REAL-TIME SPECTROELLIPSOMETRY INVESTIGATION OF THE INTERACTION OF SILANE WITH A PD THIN-FILM - FORMATION OF PALLADIUM SILICIDES

We present the application of spectroscopic phase modulated ellipsomet ry to the study of both ultrafast and slow processes of the interactio n of silane (SiH4) With thin films of palladium. Changes of the optica l properties of thin films exposed to different SiH4 fluxes are monito red by in situ single wavelength ellipsometry in the case of high flux es which lead to ultrafast processes and by in situ spectroscopic elli psometry at low fluxes and slow kinetics. The study of the interaction of SiH4 With Pd at 250-degrees-C reveals the complicated character of the process which depends on the flux of silane and leads to the form ation of palladium disilicide, palladium hydrides, and an intrinsic po rosity. A qualitative model of the process is proposed. The initial st age of the reaction at high fluxes of SiH, is dominated by a grain bou ndary diffusion of SiH4 inside the Pd film, followed by the catalytic decomposition of SiH4 and a strong process of an intrinsic formation o f porosity. This fast process (duration of 10 ms) proceeds through the formation of a metastable Pd-rich phase. The appearance of the intrin sic porosity enhances the diffusion of SiH4 inside the Pd film, which results in a drastic acceleration of the silicide formation. At low Si H4 fluxes the characteristic time of the reaction increases up to some tens of minutes and proceeds through the formation of both silicide a nd palladium hydride.