LETTER TO THE EDITOR: Ni/Ag metallization for SiGe HBTs using a Ni silicide contact
We developed a self-aligned low-temperature process for the production of SiGe hetero bipolar transistors (HBTs) using a new metallization scheme with Ni/Ag taking advantage of the low specific resistivity of Ag and good contact resistance and low silicon consumption of the Ni silicide. Gummel plots of fabricated HBTs show sufficiently good behaviour. The formation of Ni silicide over temperature (325-500 °C) in a rapid thermal process system is studied. At temperatures above 425 °C a rather smooth film of monosilicide NiSi is formed. The resistivity of the thin (110 nm) NiSi was found to be excellent (11 µΩ cm) compared with bulk values. The contact resistance to n- and p-type silicon of 5×1019 cm-3 is determined. Formation of self-aligned Ni silicide/Ag contacts is investigated and compared to non-self-aligned contacts.