Ion Densities and Ionization Fractions of Sputtered Titanium in Inductively Coupled Plasma Assisted Sputtering

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Ion densities of sputtered titanium (Ti) in Inductively Coupled Plasma (ICP)-assisted magnetron sputtering biased by rf (13.56 MHz) and dc voltages were measured using an optical absorption method. A spectral line with the wavelength of 336.1 nm (z4G$_{9/2}^{\circ}$ $\rightarrow$ a4F7/2) was used as the absorption line. In the case of rf sputtering, at Ar pressures of several Pa, the Ti ion density jumped to higher value at a certain coil rf power while at the same time Ti atom density decreased gradually with increasing coil rf power due to a decrease in the self-bias voltage. For instance, ionization fractions showed increases at the threshold coil rf power of 160 W and rose to a value of 0.29 for Ar pressure of 7.0 Pa. Even at the low pressure of 0.6 Pa, the ionization fraction was 0.08 at coil rf power of 240 W, twice as high as that in sputtering that are not ICP-assisted. The Ti ion density against axial distance from the target showed characteristic peaked profile with its maximum at $z=20$ mm in contrast with the change of Ti atom density, resulting maximum ionization fraction at a position around lower edge of the inserted coil, $z=30$ mm. In the case of dc sputtering biased with $-600$ V, ion density and ionization fraction of Ti were slightly higher than those of rf sputtering with the same coil rf power though self-bias voltage in rf sputtering was $-560$ V, at Ar pressure of 3.5 Pa. It was found that ionization fractions of Ti in the dc sputtering biased with $-400$ V were higher than in the dc sputtering biased with $-600$ V.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2003-09-15

Ion Densities and Ionization Fractions of Sputtered Titanium in Inductively Coupled Plasma Assisted Sputtering

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