Laser-induced titanium disilicide formation for submicron technologies

Abstract

A great deal of studies on thin-film silicides have been conducted over the past 15 years due to their applications in the fabrication of complementary metal oxide semiconductor devices. 1-7 Silicides can significantly reduce the contact resistance of the gate electrode and the source/drain regions as compared to nonsilicided structures. In particular, titanium disilicide (TiSi 2 ) has been used extensively as a contact material in ultra-large-scale integration technology because of its low electrical resistivity and good thermal stability. 2,3 TiSi 2 is a polymorphic material and may exist either as a high resistivity (ϳ60-90 ⍀cm) base-centered orthorhombic C49 phase or a low resistivity (ϳ15-20 ⍀cm) face-centered orthorhombic C54 phase. 2-4 When titanium reacts with silicon, the high resistivity C49 phase forms at temperatures ranging between 550 and 650°C and then transforms into the low resistivity C54 phase at annealing temperatures greater than 650°C. The C49 structure usually forms first due to a lower barrier to nucleation that has been attributed to a lower surface energy of this phase. On the other hand, the subsequent transformation from the C49 to the C54 phase is limited by a low driving force and a high activation energy. 3,4 Currently, a two-step anneal process is employed for the silicidation of titanium. The first rapid thermal anneal (RTA) step is to achieve the C49 TiSi 2 phase, and the second step is to form the low resistivity C54 TiSi 2 . However, as the width of the polysilicon line decreases to sub-0.25 m, conversion of C49 TiSi 2 to C54 phase becomes increasingly difficult. This is because the C49 to C54 phase transformation nucleates only at locations where three C49 grains intersect and the number of such intersection points (triple grain boundaries) is reduced as the gate length/polysilicon linewidth decreases. 5-7 As a consequence, the TiSi 2 films will be composed of a mixture of C49 and C54 phase and have a higher resistivity than if they are completely in the C54 phase. The need to completely form the C54 phase in submicron structures has encouraged numerous efforts to increase the density of C54 nucleation sites. They include rapid thermal processing, refractory metal ion implantation, and preamorphization of the silicon substrate prior to titanium deposition. [6][7][8] Pulsed laser beams are known to offer the advantage of rapidly heating and cooling localized areas near the top surface regions, while the underlying substrate remains at a much lower temperature. 9,10 Currently, a two-step anneal is employed for the formation of titanium selfaligned silicide (Salicide). The first rapid thermal anneal (RTA) step is to achieve the C49 TiSi 2 phase, and the second step is to form the low resistivity C54 phase. However, as the width of the polysilicon line decreases, conversion of C49 to C54 TiSi 2 becomes increasingly difficult. This is because the C49 to C54 phase transformation nucleates only at locations where three C49 grains intersect and the number of such intersection points i...

Impact of nanosecond laser energy density on the C40-TiSi2 formation and C54-TiSi2 transformation temperature

“…Pulsed laser annealing has also been investigated and several important benefits have been demonstrated. First, due to its fast ramping rate and short anneal duration, nanosecond laser annealing (UV-NLA) has been found to enable the formation of smaller grains of C49-TiSi2 than RTA [30][31][32] , increasing the density of C54-TiSi2 nucleation sites. Chen et al 30 have also reported that the transformation temperature into C54-TiSi2 can be significantly reduced by pulsed laser annealing.…”

“…investigation performed so far on leveraging UV-NLA for the formation of TiSi2 have been mainly conducted with small laser beams (diameter ~160-200 µm) with a near Gaussian shape scanning the surface with a controlled speed, resulting in a large number of pulses at the same location (typically more than 100 pulses) [30][31][32][33][34][35][36] . Such studies did not properly explore the effect of the laser energy density.…”

Formation of silicide films in advanced silicon devices using excimer pulsed laser annealing

“…It has been used to eliminate the fine line effect that occurs during the Ti silicide transformation from C49 to C54 phase. A fine and nanogram of C49 can be achieved by using single pulsed laser annealing, in which subsequently the formation temperature of C54 TiSi 2 can be lowered [44].…”