Field-Limiting Rings with Shallow Implants for Power Semiconductor Surface Charge
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Solution Overview
Problem
High-voltage semiconductor devices are sensitive to electrostatic charge at the surface, which degrades their breakdown voltage characteristics, particularly when positive or negative charge is present in the oxide layer, leading to reduced voltage handling ability.
Innovation Solution
The implementation of field-limiting rings around the active area of power semiconductor devices, which include replicated carrier-emission structures and field plates capacitively coupled to dielectric, helps to mitigate the effects of surface charge by using shallow implants of opposite conductivity types to counterdope the surface and form rings that shield deeper field-limiting structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional termination structures are used in high-voltage semiconductor devices, then the device can operate under normal conditions, but the breakdown voltage is significantly reduced when positive or negative charge is present in the oxide layer
Solution Approach 1:
The patent applies preliminary anti-action by introducing shallow implant regions with conductivity type opposite to the deep field-limiting ring before the harmful surface charge can degrade the breakdown voltage. These preliminary structures counterdope the surface and create opposing electric fields that neutralize the harmful effects of positive or negative charge in the oxide layer, thereby maintaining reliable high-voltage operation
Solution Approach 2:
The patent changes the doping parameters by creating multiple shallow implant regions with different conductivity types (n-type and p-type) at different locations around the active area. This parameter change allows the termination structure to adapt to different charge conditions - n-type shallow implants counteract positive charge while p-type shallow implants counteract negative charge, thus maintaining breakdown voltage under varying surface charge conditions
2Reliability
If shallow implants of opposite conductivity types are added to counterdope the surface, then sensitivity to surface charge is reduced, but device structure and fabrication complexity increase
Solution Approach 1:
The patent merges multiple functions into the termination structure by combining the deep field-limiting ring with multiple shallow implant regions in a single integrated design. The shallow implants are incorporated into the same termination region that contains the deep field-limiting ring, allowing the structure to perform both field-limiting and surface counterdoping functions simultaneously, thereby reducing overall device complexity while improving voltage handling
Solution Approach 2:
The termination structure is designed with multi-functionality by incorporating shallow implant regions that can counteract both positive and negative surface charge, in addition to the deep field-limiting ring's primary function. This universal design allows a single termination structure to handle multiple types of surface charge conditions and maintain breakdown voltage across different operating scenarios
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 reduces the sensitivity of semiconductor devices to surface charge, enhancing their breakdown voltage and preventing voltage-reducing changes in the electric field, thereby improving their voltage handling capability.
Implementation Method 1
field plates which extend out over, and are capacitively coupled to, an adjacent annulus of dielectric
Implementation Method 2
using shallow implants of opposite conductivity types to counterdope the surface
Data Source
AI summary
The present application provides (in addition to more broadly applicable inventions) improvements which are particularly applicable to two-sided power semiconductor devices which use bipolar conduction. In this class of devices, the inventor has realized that two or three of the four (or more) semiconductor doping components which form the carrier-emission structures and control structures in the active device (array) portion of a two-sided power device can also be used, with surprising advantages, to form field-limiting rings around the active arrays on both surfaces. Most preferably, in some but not necessarily all embodiments, a shallow implant of one conductivity type is used to counterdope the surface of a well having the other conductivity type. This shallow implant, singly or in combination with another shallow implant of the same conductivity type, works to shield the well from the effects of excess charge at or above the surface of the semiconductor material.