The Use of Power Spectrum Density for Surface Characterization of Thin Films

Abstract

A step-by-step framework for undertaking PSD characterization of the surface topography of radio frequency (rf) magnetron sputtered thin Al films is presented in this chapter. The work aims to illustrate the significance of PSD method in analyzing the surface properties of thin films based on AFM imaging. It also aims at illustrating a repeatable procedure for undertaking PSD analysis on thin films. Brief theoretical background of power spectral density, with highlights on the fundamental theory, is herein presented. A two-dimensional power spectral computation of thin Al films sputtered on a titanium substrate at 150 W and 200 W rf powers for 2 hr is undertaken. Prior to the computation, a detailed image analysis theory and procedure of the AFM micrographs are presented. The calculation of power densities of the AFM images is conducted using the fast Fourier (FFT) algorithm of discrete Fourier transformation (DFT) in MATLAB script. The power spectral results are then fitted into k-correlation and inverse power models to interpret the spectral profiles. From the modelling, the equivalent root means square, correlation length and Hurst components have been determined. These values were distinctly discussed in relation to the sputtering power and morphological observations of the 3D AFM microscopy. The PSD results correlate well with the morphological observations of the atomic force microscopy.