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Thermalization process in sputtering systems by atomic absorption spectroscopy

Atomic absorption (AA) spectroscopy was applied to study thermalization of neutral atomic species in a dc magnetron sputtering system. Resonance absorption by Ti atoms was measured with a hollow cathode lamp based AA monitor. Absorption versus deposition rate curves for Ti were obtained at different pressures, ranging from 2 to 38 mTorr, using a quartz crystal microbalance for mass measurements. To study the thermalization of sputtered atoms as a function of distance from the target, the probing beam was positioned at different locations. Experimental data were collected on the influence of argon pressure, sputtering power, and chamber geometry on the absorption signal. The thermalized atoms were found to play a dominant role in determining the sensitivity of AA monitor. Comparisons were also made between the sensitivities of AA monitor for sputtering and thermal evaporation processes. The feasibility of using a tunable diode laser to measure the absorption line profile was established and demonstrated on Zr sputtering process. We found the AA monitor to be a powerful tool for studying sputtering. With proper procedures, the AA monitor can also be used for real-time control of deposition rate in sputtering processes.