaces the mechanical ion implantation process with a chemical epitaxial growth process. Instead of physically implanting ions into the crystal and then thermally activating them through high-temperature annealing, the P-type doping is achieved through in-situ incorporation of dopants during low-temperature epitaxial growth, substituting a complex mechanical-thermal process with a simpler chemical vapor deposition process.
2Stress or pressure
If P-type ring is embedded in N-type SiC layer, then electric field at edge is reduced, but acceptor charge accumulation increases leakage
Solution Approach 1:
The invention applies local quality by creating a P-type epitaxial layer with specifically engineered dopant concentration profiles only in the edge termination regions, while maintaining N-type doping in the bulk active area. The P-type layer is localized to where edge termination is needed, and the dopant concentration is optimized locally to provide field reduction without excessive charge accumulation. This spatially selective doping approach allows the structure to have different electrical properties in different regions.
Solution Approach 2:
The invention introduces dynamic control of charge distribution through the sloped edge geometry of the P-type epitaxial layer. The sloped edge creates a gradual transition in the depletion region, allowing the electric field to be dynamically distributed along the slope rather than concentrated at a sharp edge. This geometric dynamic approach enables the structure to adapt the field distribution under reverse bias conditions.
3Quantity of substance
If Ohmic contact is formed with P-type ring, then charge accumulation is reduced, but hole injection occurs during forward bias
Solution Approach 1:
The invention inverts the conventional approach by forming a Schottky contact instead of an Ohmic contact with the P-type epitaxial layer. Conventionally, Ohmic contacts are used to provide low-resistance electrical connection, but this causes hole injection during forward bias. The invention reverses this by using a Schottky contact, which forms a rectifying barrier that prevents hole injection while still providing adequate electrical connection for the edge termination function.
4Manufacturing precision
If multiple implantation steps are used for edge termination, then charge density distribution is optimized, but fabrication cost significantly increases
Solution Approach 1:
The invention applies preliminary action by incorporating the P-type doping directly during the epitaxial growth process itself, before any subsequent processing steps. The dopants are introduced and activated in-situ during the low-temperature epitaxial deposition, eliminating the need for multiple separate ion implantation steps and associated photolithography processes. This preliminary incorporation of the doping function during growth simplifies the overall fabrication sequence.
Solution Approach 2:
The invention merges the epitaxial growth process with the doping process into a single in-situ operation. Instead of separating these functions into distinct process steps (epitaxy followed by multiple ion implantations and annealing steps), the invention combines them by incorporating dopants directly during the epitaxial growth, thereby reducing the total number of process steps and associated costs.
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 significantly reduces perimeter leakage, eliminates the need for costly micrometre photolithography, and enhances reliability by creating a tapered charge density that minimizes electric field peaks, achieving a perimeter leakage fraction of less than 2% while maintaining high blocking voltages.
Implementation Method 1
The use of a P-type epitaxial layer grown on top of the N-type SiC layer
Implementation Method 2
a sloped edge created by plasma etching
Data Source
Figure 1~2
Figure 3~4B
Figure 5A~5C
AI summary
A silicon carbide (SiC) Schottky diode comprises a layer of N-type SiC and a layer of P-type SiC in contact with the layer of N-type SiC creating a P-N junction. An anode is in contact with both the layer of N-type SiC and the layer of P-type SiC creating Schottky contacts between the anode and both the layer of N-type SiC and the layer of P-type SiC. An edge of the layer of P-type SiC is electrically active and comprises a tapered negative charge density at the P-N junction, which can be achieved by a tapered or sloping edge the layer of P-type SiC.