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REACTION RATE KINETICS AND FILM TEXTURES OF PALLADIUM SILICIDE FORMED ON HYDROGENATED AMORPHOUS SILICON N. R. MANNING*, HAYDN CHEN, J. R. ABELSON, AND L. H. ALLEN Department of Materials Science and Engineering, University of lllinois,Urbana, IL 61801 *Current address: The Arnold Engineering Company, Marengo, IL 60152 ABSTRACT The reaction rate kinetics of the thin film solid-state reaction between 120 nm of Pd and 100 or 300 nm of a-Si:H(18at%) to form Pd2Si were studied in situ using x-ray diffraction and four-point probe resistivity measurements during isothermal annealing. These two techniques yielded activation energies and prefactors of Ea=1. 36±:0.11 eV with ko--4.29 cm 2/sec for the xray diffraction experiments; and Ea=0.97±0.22 eV with ko=3.42x10-4 cm 2/sec for the resistivity measurements. The activation energy and prefactor obtained from the c-Si substrate of the resistivity measurements yielded Ea=l. 4 l±0.3 1 eV and k0=10.6 cm 2/sec. Comparisons showed that the silicide formed from the a-Si:H reacted approximately 1.4 times faster than the silicide formed from the c-Si in the same sample, but three times faster than silicide formed on pure cSi(111). The crystalline texture and grain size of the metal and silicide films were examined. Introduction Thin films of transition metals and their corresponding silicides possess properties that have made them very attractive in VLSI fabrication [1]. Palladium silicide is one that has been of particular interest. Besides being relatively chemically inert, it exhibits some interesting crystallographic properties. When formed by annealing deposited Pd metal film on Si(1 11), an epitaxial crystalline Pd2Si forms with the basal plane of the hexagonal structure parallel to the Si(1 11) planes with a linear mismatch of 1.8%. However, using any other orientation or form of Si results in polycrystalline Pd2Si [1,2]. The silicide reaction has been found to be a diffusion limited reaction by many researchers [3,4,5], following the equation Tt2"To2=k(tf-t0)

(1)

where Tf=the film thickness at time tf, To=the film thickness at time to, and k=the rate constant. The rate constant is defined as k=koexp(-Ea/kBT)

(2)

where ko is a prefactor, Ea is the activation energy of Pd2Si formation, kB is the Boltzmann constant, and T is the absolute temperature. The unique electronic properties of hydrogenated amorphous silicon (a-Si:H) have made it one of the industry's more interesting recent materials. Hydrogen incorporated into the film allows the electrical properties to be controlled by dopants [6]. In amorphous Si the dangling

Mat. Res. Soc. Symp. Proc. Vol. 311. ©1993 Materials Research Society

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bonds appear as electronic states in the energy gap. The hydrogen passivates the dangling bonds in the structure, allowing structural relaxation in the amorphous silicon to occur, eliminating the electronic states in the gap. By depositing the a-Si:H using reactive d.c. magnetron sputtering, the hydrogen content in the film can be determined by the partial pressure of the hydrogen