SiC Gate Oxide Steplike Portions for Edge Field Relaxation
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Solution Overview
Problem
The existing silicon carbide semiconductor devices face dielectric breakdown and reduced insulation withstand-voltage due to electric field concentration at the edge of the gate oxide film adjacent to the outer peripheral insulating film, leading to reliability issues.
Innovation Solution
The solution involves forming steplike portions thicker than the gate oxide film at the edge of the gate oxide film adjacent to the outer peripheral insulating film, achieved through speed-increasing oxidation of an amorphous layer, which relaxes the electric field concentration and prevents dielectric breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a thick outer peripheral insulating film is formed on the N- semiconductor layer in the outer peripheral area, then the gate oxide film thickness at the boundary becomes thinner (about half the gate oxide film thickness), but this causes electric field concentration and dielectric breakdown at the edge portion of the gate oxide film
Solution Approach 1:
The invention applies different oxidation treatments to different regions: the amorphous layer at the boundary between the cell forming area and outer peripheral area undergoes speed-increasing oxidation to form a thicker gate oxide film (steplike portion), while the gate oxide film in the cell forming area is formed by conventional thermal oxidation. This local differentiation prevents electric field concentration at the boundary while maintaining proper gate oxide thickness in the active area.
Solution Approach 2:
An amorphous layer is formed in advance at the boundary region before the gate oxide film formation step. This preliminary action enables the subsequent speed-increasing oxidation to create a thicker gate oxide film at the critical boundary area, preventing dielectric breakdown before the device operates.
2Manufacturing precision
If the gate oxide film is formed by thermal oxidation method, then the gate oxide film thickness is uniform, but the electric field concentrates at the edge portion adjacent to the outer peripheral insulating film causing dielectric breakdown
Solution Approach 1:
The invention creates a steplike portion with different thickness at the boundary region compared to the cell forming area. The amorphous layer at the boundary undergoes speed-increasing oxidation to form a thicker gate oxide film segment, while the cell forming area receives conventional thermal oxidation. This local quality differentiation eliminates electric field concentration at the boundary while maintaining manufacturing precision through controlled oxidation processes.
3Device complexity
If the gate electrode layer extends from above the gate oxide film to above the outer peripheral insulating film, then the device structure is simplified, but the electric field concentrates at the rise portion of the gate electrode layer causing dielectric breakdown
Solution Approach 1:
The invention maintains the simplified gate electrode layer structure that extends continuously from above the gate oxide film to above the outer peripheral insulating film. However, it locally thickens the gate oxide film at the boundary region by forming a steplike portion through speed-increasing oxidation of the amorphous layer. This local modification prevents electric field concentration at the gate electrode rise portion while preserving the simplified overall structure.
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 enhances the insulation withstand-voltage and breakdown lifetime of the gate oxide film, thereby improving the reliability of the silicon carbide semiconductor device by preventing dielectric breakdown and maintaining the integrity of the gate oxide film.
Implementation Method 1
an amorphous layer of silicon carbide is formed at the bottom of each trench provided between source layers, the amorphous layer is subjected to speed-increasing oxidation upon thermal oxidation for forming a gate oxide film
Implementation Method 2
a gate oxide film comprised of silicon oxide, which is formed on the front surface of the N− semiconductor layer in the cell forming area by a thermal oxidation method
Data Source
AI summary
A silicon carbide semiconductor device includes a semiconductor substrate containing silicon carbide, a semiconductor layer formed over the semiconductor substrate, and a plurality of well regions formed on a front surface side of a cell forming area set to the semiconductor layer. The device further includes source layers formed on the front surface side lying within the well regions, an outer peripheral insulating film thick in thickness, which is formed over the semiconductor layer in an outer peripheral area surrounding the cell forming area, a gate oxide film formed over the front surface of the semiconductor layer in the cell forming area, and a gate electrode layer formed so as to extend from above the gate oxide film to above the outer peripheral insulating film.