JOURNAL OF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS, 5 (1994) 272-274 Modification of the properties of HTSC YBCO thin films on silicon by superfast laser annealing in oxygen with a CW CO2 Laser V. S. SERBESOV, P. A. ATANASOV, R. I. TOMOV* Institute of Electronics, Bulgarian Academy of Sciences, 72 Tsarigradsko shose, Sofia 1784, Bulgaria The use of superfast CW C02 laser annealing in 02 for modifying the properties of laser deposited Y1Ba2Cu30?-, thin films is described. The film resistivity could be controlled reversibly by laser irradiation at 40 Wcm -2. The resistivity was measured in situ during the annealing process. 1. Introduction One of the most important characteristics of the new HTSC (high-temperature superconducting) materials is the fact that their optical and electrical properties span the range from an insulating dielectric to a superconductor [1 4] providing considerable oppor- tunities for fabricating novel optoelectronic and microelectronic devices. The deposition of high-quality HTSC thin films on Si substrates is being intensely investigated by many groups [5-10], the aim being the integration of HTSC with conventional semiconductor technology. It would have important applications in creating high performance hybrid circuits, incorporating the best of what superconductors and semiconductors have to offer. Such a task demands development of repro- ducible methods for obtaining regions with different types of conductivity realized in a single HTSC layer deposited onto a Si substrate. In order to avoid deterioration of the film-Si sub- strate interface, due to reaction at high deposition temperatures, a number of groups have prepared Y1Ba2Cu3OT_x films on Si by various buffer layers [7-103, as well as by rapid laser annealing [11 15]. The laser annealing technique allows films to crystal- lize by heating only the thin surface layer for a short period with laser radiation CW Ar laser (488.0, 514.5 ~tm)[11]; CW Nd:YAG laser (1.06 Ixm) [12]; pulsed CO 2 laser (10.6 lam) [13, 143; CW CO2 laser [15]. Laser annealing also permits reversible resistiv- ity control in the chosen dimensions of the region annealed. This group has previously described [15] ex situ YIBa2Cu307 ~ thin film deposition on Si substrates, without intermediate buffer layers, using N 2 laser ablation and CW CO2-1aser annealing in 02. In this paper an investigation on the relationship between laser annealing conditions and the R versus T characteristics of Y1Ba2Cu3Ov_x thin films on Si, * Author to whom all correspondence should be directed. with the aim of modifying them at selected sites without destroying the film, is reported. 2. Experimental details and discussion A detailed description of the experimental set-up has been given previously [15]. The deposition was car- ried out in a vacuum (1.333 × 10 -2 Pa) by a N 2 laser (337.1 nm, 6ns, 8 mJpulse -1) ablation of a stoichi- ometric Y1Ba2Cu3OT_ x target on a (100) Si sub- strate. The thin films deposited were annealed in an 02 atmosphere [p(Oz) = 1.333 Pal by CW CO2-1aser radiation (10.6 I~m) directed onto the film surface. The maximum laser power density was 40 W cm-2. The film resistivity was measured in situ during the annealing process by stainless-steel lamellar spring electrodes mounted on the substrate holder and con- nected to a Philips PM 2521 multimeter. The elec- trodes were 0.5 mm thick, 25 mm long and 2 mm wide at the point of direct contact with the film surface. The resistivity of the electrical circuit without layers was 0.2 f~. A stainless-steel shield protected the strings from the laser radiation. This groups earlier investigation [15] found that direct CW COz-laser annealing for 8-10s at 40 W cm- z (annealing temperature T, = 800-1000 °C) formed structures with the presence of a metal Si-like transition. Longer laser annealing (G > 9-10 s) des- troyed the film. Such superfast annealed films were oxygen deficient and not superconductive. In the present work, to solve the problem of oxygen saturation multistep laser annealing was used instead of the superfast one. Three cycles of laser treatment were tested. During the first one the film was heated up to 420 °C for 1 s, whereupon the temperature was set at 350 °C for 1 min; this was followed by a second rise up to 420 °C for 2 s, a reduction to 350 °C for 2 min and one more heating up to 420 °C for 2 s. After that the 272 09574522 © 1994 Chapman & Hall