Dual-Layer Field Plate Edge Termination for Power Semiconductor
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Solution Overview
Problem
Conventional power semiconductor devices face challenges in reducing the width of the edge termination structure while maintaining superior long-term forward blocking voltage capability reliability, due to large side etching and low etching accuracy associated with wet etching processes.
Innovation Solution
A power semiconductor device design featuring a dual-layer field plate structure with a conductive thin film and a metal film, where the first field plate is thinner and formed from polycrystalline silicon, and the second field plate is thicker and made of the same metal as the electrode, both covered by insulating films, allowing for reduced edge termination width and improved etching accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick metal film is used for the field plate and processed by wet etching, then the long-term forward blocking voltage capability reliability is improved through shielding external charge, but the side etching amount increases and etching accuracy decreases
Solution Approach 1:
The field plate structure is segmented into two distinct layers: a first field plate made of a thin metal film (30-100 nm) processed by sputtering, and a second field plate made of a thick metal film (3-5 μm) processed by wet etching. The thin first field plate is formed with high precision using sputtering, which eliminates the side etching and accuracy problems associated with wet etching thick metal films. The thick second field plate provides the necessary charge shielding function for long-term reliability. This segmentation allows each layer to be optimized for its specific function without the trade-offs of the conventional single-layer approach.
2Area of moving object
If the edge termination structure width is reduced to increase the active region surface area, then the device efficiency is improved, but the forward blocking voltage capability becomes difficult to maintain
Solution Approach 1:
The invention changes the physical parameters of the field plate structure by using a dual-layer configuration with different material compositions and thicknesses. The first field plate uses a thin metal film (30-100 nm) with different electrical properties than the conventional thick metal film, allowing for a reduced edge termination structure width while maintaining the necessary electric field relaxation effect. The second field plate's thick metal film provides superior charge shielding, enabling the overall structure to be more compact while maintaining voltage blocking capability.
3Ease of manufacture
If wet etching is used to process the thick metal film field plate pattern, then the fabrication process efficiency is improved, but the scatter in forward blocking voltage capability characteristic increases
Solution Approach 1:
The field plate fabrication is segmented into two separate processes: the first field plate is formed by sputtering a thin metal film (30-100 nm) which provides excellent etching accuracy and minimal scatter, and the second field plate is formed by wet etching a thick metal film (3-5 μm) which maintains fabrication efficiency. By separating these functions into two layers, the invention eliminates the scatter problem that would occur if wet etching were applied to a single thick field plate, while still maintaining the ease of manufacture benefits for the thick film portion.
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 design minimizes the scatter in forward blocking voltage capability characteristics and allows for a narrower edge termination structure with enhanced reliability, even with large side etching or etching scatter, maintaining stable forward blocking voltage performance.
Implementation Method 1
the field plate 80 which employs a metal film of this kind also possesses a function for maintaining long-term reliability of the forward blocking voltage capability function by shielding unnecessary charge (referred to as 'external charge' hereinbelow) which is harmful and applied from the external environment to the insulating film on the surface of the edge termination structure
Implementation Method 2
not only is a local concentration of the internal electric field prevented in order to secure the rated forward blocking voltage capability
Data Source
AI summary
A power semiconductor device is provided having a field plate that employs a thick metal film in an edge termination structure and which permits edge termination structure width reduction even with large side etching or etching variation, which exhibits superior long-term forward blocking voltage capability reliability, and which allows minimal forward blocking voltage capability variation. The edge termination structure has multiple ring-like p-type guard rings, a first insulating film covering the guard rings, and ring-like field plates, provided via the first insulating film atop the guard rings. The field plates have a polysilicon film and a thicker metal film. The polysilicon film is provided on a first guard ring via first insulating film, and a dual field plate made of the polysilicon film and metal film is provided on a second guard ring. The dual field plate is stacked via a second insulating film. The first and second guard rings alternate.