Wide-Bandgap Trench MOSFET Structure for Gate Oxide Breakdown
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Solution Overview
Problem
The concentration of electric field at the bottom portion of the gate trench in trench gate MOSFETs leads to dielectric breakdown, reducing the breakdown voltage and affecting channel characteristics due to high potential differences between the gate and drain electrodes.
Innovation Solution
A semiconductor device with a wide bandgap semiconductor layer featuring a gate trench structure, including a first breakdown voltage holding region on the edge portion of the gate trench and a second conductivity type drift region, which generates a depletion layer to reduce the electric field on the gate insulating film, while maintaining controlled channel characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a trench gate structure is used to form the gate electrode, then the device can be manufactured with standard processes, but electric field concentration at the bottom portion of the gate trench causes dielectric breakdown and reduces breakdown voltage
Solution Approach 1:
The patent applies local quality by creating a breakdown voltage holding region with different impurity concentration specifically at the bottom portion of the gate trench where electric field concentration occurs. This localized modification of material properties (higher p-type impurity concentration) addresses the field concentration problem at the critical location without changing the overall trench gate structure, thereby maintaining manufacturability while improving breakdown voltage resistance.
2Reliability
If p-type impurity is implanted into the bottom portion of the gate trench to relax field concentration, then breakdown voltage resistance improves, but channel characteristics become difficult to control due to impurity intrusion into the channel region
Solution Approach 1:
The patent uses local quality by confining the p-type impurity region specifically to the bottom portion of the gate trench below the channel formation region. This spatial localization ensures that the impurity enhances breakdown voltage resistance at the critical field concentration point while preventing intrusion into the channel region, thus maintaining precise channel characteristic control.
Solution Approach 2:
The patent applies segmentation by dividing the gate trench into distinct functional regions: the channel formation region on the sidewall and the breakdown voltage holding region at the bottom portion. This segmentation allows independent optimization of each region's properties - the sidewall maintains low impurity for channel control while the bottom receives high impurity concentration for field relaxation.
3Reliability
If the depletion layer spreads excessively in the drift region, then electric field distribution improves, but channel characteristics and device performance deteriorate
Solution Approach 1:
The patent applies local quality by creating the breakdown voltage holding region with specific impurity concentration and dimensions localized at the bottom portion of the gate trench. This localized structure generates a depletion layer that is confined to the drift region below the channel, improving electric field distribution without allowing excessive depletion layer spread that would intrude into the channel formation region and deteriorate channel characteristics.
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 suppresses dielectric breakdown and enhances breakdown voltage resistance by distributing equipotential surfaces away from the gate insulating film, preventing excessive depletion layer spread and maintaining channel performance.
Implementation Method 1
a second conductivity type drift region, which generates a depletion layer to reduce the electric field on the gate insulating film
Implementation Method 2
it may be possible to relax this type of field concentration by implanting a p-type impurity into the bottom portion of the gate trench
Data Source
AI summary
A semiconductor device includes a semiconductor layer made of a wide bandgap semiconductor and including a gate trench; a gate insulating film formed on the gate trench; and a gate electrode embedded in the gate trench to be opposed to the semiconductor layer through the gate insulating film. The semiconductor layer includes a first conductivity type source region; a second conductivity type body region; a first conductivity type drift region; a second conductivity type first breakdown voltage holding region; a source trench passing through the first conductivity type source region and the second conductivity type body region from the front surface and reaching a drain region; and a second conductivity type second breakdown voltage region selectively formed on an edge portion of the source trench where the sidewall and the bottom wall thereof intersect with each other in a parallel region of the source trench.