Surfactant Based Alumina Slurries for Copper CMP
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HLB of the nonionic surfactants. The Hydrophile-Lipophile Balance (HLB) is related to the solubility of the surfactant, with higher number corresponding to increased water dispersibility. The surfactant BrijR 35, with the nonionic composition polyoxyethylene(23) lauryl ether, resulted in a dramatic improvement in the average surface uniformity when compared with the control at pH 2, and Sodium Dodecyl Sulfate produced even greater uniformity. Additionally, the effect of BrijR 35 surfactant was maintained with change in abrasive size, pad and polishing tool. In order to insure that surfactants are compatible with the chemical reagents contained in the commercial slurries, two chemistries (ferric nitrate and hydrogen peroxide) were employed to test the efficiency of the selected surfactants in their presence. The results showed that the effect of surfactant on stability and removal rate is not influenced by the presence of the chemicals. Preliminary results indicate that surfactants can have a beneficial effect on both defects and post polish clean. INTRODUCTION
With the introduction of copper as an interconnect material of choice in the fabrication of microelectronic circuits, there is a considerable interest in the optimization of the planarization technique used to flatten the deposited copper thin films [3,81. Chemical mechanical planarization (CMP) is identified as the most suitable method to achieve the global planarization. The CMP technique consists of rotating a polishing media against the rotating or stationary wafer while a polishing slurry is passed between the two surfaces. The pad is usually a stacked polymer structure which applied pressure to the wafer and carries the slurry between sample surface and the pad. A typical schematic of a CMP apparatus is shown in figure 1. The wafer is pressed against the pad with a known downward pressure. Polishing slurry is one of the main variables of the process affecting the polishing performance. The slurry consists of a dispersion of abrasive particles in deionized (DI) water with the added reagents (e. g. oxidizers, passivating agents, and other additives), adjusted to a desired pH. Addition of chemical reagents often causes the suspension to destabilize. Copper, being a soft material, is particularly vulnerable to scratches and defect often caused by presence of agglomerated abrasive particles. Physical modification of these abrasive particulates in order to enhance suspension stability, and thus to enhance uniformity across the polished wafer, and control the post polish surface defects (scratches and chemical and physical contamination) are the motivation behind this study. The use of surfactants for colloid suspension is well established in other areas [I]. Recently, there has been interest shown in the application of surfactants for CMP slurries as well [2,4-7]. This 135 Mat. Res. Soc. Symp. Proc. Vol. 566 ©2000 Materials Research Society
paper describes the results we have obtained with the use of nonionic surfactants in alumina based slurries for the p
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