Effect of the deposition temperature on the properties of iridium thin films grown by means of pulsed laser deposition
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Effect of the deposition temperature on the properties of iridium thin films grown by means of pulsed laser deposition M.A. El Khakani,a) B. Le Drogoff, and M. Chaker
Institut National de la Recherche Scientifique, INRS-E´nergie et Mate´riaux, 1650 Boulevard Lionel-Boulet, C.P. 1020, Varennes, Que´bec, Canada J3X 1S2 (Received 18 December 1998; accepted 15 March 1999)
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 (Ra) 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 ⍀ cm, which is very close to the iridium bulk value of 5.1 ⍀ 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.
I. INTRODUCTION
Iridium thin films are of great interest for many applications because of the excellent intrinsic properties of this noble metal. These attractive properties include the following: high melting point, high mechanical strength, excellent chemical stability, superior oxidation resistance, and very low electrical resistivity.1,2 Use in metaltrace electroanalytical sensors is one of the applications for which iridium is the microelectrode-material of choice so far since it satisfies best the overall requirements,3,4 especially the important criterion of low solubility in mercury (which is of about 3 × 10−12 at.% for Ir).5 For these metal trace sensors, the iridium microelectrode array constitutes the conducting base on which mercury hemispherical microdrops (the sensing material) are electroplated.4 Microfabrication processes for such sensors involve multilayer processing schemes, consequently the control of the mechanical stress of each layer, including the iridium thin film, is an important step in ensuring the mechanical stability of the whole multi-
a)
Address all correspondence to this author. e-mail: [email protected] J. Mate
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