Particles in Ulsi Grade Chemicals and Their Adhesion to Silicon Surfaces
Despite the advancement of dry processing in ULSI manufacturing, wet chemical cleaning remains the only reliable method for controlling particulate contamination on semiconductor wafer surfaces.
It is necessary to accurately measure the number of particles in all liquid chemicals and understand the mechanisms of particulate adhesion so that this form of contamination may be minimized on silicon surfaces. We believe that the particle concentration and zeta potential, and the condition of the wafer surface are all factors which determine the number of particles which deposit on surfaces immersed in liquids.
A new laser particle counter, the Horiba PLCA 520, with specifications for detecting particles to 0.2 μm in chemicals was used in this study. This particle counter is unique in its ability to use either pressure or suction fluid sampling. Thus, the question of whether particle counts are inflated through the inclusion of bubbles during suction sampling may be addressed. No appreciable difference between suction and pressure sampling was found, with two exceptions: nitric acid and ammonium hydroxide. Calibration tests, as well as pressure/suction sampling characterizations of common ULSI-grade processing chemicals are presented.
We have demonstrated that particles adhere to bare silicon wafers in proportion to their zeta potential and concentration in liquids. Furthermore, it is shown that the number of particles deposited in acidic and alkaline solutions are quite different, in keeping with published data on zeta potentials as a function of solution pH.
KeywordsHydroxide Syringe H2SO4 Stratification Polystyrene
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- 1.K. L. Mittal, editor “Particles in Gasses and Liquids 1: Detection, Characterization and Control”, Plenum Press, New York (1989)Google Scholar
- 2.L. D. Michaels. V. B. Menon, R. P. Donovan and D. S. Ensor, Particle Deposition at the Solid-Liquid Interface, Proceedings, 34th Annual Technical Meeting of the Institute of Environmental Sciences, 438–442 (1988)Google Scholar
- 3.H. Mishima, T. Yasui, T. Mizuniwa, M. Abe and T. Ohmi, Particle-Free Wafer Cleaning and Drying Technology, IEEE Trans. on Semiconductor Manufacturing, 2 No. 3, 69–75 (August, 1989)Google Scholar
- 4.A. Saito, K. Ohta, M. Watanabe and H. Oka, Particle Deposition Mechanism onto Silicon Wafer, Extended Abstract of the 21st Conference on Solid State Devices and Materials, (409–412), Tokyo, Japan (August, 1989).Google Scholar
- 5.T. Niida, Controlling for Particle Adhesion in Liquids — a Basic Way of Thinking, Chemical Engineering Institute of Japan, Kansai Branch, Osaka, Japan 14–25, (September, 1989)Google Scholar
- 6.D. J. Riley and R. G. Carbonell. The Deposition of Liquid-Based Contaminants onto Silicon Surfaces Proceedings, 36th Annual Technical Meeting of the Institute of Environmental Sciences, 224–228 (1990)Google Scholar
- 7.A. W. Adamson, “Physical Chemistry of Surfaces, 4th Edition”, John Wiley & Sons, New York (1982)Google Scholar
- 8.D. W. Cooper, Statistical Analysis Relating to Recent Federal Standard 209 (Cleanrooms) Revisions, J. Environ. Sci. 31 No. 5, 48–52 (1988)Google Scholar
- 9.Robert K.Perry and C.H. Chilton, “Chemical Engineers’ Handbook”, 5th ed., pp. 3–68, McGraw Hill Book Company, New York (1973)Google Scholar
- 10.Y. Kasama, Y. Yagi, T. Imaoka, M. Kawakami and T. Ohmi, Advanced DI Water System with Low Dissolved Oxygen for ULSI Processing, Proceedings, 36th Annual Technical Meeting of the Institute of Environmental Sciences, 344–349 (1990)Google Scholar
- 11.T. Ohmi, Future Trends and Applications of Ultra-clean Technologies, Technical Digest, International Electron Device Meeting, Washington, D.C. (1989)Google Scholar
- 12.T. Ohmi, Ultra-clean Technology: ULSI Processing’s Crucial Factor, Microcontamination, 6, No. 10, pp. 49–58 (October, 1988)Google Scholar