The use of aluminium ion implantation for power semiconductor devices

Abstract

Because of its high diffusivity in silicon, aluminium is best suited for the deep diffusions often required in high voltage power semiconductor devices. The ion implantation technique allows the reproducible low dosage doping necessary, e.g., for the new concepts of junction termination systems.The most important draw back of the use of aluminium as a p-type dopant in silicon is its low electrical activity after the anneal. The main problem therefore is the enhancement of the aluminium yield (the amount of electrically active Al with respect to the implanted dose). Sheet resistivity and spreading resistance measurements after various annealing processes are presented as well as a triple implant process, which allows to enhance the aluminium yield.

On a Novel Source Technology for Deep Aluminum Diffusion for Silicon Power Electronics

“…During subsequent drive‐in processes, the redistribution of aluminum in the silicon was characterized by a significant out‐diffusion so that a large fraction of the predeposited aluminum was lost. With the intention to improve reproducibility and uniformity, the predeposition steps in vacuum were replaced for many applications by even more expensive ion implantation processes . Ion implantation has also the advantage that photoresist can be used for masking areas which should not be doped.…”

“…During postimplantation annealing, aluminum will precipitate if its concentration exceeds the solubility limit . For practical applications, this limits the maximum concentration of as‐implanted profiles in float‐zone (FZ) wafers to about 2 10 19 cm −3 . In Czochralski‐grown (CZ) wafers, this limit would be even smaller due to the detrimental influence of oxygen on the formation of precipitates .…”

“…With the intention to improve reproducibility and uniformity, the predeposition steps in vacuum were replaced for many applications by even more expensive ion implantation processes. [4] Ion implantation has also the advantage that photoresist can be used for masking areas which should not be doped. During postimplantation annealing, aluminum will precipitate if its concentration exceeds the solubility limit.…”

“…[5] For practical applications, this limits the maximum concentration of as-implanted profiles in float-zone (FZ) wafers to about 2 Â 10 19 cm À3 . [4,6] In Czochralski-grown (CZ) wafers, this limit would be even smaller due to the detrimental influence of oxygen on the formation of precipitates. [6] Using multiply charged ions, implantation energies of up to 600 keV are possible for conventional implanters.…”