Ionized physical vapor deposition of Cu using a mixture of rare gases

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Ionized physical vapor deposition of Cu in a mixture of three rare gases (He–Ar–Xe) is explored in this article. Results indicate that total Cu flux to the wafer, ionization fraction of Cu at the wafer, and ratio of total effective ion flux to total Cu flux increase with increasing Xe concentration in the gas mixture. This is because of enhancement of electron density and Xe+ ions having a larger sputter yield on Cu than other ions. Increase in He concentration decreases the ionization fraction due to a lower electron density. However, Cu flux to the wafer increases because He is less effective in thermalizing the hot sputtered neutrals. One major consequence of these trends is that one can independently control total Cu flux to the wafer (corresponding to deposition rate) and ionization fraction (a major factor controlling the deposition profile) over a wide range by means of the buffer gas composition.