Protons solve a long-standing problem in silicon carbide electronics – ScienceDaily

Silicon Carbide (SiC) is a semiconductor material that outperforms pure silicon-based semiconductors in several applications. Mainly used in inverters, motor drives and battery chargers, SiC devices offer advantages such as high power density and reduced power losses at high frequencies, even at high voltages. Although these properties and its relatively low cost make SiC a promising competitor in various sectors of the semiconductor market, its poor long-term reliability has been an insurmountable obstacle for the past two decades.

One of the most pressing issues with 4H-SiC—a type of SiC with superior physical properties—is bipolar degradation. This phenomenon is caused by the expansion of stacking faults in 4H-SiC crystals. Simply put, small dislocations in the crystal structure grow over time into large defects called “single Shockley stacking faults” that progressively degrade performance and lead to device failure. Although some methods exist to mitigate this problem, they add cost to the device manufacturing process.

Fortunately, a team of researchers from Japan, led by Associate Professor Masashi Kato of the Nagoya Institute of Technology, has now found a workable solution to this problem. In their study, available online on November 5, 2022 and published in the journal Scientific Reports on November 5, 2022, they present an error suppression technique called “proton implantation” that can prevent bipolar degradation in 4H-SiC semiconductor wafers, when applied prior to the device manufacturing process. dr Kato explains the motivation for this study: “Even with the recently developed SiC epitaxial wafers, the bipolar degradation in the substrate layers persists. We wanted to help the industry overcome this challenge and find a way to develop reliable SiC devices, so we decided to investigate this method to eliminate bipolar degradation.” Associate Professor Shunta Harada from Nagoya University also participated in this study and Hitoshi Sakane, an academic researcher from SHI-ATEX, both in Japan.

In proton implantation, hydrogen ions are “injected” into the substrate using a particle accelerator. The idea is to prevent the formation of single Shockley stacking faults by pinning partial dislocations in the crystal, one of the effects of introducing proton impurities. However, the 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 research team wanted to verify whether proton implantation would be effective if applied prior to the device manufacturing process, which typically includes a high-temperature annealing step. Accordingly, they applied proton implantation with different doses to 4H-SiC wafers and used them to fabricate PiN diodes. They then analyzed the current-voltage characteristics of these diodes and compared them with those of a normal diode without proton implantation. Finally, they took electroluminescence images of the diodes to check whether stacking faults had formed or not.

Overall, the results were very promising, as diodes that underwent proton implantation performed just as well as normal diodes, but with no signs of bipolar degradation. The degradation of the current-voltage characteristics of the diodes caused by proton implantation at lower doses was not significant. However, the suppression of the extent of individual Shockley stack faults was significant.

Researchers hope these results will help realize more reliable and less expensive SiC devices that can reduce power consumption in trains and vehicles. “Although the additional manufacturing costs of proton implantation should be considered, they would be similar to aluminum ion implantation, which is currently an essential step in the fabrication of 4H-SiC power devices.” speculates dr. cat. “Furthermore, with further optimization of the implantation conditions, there is an opportunity to apply this process to the fabrication of other types of 4H-SiC-based devices.”

Hopefully, these results will help unlock the full potential of SiC as a semiconductor material for powering next-generation electronics.

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Materials provided by Nagoya Institute of Technology. Note: Content can be edited for style and length.

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