Trench Gate Structure with Face-Selective Etching for Oxide Thickness Control
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Solution Overview
Problem
The existing trench gate structures in semiconductor power devices face challenges due to thinner bottom gate oxide layers, which lead to easier breakdown and affect device performance, as current methods to increase thickness are either insufficient or costly and complex.
Innovation Solution
A novel trench gate structure and method involving face-selective wet etching to form a second trench with a higher atomic density crystal face, allowing for a thicker thermal oxidation layer on the bottom of the trench compared to the sidewall, using specific crystal face families like {100}, {110}, and {111} on a silicon substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal oxidation process is performed on the trench gate structure, then gate oxide layer is formed on the sidewall and bottom of the trench, but the gate oxide layer on the bottom of the trench is always thinner than that on the sidewall
Solution Approach 1:
The patent applies local quality by creating different crystal orientations at different locations within the trench structure. The sidewall is maintained with original crystal orientation while the bottom is transformed to a different crystal orientation through face-selective wet etching, resulting in locally different oxidation rates and oxide thicknesses that optimize both reliability and manufacturing precision
Solution Approach 2:
The patent changes the crystal orientation parameter at the trench bottom through face-selective wet etching, which fundamentally alters the oxidation characteristics. This parameter change transforms the oxidation rate and oxide thickness at the bottom location, resolving the contradiction between uniform thickness and breakdown voltage requirements
2Reliability
If additional oxidation growing step is added after covering the sidewall of the trench, then bottom gate oxide thickness is increased, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies preliminary action by performing face-selective wet etching on the trench bottom before the thermal oxidation process. This preliminary modification of the bottom crystal orientation ensures that during the subsequent oxidation step, the bottom automatically forms thicker oxide without requiring additional oxidation steps, thereby reducing process complexity while improving reliability
3Manufacturing precision
If ion implantation is performed at the bottom of the trench to increase thermal oxidation growing rate, then bottom gate oxide thickness is improved, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent replaces the mechanical/chemical process of ion implantation with a face-selective wet etching process that utilizes crystallographic orientation differences. This substitution achieves the same goal of increasing bottom oxide thickness through a simpler, more cost-effective chemical etching process that exploits the inherent crystal structure rather than requiring complex ion implantation equipment and processes
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 approach effectively increases breakdown voltage, improves threshold voltage consistency, and enhances device reliability by forming a thicker gate oxide layer on the bottom of the trench without increasing costs or complexity, while maintaining a thinner gate oxide layer on the sidewall.
Implementation Method 1
forming a thermal oxidation layer on the surface of the sidewall of the first trench and the surface of the second trench through a thermal oxidation process
Implementation Method 2
performing face-selective wet etching on the surface of the bottom of the first trench and forming a second trench
Data Source
AI summary
The present invention provides a trench gate structure and a method of forming the same. The method comprises steps of forming a first trench on the surface of a substrate, a surface of a bottom of the first trench comprising a crystal face belonging to the first family of crystal faces, and a surface of a sidewall of the first trench comprising another crystal face belonging to a second family of crystal faces. With a face-selective wet etching, a specific crystal face is presented on the surface of the bottom of the trench and a thicker gate oxide layer is formed thereon after performing thermal oxidation to avoid from failure due to thinner gate oxide layer on the surface of the bottom, increase breakdown voltage, and improve reliability of the device.