Trench MOSFET Sidewall Geometry for Stable Saturated Current
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Solution Overview
Problem
The existing trench-type vertical MOSFETs experience variations in saturated current due to tilt angles at channel portions, leading to increased variations in switching time and performance.
Innovation Solution
A semiconductor device with a trench structure where the inner side surface has a first surface and a second surface that tilts inward, with the intersection point of these surfaces positioned below the base layer, formed using specific etching conditions to control the angle and depth of the trench, reducing variation in saturated current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the trench has a γ shape to reduce surface area and capacity, then switching time is shortened, but tilt occurs at channel portions resulting in increased variation in saturated current
Solution Approach 1:
The trench inner side surface is divided into two distinct surfaces: a first surface that is substantially perpendicular to the substrate, and a second surface that tilts inward. This segmentation allows each surface to fulfill different functions - the first surface maintains channel alignment while the second surface reduces overall trench capacity, thereby resolving the contradiction between switching speed and current uniformity
Solution Approach 2:
Different portions of the trench inner side surface are given different geometric properties - the upper portion (first surface) has a perpendicular orientation to ensure proper channel formation and reduce variation, while the lower portion (second surface) has an inward tilt to reduce capacity. This local differentiation resolves the contradiction by optimizing each region for its specific function
2Productivity
If the trench has a γ shape to reduce capacity between gate and source/drain, then switching performance is improved, but tilt at channel portions increases variation in saturated current
Solution Approach 1:
The trench is segmented into two surface portions with different orientations. The first perpendicular surface maintains channel alignment for consistent saturated current, while the second tilted surface reduces gate-to-source/drain capacity, thereby achieving both improved switching performance and reduced current variation
Solution Approach 2:
The trench structure applies different geometric qualities at different locations - the upper first surface has perpendicular orientation for channel stability, while the lower second surface has inward tilt for capacity reduction, resolving the contradiction between switching performance and current uniformity
3Manufacturing precision
If etching conditions are changed to form the trench with specific angle and depth, then manufacturing precision of trench shape is improved, but process complexity increases
Solution Approach 1:
The etching process is performed in two distinct stages with different conditions. The first etching step creates the initial trench structure, and the second etching step modifies the lower portion to create the inward tilt. This preliminary action approach allows precise control of the complex two-surface trench shape through sequential, controlled 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
The solution effectively reduces variation in saturated current, maintains short channel length, and improves switching performance by stabilizing the channel length and reducing ON voltage, enhancing short circuit tolerance and withstand voltage.
Implementation Method 1
forming a first trench extending to a depth below the base layer from the upper surface of the substrate through etching, performing etching from a bottom portion of the first trench to form a second trench
Data Source
AI summary
A semiconductor device includes a substrate, a drift layer provided on an upper surface side of the substrate, a base layer provided on the upper surface side of the drift layer, an upper semiconductor layer provided on the upper surface side of the base layer, a first electrode provided on the upper surface of the substrate, a second electrode provided on a rear surface of the substrate, a trench extending to the drift layer from the upper surface of the substrate and a gate electrode provided inside the trench, wherein an inner side surface of the trench has a first surface and a second surface provided below the first surface, the second surface tilts inward of the trench with respect to the first surface, and an intersection point of the first surface and the second surface is provided below the base layer.