LDMOS Gate Trench for Electric Field Control
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Solution Overview
Problem
Laterally diffused MOS (LDMOS) transistors face issues with on-resistance fluctuation and breakdown voltage decline due to electric field concentration at the source-side edge of the STI structure, leading to interface states and electron injection into the gate oxide film, which damages the gate oxide film and results in unbalanced electric fields.
Innovation Solution
The formation of trenches over the upper surface of the LDMOS transistor separation insulating film, with the gate electrodes partially embedded in these trenches, helps to ease the electric field concentration and reduce electron injection into the gate oxide film, thereby stabilizing the on-resistance and breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the STI structure is used for internal gate-drain isolation, then breakdown voltage is ensured, but electric field concentration occurs at the source-side edge of the STI structure leading to on-resistance fluctuation and interface state generation
Solution Approach 1:
The gate electrode is selectively positioned to extend over the drift region and partially cover the STI structure only in specific areas. This local extension creates a non-uniform electric field distribution that specifically addresses the high-field region at the STI edge without affecting other areas, thereby reducing on-resistance fluctuation while maintaining breakdown voltage
Solution Approach 2:
The gate electrode is extended in the lateral dimension beyond the conventional boundaries, projecting over the drift region and partially onto the STI structure. This dimensional extension allows the gate to directly modulate the electric field at the problematic STI edge region, suppressing interface state generation and on-resistance fluctuation
2Reliability
If the gate electrode is extended over the drift region and partially on the STI structure, then on-resistance fluctuation is suppressed, but device complexity increases
Solution Approach 1:
The extended gate electrode structure serves multiple functions simultaneously: it acts as the conventional gate for channel modulation, extends laterally to modulate the electric field at the STI edge, and partially covers the drift region to reduce on-resistance. This multi-functionality achieves improved reliability without requiring additional separate structures
Data Source
AI summary
There is provided a semiconductor device having LDMOS transistors embedded in a semiconductor substrate to boost source-drain breakdown voltage, with arrangements to prevent fluctuations of element characteristics caused by electric field concentration so that the reliability of the semiconductor device is improved. A trench is formed over the upper surface of a separation insulating film of each LDMOS transistor, the trench having a gate electrode partially embedded therein. This structure prevents electric field concentration in the semiconductor substrate near the source-side edge of the separation insulating film.