Study Of Measurement Method Of Microscale Subsurface Structure

This program aims mainly at find out a feasible method to determine the subsurface thermal properties distribution, implement the key technology, set up a system with the resolution of micron in face and the resolution of submicron in depth, which are prepared for the study of nanoscale scanning thermal microscopy.With periodically modulated semiconductor laser used as the heating source, continuing semiconductor laser used as probing laser, optic microscopy objective used as focusing optics, the steady photo thermoreflectance experiments are performed. The reflectance signal corresponding to the temperature response is detected. The setup includes periodical heating laser, continuing probing laser, objective, silicon photodiode, lock-in amplifier, 2D microscale scanning stage.The multilayer heat conduction is analyzed. The transmission line theory is described and used in the solving of heat conduction equations. Using Laplace transform, Hankel transform and transmission line theory, the expression of surface temperature is deduced in Laplace domain and Hankie domain. The temperature in frequency domain and space domain can be deduced by inverse transformation accordingly. The measurement principles of thermal characteristic are determined by the functions of phase lag or amplitude ratio between heating signal and probing signal. The simulated annealing algorithm in the inverse analysis for determining the thermal conductivity and thermal boundary resistance is developed. The sensitivity of the considered parameter is analyzed.The experiment principle and method of measurement of microscale subsurface thermo characteristics distribution are described numerically and experimentally. A laboratory measurement setup with resolutions of 5-10 micron is developed. The measurement of thermo conductivity distribution of microscale composite sample isrealized.The thermal conductivities of thermally oxidized SiO₂ films of 98nm, 148nm, and 322nm in thickness deposited on Si substrate are measured. The thermal conductivity of the nano SiO₂ film is found to be less than its bulk value, and thickness dependent. The thermal boundary resistance between SiO₂ and Al coating is found to be comparable to the thermal resistance of the SiO₂ layer. The thermal boundary resistance between SiO₂ and Si can be neglected.The results of scanning sample with buried inhomogeneities show that the sensitivity is the highest when the thermal diffusion length is comparatable to the depth of the buried inhomogeneities. The order of magnitude of thermal diffusion can be deduced. Accurate dimension of diameter of heating beam and probing beam and 3D thermal wave model are necessary for determining the exact thermal diffusivity.The process of heat conduction is analyzed numerically. Based on the simulation results, various depth and effusivity of the buried inhomogeneities in the microscale subsurface structure measurement is discussed.