Fundamental Study of Iodate and Iodine Based Slurries for Copper CMP
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Fundamental Study of Iodate and Iodine Based Slurries for Copper CMP Seung-Mahn Lee, Uday Mahajan, Zhan Chen and Rajiv K. Singh Department of Materials Science and Engineering and Engineering Research Center for Particle Science and Technology, University of Florida, Gainesville, FL 32611 ABSTRACT The chemical mechanical polishing of copper in several slurry chemistries based on iodate and iodine oxidizers has been investigated. Benzotriazole (BTA) and potassium iodide (KI) were used for preparing the polishing slurry chemistries based iodate. As observed by the anodic electrochemical behavior of copper and the surface analyses of EDS, it was determined that CuI layer formed in the iodate and iodine based solutions. Especially, in I2 slurry in pH 4, CuI layer formed very fast and uniformly, and passivated the copper. In addition, the highest removal rate using this slurry was obtained. These results were compared to H2O2 based slurries. From these experimental results, the slurry containing 0.1M KIO3 and 0.01M KI, and 0.01N I2 give better results than H2O2 based slurry in copper CMP. INTRODUCTION Recently, copper has emerged as an attractive material for interconnect applications, as compared to aluminum, with close to half the resistivity (reduced RC time delay and the number of levels of metal required) and with improved reliability due to electromigration resistance on the order of 10 times higher [1-4]. Therefore, Copper CMP has now been recognized and accepted as the process that is capable of providing the planarity to build multilevel interconnects schemes with below quarter-micron lines. One of the key issues in copper CMP is the development of slurries which can provide high removal rates, good planarity and high selectivity [5]. A number of slurry chemistries have been studied to optimize copper CMP conditions: HNO3 and H2O2 as oxidizers [3,6], benzotriazole (BTA) as an inhibitor [3,4], NH4OH as a complexing agent [7,8], etc. It is well known that H2O2 being used in all copper CMP slurries as an oxidizer in order to make stable oxide passive layer on the copper surface. However, it was observed that copper oxide layer by H2O2 is not a passive film by (a) potentiodynamic measurements (no level off region) and (b) surface morphology from SEM. In previous studies, we have reported that a passive layer is necessary to obtain high removal rate as well as low roughness in tungsten CMP [10,11]. In this paper, we have investigated iodate and iodine based slurry chemistries for copper CMP with the goal of forming a copper-compound passive layer instead of oxide layer on the surface in order to obtain high removal rate with good planarity and without any surface damage, operating in intermediate pH ranges. We have used potassium iodate (KIO3) and iodine (I2) solution as a copper oxidizer, benzotriazole (BTA) as an inhibitor of copper corrosion, and potassium iodide (KI) [12,13] as an additive to supply iodide ions. In addition, the CMP results of H2O2 based slurry are shown to compare our results using iodate and io
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