Characteristics of metal thin film deposition by laser ablation and laser-ablation-assisted-plasma-discharge

摘要

Experiments are under way to deposit thin films of Al on Si substrates by two laser-ablative deposition processes: KrF excimer laser ablation and laser-ablation-assisted-plasma-discharges. Laser ablation is accomplished by focusing a KrF excimer laser (>1.2 J, 40 ns, 248 nm) onto a pure (99.999%) solid aluminum target. Typical ablation fluences range from 4-10 J/cm/sup 2/. Through gated optical emission spectroscopy, the laser ablation plume optical emission is observed to contain only aluminum neutral transitions after approximately 100 ns. With the application of a 3.6 kV, 760 A discharge, the neutral atom plume is transformed into a plasma with the emission dominated by Al/sup +/ and Al/sup 2+/ transitions. Spectroscopic measurements indicate an Al/sup +/ electronic temperature of 1 eV and an Al/sup 2+/ electronic temperature of 3 eV. Since LTE is applicable for the observed emission, the free electron temperature of the discharge plasma is between 1 and 3 eV. A floating double-Langmuir probe measurement indicates a discharge electron temperature of 1 eV and an ion density of approximately 5/spl times/10/sup 14/ cm/sup -3/. Film characteristics under investigation include the material deposition rate and the particulate density and size. Initial studies find particulate diameters up to 20 microns with laser alone. Optical diagnostics have also been applied to monitor the ablation plasma plume and the discharge plasma during the deposition.