Accelerating Effect of Additives in Damascene Electrodeposition

The void-free filling in damascene electrodeposition strongly depends upon the accelerating effect of additive agents. SPS is commonly used accelerator which works in the presence of cuprous and chloride ion. Although several models have been reported to explain the effect of SPS, the precise mechanism of acceleration has not clearly been understood. 

 Chloride ion also has an accelerating effect through the electron bridge as reported by Nagy et. al. [1]. The bottom-up filling in damascene electrodeposition is expected to be achieved by the accelerating effects of SPS and chloride ion in combination with the suppressing effect of PEG around the via opening. Recently, Kondo et. al.studied the detailed mechanism of acceleration of SPS  in relation to the distribution of cuprous ion . They also studied the dependence of the acceleration on the feature size, especially, the width of the trenches [4]. They measured the distribution of cuprous ion using the rotating ring disk technique and discussed that the filling process can be explained in terms of the cuprous ion distribution. 

The purpose of the present work is to study the effects of chloride ion and SPS paying attention to the distribution of cuprous ion to clarify the mechanism of acceleration. We first studied the dependence of the current density on the width of the trench in the presence of chloride ion . The acceleration effect due to the electron bridge is taken into account.

The simulation system and additive modeling are the same as those used in our previous works. The system is a two dimensional square lattice and the Cu deposition is simulated by the Kinetic Monte Carlo (KMC) method. The electrode consists of through-mask trench. The basic reactions are 

Cu²⁺ + e^- → Cu⁺   (1)

Cu⁺ +  e^- →  Cu    (2)

　                      

The rate constant of reaction (2) is about 1000 times larger than that of reaction (1).  Therefore, reaction (1) is the rate determining step [5]. Chloride ions have the effect of accelerating reaction (1) due to the electron bridge, which leads to the overall acceleration of Cu deposition.  We have performed a series of KMC simulations of trench filling for different values of the width of the trench. 

It is shown that for the small system (the width is much smaller than 1μm)  the current density increases as the trench width becomes small. This is consistent with the experimental results. For the trench width ~ 10μm, however, the difference in the current density becomes small as the system becomes large. These results are explained by the distribution of cupric and cuprous ions.  The mechanism of acceleration is discussed from the simulation data. 

References

[1] Z.Nagy; J.Electrochem.Soc. 142, L87 (1995).

[2] K.Kondo, T.Matsumoto, K.Watanabe; J.Electrochem.Soc.151,C250 (2004).

[3] K.Kondo, T.Nakamura, N.Okamoto; J.Appl.Electrochem. 39, 1789 (2009).

[4] K.Kondo, H.Kouta, M.Yokoi, N.Okamoto, T.Saito and T.Hayashi;  Electrochem.

 Lett.  3 (4) D3 (2014).

[5] N.Tantavichet, M.D.Pritzker; J. Electrochem. Soc., 150, C665 (2003).