Substrate Heating Measurements in Pulsed Ion Beam Film Deposition
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ABSTRACT Diamond-like Carbon(DLC) films have been deposited at Los Alamos National Laboratory by pulsed ion beam ablation of graphite targets. The targets are illuminated by an intense beam of hydrogen, carbon, and oxygen ions at a fluence of 15-45 J/cm2 . Ion energies are on the order of 350 keV, with beam current rising to 35 kA over a 400 ns ion current pulse. Raman spectra of the deposited films indicate an increasing ratio of sp3 to sp 2 bonding as the substrate is moved further away from the target and further off the target normal. Using a thin film platinum resistor at various positions, we have measured the heating of the substrate surface due to the kinetic energy and heat of condensation of the ablated material. Plume power density and energy input are inferred from the temperature measurements. This information is used to determine if substrate heating is responsible for the lack of DLC in positions close to the target and near the target normal.
INTRODUCTION Pulsed ion beam deposition has the potential to become a low cost, high throughput (a few $/m 2 at 50 m 2/hr for 1 pm coatings) film production process for flat panel displays, photovoltaic cells, and other applications. This process is similar to pulsed laser deposition. An intense beam of ions (100-1000 keV, 10-100 kA, 0.1-1.0 ps) strikes a target, ablating target material which condenses on a substrate as a thin film. Experiments at Los Alamos National Laboratory are examining both science and technology issues related to pulsed ion beam deposition. The present work is concerned with heating of the substrate by the hot, dense ablation plume from a graphite target and the effect of this heating on the properties of the deposited material. Substrate heating by the ablated material was examined using thin film metal thermometers. EXPERIMENTAL SETUP A schematic of the experimental configuration is shown in Figure 1. The intense ion beams used in these experiments is produced by the Anaconda generator at Los Alamos. The machine is coupled to a focusing, magnetically insulated diode, out of which a 400 keV, 30 kA, 700 ns ion beam is extracted. Ablation targets are placed 35 cm from the anode, at the beam focus, where a peak beam energy density of approximately 30(±15) J/cm2 is 171 Mat. Res. Soc. Symp. Proc. Vol. 388 01995 Materials Research Society
7 ms duration, and was necessary in order to acquire reasonable signals from the thermometers without heating them appreciably. The voltages above and below the thin film thermometer layer, Vi,,(t) and V00t(t) respectively, were monitored using HP54111D digitizing oscilloscopes. The quantity V•(t) + Vo,,t(t) should remain equal to V0 and provided a measure of the noise. A signal to noise ratio, S/N, was computed from
SIN ( t) = [V.(t) - V0,(t)] - [vl,(o) - V0.-(o)]1 Vo - (V(t) ±! Vou (t)) 1
Shots with a peak S/N of less than 5 were rejected. Out of forty shots taken at the thermometer positions discussed in this report, 34 produced data with acceptable S/N. All of the rejected shots were at the d
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