Chemical reaction and silicide formation at the Pt/Si interface

Abstract

Surface spectroscopy (UPS and AES) and transmission electron microscopy (TEM) techniques have been used to study the chemical behavior of interfaces formed by Pt deposition (~ 0.1-100 Å) on atomically clean Si(111) and Si(100) surfaces prepared by sputter/annealing. As shown by the annealing behavior of a thicker (~ 100 Å) overlayer, growth of an intermixed phase begins only at ~ 200–300 °C and leads to formation of a product which is stable to 500 °C. TEM observations show this product to be single-phase PtSi. The UPS spectrum for PtSi is dominated by two distinct peaks at —3.7 and —6.2 eV, while the Si L2,3VV AES spectrum also show features characteristic of silicidelike bonding. With annealing above ~400 °C, excess Si segregates to the top surface of the PtSi overlayer. Upon 25 °C deposition, both UPS and AES show clear indications of strong Pt/Si intermixing across the interface from the submonolayer range to ~ 40 Å. In the low (submonolayer to few monolayer) coverage range at temperatures >300 °C, the new chemical bonds formed are similar but not identical to those for the PtSi. With increasing coverage the UPS peaks shift toward the Fermi energy as expected for a more Pt-rich environment. For these thin layers (~ 5–30 Å), TEM shows the presence of both Pt and silicide. Upon annealing to ~ 300–400 °C, a mixture of PtSi with some Pt2Si is observed and the UPS and AES features become typical of PtSi; these features remain unchanged with higher temperature annealing until the Si surface segregation becomes appreciable. © 1984, American Vacuum Society. All rights reserved.