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EFFECTS OF PROCESSING PARAMETERS ON THE LASER DEPOSITION OF HIGH TEMPERATURE SUPERCONDUCTING THIN FILMS

N. S. Nogara, R. Castaina, R. C. Dyea, S. Foltyna, R. E. Muenchausenb and X. D. Wub aChemical and Laser Sciences Division, MS G738 bExploratory Research and Development Center, MS K778 Los Alamos National Laboratory, Los Alamos, New Mexico 87545 ABSTRACT: Y2 0 3 pressed powders were ablated by pulses from a XeCI excimer laser, operating at 308 nm, 150 mJ/pulse, =15 nsec/pulse and 20 Hz. Emission spectra from Y* and YO' were recorded as a function of ambient oxygen pressure in the range i0.5 - 4x10-1 Torr, at a laser fluence of =4 Jlcm 2 . A kinetic model is developed to describe the results, and the application to production of laser-deposited high-

temperature superconductor thin films is discussed. INTRODU CTION:

Laser ablation for the deposition of thin films is becoming a widely used technology. This process has some advantages relative to conventional deposition technologies (1 ,2] including rapid growth rates, the ability to congruently evaporate

multicomponent targets, and the production of high-energy (eV) atoms, molecules, ions and clusters which enhance the production of epitaxial films. Laser ablation has been used most recently for the production of high-temperature superconducting (HTSC) thin films [3-5].Recent work in this laboratory has demonstrated the production of high-quality

epitaxial HTSC thin films using the laser deposition technique (6-8]. In this process, a pressed oxide target, containing a stoichiometric mixture of yttrium, barium and copper is ablated at fluences =4 J/cm 2 . The vaporized material passes through a lowpressure oxygen atmosphere, 0.2 Torr, and is subsequently deposited on a heated (700 oC) substrate. The film is cooled in a relatively high-pressure oxygen atmosphere, 200 Torr. Despite efforts to understand the chemistry of this process [91, little is known about the gas phase or surface chemistry occuring during the deposition process. In an effort to elucidate the mechanisms for the gas phase chemistry, we have undertaken a study of single-component metal and metal oxide laser ablation. In this work, we report on the ablation of Y2 0 3 , with a XeCI excimer laser. EXPERIMENTAL: The bulk of the apparatus has been described previously [6]. Briefly, the deposition chamber consists of a modified six way 6" dia. stainless steel cross, as shown in Figure 1. Load locks are provided for target and substrate introduction to minimize pumping times. The target can be rotated in conjunction with horizontal

Mat. Res. Soc. Symp. Proc. Vol. 201. •c1991 Materials Research Society

166

rastering of the laser beam while the substrate is rotated to ensure uniform thickness (±10%) across the substrate diameter. Provisions are made to heat the substrate, either indirectly on a Ni block or radiatively. Processing gases can be introduced into the deposition chamber using mass flow control to maintain a constant pressure or by a pulsed valve. The excimer laser used in these experiments