Category Archives: Ion Sources

Information on PHI (Physical Electronics) ion source repair, maintenance, and operation

Faraday cup procedure to align ion beam current

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Using Ta2O5 or SiO2 works well for aligning an ion beam to the focal point of an X-ray photoelectron or scanning Auger electron spectrometer. But, in order to optimize the ion beam focus at larger beam sizes, a Faraday cup is required.

The Faraday cup used on many Physical Electronics/PHI surface analysis systems comprises a specially configured sample mount with a molybdenum aperture that has a diameter of 250um.

faraday cup sample mount

 

 

 

 

Because the current measured into the Faraday cup is in the low nA range, a picoammeter (such as the RBD Instruments Inc. 9103 USB picoammeter) and bias box are required. When the bias box is set to the ion input, the target is grounded and the output of the bias box is routed from the ion lead (Faraday cup) on the specimen stage to the input of the picoammeter. When an ion beam is larger than the 250um Faraday cup aperture, only the portion of the beam that is 250um or smaller is measured. By adjusting the ion beam focus and position for maximum current into the Faraday cup, the ion beam can be aligned and the current density can be optimized for any ion beam condition. In general, larger beam sizes result in more total current and faster sputter rates.

faraday cup

 

 

 

 

 

 

 

 

Another benefit of using a Faraday cup is that you can also determine the electric current density using a multiplication factor. Ion current density is rated in mA/cm2.Dividing the area of the 250um Faraday cup hole into one square centimeter gives us a factor of 2037.18. So, to calculate the ion beam current density using a 250um Faraday cup, measure the ion current that enters the Faraday cup and multiply it by 2037.18 to get the current density in mA/cm2. For example, the PHI 04-303 5kV differential ion source has a maximum current density specification of 600 mA/cm2 at 5kV ion beam voltage and 25 MPa of argon gas pressure. That works out to just under 300nA of ion current passing into the Faraday cup. Typically, though, the 04-303 ion source is operated at 3-to-4kV with 15MPa of argon pressure. Therefore, the maximum ion current passing into a Faraday cup under those conditions is more in the range of 150 to 200nA.

Procedure to Maximize the Ion Current Passing into a Faraday Cup

 

  1. First you need to align the Faraday cup to the focal point of the analyzer. For Auger electron spectrometers, acquire an elastic peak just to the side of the Faraday cup hole and then move the Faraday cup hole to the center of the TV image. For X-ray photoelectron spectroscopy systems, move the Faraday cup hole to the center of the system microscope’s image at the highest possible magnification setting.
  2. Turn the ion beam ON (make sure the electron beam is off).
  3. Set the bias box to Ion and the bias to ON. This will ground the target and apply +90V to the ion lead on the specimen stage (which in turn makes the electrical contact to the Faraday cup). Note that there are different versions of the bias box used on PHI systems. Some systems do not have bias boxes. In those cases, short out the target and and connect the picoammeter to the ion lead on the specimen stage.
  4. While observing the picoammeter, adjust the focus (objective) and condenser on the ion gun control and the mechanical offsets (thumbscrews) on the ion gun for maximum current into the Faraday cup. This will take several iterations to optimize. Once the mechanical offsets on the ion gun have been adjusted to where no further increase in current is noted, lock them down securely and also make sure that the ion gun housing is tight. Do not adjust the mechanical offsets for subsequent focus adjustments at different condenser (COND) or beam voltage settings. Instead, you can optimize the position of the ion beam into the Faraday cup by using the offset adjustments on the ion gun control if necessary.
  5. Note the measured current and ion gun settings in a form such as the table shown below. By optimizing a few ranges of current and using those parameters to acquire depth profiles on a standard such as SiO2 or TaO5 (both available from RBD) you can create a matrix of reproducible sputter rates.

Ion sputter rate table

 

 

 

 

Here is a link to a technical report in the Journal of Surface Analysis, which provides additional information:

http://www.sasj.jp/JSA/CONTENTS/vol.14_2/Vol.14%20No.2/Vol.14%20No.2%20124-130.pdf

And here is a link to a video that shows an ion source being aligned using a Faraday cup – http://www.youtube.com/watch?v=uKg9GLkXT3s

How to align the 04-303 ion gun

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This post explains how to align the Physical Electronics 04-303 ion gun typically found on PHI Auger electron spectroscopy and X-ray photoelectron spectroscopy systems. The alignment principles explained here will apply to just about any surface analysis ion source.

First, here is a video that explains all of the alignment methods:

Next, here is a link to a tech tip that explains the theory and operation of the 04-303 ion gun: 04-303 Ion Source Theory and Alignment

Finally, here is the basic operation and alignment taken from the tech tip:

04-303 Ion Gun Operation

Basic Operation:

1. On the 11-065, set the Emission/Pressure meter switch to Emission. Make sure that the scale switch is in the X1 (times one) position.

2. Press the Diff Pump Ion Gun button on the AVC remote, or manually pump the ion gun.

3. Slowly turn up the Emission knob until you have 25mA of emission current (X1 position).

4. Switch the Emission/Pressure meter switch to Pressure.

5. Slowly open the argon leak valve on the 04-303 ion gun until you have 15 mPa of pressure on the meter. This corresponds to approximately 2 x 10-8 torr when differentially pumped, and 2 x 10-7 torr when not differentially pumped.

You are now ready to sputter. When you turn the ion beam voltage on, the ion gun will be sputtering.

Alignment: Visual Method

This works in both ABS and SED image modes. SED mode is sometimes easier to work with.

1. Insert a SiO2 sample and position it to the focal point of the analyzer. Use 30o to 60o of tilt.

2. Get a low magnification image of the SiO2. Use a low electron beam voltage, such as 1.5kV in order to get the largest possible image size (the lowest possible magnification).

3. Set up the ion gun as discussed above. Set the condenser to 5.00 (the smallest spot size) and the objective to 3.40.

4. Turn on the ion gun beam voltage. If the electron beam current and the ion beam current are approximately the same value, the ion beam spot should be visible on the TV monitor.

5. Mechanically adjust the position of the ion gun (turn the thumb screws) to center the ion beam spot on the TV monitor. Adjust the OBJ for the smallest spot size.

For more information or to order a replacement ionizer for your 04-303 ion gun, visit our website at www dot rbdinstruments dot com

04-303 or 06-350 Ionizer replacement procedure video

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The procedure to replace the ionizer on a 04-303 or 06-350  ion gun is one of those things that once you see it done, you know how to do it. You can expect to replace your ionizer anywhere from once every few years to once every few months, depending on how much sputtering you do. For most people it will be about once every 6 months.

It takes about 10 minutes to replace the ionizer once the system has been vented, and this video takes you through the process from start to finish:

TIP: Be careful not to drop the flat head ionizer retainer screws into the source as you remove or install the ionizer assembly. If you do, they usually fall down to the inside of the ion gun wall and you can get them out using a screw driver or wire with some tape on the end of it (clean the screw afterwards). If you can’t see them, you will need to pull the source off and find them for sure as there is a slight chance that they can fall into the differential pumping port and eventually work their way down to the turbo pump.   Turbo pumps blades that are spinning at 60,0000 RPMs or more do not like to get hit with small stainless steel screws.

RBD Instruments provides a rebuilding service for the 04-303 and 06-360 ionizers as well as an Argon bottle gas refill service. Our filaments typically last for 1100 hours under normal operating conditions.

In addition to the 04-303 ionizers, we also provide filaments for the 04-300, 04-191/2 and 04-161/2 ion guns.

For more information, please visit the Ion Gun Filaments and Grids section of our website.

04303-ionizer

04303 high voltage feedthrough

Filament – Pins 1 and 2
Grid – Pin 5
Extractor – Pin 4