Laser Thermoreflectance Measurement for Evaluating Heat Capacity and Interface Heat Resistance of Low-k Films
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Laser Thermoreflectance Measurement for Evaluating Heat Capacity and Interface Heat Resistance of Low-k Films Jiping Ye, Takeo Okamura, and Shigeo Sato Research Department, Nissan ARC Ltd., 1, Natsushima-cho, Yokosuka, 237-0061, Japan ABSTRACT A novel technique that combines laser thermoreflectance measurement with the 3-omega method is proposed for evaluating the heat capacity of low-k films and the heat resistance at the interface between the low-k film and Si substrate. It was demonstrated that the heat capacity of thin films and the heat resistance at the interface can be determined by obtaining the heat effusivity of the film from laser thermoreflectance measurements, the total heat resistance obtained with the 3-omerga method, and the film density and thickness found from x-ray reflectivity measurements. The heat capacity of SiOC films was determined to be Cp(SiOC) =1.1 kJ/kgK with interface heat resistance of Rint(SiOC) = -2.37x10-8 m2k/W, while the heat capacity of Th-ox films was determined to be Cp(Th-ox) =0.61 kJ/kgK with Rint(Th-ox) = +1.74x10-8 m2k/W. A DSC heat capacity measurement confirmed the reliability of the evaluated Cp data. XRR and TEM examinations revealed that the negative interface heat resistance exhibited by the SiOC films is deeply relative to a high density layer at the interface between the film and Si substrate; and the positive interface heat resistance displayed by the Th-ox films stemmed from atomic defects at the interface between the film and Si substrate. The measured negative interface heat resistance is an apparent value, which does not mean a real negative interface heat resistance physically existing at the interface, but the easiness for heat to flow from the film to the substrate. INTRODUCTION High thermal stability and low thermal stress are required for low-k films to prevent thermal deterioration, fracture such as debonding of the interface and cracking of the thin film, and property changes in Cu/low-k interconnect structures during thermal treatment processes. Thermophysical properties such as thermal conductivity, thermal expansion coefficient and glass-transition temperature have been widely estimated with the aim of improving the thermo-mechanical performance of these low-k films. Techniques for measuring these thermophysical properties are well-known and the associated equipment is commercially available. Besides these properties, heat capacity and heat resistance are also very important attributes. The low heat capacity of low-k films and high heat resistance at the interface can elevate the film temperature to a high level, resulting in high thermal stress and damage to the films. However, it is extremely difficult to determine the heat capacity Cp and heat resistance Rint of thin films, and, until recently, measurements of Cp and R have generally been restricted to bulk materials. In this work, an attempt was made to apply a laser thermoreflectance (LTR) measurement method in combination with the 3-omega method for evaluating the heat capacity of l
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