Columnar Trench Transistor Structure for Lower On-State Resistance
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Solution Overview
Problem
Transistor devices for power applications, particularly those with columnar field plates, face challenges in reducing on-state resistance (RDS(on)) and achieving optimal performance due to mechanical stress and process non-uniformities associated with traditional field oxide thickness distributions.
Innovation Solution
The design incorporates a semiconductor substrate with columnar trenches and field plates featuring a stepped field dielectric, where the field oxide thickness decreases from the top to the bottom of the trench, reducing mechanical stress and allowing for a more homogeneous stress distribution, along with a ring-shaped contact that simplifies the manufacturing process and enhances integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional uniform field oxide thickness is used in columnar trenches, then manufacturing process is simpler, but mechanical stress distribution is non-uniform causing device reliability issues
Solution Approach 1:
The field dielectric is configured with varying thickness along the depth of the columnar trench, creating different local properties at different positions. The upper portion has a first thickness while the lower portion has a second thickness greater than the first, optimizing stress distribution and device reliability at different locations within the trench structure.
2Reliability
If columnar field plates with increased perimeter are used, then charge compensation performance is improved, but on-state resistance reduction is limited due to mechanical stress constraints
Solution Approach 1:
The invention changes the geometric parameters of the columnar field plate by increasing its perimeter relative to the trench opening. This enhanced perimeter provides improved charge compensation performance while the varying field dielectric thickness manages the mechanical stress to enable greater resistance reduction.
3Stability of the object's composition
If stepped field dielectric with varying thickness is implemented, then mechanical stress distribution becomes more homogeneous, but manufacturing process complexity increases
Solution Approach 1:
The field dielectric structure is segmented into distinct thickness regions along the trench depth. The upper portion and lower portion have different thicknesses, which can be achieved through selective deposition or etching processes, making the complex stress distribution manageable through staged manufacturing steps.
Data Source
Figure 1A
Figure 1B
Figure 1C~2A
AI summary
According to an embodiment, a transistor device is provided that comprises a semiconductor substrate having a first major surface and one or more transistor cells. Each transistor cell comprises a columnar trench formed in the semiconductor substrate, a columnar field plate arranged in the columnar trench and a mesa arranged around the columnar trench. The columnar trench comprises a field dielectric, a base and a side wall. The side wall extends from the base to the first major surface and the field dielectric lines the base and side wall of the columnar trench. A first thickness of the field dielectric at a first distance from the base is smaller than a second thickness of the field dielectric at a second distance from the base, wherein the first distance is greater than the second distance. A first perimeter of the columnar field plate at the first distance is greater than a second perimeter of the columnar field plate at the second distance.