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J. Phys. Chem. B 1998, 102, 6202-6211
Chemisorption Properties and Structural Evolution of Pt-Si Intermetallic Thin Films Prepared by the Activated Adsorption of SiH4 on Pt(111) Michael S. Nashner,† Joseph C. Bondos, Michael J. Hostetler,‡ Andrew A. Gewirth,* and Ralph G. Nuzzo* School of Chemical Sciences and the Frederick Seitz Materials Research Laboratory, UniVersity of Illinois, Urbana, Illinois 61801 ReceiVed: March 10, 1998; In Final Form: May 12, 1998
The reaction of a silicon adlayer deposited on Pt(111) by chemical vapor deposition (CVD) using silane (SiH4) is described. Data from Auger electron spectroscopy (AES) reveal that Si readily diffuses into the Pt substrate and sequentially forms at least two unique intermetallic Pt-Si surface structural phases with (x7 × x7)R19.1° and (x19 × x19)R23.4° real space unit cells as characterized by low-energy electron diffraction (LEED). The chemisorption properties of each of the ordered overlayers were studied using CO as a molecular probe. Reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) studies indicated that CO was mostly limited to chemisorption at “atop” Pt sites in the x7 phase with a significant reduction of the heat of adsorption with respect to the Pt(111) surface. The x19 phase also showed a significant modification of the chemisorption properties although it is not as pronounced as that seen for the x7 structure. The relevance of these studies to intermetallic thin film growth is discussed.
Introduction Intermetallic thin films prepared via metal-semiconductor reactions are of fundamental importance in the microelectronics industry.1,2 For example, transition-metal silicides have been widely used as interconnects, gates, and contacts (Schottky barrier and Ohmic) in very large scale integration (VLSI) device technology.1-3 More recently, Pt-Si/Si Schottky diodes have emerged as promising new infrared detectors in the 3-5 µm wavelength range.4 As device dimensions have decreased, the need to develop a better understanding of the structure, physical, and chemical properties of metal-semiconductor intermetallic thin films has become increasingly important. One key to understanding the nature of the thin-film reactions used to prepare these materials lies at the metal-silicon interface, where nonequilibrium phase behavior is strongly influenced by the interfacial reaction kinetics.1-3,5-8 Most solid-solid reaction studies of the metal-semiconductor interface involve the deposition of metal thin films (
