Studies of the Coefficient of Thermal Expansion of Low-k ILD Materials by X-Ray Reflectivity
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0914-F11-02
Studies of the Coefficient of Thermal Expansion of Low-k ILD Materials by X-Ray Reflectivity George A. Antonelli1,2, Tran M. Phung3, Clay D. Mortensen3, David Johnson3, Michael D. Goodner4, and Mansour Moinpour5 1 Assembly Capital Equipment Development, Intel Corporation, 5000 W. Chandler Blvd., Chandler, AZ, 85226 2 Physics Department, Brown University, 182 Hope St., Providence, RI, 02912 3 Chemistry Department, University of Oregon, 1253 University of Oregon, Eugene, OR, 97403 4 Fab Materials Operations, Intel Corporation, 5200 NE. Elam Young Parkway, Hillsboro, OR, 97124 5 Fab Materials Operations, Intel Corporation, 2200 Mission College Blvd., Santa Clara, CA, 95054 ABSTRACT The electrical and mechanical properties of low-k dielectric materials have received a great deal of attention in recent years; however, measurements of thermal properties such as the coefficient of thermal expansion remain minimal. This absence of data is due in part to the limited number of experimental techniques capable of measuring this parameter. Even when data does exist, it has generally not been collected on samples of a thickness relevant to current and future integrated processes. We present a procedure for using x-ray reflectivity to measure the coefficient of thermal expansion of sub-micron dielectric thin films. In particular, we elucidate the thin film mechanics required to extract this parameter for a supported film as opposed to a free-standing film. Results of measurements for a series of plasma-enhanced chemical vapor deposited and spin-on low-k dielectric thin films will be provided and compared. INTRODUCTION There has been a considerable effort to integrate low-k dielectric materials as interlayer dielectrics (ILD) to increase the speed of microelectronic devices by decreasing the resistancecapacitance (RC) time delay of their interconnects [1]. Many classes of these materials lower the dielectric constant through the introduction of porosity into the matrix of a given dielectric such as SiO2. The elastic moduli of the resultant thin films are generally much lower than those of the matrix itself which can make them incompatible with processes such as chemical-mechanical polishing (CMP) and die attach in assembly. For these reasons, experimental techniques such as nanoindentation, Brillouin scattering, and laser-induced acoustics have been used to evaluate the elastic moduli of these thin film materials [2,3,4]. Other properties are also relevant to the integration of these materials. For example, the coefficient of thermal expansion (CTE) is a key factor in determining how stress and/or strain develops in interconnects during a thermal cycle. This parameter has been largely ignored for dielectrics prior to the introduction of low-k materials because the ILD materials previously used had a CTE much smaller than any metals in an interconnect. However, some low-k materials have a CTE not only on the order of a metal but significantly greater. For this reason, the study of this property for new classes of materi
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