Characterization of the Depositing Flux in Laser Ablation Deposition (LAD).
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CHARACTERIZATION OF THE DEPOSITING FLUX IN LASER ABLATION DEPOSITION (LAD).
Jacques C.S.Kools and Jan Dieleman
Philips Research Labs. P.O.Box 80.000 5600 JA Eindhoven, The Netherlands
ABSTRACT Angular-resolved time-of-flight (ARTOF) studies have been performed on ablation plumes of copper generated by excimer laser fluences just above threshold in vacuum. neutrals are observed. Relative Positive ions, Rydberg atoms and ground-state concentrations, angular intensity distributions and angular- resolved velocity distributions are measured for ground state neutrals and ions . Ions have the highest kinetic energies ( 20-80 eV) . Their angular distribution is isotropic. Their concentration at the substrate is very low ( < 10-6) . Ground state neutrals have lower energies ( P 1 eV) . Their intensity and velocity is a strongly decreasing function of the polar angle. Rydberg-atoms have energies in between those of ground-state neutrals and ions. Their angular distribution is also dependent on tile polar angle. The concentration , kinetic energy and angular distribution of the ionised species arc very well explained by a mechanism of thermal ionization and subsequent space-charge induced repulsion. The velocity distributions and angular intensity distributions of the ground-state neutrals are quantitatively predicted by a model for the flow dynamics of pulsed laser generated gas clouds.
INTRODUCTION The characterization and , if possible, quantitative description of the depositing flux in Laser Ablation Deposition (= Pulsed Laser Deposition) is a key issue in the control of the deposition process. The composition of this flux has direct consequences for the details of the thin film growth process, and thus for the quality of the deposited film. While the presence of species with an important amount of electronic or kinetic energy stimulates the growth of a high quality, dense film due to the increased reactivity of these species. However, particles with kinetic energies above a certain level cause atomic displacements. This results in undesirable effects such as lattice defects in the film as well as atomic mixing near interfaces. The flow of the majority of the particles, i.e. ground state neutrals , dictates the deposition geometry. A thorough solution of one of the major problems in current LAD technology, viz the lack of uniformity over large areas, requires quantitative information on this flow. the problem of Given these considerations, it will be understood that characterization of the depositing flux has received considerable attention during the last few years. However, in many cases, the interpretation of the data obtained is complicated by the diversity of species present in the flux, especially for the case of multicomponient materials such as high T. superconductors. The relatively simple system of copper
Mat. Res. Soc. Symp. Proc. Vol. 236. ©1992 Materials Research Society
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ablation by excimer laser pulses has been the subject of a variety of studies during the 1-7 past years , making it one of the b
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