Nanoscale {\eta}-NiSi formation via ion irradiation of Si/Ni/Si

TL;DR

This study demonstrates the formation of nanoscale {ta}-NiSi through ion irradiation of Si/Ni/Si layers, revealing unique oscillatory amorphization and recrystallization phenomena in silicon induced by ion beam mixing.

Contribution

It reports the first observation of oscillatory amorphization and recrystallization in silicon caused by ion irradiation, linked to Ni-induced effects, and details the formation of uniform {ta}-NiSi at nanoscale.

Findings

Recrystallized {ta}-NiSi layer formed at high ion fluence.

Oscillatory amorphization and recrystallization observed in silicon substrate.

Ni distribution influences silicon's phase transformations during irradiation.

Abstract

Nickel monosilicide (NiSi) has emerged as an excellent material of choice for source-drain contact applications below 45 nm node complementary metal-oxide-semiconductor (CMOS) technology. We have investigated the formation of nanoscale NiSi by ion irradiation of Si (~5 nm)/Ni(~15 nm)/Si, grown under ultrahigh vacuum environment. Irradiation was carried out at room temperature with 1 MeV Si+ ions. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed for analysis. With increasing ion fluence ion beam mixing occurs and more and more Si is incorporated into the Ni layer and this layer gets amorphized. At an even higher fluence a recrystallized uniform nickel monosilicide ({\eta}-NiSi) layer is formed. Several planar spacings of different Miller indices of {\eta}-NiSi have been observed in XRD and TEM. Additionally, an oscillatory amorphization and recrystallization has been observed in the substrate Si with increasing ion fluence. To our knowledge, this has never been observed in ion irradiation of bare Si in decades of work in this area. The oscillatory amorphization/recrystallization in Si is apparently Ni-induced. Irradiation displaces Ni and produces a distribution of Ni in amorphized Si. Irradiation at a higher fluence produces two recrystallized Si bands in amorphous Si with concomitant accumulation of Ni at the amorphous/crystalline interfaces. On further increase of irradiation fluence the recrystallized Si bands again pass through amorphization and recrystallization. The total thickness of recrystallized as well as amorphous Si shows an oscillatory behavior as a function of ion fluence.