RF matching network characterisation using Octiv Mono sensors

One critical component of a radio-frequency (RF) plasma processing equipment’s power delivery system is the RF matching unit which usually consists of load and tune capacitors as well as an inductive coil. In the ideal world, the matching unit should not absorb any power. In practice, the coil has some resistance and there is power loss through ohmic heating. This reduces the matching network efficiency and may cause the coil to fail over time. High voltages across the capacitors (and high current flow through them) can also cause degradation over time. Continuous changes in the quality of the match components cause process drift and even worse, it can lead to a catastrophic failure event.

Matching unit characterisation is now a key requirement for fab managers and process engineers throughout the industry.

There are three key performance indicators for the matching network; the match impedance range, the match quality and the match efficiency including the internal resistance. The Octiv VI probe and impedance meter is the ideal product for characterizing the matching network in terms of these three parameters.

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Measurement setup

The experimental setup used to characterize a typical RF matching unit is shown in the adjacent figure. This setup operates the match unit in reverse, i.e. the RF generator is connected to the RF output of the match and the 50 Ohm load is connected to the RF input. This allows measurement of the match at each position that gives an input impedance of 50 Ohm.

The Octiv mono sensors are added as close as possible to the input and output of the match to measure the voltage and current at these points. The RF generator is connected to the input of the first Octiv Mono unit using a short length of co-axial cable (transmission line). The output of the first Octiv Mono is connected to the output of the matching unit (this is opposite to normal use) with another short co-axial cable. The input and output of the second Octiv Mono unit are connected to the match unit input and 50 Ohm load respectively using two short lengths of co-axial cable.

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Characterisation procedure

The procedure for measuring the key matching unit parameters can be carried out as follows:

  • Set the RF generator power level to the desired power
  • Connect the Octiv units to the PC using the USB interface
  • Select the ‘time trend’ mode of operation
  • Manually move the load and tune capacitors through their full range (this process takes about 10 minutes)
  • Export the data file to CSV format for further analysis in excel.

Watch a video demonstration of these simple steps.

Learn more about our advanced calibration laboratory.

More details about the Octiv Mono sensor.

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The outcome of the characterization will be the information on:

  • RF match unit impedance range
  • Matching network efficiency
  • Quality factor
  • Power measurement accuracy
  • Internal resistance.

Knowing these parameters are critical for a RF plasma process or any RF power delivery system where you have a non-50 ohm load.

For more information, download the detailed application note on Octiv VI probe – Match Box Characterisation.