SiC Superjunction Structure for Low On-Resistance and High Breakdown
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Solution Overview
Problem
Conventional superjunction silicon carbide semiconductor devices face a tradeoff between reducing on-resistance and maintaining breakdown voltage, as the thickness of the n-type drift layer affects both parameters, and the distribution of carrier concentration is influenced by substrate warpage and temperature during epitaxial growth.
Innovation Solution
The use of phosphorus ions for ion implantation in the n-type column regions and aluminum ions in the p-type column regions, combined with epitaxial growth, to form a parallel pn structure that balances dopant concentrations and reduces carrier spreading resistance, while increasing the depth of dopant penetration and ion implantation damage to improve carrier distribution and reduce switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the n-type drift layer is decreased to reduce on-resistance, then the on-resistance is reduced, but the breakdown voltage decreases
Solution Approach 1:
The drift layer is segmented into multiple n-type drift layers with different thicknesses and doping concentrations. The first n-type drift layer has a smaller thickness and higher doping concentration, while the second n-type drift layer has a larger thickness and lower doping concentration. This segmentation allows the device to achieve low on-resistance through the thinner first layer while maintaining high breakdown voltage through the thicker second layer.
Solution Approach 2:
Different regions of the drift layer structure are assigned different local qualities in terms of thickness and doping concentration. The first n-type drift layer positioned near the surface has optimized parameters for low resistance, while the second n-type drift layer positioned deeper provides optimized parameters for high voltage sustenance. This local quality differentiation resolves the tradeoff between on-resistance and breakdown voltage.
2Reliability
If the thickness of the n-type drift layer is increased to increase breakdown voltage, then the breakdown voltage is increased, but the on-resistance increases
Solution Approach 1:
The drift layer is divided into multiple segments with different characteristics. The second n-type drift layer provides the necessary thickness for high breakdown voltage, while the first n-type drift layer compensates for the resistance increase by providing a low-resistance path near the surface. This segmentation strategy allows independent optimization of voltage and resistance parameters.
Solution Approach 2:
The drift layer structure functions as a composite material system where the first and second n-type drift layers are combined to achieve properties that neither layer could provide alone. The composite structure integrates the voltage-sustaining capability of the thicker second layer with the low-resistance property of the thinner first layer, effectively resolving the tradeoff contradiction.
3Manufacturing precision
If ion implantation is performed to increase dopant concentration and reduce on-resistance, then the doping concentration is increased and on-resistance is reduced, but substrate warpage and temperature distribution affect the uniformity of dopant distribution
Solution Approach 1:
Ion implantation is performed as a preliminary action before the epitaxial growth of the second n-type drift layer. This preliminary ion implantation establishes the doping concentration profile in the first n-type drift layer region, and the subsequent epitaxial growth process uniformly distributes dopants throughout the second layer. This preliminary action approach reduces the direct impact of substrate warpage and temperature distribution on the final dopant uniformity.
Solution Approach 2:
The invention changes the processing parameters by performing ion implantation at a specific stage before completing the drift layer formation, and then using epitaxial growth with controlled temperature and atmosphere to uniformly distribute dopants. This parameter change strategy mitigates the adverse effects of substrate warpage and temperature distribution, achieving more uniform dopant concentration despite the inherent process complexities.
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
This approach enhances the in-plane distribution of carrier concentration, reduces switching losses, and suppresses conduction degradation, allowing for higher breakdown voltage and lower on-resistance in silicon carbide semiconductor devices, particularly in high-voltage applications like power converting equipment.
Implementation Method 1
The plurality of first column regions and the plurality of second column regions contain phosphorus as a dopant thereof
Implementation Method 2
combining epitaxial growth and ion implantation
Data Source
AI summary
A superjunction silicon carbide semiconductor device has a silicon carbide semiconductor substrate, a first semiconductor layer of the first conductivity type, a parallel pn region with first column regions of the first conductivity type and second column regions of a second conductivity type disposed therein repeatedly alternating with one another, a second semiconductor layer of the first conductivity type, a third semiconductor layer of the second conductivity type, a first semiconductor region of the first conductivity type, trenches, a second semiconductor region of the second conductivity type, a third semiconductor region of the second conductivity type, gate electrodes, and an electrode. The first column regions and the second column regions contain phosphorus as a dopant.