Plasma flux and energy enhancement in BP-HiPIMS discharge via auxiliary anode and solenoidal coil

Abstract

As an emerging and extraordinary plasma source, the bipolar-pulse high power impulse magnetron sputtering (BP-HiPIMS) has promising prospects and wide industrial applications. In this paper, an effort to optimize the plasma flux and energy in BP-HiPIMS via auxiliary anode and solenoidal coil was made. This novel plasma source contains two types of auxiliary anode voltage (direct current and pulse) and one type of solenoidal coil current (direct current) to synergistically enhance the plasma generation and diffusion by electric field and magnetic field together. Systematic evaluations of discharge characteristics demonstrate that applying auxiliary anode voltage and coil magnetic field effectively contribute to a reduction in delay time of target current onset and increase in peak amplitude of target current, which are beneficial for improving plasma generation and target sputtering. The complex plasma dynamics are diagnosed by Langmuir probe and optical emission spectroscopy, and simulated by particle-in-cell/Monte Carlo collision approach. These comprehensive investigations on plasma parameters demonstrate that the plasma density, emission intensity of the metal ions, substrate current density, and ionization fraction of sputtered target particles have been improved with the increase of coil current. The observations of the increase in excitation temperature T exc of Ar atoms, and more extended high-energy tails in electron energy distribution function curves imply that the plasma can be significantly heated by the auxiliary anode. Combining the simulation results and theoretical model proposed in the last sub-content, the diffusion and transport mechanism of charged-particles in complex electric and magnetic fields are discussed. From the theoretical analysis, the qualitative relation between the plasma density and coil current is well consistent with the measurements of electron density obtained by Langmuir probe. These evidences all support the idea that the plasma flux and energy can be enhanced in BP-HiPIMS discharge via auxiliary anode and solenoidal coil together.

Ion energy distribution and non-linear ion dynamics in BP-HiPIMS and ACBP-HiPIMS discharge

“…The magnetron discharges were carried out in a stainless-steel vacuum chamber with 600 mm in diameter and 800 mm in height, as described previously [5,[35][36][37]. An unbalanced magnetron plasma source (type II [1,26]) was configured, and the maximum radial component of the magnetic field B r above the target racetrack centre was B r = 105 mT. A titanium target (Ti, 99.99% in purity) with 50 mm in diameter and 5 mm in thickness was installed in front of the magnets and cooled by the recycled pure water (kept at a constant temperature of 15 • C).…”

“…The resistance of the coil was ∼2 Ω, and the upper limitation of coil current I coil was 5.0 A which was powered by a DC power supply (ZHAOXIN, KXN3020D). The axial component of induced coil magnetic field B z at position of r = 0 and z = 65 mm and coil current I coil have the relation of B z = 3.0I coil (in numerical value, units: B z in mT and I coil in A) in theory and B z = 2.3I coil in measurement (obtained by a Tesla meter, Tunkia TD8620, as described in [26]). The radial component of induced magnetic field in front of the target surface was in the same direction with the inherent magnetron field.…”

“…To enable the development of BP-HiPIMS in the modern industry, some advanced plasma sources based on the BP-HiPIMS approach have been introduced to further improve and control the deposited ion energy and flux [24][25][26]. In our previous work [25], an auxiliary anode was applied in front of the sputtering target (named as AABP-HiPIMS) to reduce the ion loss towards the sideways during the positive pulse, where this anode was connected to the target through a diode.…”

“…The results demonstrated that the electron density in AABP-HiPIMS was effectively increased to ∼2.5 times that in the conventional BP-HiPIMS on average. Later, we attempt to introduce a solenoidal coil together with this auxiliary anode to synergistically enhance the plasma flux during the positive pulse [26], and we named this advanced plasma source as ACBP-HiPIMS here ('A'-anode, 'C'-coil). As expected, the magnetic field induced by the coil plays an important role in enhancing the inherent magnetron magnetic field in front of the target surface and optimizing the electron mobility at the downstream.…”

“…As expected, the magnetic field induced by the coil plays an important role in enhancing the inherent magnetron magnetic field in front of the target surface and optimizing the electron mobility at the downstream. Finally, both the plasma generation and plasma flux towards the substrate have been significantly improved, and the electron density at the downstream n e and the coil current I coil have the relation of n e ∝ I coil − I coil −2 ± I coil 2 [26].…”