Mechanism of Cu removal during CMP in H 2 O 2 -glycine based slurries
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M. Hariharaputhirana, S. Ramarajana, Y.Lib, S.V. Babuac Departments of Chemical Engineeringa and Chemistryb, Clarkson University CCenter for Advanced Materials Processing, Clarkson University, Potsdam, NY Abstract Hydroxyl radical generation has been observed during Cu CMP using hydrogen peroxide-glycine based slurries. While the Cu dissolution/polish rates increased with increasing glycine concentration, the copper dissolution rate decreased with increasing peroxide concentration indicating the occurrence of both dissolution and passive film formation during CMP. This is further confirmed by both in situ and ex situ electrochemical experiments. Introduction Copper CMP under highly acidic conditions leads to severe corrosion problems while under alkaline conditions Cu polish rate selectivity with respect to SiO 2 is unfavorable leading to ILD erosion. Thus an intermediate pH condition (3-7) is better for Cu CMPI. H 20 2-glycine (an amino acid) based slurries containing either silica or alumina abrasive particles are one of the more attractive slurries in this pH regime for Cu CMP '3,4,5. We recently reported3 that the Cu2รท(glycine) 2 complex (chelate) catalyzes the decomposition of hydrogen peroxide to yield hydroxyl radicals (*OH) which play a major role in Cu removal when polished using these slurries. This paper will report on the mechanism of Cu removal during CMP in H 20 2-glycine based slurries. Results from both in situ (during polishing) and ex situ (rotating disc electrode) electrochemical experiments and polishing experiments are reported. The effect of benzotriazole as a dissolution inhibitor during CMP in these slurries has also been studied. 2. Experiment 2.1 Chemical-Mechanical Polishing and 3 Polishing experiments were performed using a bench-top Struers DAP-V polisher 2 mm thick copper disks (99.99% pure, Aldrich) with a cross sectional area of 7.5 cm . The table
speed was set at 90 rpm and the disk holder was held stationary. The applied downward pressure was about 6.3 psi (41.4 KN/m2). Alumina particles with a mean aggregate size of around 350 nm, prepared and supplied by Ferro Corporation, were used as the abrasives 6 . The solids concentration in the slurries was maintained at 3 % by weight and the slurry feed rate was I ml/s for all the experiments. The slurry in the supply tank was stirred continuously with a magnetic stirrer to avoid settling of aggregated particles. Suba 500 was used as the polish pad. The pad was hand conditioned prior to each experiment using a 220 grit sand paper and a nylon brush. The polish rate was determined from the difference in the weights of the disk before and after polishing for at least three minutes and the reported values were obtained by averaging over four experiments 2.2 Copper Dissolution Dissolution experiments were carried out in a 500 ml glass beaker containing 400 ml of the etchant solution. A rectangular copper coupon (2.3 cm x 2.3 cm x 0.2 cm, 99.99 % pure) was used as the sample. The copper coupon was first washed with dilute HC1 to remove any nat
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