Retarding field energy analyser ion current calibration and transmission

Abstract

Accurate measurement of ion current density and ion energy distributions (IED) is often critical for plasma processes in both industrial and research settings. Retarding field energy analyzers (RFEA) have been used to measure IEDs because they are considered accurate, relatively simple and cost effective. However, their usage for critical measurement of ion current density is less common due to difficulties in estimating the proportion of incident ion current reaching the current collector through the RFEA retarding grids. In this paper an RFEA has been calibrated to measure ion current density from an ion beam at pressures ranging from 0.5 to 50.0 mTorr. A unique method is presented where the currents generated at each of the retarding grids and the RFEA upper face are measured separately, allowing the reduction in ion current to be monitored and accounted for at each stage of ion transit to the collector. From these I-V measurements a physical model is described. Subsequently, a mathematical description is extracted which includes parameters to account for grid transmissions, upper face secondary electron emission and collisionality. Pressure-dependant calibration factors can be calculated from least mean square best fits of the collector current to the model allowing quantitative measurement of ion current density.

Plasma diagnostics of low pressure high power impulse magnetron sputtering assisted by electron cyclotron wave resonance plasma

“…51,52 The transmission of each of the 3 grids is 33%. 53 The entrance orifice of the RFA sensor was placed in the magnetron's axis z.…”

Analysis of retarding field energy analyzer transmission by simulation of ion trajectories

“…The important assumption made here is that the individual beamlets passing through the grid apertures diverge sufficiently (due to ion lensing effects) so that a uniform flux is incident on each grid. 11,14 This is illustrated in Fig. 2.…”

“…3,5,6,9,10 However, in most cases, the measured ion flux density is considered unreliable and therefore not usable due to the unknown transmission of ions through the device. 9,11 Understanding this transmission could greatly enhance the usability of the RFEA as it could be used simultaneously for IEDF and ion flux density measurements. a) j.beckers@tue.nl This work describes the analysis of the effective transmission by simulating ion trajectories through an RFEA using the commercially available charged particle optics simulation software SIMION.…”

“…a) j.beckers@tue.nl This work describes the analysis of the effective transmission by simulating ion trajectories through an RFEA using the commercially available charged particle optics simulation software SIMION. 12,13 Focus is on the effects of grid alignment because poor alignment impacts the transmission 11,14,15 and energy resolution 16 significantly.…”

“…The RFEA operating principles have been described extensively in the literature 5,9,11,14 and are therefore only summarized here. Figure 1 shows a schematic of a three-gridded RFEA consisting of a stack of electrically insulated grids, G 0 through G 2 , and an ion collecting electrode C. The potential distribution inside the device is also shown.…”