Dual Trench Isolation for LDMOS Ron Reduction
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Solution Overview
Problem
LDMOS transistors face challenges in achieving low output resistance (Ron) while maintaining high drain-source-saturated breakdown voltage (BVDSS), as attempts to reduce Ron through increased N-well implant dose degrade the breakdown voltage.
Innovation Solution
A dual trench isolation structure is implemented, comprising a shallow trench isolation structure adjacent to and connecting with a deep trench isolation structure, forming a stepped isolation structure within the LDMOS transistor, which reduces Ron levels and preserves BVDSS by shortening the electron path without degrading the breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher implant dose is used in the N-well to reduce Ron, then Ron levels decrease, but breakdown voltage BVDSS degrades
Solution Approach 1:
The isolation structure is divided into two distinct segments: a shallow trench isolation region and a deep trench isolation region. The shallow trench extends to a first depth while the deep trench extends to a second depth greater than the first depth. This segmentation allows different regions to serve different functions - the shallow trench provides basic isolation while the deep trench specifically targets electron path reduction without affecting the breakdown voltage-critical regions.
Solution Approach 2:
Different depth regions are assigned different isolation properties. The shallow trench isolation region and deep trench isolation region have different depths and are positioned at different locations within the semiconductor structure. This local differentiation enables the deep trench to shorten electron paths in specific regions to reduce Ron, while the overall structure maintains the breakdown voltage characteristics through the shallow trench region.
2Reliability
If increased conductivity is implemented to reduce Ron, then Ron levels decrease, but breakdown voltage BVDSS degrades
Solution Approach 1:
The solution transitions from modifying material properties (increasing conductivity through implantation) to modifying the geometric dimension of the isolation structure. By creating a deep trench isolation region that extends deeper into the substrate, the patent shortens the electron path length in the vertical dimension, thereby reducing Ron without relying on increased doping concentrations that would compromise BVDSS.
Data Source
AI summary
The present disclosure generally relates to semiconductor structures and, more particularly, to dual trench isolation structures and methods of manufacture. The structure includes: a doped well region in a substrate; a dual trench isolation region within the doped well region, the dual trench isolation region comprising a first isolation region of a first depth and a second isolation region of a second depth, different than the first depth; and a gate structure on the substrate and extending over a portion of the dual trench isolation region.