Sub Surface Material Characterization using High Frequency Eddy Current Spectroscopy
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1195-B09-02
Sub Surface Material Characterization using High Frequency Eddy Current Spectroscopy Henning Heuer, Susanne Hillmann, Marcus Klein and Norbert Meyendorf Fraunhofer Institute for Non Destructive Testing, Dresden
ABSTRACT New processes introduced by nano science into much more conventional industrial applications require fast, robust and economical reasonable inspection methods for process control and quality assurance. Developed for semiconductor industries the methods available for thin film characterization and quality control are often complex and require highly skilled operation personnel. This paper presents a new concept based on high frequency eddy current spectroscopy that allows reliable and robust thickness measurements of thin conducting films on silicon or insulation substrates with a thickness resolution of about 2.5 nm. The transmission mode sensor configuration is a more practical method for inline-monitoring of thin film characterization. Due to the insensitivity of the transmission mode to dislocations or slight tilting of the sample the high frequency eddy current method is a practical method for thin film characterization in the industrial environment. INTRODUCTION Due to the complexity of thin film deposition processes variations of material parameters like microstructures, grain size, particle or void density can occur by a minor shift of process parameters. Developed for semiconductor industries the methods available for thin film characterization and quality control are complex and often require highly technical skilled personnel. This paper presents first results obtained by a newly developed high frequency eddy current spectrograph on thin film coatings and multilayer thin film systems. The value of electrical conductivity contains information on the chemical composition, micro structural and mechanical properties of the material. Not only the chemical composition and thickness, but also grain size, strain gradients or precipitates influences in different amounts the electrical conductivity. [1,2,3,4] The characterization of electrical conductivity as sheet resistance by using four probe measurements is a well established method for characterization of thin films systems. Sheet resistivity is used for homogeneity control, film thickness measurements or quality assurance in a broader understanding. Hence performing mappings allows the detection of deviation and delaminations (or cracks) by directly contacting the surface. As the four point technique works in direct contact, the quality of the contact underlies several influences like contact force, surface oxides or impurities. Beside these effects, small damage to the surface can cause negative effects to the performance of the thin film system. Additionally a complex mechanical manipulator is required to perform mappings to image a sample or to apply the method as an in-line device. Using electromagnetically induced eddy currents inside the specimen the characterization of electrical properties of thin films becomes possible wi
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