Columnar Field Plate Structure for Lower RDS(on) in Transistors
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Solution Overview
Problem
Existing transistor devices with columnar field plates face challenges in reducing the on-state resistance (RDS(on).Area) while maintaining or improving figure of merit (FOMs).
Innovation Solution
A transistor device design featuring a semiconductor substrate with columnar trenches, where the field dielectric has a stepped thickness and the columnar field plate has a cavity, is implemented. This design includes a method of forming the columnar trench, depositing dielectric layers, and inserting conductive material to create the field plate with a cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a columnar field plate with uniform thickness is used, then the manufacturing process is simpler, but the on-state resistance cannot be sufficiently reduced
Solution Approach 1:
The field plate is designed with non-uniform thickness, where the thickness varies at different locations (first thickness at first distance from base, second thickness at second distance from base). This local variation optimizes charge compensation and reduces on-state resistance in different regions of the device, resolving the contradiction between manufacturing simplicity and performance optimization.
2Reliability
If the field dielectric thickness is increased throughout, then breakdown voltage improves, but on-state resistance increases
Solution Approach 1:
The field dielectric thickness is optimized locally rather than uniformly. By having different thicknesses at different distances from the base, the design achieves sufficient breakdown voltage where needed while minimizing resistance in critical current paths, thus resolving the trade-off between reliability and on-state resistance.
Solution Approach 2:
The solution moves from a two-dimensional uniform thickness parameter to a three-dimensional variable thickness distribution. The field dielectric thickness becomes a function of position (first thickness at first distance, second thickness at second distance), allowing independent optimization of breakdown voltage and on-state resistance through spatial variation.
3Area of stationary object
If the field plate perimeter is reduced, then the device area decreases, but the charge compensation effect weakens
Solution Approach 1:
The field plate geometry is modified by changing the perimeter relationship at different heights. The first perimeter at the first distance from base is greater than the second perimeter at the second distance, creating a tapered or stepped structure that maintains effective charge compensation while reducing overall device area.
Data Source
AI summary
A transistor device includes a semiconductor substrate having a first major surface and one or more transistor cells. Each transistor cell may include a columnar trench in the semiconductor substrate. The columnar trench includes a field dielectric, base, and a side wall. The side wall may extend from the base to the first major surface. The field dielectric may line 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. The first distance is greater than the second distance. A columnar field plate with a cavity may be arranged in the columnar trench. 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.