Monitoring of the aluminum nitride sputtering deposition by soft x-ray emission spectroscopy

Abstract

The deposition of aluminum nitride, by dc diode reactive sputtering has been studied by in situ soft x-ray emission spectroscopy. The deposition chamber is coupled with a vacuum x-ray computerized spectrometer. The x-ray emission from the film is excited by high energy secondary electrons from the electric discharge. The Al cathode is sputtered at constant current and voltage mode. Films are deposited at different argon/nitrogen gas mixtures, in the bias mode. For each cycle, x-ray intensities, deposition rate at the quartz microbalance and total pressure are recorded. It has been found that the Al Kα and N Kα x-ray intensity ratio decreases with increasing nitrogen flow rate. At partial nitrogen flow rates of 8.5%, a sharp decrease appears, followed by a plateau, where the film has the bulk stoichiometry. Films have been characterized for ultraviolet-visible absorption. Optical band gap and refractive index have been calculated. The fine structure of the Al Kβ line has been studied. A shift in the maximum intensity position is coupled with a satellite line toward the low energy side, both appear before the transition. These effects are characteristic of the chemical bonding between Al and N. X-ray diffractograms show a preferential orientation depending on the gas mixture composition, but the peaks are small and broad.