Split-Gate Trench MOSFET With Stepped Shield for Lower Rsp
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Solution Overview
Problem
Shielded-gate trench MOSFET devices experience high shield resistance, capacitive coupling issues, and poor specific on-resistance (Rsp) performance, particularly at higher voltages, due to inadequate dopant concentration and floating gate electrode regions, which affect manufacturability and device performance.
Innovation Solution
The introduction of a stepped shield electrode and split gate electrode configuration with varying dielectric thicknesses and lateral widths, along with a recessed design, facilitates higher dopant concentration in the drift region, reducing gate-to-shield capacitance and avoiding floating gate regions, thereby improving Rsp and manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shield electrode is added to reduce capacitive coupling issues, then gate turn-on reliability improves, but shield resistance increases causing unwanted gate turn-on and dynamic avalanche issues
Solution Approach 1:
The shield electrode is segmented into multiple sections with varying dielectric thicknesses between the shield electrode and drift region. This segmentation allows different portions of the shield electrode to have different capacitance values, enabling optimization of both shield resistance and capacitive coupling effects. The first section has a first dielectric thickness while the second section has a second dielectric thickness that is greater than the first, creating a gradient structure that balances reliability improvement with resistance control.
Solution Approach 2:
Different sections of the shield electrode are assigned different local properties through varying dielectric thicknesses. The first section near the gate electrode uses a thinner dielectric to reduce capacitive coupling, while the second section uses a thicker dielectric to control resistance. This local quality variation allows each section to address specific issues without compromising overall device performance.
2Object-affected harmful factors
If multiple shield contacts are used to reduce shield resistance, then shield electrode connectivity improves, but floating gate electrode regions are created impairing device performance
Solution Approach 1:
The patent extracts the problematic floating gate regions by carefully designing the shield electrode configuration and dielectric structure. The shield electrode is positioned and dimensioned such that it does not create isolated floating gate regions, while still providing multiple contact points to reduce resistance. The varying dielectric thicknesses ensure continuous electrical pathways are maintained.
3Object-affected harmful factors
If dopant concentration in drift region is increased to improve specific on-resistance, then Rsp performance improves, but previous split gate designs exhibited poor Rsp performance at higher voltages
Solution Approach 1:
The patent changes the dielectric thickness parameter across different sections of the device to enable higher dopant concentration in the drift region. By having a thinner dielectric in the first section and a thicker dielectric in the second section, the structure accommodates higher dopant concentrations that improve specific on-resistance while maintaining proper voltage breakdown characteristics for higher voltage operation.
Data Source
AI summary
A semiconductor device includes a body of semiconductor material and a trench within the body of semiconductor material. A stepped shield electrode is within the trench and includes a wide first portion and a narrower second portion below the first portion. A first dielectric separates the first portion from the body of semiconductor material. A second dielectric separates the second portion from the body of semiconductor material. A split gate electrode structure is within the trench and includes a first gate electrode proximate to a first side of the trench and second gate electrode proximate to a second side of the trench. A gate dielectric separates the first gate electrode from the body of semiconductor material and separates the second gate electrode from the body of semiconductor material. A third dielectric separates the stepped shield electrode from the first gate electrode and the second gate electrode.