This article describes how the base vacuum in a PHI 5600 X-ray photoelectron spectrometer can be improved using the bakeout procedure. The bakeout procedure is essentially the same for a majority of the older Physical Electronics (PHI) spherical capacitive analyzer (SCA) XPS surface analysis systems.
Generally, PHI X-ray photoelectron spectrometers have integrated radiant heaters, and also heaters under the magnets in the ion pumps. These pumps heat up the system as high as 200 °C. Once the system is prepared for the bakeout procedure, the vacuum chamber is covered with a heat-insulating blanket to capture the heat produced by the heaters.
Bakeout times usually take 12 to 20 hours based on the amount of water vapor present in the chamber, which is directly proportional to the duration for which the vacuum chamber has been exposed to air.
Using the ion pumps, the system should be pumped down and the vacuum should be maintained in the low 10−7 Torr range or better prior to initiating a bakeout procedure—except when users are baking out new ion pumps into the turbo pump; this has been illustrated in more detail in the following sections. Users can simply follow these steps and refer to the pictures below:
- Samples should be removed from the chamber that should not be baked out. These comprise gas samples and samples that are placed with a silver or carbon tape. Semiconductors and metals can be left in the chamber.
- All the valves on the AVC should be closed, and the turbo pump should be turned off.
- The card rack power should be turned off.
- The X-ray source control, ion gun control, and any other controls that are likely to have high voltage or filament should be turned off. Auto valve control (AVC), Boostivac ion pump control, and the DGC III ion gauge control are the only units that should continue to have power.
- All the cables connected to all optics units on the vacuum chamber should be removed, except the ion gauge control cable. This cable can be baked and always remains connected. Only cables meant for the X-ray source, neutralizer, ion gun, and electron gun, if present, should be disconnected.
- In case the system contains motors on the stage, they should be removed. If the user’s system happens to be a 5000 series LS (large sample), the stage should be put in the bakeout position before the motors are removed.
- The water should be drained out of the typical X-ray source (if present). This can be done by first disconnecting the IN water line from the source while making sure that the OUT water line stays connected, and then removing the IN water coupler. Through gravity, water is drawn out of the X-ray source in approximately 20 seconds. After the water is removed from the source, the OUT water line should be disconnected and the IN water coupler should be reconnected to the source.
- The water cooling lines and the HV connection on the typical source, as well as on the second half of the shroud, should be removed. The water swag lock fittings should be covered with an aluminum foil.
- If a monochromator is included in the system, the shield aperture should be set to a mid-range. This will prevent any coating from occurring on the monochromator crystals during the bakeout process, and will also reduce the need to direct the radiant heat on the crystals’ surface.
- The Teflon block, base (the HV coupler should be removed first), the 10-610 monochromator X-ray source cover, and seals should be removed. The O-ring seals located on the mono anode should be removed, or else they will become dry during the bakeout procedure, which may consequently lead to a host of issues such as water leakage and current leakage on the mono X-ray source. The O-rings should be removed before the bakeout procedure and should be coated with some vacuum grease so that they do not dry out and cause these leaks. This is highly crucial. The following pictures demonstrate how the Teflon block is likely to get burned and lead to electrical leakage when the O-rings are not removed for the bakeout procedure.
Image Credit: RBD Instruments.
Image Credit: RBD Instruments.
- If a microscope is included in the system, it should be removed by unscrewing the collar and then lifting it out of the base. The base should never be moved or removed because that will make it relatively harder to realign the microscope to the SCA’s point following the bakeout.
- When wearing laboratory gloves, the system should be wiped down with some amount of isopropanol to remove any traces of oils or other contaminants. Isopropanol is recommended because it is readily available and much safer, but any degreasing agent is suitable. After baking out the system, any oils from handprints or fingerprints left on the chamber’s surface may become eternally etched onto the chamber.
- All the viewports and exposed connectors and feed-throughs should be covered with an aluminum foil. Through this step, the thermal conductivity can be balanced during the heat-up and cool-down cycles.
- The tabletops close to the vacuum chamber should be removed. The 5400, 5300, and 5100 type vacuum consoles are incorporated with the electronics console; hence, only the tabletops close to the vacuum chamber have to be removed. The vacuum console on the 5600 and later systems is separate, and therefore, the tabletops on the vacuum console should be fully removed.
- The tabletop interlock switches should be pulled up. These are developed to prevent the bakeout heaters from switching on unless the tabletops have been taken off.
- The blanket should be placed over the chamber; users are advised to wear a mask at the time of this process. The blanket could be either one piece or two or more pieces joined with Velcro. Gloves are recommended, as well as a laboratory coat, if possible. This is because the older blankets are aluminized fiberglass and the fibers are bound to itch. Moreover, if users are unable to wear a mask, they should not inhale the fibers while putting the blankets on.
- The monochromator crystals, turbo pump (if placed on the load lock), and V1 gate valve should be located outside the blanket. If any gaps exist in the blankets, an aluminum foil should be used to cover them.
- In case the system is not fitted with a cooling fan for the V1 gate valve, a floor fan set on low speed should be used to cool the V1 gate valve. While the vacuum chamber will reach temperatures as high as 200 °C, the gate valve can only be baked to 150 °C.
- It should be ensured that set point 4 on the DGC III ion gauge control is set to 3 x 10−6 Torr.
- The Boostivac ion pump control should be set to the run position. This ensures that the Boostivac turns off if the system’s outgassing becomes greater than the low 10−5 Torr range.
- The bakeout timer should be set to 12–20 hours and the bakeout power button should be pressed (on previous 5000 series systems, a bakeout power circuit breaker is provided and not a switch).
- Once the bakeout procedure is over, the system should be allowed to cool down to room temperature. Following this, the bakeout blanket(s) should be removed, the tabletops should be replaced, and the cables to the system should be reconnected. The electron multiplier, X-ray source, neutralizer, electron gun, and ion gun all have to be outgassed. Users can refer the manual for each of those components for the outgassing process, or they can contact the technical support at RBD Instruments for further information.
Baking of Turbo Pumps
If users are baking the system into the turbo pump without turning on the ion pumps, they will be pumping on the chamber during the bakeout procedure.
During turbo bakeout, V1 and V3 are open, and the ion pump should be turned off. Also, set-point 1 on the DIG III ion gauge control should be set to 8 x 10−4 Torr, and set-point 4 should be set to 5 x 10−4 Torr. The turbo pump bakeouts are usually set to 4 hours; this time is just sufficient to remove the water vapor from the ion pump elements.
After the turbo pump is baked out, the system should be allowed to cool down and the ion pumps should be started. Then, the V1 and V3 should be closed and the DIG III set-points should be set back to normal (set-point 1 = 5 x 10−5, set-point 4 = 3 x 10−6 Torr), and the chamber should be baked out normally.
The following photos demonstrate the steps of the bakeout process.
If users do not prefer to utilize a bulky bakeout blanket to desorb water vapor, they can check out other options available from RBD Instruments.
5600 XPS system with mono. Image Credit: RBD Instruments.
Side view of the XPS system. Image Credit: RBD Instruments.
Drain X-ray source water. Image Credit: RBD Instruments.
Standard X-ray source housing. Image Credit: RBD Instruments.
Remove water line couplers. Image Credit: RBD Instruments.
Standard source ready for bakeout. Image Credit: RBD Instruments.
Monochromator. Image Credit: RBD Instruments.
Monochromator shield aperture. Image Credit: RBD Instruments.
Remove mono block. Image Credit: RBD Instruments.
Remove mono O-rings. Image Credit: RBD Instruments.
Remove mono base and rubber insulator. Image Credit: RBD Instruments.
Mono anode. Image Credit: RBD Instruments.
System microscope. Image Credit: RBD Instruments.
System microscope removed. Image Credit: RBD Instruments.
Wipe down the chamber with Isopropanol. Image Credit: RBD Instruments.
Cover viewports. Image Credit: RBD Instruments.
A window covered with aluminum foil. Image Credit: RBD Instruments.
Covered with aluminum foil. Image Credit: RBD Instruments.
Mono anode covered with aluminum foil. Image Credit: RBD Instruments.
Remove tabletops. Image Credit: RBD Instruments.
Tabletops removed. Image Credit: RBD Instruments.
Pull up tabletop switches. Image Credit: RBD Instruments.
Bakeout blankets on the chamber. Image Credit: RBD Instruments.
DIG III setpoint 4. Image Credit: RBD Instruments.
Boostivac set to run. Image Credit: RBD Instruments.
Bakeout timer and power switch. Image Credit: RBD Instruments.
The cooling fan on the gate valve. Image Credit: RBD Instruments.
X-ray source bakeout shortcut. Image Credit: RBD Instruments.
This information has been sourced, reviewed and adapted from materials provided by RBD Instruments, Inc.
For more information on this source, please visit RBD Instruments, Inc.