Substrate temperature dependence on the optical properties of Cu and Ag thin films

¹ Department of Physics, University of Tehran, North-Kargar Street, Tehran, Iran
² Iranian Aerospace Organization, Fajre Industrial Group, Tehran, Iran

Corresponding author: savaloni@khayam.ut.ac.ir

Received: 29 June 2004
Revised: 4 April 2005
Accepted: 17 May 2005
Published online: 18 August 2005

Abstract

Copper (260 nm) and Ag (1000 nm) films deposited on glass substrates, at different substrate temperatures. Their optical properties were measured by ellipsometry (single wavelength of 589.3 nm) and spectrophotometry in the spectral range of 200–2600 nm. Kramers Kronig method was used for the analysis of the reflectivity curves of Cu and Ag films to obtain the optical constants of the films, while ellipsometry measurements was carried out as an independent method. The influence of substrate temperature on the microstructure of thin metallic films [Structure Zone Model (SZM)] is well established [Movchan and Demchishin, Phys. Met. Metall. 28, 83 (1969); Thornton, J. Vac. Sci. Technol. 12, 830 (1975); Savaloni and Bagheri Najmi, Vacuum 66, 49 (2002); Savaloni and Player, Vacuum 46, 167 (1995); Savaloni et al., Vacuum 43, 965 (1992)]. The Effective Medium Approximation (EMA) analysis was used to establish the relationship between the SZM and EMA predictions. Good agreements between SZM as a function of substrate temperature and the values of volume fraction of voids obtained from EMA analysis, is achieved; by increasing the substrate temperature the separation of the metallic grains decreases, hence, the volume fraction of voids decreases and denser films formed. The predictions of the Drude free-electron theory are compared with experimental results for dielectric functions of Cu and Ag films of different substrate temperature. The real part of the dielectric constant is decreased with increasing the substrate temperature, while the imaginary part of the dielectric constant increased with temperature for both materials over the whole energy range measured, including intraband and interband regions. The increase of the imaginary part in the interband region suggests a temperature and frequency dependence of the relaxation time in the Drude model, namely