Investigating the plasma parameters and discharge asymmetry in dual magnetron reactive high power impulse magnetron sputtering discharge with Al in Ar/O2 mixture

Abstract

Dual magnetron reactive high power impulse magnetron sputtering (dual magnetron R-HiPIMS) provides a deposition process favor for low temperature crystallization of high quality dielectric films. However, lack of detailed measurements is blocking the accurate understanding of the resulting film quality to the plasma parameters. In this work, a dual magnetron R-HiPIMS discharge with Al in a fixed Ar/O2 mixture has been investigated by means of time-resolved Langmuir probe and energy-resolving quadrupole mass spectrometry. Fine temporal resolution of the measured probe characteristics revealed a rapidly climbing and sinking followed by a gradual increasing again in the plasma potential (Vp), floating potential (Vf) and effective electron temperature (Teff) during the pulse-on period. In the pulse-off time, two-fold decay, the initial fast drift decay and the subsequent slower diffusive decay, was observed for these parameters. While for the electron density (ne), it demonstrated a steep increase up to 60 μs after the initial of voltage pulse, followed also by a two-stage exponential-like decrease with two characteristic decay times of τ1 = 80 μs and τ2 = 120 μs in the remainder of the off-time. Ion energy distribution functions (IEDFs) were recorded in time averaged and time resolved mode for 36Ar+, 27Al+, 16O+ and 32O2+ ions. Time averaged results showed that there are generally two peaks in the corresponding IEDFs — a lower peak corresponding to Vp and a high energy tails originate from different physical mechanisms. The time evolution of the ion fluxes corresponds well with discharge current and revealed the sequential arrival of working gas ions (36Ar+ and 32O2+) and ions ejected from the targets (27Al+ and 16O+). Moreover, for the first time, the plasma parameters (Vp, Vf, Teff and ne) at symmetry positions (y = −40 mm and y = 40 mm) with respect to the plane of geometric symmetry of the dual magnetron (the plane crosses both axes of the magnetrons) are compared, and the observed asymmetry behavior of Vf, Teff and ne is explained in view of “the gradient drift” of high energy electrons pointing to the +y direction.