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Unique Application of CO2 Cryogenic Aerosol Cleaning for Particle Removal in MEMS and Packaging Fabrication Processes
Keywords: MEMS Cleaning, Particle Removal, Cryogenic Aerosol
The MEMS technology is gaining momentum as more breakthroughs and product launches are witnessed in recent years. Modern MEMS and ICs have many similarities as well as dissimilarities. MEMS adopt modified semiconductor process technology to create mechanical structures on wafers, but the chips function combines mechanics, optics, and electronics, to provide the highest level of functionalities integration. There is no doubt that the huge semiconductor processing knowledge is leveraged to build synergy, there are also some unique challenges that need to be addressed specifically in the MEMS manufacturing processes. Particle or foreign material removal has been driven by the semiconductor process to the nanometer scale. While the current MEMS may not be sensitive to nanometer size particle, but the impact could be more detrimental as the particle can immobilize the motion completely and cause not only the yield but also the reliability issues. Wet cleaning is historically used for particle removal, but it has to overcome the sticking and drying issues once the mechanical member is released due to the fluid surface tension, in order to provide a robust cleaning solution. CO2 cryogenic aerosol cleaning is dry, and its non-oxidizing and non-etching nature has the potential to render a wide process window for particle removal in MEMS device. Liquid CO2 is delivered to the cleaning nozzle, expands through the orifice, and becomes a mixture of solid and gas CO2 toward the wafer surface for cleaning. Particle removal is primarily achieved by momentum transfer from the solid CO2 particles accompanied by drag force from the gas. In this paper, we will also discuss the cleaning nozzle technology where the size and velocity of solid CO2 particles are controlled to deliver the optimal particle removal performance without inducing any damage to the device. Other applications such as post dicing cleaning and post-ash fencing removal are proposed as well.
Paul Cheng, Director of Technology
Eco-Snow Systems LLC
Livermore, CA

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