Characterization of energetic and thermalized sputtered tungsten atoms using tuneable diode-laser induced fluorescence in direct current magnetron discharge

Abstract

In this study a tuneable diode-laser induced fluorescence (TD-LIF) technique (λ 0 = 407.4358 nm) is used to determine the atoms' velocity distribution function (AVDF) of energetic and thermalized sputtered tungsten (W) atoms in direct current magnetron discharge. The AVDF is characterized by probing the plasma above the centre of the target racetrack along the magnetron cathode axis in an argon-helium (Ar-He) mixture. Quantitative absorption measurements corroborated by deposition on silicon substrates are used to calibrate the TD-LIF relative measurements. Density, flux, temperature, AVDF and the flux velocity distribution function are derived from fitting the TD-LIF signals with four Gaussians (thermalized atoms) and four (energetic atom) functions (Stepanova and Dew 2004 Nucl. Instrum. Methods Phys. Res. B 215 357) taking into account the natural abundance and resonance wavelength shifts of the four main isotopes. Measurements show transport improvement for W atoms and an increase of the ratio of Ar ions to Ar neutrals with the increase of the percentage of He. All measurements are performed at 0.4 Pa and 100 W. The mean velocity of energetic W atoms typically ranges from 1900 to 2200 m s −1. The densities of thermalized and energetic atoms are in the same order of magnitude (∼10 9 cm −3) and their corresponding fluxes are several tens of times higher for energetic atoms (∼10 15 cm −2 s −1).

Ionized particle transport in reactive HiPIMS discharge: correlation between the energy distribution functions of neutral and ionized atoms

“…The experiments were conducted in the reactor used in our previous work [6], comprising a cylindrical stainless-steel chamber 35 cm in height and 30 cm in diameter and equipped with a turbomolecular pump to achieve a vacuum pressure of 2 × 10 −4 Pa before injecting gas into the chamber. A water-cooled 2-inch balanced magnetron cathode with a 99.99% purity titanium target 3 mm thick was used as the sputtering source.…”

Transition from ballistic to thermalized transport of metal-sputtered species in a DC magnetron

“…The experiments have been carried out in a reactor described in detail elsewhere [4,32,31]. Briefly, a titanium target (99.9%) of 5 cm in diameter was used as cathode in a planar circular balanced magnetron.…”

“…The optical configuration of TD-LIF is very similar to that used in [32]. The tunable diode laser (Toptica Photonics DL 100) allows scanning 9 pm wavelength range with locked single mode.…”

“…Figure 3 shows the temperature of the background gas (argon), assuming the same temperature for the ground state of argon and its metastable, for which Doppler broadening was probed by Tuneable Diode-Laser Absorption Spectroscopy (TD-LAS) technique. For a detailed description of TD-LAS experimental setup the reader is referred to Desecures et al [4]. The measurements were performed on the metastable argon state, given in table 1, around λ 0 = 801.69 nm.…”

“…Therefore, it is highly suitable to study the inhomogeneity of the densities and the fluxes from the target to the substrate, with high spectral resolution and relatively wide scanning range of wavelength (about 18 GHz without hope mode). TD-LIF allows probing all populations of sputtered atoms, even if they spread over a wide range (up to 8 km/s) [4,6,31]. Thus, with a theoretical adjustment procedure (see section 2.1), we can distinguish the different groups of particles that correspond to the energetic (most of them performing a "ballistic" or collisionless transport) after the ejection from the target, which survive as long as they are not interacting with the buffer gas, and those that underwent collisions evolving towards thermal population.…”