Measured density of copper atoms in the ground and metastable states in argon magnetron discharge correlated with the deposition rate

In a dc-magnetron discharge with argon feed gas, densities of copper atoms in the ground state Cu(S1/2) and metastable state Cu*(D5/2) were measured by resonance absorption technique, using a commercial hollow cathode lamp as light source. The operating conditions were 0.3 14 μbar argon pressure and 10 200 W magnetron discharge power. The deposition rate of copper in a substrate positioned at 18 cm from the target was also measured with a quartz microbalance. The gas temperature, in the range of 300 to 380 K, was deduced from the emission spectral profile of N2(CΠu − BΠg) 0-0 band at 337 nm when trace of nitrogen was added to the argon feed gas. The isotope-shifts and hyperfine structures of electronic states of Cu have been taken into account to deduce the emission and absorption line profiles, and hence for the determination of atoms densities from the measured absorption rates. To prevent error in evaluation of Cu density, attributed to the line profile distortion by autoabsorption inside the lamp, the lamp current was limited to 5 mA. Density of Cu(S1/2) atoms and deposition rate both increased with the enhanced magnetron discharge power but at fixed power the copper density augmented with argon pressure whereas the deposition rate followed the opposite trend. Whatever the gas pressure, the density of Cu*(D5/2) metastable atoms remained below the detection limit of 1 x 10 cm for magnetron discharge powers below 50 W and hence increased much rapidly than the density of Cu(S1/2) atoms, over passing this later at some discharge power, whose value decreases with increasing argon pressure. This behavior is believed to result from the enhancement of plasma density with increasing discharge power and argon pressure, which would increase the excitation rate of copper into metastable states. At fixed pressure, the deposition rate followed the same trend than the total density of copper atoms in the ground and metastable states. Two important conclusions of this work are: i) copper atoms sputtered from the target under ion bombardment are almost all in the ground state Cu(S1/2) and hence in the plasma volume they can be excited into the metastable states; ii) all atoms in the long-lived ground and metastable states contributes to the deposition of copper layer on the substrate. a Corresponding author ; E-mail : [email protected]