Chemical-Mechanical Planarization of Copper: The Effect of Inhibitor and Complexing Agent
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Chemical-Mechanical Planarization of Copper: The Effect of Inhibitor and Complexing Agent Ying Luo, Tianbao Du and Vimal Desai Advanced Materials Processing and Analysis Center University of Central Florida Orlando, FL 32816 U.S.A. ABSTRACT The present investigation was focused on understanding of the oxidation, dissolution and modification of Cu surface in slurries at various pH using hydrogen peroxide as oxidizer, glycine as complexing agent and 3-amino-triazol (ATA) as inhibitor during Cu-CMP. The electrochemical process involved in the oxidative dissolution of copper was investigated by potentiodynamic polarization studies. Surface modification of copper was investigated using Xray photoelectron spectroscopy to understand the interaction of Cu-H2O2-glycine-ATA during CMP. In the absence of glycine and ATA, the copper removal rate is found to be high in a slurry with 5% H2O2 at pH 2, then it decreases with increasing pH and reaches the minimum at pH 6, it continuously increases at alkaline condition. In the presence of 0.01M glycine, the removal rate of copper decreases in acidic slurries while increases significantly in alkaline slurries. With the further addition of ATA, the copper removal rate was reduced. However, better surface planarity was obtained. The present investigation enhanced understanding of the mechanism of Cu CMP in the presence of oxidizer, complexing agent and inhibitor for formulation of a highly effective CMP-slurry. INTRODUCTION Copper is currently used as an interconnect material in integrated circuits (ICs) due to its low resistivity and high electromigration resistance [1,2]. Integration of copper into an IC manufacturing process is implemented by using the dual Damascene technique [3,4], where copper is deposited by chemical vapor deposition (CVD) or electroplating into vias and trenches. Those vias and trenches are etched in the interlayer dielectric (ILD) over a diffusion barrier usually made from titanium, tantalum, or their nitrides. Chemical-mechanical polishing (CMP) technique has been applied to remove the overburden material and to planarize the wafer surface. The planarization capability is an important advantage of the CMP process. It prevents problems associated with the increasing number of interconnect layers in multilevel metallization of ICs, where the topography of device structures varies significantly as additional layers are stacked on top of one another. High dissolution rates of copper at low pH without any formation of protective oxide layer and the selectivity issues due to wide differences in mechanical properties of copper and its barrier layer, render the Cu-CMP process not only important but a challenging task for developing interconnect technology. CMP of copper has been investigated extensively in recent years and can be conducted in acidic, neutral or alkaline media [5-7]. Carpio and co-workers [8] have studied copper CMP in slurries including oxidizing agents, complexing agents, and corrosion inhibitors and buffering agents. Several promising chem
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