Analysis of the performance of a micromechanical test structure to measure stress in thick electroplated metal films
ABSTRACT Previously reported suspended microrotating test structures designed to measure the stress in thick layers of electroplated Permalloy (NiFe alloy) have been analysed using finite element modelling and compared with experimental measurements. These results have been used to optimise a stress sensor test structure and design a new mask, with an array of test structures specifically designed to wafer map the stress of thick nickel and Permalloy films. This is the first time these structures have been employed for determining spatial variation in film stress and the results of this characterisation are reported for nickel.
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ABSTRACT: Nickel-iron alloys have useful magnetic properties that are of interest to the MEMS industry, but the high stress levels that can develop during the fabrication process pose a real challenge. This paper addresses the characterisation of NiFe films using suspended rotating structures, electrical test structures and X-ray fluorescence measurements. An automated measurement system has been developed, which facilitates rapid wafer mapping to spatially compare stress levels at different stages of the fabrication process. This has been used, together with other wafer mapped parameters such as alloy composition, sheet resistance and layer thickness, to identify correlations and provide an increased understanding of the relationships between the different process control factors.IEEE International Conference on Microelectronic Test Structures (ICMTS 2011); 01/2011