Process diagnostics and monitoring using the multipole resonance probe in an inhomogeneous plasma for ion-assisted deposition of optical coatings

Abstract

The application of a multipole resonance probe (MRP) for diagnostic and monitoring purposes in a plasma ion-assisted deposition (PIAD) process is reported. Recently, the MRP was proposed as an economical and industry compatible plasma diagnostic device (Lapke et al 2011 Plasma Sources Sci. Technol. 20 042001). The major advantages of the MRP are its robustness against dielectric coating and its high sensitivity to measure the electron density. The PIAD process investigated is driven by the advanced plasma source (APS), which generates an ion beam in the deposition chamber for the production of high performance optical coatings. With a background neutral pressure of p 0 ∼ 20 mPa the plasma expands from the source region into the recipient, leading to an inhomogeneous spatial distribution. Electron density and electron temperature vary over the distance from substrate (n e ∼ 10 9 cm −3 and T e,eff ∼ 2 eV) to the APS (n e 10 12 cm −3 and T e,eff ∼ 20 eV) (Harhausen et al 2012 Plasma Sources Sci. Technol. 21 035012). This huge variation of the plasma parameters represents a big challenge for plasma diagnostics to operate precisely for all plasma conditions. The results obtained by the MRP are compared to those from a Langmuir probe chosen as reference diagnostics. It is demonstrated that the MRP is suited for the characterization of the PIAD plasma as well as for electron density monitoring. The latter aspect offers the possibility to develop new control schemes for complex industrial plasma environments.

Modelling and Simulation of the Advanced Plasma Source

“…An add-on Monte-Carlo simulation is employed to calculate the energetic particle distribution functions at the substrate. All results compare well to electrical and optical measurements conducted at a commercial APS system [2,3,4,5].…”

The 2017 Plasma Roadmap: Low temperature plasma science and technology

“…For low pressure diagnostics, the multi-pole resonance probe has become rather mature in recent years and has demonstrated its capability of measuring plasma densities under various conditions [136]. A new development is an inductively coupled plasma based sensor that can probe the electron density within the skin layer in front of the sensor [137].…”

Kinetic Simulation of the Ideal Multipole Resonance Probe

“…The theoretical and numerical results are substantially confirmed through the simulation and experimental work [20][21][22][23]. Nevertheless, there are deviations: the fluid approach has a poor prediction in a pressure regime of a few Pa and lower.…”