Interaction Between Ceria and Hydroxylamine
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Interaction Between Ceria and Hydroxylamine Subramanian Tamilmani, Jilei Shan, Wayne Huang and Srini Raghavan Department of Materials Science and Engineering, University of Arizona, Tucson, AZ. Robert Small, Cass Shang and Brandon Scott EKC Technology, Inc., Hayward, CA. Abstract Ceria containing slurries are increasingly used in the chemical mechanical polishing of CVD silicon oxide films to obtain STI structures. Unlike silica or alumina, ceria has redox characteristics. Because of this characteristic, removal of ceria particles from planarized surfaces may be possible using chemical reagents that can participate in redox reactions. One such reagent is hydroxylamine, which is already being used in copper CMP. The objective of the work reported in this paper was to characterize the reaction between ceria and hydroxylamine, especially with respect to dissolution of ceria particles. A kinetic study of the dissolution of ceria in hydroxylamine solutions maintained at various pH values has been performed. The extent and kinetics of dissolution of ceria has been determined by ICPMS. Removal of ceria particles from oxide surfaces using hydroxylamine-based chemistries has been investigated. Introduction Chemical mechanical polishing of CVD silicon oxide films is a key step in forming 1 shallow trench isolation (STI) structures. Both silica 2 and ceria based 3 slurries have been used for this process. Silica based slurries often result in over polishing of certain features. Reports indicate that ceria slurries show promise in polishing STI structures without using the reverse mask process and stop on SiN layers 4. Properly formulated ceria slurries appear to achieve STI pattern planarization with minimal oxide erosion 5. Post CMP cleaning of the polished wafers to remove particles adhering to the wafers is very critical. The effectiveness of the cleaning process can be enhanced if the particles can be partly dissolved such that the adhesion between the particles and wafer can be reduced. Unlike silica or alumina, ceria has redox characteristics. Because of this characteristic, removal of ceria particles from planarized surfaces may be possible using chemical reagents that can participate in redox reactions. Under such conditions the parameters like solution redox potential (controlled by concentrations of redox agent), pH, and the presence of a chemical that can adsorb on the dislodged particles and prevent its redeposition can modulate the cleaning efficiency. One such redox reagent is hydroxylamine, which is already being used in copper CMP 6, 7. Hydroxylamine tends to function as an oxidizing agent at acidic pH values and as a reducing agent at alkaline pH values 8. Dissolution of ceria particles in alkaline hydroxylamine chemistries, if it occurs, can be utilized to increase the effectiveness of cleaning. The primary objective of the work reported in this paper was to characterize the reaction between ceria and hydroxylamine, especially with respect to dissolution of ceria particles. Based on the results from d
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