Mechanisms of the Redistribution of Carbon Contamination in Films Formed by Atomic Layer Deposition

Abstract

The depth distribution of carbon impurities in hafnium oxide films obtained by plasma-assisted atomic layer deposition is studied experimentally and theoretically. An analytical model is proposed that describes the dependence of the carbon impurity concentration profile in the film. The model takes into account the fact that the formation of a carbon impurity in the growing film may be caused by the incomplete oxidation of the organometallic precursor. The diffusion redistribution of impurities is determined by mech-anisms that take into account the presence of carbon in different kinds of states: an insoluble state (carbides, carbonates), a highly mobile state (CO, CO2), and an unstable state whose lifetime is longer than the film’s growth time. The possibility of controlling the carbon impurity both in deep and near-surface layers is shown. The predictions of the model are confirmed experimentally using the mass spectrometry of the secondary ions in the films obtained by atomic layer deposition. To test the theory, special structures of hafnium oxide are developed, consisting of several layers, in which the time of the plasma exposure to the sample is varied at the same dosage of the organometallic precursor. The layer with the shortest exposure time to the plasma is deposited on the substrate, then the same number of cycles on the next layer take place, provided that the exposure time is increased by a factor of n. This makes it possible to deepen the transition zones and thus pro-tect them from the effects of the atmosphere.