IGBT Termination Region Doping for Reduced Carrier Injection
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Solution Overview
Problem
Vertical insulated-gate devices, such as IGBTs and IGTOs, face issues with high carrier injection into the termination region during switching, leading to thermal destruction and limited maximum current capacity due to high heat generation when turning off, especially when the active region is formed in an epitaxial layer over a p+ substrate.
Innovation Solution
Various masking and doping techniques are employed to reduce carrier injection into the termination region by implanting n-type dopants or forming insulating layers in the termination region, while maintaining high hole injection efficiency in the active region, thereby reducing hole concentration and local power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the device uses a p+ substrate to form the active region in an epitaxial layer, then the breakdown voltage and current handling capacity are improved, but high carrier injection into the termination region causes thermal destruction and limits maximum current when switching off
Solution Approach 1:
The patent applies different doping characteristics to different regions: the active region maintains high hole injection efficiency for optimal on-state performance, while the termination region is modified to have low hole injection efficiency to prevent carrier accumulation. This local differentiation resolves the contradiction by allowing high current handling in the active region while preventing thermal destruction in the termination region during switching off.
Solution Approach 2:
The device is segmented into functionally distinct regions with different doping profiles. The active region and termination region are separated and independently optimized, with the termination region specifically engineered to reject minority carrier injection. This segmentation allows each region to be optimized for its specific function without compromising the other.
2Strength
If the termination region is designed to break down at higher voltage than the active region, then the breakdown voltage is improved, but carrier injection into the termination region during switching causes heat generation and potential device failure
Solution Approach 1:
The termination region is given specialized doping characteristics (low hole injection efficiency) that differentiate it from the active region. This local quality modification allows the termination region to withstand high breakdown voltages while simultaneously preventing the carrier injection that leads to heat generation during switching operations.
Solution Approach 2:
The patent converts the potentially harmful effect of high voltage stress in the termination region into a benefit by engineering the doping profile to inherently reject carrier injection. The high voltage capability is maintained while the harmful carrier accumulation is prevented through the specialized doping structure.
3Productivity
If the active region is formed in an epitaxial layer over a p+ substrate, then the device efficiency is improved, but hole injection into the termination region increases leading to extended turn-off time
Solution Approach 1:
The patent creates a localized doping structure in the termination region that specifically addresses carrier injection without affecting the overall device efficiency. The low hole injection efficiency in the termination region is achieved through targeted doping modifications that preserve the efficient operation of the active region while enabling faster turn-off.
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
The techniques effectively lower hole injection in the termination region, enhancing turn-off time and current handling capacity without reducing breakdown voltage or efficiency, allowing for larger current handling without device failure.
Implementation Method 1
The n-type buffer layer 35, which may epitaxially grown or formed by implantation into the substrate 30, has a dopant concentration higher than that of the n-epi layer 32. The buffer layer 35 helps to set the breakdown voltage and reduces hole injection into the n-epi layer 32.
Implementation Method 2
n-type dopants are implanted into the termination region to create either a very low concentration p-type layer or an n-layer below the intended termination region. The dopants implanted into the substrate are driven in by subsequent thermal processes.
Implementation Method 3
The n-type buffer layer 35, which may epitaxially grown or formed by implantation into the substrate 30, has a dopant concentration higher than that of the n-epi layer 32.
Data Source
AI summary
A high power vertical insulated-gate switch is described that includes an active region, containing a cell array, and a surrounding termination region. The termination region is for at least the purpose of controlling a breakdown voltage and does not contain any switching cells. Assuming the anode is the silicon substrate (p-type), it is desirable to have good hole injection efficiency from the substrate in the active region in the device's on-state. Therefore, the substrate should be highly doped (p++) in the active region. It is desirable to have poor hole injection efficiency in the termination region so that there is a minimum concentration of holes in the termination region when the switch is turned off. Various doping techniques are disclosed that cause the substrate to efficiency inject holes into the active region but inefficiently inject holes into the termination region during the on-state.