Cobalt Polishing with Reduced Galvanic Corrosion at Copper/Cobalt Interface Using Hydrogen Peroxide as an Oxidizer in Colloidal Silica-Based Slurries

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A colloidal silica-based slurry (3-10 wt%) containing H 2 O 2 (1 wt%) and citric acid (50 mM) was found to polish chemical vapordeposited (CVD) cobalt (Co) films with removal rates (RRs) of ∼180-500 nm/min and a dissolution rate (DR) of ∼0 nm/min at pH 8 along with an RMS roughness of ∼0.5 nm and a corrosion current of ∼50 μA/cm 2 . Our results suggest that, in the presence of H 2 O 2 , the Co film surface was covered with a passive film of CoO in acidic conditions and Co 3 O 4 in alkaline conditions. However, in the presence of H 2 O 2 and citric acid in acidic conditions, formation of the soluble complex [Co(C 6 H 5 O 7 ) 2 ] 3− from abraded Co enhanced the RRs significantly. The roles of H 2 O 2 , citric acid, and silica abrasives as well as the pH on the Co material removal process are discussed and a removal mechanism is proposed. Two inhibitors namely, 1, 2, 4-Triazole (TAZ) and Benzotriazole (BTA), were tested in the presence of 50 mM citric acid at pH 8 but were found to be ineffective even at concentrations of 100 mM in reducing the E corr of Co-Ti couple to minimize galvanic corrosion that is essential when the Co/Ti structure is polished after the removal of bulk of Co and requires further study. Sub-10 nm devices face several challenges with copper as an interconnect material for back-end-of-the-line (BEOL) processes during the manufacture of integrated circuits. These include increasing resistivity with decreasing thickness, 1 non-conformal deposition at narrow trench widths ∼20 nm or less, 2 and scaling limitations of the diffusion barrier/liner.3 This led to the investigation of new trench filling materials. Cobalt is a promising alternative to meet the challenges of interconnect lines at these lower nodes for the first two metal layers M1 and M2, due to its lower resistivity at smaller dimensions (∼10 nm) compared to copper. [4][5][6] Kamineni et al. 7 proposed the use of chemical vapor deposited (CVD) cobalt to replace the widely used tungsten for local interconnects for 10 nm and smaller nodes. They emphasized two main advantages of CVD Co metallization which are a) CVD Co precursors do not damage the Ti liner enabling barrier scaling and b) it achieves void free fill in high aspect ratio features without defects, something that is difficult to achieve with a conventional physical vapor deposited (PVD) Co process. 8,9 Hence, CVD-based Co metallization is an attractive option for the technology nodes below 10 nm.CVD-based cobalt has also gained prominence in the advanced copper interconnects below 22 nm as liner [10][11][12][13][14][15][16][17] to improve adhesion between the barrier (TaN, TiN) and Cu seed layer where the Co film thickness is only ∼2 nm. Several authors 18-26 have investigated cobalt polishing for such applications where RR requirements are typically <20 nm/min and Co loss due to corrosion has to be as close to zero as possible, since even a minute loss of Co material can degrade the device reliability significantly. Hence, since the potential gap between Co and Cu is a large ∼0...

mentioning

confidence: 99%

“…Furthermore, during the polish step, the RRs for Co:Cu should be ∼1:1 to minimize Cu dishing. Therefore, the barrier slurries 27 were typically formulated in near neutral to highly alkaline 28 regions where the formation of compact and passive oxides 19,22,25 on the cobalt surface lowers the RRs and helps in minimizing corrosion.…”

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confidence: 99%

Citric Acid as a Complexing Agent in Chemical Mechanical Polishing Slurries for Cobalt Films for Interconnect Applications

Popuri

Sagi

Alety

et al. 2017

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“…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.…”

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confidence: 99%

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

Popuri

Amanapu

Ranaweera

et al. 2017

Self Cite

1,2-4 Triazole (TAZ), N-lauroylsarcosine sodium salt (NLS) and potassium oleate (PO) were tested as passivating additives to previously developed H 2 O 2 and citric acid-based silica dispersions for the polishing of chemical vapor deposited Co films for interconnect applications. In comparison to TAZ and NLS, Co corrosion currents are ∼1 to 2 order of magnitude lower (∼1-3 μA cm −2 ) at pH 7 with PO and post-polish surface quality was much better. The galvanic corrosion currents between Co-Ti and Ti-TiN couples with PO were also very low (∼0.1 μA cm −2 ), making the previously developed silica and citric acid-based dispersion, now containing PO, suitable for both bulk removal of Co (step I) and for planarizing Co/Ti/TiN structures (step II) with excellent selectivity while stopping on low-k dielectric. Langmuir adsorption isotherm model analysis showed that the standard free energies of adsorption values were ∼−40 kJ/mol for PO suggesting chemisorption. Fourier transform infra-red (FTIR) and attenuated FTIR spectroscopy data show bridging coordination between the carboxylate ligand of PO and the Co surface. Cobalt is being evaluated as a possible alternative to replace copper as an interconnect metal for 10 nm and smaller technology nodes.1-5 The fabrication of the interconnects starts with the formation of trenches in a low-k dielectric. Liner/barrier layer, typically Ti/TiN 6 , is then deposited, followed by the filling of the trenches with Co by physical vapor deposition (PVD), 7,8 chemical vapor deposition (CVD) 6 or electroplating (ECP), and then removing the metal overburden by chemical mechanical planarization (CMP). 9 To prevent damage to the underlying softer low-k structures, the polishing of the metal films has to be performed at low pressures (∼1-2 psi) requiring the chemical component of the CMP process to be more dominant. 10Typically, interconnect CMP is a two-step process.2 The first step involves removal of the overburden at ∼300 nm/min or more 11 till about 10-20 nm of it remains. Then, a second step removes the residual Co along with the underlying liner/barrier at a relatively slower rate of ∼20-50 nm/min 12,13 while, and more importantly, controlling the galvanic corrosion between Co-Ti (liner) and Ti-TiN (barrier) couples and achieving close to 1:1:1 removal rate (RR) selectivity for Co:Ti:TiN and stopping on the low-k dielectric.An important aspect of polishing the interconnects is to protect the recessed regions of the wafer surface from dissolution while the protruding areas are selectively planarized.14 Controlling dissolution during CMP minimizes dishing (Figure 1) and helps achieve effective planarization. It is known that Co corrodes very easily in aqueous solutions.15 For example, it was shown recently that pits were generated on the film surface even at neutral conditions of pH ∼7, when exposed to a mixture of H 2 O 2 and citric acid 9 caused by the soluble complexation reaction between CoO formed at the surface and the citrate ligands, creating localized cavities in the surface la...

“…8,9 Therefore, it is ideal if the galvanic corrosion current (i g ) could be measured. The general approach to estimate the i g of Cu is to measure the intersection of Cu anodic branch and Ru cathodic branch by conducting the electrochemical potentiodynamic polarization measurements, 5,10 as is schematically shown in Fig. 1a.…”

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confidence: 99%

Galvanic Corrosion Inhibitors for Cu/Ru Couple during Chemical Mechanical Polishing of Ru

Cheng

Wang

2016

Galvanic corrosion of Cu is a critical issue during the chemical mechanical polishing (CMP) process of barrier layer, especially when KIO 4 is used as the oxidant in the polishing slurry. This paper focuses on the investigation of galvanic corrosion inhibitors (BTA and 1, 2, 4-triazole) for Cu/Ru couple in the KIO 4 -based solutions. The galvanic corrosion current of Cu was directly measured, and the corrosion inhibition efficiencies (CIE) were calculated. Results show that both BTA and 1, 2, 4-triazole are effective galvanic corrosion inhibitors of Cu. The CIE of 5 mM BTA and 2 mM 1, 2, 4-triazole is up to 69.4 and 59.7, respectively. On this basis, the corrosion inhibition mechanism was proposed. BTA forms a complete and tight three-dimensional multilayer structure on Cu when the concentration is over 0.5 mM. With regard to 1, 2, 4-triazole, the protective film on Cu is two-dimensional, and excessive dosage of 1, 2, 4-triazole will reduce the stability of the surface film, as well as the corrosion inhibition efficiency of Cu. © 2016 The Electrochemical Society. [DOI: 10.1149/2.0181701jss] All rights reserved.Manuscript submitted November 1, 2016; revised manuscript received December 7, 2016. Published December 30, 2016 Corrosion plays a critical role in diverse industrial fields, and consequently, in the chemical mechanical polishing process (CMP) of the chip manufacturing process. During the CMP process, dissimilar metal surfaces are exposed to the polishing solutions, which could provide electrolyte-conducting paths for the corrosion and galvanic corrosion between Cu wiring and the directly contacting barrier metals. Ruthenium (Ru), a novel barrier layer material, the application of which is quite promising in the new generation of integrated circuit. 1A thin film of Ru (several nanometers) often lies between Cu and the low-k dielectric material, preventing interfacial diffusion between Cu and the substrate.2,3 Since the polishing solutions used in the CMP process are corrosive and abrasive, the galvanic corrosion at the Cu/Ru interface is unavoidable and detrimental. It has been reported that the resulting interfacial defects from galvanic corrosion could cause severe Cu pitting and dishing problems, and even affect the reliability of Cu interconnection. 4 Galvanic corrosion refers to the accelerated corrosion of Cu when connected with Ru, occurring at the mixed potential between the corrosion potentials of Cu and Ru under uncoupled conditions. Ru is much nobler than Cu, thus acting as the cathode and Cu acting as the anode, comparatively. It is commonly recognized that a bigger corrosion potential difference ( E cor ) between two metals will cause a serious trend of galvanic corrosion, and therefore a minimizing E cor is the goal when evaluating the corrosion inhibition effect of various inhibitors in most of the relevant researches.5-7 However, practical corrosion process is influenced by many other factors such as the area ratio of anode/cathode, and the properties of the surface passive film. 8,9 Theref...