Voids in silicon power devices

Abstract

Formation and properties of voids in silicon obtained by high dose helium implants are described and discussed in view of their applications in localised lifetime engineering. Voids are stable even after huge thermal budget as observed by transmission electron microscopy analyses. Leakage measurements on p +n diodes as a function of temperature allowed us to determine the hole trap level ( ΔE=0.16 from the Fermi level above the valence band) and the generation and recombination lifetime values. To demonstrate the advantage of the method in power device applications, high-speed IGBTs were fabricated both with voids in the buffer layer or with unlocalised recombination centres. The devices with voids show a lower on-resistance and a fast turn-off behaviour. Map measurements on 150 mm silicon wafers demonstrate the good uniformity that can be reached by the method in an industrial environment.