Deposition of Ba_xSr_1–xTiO₃ thin Films by Double RF Hollow Cathode Plasma Jet System

Abstract

Low-pressure plasma jet system with two hollow cathodes was used for deposition of BaxSr1−xTiO3 (BSTO) ferroelectric thin films. Two RF hollow cathode plasma jet guns were pointed to the substrate where BSTO thin films were deposited. High density RF hollow cathode discharge was generated in ceramic nozzles made of SrTiO3 (STO) and BaTiO3 (BTO). Pulse modulated RF power was applied on water-cooled copper block insulated from the plasma by ceramic and grounded stainless steel shield. In the experiment, the composition of BSTO films was controlled by magnitude of average RF power applied on particular plasma jet guns with STO and BTO nozzles. By this method, BSTO films were deposited on single crystal silicon substrate and on Pt top of Pt/TiO2/SiO2/Si multi-layer system. X-ray diffraction proved that BSTO thin films were polycrystalline with perovskite structure and measurement of dielectric properties showed ferroelectric hysteresis loop at room temperature. Time resolved Langmuir probe system and plasma impedance monitor were used for in situ plasma diagnostics and control of deposition conditions. Furthermore, plasma jets were analyzed during the deposition process by spatially resolved optical emission spectroscopy.

Langmuir probe diagnostics of a plasma jet system

“…The probe measurements were performed at a position close to the substrate, see figure 6. The experimental system is described in detail in [35] so we shall present just the probe measurement results. The motivation of this measurement was to control the plasma microparameters at the substrate at the place of deposition.…”

“…The motivation of this measurement was to control the plasma microparameters at the substrate at the place of deposition. This also allowed us to better reproduce the deposition conditions and set up the instant RF power in each nozzle in such a way that the plasma density and effective electron [35] temperature were similar in both active STO and BTO parts of modulation cycle. An RF compensated [28] cylindrical probe with radius 150 µm and length 1 mm was used.…”

Cavity-hollow cathode-sputtering source for titanium films

“…A cylindrical cavity (5 mm in diameter) (5) inside the lower disk further enhances ionization [14]. Both disks contain channels for the application of the operating gas argon (Ar) in front of the muzzle (7,9,10). The cathode ensemble is introduced into a glass tube ( Fig.…”

“…They do not need a magnetic field, which makes them particularly useful for sputtering of ferromagnetics. Hollow cathodes are used as intensive light sources [1], spectroscopic light sources [2], cluster sources [3], electron beam sources [4,5], ion thrusters [6] and for deposition [7][8][9][10]. The most important part of an HC is its hollow cathode cylinder.…”