Development of thin film reference material for thermal diffusivity ○Takashi YAGI 1 , Naoyuki TAKETOSHI 1 , Tetsuya BABA 2 1. Thermophysical Properties Section, NMIJ, AIST Tsukuba Central 3, 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, JAPAN Corresponding author: Takashi YAGI, E-mail: t-yagi@aist.go.jp 2. Material Properties and Metrological Statistics Division, NMIJ, AIST Tsukuba Central 3, 1-1-1, Umezono, Tsukuba, Ibaraki 305-8563, JAPAN There has came into existence some practical instruments to measure the thermophysical properties of thin films, and those instruments have been recognized to be of benefit to R&D in the thin film technology. However, there are no systems to calibrate such instruments by standards that are guaranteed to trace up to national standards or reference materials. Accordingly, NMIJ/AIST has established a high speed laser flash apparatus as a national standard in Japan. The apparatus can measure the thermal diffusivity of thin films normal to the surface with small uncertainty using a thermoreflectance technique. Based on this apparatus, a calibration service of the thermal diffusion time for user’s specimen has started at the end of 2007 FY. We have moved to develop a thin film reference material for thermal diffusivity, since the reference material is more useful to calibrate the practical instrument. The reference material is made of a titanium nitride (TiN) thin film with 700 nm in thickness. The TiN film was deposited on a synthesized silica wafer (76.2 mm in diameter, 0.525 mm in thickness, Shin-Etsu Chemical Co., Ltd.) using a reactive dc magnetron sputtering. The target metal is pure Ti and the sputtering gas is pure N 2 gas. The TiN film on the wafer was patterned with each individual chips using a photo-resist and metal-resist coatings by lithography technique. The chip is 10mm x 10 mm, and an etched line of 1 mm x 100 μm is positioned at the center of the film. This etched line is for a surface profiler in order to measure the film thickness. The thermal diffusion time of a typical film is 145.9 × 10 -9 s, and its expanded uncertainty is 3.6 %. We are planning to establish the thin film reference materials ｂｙ end of 2008 FY in Japan. 1. Introduction Thermophysical properties for thin films become important in order to manage heat transport in high technology devices. For example, heat management between interconnects and interlayer dielectric materials for a microprocessor will be a critical problem in very near future. In additions, rewritable optical disks, hard disks using heat assisted magnetic recording technology, phase change memories and thermo-electric devices also require reliable thermophysical properties values of the thin film materials for the optimum thermal design. There has came into existence some practical instruments [1-3] and methods [4] to measure the thermophysical properties of thin films, and those instruments have been recognized to be of benefit to R&D in the thin film technology. Accordingly, NMIJ/AIST has established a high speed laser flash apparatus as a national standard in Japan. The apparatus can measure the thermal diffusion time of thin films normal to the surface with small uncertainty using a thermoreflectance technique. We have moved to develop a thin film reference material for thermal diffusivity. This reference film is of use to guarantee the practical instruments for suppliers, and instrument users also have the benefit with regard to calibration for their own instrument. In this paper, preparation of the reference material and measurement procedure are reported. 2. Development of Reference thin film 2.1 Standard apparatus for thermal diffusion time NMIJ/AIST has established a standard apparatus to measure the thermal diffusion time, τ f of the reference film. The thermal diffusivity, κ f is represented as follows equation, f f d τ κ 2 = (1) where d is a characteristic length, i.e. film thickness. Thus, the value of κ f can be derived from the data of τ f and d. The standard apparatus is shown in Figure 1. Two sub-nanosecond pulsed lasers with wavelength of 1064 nm 1ｓｔ International Symposium on Thermal Design and Thermophysical Property for Electronics, June 18-20, 2008, Tsukuba Figure 1 Block diagram of a standard apparatus for the thermal diffusion time measurement.