Instantaneous Fluid Film Imaging in Chemical Mechanical Planarization
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Instantaneous Fluid Film Imaging in Chemical Mechanical Planarization Daniel Aponea, Caprice Graya, Chris Rogersa, Vincent P. Mannoa, Chris Barnsb, Mansour Moinpourb, Sriram Anjurc, Ara Philipossiand a Tufts University, Department of Mechanical Engineering, Medford, MA, USA b Intel Corporation, Santa Clara, CA, USA c Cabot Microelectronics Corporation, Aurora, IL, USA d University of Arizona, Department of Chemical Engineering, Tucson, AZ, USA ABSTRACT Dual Emission Laser Induced Fluorescence (DELIF) is employed to attempt to experimentally determine the nature of the lubrication regime in Chemical Mechanical Planarization. Our DELIF setup provides images of the polishing slurry between the wafer and pad. Static images were taken to provide a baseline, then dynamic runs were conducted. Analyzing these images shows that the wafer only contacts the pad in a small number of places around the wafer, mainly due to the pad’s topography. INTRODUCTION For many years the semi conductor industry has employed a polishing technique known as Chemical Mechanical Planarization. Ultra flat surfaces are needed during the production of integrated circuits, both on a local (nearly molecular level) and a global (12 inch silicon wafers) scale. In this process a silicon wafer is pressed a against a polyurethane polishing pad. Each is rotated, with a liquid slurry lubricating the interface. There are many variables in this process, such as pad type, rotation speeds, applied pressure, pad conditioning, as well as slurry composition and flow rate. Industry and the research community have long teamed to characterize this complex process, yet many questions still remain. This research aims to observe the interaction of pad and wafer determine which lubrication regime the CMP process lies in. There has been much debate as to whether or not the pad is supporting the wafer, or if the two are fully separated by a layer of slurry. Most likely it is a mixed polishing regime, with the pad's asperities partly supporting the wafer, and the fluid layer supporting load too. Much work has been done to try to determine the exact nature of the wafer/pad contact. There are several lubrication regimes that the CMP process is thought to encompass. Modeling work indicates that it is a delicate balance between hydrodynamic lubrication, mixed solid-liquid contact and even direct solid-solid contact. [1] The hydrodynamic lubrication occurs when the wafer is fully supported by a layer of slurry, with no contact between the wafer and polishing pad. Mixed solid-liquid contact is the case when the wafer is partly supported by the pressure in the liquid layer, and partly resting on the polyurethane asperities that rise up out of the pad. Solid-solid contact would occur most often in either static or super high downforce experimental cases, where the wafer is entirely supported by the pad. More complex models have begun to take into account the pad porosity and compressibility. Modeling efforts have been employed to predict the film thickness and removal rate b
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