Determination of the number and size of inhomogeneities in thin films by ion beam analysis

Abstract

Ion beam analysis techniques are routinely used to determine elemental concentration profiles in thin layers of thicknesses between tens of nanometers and micrometers. The analysis of the energy spreading of the analyzing ion beam, as described in this paper, represents a different approach to the determination of the dimension and number density of nanometer-size inhomogeneities in the films and opens interesting possibilities in the noninvasive characterization of film microstructure by ion beam techniques. The sensitivity of the method depends on the energy resolution of the detecting system: in usual configurations the presence of inclusions of dimensions down to a few nanometers can be detected. Procedures for calculation of the size and number density of spherical inclusions are presented. The case of columnar inhomogeneities is also described in detail and a parameter characterizing the degree of organization of the spatial distribution of inclusions is introduced. Examples of application in Rutherford backscattering spectroscopy, elastic recoil detection analysis, and nuclear reaction analysis reveal that the method described allows fast and accurate measurement without destruction of the samples in all cases. Comparison of feature dimensions derived from the analysis of the energy spreading with results of direct measurements, wherever possible, demonstrates the strength of the method.