20-805 analyzer control calibrations

Posted on April 7, 2014 by Randy

This post explains some tests and calibrations for the 20-805 analyzer control which is used on older Physical Electronics (PHI) ESCA, XPS and AES surface analysis systems. The 20-805 analyzer control is typically used to control the 15-255G and 25-260 double pass cylindrical mirror analyzers.

20-805 Analog AES Input Test Procedure

This section explains the procedure for testing whether or not the 0 to 10 volt drive signal from the PC137A or RBD147 interface unit is working properly.

Equipment needed: DVM and BNC adaptor cable

The 20-805 has a gain of 200:1 and the analyzer scale factor is 1.7. This means that the ratio between eV detected and the DC voltage applied to the outer cylinder of the analyzer is 1.7 to 1. For example, to measure a 1000eV electron, 588.823 DC volts must be applied to the outer cylinder.

To calculate what the Analog or Input voltage should be for a particular eV, use the following formula:

Analog or Input voltage = eV divided by 1.7 divided by 200.

Example: 2000 eV divided by 1.7 = 1776.47 divided by 200 = 5.8823 volts on the Analog or Input cable.

Procedure:

Turn the power off on the 20-805 analyzer control.
Remove the Analog Input cable and connect it to a DVM.
1. Set up an elastic peak alignment with a lower limit of 100 and an upper limit of 100. (This will put the sweep voltage at a single fixed value).
2. Acquire the alignment and measure the voltage on the Analog or Input cable. The voltage should be about .294 volts DC.
  1. Set up an elastic peak alignment with a lower limit of 2000 and an upper limit of 2000.
  2. Acquire the alignment and measure the voltage on the Analog or Input cable. The voltage should be about 5.88 volts DC.

If the Analog or Input voltage is correct, then the D/A on the PC 137A or RBD147 is working properly.

20-805 Pass Energy Supply Test

The 20-805 Pass Energy Supplies provide the proper voltages to the PHI double pass CMA when used in the XPS mode.

To test:

Short out the Analog Input on the back of the 20-805 with a bnc shorting plug. This will ensure that the high voltage output is zero.
Set the pass energy switch on the 20-805 to 100.
Measure between the HV and IC connectors on the back of the 20-805. The voltage there should track the Pass Energy switch on the front panel with-in .5 volts.
Check that the HV to IC voltage matches the front panel for all pass energy settings.
Measure between the IC and OC connectors on the back of the 20-805. The voltage there should track the Pass Energy divided by 1.7 on the front panel with-in .5 volts.
Check that the IC to OC voltage matches the front panel for all passed energy settings.

Pass Energy Setting	HV to IC voltage	IC to OC voltage
10	10	5.88
25	25	14.7
50	50	29.4
100	100	58.8
200	200	117.64

If the voltages are not correct, check the 20-805 Pass Energy Supply capacitors and TIP53 transistors.

The 20-805 gain is 200:1. You can use AugerScan to send out specific voltages on the D/A output (analog input) cable –

1) With the RBD147 on, run AugerScan.
2) Select “Diagnostics” from the “System” menu.
3) At the bottom of the dialog box, make sure the option for “Hexidecimal” is checked.
4) In the Address field for RBD147, enter 10
5) Individually enter the following in the Data field, and hit the Write button for each while checking the 20-805 control voltage:

8000 (0 V)
9FFF (1.25 V)
BFFF (2.5 V)
FFFF (5 V)
7FFF (10 V)

AES Calibration when using a 20-805 Analyzer Control – For a 10-155 or 15-255G Analyzer.

This section explains how to calibrate the AES peak energies and 2 kV elastic peak crossover.

Tools needed: Insulated adjustment screwdriver (pot tweaker)

Copper foil or gasket material.

Procedure:

Read this entire procedure before starting the calibration.
Load a sample of copper foil into the system and set the beam voltage on the 11-010 electron gun control to 2kV.
Position the sample to the focal point of the analyzer using the AES Align routine. At this point it does not need to be exactly at 2kV, just make sure that the peak is maximized.
Sputter the sample clean. Note: If you do not have a sputter ion gun on your system, then scrape the sample with a razor blade or exacto knife before you load it into the system to remove the surface carbon and oxygen.
After the sample is clean, re-acquire the elastic peak and re-check that the peak is at maximum counts and beast shape. Do not worry if it is not at 2kV crossover, that will be adjusted later.
From this point on, DO NOT MOVE THE SAMPLE!
Acquire an alignment from 900 to 960 eV and differentiate the data. The peak should be at 920 differentiated. If not, adjust the scale factor in the AugerScan Hardware Configuration menu a little bit and re-acquire the alignment and check the position. A large scale factor number will move the peak down in eV.

elastic-peak

Re-peat and adjust the scale factor as necessary until the differentiated copper peak is at 920eV.
Change the alignment settings to 2kV default and re-acquire the elastic peak. But, DO NOT MOVE THE SAMPLE! If the peak is not at 2kV, then adjust P1 in the 11-010 to move the peak so that it is at 2kV. Caution! There is high voltage present in the 11-010, do not perform this adjustment unless you are qualified to work on high voltage. Refer servicing to qualified personnel.

beam-voltage-adjustment-potentiometer

Location of P1 in the 11-010 Electron Gun Control is shown above.

Once you have the 11-010 adjusted to 2kV, change the beam voltage to 3kV and acquire a survey from 30eV to 1030eV, 1 eV per step, 50 ms per point, and 3 sweeps.
When complete, the survey should look like the date below after it is differentiated:

auger-copper-data

Calibration Complete!

Need more help with your 20-805? Contact us.

Measuring electron beam diameter

Posted on March 17, 2014 by Randy

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

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.

AugerMap 2 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

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

Posted on March 12, 2014 by Randy

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.