Interactions of Polysilicon with Aluminum

Abstract

ABSTRACTIn-situ resistivity measurements togheter with Auger electron spectroscopy, MeV 4He+ backscattering spectrometry, scanning electron microscope and x-ray diffraction have been used to investigate interactions between Al films and CVD polycristalline silicon layers deposited on thermally grown SiO2 on silicon. A sharp and well defined increase in resistivity around 450 °C has been associated to the erosion of the polysilicon and growth of Si crystallites in the metal film. The kinetic of the transformation has been studied by isothermal treatment over the 390–450 °C temperature range. An activation energy of 2.2 ± 0.2 eV has been measured. Similar results have been obtained by using treatments at constant heating rate. A critical analysis of the available data suggests that the rate limiting step is the nucleation of Si grains in the aluminum film. The driving force for the process can be identified to be the free energy difference between the initial and final states.