Stepped Gate Trench III-Nitride Device for Reduced Qgd
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Solution Overview
Problem
III-nitride semiconductor devices face challenges in reducing gate-to-drain capacitance (Qgd) and increasing breakdown voltage due to sharp cornered trenches that create high field regions and increased overlap between the gate electrode and the two-dimensional electron gas (2-DEG).
Innovation Solution
The fabrication process involves forming a gate well with ledges at the corners instead of sharp corners, achieved by isotropically etching through dielectric layers and selectively enlarging the opening in the top nitride layer while maintaining the bottom layer's dimensions, resulting in a step-like feature that reduces Qgd and enhances breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If vertical sidewalks with sharp corners are used in the gate trench, then the device structure is simple and easy to manufacture, but high field regions are created at the bottom corners reducing breakdown voltage
Solution Approach 1:
The trench sidewall is segmented into multiple portions with different orientations. The method forms a first trench with vertical sidewalls, then forms a second trench offset from the first, creating a stepped configuration. This segmentation eliminates sharp corners while maintaining manufacturability through standard trenching processes applied in sequence.
Solution Approach 2:
The solution transitions from a two-dimensional vertical trench to a three-dimensional stepped structure by introducing horizontal offsets between successive trench portions. This dimensional change eliminates the problematic sharp corners at the trench bottom while distributing the electric field more uniformly across the stepped surfaces.
2Device complexity
If vertical sidewalks with sharp corners are used in the gate trench, then the device structure is simple, but the overlap between gate electrode and 2-DEG increases causing high Qgd
Solution Approach 1:
The gate trench is segmented into multiple offset portions, which reduces the effective overlap area between the gate electrode and the 2-DEG channel. This segmentation lowers the gate-to-drain capacitance (Qgd) while the segmented structure can still be formed using conventional trenching and filling processes applied in sequence.
3Reliability
If ledges are added at the trench corners to reduce Qgd and increase breakdown voltage, then device performance improves, but the fabrication process becomes more complex
Solution Approach 1:
The ledges are formed by segmenting the trench formation into multiple steps: forming a first trench, forming a second trench offset from the first, and selectively removing material. This segmentation achieves the complex ledge geometry using multiple applications of standard trenching processes rather than requiring a single complex etching step.
Solution Approach 2:
The method performs preliminary trench formation actions in sequence before finalizing the gate structure. By pre-forming offset trenches and selectively removing material at intermediate stages, the process creates the ledge structure in advance, simplifying subsequent gate electrode fabrication.
Data Source
AI summary
A III-nitride heterojunction power semiconductor device that includes a passivation body with a gate well having a top mouth that is wider than the bottom mouth thereof, and a method of fabrication for the same.