Effect of the deposition temperature on the properties of iridium thin films grown by means of pulsed laser deposition

Abstract

Pulsed laser deposition (PLD) of Ir thin films has been achieved by ablating an iridium target with a KrF excimer laser. The iridium deposition rate was investigated, over the (0.4–2) × 10⁹ W/cm² laser intensity range, and found to reach its maximum at (1.6 ± 0.1) × 10⁹ W/cm². At this laser intensity, the PLD Ir films were deposited at substrate deposition temperatures ranging from 20 to 600 °C. The PLD Ir films exhibited a (111) preferentially oriented polycrystalline structure with their average grain size increasing from about 10 to 30 nm as the deposition temperature was raised from 20 to 600 °C. Their mean surface microroughness (R_a) was found to change from an average value of about 1 nm in the 20–400 °C temperature range to a value of about 4.5 nm at 600 °C. As the deposition temperature is varied from 20 to 600 °C, not only does the stress of PLD Ir films change drastically from highly compressive (−2.5 GPa) to tensile (+0.8 GPa), but their room-temperature resistivity also gradually decreases in the 20–400 °C range and stabilizes for higher temperatures. In the 400–600 °C range, the resistivity of PLD Ir films was as low as 6.0 ± 0.2 μΩ cm, which is very close to the iridium bulk value of 5.1 μΩ cm. Thus, PLD Ir films exhibiting not only the lowest resistivity but also a nearly zero stress level can be grown at a deposition temperature of about 400 °C. The resistivity of the PLD Ir films can be described by a grain boundary scattering model.