Role of 1,2,4-Triazole as a Passivating Agent for Cobalt during Post-Chemical Mechanical Planarization Cleaning

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...

Section: Choice Of Inhibitormentioning

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

“…Several authors [18][19][20][21][22][23][24][25][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 ∼0.61 V, it is very important to lower this to ∼10-20 mV.…”

mentioning

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

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...

“…Using polishing and cleaning formulations at alkaline pH values galvanic corrosion can be highly suppressed. 12,13 However, under CMP conditions, due to abrasion of passive oxide layers galvanic corrosion may continue to occur but the repassivation kinetics of the corroding surface would determine if corrosion is likely to continue after the cessation of polishing.…”

Section: Galvanic Corrosion Issuesmentioning

confidence: 99%

Review—Understanding and Controlling Electrochemical Effects in Wet Processing

Raghavan

Chiang

2016

Electrochemical techniques have long been used in understanding and improving the performance of various wet chemical processing steps such as etching, cleaning, passivation and rinsing used in integrated circuit (IC) manufacturing. The objective of this paper is to provide a few examples of how electrochemical techniques can be used to probe some important areas in wet processing. It is not intended to be an exhaustive review of techniques and problems reported in the literature.