Lifetime control by low energy electron irradiation and hydrogen annealing [Si power diodes]

Lifetime control in silicon power devices is required to reduce turn-off time and energy loss during switching. High energy (2 MeV range) electron and proton irradiations have been used for this purpose. We developed a new method of introducing defects by using low energy (270 keV) electron irradiation and hydrogen annealing. It was generally considered that 270 keV energy electrons are not strong enough to introduce defects. It is thought that the silicon knocked out by a low energy electron stays around the vacancy, and that the silicon can come back to the vacancy very easily. However, if the defect is filled by some other atom, such as hydrogen, the knocked-out silicon can not come back easily, and a higher and more stable defect concentration can be expected. This is why we used hydrogen annealing after low energy electron irradiation. We annealed the irradiated diodes in nitrogen or hydrogen atmosphere. The diodes annealed in hydrogen showed a significant lifetime reduction. This was manifested by increase in forward diode voltage, and decrease in turn-off charge.