Electrolyzed Water as an Alternative for Environmentally Benign Semiconductor Cleaning

Abstract

The present semiconductor cleaning technology is based upon RCA cleaning [W. Kern and D.A. Puotinen, Cleaning Solutions Based on Hydrogen Peroxide for use in Silicon Semiconductor Technology (RCA Rev., 1970) pp. 187-206], a high-temperature process that consumes vast amounts of chemicals and ultrapure water (UPW) [T. Futatsuki, T. Imaoka, Y. Yamashita, and K. Mitsumori, J. Electrochem. Soc., 142, 966 (1995)]. Therefore, this technology gives rise to many environmental issues, and some alternatives such as electrolyzed water (EW) are being studied. In this work, intentionally contaminated Si wafers were cleaned using electrolyzed water. The electrolyzed water was generated by an electrolysis system that consists of anode, cathode, and middle chambers. Oxidative water and reductive water were obtained in the anode and cathode chambers, respectively. When a NH 4 Cl electrolyte was supplied in the middle chamber, the oxidation-reduction potential and pH for anode water (AW) and cathode water (CW) were +1050 mV and 4.8, and −750 mV and 10.0, respectively. AW and CW deterioriated after electrolysis but maintained their characteristics for more than 40 min, which was sufficient for cleaning. Their deterioration was correlated with CO 2 concentration changes dissolved from air. Contact angles of UPW, AW, and CW on DHF-treated Si wafer surfaces were 65.9°, 66.5°, and 56.8°, respectively, which characterizes clearly the electrolyzed water. To analyze the amount of metallic impurities on Si wafer surface, inductively coupled plasma, mass spectroscopy was introduced. AW was effective for Cu removal, while CW was more effective for Fe removal. To analyze the number of particles on Si wafer surfaces, we used the particle measurement Tencor 6220. The particle distributions after various particle removal processes maintained the same pattern. Overflow of EW during cleaning particles resulted in the same cleanness as that obtained with the RCA cleaning process. The roughness of patterned wafer surfaces after EW cleaning was similar to that of as-received wafers. Regardless of process sequence in this work, RCA consumed about 9 l of chemicals, while EW consumed only 400 ml HCl electrolyte or 600 ml NH 4 Cl electrolyte to clean 8-in. wafers. It was thus concluded that EW cleaning technology would be very effective for releasing environmental safety, and health issues in the next generation of semiconductor manufacturing.

Effects of ozonation, alkaline ionized water, and their combination on surface disinfection and shelf life extension of tomatoes

“…The hydrophobicity of the fruit surface decreased when washed with AEW since it acts as a surfactant. Consequently, any microorganisms on the surface of the fruit could be easily accessed, and a high reduction of levels of microbial populations would thus be achieved (Ryoo, Kang, & Sumita, 2002). It was also reported that pH of cathodic solutions can be stable for at least three days, and the pH stability provides a long lasting inhibitory effect.…”

Review—Understanding and Controlling Electrochemical Effects in Wet Processing

“…The one drawback of the E-sulfuric acid process is that electrolysis needs to be conducted at temperatures below 90 • C and the product from the electrolysis cell has to be heated to achieve temperatures attainable in conventional SPM. 17 18 Oxygen and hydrogen dissolved water produced in anode and cathode compartments of an electrolysis cell has shown some promise for cleaning. 18 Such water is termed 'Electrolyzed Water' and is generated in an apparatus shown schematically in Figure 12.…”

“…17 18 Oxygen and hydrogen dissolved water produced in anode and cathode compartments of an electrolysis cell has shown some promise for cleaning. 18 Such water is termed 'Electrolyzed Water' and is generated in an apparatus shown schematically in Figure 12. The apparatus consists of three chambers: anode, cathode, and middle.…”

“…Block flow diagram of electrolyzed water generation. Reprinted with permission from Journal of Materials Research 18.…”

Metal Oxide Particle Removal Using Electrolyzed Anode Water

“…4,5 As substrate sizes of silicon wafer or glass plate increase, the number of cleaning process steps increases so that the amount of chemicals and ultrapure water ͑UPW͒ consumed in the RCA cleaning process increases drastically and production cost and environmental burden increase as well. In order to resolve these issues, several alternatives to functional waters, such as hydrogenated ultrapure water, 6 ozonized water, 7,8 and electrolyzed water, [9][10][11][12] have been studied. However, their applications have not overcome the two-step RCA concept as mentioned above.…”