Author Archives: Randy

Measuring electron beam diameter

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This procedure will allow you to determine the electron beam diameter diameter on scanning auger electron spectrometers using the line scan feature of AugerMap software and the magnification standard (or, a straight edged sample). Although written for scanning auger electron spectrometer systems, the principle is the same for SEMs – scanning electron microscopes – measure the slope across an edge at a known magnification.

1. Insert the beam size standard into the system and perform an elastic peak alignment on the top surface of the sample to ensure that the sample is at the correct Z position with respect to the analyzer.  Do not tilt the sample.

set-elastic-peak

Set elastic peak

 2. Next, change the beam voltage to 10KV and adjust the electron gun parameters for a good image at 5000X or higher magnification.

3. if so equipped, adjust the Condenser and Objective steering plates for minimum movement. (If an SEM, rock the lenses).

4. Ensure that the image is in the best possible focus.

5. Lower the magnification to the lowest possible setting and move the beam size standard to the center hole to find the grid and adjust the Z position until the grid is in focus.  The sample is now at the correct focal point on the analyzer. This is a good trick that you can use on any scanning auger system – if you first set the elastic peak and then the focus, as long as you mechanically bring the sample back into focus after moving to a different location on the sample (and do not change the focus knob or settings in the software), the sample to analyzer distance is still correct.

6. Set the magnification to 100KX and fine-tune the focus and stigmators as required. The sample can be moved on either the X or Y axis until you are able to line up on one grid line.

7. Obtain an SED video map and use the quantization feature if necessary.

8. Select the line scan feature in AugerMap and draw a line horizontally across the grid line.

9. For AugerMap1, Add region – SED line.

10. Select Video input; point one ms per step, number of sweeps one, and resolution 256 points per line.    For AugerMap II, select SED video map.

auger-map-2-sed-dialog-box

AugerMap 2 SED dialog box

 

 

 

 

 

auger-map-sed-dialog-box

Auger Map version 1 SED dialog box

 

 

 

 

 

 

 

 

 

 

 

11. Acquire the line scan.

12. After the line scan is completed it will show a display of signal intensity on the Y-axis vs. distance scanned on the X-axis. At 100KX magnification, this distance is 1uM, or, 10,000 angstroms. By determining the slope of the beam diameter as it crosses the edge of the sample, the beam diameter can be determined.

13. Print out the line scan and use a ruler to determine the top 20% and bottom 20% of the line scan. Draw a line across the top 20% and bottom 20% of the line scan.

14. Next, draw a line on the slope of the beam diameter as it drops down or up between the 20% lines.

15. Determine the distance between the slope of the line at the top of the scan and the bottom of the scan.  This distance represents the beam diameter in relationship to the full scan (10,000 angstroms at 100KX).

16. The example below shows in detail how this measurement is calculated.

beam-size-measurement

Beam Size Measurement

 

Perform this measurement anytime that you wish to know the size of the electron beam diameter for any given set of conditions.  If the beam size is too large to see one grid line, you can reduce the magnification to 50KX, in which case full scale on the X-axis would be equal to 20,000 angstroms.

Ion Pump Rejuvenation Procedure

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After prolonged periods of sputtering with Argon gas, the ion pumps can become saturated, resulting in occasional “belches” of Argon during which the ion pumps overheat and release large amounts of gas. These belches usually result in a snowball effect that can dump the system. Rejuvenating the ion pumps once every few months (more often if you do a lot of sputtering) will help to prevent the belch problem from recurring.

To rejuvenate the ion pumps with O2:

1. Turn off all filaments, including the ionization tube (DIG).

2. Set the ion pump control panel meter to the 200mA current settings and set the

ion pump to the run (protected) mode.

3. Slowly bleed in O2 until there are 40mA of current shown on the ion pump panel meter. You will need to change ranges on the panel meter as the current is increased.

4. Adjust the leak valve as needed to maintain 40mA of current for 20 to 30 minutes.

5. Close the leak valve. It takes about one day for the vacuum to return to its previous level.

 

For more information on rebuilding ion pumps, search for Ion Pump in the RBD TechSpot blog search box.

For more information on ion pump theory, here is a link to an informative paper – https://cds.cern.ch/record/454179/files/p37.pdf

And, from Wikipedia:

An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump capable of reaching pressures as low as 10−11 mbar under ideal conditions.An ion pump ionizes gas within the vessel it is attached to and employs a strong electrical potential, typically 3kV to 7kV, which allows the ions to accelerate into and be captured by a solid electrode and its residue.

The basic element of the common ion pump is a Penning trap. A swirling cloud of electrons produced by an electric discharge are temporarily stored in the anode region of a Penning trap. These electrons ionize incoming gas atoms and molecules. The resultant swirling ions are accelerated to strike a chemically active cathode (usually titanium). On impact the accelerated ions will either become buried within the cathode or sputter cathode material onto the walls of the pump. The freshly sputtered chemically active cathode material acts as a getter that then evacuates the gas by both chemisorption and physisorption resulting in a net pumping action. Inert and lighter gases, such as He and H2 tend not sputter and are absorbed by physisorption. Some fraction of the energetic gas ions (including gas that is not chemically active with the cathode material) can strike the cathode and acquire an electron from the surface neutralizing it as it rebounds. These rebounding energetic neutrals are buried in exposed pump surfaces.

Both the pumping rate and capacity of such capture methods are dependent on the specific gas species being collected and the cathode material absorbing it. Some species, such as carbon monoxide, will chemically bind to the surface of a cathode material. Others, such as hydrogen, will diffuse into the metallic structure. In the former example, the pump rate can drop as the cathode material becomes coated. And, in the latter, the rate remains fixed by the rate at which the hydrogen diffuses.

There are three main types of ion pumps, the conventional or standard diode pump, the noble diode pump and the triode pump.

Ion pumps are commonly used in ultra-high vacuum (UHV) systems, as they can attain ultimate pressures less than 10−11 mbar. In contrast to other common UHV pumps, such as turbomolecular pumps and diffusion pumps, ion pumps have no moving parts and use no oil. They are therefore clean, need little maintenance, and produce no vibrations. These advantages make ion pumps well-suited for use in scanning probe microscopy and other high-precision apparatus.

Planned power outage procedures for scanning Auger

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This planned power outage procedure is written for a Physical Electronics (PHI) 600 scanning Auger system, but it applies to all older PHI systems including the 5000 series X-ray photoelectron spectrometers.

At many companies and universities the facilities departments occasionally have planned power outages for maintenance purposes. The following procedures detail the steps that you need to take to safely shut down and then power up your PHI Auger, XPS or SIMS surface analysis system.

Shutdown procedure

Vacuum Console:

  1. Make sure that all valves are closed on the auto valve control remote.
  2. If necessary, use the manual valve control buttons on the AVC to close any open valves.
  3. Check that the auto valve control auto/manual switch is in the auto setting.
  4. Turn off the turbo pump(s) and mechanical pump(s)
  5. Turn off the auto valve control power.
  6. Make sure that the leak valve on the ion gun is closed (fully CW, do not over tighten)

Electronic Console:

  1. Turn off the electron gun units – 20-610, RBD110
  2. Turn off the analyzer units – 32-150, 32-100
  3. Turn off the 11-065 ion gun control
  4. Shutdown the PC and monitor
  5. Turn off the RBD147 PC interface unit
  6. Turn off the DIGIII ion gauge control
  7. Turn off the Boostivac ion pump control
  8. Turn off the main and interlock circuit breakers on the 18-030 power interlock

660 Scanning Auger and 5000 series XPS shutdown:

  1. Turn off units on vacuum console as per the above procedure
  2. On the electronics console, turn off the card rack power
  3. Turn off the PC and RBD147 PC interface unit
  4. Turn off the 11-065 ion gun control
  5. If an XPS system, turn off the x-ray source control and the HV power supply
  6. Turn off the DIGIII ion gauge control
  7. Turn off the Boostivac ion pump control
  8. On the EMO (emergency off) box, press the RED shutdown button

 

Power up procedure

Vacuum Console:

  1. Turn ON the auto valve control power
  2. Make sure that all valves on the AVC remote show red for closed
  3. Turn on the turbo pump(s) and rough pump(s)

Electronic Console:

  1. Turn ON the main and interlock circuit breakers on the 18-030 power interlock
  2. Turn the Boostivac ion pump meter to 10kV
  3. Turn the Boostivac power to Start and check that the high voltage comes up to 5kV or more. If the voltage does not come up the system may be partially up to air. If the high voltage does come up, set the Boostivac power switch to Run
  4. Turn on the DIGIII ion gauge control by setting the power switch to UHV, then press I/T3 to start the ion gauge. Normally the reading will be in the low 10-9 Torr range or lower.
  5. After 10 to 30 seconds the interlocked power on the 18-030 should turn on.
  6. The system is now under vacuum.  The rest of the units will be turned on by the operator of the system the next time the system is used.

660 Scanning Auger and 5000 series XPS power up:

  1. On the EMO box, press the yellow reset button
  2. On the EMO box, press the Vacuum console and Electronics console buttons.
  3. Turn ON units on vacuum console as per the above procedure
  4. Turn the Boostivac power to Start and check that the high voltage comes up to 5kV or more. If the voltage does not come up the system may be partially up to air. If the high voltage does come up, set the Boostivac power switch to Run
  5. Turn on the DIGIII ion gauge control by setting the power switch to UHV, then press I/T3 to start the ion gauge. Normally the reading will be in the low 10-9 Torr range or lower
  6. The system is now under vacuum. The rest of the units will be turned on by the operator of the system the next time the system is used

Additional Information:

Sometimes the Boostivac high voltage meter does not read properly. If it does not indicate 5kV when turned to Start, you can set it to Run and if the Boostivac does not shut off in a few seconds, then the meter circuit is defective and the high voltage is probably working properly. If the Boostivac shuts down after a few seconds when set to run, then the system probably leaked up to air and needs to be pumped down.

scanning-auger-electronic-console

scanning-auger-electronic-console