Measurements of sputtered neutrals and ions and investigation of their roles on the plasma properties during rf magnetron sputtering of Zn and ZnO targets

Abstract

Langmuir probe and optical absorption spectroscopy measurements were used to determine the line-integrated electron density, electron temperature, and number density of Ar atoms in metastable 3P2 and 3P0 levels in a 5 mTorr, rf magnetron sputtering plasmas used for the deposition of ZnO-based thin films. While the average electron energy and density of Ar atoms in 3P2 and 3P0 excited states were fairly independent of self-bias voltage, the Ar 3P2-to-electron number density ratio decreased by approximately a factor of 5 when going from −115 V to −300 V. This decrease was correlated to an increase by about one order of magnitude of the number density of sputtered Zn atoms determined by absolute actinometry measurements on Zn I using either Ar or Xe as the actinometer gas. These results were also found to be in excellent agreement with the predictions of a global model accounting for Penning ionization of sputtered Zn particles. The importance of the latter reactions was further confirmed by plasma sampling mass spectrometry showing a double peak structure for Zn ions: a low-energy component ascribed to thermalized ions created in the gas phase (by direct electron impact and by Penning ionization) and a high-energy tail due to ions ejected from the target and reaching quasi-collisionlessly the substrate surface.

Spatial Distributions of 3p54s States of Argon Atoms in RF Magnetron Sputtering Plasma with a Collisional-Radiative Model

“…The population of 3p 5 4s states is consistent with the data reported by L. Maaloul et al [5] and by L. Maaloul and L. Stafford [19] in RF magnetron sputtering. For atomic metastable states of Ar, the density of Ar 1s5 is of the order of 10 9 cm -3 and of Ar 1s3 is of the order of 10 8 cm -3 ; for atomic resonant states of Ar, the densities of Ar 1s4 and Ar 1s2 are of the order of 10 8 cm -3 .…”

“…-The dominant process is the Penning ionization with sputtered Zn atoms, its relative contribution is about 90 % at NZn = 10 11 cm -3 . The importance of Penning ionization reactions on plasma kinetics during magnetron sputtering with Zn targets illustrated above is in good agreement with the work of L. Maaloul and L. Stafford [19]. Indeed, the authors have shown that in plasmas characterized by relatively low charged particle densities, Penning ionization reactions are the dominant mechanisms for pulverized particles.…”

“…For atomic metastable states of Ar, the density of Ar 1s5 is of the order of 10 9 cm -3 and of Ar 1s3 is of the order of 10 8 cm -3 ; for atomic resonant states of Ar, the densities of Ar 1s4 and Ar 1s2 are of the order of 10 8 cm -3 . The ratio of the densities of atoms in 1s5 to the densities of atoms in 1s3 was found to be around 6 ± 0.5, which is close to that found in the research papers of L. Maaloul et al [5,19] and J.B. Boffard et al [16]. In order to estimate the respective contributions of different processes taken into account in our model (Eq.…”

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

“…1 The results are also in excellent agreement with those obtained in previous actinometry measurements on Zn atoms using Ar as the actinometer gas. 21 To gain further insights into the respective roles of Zn metastable atoms and Zn ground state atoms on the plasma deposition dynamics of ZnO-based thin films, the results presented above were compared to spectroscopic ellipsometry measurements of the deposition rate on a Si substrate located at 12 cm from the ZnO target. As shown in Fig.…”

“…21,22 In the present study, the discharge was sustained in pure Ar gas at a pressure of 5 mTorr using ZnO as the sputtering target (Kurt J Lesker). The self-bias voltage resulting from the 13.56 MHz electric field applied to the magnetron apparatus (provided by Plasmionique, Canada) was varied between À115 and À300 V by adjusting the absorbed (i.e., incident minus reflected) RF power.…”