Effects of Additives in KOH Based Electrolytes on Cu ECMP
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0991-C11-02
Effects of Additives in KOH Based Electrolytes on Cu ECMP Tae-Young Kwon, In-Kwon Kim, and Jin-Goo Park Division of Materials and Chemical Engineering, Hanyang university, 1271, Sa 1-dong, Sangrok-gu, Ansan, Gyungki-do, 426-791, Korea, Ansna, 426-791, Korea, Republic of ABSTRACT The purpose of this study was to characterize KOH based electrolytes and effects of additives on electro-chemical mechanical planarization. The electrochemical mechanical polisher was made to measure the potentiodynamic curve and removal rate of Cu. The potentiodynamic curves were measured in static and dynamic states in investigated electrolytes using a potentiostat. A Cu disk of 2 inch was used as a working electrode and a Pt electroplated platen was used as a counter electrode. KOH was used as the electrolyte. H2O2 and citric acid were used as additives for the ECMP of Cu. In static and dynamic potentiodynamic measurements, the corrosion potential decreased and the corrosion current increased as a function of the KOH concentration. In a dynamic state, different potentiodynamic curves were obtained when compared to the static state. The current density did not decrease in the passivation region by mechanical polishing effect. The static etch and removal rate were measured as function of KOH concentration and applied voltage. In the ECMP system, polishing was performed at 30 rpm and 1 psi. The removal rate was about 60 nm/min at 0.3 V when 5 wt% KOH was used. Also, the effect of additive was investigated in KOH based electrolyte on removal rates. As a result, the removal rate was increased to 350 nm/min when 5wt% KOH, 5vol% H2O2, 0.3 M citric acid was used. INTRODUCTION In the fabrication of semiconductor devices, Cu has been chosen as a material for interconnects because of its higher electric conductivity and electromigration resistance. Chemical-mechanical planarization (CMP) of Cu is currently used in semiconductor process for the formation of multilevel metal interconnects by the damascene technique. However, high process pressure of the conventional Cu CMP process can generate severe damage to porous low-k materials in the Cu multilevel interconnects of the 45-65 nm technology node. Also, Cu surface is vulnerable to surface scratches by abrasive particles in CMP slurry. In order to overcome these technical difficulties in CMP, electro-chemical mechanical planarization (ECMP) has been introduced. ECMP utilizes electrochemical and mechanical actions to form or remove the passivation layer on a Cu surface. Abrasive free electrolyte, soft pad and low downforce are also used [1-6]. Since electrolyte is an important process chemical in ECMP, several researchers have studied electrolytes and the effect of additives on ECMP [1-3]. However, KOH based electrolyte has not yet drawn much attention in ECMP. In this study, the effect of additives such as an organic acid and oxidizer on ECMP behavior was investigated. The removal rate was measured with the electrochemical potentiostatic studies and static etch rates.
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