Effect of stress on silicide formation kinetics in thin film titanium–selicon system

Abstract

As the CMOS device feature size scales below sub 0.5 μm, formation of low resistive C54 phase TiSi 2 becomes increasingly difficult. With the decreasing silicide thickness and shrinking line widths, unrealistic thermal budgets are required to transform the high resistive C49 phase to the low resistive C54 phase [Kittl J.A., Prinslow D.A., Apte P.P., Das M.F. Appl Phys Lett 1995;67:2308; Saenger K.L., Cabral Jr. C., Clevenger L.A., Roy R.A., Wind S. J Appl Phys 1995;78:7040; Clevenger L.A., Cabral Jr. C., Roy R.A., Lavoie C., Viswanathan R., Saenger K.L., Jordon-Sweet J., Morales G., Ludwig Jr. K.L., Stephenson G.B. Mater Res Soc Symp Proc 1996;402:257]. This phenomenon of sluggish C49 to C54 phase transformation, according to various researchers, has been attributed to the reduced nucleation density. i.e. relatively larger grained C49 phase formed as compared to the vertical and the lateral dimensions of the silicide. Motivated by this technologically important C49 to C54 phase transformation, we have studied the ways in which a nonthermal parameter such as the `stress state', of the Ti–Si diffusion couple, could affect the silicide formation and the C49 to C54 phase transformation. The stress state of the Ti–Si diffusion couple was varied in two different ways: (i) stress state of the Ti film and (ii) stress state of the silicon surface. The stress state of the Ti film was varied by changing the deposition parameters during sputtering. We have observed that thin titanium films, when deposited under compressive stress, result in a silicide film with a small grained C49 phase. Hence, an enhanced C49 to C54 phase transformation was observed for compressive Ti films as compared to tensile Ti films. The activation energies associated with the C49 to C54 transformation in these thin compressive Ti films are about 2 to 2.25 eV lower than those commonly reported in the literature [Kittl J.A., Prinslow D.A., Apte P.P., Das M.F. Appl Phys Lett 1995;67:2308; Saenger K.L., Cabral Jr. C., Clevenger L.A., Roy R.A., Wind S. J Appl Phys 1995;78:7040; Clevenger L.A., Cabral Jr. C., Roy R.A., Lavoie C., Viswanathan R., Saenger K.L., Jordon-Sweet J., Morales G., Ludwig Jr. K.L., Stephenson G.B. Mater Res Soc Symp Proc 1996;402:257; Matsubara Y., Horiuchi T., Okumura K. Appl Phys Lett 1993;62:2634; Mann R.W., Clevenger L.A. J Electrochem Soc 1994;141:1347; Ma Z., Allen L.H. Phys Rev B 1994;49:13501] for similar annealing conditions. The stress state of the silicon surface was varied by implanting low doses (1e13/cm 2) of three different species such as boron, arsenic and phosphorus. As in the case of compressive Ti films, the C49 to C54 transformation was found to be enhanced for the silicon surface with the lowest compressive stress.