Evidence for the physical basis and universality of the elimination of particulates using dual-laser ablation. I. Dynamic time-resolved target melt studies, and film growth of Y2O3 and ZnO

Abstract

The application of a dual-laser ablation process, incorporating the addition of a synchronized CO2 laser to the traditional excimer (KrF) laser used for the ablation of targets in thin film deposition, has been previously demonstrated to be effective in the elimination of particulates in films of Y2O3 [J. Vac. Sci. Technol. A 13, 1171 (1995)]. It has been hypothesized that the efficacy of particulate removal is related to phase transformation from the solid to liquid phase prior to excimer laser ablation of the target material. In this series of two articles we present direct physical evidence of the dynamics of the phase transformation occurring on the target surface and its effect on the morphology of film growth. Pump–probe experiments have been conducted using the CO2 laser to probe the dynamic reflectivity of the target surface on the nanosecond timescale. These experiments were conducted for a range of materials spanning a wide range of thermal conductivity including a low thermal conductivity insulator (Y2O3), and a sublimating oxide (ZnO), as well as a high thermal conductivity metal (Zn) to assess the universal applicability of the results. In this article (Part I) the results of these dynamic reflectivity experiments are correlated with previously reported particulate-free deposition of thin films of Y2O3. Similar experiments are conducted for ZnO. In both cases, the reflectivity measurements yielded times for the onset of melt at a variety of CO2 laser fluences. Synchronization of the KrF laser to coincide with the onset of melt resulted in particulate-free film growth. The effect of mistiming on the quality of the deposited film is presented for ZnO.