SiC MOSFET Source Region Doping for Gate Reliability
Solution Overview
Problem
Silicon carbide MOSFETs experience high gate current density due to lower barrier energy between the gate insulating film and silicon carbide, leading to reduced gate reliability, especially in n-type source regions.
Innovation Solution
The design includes a source region with a first source region below the source electrode and a second source region surrounding it, with a lower doping concentration in the superficial layer of the second source region and a higher concentration in its deep portion, and a source electrode buried in the second source region, to suppress gate current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the source region is doped with high concentration n-type dopant to achieve ohmic contact, then the ohmic contact is improved, but gate current increases due to Fowler-Nordheim tunneling
Solution Approach 1:
The source region is divided into two zones with different doping concentrations: a first zone with high doping concentration for ohmic contact and a second zone with low doping concentration to suppress Fowler-Nordheim tunneling. This local differentiation allows each zone to fulfill its specific function optimally.
Solution Approach 2:
The source region is segmented into multiple zones with different doping characteristics. The first zone (high concentration) handles current conduction while the second zone (low concentration) acts as a barrier to electron tunneling into the gate insulating film.
2Object-generated harmful factors
If the source region doping concentration is reduced to suppress gate current, then gate reliability is improved, but ohmic contact quality deteriorates
Solution Approach 1:
Different regions of the source are assigned different doping concentrations tailored to their specific functions: the contact region uses high doping for low resistance while the region adjacent to the gate insulating film uses low doping to prevent tunneling.
Solution Approach 2:
The source region is divided into functionally distinct segments that can be independently optimized. The first zone provides ohmic contact while the second zone suppresses harmful tunneling effects.
3Reliability
If a trench is engraved to form source electrode for ohmic contact, then contact quality is improved, but device complexity increases
Solution Approach 1:
The source electrode is extracted from the conventional planar configuration and positioned within a trench structure. This extraction allows the electrode to reach the high-doping region while being isolated from areas where tunneling occurs.
Solution Approach 2:
The source electrode formation transitions from a two-dimensional planar structure to a three-dimensional trench structure, enabling the electrode to access specific regions at different depths and achieve better contact properties.
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 configuration effectively reduces gate current and enhances gate reliability by minimizing Fowler-Nordheim tunneling, allowing for improved ohmic contact and reduced on-resistance.
Implementation Method 1
Applying a high positive voltage to a gate electrode of a MOSFET may cause a gate current to flow through a gate insulating film. This is because conduction electrons at the semiconductor side tunnel through a barrier that is formed against the gate insulating film and flow into the gate electrode side.
Data Source
AI summary
A silicon carbide semiconductor device that is able to increase the gate reliability, and to provide a method for manufacturing the silicon carbide semiconductor device, and that includes: a source electrode selectively formed on a source region; a gate insulating film formed so as to extend over the source region; and a gate electrode formed on the gate insulating film. The source region includes a first source region located below the source electrode, and a second source region surrounding the first source region. The doping concentration in a superficial layer of the second source region is lower than the doping concentration in a superficial layer of the first source region. The doping concentration in the second source region is higher in a deep portion than in a superficial portion thereof.