GOALI - Particle Adhesion in Semiconductor Wafer Cleaning

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CBET-0829086BeaudoinThis proposed research is a combined theoretical and experimental study of the adhesion of micro- and nano-scale particles to nano-structured wafers of interest to the microelectronics community. At present the microelectronics industry has no manufacturable technologies for cleaning future wafers. In particular, the patterns of interest on the wafers are too fragile to be subjected to existing cleaning approaches. The development of new cleaning technologies requires understanding of the contaminant adhesion forces, but the length scales of the patterns on the wafers are rapidly approaching the length scales of the basic forces that control the particle adhesion. This work will measure and model this adhesion. The Intellectual Merit of the proposed work lies in the new theoretical and experimental methods to be employed to categorize the adhesion of micro- and nano-scale particles to rough nano-patterned or nano-layered surfaces. New theoretical descriptions of the effects of finite, patterned surfaces on the van der Waals and electrostatic adhesion forces between the surfaces will be developed and validated experimentally. Provisions within the research have been made to measure and model capillary forces, should they arise. Colloidal probe microscopy will be performed to allow adhesion forces between the substrates and the particles to be measured directly. The use of focused ion beam/scanning electron microscopy (FIB/SEM) or scanning transmission electron microscopy/energy-filtered transmission electron microscopy (STEM/EFTEM) to create 3D maps of particle geometry and morphology with nano-scale precision will allow creation of detailed models of the particle surfaces. These will be used in force models that predict the observed adhesion. Such models will be the first of their kind. The Broader Impacts of this work are articulated in several fashions. First, the technical results of the work are of profound importance to the microelectonics industry, as the industry currently possesses no manufacturable approaches for cleaning future wafers and photomasks. Particle adhesion is also critically important to the pharmaceutical industry where particle flows and particle mixing are essential processes, and in homeland security matters, where sampling and sensing of nano- and micro-particles of explosives, biological agents, or radioactive agents is necessary. The proposed work will also be part of an outreach effort to a local elementary school that will involve over 120 second graders and 6 teachers each year. The students and teachers will travel to Purdue in small groups and will use the AFM to make topographical maps of leaves, grass, CDs, DVDs, fingernails, hair and skin. They will take the images they collect and use them to reinforce the content they are learning in the classroom using lessons jointly developed by Beaudoin and the teaching staff. The industry partner in this work, FSI International (FSI), will provide wafers, particle deposition capability, wafer cleaning capability, and metrology for evaluating wafer cleaning effectiveness. Beaudoin will perform particle adhesion and modeling studies on the wafers provided by FSI, and will feed the results of these studies back to FSI. FSI, in turn, will use these results to optimize the operation of its cryogenic aerosol-based wafer cleaner, and will document the accuracy of Beaudoin's adhesion models. FSI also will host Beaudoin's student for one month each summer to perform experiments in an industrial setting at FSI.