Ion Backscattering Study of WSi2 Layer Growth in Sputtered W Contacts on Silicon
Helium ion backscattering has been used to study the reaction kinetics in samples composed of thin (~ 2200 Å) W films dc sputtered onto chemically cleaned P or B doped (111) single crystal Si substrates. At temperatures in the range 625 C to 750 C, Si is observed to migrate into the W films and form a well-defined WSi2 reaction layer. Typically, at 650 C, about 750 Å of W is consumed in four hours. A detailed comparison of the backscattering spectra indicates that the WSi2 reaction layer grows approximately as tn where n ≈ 1 during the initial growth but then decreases to n ≃ 1/2 when the W films are over 30% reacted. An activation energy which characterizes the initial stage of WSi2 layer growth is 63–71 kcal/ mole for 35% W film reaction (2000 Å WSi2 formed). This activation energy is somewhat higher than the 50 kcal/mole reported by other investigators for WSi2 layer growth at temperatures over 850 C where layer growth was observed to be governed by t1/2 kinetics. A preliminary estimate of the activation energy governing the beginning of the t1/2 layer growth observed here is 60 ± 15 kcal/mole. Prior to complete reaction of W films aged in the temperature range 625 C to 730 C, an upper limit of 2 at.% Si is observed for the Si concentration in the unreacted portion of the W film.
KeywordsActivation Energy Reaction Layer Layer Growth Growth Rate Constant Oxide Barrier
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