High-Temperature Nanoindentation Measurement for Hardness and Modulus Evaluation of Low-k Films
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High-Temperature Nanoindentation Measurement for Hardness and Modulus Evaluation of Low-k Films Jiping Ye, Nobuo Kojima, Satoshi Shimizu and James M. Burkstrand1 Research Department, NISSAN ARC, LTD., 1 Natsushima-cho, Yokosuka 237-0061, Japan 1 Hysitron, Inc., 10025 Valley View Rd., Minneapolis, MN 55344, U.S.A. ABSTRACT A high-temperature nanoindentation measurement method has been developed for evaluating the hardness and modulus of low-k films when the temperature is raised from R.T. to 200oC. Thermal stability and chemical changes due to heating were investigated by Raman spectroscopy, Fourier transform infrared spectroscopy and thermogravimetry-differential thermal analysis, and by thermal desorption spectroscopy, respectively. Two different classes of low-k materials, organic polyarylence ether film and methyl-hydrogen-silsesquioxane film, were examined. The hardness and modulus of the former film during heating increased due to water desorption in the lower temperature range, and then decreased due to the evolution of hydrocarbon gas from some unreacted components or solvent residuals in the higher temperature range. In regard to the latter film, the hardness and modulus of a specimen (A) having a higher hydrocarbon content decreased during heating and reached the lowest value at 200oC and then constantly remained at the lowest levels during cooling. In contrast, no significant changes in hardness and modulus were observed for a specimen (B) having a lower hydrocarbon content in either the heating or cooling process. The reduction of the hardness and modulus of specimen A was attributed to thermal decomposition of most of its Si-CH3 and SiH/SiH2 chains. These results revealed that the temperature dependence of the hardness and modulus of low-k films is significantly affected by physical and/or chemical changes during heating due to moisture absorption, thermal evolution of organic residuals and thermal decomposition, rather than other factors such as thermal stress. INTRODUCTION Low-k dielectrics have attracted widespread interest for use as inter-metal dielectric materials to reduce interconnect resistance in ultra-large-scale integrated devices. Integration processes and practical use environments require that low-k dielectric materials possess not only a low, stable and isotropic dielectric constant, but also high mechanical strength as well as good thermal and chemical stability at high temperature [1, 2]. Moisture absorption, thermal decomposition, and other factors such as thermal or structural changes or stress may lower the mechanical properties of low-k films at high temperature, resulting in thermal deterioration or fracture. It is essential to evaluate the thermo-mechanical properties of low-k films for screening out unacceptable dielectric materials and for optimizing film growth process conditions to improve the reliability of low-k interconnect structures. As a technique for estimating mechanical properties, nanoindentation measurement has been widely used to evaluate the hardness and m
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