Dynamical study of ion-beam oxidation: Incorporation of hyperthermal oxygen ions into silicon oxide thin films

The complex dynamics associated with ion-beam oxidation of Si(001) by 5–100-eV ${\mathrm{O}}^{+}$ and ${\mathrm{O}}_2^{+}$ is studied in situ. Room-temperature oxidation of silicon under ultrahigh vacuum conditions is accomplished with a mass-selected, monoenergetic, oxygen ion beam. Initially, a thin ${\mathrm{Si}}^{16}{\mathrm{O}}_x$ film is prepared by bombarding clean Si(001) with hyperthermal energy ${}^{16}{\mathrm{O}}^{+}.$ Switching the incident ion flux to ${}^{18}{\mathrm{O}}^{+}$ or ${}^{36}{\mathrm{O}}_2^{+}$ creates an isotopically labeled tracer for monitoring the rate at which subsequent incident oxygen ions are incorporated into the topmost layer of the growing silicon oxide film. The cross section for oxygen incorporation is found to depend strongly on (i) the conditions under which the underlying oxide layer was grown, (ii) the kinetic energy of the incorporating ion, and (iii) whether the incident ion is atomic or molecular oxygen.