Chemical reaction and silicide formation at the Pt/Si interface

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 L_2,3VV 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.