Editors' Choice—In Situ Electrochemical Evaluation of Post-CMP Cleaning Reactions for Cobalt and Copper Films under Brushing Conditions

Abstract

The sub-10 nm technology node has introduced significant chemical complexities in the associated processing steps of chemical mechanical planarization (CMP), and this has correspondingly convoluted the post-CMP cleaning (PCMPC) protocols. Focusing on selected cleaning chemistries, the present work demonstrates an in-situ tribo-electrochemical approach to developing fundamental knowledge of the PCMPC mechanisms for such systems. As model samples, the experiments use cobalt and copper thin films, deposited on wafer coupons, and treated in an alkaline CMP solution of acetate, H2O2 and benzotriazole. These samples are subsequently studied in an alkaline PCMPC solution of oxalic acid, designed for cleaning both Co and Cu. The surface cleaning characteristics of the metals are assessed by tribo-electrochemical measurements in the presence of mechanical brushing with a commercial rotary brush for PCMPC. The tribo-electrochemical parameters of the PCMPC-active brushed wafer regions are extracted from the recorded data to determine the cleaning mechanisms. Open circuit potential and voltammetric measurements indicate that oxalate ions serve to remove the CMP residues, Co(OH)2 and Cu-oxides from Co and Cu surfaces, respectively, in the forms of oxalate complexes. The residue removal efficiencies, measured by ex-situ impedance spectroscopy, are found in the 85–89% range for both Co and C

Tribo-Electrochemistry of Post-CMP Cleaning: Results for Co and Cu Wafer Films Brushed in Different Solutions

“…7 The strategy of maintaining mutually similar chemical environment between CMP and PCMPC processes has been used by other authors, 26 and this approach has been helpful for developing analytical PCMPC characterization protocols. 5 In the PCMPC setting, surface coverages of CMP residues should be substantially lower than those of the same species being generated in a CMP solution as primary materials for planarization. Therefore, while using mutually similar chemical routes to CMP and PCMPC, the overall surface activity of the PCMPC solution should be maintained at a substantially lower level than that of the CMP solution.…”

“…A stainless-steel counter electrode (CE) and a saturated calomel (SCE) reference electrode (RE, separated from the main solution with a salt bridge), completed the three-electrode setup. The detailed components of this cell have been previously discussed, 5 and for ease of reference, is schematically depicted here in Fig. 1.…”

“…A triboelectrochemical framework designed to assess PCMPC formulations in the presence of brushing wafer samples has been recently demonstrated. 5 The present work further extends this approach to evaluate three different PCMPC solutions that are aimed at cleaning (abrasive-free) CMP residues from Co and Cu wafer films. Cu and Co are used, respectively, for wiring and for diffusion barrier liners in interconnect structures.…”

“…We employ this solution to further standardize the protocols for triboelectrochemical data analyses reported in our previous investigation of PCMPC. 5 The selective range of CMP deposits targeted for cleaning by this base solution simplifies the essential optimization steps of these experiments.…”

Review—Post-Chemical Mechanical Planarization Cleaning Technology

“…This occurs mainly due to the chemisorption and physisorption of the TAZ molecules on the metal surfaces. 186 Johnson et al 187 reported that oxalate ions of oxalic acid accompanied by brush scrubbing effectively removed the residues such as Co(OH) 2 ,Co(BTA) 2 ,Cu-oxides and Cu-BTA from Co and Cu obtained after polishing in an abrasives free CMP slurry. Surface alterations were not observed post cleaning and a removal efficiency of 85% -89% was obtained for both the metals.…”