Oxidation of NiSi and Ni(Pt)Si: Molecular vs. Atomic Oxygen
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1074-I03-04
Oxidation of NiSi and Ni(Pt)Si: Molecular vs. Atomic Oxygen Sudha Manandhar1, Brian Copp2, Chiranjeevi Vamala2, and Jeffry Kelber1,2 1 Department of Chemistry, University of North Texas, Denton, TX, 76203 2 Department of Materials Science and Engineering, University of North Texas, Denton, TX, 76201 ABSTRACT X-ray photoelectron spectroscopy (XPS) has been used to characterize the reactivities of clean, stoichiometric NiSi and Ni(Pt)Si films on n-doped Si(100) substrates in O2, and in O+O2 environments. In the presence of O+O2, NiSi and Ni(Pt)Si form Ni silicate and Pt silicate overlayers, respectively, with oxide/silicate overlayer thicknesses of 41(4) Å (NiSi) and 28(3) Å (Ni(Pt)Si) after 4.5x104 L exposure. Exposure to O2 yields, for each material, a ~7(1) Å thick SiO2 overlayer without transition metal oxidation. O+O2 induces rapid Si oxidation, formation of metal-rich silicides, and then the kinetically-driven oxidation of Ni or Pt to form a silicate. This may pose significant processing problems in silicate removal and unwanted Ni diffusion into other areas of the device. INTRODUCTION NiSi and Pt-doped NiSi (Ni(Pt)Si) are of significant interest for source, drain and gate metallization for the 65 nm node and beyond [1]. Previous studies of NiSi [2-4] demonstrate that plasma processing results in Ni oxidation. XPS data acquired after oxidation, but without uncontrolled sample exposure to ambient, can yield considerable insight into the mechanisms of oxidation in different environments. The data presented here compare the response of NiSi and Ni(Pt)Si to O+O2 (i.e., combined atomic and molecular oxygen flux) vs. pure O2 environments at ambient sample temperature (300 K -320 K). This account compares only films formed on ndoped Si(100) substrates. A detailed account of Ni(Pt)Si oxidation is presented elsewhere [5], while possible effects of p- vs. n-substrate doping will be dealt with in a future publication. Studies were carried out with controlled sample transfer under vacuum between processing and analytical environments. This is in contrast to some previous studies [1,3,4,6] and permits a greater degree of control of initial surface composition, and therefore a more detailed understanding of relevant surface chemistry. EXPERIMENT Studies were carried out in a system comprising separate processing and analysis chambers. The turbomolecularly pumped analysis chamber (base pressure = 2 x 10-10 Torr) was equipped with a hemispherical analyzer, polychromatic dual anode x-ray source, ion gun for sample cleaning, reverse-view LEED, and sample heating/cooling capability (150 K -1300 K). The turbo-pumped processing chamber (base pressure = 5 x 10-9 Torr) was equipped with a thermally shielded catalytic cracker for producing free radicals by dissociation on the inner surface of an Ir tube heated to 1300 K by electron bombardment. Pressure in each chamber was
monitored by a nude ion gauge out of line of site to the sample, and gases were admitted to the chamber through manual leak valves. The chambers were
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