Split-Gate Trench MOSFET With Thick Interpoly Isolation
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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 due to the thinning of insulating layers, which leads to weak poly-to-poly isolation.
Innovation Solution
A manufacturing process that decouples the formation of the interpoly oxide from the gate oxidation process, allowing for a thick interpoly oxide layer to improve isolation and reduce gate-to-source leakage current, while maintaining a thin gate oxide layer for lower threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gate oxide layer is made thin to reduce threshold voltage, then the threshold voltage decreases, but the poly-to-poly isolation weakens leading to increased gate-to-source leakage current
Solution Approach 1:
The patent divides the insulating layer into two distinct segments: a first insulating layer (interpoly oxide) providing thick isolation between polysilicon regions, and a second insulating layer (gate oxide) providing thin gate control. This segmentation allows each layer to be optimized independently for its specific function, resolving the contradiction between low threshold voltage and low leakage current.
Solution Approach 2:
The first insulating layer acts as an intermediary between the polysilicon regions, providing a thick barrier that prevents charge leakage. This intermediary structure enables the second insulating layer to be made thin for low threshold voltage without compromising the isolation function, as the intermediary first layer bears the isolation responsibility.
2Ease of manufacture
If the interpoly oxide layer is made thin to simplify manufacturing, then the manufacturing process is simplified, but the gate-to-source leakage current increases
Solution Approach 1:
The manufacturing process is segmented into two independent oxidation steps: first forming a thick interpoly oxide layer, then forming a thin gate oxide layer. This segmentation allows each oxidation step to be optimized for its specific thickness requirement, achieving both reliability and manufacturing feasibility.
Solution Approach 2:
The first insulating layer is formed in advance before the second insulating layer. This preliminary action establishes the isolation structure first, allowing subsequent processing to focus on creating the thin gate oxide without compromising the already-formed isolation layer.
3Device complexity
If a single oxidation process is used to form both gate oxide and interpoly oxide, then the manufacturing process is simplified, but the thickness control for both layers is compromised
Solution Approach 1:
The single oxidation process is segmented into two separate oxidation processes, each tailored to create the specific thickness required for its target layer. This segmentation enables precise thickness control for both the thick interpoly oxide and thin gate oxide, overcoming the limitations of a single oxidation step.
Solution Approach 2:
The oxidation parameters (time, temperature, atmosphere) are changed between the two oxidation steps to achieve different thicknesses. The first oxidation uses parameters optimized for thick layer formation, while the second oxidation uses parameters optimized for thin layer formation, enabling precise thickness control for both layers.
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 process enhances transistor performance by reducing gate leakage, improving high-temperature gate bias reliability, and input capacitance without compromising the gate oxide thickness, thus achieving a lower threshold voltage without unacceptable leakage current.
Implementation Method 1
The second and third insulating layers 30a, 30b may each comprise an oxide layer (which, in an embodiment, is thermally grown from the exposed surfaces of the substrate 12 in each annular trench and the exposed surfaces of the upper portion 22a of the first polysilicon material 22)
Implementation Method 2
The second insulating layer 30a insulates the second polysilicon material (gate) 32 from the substrate 12 and forms the gate oxide layer for the transistor
Data Source
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.