Electrical Characterization of Slurry Particles and their Interactions with Wafer Surfaces
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repulsion of two surfaces and vice versa depending on the magnitude of van der Waals force. DLVO theory [2,3] can be used to calculate the interaction forces between the slurry particle and the wafer surface to be polished. The interaction forces between particles and between particles and surfaces could provide important information on the stability of slurry and the degree of particle contamination on surfaces after CMP. Post CMP cleaning is a very important process to accomplish the main purpose of planarization. Particles in slurry are usually left on polished surfaces and can be removed by either contact [4] or non-contact [5] mode cleanings. Metal CMP has been known to leave severe particles and metallic contaminants on polished surfaces when compared to oxide CMP. In this paper the zeta potentials of slurry particles and wafer surfaces to be polished were measured as a function of solution pH and the interactions forces between them were calculated to correlate the level of contamination after CMP. The deposition of particles were also performed to verify the theoretical calculation. EXPERIMENT For the experiment, bare silicon, thermal oxide (600 nm) and TEOS (1.5 [tm) coated silicon, Al (500 nm) and W (700 nm) deposited wafers were used as substrates. Al was sputter coated on SiO, and W was prepared by CVD on Ti/TiN (20/60 nm) layers. Substrates were cut into 15 mm x 30 mm for the zeta potential measurements and pre-cleaned before the 173 Mat. Res. Soc. Symp. Proc. Vol. 566 ©2000 Materials Research Society
measurements. Si and oxide substrates were cleaned in the mixture of H 2SO 4 and H20 2 (4:1) followed by HF treatment and finally rinsed with high purity deionized (DI) water (18.2 Mo-cm, manufactured by Millipore Milli-Q Plus). Al substrate was slightly etched in the solution mixture of 73% H3PO 4, 4% HNO 3, 3.5% CH 3COOH, and 19.5% DI water for 1 min 30 sec and rinsed with DI water. W was etched in the solution mixture of 3.4 % KH2 PO 4, 1.34% KOH, 3.3% K 3Fe(CN) 6 and DI water for 2 min. All samples were N2 dried after cleanings. •y-alumina of 0.05 jim and colloidal silica of 0.06 pm in diameter were purchased from Buehler Co. Fumed silica of 0.014 jim was obtained from Sigma Co.. Ceria and MnO 2 particles were provided by Mitsui Mining and Smelting Co. W particles of -325 mesh size were purchased from Cerac. Also commercial oxide and metal slurries were analyzed for the evaluation and comparison purpose. The zeta potentials of slurry particles and substrates have been measured by electrophoretic and electroosmosis method to evaluate the electrical properties of surfaces, respectively, by using a LEZA-600 Laser Electrophoresis Zeta Potential Analyzer of Otsuka Electronics Co. The zeta potential of particles and plate was measured in I 0-3M KCI and 102M NaCl solution, respectively. The zeta potential of plate was measured by using a proprietary monitor solution provided by Otsuka Electronics Co. pH and redox potentials of slurry solutions were measured by a Orion's 520A pH meter with Ag/AgCl electrode
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