Outermost Trench Gate Insulator Thickness for Semiconductor Reliability
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Solution Overview
Problem
In semiconductor devices with a trench gate structure, the breakdown of gate insulators at the outermost trenches occurs due to potential differences between adjacent MISFETs, leading to reliability issues when used as bidirectional switches.
Innovation Solution
The semiconductor device incorporates a design where the trench at the outermost positions of MISFETs features a thicker field insulator not only at the bottom but also at the top, mitigating electric fields and preventing breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench gate structure is used with uniform gate insulator thickness, then the device structure is simple and easy to manufacture, but the gate insulator breaks down at outermost trenches due to potential differences between adjacent MISFETs
Solution Approach 1:
The gate insulator thickness is made non-uniform by increasing the thickness at the outermost trenches compared to inner trenches. This local variation in insulator thickness provides enhanced breakdown voltage at the outermost trenches where potential differences occur, while maintaining standard thickness at inner trenches where uniform potential exists.
2Reliability
If the gate insulator thickness is increased at outermost trenches, then breakdown resistance is improved, but the manufacturing precision and process complexity increase
Solution Approach 1:
A thick insulator layer is formed in advance to cover all trenches including the outermost ones. Subsequently, the insulator at inner trenches is selectively removed to expose the semiconductor substrate, leaving the thick insulator intact at the outermost trenches. This preliminary formation approach simplifies thickness control compared to directly forming different thicknesses.
Solution Approach 2:
Instead of adding material selectively to outermost trenches, the solution removes the insulator from inner trenches. This extraction approach achieves the desired thickness differential more easily and reduces manufacturing precision requirements.
3Reliability
If a thick insulator is formed at the top part of the trench, then electric field mitigation is improved, but the device area and structural complexity increase
Solution Approach 1:
The solution addresses electric field mitigation by modifying the insulator thickness in the vertical dimension rather than expanding the horizontal area. The thick insulator at the outermost trench top provides electric field mitigation through increased vertical thickness, maintaining compact device area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances the reliability of the semiconductor device by preventing gate insulator breakdown, even under high electric potentials, thereby improving the device's operational stability.
Implementation Method 1
a potential difference occurs to one of an outermost trench of the first MISFET and an outermost trench of the second MISFET which are next to each other, resulting in breakdown of a gate insulator formed in the outermost trench
Data Source
AI summary
Reliability of a semiconductor device is improved. The semiconductor device including a first MISFET group of a plurality of first MISFETs and a second MISFET group of a plurality of second MISFETs has a plurality of trenches each formed in a semiconductor layer and formed of an upper trench part and a lower trench part, and a plurality of gate electrodes formed inside the plurality of trenches. A thinner gate insulator is formed to the upper trench part and a thicker field insulator is formed to the lower trench part. In a trench at the outermost position in the first MISFET group and a trench at the outermost position in the second MISFET group, the gate insulator is not formed in the upper trench part, but the field insulator is formed in the upper trench part and the lower trench part.