Protons fix long-term problems in silicon carbide electronics
Silicon carbide (SiC) is a semiconductor material that outperforms pure silicon-based semiconductors in some applications. Primarily used in inverters, motor drives and battery chargers, SiC devices offer benefits such as high energy density and reduced power loss at high frequencies even at high voltages. . Although these properties and its relatively low cost make SiC a promising candidate in various areas of the semiconductor market, its poor long-term reliability has been a problem. insurmountable barriers over the past two decades.
One of the most pressing problems with 4H-SiC—a type of SiC with outstanding physical properties—is dipole decay. This phenomenon is due to the extension of the stacking faults in the 4H-SiC crystal. Simply put, small deviations in the crystal structure evolve over time into large defects known as “single Shockley stacking errors” that gradually degrade performance and cause the device to fail. Although a number of methods exist to mitigate this problem, they make the device fabrication process more expensive.
Fortunately, a team of researchers from Japan, led by Associate Professor Masashi Kato from the Nagoya Institute of Technology, has now found a possible solution to this problem. In their study published in the journal Scientific reportsthey present an error suppression technique called “proton implantation” that can prevent dipole degradation in 4H-SiC semiconductor wafers when applied prior to the device fabrication process.
Explaining the dynamics of this study, Dr. Kato said: “Even in recently developed SiC epitaxial wafers, dipole decay persists in the substrate layers. We want to help the industry. industry overcame this challenge and sought to develop reliable SiC devices, and, therefore, decided to investigate this approach to eliminate dipole degradation.” Associate professors Shunta Harada from Nagoya University and Hitoshi Sakane, an academic researcher from SHI-ATEX, both in Japan, also participated in this study.
Proton implantation involves “pumping” hydrogen ions into the substrate using a particle accelerator. The idea is to prevent the formation of single Shockley superposition errors by pinning local dislocations in the crystal, one of the effects of introducing proton impurities. However, proton implantation itself can damage the 4H-SiC substrate, so high-temperature annealing is used as an additional processing step to repair this damage.
The team wanted to verify if proton implantation is effective when applied prior to a device fabrication process, which typically involves a high-temperature annealing step. Accordingly, they applied proton implantation at different doses on 4H-SiC semiconductor wafers and used them to make PiN diodes.
They then analyzed the voltage-current characteristics of these diodes and compared them with those of a conventional diode without proton implantation. Finally, they took electroluminescent images of the diodes to check if stacking errors had formed.
Overall, the results are promising as the diodes that have undergone proton implantation perform as well as conventional diodes but show no signs of dipole depletion. The decrease in the voltage-current characteristics of the diodes caused by proton implantation at lower doses is negligible. However, preventing the expansion of single Shockley stacking errors is significant.
The researchers hope that the findings will help realize more reliable and cost-effective SiC devices that can reduce power consumption in trains and vehicles.
“Although the additional crafting cost of proton “The implants should be considered, they should be similar to those that arise during aluminum ion implantation, which is currently an essential step in the fabrication of 4H-SiC power devices,” said Dr Kato. “Moreover, with further optimization of the implantation conditions, it will be possible to apply this method to fabricate other types of devices based on 4H-SiC.”
Masashi Kato et al., Prevention of stacking error scaling in 4H-SiC PiN diodes by proton implantation to resolve dipole degradation, Scientific reports (2022). DOI: 10.1038/s41598-022-23691-y
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Nagoya Institute of Technology
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