Trench Gate MOSFET Well Structure for Electric Field Relief
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Solution Overview
Problem
Trench gate structures in MOSFETs induce large electric field concentrations, leading to reduced breakdown voltage and reliability issues.
Innovation Solution
A semiconductor device with an epitaxial layer and a well structure is formed by ion implantation processes to increase the depth of the well, covering the corner points of the gate structure, thereby reducing electric field accumulation and improving breakdown voltage while reducing on-state resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trench gate structures are used to increase channel density, then on-state resistance is reduced and component size is scaled down, but electric field concentrations are induced that reduce breakdown voltage and cause reliability problems
Solution Approach 1:
The patent applies local quality by creating a well structure with specific doping characteristics at critical locations (corner points of the gate structure) rather than uniform doping throughout. The well has a doping concentration that differs from both the drift region and the heavily doped region, providing localized electric field management exactly where the trench gate structure creates concentration problems.
Solution Approach 2:
The patent transitions from a two-dimensional planar structure to a three-dimensional well structure that extends vertically and laterally. The well structure adds a depth dimension, allowing it to cover the corner points of the gate structure from below, effectively distributing the electric field in three dimensions rather than allowing concentration at sharp corners in a planar configuration.
2Reliability
If the well depth is increased to cover the corner points of the gate structure, then electric field accumulation is reduced and breakdown voltage is improved, but the manufacturing process complexity increases due to multiple ion implantation processes
Solution Approach 1:
The patent segments the well formation into multiple ion implantation processes: a first ion implantation to form a preliminary well structure, and a second ion implantation to deepen and adjust the well characteristics. This segmentation allows precise control over the well's depth and doping concentration profile, enabling the well to accurately cover the gate corner points while maintaining manufacturability through standardized multi-step implantation processes.
Solution Approach 2:
The patent performs preliminary actions by first forming a preliminary well structure through the first ion implantation process before completing the final well structure. This preliminary well provides a foundation that can be subsequently deepened and adjusted, allowing the manufacturing process to build the complex three-dimensional well structure in manageable stages rather than requiring a single complex implantation step.
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
The solution effectively increases breakdown voltage and reduces on-state resistance by covering the junctions of the gate structure with the well, enhancing the reliability of the semiconductor device.
Implementation Method 1
performing a first implantation process to form a first portion of a well in the epitaxial layer. The first portion of the well has a second conductive type different from the first conductive type
Data Source
AI summary
A semiconductor device includes an epitaxial layer, a gate structure, a well, and a source electrode. The epitaxial layer has a first conductive type. The gate structure and the well are disposed in the epitaxial layer. The well has a second conductive type different from the first conductive type. The well extends from a sidewall of the gate structure to a bottom surface of the gate structure. The source electrode is disposed above the epitaxial layer and is electrically connected to the well.