Japan invents new fault suppression technology to solve the double click degradation problem of SiC

2024-01-22

Silicon carbide (SiC), as a semiconductor material, is superior to pure silicon-based semiconductors in various applications and is widely used in power inverters, motor drivers, and battery chargers. SiC devices have advantages such as high power density and reduced high-frequency power loss, which can be maintained even under high voltage, and have relatively low costs. However, SiC still has long-term reliability issues.

One of the most pressing issues for 4H SiC (a SiC with excellent physical properties) is bipolar degradation. This phenomenon is caused by the extension of stacking faults in 4H SiC crystals. In short, small dislocations in crystal structures can become large defects of single Shockley stacking faults over time, gradually reducing performance and leading to device failure. Although there are currently some methods to alleviate this defect, it actually makes the equipment manufacturing process more expensive.

According to foreign media reports, a Japanese research team led by Associate Professor Masashi Kato from Nagoya Institute of Technology has found a feasible solution to the problem and has published it in the journal Scientific Reports. Researchers have proposed a fault suppression technique called proton injection, which can prevent bipolar degradation of 4H SiC semiconductor chips before the device manufacturing process.

Proton injection involves using a particle accelerator to "inject" hydrogen ions into the substrate. This idea is to prevent the formation of individual Shockley stacking faults by fixing some dislocations in the crystal, which is also one of the effects of introducing proton impurities. However, proton injection itself can damage the 4H SiC substrate, so high-temperature annealing is used as an additional treatment step to repair this damage.

The research team wants to verify whether proton injection is effective when applied before the equipment manufacturing process, which typically includes a high-temperature annealing step. Therefore, researchers performed different doses of proton injection on 4H SiC wafers and used them to manufacture PiN diodes.

Then the researchers analyzed the current voltage characteristics of these diodes and compared them with ordinary diodes without proton injection. Finally, researchers captured electroluminescent images of diodes to check for the formation of stacking faults.

The result is good because the performance of the diode injected with protons is as good as that of a regular diode, but there is no sign of bipolar degradation. The degradation of diode current voltage characteristics caused by lower dose proton injection is not significant. However, the suppression of the expansion of individual Shockley stacking faults is very significant.

Researchers hope that these findings will help achieve more reliable and cost-effective SiC devices, thereby reducing the power consumption of trains and vehicles.

Dr. Kato said, "Although the additional manufacturing cost of proton implantation should be considered, it is similar to the cost generated by aluminum ion implantation, which is currently an important step in manufacturing 4H SiC power devices. In addition, with further optimization of injection conditions, this method may be applied to manufacture other types of 4H SiC based devices."

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