Trench MOSFET Shielded Gate Segmentation
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Solution Overview
Problem
The existing fabrication processes for trench MOSFETs face challenges in controlling the formation of gate electrodes and shielded source electrodes, especially in small die sizes, which affects the overall performance and reliability of semiconductor power devices.
Innovation Solution
A novel trench MOSFET design featuring a shielded gate and diffused drift region, with a deep trench surrounded by a gate trench and a trenched source-body contact, along with a specific fabrication process that includes growing an epitaxial layer, forming deep and gate trenches, and implementing a doping profile with higher concentration near trench sidewalls, is introduced. This design incorporates a dielectric material for the shielded gate and uses tungsten plugs with barrier layers for contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If deep trenches are formed in small die size trench MOSFETs, then the device can achieve higher power density and better performance, but it becomes hard to control the formation of gate electrodes and shielded source electrodes
Solution Approach 1:
The device is divided into separate deep trenches for shielded gates and shallower gate trenches, with source regions formed in the mesas between them. This segmentation allows independent formation and control of each component, solving the manufacturing difficulty of forming both gate electrodes and shielded source electrodes in a single deep trench structure while maintaining high power density.
Solution Approach 2:
The invention transitions from a planar structure to a three-dimensional trench structure with multiple depth levels. Deep trenches extend further into the substrate to form shielded gates, while shallower gate trenches form control gates. This dimensional approach enables high power density through vertical integration while maintaining manufacturability through staged trench formation processes.
2Power
If the gate insulation layer is made thinner to improve device performance, then the electric field control is enhanced, but the risk of breakdown increases
Solution Approach 1:
The gate insulation layer thickness is optimized locally for each trench type. The deep trench shielded gates use thicker insulation to prevent breakdown from high voltage stress, while the shallower control gate trenches can use thinner insulation for better electric field control. This local quality differentiation allows enhanced performance where needed while maintaining reliability in high-stress regions.
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 enhances control over trench formation, improves contact resistance, and allows for more precise doping profiles, leading to improved performance and reliability of trench MOSFETs, particularly in small die sizes.
Implementation Method 1
growing an epitaxial layer of a first conductivity type upon a substrate of the first conductivity type
Implementation Method 2
a diffused drift region of the first conductivity type formed in the mesa area and having a higher doping concentration than the epitaxial layer
Data Source
AI summary
A trench MOSFET with diffused drift region and closed cell layout having shielded gate is disclosed, wherein closed gate trenches surrounding a deep trench in each unit cell and the shielded gate disposed in the deep trench. Trenched source-body contacts are formed between the closed gate trenches and the deep trench. The deep trench has square, rectangular, circle or hexagon shape.