Spectroscopic ellipsometry of palladium thin films.

摘要

Spectroscropic ellipsometry is a nondestructive, ambient surface analysis technique for studying surfaces, interfaces and thin films. To take advantage of this method an automatic spectroscopic ellipsometer was designed and constructed for the microstructural characterization of thin films. This high precision instrument is capable of measuring in real-time the optical properties of bulk or thin film materials over the visible-UV region (1.5-6.0 eV). The microstructure of thin films can then be determined from an effective medium analysis of the spectroellipsometric data to investigate how the film morphology is influenced by the film preparation conditions.; In this thesis the pseudodielectric function of palladium films prepared by dc planar magentron sputtering was measured while the substrate temperature, argon partial pressure and rf-induced substrate bias were varied independently during deposition. Through spectroellipsometry, the evolution of the microstructure of the films was correlated to the changing deposition environment. The film data are in excellent agreement with the effective medium theory of Sen, Scala, and Cohen, relevant for a random coated-particle microstructure where the grains are optically isolated from each other, and which had been previously applied to only rhodium films. A microstructural analysis indicated a general trend towards increased porosity and microroughness of the films with higher argon pressures and substrate temperatures. The films deposited above a transition pressure of 15 mTorr were best described optically by a random coated-particle microstructure and electron microscopy confirmed the isolation of grains by void boundaries. With increasing rf-induced substrate biasing, the Pd film microstructure was modified in a manner similar to that obtained by varying the substrate temperature alone. The measured deposition rate while bias sputtering was significantly higher than that expected based upon the measured resputtering rate and several mechanisms were proposed to account for the enhancement in the deposition rate. The films were best characterized by a 2-dimensional isotropy which was supported by the columnar nature of the films observed by electron microscopy. Finally, the dielectric function of the "best" palladium film was compared to optical constants of Pd previously reported in the literature for bulk and thin film specimens.