Trench MOSFET Split Gate Self-Aligned Fabrication
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Solution Overview
Problem
The existing trench MOSFET designs for semiconductor power devices require multiple epitaxial layers and additional masks for split gate electrodes, making them costly and difficult to manufacture effectively, especially for mass production, and the doping profiles are hard to control.
Innovation Solution
A trench MOSFET with a resurf stepped oxide structure that uses a single epitaxial layer and no additional mask for split gate electrodes, featuring a diffused drift region with higher doping concentration, which is easier to control and more cost-effective, and symmetrically disposed split gate electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple epitaxial layers with different gradient doping profiles are used to optimize breakdown voltage, then the breakdown voltage performance is improved, but the manufacturing cost increases and the doping profile control becomes difficult
Solution Approach 1:
The patent changes the doping profile parameters by using a single epitaxial layer with a specific doping concentration (e.g., 1E16 to 1E18 atoms/cm³) combined with a diffused drift region having higher doping concentration (e.g., 1E18 to 1E20 atoms/cm³). This parameter change allows achieving the desired breakdown voltage without the complexity of multiple epitaxial layers with different gradient profiles, thereby reducing manufacturing cost and improving doping profile control.
2Manufacturing precision
If additional masks are used for definition of split gate electrodes, then the gate electrode positioning precision is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent employs a self-aligned fabrication process where the split gate electrodes are automatically positioned relative to the trench structure and source region without requiring additional masks. The gate electrodes are formed by depositing conductive material that naturally aligns with the trench sidewalls and source electrode, eliminating the need for separate masking steps while maintaining precise positioning.
Solution Approach 2:
The patent performs preliminary formation of the trench structure and source electrode before forming the split gate electrodes. This preliminary action creates a self-aligned template that guides the subsequent gate electrode formation, ensuring precise positioning without additional masks. The trench sidewalls and source electrode serve as pre-established alignment references.
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 solution reduces manufacturing costs and simplifies the process by eliminating the need for additional masks and improving doping profile control, achieving better on-resistance reduction and cost-effectiveness compared to prior art.
Implementation Method 1
an epitaxial layer of a first conductivity type onto the substrate, wherein the epitaxial layer has a lower doping concentration than the substrate
Implementation Method 2
a diffused drift region having a higher doping concentration than the epitaxial layer
Data Source
AI summary
A trench MOSFET with split gates and diffused drift region for on-resistance reduction is disclosed. Each of the split gates is symmetrically disposed in the middle of the source electrode and adjacent trench sidewall of a deep trench. The inventive structure can save a mask for definition of the location of the split gate electrodes. Furthermore, the fabrication method can be implemented more reliably with lower cost.