Amorphous Ti-Si-N Barrier Metal for Cu Metallization on Ulsis
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We have investigated the physical properties of Ti-Si-N films for future Cu metallization on ULSIs. Our Ti-Si-N films were found to be amorphous by X-ray diffraction measurements. Thermal stability of the amorphous structure was confirmed, even after annealing at 600°C for 30 minutes in an Ar ambient. The atomic composition of the film was identified as Ti:Si:N=1:0.6:1.6 by chemical analysis. The film stress was found to be tensile and 0.3GPa. The electrical resistivity was about 0.5mfcm at room temperature. The effectiveness of the film as a diffusion barrier was evaluated by n+/p and p+/n junction leakage measurements. The junction depth was 0.2/ym and the contact area was 300x80/um'. No degradation of leakage characteristics was observed for these diodes, even after annealing at 600°C for 30 minutes in an N2/H2 ambient. These results demonstrate that amorphous Ti-Si-N barrier metal is a promising candidate for application in deep-submicron ULSIs.
INTRODUCTION
The aluminum alloy interconnect is the most commonly used ULSI metallization. However, as device dimensions approach the deep submicron regime, several problems arise. Higher speed and higher electromigration reliability are required, and consequently a new metallization material with lower resistivity and higher resistance to electromigration is needed to replace aluminum. Copper is expected to be used in place of aluminum to answer this need. However, there are several issues regarding copper metallization. Cu rapidly diffuses in Si and SiO 2 . The diffusion length is about 1mm in Si, and 3/pm in SiO 2, at 450"C for 30 minutes[5,6]. In an Si substrate, a deep level that act as a generation-recombination center is formed as a result of diffusion. This causes degradation of junction leakage characteristics. On the other hand, if the Cu diffuses in SiO 2, then MOS capacitor characteristics are degraded due to Cu ion charge trapping. To overcome these problems, a diffusion barrier is necessary between the Cu and Si or SiO 2. TiN act as a known to be good diffusion bamer for Cu, with its polycrystalline, columnar structure, and investigate its use TiN and Cu films were sequentially sputtered on to Si-substrate in the same chamber without breaking the vacuum, thus forming a Cu(400nm)/TiN(30nm)/Si-substrate structure. During annealing at 450°C for 30 minutes in an N2/H2 ambient, Cu diffused to the TiN/Si interface and a reaction between Cu and Si occurred; i.e., Cu silicide was formed at the TiN/Si interface. This degraded the diffusion barrier properties of the TiN. In order to improve the barrier effect of TiN,
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Mat. Res. Soc. Symp. Proc. Vol. 355 0 1995 Materials Research Society
Table 1 Heat of formation for metal(M) silicides and nitrides (kcal/mol) Ta
W
Mo
Ti
M5 Si 3
16.0
9.3
13.4
27.8
Table 2 Resistivity of Cu before and after annealing (YQcm)
MSi 2
28.5 22.2 26.0
32
As dep. 450C 600C
MN
59.0 ----------
80.4
M2N
64.7
17.2
1.9
1.7
1.7
16.6
a thin (1~2nm) TiOxNy layer is needed to stuff the grain boundary on the TiN surface
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