Energy fluxes in a radio-frequency magnetron discharge for the deposition of superhard cubic boron nitride coatings

Abstract

Energy flux measurements by a calorimetric probe in a rf-magnetron plasma used for the deposition of super-hard c-BN coatings are presented and discussed. Argon as working gas is used for sputtering a h-BN target. Adding a certain amount of N2 is essential for the formation of stoichiometric BN films, since a lack of nitrogen will lead to boron rich films. Subsequently, the contributions of different plasma species, surface reactions, and film growth to the resulting variation of the substrate temperature in dependence on nitrogen admixture are estimated and discussed. In addition, SRIM simulations are performed to estimate the energy influx by sputtered neutral atoms. The influence of magnetron target power and oxygen admixture (for comparison with nitrogen) to the process gas on the total energy flux is determined and discussed qualitatively, too. The results indicate that variation of the energy influx due to additional nitrogen flow, which causes a decrease of electron and ion densities, electron temperature and plasma potential, is negligible, while the admixture of oxygen leads to a drastic increase of the energy influx. The typical hysteresis effect which can be observed during magnetron sputtering in oxygen containing gas mixtures has also been confirmed in the energy influx measurements for the investigated system. However, the underlying mechanism is not understood yet, and will be addressed in further investigations.

On the Impact of Electron Temperature in Magnetron Sputtering Benchmarked with Energy Flux Measurements

“…However, the differences, which are most obvious at the electron acceleration and saturation regions (not shown), may be attributed to resistive heating of the bias wire due to relatively high currents. The differences between calculation and experiment in the ion saturation www.cpp-journal.org regime have been measured in different experiments [23] and are attributed to the fact that collisions of ions are not accounted for in this treatment. For all investigated sputter gases there is only a slight reduction of the total energy flux with increasing pressure.…”

“…In this work we have taken into account contributions caused by electrons J e , ions J ion , electron-ion recombination J rec , impact of sputtered neutrals J n , and film growth J cond . The procedure for these calculations is described in [2,23], but will here be summarized for increased clarity when interpreting the energy flux results.…”

Calorimetric Probes for Energy Flux Measurements in Process Plasmas

“…Of course the maximum energy of the ions is also determined by the sheath potential, but the mean energy is well below that value. It has recently been shown, that the mean kinetic energy is in the range of 0.3 − 0.5 · Φ sh [74,75]. • When they are formed in the bulk plasma they are attracted to the most dense region where the plasma potential has its most positive value.…”

Analysis of passive calorimetric probe measurements at high energy influxes

“…P in is the net incoming power containing the heating processes as well as losses due to plasma-wall-interactions. A list of the various contributions to the thermal energy balance at the substrate (probe) can be found in [12,13]. P out , on the other hand, includes all loss processes dependent on the rising temperature of the probe.…”