Shielded Gate SBR With Stepped Epitaxy for Avalanche Ruggedness
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Solution Overview
Problem
Conventional Shielded Gate Trench (SGT) MOSFETs face avalanche capability degradation due to higher electric fields near the channel region, leading to device failure at lower avalanche energy ratings, and there is a tradeoff between breakdown voltage and forward voltage, which affects DC/AC performance and device ruggedness.
Innovation Solution
A Shielded Gate Trench (SGT) Super Barrier Rectifier (SBR) with a Multiple Stepped Epitaxial (MSE) structure is introduced, featuring epitaxial layers with decreasing doping concentrations from the substrate to the surface, ensuring a lower electric field near the channel region and reducing the forward voltage, thereby enhancing avalanche capability and device ruggedness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform epitaxial layer is used in conventional SGT MOSFETs, then the device achieves lower gate charge and specific on-resistance, but the electric field near the channel region becomes higher than at the trench bottom, causing avalanche occurrence near the channel region and device failure at lower avalanche energy ratings
Solution Approach 1:
The patent applies local quality by creating non-uniform doping concentration distribution within the epitaxial layer. Specifically, the drift region has a first doping concentration while the channel stop region has a second doping concentration that is different (typically lower) to reduce electric field concentration near the channel. This localized modification of material properties addresses the harmful electric field concentration without compromising overall device performance.
Solution Approach 2:
The patent changes the doping concentration parameter within the epitaxial layer to resolve the contradiction. By adjusting the doping concentration in different regions (drift region versus channel stop region), the electric field distribution is modified. The channel stop region is designed with optimized doping concentration to reduce peak electric field near the channel, thereby preventing premature avalanche breakdown while maintaining the benefits of the uniform epitaxial layer structure.
2Strength
If breakdown voltage is increased, then the forward voltage Vf is also increased due to higher resistivity in drift region, creating a tradeoff between breakdown voltage and forward voltage
Solution Approach 1:
The patent applies local quality by differentiating doping concentrations in specific regions. The drift region maintains sufficient doping to limit forward voltage, while the channel stop region is optimized for breakdown voltage enhancement. This spatial differentiation allows independent optimization of forward voltage and breakdown voltage characteristics that would be conflicting in a completely uniform structure.
Solution Approach 2:
The epitaxial layer is segmented into functionally distinct regions with different doping concentrations - the drift region and the channel stop region. This segmentation allows each region to be optimized for its specific function: the drift region for controlling forward voltage through its resistivity, and the channel stop region for enhancing breakdown voltage by managing electric field distribution. The segmentation resolves the tradeoff by decoupling the optimization of these two conflicting parameters.
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 MSE structure effectively redirects avalanche occurrence to the trench bottom, reducing the electric field near the channel region, enhancing device ruggedness and lowering the forward voltage, thus improving DC/AC performance and device reliability.
Implementation Method 1
the electric field near channel region is lower than the trench bottom. The avalanche capability or device ruggedness is thus enhanced because the avalanche occurs at trench bottom not in channel region
Implementation Method 2
two electric field and impact ionization peaks locate near channel region and trench bottom respectively (as shown in FIG. 1B), and the electric field near channel region is always higher than trench bottom in the uniform epitaxial layer, causing avalanche occurrence near the channel region
Implementation Method 3
an epitaxial layer having special MSE layers with different doping concentrations decreasing stepwise in a direction from a substrate to a top surface of the epitaxial layer, wherein each of the MSE layers has a uniform doping concentration as grown
Data Source
AI summary
The present invention introduces a new shielded gate trench SBR (Super Barrier Rectifier) wherein an epitaxial layer having special MSE (multiple stepped epitaxial) layers with different doping concentrations decreasing in a direction from a substrate to a top surface of the epitaxial layer, wherein each of the MSE layers has an uniform doping concentration as grown. Forward voltage Vf is significantly reduced with the special MSE layers. An integrated circuit comprising a SGT MOSFET and a SBR formed on a single chip obtains benefits of low on-resistance, low reverse recovery time and high avalanche capability from the special MSE layers.