Copper CMP Formulation for 65 nm Device Planarization
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Copper CMP Formulation for 65 nm Device Planarization Gregory T. Stauf, Karl Boggs, Peter Wrschka, Craig Ragaglia, Michael Darsillo, Jeffrey F. Roeder, Mackenzie King, Jun Liu, and Thomas Baum ATMI, 7 Commerce Drive, Danbury, CT 06810, U.S.A.
ABSTRACT To achieve 65 nm technology node requirements, CMP processes must provide improved control of selectivity, topography, wire cross section, and process robustness. Slurries and processes must also be compatible with fragile low k materials by providing low erosion and shear forces. We present data on a unique step 1 bulk Cu removal slurry with high selectivity, removal rates over 8000 Å/min, and extremely low liner removal/erosion in high (90%) density structures. This is achieved through a combination of surface modified abrasives and alternative inhibitors which provide superior performance and reduced electrochemical activity compared to benzotriazole, a commonly used inhibitor. The step 1 slurry was used with a step 2 liner removal slurry that can be chemically tuned to adjust relative selectivities of Cu:Ta:oxide from the nominal ratio of 1:0.9:1.6, allowing its use with a variety of integration schemes. Results of CMP planarization experiments on 200 mm blanket and patterned single damascene test wafers are described, including electrical data which demonstrates low overpolish sensitivity.
INTRODUCTION Copper is rapidly replacing aluminum in advanced integrated circuits, particularly at lower wiring levels on chips, due to its lower resistivity and better electromigration resistance.[1] Patterning of Cu metal lines typically requires chemical mechanical planarization (CMP) in order to remove excess electroplated Cu and to planarize structures for fine feature photolithography. A selective step 1 slurry typically removes the copper, stopping on the barrier layer of Ta/TaN[2], followed by a step 2 slurry that removes the conductive barrier to provide electrical isolation between lines. Development of a step 1 slurry that removes Cu at a high rate for good tool throughput without dishing has been a challenge since the inception of the damascene polishing method. Further challenges include the ability to stop on the barrier without eroding it during overpolish particularly for the very fine line features used in newer technology nodes such as 90 and 65 nm.[3] Thus, a high performance slurry needs to have reasonable removal rates at the low down forces used on low k dielectrics, low liner erosion in dense structures, and low dishing. The last two attributes combine to determine total Cu line loss. Here we report on the results of development of such a formulation for step 1 Cu removal, and results for Cu polishing. We also discuss some of the interaction effects of abrasive, passivator and copper content in slurry chemistry that can lead to improved topography in line structures.
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EXPERIMENT Copper removal and planarization was carried out on an AMAT Mirra polisher with an ISRM optical end point detector and Titan 1 heads, using Rodel IC1000 k-groove
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