Plasma diagnostics

 

 

 

 

 

 

 

 

 

  

L2P - Double Langmuir probe for plasma diagnostics


 

Features:

  • efficient and reliable plasma characterization
  • Probe cleaning with ion or electron bombardment
  • single and double probe mode
  • azimuthal and axial spatially resolved measurement
  • software controlled data acquisition and analysis



Applications:

  • characterization of technical plasmas
  • plasma und process control
  • process development
  • fundamental plasma research

 

JE PlasmaConsult GmbH has developed an advanced and yet, cost effective LANGMUIR Probe System (L2P) based on years of experience with the generation and control of technical plasmas.
The L2P system is capable of working in the so-called single or double probe mode. Which mode to choose depends on the specific plasma generation scheme and process requirements.

The JE PlasmaConsult L2P LANGMUIR Probe System consists of the following components:

  • LANGMUIR single or double probe, with fixture, vacuum feedthrough and connecting cables
  • potential-free computer-controlled interface with cabling, included are
    • generation of probe voltage
    • amplification and measurement of probe current
    • complete electrical isolation to keep the probe system electrically floating
    • probe cleaning with ion or electron bombardment when using the system in contaminating plasmas),
  • RS 232 cable to desktop computer or laptop
  • proprietary JE PlasmaConsult software for data acquisition, evaluation and graphic representation. The software can be installed under Windows 95/98/METM and Windows NT4.0/2000TM

Depending on the probe system (single or double LANGMUIR probe), different evaluation algorithms are used. In case of single probe measurements the Druyvesteyn-method, that is the relation between EEDF and the second derivative of the current- voltage characteristics is applied, while for double probe measurements the evaluation is done by use of the Laframboise theory.


 Single probe operation:

Basically, the LANGMUIR probe consists of one electrode inserted into a plasma. In the single-probe configuration the current collected by the probe tip is measured as a function of the voltage between the electrode and the plasma chamber. Main plasma parameters which can be identified by this mode are:

  • electron and ion density
  • electron temperature
  • electron energy distribution function EEDF (electron energy distribution function)
  • plasma and floating potential

Single probes should not be used in magnetized plasmas.

Double probe operation:

In the double probe configuration the current is measured as a function of the voltage applied between the probe tips 1, 2.This is especially useful when dealing with electrodeless discharges (e.g. rf- and microwave excited plasmas) or in cases where a reference potential is not well defined. Main plasma parameters which can be identified by this mode are:

  • ion density
  • electron temperature


 

Technical data:

Probe voltage:                          -120 V to +120 V

Probe current:                           10-4 mA to 15 mA

measurable plasma densities:   108 cm-3 to 1012 cm-3

Materials

  • Probe tips:                   tungsten (platinum or other materials optionally)
  • Probe head:                stainless steel
  • Mech. feedthrough:     aluminium
  • Isolators:                      Al2O3

Dimension of probe tips:

  • Lenght:                                10 mm (other lengths optionally)
  • Diameter single probe:        0.25 mm (other diameters optionally)
  • Diameter double probe:         0.25 mm (other diameters optionally)

 

Application note: