Surface roughness of aluminum thin films deposited by effusive and ionized cluster beams

Abstract

The surface roughness of aluminum thin films is of importance in a number of microelectronic device applications as well as in other technologies. A question one needs to address is how thin film surface roughness depends on substrate temperature and film thickness for various deposition methods. We have used an effusive source and an ionized cluster beam (ICB) source in the same apparatus to deposit pure aluminum films. A study of the surface roughness of these films shows that for a fixed substrate temperature T s (1) the roughness average R a is a power function of the film thickness t such that R a = At n where A and n are constants, (2) A and n do not depend on the deposition method except at T s = 200 °C, and (3) for ICB deposition, A and n are not dependent on acceleration voltages between 0 and 6 kV. These results apply for oxidized silicon substrates with T s between 70 and 400 °C and for aluminum thicknesses less than 800 nm. The initial substrate R a was less than 1 nm. At T s between 70 and 100 °C, R a = 1.5 × 10 −3 t 1.5, at T s = 200 °C, R a = 3.5 × 10 −2 t 1.08 for ICB deposition, and R a = 0.36 t 0.61 for physical vapor deposition, at T s = 300 °C, R a = 1.0 × 10 −2 t 1.30, and at T s = 400 °C, R a = 6.53 × 10 −3 t 1.38, where R a and t are expressed in nanometers.