Plasma sources

 

 

 

 

 

 

 

 

 

  

µ-SLAN

2.45 GHz microwave plasma source

Features:

  • high plasma and radical densities
  • compatible with chemically reactive and nonreactive gases
  • low contamination
  • ECR operation optionally
  • cw and pulsed operation


Applications:

  • plasma-enhanced chemical vapor deposition (PE-CVD)
  • surface modification
  • plasma cleaning
  • plasma etching
  • reaktive and non-reactive ion etching
  • basic reasearch in the material sciences

 

Working principle:

The SLAN basically consists of an annular wave guide (ring resonator) with slot antennas positioned at regular intervals on the innner side feeding microwave energy into the plasma. A magnetron which generates microwave power of 2.45 GHz frequency couples to the SLAN via R 26 wave guide. Between the generator and the plasma load a three port circulator directs the reflected power from the plasma into a water cooled dummy load to protect the magnetron from possible damage. The microwaves are coupled by a moveable antenna into the annular ring. Because of the highly nonlinear plasma impedance the active antenna length as well as the plunger position can be adjusted for minimum reflected power. A three stub tuner is not necessary. By changing the antenna and plunger position virtually any plasma load for an extended power and pressure range can be handled for atomic and molecular gases. Necessary calculations and simulations for construction were done using the software package MAFIA from Computer Simulation Technology (CST GmbH).

Electron cyclotron resonance (ECR)
 A permanent 875 G SmCo-magnet assembly can be inserted into the SLAN to increase dramatically the power absorption in the lower pressure range at around 10-4 to 10-2 mbar. Ionization ratios of several percent (depending on the gas used) thereby yielding maximum ion concentrations of the order of 10-11 cm-3 are typical. At the same time the electron temperature increases with decreasing pressure approaching several eV.

Surface wave generation
 The mSLAN generates axial surface waves at higher power levels (with argon in excess of 1 kW cw, with molecular gases higher power levels are necessary). Perequisite is that the plasma is overdense which is easily achieved for Ar. When operating in this mode the plasma volume increases with increasing power providing interesting options for advanced materials processing.

 

 

Technical data:

                                            µSLAN          SLAN I           SLAN II

Plasma diameter                 4 cm              16 cm             67 cm

max. mw power:               1,2 kW             2 kW               6 kW

working range                          

    with ECR (mbar)            10-4 - 50             10-4 - 10              N/A                                                                                   

    without ECR                  10-2 - 50          10-2 - 10          10-2  - 2      

pulsable                               yes                 yes                 yes

 

Application note: