Trench MOS Termination Structure for High Voltage
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Solution Overview
Problem
Conventional termination structures for high voltage Schottky diodes face challenges in maintaining ideal breakdown voltage due to electric field crowding and degradation from hot carrier injection and parasitic charges, with existing designs failing to effectively distribute electric fields and shield charge traps.
Innovation Solution
A termination structure for a power transistor is designed with a termination trench, a doped region, and a MOS gate, featuring an implantation region that extends beneath the MOS gate and termination oxide layer, which reduces electric field peaks and enhances breakdown voltage by enlarging the depletion region and shielding parasitic charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional termination structures are used, then manufacturing is simplified, but electric field crowding occurs at the edge of the device causing breakdown voltage to be dramatically reduced
Solution Approach 1:
The termination region is segmented into multiple functional zones: a first termination region with a first breakdown voltage and a second termination region with a second breakdown voltage. This segmentation allows different portions of the termination region to handle different electric field strengths, preventing field crowding while maintaining manufacturability through standardized processing steps.
Solution Approach 2:
Different doping concentrations and structures are applied to different locations within the termination region. The first termination region has a first doping concentration while the second termination region has a second doping concentration, creating local quality variations that optimize electric field distribution at specific device edges without requiring complete redesign of the entire termination structure.
2Loss of energy
If the drift region doping is increased to reduce on-state resistance, then on-state resistance decreases, but reverse breakdown voltage is adversely affected
Solution Approach 1:
The invention transitions from a single-dimensional doping profile to a multi-dimensional structure with vertically stacked drift regions of different doping concentrations. The first drift region and second drift region are arranged in series vertically, allowing current to flow through both regions. This enables the device to achieve low on-state resistance through the highly doped first drift region while maintaining high breakdown voltage through the combined effect of both drift regions in series.
Solution Approach 2:
The drift region is constructed as a composite structure with two distinct regions having different doping concentrations. The first drift region has a first doping concentration optimized for low resistance, while the second drift region has a second doping concentration optimized for high breakdown voltage. This composite structure allows the device to simultaneously achieve both low on-state resistance and high reverse breakdown voltage by combining the advantages of differently doped 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 proposed termination structure achieves a breakdown voltage of up to 95% of the ideal value while improving immunity to hot carrier injection degradation by reducing orthogonal electric fields and peak electric field presence near the active region.
Implementation Method 1
When reverse biased, the insulated conductive areas cause a lateral depletion of into the drift region, which modifies the distribution of the equipotential surfaces in this layer.
Implementation Method 2
the insulated conductive areas cause a lateral depletion of into the drift region
Implementation Method 3
A termination structure for a power transistor is designed with a termination trench, a doped region, and a MOS gate, featuring an implantation region that extends beneath the MOS gate and termination oxide layer, which reduces electric field peaks and enhances breakdown voltage by enlarging the depletion region and shielding parasitic charges.
Implementation Method 4
enlarging the depletion region and shielding parasitic charges
Implementation Method 5
A metal layer or a metal silicide layer forms a Schottky contact with the lightly-doped drift region and forms the diode anode.
Data Source
AI summary
A termination structure is provided for a power transistor. The termination structure includes a semiconductor substrate having an active region and a termination region. The substrate has a first type of conductivity. A termination trench is located in the termination region and extends from a boundary of the active region toward an edge of the semiconductor substrate. A doped region having a second type of conductivity is disposed in the substrate below the termination trench. A MOS gate is formed on a sidewall adjacent the boundary. The doped region extends from below a portion of the MOS gate spaced apart from the boundary toward the edge of the semiconductor substrate. A termination structure oxide layer is formed on the termination trench covering a portion of the MOS gate and extends toward the edge of the substrate. A first conductive layer is formed on a backside surface of the semiconductor substrate and a second conductive layer is formed atop the active region, an exposed portion of the MOS gate, and extends to cover a portion of the termination structure oxide layer.