THE EFFECT OF CLEANING PROCEDURES ON SURFACE CHARGING OF VARIOUS SUBSTRATES

Contact electrification occurs when two dissimilar materials are broug ht into contact. Each surface is left positively or negatively charged depending on the relative difference between surface state electron d ensity in each material. A technique is described which measures the c urrent generated when two solid surfaces are abruptly brought into con tact and the current that results when they are subsequently separated . The theory of metal-insulator contacts forms the basis for this uniq ue measurement. The technique allows measurement of surface charging o f a variety of substrates after immersion in solvents used in routine semiconductor wafer cleaning and deionized water (DI) rinsing. Quantit ative results are used to describe the effect of cleaning on generatio n of surface charge. Advantages of this technique are its simplicity a nd the fact that the measurement requires much less time than conventi onal charge measurement techniques. All the substrates in this study w ere significantly charged by immersion in deionized water. Charging du e 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 i sopropyl alcohol the final rinsing agent.