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Piezoelectric sensor array for pressure uniformity measurements
Keywords: bonding, piezoelectric sensor, pressure uniformity
The further development of 3D integration technology requires uniform bond quality across 300 mm wafer stacks. To reliably perform a bonding process, the bond tool piston uniformity evaluation has to be done with high accuracy. Currently, Fujifilm pressure paper is used to measure the applied pressure uniformity in the tools. However, this method does not give high accuracy without additional analysis of data using special software. An alternative is to measure the tool pressure uniformity in real time using an array of piezoelectric sensors created on a polarized polyvinylidene fluoride film in a 300 mm wafer format. This film has a high voltage output: 10 times higher than piezoceramics for the same force input. It generates charge when compressed by the bonder plates. The amplitude of the signal is directly proportional to the film mechanical deformation or applied force. However, the measurements of the voltage created can be considered static and require a special data acquisition system (DAS) because the electrical charges developed by the piezo film decay with a time constant that is determined by the dielectric constant, the internal resistance of the film and the input impedance of the used electronics. The film is sandwiched between multiple patterned metal electrodes in an array of individual sensors of any required density. As a result, the array of precisely defined piezo-active sensors (where the top and bottom Cu/Ni electrodes fully overlap) is produced by a combination of photolithography and chemical wet etching. Metal lines are patterned simultaneously with the electrodes and connected to the DAS through Flexible Printed Circuit (FPC) connectors. The resulting deformation causes a voltage to appear between the patterned electrodes and analyzed in real time by the NI X Series Data Acquisition under LabView control.
Graham Potter, Graduate Student/Research Assistant
College of Nanoscale Science and Engineering (SUNY Albany)
Albany, NY

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