Effects of Liner Metal and CMP Slurry Oxidizer on Copper Galvanic Corrosion

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...

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

Sagi

Amanapu

Teugels

et al. 2014

“…That is, when polishing slurry contains KIO 4 as oxidant, the galvanic corrosion of Cu is much severe, which is in line with the previous researches. 20 Therefore, the galvanic corrosion inhibition properties of inhibitors will be discussed below using KIO 4 -based solutions. and 1, 2, 4-triazole at different concentrations.…”

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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...

“…However, as per some of the works reported, Co seems to have better properties as compared to Ru. [6][7][8][9][10][11][12] It does not emit any toxic gases unlike Ru, which releases toxic RuO 4 gas in acidic medium. Moreover, Ru being a hard metal in nature (hardness of 6.5 Mohs), it is hard to find chemicals that provide higher polish rates.…”

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Formulation of Sodium Hypochlorite Based Slurry for Copper-Cobalt Chemical Mechanical Planarization Process

Hazarika

Rajaraman

2020

Chemical mechanical planarization of interconnect metal copper and barrier metal cobalt using NaOCl based slurry is investigated in this study. The slurry consists of 2 wt% silica, 0.5 wt% NaOCl and 5 mM BTA as inhibitor. The formulated slurry gives a combination of low etch rates and comparatively fair removal rates along with selectivity of ∼1:1.006 at pH 9, which are desired to be used in semiconductor industry. A decrease in removal rates for both Cu and Co is observed as the pH regime changes from acidic to alkaline. At acidic pH, the passive layer if any formed on the surface becomes very unstable resulting in higher polish rates. However, at neutral and alkaline medium, the passivation layer comprising of Co (II) oxide/hydroxides is formed which subsequently decreases the polish rate. A highly stable and dense passivation layer of Co (III) oxides comprising of mostly Co 3 O 4 and CoOOH is formed at the highly alkaline region explaining the reason behind lower removal rates. The variation in turntable speed and down force pressure does not have any significant impact on selectivity obtained at optimum conditions. XRD analysis reveals the formation of oxide on Co surface after etching at pH 9.