Characterizing the Modulus and Hardness of Photopatternable Silicone Compositions Using Depth Sensing Nanoindentation
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Characterizing the Modulus and Hardness of Photopatternable Silicone Compositions Using Depth Sensing Nanoindentation Brian R. Harkness, Richard L. Schalek1, Satyen K. Sarmah and Lawrence T. Drzal1 Dow Corning Corporation 2200 W. Salzburg Road, Midland, MI 48686, U.S.A 1 Department of Chemical Engineering and Materials Science Michigan State University, East Lansing, MI, 48824, U.S.A. Abstract The mechanical properties of two cured silicone monolithic specimens with targeted bulk moduli of 300 and 10 MPa have been evaluated by DMA and regionally by CSM nanoindentation. The results showed that the mechanical properties of the monolithic samples were heterogeneous, with the DMA and nanoindention results only in agreement at the midplane of cleaved bulk samples. The specimens showed a significantly higher modulus at the sample surfaces compared to the bulk. Thin films of the same silicones displayed a modulus closer to that of the bulk sample surface. The nanoindentation results of this study were reliable and consistent, and are being used to assess the effects of material and microelectronic device integration processes on the mechanical properties of a series of low modulus photopatternable silicone thin film dielectrics. Introduction The development of the next generation of electrical, optical, bio and MEMS devices is creating a need for new specialized building materials, application and integration processes to facilitate their introduction into increasingly sophisticated device architectures. Key physical property attributes of these new materials include high optical transparency, flexibility, low stress and high thermal stability. Process simplicity and ease of integration are equally important and can have considerable bearing on the final properties of the material in the device. Silicone materials can be designed to accommodate many of the key device requirements and also provide application simplicity when combined with lithographic patterning capability1. A concern for any material exposed to multistep integration is the impact of these processes on the final material properties. Examples of these processes include exposure to plasma cleaning, metal sputtering and etching, dielectric and photoresist coating and development, and high temperature exposures that accommodate these and other processing steps. It is not possible to evaluate changes in the mechanical properties using bulk methodologies, as these would not accurately reflect the scale of the actual device, therefore nanoindentation was viewed as an alternative method. The objective of this study was to assess the applicability of depth sensing CSM nanoindentation2,3 to quantify the mechanical properties of a series of newly developed low stress, low modulus photodefinable silicones. Samples of the materials were prepared as 20 µm thick films on a silicon wafer substrate, as well as 2 mm thick monolithic specimens. The films were examined by CSM nanoindentation and the monoliths examined by both CSM nanoindentation and dynamic mechanical
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