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

Abstract

Chemical mechanical polishing (CMP) behavior of Cu/Ru/TiN barrier liner stack was investigated with a slurry comprising of silica abrasives, potassium permanganate (KMnO 4 ) , guanidine carbonate (GC) and benzotriazole (BTA) in the alkaline region. The corrosion and polishing behavior of the Cu, Ru and TiN films in the solution consisting of the above additives were characterized by open circuit potential and potentiodynamic measurements, polishing rates, dissolution rates and contact angle measurements. A slurry comprising of 10 mM KMnO 4 , 1 wt% GC and 5 wt% Silica at pH 10 has shown adequate polish rates as well as low individual film corrosion. However, 1 mM BTA was needed to maintain the E CORR of both the Cu/Ru and Ru/TiN couples at <20 mV essential to inhibit any galvanic corrosion while still maintaining low corrosion rates for Cu, Ru and TiN films. The removal rate ratio of Ru:Cu with the optimized slurry was ∼0.8, minimizing the possibility of dishing. As the scaling of trenches and vias continue, making high volume manufacturing of 14 nm devices feasible, deposition of defect free Cu seed layer upon the TaN/Ta barrier liner 1,2 used in earlier generation Cu interconnects has become a challenge. At the reduced trench widths of ∼50 nm or less associated with these devices, it is not possible to deposit a conformal Cu seed layer without voids.3-6 Also, as the TaN/Ta barrier liner is scaled to ∼5 nm or less in thickness, its increased electrical resistance causes the resistance-capacitance delay to increase. Hence, the advantages of replacing it with several other barrier and barrier liner candidate materials and have been investigated by various authors.7-9 These include Ru, Co and Mn and their alloys.Among these, Ru has good barrier properties with a high melting point of 2310• C. 7 Due to its low resistivity (∼7 μ cm) and excellent wettability characteristics with Cu, direct electroplating of Cu is possible eliminating the need for a seed layer.7 However, it was found that atomic layer deposited (ALD) Ru alone is not a good diffusion barrier due to its columnar growth structure that provides diffusion paths for Cu at the grain boundaries 10,11 and poor adherence to underlying dielectric.12 Hence, it was proposed that a thin TaN barrier layer (∼2-3 nm) be first deposited followed by a ∼1-2 nm thick Ru liner, alleviating the need for a Cu seed layer. 13,14 However, the higher resistivity of TaN (∼200 μ cm) is still a concern.Recently, Amanapu et al. 15 showed that Ru films deposited on TiN, another commonly used barrier layer 16,17 with a lower resistivity of ∼130 μ cm, have higher removal rates (RRs) compared to those deposited on TaN due to the difference in the crystalline orientation of the Ru films deposited on these two materials. Hence, a thin Ru liner (∼2 nm) over a thin TiN barrier layer (∼2 nm), both deposited by ALD, has been proposed as a promising barrier liner for future Cu interconnects.In these structures, since Ru is in contact with both TiN and Cu (Figure 1), there is a possibility of g...

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

“…The measured RRs and DRs of Ru on Mn/BD films with this same dispersion are ∼17 nm/min and <1 nm/min, respectively, similar to rates reported by Amanapu et al 18 and Sagi et al 22,23 for Ru films on TiN substrate. So, not surprisingly, when the crystalline structure of the Ru film on Mn/BD substrate was determined using GIXRD technique, we found the same mix of (002) and (101) orientations (see Figure 2) that was also reported by Amanapu et al 18 Thus it appears that the crystalline orientation is the primary factor in determining the RRs of the Ru films in this particular slurry.…”

“…RRs, DRs and XRD analysis of Ru on Mn substrates.-As stated earlier, in our experiments here, we used the same 10 mMKMnO 4 + 1 wt% guanidine carbonate (GC) + 1 mM BTA (referred to as the reference solution the following) solutions at pH 10 that was shown by Sagi et al 23 to minimize galvanic corrosion between Ru and Cu and as well yielded adequate RRs of Ru on TiN and Cu films when 5 wt% silica abrasives were added to the above solution. The measured RRs and DRs of Ru on Mn/BD films with this same dispersion are ∼17 nm/min and <1 nm/min, respectively, similar to rates reported by Amanapu et al 18 and Sagi et al 22,23 for Ru films on TiN substrate.…”

“…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.…”

“…Of course, the very thin Mn films posed challenges for characterization and polish rate measurements and required the use of X-ray fluorescence (XRF) technique. Recently, Sagi et al 23 used a KMnO 4 -based silica dispersion consisting of guanidine carbonate (GC) and benzotriazole (BTA) as additives to polish Cu and Ru and reported minimal galvanic corrosion and adequate RR selectivities. Hence, we use the same slurry as a starting point here and show that it meets the targets for all these structures.…”

Potassium Oleate as a Dissolution and Corrosion Inhibitor during Chemical Mechanical Planarization of Chemical Vapor Deposited Co Films for Interconnect Applications

“…In addition, Co structures must be polished at a sufficiently low (≤ 2 psi) down-pressure to avoid structural deformation of the underlying ultralow-k materials and to avoid erosion 17 ( Figure 1). Furthermore, during barrier polishing, galvanic corrosion 12,16,[18][19][20][21] can occur when electrochemically different materials are electrically connected and immersed in an electrolyte, as shown in Figure 2. The standard reduction potentials of Co/Co 2+ and Ti/Ti 2+ couples are −0.28 V and −1.63 V, respectively.…”