Development of method for measuring three dimensional thermal properties of Si/NiFe/AIN thin film using a angle femtosecond thermoreflectance technique

本研究的目的是发展一种非接触式、非破坏性的测量垂直于薄膜表面的热扩散率的方法，该方法要求利用飞秒热反射技术获得足够高的时间分辨率的温度响应。利用飞秒脉冲激光的热反射技术，研制了一种能够测量几十个微微秒到几百微微秒范围内温度响应的仪器。通过对铝、钼大块样品的测量，验证了仪器的有效性和测量原理。在本研究中，通过对光学系统和检测系统的改进和优化，获得了足以分析垂直于薄膜表面的热扩散率而不受衬底影响的热反射信号。热扩散系数值由最小二乘法确定，用最小二乘法拟合观测到的热折射…更多的电感信号，带有温度变化公式，从单层模型中推导出来，排除了衬底的影响。该技术也应用于块状样品，并与薄膜样品的结果进行了比较。由于具有较高的时间分辨率，可以在较短的时间范围内进行测量，因此我们可以在脉冲激光加热后立即讨论电子和声子在物质中的行为。XPS测试证实了样品表面存在天然氧化层。用椭圆偏振光谱仪对样品表面进行了光学常数测量和结构分析。还给出了天然氧化层对热输运现象的影响。结果表明，在足够的时间分辨率和信噪比下，获得了脉冲加热后100ps内的快速能量传输，其热扩散系数κ=1.5x10^&lt；-5&gt；m^2 S^-1&gt；得到Mo块材的热扩散率为κ=2.1x10^&lt；-5；m^2s^&lt；-1。因此，Mo在薄膜和块体之间的热扩散系数的差异似乎很小。然而，这些值不同于文献中给出的钼块的参考值κ=5.43x10^-5&gt；m^2 S^-1。造成这种差异的原因可能是弹道电子散射和电子-声子能量输运伴随着有限的时间滞后，这在我们的测量中很可能在飞秒脉冲加热后的皮秒时间范围内被探测到。脉冲加热在样品表面产生的弹性波也会影响热扩散率。较少

The purpose of this study is to develop a noncontact and nondestructive method for measuring thermal diffusivity perpendicular to the thin film surface, which requires obtaining temperature response with sufficiently higher time-resolution by using a femtosecond thermoreflectance technique. We have developed the instrument that is able to measure temperature response in the range from several tens of ps to several hundreds of ps by the thermoreflectance technique with a femtosecond pulse laser. The validity of the instrument and the principle of the measurement have been confirmed through measurements of Al and Mo bulk samples. In this study, thermoreflectance signal, which is sufficient to analyze the thermal diffusivity perpendicular to the thin film surface without any influence from substrate, is obtained by both improvement and optimization of the optical and the detection system. The thermal diffusivity value is determined by a least square method fitting the observed thermorefle … More ctance signal with a temperature variation formulae derived from a single layer model excluding effects of the substrate. This technique is also applied to bulk samples and the results are compared with those of thin films. Since the measurement in shorter time regime is possible due to the higher time-resolution, we are allowed to discuss behavior of electron and phonon in the substance just after the pulse laser heating. Existence of natural oxide layer on the sample surface is confirmed by XPS measurement. Measurement of optical constants and structure analyzes of the sample surface are performed by spectroscopic ellipsometry. The influence of the natural oxide layer on the thermal transport, phenomenon has also been given. It is found that rapid energy transportation within 100ps after the pulse heating is obtained with sufficient time-resolution and a signal-to-noise ratio giving the thermal diffusivity value of κ = 1. 5 x 10^<-5> m^2 s^<-1>. The thermal diffusivity of Mo bulk was obtained to be κ = 2.1 x 10^<-5>m^2s^<-1>. Thus, the difference of the thermal diffusivities of Mo between film and bulk appears to be small. However, these values differ from a reference value of κ = 5.43 x 10^<-5>m^2 s^<-1> given in the literature for the Mo bulk. The reason of this difference may be due to ballistic electron scattering and an electron-phonon energy transportation accompanying a finite time lag, which are likely detected in our measurements within picosecond time regime after the femtosecond pulse heating. An elastic wave generated on the sample surface by pulse heating may also affect the thermal diffusivity. Less