Scanning tunneling microscope study of the morphology of chemical vapor deposited copper films and its correlation with resistivity

Abstract

In this article we report the results of the scanning tunneling microscope study of the surface morphology of copper films grown by metalorganic chemical vapor deposition from the precursor Cu(tbaoac). Films ≈100 nm in thickness were grown by varying the reactor pressure. The images reveal the crucial role of the reactor pressure and growth rate on the morphology and grain growth of the films. Films grown at a low growth rate have a smooth surface with small well connected grains of ≈10-40 nm diameter with relatively lower resistivity, while films grown at higher growth rates have rougher surfaces and larger grain sizes of ≈10-100 nm diameter with poor connectivity that leads to higher resistivity. The correlation of the morphology with resistivity (ρ) and the temperature dependence of ρ in the range 300-4.2 K was investigated. Comparison with the ρ of pure bulk copper shows that these films have much higher resistivities. A large part of the high resistivity at room temperature arises from an enhanced temperature dependent part of ρ and is not due to an enhancement of the residual resistivity alone. The films exhibit deviations from Matthiessen's rule. From a semi-quantitative analysis of the data using existing theories we could assign the large ρ as well as the temperature dependence of ρ to grain boundary scattering and surface scattering. However, for T>50 K we find that an extra temperature dependent ρ term which may be related to enhancement of electron-phonon interactions by the rough film surface is required.