Ammonium Dodecyl Sulfate as a Potential Corrosion Inhibitor Surfactant for Electrochemical Mechanical Planarization of Copper

Abstract

Electrochemical mechanical planarization ͑ECMP͒ is designed for low-pressure processing of 65 nm and smaller semiconductor device structures using electrochemical reactions in abrasive-free electrolytes. In ECMP, a corrosion inhibitor facilitates uniform surface planarization through selective material removal from protrusions under voltage activation while protecting the recessed areas. We demonstrate here that ammonium dodecyl sulfate ͑ADS͒, an environmentally safe surfactant, can be utilized for this application in ECMP of copper. Using an acidic electrolyte of glycine and H 2 O 2 , and small Cu disks, we show that the corrosion inhibition efficiency of ADS is superior to that of benzotriazole.Copper damascene structures in the fabrication of integrated circuits are processed by chemical mechanical planarization ͑CMP͒, and a rapidly emerging extension of CMP is electrochemical mechanical planarization ͑ECMP͒. 1-5 ECMP utilizes voltage-activated anodic dissolution for material removal, where mechanical polishing can be performed at Ͻ1 psi applied pressure for minor leveling of topographies in nearly or completely abrasive-free electrolytes. 4,5 This low-pressure ͑and possibly abrasive-free͒ capability of ECMP is particularly attractive for processing 65 nm and smaller structures that contain mechanically fragile, porous low-permittivity materials. 1,5 ECMP involves precisely controlled ͑not necessarily maximized͒ material removal through simple adjustment of electrochemical variables. 4 Achieving uniform across-wafer planarization in this technique, however, relies on controlled and repetitive formation and subsequent removal of a thin passivating layer on the sample surface. This passive film protects the recessed areas of the surface from electrochemical corrosion, while protrusions on the same surface are planarized by the combined mechanical abrasion and electrochemical reactions. Selection of an appropriate corrosion inhibitor is difficult because the commonly used corrosion protective organics often produce unavoidable debris during polishing, eventually causing scratches and defects on the wafer surface. 1 In the present work, we demonstrate that ammonium dodecyl sulfate ͑ADS͒, an environmentally friendly surfactant, can be used as an efficient corrosion inhibitor for ECMP of Cu in hydrogen peroxide/ glycine solutions. 3,7 We use a standard acidic ͑pH 4.0͒ solution of Cu CMP/ECMP, containing 1 wt % glycine ͑complexing agent͒ and 5 wt % H 2 O 2 ͑oxidizer͒, with and without ADS ͑corrosion inhibitor͒. We obtain the corrosion inhibition efficiency of ADS at equilibrium ͑zero-current condition of CMP͒ by using potentiodynamic polarization measurements using small Cu disk samples. The inhibition efficiency of ADS against electrochemical corrosion ͑for ECMP͒ is measured in the presence of moderate and strong anodic voltage activation. The corrosion parameters for ADS are compared with those for benzotriazole ͑BTA͒, a conventional corrosion inhibitor for Cu. 8,9 This comparison is further extended to the case of...

Investigation of dissolution inhibitors for electrochemical mechanical planarization of copper using beta-alanine as a complexing agent

“…Electrochemical mechanical planarization (ECMP) offers certain advantages over the conventional chemical mechanical planarization (CMP) method used in the fabrication of semiconductor microchips [1][2][3][4][5][6]. Achieving an adequate combination of complexing agents and dissolution inhibitors is critical to designing efficient ECMP solutions.…”

“…In ECMP of Cu, the surface layer removal step is primarily controlled by voltage activated electrodissolution, and often complexing agents are used in combination with oxidizers to promote multiple branches of these reactions [1][2][3][4][5]. Generally, a dissolution inhibitor is necessary in ECMP to form thin passivating films on the surface [6]. These films protect recessed regions from dissolution as the protrusions are removed by mechanical as well as chemical and electrochemical processes [1,2].…”

“…In addition, when used in large concentrations (C10 mM), certain dissolution inhibitors, including the commonly used benzotriazole (BTAH), tend to leave insoluble debris resulting in scratches on the finished surface [7,8]. Due to these reasons, there has been considerable interest in recent years in developing novel combinations of complexing agents and dissolution inhibitors for CMP applications [9][10][11], and these efforts are now expanding to the field of ECMP [6,7]. Our present report addresses this subject of dissolution inhibition for ECMP of Cu using low concentrations of BTAH (1-5 mM) and an anionic surfactant, ammonium dodecyl sulfate (ADS), in combination with a relatively less explored complexing agent, b-alanine (3-aminopropionic acid).…”

“…Previously we have studied the general surface chemistries of BTAH and ADS for CMP and ECMP of Cu using glycine as a complexing agent [6][7][8]. More recently, we have tested b-alanine as an alternative complexing agent of glycine [12], together with ADS and BTAH used as inhibitors for CMP of Cu [13].…”

Key Chemical Components in Metal CMP Slurries

“…Thus, the attraction between a negatively charged anionic surfactant leads to lower static etch rate in comparison to nonionic and cationic surfactants. Hong and coworkers [64] studied the use of ammonium dodecyl Sulfate (ADS) instead of BTA as corrosion inhibitor in electrochemical-mechanical planarization (ECMP). ADS yielded lower corrosion currents in comparison to BTA at similar concentrations through electrochemical measurements.…”