Raman Spectroscopic Evaluation of Silicides Formed with a Scanned Electron Beam
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RAMAN SPECTROSCOPIC EVALUATION SCANNED ELECTRON BEAM
541
OF SILICIDES FORMED WITH A
R. J. NEMANICH, T. W. SIGMON*, N. M. JOHNSON, M. D. MOYER, and S. S. LAUt Xerox Palo Alto Research Center, Palo Alto, California 94304 *Stanford Electronics Laboratories, Stanford, California 94305 tUniversity of California, San Diego, La Jolla, California 92093 ABSTRACT Raman scattering and Rutherford backscattering are used to study the products of SEM processing of Pd and Pt thin films on Si(100) substrates. The RBS measurements indicate the compositional depth profile of the resulting silicide while the Raman scattering indicates the crystal structure. For both cases it is found that the resultant silicide is dominated by Pd 2 Si (or Pt 2 Si) structures but evidence of deviations are also noted. INTRODUCTION Metal silicides are of technological interest for low-resistivity interconnects and electrical contacts in silicon integrated circuits. Conventional silicide formation involves furnace annealing the deposited metal film to activate a solid-solid reaction between the metal and silicon [1]. For IC applications, film patterning and etching are also important aspects of silicide formation [2]. Energy-beam annealing has been proposed as a novel alternative for silicide formation, with results having been reported for pulse-laser annealing [3,4], pulsed electron-beam annealing [5], CW laser annealing [6], and scanned electron-beam annealing [7]. The novel features of energy beams for silicide formation are the spatial and temporal localizations of the deposited energy. This permits selective silicide formation with high spatial resolution (- 1 Mm) which offers increased flexibility for IC processing and may lead to new techniques for patterning and etching. In this article we present results from a Raman spectroscopic evaluation of silicide formation induced with a scanned electron beam. Previous physical studies of silicide formation with energy beams have utilized principally Rutherford backscattering (RBS), x-ray diffraction, and optical microscopy for film evaluation. Here we demonstrate the unique features of Raman spectroscopy for silicide studies, with results for platinum and palladium silicides formed with the electron beam in a scanning electron microscope (SEM). The complementary nature of Raman spectroscopy and RBS is highlighted. The Raman scattering or inelastic light scattering technique is sensitive to the long wavelength excitations of the solid [8]. For the cases described here the phonon excitations are probed. Generally the Raman spectrum of a crystal exhibits sharp lines at frequency shifts corresponding to the k = 0 optic phonons. The Raman activity and polarization properties of each mode are determined from the crystal symmetries. The case of light scattering from crystals is to be contrasted with amorphous materials where a continuous spectrum is observed which reflects the density of vibrational states modified only by matrix element effects. Hence the Raman spectra can be analyzed at several levels; f
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