An improved method for IEDF determination in pulsed plasmas and its application to the pulsed dc magnetron

Abstract

In this paper we demonstrate an improved technique for obtaining time-resolved ion energy distribution functions (IEDFs) in pulsed plasma discharges using a commercial quadrupole mass energy analyser. The method involves extracting ions from the plasma at selected times during the pulse cycle through the application of a synchronized electrical bias on a grid assembly built in the barrel of the instrument. Placing the triggered mesh in the barrel of the energy analyser makes the ‘transit’ gap length (between the chopping mesh and neighbour electrodes) ∼2 mm and that results in a significant increase of the time resolution. Due to the high vacuum conditions inside the barrel, no unwanted ‘parasitic’ discharge will exist between the extractor and orifice. The electrostatic chopping by the built-in mesh allows time-resolved IEDFs to be determined without reference to the inherent time delay caused by the ion flight time through the spectrometer. The technique has been applied to the low-pressure pulsed dc magnetron discharge operating in Ar gas and at a pulse frequency of 100 kHz. Time-resolved IEDFs were obtained with a 1 µs time resolution, and these revealed large variations in the form and width of the ion energy spectra at different times during the discharge cycle, governed by the temporal evolution of the plasma potential. A calculation based on ion dynamics in the grid assembly agrees well with experimentally obtained results and demonstrates that this method can provide time resolutions as small as 200 ns.

Ion Energy Distributions in Magnetron Sputtering of Zinc Aluminium Oxide

“…Figure 4a still shows a low energy peak as in the d.c. case at +7 V which does not change its energy when the duty cycle (ratio between ‘on’ time and pulse duration) is changed by an ‘off’ time variation. However, there are additional peaks at higher energies between 20 and 50 eV which were also observed by other authors 14, 16–18. Some very weak signals are observed up to 110 eV.…”

“…However, there are additional peaks at higher energies between 20 and 50 eV which were also observed by other authors. [14,[16][17][18] Some very weak signals are observed up to 110 eV. These peaks are clearly dependent on the pulse parameters.…”

Spatial and temporal development of the plasma potential in differently configured pulsed magnetron discharges

“…Positive ions which are detected against ground have to pass through the potential difference between plasma and ground so that their energy distribution reproduces the plasma potential. Due to the time-of-flight within the spectrometer, the measurement is not time-resolved unless a gating technique is used [17,18]. Therefore, the assignment of structures in the ion energy distribution function (IEDF) to changes in the plasma potential is not straightforward.…”

High Temporal Resolution Ion Energy Distribution Functions in HIPIMS Discharges

“…The plasma ions were sampled through 100 mm in diameter orifice drilled on the grounded end cap of the instrument. The electrostatic shutter [15] was made from a stainless steel mesh having 57 wires/inch and a 45% geometrical transparency. It was situated 0.5 mm behind the orifice (see Figure 2).…”