Super Junction Vertical MOSFET Trenches for Low On-Resistance Stability
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Solution Overview
Problem
The challenge in reducing the on-resistance of vertical MOSFETs with a super junction structure is that dimensional changes in the p-type column and n-type drift regions increase sensitivity to breakdown voltage and normalized on-resistance, leading to characteristic variation and manufacturing issues.
Innovation Solution
The semiconductor device design includes a semiconductor substrate with an n-type drift region, p-type base region, and p-type column regions, where trenches with gate electrodes are formed between the column regions, allowing for reduced on-resistance while minimizing sensitivity to dimensional changes, achieved by optimizing the interval and density of trench gates and p-type column regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pitching of the periodic p-type column region is decreased to reduce on-resistance, then the on-resistance decreases, but the sensitivity to dimensional changes increases leading to characteristic variation
Solution Approach 1:
The patent introduces a multi-layer trench gate structure with different trench depths and gate electrode configurations. The first trench has a gate electrode extending to a first depth, while the second trench has a gate electrode extending to a second depth greater than the first depth. This segmentation allows different regions to provide different functions: the shallower trench controls channel formation while the deeper trench provides enhanced field control and reduces sensitivity to p-type column region dimensional variations, thereby reducing characteristic variation while maintaining low on-resistance.
Solution Approach 2:
The patent applies different trench gate structures to different spatial locations. The first trench gate structure is positioned in a first region, while the second trench gate structure with greater depth is positioned in a second region. This local differentiation allows optimization of specific regions to compensate for dimensional variations in p-type column regions, reducing overall characteristic variation while maintaining low on-resistance across the device.
2Reliability
If the concentration of the n-type drift region or p-type column region is increased to reduce on-resistance, then the on-resistance decreases, but the sensitivity to dimensional changes increases leading to characteristic variation
Solution Approach 1:
The multi-layer trench gate structure segments the electric field control into different depth zones. The first trench gate electrode controls the upper region while the second trench gate electrode controls the lower region with greater depth. This segmentation provides enhanced control over the electric field distribution, reducing the sensitivity to concentration and dimensional variations in the n-type drift region and p-type column regions, thereby reducing characteristic variation while maintaining low on-resistance.
Solution Approach 2:
The patent changes the structural parameters of the trench gates by creating trenches with different depths and configuring gate electrodes at different positions. The first trench has a gate electrode extending to a first depth, while the second trench has a gate electrode extending to a second depth greater than the first depth. This parameter change in trench depth provides enhanced control over the electric field and charge distribution, reducing sensitivity to dimensional and concentration variations in the semiconductor regions, thereby reducing characteristic variation.
3Reliability
If the trench gate structure is optimized to reduce on-resistance, then the on-resistance decreases, but the breakdown voltage stability may be affected
Solution Approach 1:
The patent segments the breakdown voltage control function into two distinct trench gate structures with different depths. The first trench gate structure provides baseline control, while the second trench gate structure with greater depth provides enhanced field control and stabilization. This segmentation allows the device to achieve low on-resistance through optimized trench gate structure while the deeper second trench gate structure ensures breakdown voltage stability by providing enhanced electric field control in the lower region.
Solution Approach 2:
The patent applies different trench gate structures to different spatial locations to address different requirements. The first trench gate structure optimizes for low on-resistance in the first region, while the second trench gate structure with greater depth provides enhanced breakdown voltage stability in the second region. This local differentiation allows simultaneous optimization of both on-resistance and breakdown voltage stability.
Data Source
AI summary
To reduce on-resistance while suppressing a characteristic variation increase of a vertical MOSFET with a Super Junction structure, the vertical MOSFET includes a semiconductor substrate having an n-type drift region, a p-type base region formed on the surface of the n-type drift region, a plurality of p-type column regions disposed in the n-type drift region at a lower portion of the p-type base region by a predetermined interval, a plurality of trenches whose bottom surface reaches a position deeper than the p-type base region and that is disposed between the adjacent p-type column regions, a plurality of gate electrodes formed in the plurality of trenches, and an n-type source region formed on the side of the gate electrode in the p-type base region.