LDMOSFET STI Slit Field Concentration Mitigation

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Solution Overview

Problem

In LDMOSFETs, the use of STI structures improves breakdown voltage but increases on-resistance, and introducing slit regions to reduce on-resistance leads to electric field concentration and subsequent breakdown voltage reduction.

Innovation Solution

The solution involves modifying the LDMOSFET structure by removing a portion of the slit diffusion region where electric field concentration occurs and adjusting the gate electrode to avoid steep potential gradients, thereby reducing electric field concentration and maintaining breakdown voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an STI structure is formed in the drift region, then the breakdown voltage is improved, but the on-resistance is increased

Engineering Contradiction:

Improvebreakdown voltageVSAvoidon-resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The STI structure is segmented by introducing a slit region that divides the continuous isolation region into separate sections. This segmentation allows the drift region to be partially exposed, creating multiple current paths that reduce on-resistance while maintaining the voltage blocking capability of the STI structure in non-slit areas

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The slit region introduces local variation in the STI structure, creating regions with different electrical characteristics. The exposed drift region under the slit has different properties (lower resistance) compared to the covered drift region, allowing simultaneous optimization of local current flow and overall voltage blocking

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If a slit region is formed in the STI structure to reduce on-resistance, then the on-resistance is reduced, but an electric field concentration region is formed in the drift region exposed from the slit region, causing breakdown voltage reduction

Engineering Contradiction:

Improveon-resistanceVSAvoidbreakdown voltage

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

An isolation region is introduced as an intermediary structure positioned between the slit region and the high concentration drain region. This intermediary isolation region acts as a buffer that prevents direct electric field concentration at the slit edges while still allowing the slit to function in reducing on-resistance by exposing the drift region

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electric field concentration that occurs in the drift region exposed from the slit region is converted into a beneficial effect by positioning an isolation region to manage this concentration. The isolation region utilizes the exposed drift region's electrical characteristics to create favorable field distribution patterns that ultimately protect against breakdown while maintaining low resistance

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS20230146397A1Semiconductor device

Publication Date: 2023.05.11 RENESAS ELECTRONICS CORP

AI summary

In a LDMOSFET 100, an “STI structure 11” provided in a drain region including a high concentration drain region 10 and a drift region 12 including the high concentration drain region 10 has a slit region 11A extending in a x-direction, and in plan view, the “STI structure 11” is interposed between the slit region 11A and the high concentration drain region 10.