Surface-complex films of guanidine on tantalum nitride electrochemically characterized for applications in chemical mechanical planarization

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...

“…[38][39][40][41][42][43] R p is determined from the experimental current (i) vs overpotential (η) graphs using the definition [38][39][40][41][42]44 …”

Section: Resultsmentioning

confidence: 99%

“…Effect of the addition of DBSA.-Previously, DBSA, an anionic surfactant, was used as a corrosion inhibitor during the CMP of Cu 46 and Ta 42 since it forms a protective film on them. Hence, we explored the effect of DBSA in inhibiting Ru corrosion.…”

Section: Resultsmentioning

confidence: 99%

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

Sagi

Amanapu

Teugels

et al. 2014

“…During the potentiodynamic measurements, these multiple reactions occurring at high over potentials can affect the anodic and cathodic plots making it difficult to find well defined linear regions for calculating the I CORR using Tafel analysis. [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.…”

Section: 25mentioning

confidence: 98%

“…[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] …”

Section: 25mentioning

confidence: 98%

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

Sagi

Amanapu

Alety

et al. 2016

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...

“…EIS can only be performed under strictly steady state conditions, and thus requires the exclusion of surface abrasion by abrasive particles and/or a polishing pad during such measurements. 9,10 Nevertheless, steady-state EIS measurements can yield electrical equivalent circuit (EEC) models that are useful for probing the intrinsic CMP chemistry of a metal in the presence of various slurry components. The OCP and the polarization response characteristics of the metals considered for Cu/low-k interconnects generally exhibit strong response to tribological conditions, and depending on the polishing parameters used, can notably vary between the polishing and non-polishing situations.…”

mentioning

confidence: 99%

Tribo-Electrochemical Characterization of Ru, Ta and Cu CMP Systems Using Percarbonate Based Solutions

Shi

Simpson

Roy

2015

Self Cite

Defect-control is a critical requirement for chemical mechanical planarization (CMP) of the ultrathin diffusion barriers considered for the new Cu-interconnects. The challenging task of developing advanced CMP slurries for such systems can be aided by electrochemical evaluations of model CMP schemes under tribological conditions. The present work uses this strategy to characterize an alkaline slurry formulation aimed at minimizing galvanic corrosion in the CMP systems involving Ru, Ta (barrier metals) and Cu (wiring metal). This slurry is based on percarbonate and guanidine additives, and the test metals are polycrystalline disc samples. A particular goal of this study is to explore the essential analytical aspects of evaluating CMP systems in the triboelectrochemical approach. The CMP specific surface reactions are characterized by potentiodynamic polarization and open circuit voltage measurements, performed both in the presence and in the absence of polishing, and by employing abrasive free as well as abrasive (colloidal SiO 2 ) added solutions. The findings of these experiments are further checked by using impedance spectroscopy. The electrochemical mixed potential steps of the CMP promoting reactions are analyzed, and the removable surface species formed by these reactions are discussed. The recent developments in the manufacturing of advanced interconnects have largely centered on the Cu/low-k technology, where the processing challenges are coupled with those of material selection. The introduction of mechanically fragile low-k dielectrics has set strict limits on the usable down-pressure of chemical mechanical planarization (CMP) used in the processing of Cu interconnects. This in turn has driven the strategies for material removal more toward the chemical considerations of CMP, and less reliant on mechanical abrasion.2,3 At the same time, the CMP chemistries of the relatively unconventional new barrier materials have presented other challenges, because in the slurry environment, they often have appeared chemically too inert 4 or too corrosive.5 If the CMP chemistries for these new materials are not properly controlled, the processed wafer can develop surface defects due to erosion and galvanic corrosion activated by the wet CMP process. Such defects are detrimental to device performance, and this issue is particularly relevant for the CMP of ultrathin (< 5 nm) barrier films, where defect-control is often more critical than achieving high rates of material removal. Due to these reasons, the tasks of designing the slurry chemistries for metal CMP have become progressively more complex during recent years. This specific aspect of CMP consumable challenges can be addressed to a large extent by employing laboratory scale evaluations of slurry compositions with electrochemical measurements. The present work is based on this approach.The role of electrochemical reactions (and hence the applicability of electro-analytical tests in this context) is integrated in the overall mechanism of chemically promoted metal-C...