Eects of the process conditions on the plume of a laser-irradiated indium±tin-oxide target C. Cal õ * , R. Macaluso, M. Mosca INFM and Dipartimento di Ingegneria Elettrica, Universit a di Palermo, Viale delle Scienze, 90128 Palermo, Italy Received 14 May 2001; accepted 25 July 2001 Abstract The plume of a laser-ablated indium±tin-oxide target was investigated by optical emission spectroscopy. Atomic and ionic species of indium, tin and oxygen were observed; moreover, molecular bands of indium oxide were identi®ed in the ¯uorescent spectra. The eects of the oxygen as a background gas and of the laser ¯uence on the behaviour of the ejected particles were studied with respect to the intensity of the emission and the delay time as a function of the observation distance from the target surface. The non-linear behaviour of the ¯uorescent species with the process conditions could infer spatial variations of the plume composition. The analysis demonstrates a plume expansion process where the ejected species interact with the molecules of the background gas by reactive collisions. Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 07.60.R; 52.25; 52.50.J; 52.70; 61.80.B Keywords: Optical emission spectroscopy; Indium±tin-oxide; Pulsed laser ablation; Plasma diagnostics; Time of ¯ight 1. Introduction Optical emission spectroscopy OES) is the easiest and most promising technique of plasma analysis to detect the characteristics of the plume. Many parameters, such as temperature, density and velocity of plasma, can be obtained by OES. It has already been used to study the characteristics of plasma produced by laser ablation of various materials, such as metals [1], dielectrics [2], semi- conductors [3,4], but especially superconductors [5±9]. In this work, we report OES measurements of major emission species in the plume generated by UV laser-irradiated indium±tin-oxide ITO) tar- gets. ITO is a highly degenerate n-type semicon- ductor with a wide band gap 3.7±4 eV) and ITO thin ®lms are frequently used in optoelectronic devices as transparent contacts for semiconductors because of their properties of transparency and good conductivity. The behaviour of the ITO target-emitted par- ticles is strongly dependent on the process condi- tions, as OES measurements demonstrate. In the last ten years, many researchers have shown that the growth of the ITO thin ®lms at room tem- perature is very sensitive to several deposition parameters such as the pressure of a background 1 October 2001 Optics Communications 197 2001) 341±354 www.elsevier.com/locate/optcom * Corresponding author. Tel.: +39-91-6566231; fax: +39-91- 488452. E-mail address: cali@unipa.it C. Cal õ). 0030-4018/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0030-401801)01459-6