Investigation of Guanidine Carbonate-Based Slurries for Chemical Mechanical Polishing of Ru/TiN Barrier Films with Minimal Corrosion

Abstract

This work describes the response of Ru/TiN barrier films to solutions of H 2 O 2, guanidine carbonate (GC) and other additives in terms of open circuit potential measurements and potentiodynamic polarization data. It was found that an aqueous solution containing 1 wt% H 2 O 2 , 0.25 wt% GC and 5 mM BTA is effective in maintaining a low corrosion potential gap of Ru and Cu at ∼15 mV at pH 9. The slurry prepared by adding 5 wt% silica to this mixture yields a Ru removal rate (RR) of 10 nm/min and a Cu RR of 12 nm/min at 2 psi polishing pressure. The effect of carbonate and guanidinium ions as well as BTA on the corrosion behavior of Ru and Cu is discussed. Dodecyl-benzene-sulfonic acid (DBSA) was also found to be an effective corrosion inhibitor of Ru in the presence of H 2 O 2 and GC based solutions at pH 9 with a good post-polished surface finish but reduced the Ru RRs to ∼ 2 nm/min. As the scaling of interconnect structures continues beyond the 22 nm technology node, the width of copper lines continues to diminish. At such lower line widths, the effect of electron scattering on conductivity increases resulting in higher resistivity and reduced current carrying capacity. One way of mitigating this effect is to reduce the barrier liner thickness to less than ∼3 nm to accommodate a thicker copper line within a given trench. In such situations, the Ta/TaN bilayer, commonly used as barrier liner in the earlier copper interconnects, 1-4 faces several challenges. These include an inability to conformally deposit a thin barrier film in the high aspect ratio trenches which inevitably leads to void formation in the subsequently deposited copper seed layer. To surmount such challenges, Ruthenium (Ru) and several of its alloys have been proposed as alternative barrier liners.5-10 These have the added advantage of direct electroplating of Cu, eliminating the need for a Cu seed layer.However, Ru is not an ideal barrier as it forms columnar structures and, hence, provides diffusion paths for Cu at the grain boundaries 11,12 and also has poor adherence to the underlying dielectrics which may result in the peeling of these films during polishing.13,14 Therefore, a thin (∼1 nm) TaN or TiN layer is deposited between Ru and the dielectric interface which helps in both negating the columnar growth of Ru and improving the adherence between Ru and the dielectric. 13,14 Of these, Ru/TiN structures were chosen for the analysis here since Amanapu et al. 15 have shown that these films are polished faster compared to those on TaN. They attributed this to the difference in the crystalline orientation of the Ru films deposited on TiN and TaN layers.It is very difficult to obtain adequate removal rates (RR) of Ru during planarization since it is a noble and hard material, making it a challenge to achieve the desired RR selectivity to Cu at the barrier interface. Moreover, Ru is more cathodic to Cu since its standard reduction potential (0.21 V vs. SCE) is greater than that of Cu (0.1 V vs. SCE). Hence, there is a high possibility of Cu corro...

Potassium Permanganate-Based Slurry to Reduce the Galvanic Corrosion of the Cu/Ru/TiN Barrier Liner Stack during CMP in the BEOL Interconnects

“…The higher RR of Ru compared to that obtained by Sagi et al 19 who worked with H 2 O 2 instead of KMnO 4 , both in the presence of GC, suggests that the mechanical strength of Ru oxide-guanidinium complex layer is reduced by the Mn oxides/hydroxides present in it. In the case of Cu, as was shown already, 19 Table II. The E CORR gap for Ru/Cu couple is ∼55 mV while for Ru/TiN couple is 0 mV.…”

“…[36][37][38][39][40] Indeed, this is the case for the three potentiodynamic plots in Figure 6. Different corrosion potentials in the presence and absence of external voltage and associated problems with the calculation of I CORR in the presence of an external voltage were reported by several authors [36][37][38][39] and, in particular, with the GC system by Rock et al 40 and Sagi et al 19 Hence, similar to these authors, instead of I CORR , we chose to rely on linear polarization resistance (Rp) determined from potentiodynamic data obtained with the scan range limited to E OC ± 20 mV to obtain a qualitative measure of the corrosion currents and, therefore, the surface reactivity. 19,[36][37][38][39][40] Rp is determined from the experimental current (i) vs overpotential (η) graphs using the definition 19,[36][37][38][39][40] …”

“…The 1/Rp values of Ru and TiN remained more or less the same at 140 μS/cm 2 and 186 μS/cm 2 , respectively (as shown in Figure 11 and Table II), but increased for Cu from ∼82 μS/cm 2 to ∼255 μS/cm 2 ( Figure 11 and Table II complexes. 19,41,42 Also, the E CORR gap of Ru/Cu couple remains high at ∼50 mV and has potential to induce galvanic corrosion and needs to be reduced. Furthermore, the RR ratio of Ru:Cu is only ∼0.6 in this GC containing dispersion and needs to be closer to ∼1 as a higher Cu removal rate leads to undesirable dishing in the Cu trenches.…”

Micron-thick highly conductive PEDOT films synthesized via self-inhibited polymerization: roles of anions

“…Compared to conventional oxidants, the three new oxidants have more basic anions (pKa4 − 1.8). [39][40][41][42] Interestingly, the VPP time of PEDOT:DBSA and PEDOT:BNSA extends to 425 min and the CP time of PEDOT:CSA to 25 s. Because of the high basicity of the CSA and BNSA anions, extra acid is needed to accelerate the reaction (Supplementary Table S2). High S 2 σ was achieved in films obtained through mild reaction conditions using the oxidants containing WBAs, particularly FeDBSA 3 , without any additives.…”

Chemical Mechanical Polishing and Planarization of Mn-Based Barrier/Ru Liner Films in Cu Interconnects for Advanced Metallization Nodes

“…With that goal in mind, we investigated the polishing and electrochemical behavior of the relevant Mn-based barrier/Ru liner stack using silica based dispersions and various additives. For convenience, in the following the Mn-based films will be addressed simply as Mn films.Cu and Ru polishing behavior 12-18 and related corrosion issues [19][20][21][22][23] for barrier applications have been studied by several authors. Among these, Amanapu et al 18 showed that the underlying substrate can modify the crystalline orientation of thin Ru films with a corresponding influence on the RR of Ru films.…”