The effect of cleaning procedures on surface charging of various substrates

Contact electrification occurs when two dissimilar materials are brought into contact, Each surface is left positively or negatively charged depending on the relative difference between surface state electron density in each material. A technique is described which measures the current generated when two solid surfaces are abruptly brought into contact and the current that results when they are subsequently separated. The theory of metal-insulator contacts forms the basis for this unique measurement. The technique allows measurement of surface charging of a variety of substrates after immersion in solvents used in routine semiconductor wafer cleaning and deionized water (DI) rinsing. Quantitative results are used to describe the effect of cleaning on generation of surface charge. Advantages of this technique are its simplicity and the fact that the measurement requires much less time than conventional charge measurement techniques, All the substrates in this study were significantly charged by immersion in deionized water. Charging due to immersion in isopropyl alcohol (IPA) was significantly lower than charging due to immersion in deionized water. Surface charging after immersion in other solvents could be reduced or eliminated by making isopropyl alcohol the final rinsing agent.<
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