Crystalline intermediate phases in the formation of epitaxial NiSi2 on Si(111)

We have studied the structure and formation of nickel overlayers on Si(111) using Auger and reflection high-energy electron diffraction microanalysis in a custom-built UHV scanning electron microscope. A novel technique of generating a continuous range of coverages in a single deposition is described. Two crystalline phases were found as intermediate stages in the growth of epitaxial NiSi2: Ni2Si delta phase forms for a substrate temperature of 185 °C and coverage of 13 Å in the orientation Ni2Si (020)∥Si(111), and Ni2Si(002)∥Si(220). Also, nickel crystallites form for a substrate temperature of 185 °C and coverage of 28 Å in the orientation Ni(220)∥Si(111) and Ni(002)∥Si(220). The nickel crystallites are small and highly strained. The possible role of these two phases as precursors in the formation of NiSi2 is discussed.