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

Abstract

Abstract:In a dc-magnetron discharge with argon feed gas, densities of copper atoms in the ground state Cu( 2 S 1/2 ) and metastable state Cu*( 2 D 5/2 ) 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 N 2 (C 3 Π u − B 3 Π g ) 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( 2 S 1/2 ) 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*( 2 D 5/2 ) metastable atoms remained below the detection limit of 1 x 10 10 cm -3 for magnetron discharge powers below 50 W and hence increased much rapidly than the density of Cu( 2 S 1/2 ) 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( 2 S 1/2 ) 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 : nader.sadeghi@ujf-grenoble.fr 2 1-IntroductionMagnetron discharges are widely used for thin film deposition in surface treatment 1, 2 , magnetic and superconducting devices 3 , semiconductor industry 4 and in surface coating engineering of materials under low temperature conditions 5,6 . In these systems, the magnetic field, usually produced by placing permanent magnets behind the cathode, confines the plasma in the near cathode region, reducing the electron loss to the sidewalls. By increasing the ionization rate near the cathode, which is also the target to be sputtered, its confinement helps to maintain the plasma at much lower buffer gas pressure than...

High power impulse magnetron sputtering discharge

“…Also, the density of the sputtered particles is much lower than the density of the noble working gas. 65 The primary mechanism for the ionization of the sputtered metal vapor in a dcMS is Penning ionization through impact with the working noble gas atoms that are in the metastable state. 66 The mean free path for the sputtered vapor with respect to electron impact ionization is over 50 cm.…”

The effect of self-absorption in hollow cathode lamp on its temperature

“…The remaining light from HCL together with the light produced by Cu atoms inside the vacuum chamber after passing the 35 cm tube (9) enters the monochromator (10), through a second quartz lens with 5 cm focal distance. The spectral light is separated inside the monochromator from other lights and enters the photomultiplier tube (11). The detector counts the number of arriving photons and sends counts via RS-232 interface to the computer (12).…”

“…Thus the gas temperature is measured via N 2 molecule rotational emission light. The result of the measured variation of the number density with the input power and for three different pressures (0.3 µbar, 4.5 µbar and 14 µbar) are given in the reference 10,11 for Cu atoms in ground state and also in metastable state. For the ground state of Cu, the 327.4 nm line and for the metastable state the 510.6 nm lines are used.…”

Determination of the number density of excited and ground Zn atoms during rf magnetron sputtering of ZnO target

“…Sasaki et al 10 have suggested that dimmers and trimmers of Fe, Ti, and Cu atoms can also be sputtered from metallic targets and dissociated in the phase gas. Furthermore, Naghshara et al 11 have reported the Cu-atom densities in the ground and metastable states using resonance absorption technique. These studies concluded that the sputtered atoms from the target are almost in ground state and get excited or ionized later in the gas phase.…”

“…In addition, for Cu deposition, both metastable and ground-state Cu atoms were shown to contribute significantly to the plasma deposition rate on the substrate. 11 Because of their high carrier concentrations and high optical transmittance in the visible and near infrared, ZnO-based thin films and nanomaterials are very attractive for many applications, 12,13 including flexible electronics, 14,15 optoelectronics, 16 solar cells, 17,18 and sensors. 19 While the literature is abundant on the evolution of the film properties and their various applications, much less efforts were devoted to fundamental investigations of sputtered species and their transport properties during magnetron sputtering of technologically relevant targets such as ZnO and their alloys.…”