Ion Beam Irradiation of Metal Films on SiO 2
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ION BEAM IRRADIATION OF METAL FILMS ON SiO 2 G. J. CLARK,* J. E. E. BAGLIN,* F. M. d'HEURLE,* C. W. WHITE,** G. FARLOW,** and J. NARAYAN** *IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598; **Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830
ABSTRACT Ion beam irradiation of metal film/Si0 2 interfaces causes reactions when the metals are those chemically capable of reducing Si0 2 . These reactions result in the formation of metal rich silicides in the region of the interface and an increase in the adhesion of the film to the substrate. For other nonreactive metals ion irradiation causes lateral transport of metal atoms resulting in the formation of an island structure. The results obtained by ion irradiation are compared with previous studies of high temperature thermal processing of metal films on Si0 2 . INTRODUCTION Metallization schemes to improve the adhesion of deposited metal films on insulating substrates are important for the fabrication of electrically conductive paths on insulating substrates for semiconductor device fabrication. In many cases, interfacial reactions between the film and the insulating substrate can lead to improved adhesion. High temperature thermal processing of metal films deposited on SiO 2 has been shown previously to result in the formation of metal rich silicides at the metal/SiO 2 interface [1-51. Ion beam irradiation has previously been used to form silicides in the case of metal films deposited on silicon [6]. Also for some time people involved in fabricating Si devices [71 have been aware that a blanket implant of energetic ions through a metal film with a high melting point and consequently large atomic mobility would cause the formation of a silicide where the metal film was in contact with Si, whereas no reaction was observed in adjacent areas where the film is in contact with Si0 2 . In the work reported here, we have used ion beam irradiation as a low temperature processing technique to cause interface reactions between deposited metal films and an underlying SiO 2 substrate. Although there has been some previous work [8] on the chemical effects in ion beam mixing of transition metals on SiO 2 , to our knowledge this is the first reported use of ion beam irradiation to induce metal/Si0 2 contact reactions. In a number of cases, the result of the induced contact reactions is an increase in the adhesion of the film to the SiO 2 substrate.
EXPERIMENTAL
Thin metal films (- 300 A thick) of Nb, V, Ti, Hf, Zr, Cu and Pd were deposited in an oil free vacuum system onto thermally oxidized silicon wafers. The Si0 2 thickness was - 2000 A. Ion beam irradiation was carried out in 10-7 Torr vacuum at room temperature using Xe+ ions at energies of 200-350 keV. For each irradiation, the ion energy was chosen such that the peak in the deposited energy distribution would be in the vicinity of the metal/SiO 2 interface. A dose of Ix10 ions/cm was used for each irradiation. Following ion beam mixing, the films were examined by Rutherford backsc
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