The liquid-based deposition of particles onto semiconductor wafers has been investigated by exposing wafers to a variety of sample contaminants in stirred aqueous solutions. Test results clearly demonstrate the importance of electrostatic wafer/particle interactions in cleanroom-liquid particle deposition. While deposition from bulk DI water is often absent if an electrostatic repulsion exists, dramatic deposition can occur if an attraction exists between the wafer surface and the contaminant. Further, the importance of solution chemistry in defining deposition is demonstrated. Alterations of solution ionic strength or pH can dramatically alter the resultant particle deposition in a manner which is consistent with well-established principles of colloid science. If trace quantities of certain contaminants become present in the DI supply, particle charge reversals can occur which dramatically influence resultant deposition; despite the unplanned results that charge reversal leads to, depositions which occur have been found to be completely consistent with predictions based upon the electrostatic interactions which actually exist in the test system.
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