Measurement of energy transfer at an isolated substrate in a pulsed dc magnetron discharge

Abstract

The power density delivered by particles to an electrically isolated substrate in an asymmetric bipolar pulsed dc unbalanced magnetron has been quantified. The plasma source was operated in argon with a titanium target, and measurements were made using both a calorimeter probe and time-resolved Langmuir probe incorporated into a specially made substrate holder. The main results from the calorimeter probe show clearly that with increased pulse frequency (from dc to 350kHz) and reduced duty cycle (90%–50%), the particle power density (from ions, electrons, sputtered Ti, and backscattered Ar) at the substrate increases significantly. For instance, at 350kHz and 60% duty cycle, the total power density is 83mW∕cm2, about 60% higher than in dc mode for the same time-average discharge power. However, from an inventory of the individual particle contributions to the total power density derived from time-resolved Langmuir measurements and a simple model of the substrate sheath and plasma internal processes, we predict values of power density much lower than those measured. The measured and calculated values are in close agreement for the results obtained in dc mode but diverge at high frequencies. It is believed that this is due to the Langmuir probe measurements being unable to observe the presence of high-energy ions, created during the transient peaks in the electron temperature at the transitions from on off and off on [J. W. Bradley et al., Plasma Sources Sci. Technol. 11, 165 (2002)] which subsequently bombard the substrate. This paper shows conclusively the benefit of pulsing the magnetron over and above dc operation for enhancing the ion power per depositing neutral in the ion assisted deposition process.

Time‐Resolved Diagnostics of Dual High Power Impulse Magnetron Sputtering With Pulse Delays of 15 µs and 500 µs

“…The thermal capacity of the probe was calculated using C P = m c P = 0.31 J/K, where m = 0.803 g is the mass of the probe and c P is the specific heat of copper, with an estimated accuracy of about ±10 %. The method used to determine the heat transfer to the substrate is based on the temporal evolution of a small calorimeter probe's temperature located at the position of the substrate [30,31].…”

“…The measured power flux density was P tot−15 = 38 mW/cm 2 and P tot−500 = 33 mW/cm 2 for pulse delays of 15 μs and 500 μs, respectively. The energy fluxes of particular species (ions, electrons and neutral particles) were calculated using the model described previously [7,31]. Input parameters (plasma density, electron temperature, plasma and floating potential) were taken from our Langmuir probe measurements.…”

Electrical and Optical Properties of Fluorine Doped Tin Oxide Thin Films Prepared by Magnetron Sputtering

“…It was observed that the fluorine content in the doped thin films is in the range of 0-7.4 at.%, which is low in comparison to the amount of fluorine incorporated into the powder targets (0-13 at.%). This can be explained by the fact that fluorine is a light element (Z = 9) and may be more readily scattered during gas phase transport through the high density plasma [19]. …”

“…Čada et al measured the power density at the substrate in order to assess the interaction between the plasma and the substrate and quantify the energy balance. They concluded that pulsing the magnetron discharge provides higher energy transfer to the growing film this, in turn, produces denser film structures [19].…”

Calorimetric Probes for Energy Flux Measurements in Process Plasmas

“…Due to the simplicity of calorimetric probes they can easily be integrated into a substrate holder as performed by Ball [45] or Cada et al [49] (see Figs. 6.4f and 6.5a).…”