Cu Post-CMP Displacement Cleaning: A Mechanistic Product Development Approach Based on Selected Thermodynamic and Kinetic Data

Abstract

A mechanistic product development approach will be presented that utilized selected thermodynamic and kinetic data for development of a Cu post-CMP cleaner for use after polishing with either high or low pH slurry. A Pourbaix diagram offers the thermodynamically stable Cu species vs. pH and open circuit potential (OCP) for an aqueous cleaner. Pourbaix diagrams do not provide any information on the kinetics for dissolution of water soluble species. Cu oxide dissolution rates were measured using an electrochemical cell. Deposition and removal rates for benzotriazole (BTA) and 1,2,4-triazole (TAZ) were measured using an electrochemical cell with a quartz crystal microbalance (QCM). Passivator film deposition was investigated to determine the film type and thickness resulting from a typical CMP process. BTA and TAZ films deposited near neutral pH were thicker than those deposited at high pH. TAZ films were significantly thinner (~20≈) than BTA films deposited under similar conditions, approaching a self assembled monolayer (SAM). The BTA removal rate for a citrate solution with a pH of 4 was ~20≈/min., an order of magnitude lower than that for TMAH-containing solutions. The TAZ removal rate for an oxalate solution with a pH of 4 was 240≈/min., which was twice the removal rate for BTA deposited under similar conditions. An appropriate TAZ solution was found to displace BTA on Cu and leave a hydrophilic, thin (~10≈) passivating layer of TAZ. Other Cu passivators were also examined but only TAZ protected all Cu crystallographic orientations observed. BTA, 5-aminotetrazole (5-ATA) and 4-carboxybenzotriazole (CBTA) did not protect some Cu crystal orientations, leading to etching of entire grains and increased surface roughness. BTA and CBTA yielded hydrophobic Cu surfaces, leading to surface wetting issues and the potential for watermarks. A new alkaline Cu post-CMP cleaner was developed to remove residues resulting from slurries, regardless of their pH, which utilized TAZ to displace BTA and protect Cu, reduce organic defects, reduce surface roughness, provide a hydrophilic Cu surface, and significantly extend the staging time allowed between the clean process and subsequent wafer processing without yield loss.Mater. Res. Soc. Symp. Proc. Vol. 991

Study of Pyrazole as Copper Corrosion Inhibitor in Alkaline Post Chemical Mechanical Polishing Cleaning Solution

“…Surface hydrophobicity of BTA/TMAH-treated Cu surface is commonly attributed to a specific orientation of adsorbed BTA molecules with hydrophobic benzene ring facing away from Cu surface to form a protective hydrophobic barrier. 41 In contrast, the TMAH solution containing 1 mM Pyrazole produced a relatively hydrophilic Cu surface after immersion, Figure 10. This is likely due to relatively smaller size of Pyrazole molecule owing to its absence of large hydrophobic benzene moiety as BTA.…”

Removal of BTA Adsorbed on Cu: A Feasibility Study Using the Quartz Crystal Microbalance with Dissipation (QCMD) Technique

“…[7][8][9][10][11][12][13] Limited studies on the use of quartz crystal microbalance to investigate adsorption and removal of BTA have been reported in the literature. Peters 14 reported that BTA adsorption at pH 5 and 1000 ppm was fast, with a deposited thickness of 70 Å in 5 minutes. In contrast, a film of only 40 Å was formed at pH 11 in the same time frame.…”

“…In contrast, a film of only 40 Å was formed at pH 11 in the same time frame. BTA removal with TMAH was also investigated by Peters 14,15 using QCM method, and it was found that high alkaline TMAH solutions (pH 14) removed BTA at a rate of 150 Å/min, much faster than an acidic citrate solution (pH 4) that yielded a removal rate of 20 Å/min. The ability of TMAH to remove BTA has also been reported by Venkatesh et al 16 Peters 14,15 also found that 1,2,4-triazole (TAZ) was able to displace BTA from copper surface at a fairly high rate (∼100 Å/min).…”

“…Oxalate solution at a pH of 4 was also effective in removing BTA at a rate of 120 Å/min. 14 Copper and barrier CMP are dynamic processes, typically completed in 1 or 2 min. Thus, in-situ measurements of BTA adsorption and removal under fluid flow conditions would be more meaningful to the CMP community.…”

Electrochemical Impedance Spectroscopy (EIS) Analysis of BTA Removal by TMAH during Post Cu CMP Cleaning Process

“…[1][2][3] This makes the Cu surface more hydrophobic and leads to post CMP defects such as watermarks during drying and particles on the surface. For example, adsorption of benzotriazole (BTA) on Cu surface occurs during chemical mechanical polishing (CMP) of Cu surface using a slurry containing BTA.…”