Thermal stability study of NiSi and NiSi2 thin films

Structural and electrical characterization of the nickel silicide films formed at 850°C by rapid thermal annealing of the Ni/Si(100) films

“…5a and b, NiSi phase (bright-white) seems to be distributed uniformly on the boundaries of NiSi 2 grains and can also be observed in Si matrix (dark phases). These experimental results clearly reveal that there is island growth of NiSi 2 in NiSi matrix, in accordance with the earlier observations [6,7,25,33]. Julies et al [6] have reported through TEM and SEM measurements that the NiSi phase was stable up to about 700 • C and at about 750 • C NiSi reacted with the silicon substrate to form NiSi 2 , which seems to grow as islands in a NiSi matrix, revealing the possible growth of NiSi 2 at the expense of NiSi grains.…”

“…Therefore, thermal stability (or quality) of these films considerably degrades due to both substantial increase in Si concentration and the occurrence of the silicide islands with small visible holes, yielding a remarkable increase in sheet resistance values of the Ni-Si films thinner than 80 nm. It is also very clear from these experimental results that thinner films with thicknesses ≤80 nm are thermally less stable than thicker films of 400-105 nm and NiSi 2 agglomeration occurs at a lower temperature than both 850 • C and normally expected value of 1000 • C for NiSi 2 phase [25,28]. Therefore, in order to delay the NiSi 2 agglomeration, accompanied with grain boundary grooving, followed by grain separation and Si-rich silicide island formation, annealing temperature and/or annealing time should be fixed at <850 • C and at <60 s, respectively, for the Ni-Si films with thicknesses ≤ 42 nm.…”

“…In addition Si-enriched silicide islands with visible hole seems to precipitate finely in Si matrix. In other words, for the films with thicknesses ≤80 nm, NiSi 2 agglomeration is accompanied with grain boundary grooving, followed by grain separation and formation of Si-rich silicide islands, resulting in a dramatic increase in sheet resistance in accordance with grain grooving model [24][25][26][27]. Therefore, thermal stability (or quality) of these films considerably degrades due to both substantial increase in Si concentration and the occurrence of the silicide islands with small visible holes, yielding a remarkable increase in sheet resistance values of the Ni-Si films thinner than 80 nm.…”

“…More importantly, for the films with thicknesses 0169-4332/$ -see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.03.062 ≤50-60 nm, NiSi 2 agglomeration takes place at even lower temperatures than normally expected value of about 1000 • C [25,28]. Therefore, thickness dependence of the thermal stability of NiSi 2 thin film is crucial criterion for deep submicron devices.…”

“…However, nickel di-silicide (NiSi 2 ) formed from the low resistivity phase NiSi has the lowest lattice mismatch to Si and shows good epitaxial growth on Si [20,23]. NiSi 2 exhibits good thermal stability up to high temperatures of about 1000 • C. NiSi 2 loses adhesion to Si near its melting point of ∼993 • C [21], thereafter it starts to agglomerate with grain boundary grooving, followed by grain separation and formation of silicide islands, resulting in a dramatic increase in sheet resistance [20,[24][25][26][27]. This thermal instability is the main drawback which restricts its applications in deep submicron devices.…”