The Effect of Layer Thickness on the Reaction Kinetics of Nickel/Silicon Multilayer Films
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THE EFFECT OF LAYER THICKNESS ON THE REACTION KINETICS OF NICKEL/SILICON MULTILAYER FILMS L.A. Clevenger, C.V. Thompson and R.C. Cammarata Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 K.N. Tu IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 ABSTRACT Differential Scanning Calorimetry (DSC) and Debye-Scherrer X-ray diffraction have been used to characterize silicide formation in nickel/amorphous-silicon multilayer films. Two different Ni:Si layer thickness ratios were investigated, 3:11 and 1:1. Films with layer thickness ratio of 3:11 first formed Ni2 i followed by NiSi at a temperature 250 C higher. Multilayer films with 1:1 thickness ratios formed only Ni2Si. Activation energies for these reaction were determined and found to be in agreement with previous results on bilayer films. The temperature at which Ni 2Si formation was complete in the 1:1 films was found to decrease with decreasing layer thickness. Analysis of this phenomenon allowed determination of the interdiffusivity during silicide formation, also in agreement with previous results. Films with 1:1 layer thickness ratios and layer thickness of 125 A or less were found to sometimes undergo explosive silicidation. This presumably occurs because the rate of heat generation at the reacting interfaces exceeds the rate of heat dissipation. INTRODUCTION The kinetics of single layer nickel/crystalline-silicon reactions have been investigated by many workers '2 usually using Rutherford Backscattering and Seemann-Bohlin X-ray diffraction. In this study, freestanding nickel/amorphous-silicon multilayer films were prepared and silicidation was studied using Differential Scanning Calorimetry coupled with Debye-Scherrer Xray diffraction for phase identification. Use of multilayer films allows observation of the heat released from many reacting interfaces at once. It also allows easy variation of the overall atomic concentration ratio as well as the individual layer thicknesses so that the effects of these parameters on reaction kinetics can be studied. EXPERIMENTAL Freestanding multilayer thin films were prepared using alternating electron-beam evaporation of nickel and silicon at room temperature onto photoresist coated glass slides. Each film was composed of a total of ten layers (5 Ni and 75 Si). The base pressure before the evaporation was never higher than 1x10- torr. After deposition, the glass slides were soaked in acetone to dissolve away the photoresist and remove the multilayer films. Most of the films were then heated in the DSC for thermal analysis and X-ray sample preparation.
Mat. Res. Soc. Symp. Proc. Vol. 103. -1988 Materials Research Society
192
Atomic concentration ratios of NiSi 2 and Ni 2 Si (thickness ratios of 3:11 and 1:1 respectively) were chosen in order to determine the effects of the overall atomic concentration on the silicide formation sequence as well as the had nickel layer Films which formed NiSi 2 kinetics of the reactions. thicknesses
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