Plasma wave after HIPIMS pulse: time-resolved diagnostic of HIPIMS copper plasma using a homemade Langmuir probe

Abstract

A homemade Langmuir probe was constructed to investigate the plasma characteristics of high power impulse magnetron sputtering (HIPIMS) for copper deposition. Five sets of HIPIMS power delivery parameters were selected for use in a constant-current mode with different pulse widths (T on) and discharge frequencies (f) at a working argon pressure of 0.16 Pa. Waveforms of the HIPIMS cathode current remained constant during the pulse. The time-resolved plasma properties were examined to explore HIPIMS physics. At the end of the HIPIMS pulse, the plasma density increased and built to a second peak. Double peaks were observed in the ion and electron densities for all tested HIPIMS parameters. We discuss the mechanism responsible for the generation of the second peak, which is based on the collisions of highly energetic electrons and metastable atoms that have long lifetimes. Lifetime of the electron and ion densities after the second peak are estimated in terms of exponential decay. The lifetimes range between 30 and 40 μs.

Analysis of a second peak of electron density observed in high-power impulse magnetron sputtering plasma using a Langmuir probe

“…Figure 5 shows typical temporal behaviors of the electron density for different pulse widths and frequencies. 24) As shown in Fig. 5, the second peak of the n e appears.…”

“…The derivation of the bulk electron term of Eq. ( 1) can find 24) for detail, the derivation of the hot electron term is similar to the bulk one.…”

“…The ion density was also estimated from the ion saturation current of the I-V curve, assuming that the dominant ions were Ar ions and Cu ions. 24) The second peak of the ion density appears at the time when the electron density peaked. Note that the second peak was observed at a low pressure of 0.16 Pa in our case, while the second peak was observed at a higher pressure in other studies.…”

“…The Langmuir probe was subjected to various applied probe voltages (V p ) for conducting current measurement. 24) Fig. 2.…”

“…Figure 1 illustrates a schematic of the experimental apparatus. 24) In a grounded vacuum chamber, a rectangular pure copper target with a 0.038 m 2 surface area was installed, and it had a racetrack area of 0.024 m 2 . The target had permanent magnets attached to it.…”