Free Microplasma Source FMP

Introduction

The Free Microplasma Source FMP produces a pure localized plasma at the tip. This setup provides high purity plasma creation with effectively reduced wall interaction as well as a drastically reduced RF power consumption due to the small plasma size.

Main advantages of the FMP:

• Free microplasma in front of injector, i.e.: reduced reactions with cavity materials

• Cold plasma (low ion energy)

• Multi-gas applications are possible

• Wide gas flux range without reconfiguration: 1-10 sccm

• Wide process chamber pressure range of 10^-7 mbar to 10 ^-2 mbar possible without reconfiguration (depending on pumping system)

• No water cooling needed due to high efficiency plasma generation

• Very low HF power needed due to microplasma

• Simple and reliable operation

• Compact setup on DN40CF (O.D. 2.75") mounting flange

Application

The Free Microplasma Source FMP provides a pure localized plasma for substrate cleaning applications, surface preparation or layer growth within an UHV chamber or MBE system at low chamber pressure.

Plasma probe measurement with ion sensor

The ion sensor of the FMP can also be used as a plasma probe (Langmuir probe). The measured currents and potentials in this system allow the determination of the physical properties of the plasma. The FMP creates a non-equilibrium and non-uniform plasma in front of the source. All plasma parameters which are determined from ion sensor measurements have to be interpreted carefully. However, the ion sensor measurements may be used as a process parameter forreliable and reproducible source operation.
Typical ion current characteristics of N₂ and O₂ plasma measured with the ion sensor Langmuir probe are shown below. The measured electron current (positive bias voltage) and ion saturation current (negative bias voltage) show a strong dependency on HF power and gas flow rate.

Spectroscopy measurements with viewport

The FMP comprises a viewport for optical access to the plasma. Using the viewport different measurements are possible, e.g. optical spectroscopy or operation and power control with a photo diode. Typical optical spectra from, N₂, O₂ and H₂ are shown below.

Technical Data

Mounting flange	DN40CF (O.D. 2.75”) / DN63CF (O.D. 4.5”) with ion sensor option
Thermocouple	NiCr/NiAl (type K)
Operating temperature	up to 300°C
Bakeout temperature	250°C
In vaccum length L	287 mm (DN40CF O.D. 2.75'') 270 mm (DN63CF O.D. 4.5'') with ion sensor option
In vacuum maximum total length TL	282 mm (DN63CF O.D. 4.5'') with ion sensor option
In vaccum outer diameter D	35 mm
Maximum airside length OL	517 mm
Maximum airside radius AR	196 mm
Additional equipment	all-metal valve, gas supply, RF generator
Variants	-M (inert gas, e.g. N2, H2 ) -T (reactive gas, e.g. O2 )
Options	ion sensor, photo diode

Dimensions

Specific data

For general information on CF mounting flanges see Flange and Gasketdimensions .

*** specify UHV length L with order

Product code: e.g. FMP-T 40-L287D35 is a free microplasma source on DN40CF flange with UHV-length 287 mm and in-vacuum diameter 35 mm.