Split-Gate Trench MOSFET With Thick Poly Isolation for Low Leakage
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Solution Overview
Problem
Existing split-gate trench power MOSFET devices face challenges in reducing threshold voltage while maintaining adequate gate-to-source leakage current prevention, as thinner gate oxide layers lead to weak poly-to-poly isolation.
Innovation Solution
A manufacturing process that decouples gate oxide formation from interpoly oxide formation, allowing for a thick interpoly oxide layer to ensure strong isolation, involves forming a substrate trench, lining it with a first insulating layer, and then creating a gate trench with an integral portion of the first insulating layer to insulate a second conductive material, which enhances poly-to-poly isolation without compromising gate oxide thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gate oxide layer is made thinner to reduce threshold voltage, then the threshold voltage is reduced, but the poly-to-poly isolation becomes weak leading to increased gate-to-source leakage current
Solution Approach 1:
The patent segments the oxide layer formation into two distinct stages: first forming a thin gate oxide layer for proper threshold voltage control, then forming a separate thick interpoly oxide layer for strong poly-to-poly isolation. This segmentation allows each oxide layer to be optimized independently for its specific function without compromising the other.
Solution Approach 2:
The patent performs the gate oxide formation as a preliminary action before the interpoly oxide formation. By establishing the thin gate oxide first, the threshold voltage is properly set, and then the thick interpoly oxide is added subsequently to provide the necessary isolation without affecting the already-established gate oxide thickness.
2Reliability
If a thick interpoly oxide layer is formed to ensure strong poly-to-poly isolation, then gate-to-source leakage is reduced, but the gate oxide thickness must be reduced compromising threshold voltage control
Solution Approach 1:
The patent divides the isolation structure into two separate oxide components: a thin gate oxide layer that maintains proper threshold voltage and a thick interpoly oxide layer that provides strong poly-to-poly isolation. This segmentation eliminates the need to compromise gate oxide thickness for the sake of isolation.
Solution Approach 2:
The patent introduces an intermediary thick interpoly oxide layer between the gate polysilicon and field plate polysilicon. This intermediary layer provides the necessary isolation function without directly affecting the gate oxide thickness, allowing both requirements to be satisfied simultaneously.
3Ease of manufacture
If a single oxide layer is used for both gate oxide and interpoly isolation, then the manufacturing process is simpler, but it is impossible to achieve both thin gate oxide and thick interpoly oxide simultaneously
Solution Approach 1:
The patent segments the oxide formation process into two distinct sequential steps: first forming the gate oxide to the required thin thickness for proper threshold voltage, then forming an additional thick interpoly oxide layer for isolation. This segmented approach provides precise thickness control for each layer while maintaining manufacturing feasibility.
Solution Approach 2:
The patent performs gate oxide formation as a preliminary action with precise thickness control, then subsequently adds the interpoly oxide layer. This sequential approach allows each oxide layer to be formed with the specific thickness required for its function, achieving both thin gate oxide and thick interpoly oxide simultaneously.
Data Source
Figure 1
Figure 2A~2B
Figure 3~4B
AI summary
A semiconductor substrate has a substrate trench extending from a front surface and including a lower part and an upper part. A first insulation layer lines the substrate trench, and a first conductive material is insulated from the semiconductor substrate by the first insulating layer to form a transistor field plate electrode. A gate trench in the first insulation layer defines an integral part of the first insulating layer surrounding the first conductive material in an upper part of the substrate trench. A second insulating layer lines the semiconductor substrate at the upper part of the substrate trench in the gate trench. A second conductive material fills the gate. The second conductive material forms a transistor gate electrode that is insulated from the semiconductor substrate by the second insulating layer and further insulated from the first conductive material by the integral part of the first insulating layer.