High temperature stability of PtSi formed by reaction of metal with silicon or by cosputtering

Abstract

High temperature stability of platinum silicide, formed by reacting metal with silicon or by cosputtering metal and silicon in a desired ratio, has been studied. The properties of films, thus formed, were examined as a function of annealing temperature using a resistance measuring technique, Rutherford backscattering, Auger and x-ray analyses, transmission and scanning electron microscopic techniques, and by measuring forward current-voltge (I-V) characteristics of the silicide n-silicon Schottky diodes. It is shown that cosputtering silicon rich alloys prevents agglomeration of the silicide, but increases the resistivity and decreases the Schottky barrier height of the film. Platinum silicide dissolves increasing amounts of silicon on high temperature (700–1000 °C) treatments causing considerable degradation of properties. Although cosputtering silicon rich alloys reduces this behavior, electrical properties such as forward I-V characteristics still degrade due to high temperature anneals.

Synthesis and thermal stability of Pt3Si, Pt2Si, and PtSi films grown by e-beam co-evaporation

“…The values for Pt 2 Si and PtSi are roughly half of those for Pt 2 Si and PtSi films formed by solid-state reaction [6], which generally yields larger grain sizes compared to co-deposition [29]. On the other hand, the values are quite consistent with the conductivities of annealed Pt silicide films grown by co-sputtering [21].…”

“…Murarka et al [21] also observed a Pt 3 Si phase present in codeposited PteSi films with X Si ¼ 0.25, which were grown by room-temperature dc magnetron sputtering onto poly-Si and SiO 2 substrates. However, unlike the co-evaporated films presented here, a transformation of the Pt 3 Si phase to either PtSi or Pt 12 Si 5 phases was observed (for films grown on poly-Si and SiO 2 , respectively) when these films were annealed at 400e900 C in a forming gas mixture.…”

“…830 C) is found at the Pt-rich eutectic situated at X Si ¼ 0.23. It is assumed that near 830 C, melting of Pt 3 Si-like regions produce spots of enhanced diffusion that serve as activation sites for film dewetting and lead to the decrease in film conductivities reportedly observed around 800e900 C [21,75].…”

“…Co-deposition of metal and Si has been suggested as a means of minimizing the consumption of substrate Si during metal silicide formation (silicidation), and this approach has been demonstrated for coevaporated Pt silicides in a series of experiments by Eizenberg and Tu [18e20], in which PteSi films with X Si ranging from 0.25 to 0.50 were co-deposited on n-type Si and annealed; the results indicated that contact depth can be directly controlled via deposited film compositions. Secondly, the tunability of film composition affords the deposition of Si-rich (off-stoichiometric) films in which the excess Si offers a safety margin during thermal oxidation, as has been demonstrated for co-sputtered PteSi thin films by Murarka et al [21]. Finally, by co-depositing films with appropriate metalto-Si ratios, crystalline phases that do not form during selfaligned silicide growth can be targeted; as is characteristic of diffusion-limited solid-state reactions, only a subset of all thermodynamically stable phases can kinetically form throughout the duration of the reaction.…”

“…Thus, growth by electron beam co-evaporation is proposed as an approach to suppress agglomeration effects in PteSi thin films. Indeed, these films are shown herein to be morphologically stable at temperatures up to 1000 C and for vacuum annealing times well beyond where solid-state reacted Pt silicides routinely agglomerate [21].…”