Direct Cu Electrodeposition on the Ni Alloy Barrier Layer Prepared By Electroless Deposition on SiO2

The formation of barrier layer by electroless deposition (ELD) takes great interest for the next generation ULSI metallization, because ELD contains various advantages including low process cost, low process temperature, and the excellent conformality[1,2]. Especially, the research on the Ni or Co based alloy barrier layer is widely conducted as the barrier layer property of the film was superior[1-3].

Some researches realized the all-wet metallization by using ELD barrier layer, however, the formation of the conformal Cu seed layer is still a big issue before the electrodeposition (ED) of Cu. The Cu seed layer formation on the ELD barrier layer usually conducted by ELD of Cu and/or the displacement reaction between Cu and barrier metal. In the point of the productivity of the device, however, the elimination of the Cu seed layer formation step would be preferred. Hence, in this study, we investigated the direct ED of Cu without Cu seed layer on the electroless NiWP barrier layer.

NiWP barrier layer was formed on a Pd-activated SiO₂ substrate by ELD in an acidic electrolyte. The SiO₂substrate was activated by the Pd nanocolloids immobilized via the self-assembled monolayer on the surface. Prior to the direct ED of Cu, the native oxide of the NiWP barrier layer was removed by the coulometric reduction method.

The linear sweep voltammetry (LSV) for the Cu reduction was investigated on the electroless NiWP barrier layer after the native oxide removal. As can be seen in Figure 1, the charge transfer limiting region of Cu deposition was separated into two stages: the Cu nucleation stage and the Cu film growth stage. However, because the resistivity of the electroless NiWP barrier layer was high, it was difficult to form a smooth and uniform Cu film by means of the one-step potentiostatic method. The low nucleation density of Cu or the non-uniform Cu deposition was problematic at low or high overpotential case, respectively (Figure 2a and 2b)[4]. On the other hand, the two-step potentiostatic method could successfully deposit the smooth and uniform Cu film, because the high overpotential induced higher nucleation of Cu and the low overpotential resulted in the smooth and uniform film growth (Figure 2c).

The barrier layer property was studied using the ED Cu / ELD NiWP / SiO₂ stacked specimen. The adhesion between each layer (ELD NiWP / SiO₂and ED Cu / ELD NiWP) was excellent, which was evaluated by the tape test method. The electroless NiWP barrier layer could endure the 500°C and 30 min of thermal treatment. The minimal change in sheet resistance and the absence of silicide-related peaks in XRD analysis attested the thermal stability of the barrier layer. In addition, the patterned specimen covered with the electroless NiWP barrier layer was successfully filled by the direct ED of Cu with the conventional additive combination for the gap-filling. 

In this symposium, the direct Cu ED process on the electroless NiWP barrier layer will be addressed in detail. In addition, we will also discuss the trench filling by the proposed method.

References

1. T. Osaka, H. Aramaki, M. Yoshino, K. Ueno, I. Matsuda, and Y. Shacham-Diamand, J. Electrochem. Soc., 156, H707 (2009).

2. H.-C. Koo, S. K. Cho, O. J. Kwon, M.-W. Suh, Y. Im, and J. J. Kim, J. Electrochem. Soc., 156, D236 (2009).

3. M. Yoshino, Y. Nonaka, J. Sasano, I. Matsuda, Y. Shacham-Diamand, T. Osaka, Electrochim. Acta, 51, 916 (2005).

4. S. Choe, M. J. Kim, H. C. Kim, T. Lim, K. J. Park, S. K. Cho, S.-K. Kim, and J. J. Kim, J. Electrochem. Soc., 160, D202 (2013).

Figure Captions

Figure 1. LSV on a electroless NiWP barrier layer deposited on a SiO₂ substrate (scan rate = 10 mV s^-1).

Figure 2. Potential profile and the surface morphology of the directly electrodeposited Cu on the electroless NiWP barrier layer.