Trench Bottom Polysilicon for Power Semiconductor Capacitance Reduction
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Solution Overview
Problem
Existing power semiconductor devices face challenges in reducing input capacitance and reverse transfer capacitance, which contribute to switching loss, particularly under high-frequency applications, and current fabrication methods are complex and costly.
Innovation Solution
A power semiconductor device with a trench-based design featuring a heavily doped polysilicon structure and a gate dielectric layer, where dopants are driven to form a heavily doped region, reducing capacitance through a thermal drive-in step and optimized trench formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional fabrication methods are used to reduce input capacitance and reverse transfer capacitance, then switching loss is reduced, but fabrication process becomes complicated and cost increases
Solution Approach 1:
The patent changes the doping concentration parameter by forming a heavily doped polysilicon region at the trench bottom with high doping concentration (e.g., 1E19 to 1E21 atoms/cm³), which modifies the electric field distribution and reduces capacitance values without requiring complex fabrication processes
Solution Approach 2:
The patent performs preliminary doping action by forming the heavily doped polysilicon region at the trench bottom before final device completion. This preliminary doping establishes the desired capacitance characteristics early in the process, simplifying subsequent fabrication steps
2Area of moving object
If trench-based structure is implemented to reduce unit cell size, then cell integration is enhanced, but fabrication process becomes more complex
Solution Approach 1:
The patent merges the trench isolation structure with the gate electrode formation into a single integrated structure. The gate electrode is formed within the trench, combining what would traditionally be separate isolation and gating elements into one unified fabrication sequence, thereby reducing process complexity while maintaining compact unit cell dimensions
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 solution effectively reduces input capacitance and reverse transfer capacitance, enhancing switching speed and minimizing switching loss while simplifying the fabrication process.
Implementation Method 1
The dopants in the heavily doped polysilicon structure are driven through at least the side surface thereof to form a heavily doped region in the base
Implementation Method 2
applying a thermal drive-in step to diffuse dopants in the heavily doped polysilicon structure
Data Source
AI summary
A power semiconductor device comprising a base, a trench, a heavily doped polysilicon structure, a polysilicon gate, a gate dielectric layer, and a heavily doped region is provided. The trench is formed in the base. The heavily doped polysilicon structure is formed in the lower portion of the trench. At least a side surface of the heavily doped polysilicon structure touches the naked base. The polysilicon gate is located in the upper portion of the trench. The gate dielectric layer is interposed between the polysilicon gate and the heavily doped polysilicon structure. The dopants in the heavily doped polysilicon structure are diffused outward to form a heavily doped region.