Venting and Pumping the MBE System Written from multiple notes starting January 2014. Updated April 17, 2016.

1 Venting the MBE
- 1.1 Pre-Prep
- 1.2 Get RM and LC to UHV
- 1.3 Prep N2 and Growth Chamber
- 1.4 Vent System
- 1.5 Opening System
2 Pumping Down the MBE
- 2.1 Pump down to Rough Vac
- 2.2 Pump down to UHV
- 2.3 Secure Growth Chamber

Venting the MBE

When maintenance on the Growth Chamber is needed, we must go through the required steps to prep the system and bring it to atm for repairs. Once the system is prepped (Steps 1-3), bringing the Roughing Manifold (RM) and Load Chamber (LC) to UHV (Steps 4-7) can be done the night before venting the GC to atm pressure with UHP N2. Steps 8-16 take ~40 minutes.

Pre-Prep

Prepare Growth Chamber for Maintenance.
1. Cool down Sublimators and Crackers, and other cells (not Al) to very low idle.
2. Freeze Al.
3. The cryoshroud has to be turned off and LN2 evaporated out. Wait for pressure to stabilize.
4. Turn all cells off (except for ones retaining power such as Ga), and CAR heater.
5. Set up interlock overrides as needed, typically Ga Tip and Base.
Prepare Source Flange for Maintenance
1. Disconnect shutters, remove the shutter wheel, tape shutters, and double check them.
2. Any cells we glovebag have to have the water drained, and thermocouple and power cords removed (unless we’re keeping power to a cell, such as Ga). Zip tie loose cell cords.
3. Remove N2 station
4. The cracker valves have to be opened to 100, motors removed, and valves taped rigid
5. Cover pointy parts of system and surroundings with kimwipes (taped-on) to prevent sharp edges contacting the glovebag, including sublimator pressure points and SF water pipes.
Prepare a glovebag (and other thing as needed). Glovebagging
Secure Buffer Chamber
1. Make sure the Load Chamber (LC) to Buffer Chamber (BC) gate valve (GV) is closed.
2. Make sure the Growth Chamber (GC) to BC GV is fully closed.

Get RM and LC to UHV

Equalize the RM and LC pressures (watch BC pressure)
1. If RM is at UHV, then the RM and LC are already connected, proceed to 7.
2. If RM is at rough vacuum, we must also get the LC to rough vacuum.
  1. Turn off the LC IG.
  2. Turn off the LC turbo, wait for it to spin down, proceed to 5.
3. If RM is at atm, we must also get the LC to atm.
  1. Turn off the LC IG.
  2. Turn off the LC turbo, wait for it to spin down.
  3. Turn off the LC scroll pump (VPI then scroll).
  4. Wait for the pressure to get near atm, proceed to 5.
Open the all-metal valve (AMV) between the RM and LC
Pump down the LC and RM to UHV
1. If RM and LC are at rough vacuum:
  1. Turn on the LC turbo, wait for it to spin up.
2. If the LC and RM are at atm:
  1. Turn on the LC scroll pump (scroll then VPI) to pump down the LC and RM to rough vac.
  2. Wait for the pressure to be down to rough vac, ~10 torr (with the turbo N2 leak on).
  3. Turn on the LC turbo, wait for it to spin up.
3. When the LC and RM get to UHV, the RM pirani gauge (PG2) should read ~0 mT.
4. Turn on the LC IG to confirm.

Prep N2 and Growth Chamber

Setup Glovebag N2
1. Start glovebag purge at >25 psi, and prepare whatever needs to be prepared for opening
2. Glovebag purge can take ~20-80 minutes or more depending on previous state, whereas Steps 8-13 take ~40 minutes—minimize the amount of time GC is at atm but cannot be opened.
Setup RM N2
1. Make sure the roughing manifold (RM) viton valve is closed.
2. Turn on Growth chamber nitrogen to >15 psi.
3. Purge the pre-roughing manifold pipe with clean nitrogen: Open green quarter turn valve, wait a minute, close green quarter turn valve.
Secure Growth Chamber
1. Turn off all non-essential filaments in the growth chamber (BF IG, HVP, heaters).
2. Stop (End) and save the RGA scan, turn off the filaments, connection, and box. RGA should not have com cable plugged in without power cable plugged in. Don't just unplug power cable.
3. Close cryo gate valves, one at a time, see pressure rise up to confirm closure.
4. Turn off the GC IG.
5. Turn off all filaments in Growth chamber (Ga, RGA, etc.)
Monitor Ga temperature during opening, if it freezes the crucible may crack
1. We need to keep the Ga warm to prevent freezing, but running the cell filaments at non-vacuum pressures can prematurely age or damage them.
2. We strike a balance by turning the power to 0%, and raising it slightly as needed during opening to keep the Ga molten.
3. Bump up power as needed.
4. We want Ga not to go below 31 C, start bumping up power at 40 C.
5. Keep the Tip warmer than the Base
6. Do not let either Tip or Base Sorenson go over 1 A.
7. Concern for the Ga cell is crucial; Re-melting in a cracked crucible can ruin the cell!
8. Recall it idles at 100-150 C for maintenance.

Vent System

Open the AMV between the RM and GC; GC-RM-LC are now connected at UHV
Turn off LC IG
Turn off the LC turbo pump and it will bring the three chambers up to rough vacuum
Close the AMV between the RM and LC; GC-RM are now connected and at rough vac
Bring GC and RM up to atm slowly
1. Open the black viton valve on the RM
2. Slowly open green quarter turn valve, to leak in nitrogen, can open in fractions
3. The pirani gauge (PG) is less accurate at low and high pressures, use the analog gauge
4. Use the analog gauge to bring the GC and RM up to atm
5. Tap the gauge often, as it tends to get stuck
6. Close the quarter turn valve when the pressure gets into the 0 area. Leak in slightly more N2 to get to 0+ relative pressure, e.g. the needle is barely on the CW/right side of the 0 digit, or the needle barely goes beyond overlap with the 0 tick mark. Do not pressurize the system!
7. Turn up Chamber N2 flow to 25 psi

Opening System

Prepare for opening
1. Walk through opening.
2. Double check everything is prepped.
3. Let glovebag humidity get down to 0.1%
While Working
1. When the system is being opened, turn on the nitrogen to the RM-GC simultaneous with opening (e.g. removing a cell, blank, etc.), and turn up the GC N2 flow to >30 psi/maxed out.
2. Make sure the nitrogen flow to the chamber is higher than that to the glovebag. This keeps a positive pressure for the chamber so nothing from the glovebag goes into the GC.
3. Keep track of pressures. Do not pressurize the system!
4. When closing a port with a cell, blank, etc., turn off the nitrogen flow to the chamber. Turn off the gas right as the flanges connect. Do not pressurize the system!
5. Monitor the Ga temperature and power during opening. See Step 11 above.
6. Turn off the LC scroll pump anytime between venting the GC and 30 minutes before closing up the GC for pumping down to UHV. Tighten the LC door lock when you do so.

Pumping Down the MBE

We are now done with having the MBE open. The GC and RM are connected and at atm. The LC is isolated and also at atm because the scroll is off.

Pump down to Rough Vac

Connect LC to RM and GC by opening the RM-LC AMV
Turn on scroll pump for LC (pump then VPI) to pump down the LC-RM-GC to rough vac
Close Turbo Pump N2 Leak Valve
1. Turn on the turbo laptop and login
2. Plug in turbo pump cable to pump and laptop
3. Open LeyAssist software (slow to open; if it freezes, close and re-open)
4. Maximize the program window (or you can’t access buttons)
5. Click on Menu button on right (hamburger button), opens list of Accessories
6. Click on Edit button for X203, opens a Settings box; right now it’s on “33: Purge Valve 3 (Start Command)”
7. Change to “19: Always On” and press OK on Settings and Accessories (closes off N2 leak).
8. Look at turbo pump, little red light on pump valve should be lit.
Wait for the two PG pressures to get to under 1 torr (takes ~30 minutes)

Pump down to UHV

Close the RM black viton valve (green quarter turn valve should already be closed).
Pump LC-RM-GC to UHV (takes ~25 minutes)
1. Turn on the LC turbo pump and monitor it
2. Wait for the LC turbo pump to fully spin up.
3. Wait for the RM PG to be below 50 mTorr. The RM PG is typically below 5 mTorr after the turbo pump is fully spun up.
4. Turn on the LC IG to confirm LC is at UHV.
5. Follow Step 3 above to set turbo leak valve back to 33 (can do any time after turbo starts).
Isolate GC, Close the AMV between the GC and RM

Secure Growth Chamber

Enable GC Pumps
1. Disable cryo interlock
  1. On GC IG SRS, press Process
  2. For IG 1 box, press it and turn it from Auto to Manual
  3. Press Pressure:Back to return to normal IG pressure screen
2. Open the cryo gate valves, one at a time
3. Enable cryo interlock
  1. On GC IG SRS, press Process
  2. For IG 1 box, press it and turn it from Manual to Auto
  3. Press Pressure:Back to return to normal IG pressure screen
Enable GC IG and Monitor
1. Turn on the GC IG
2. It should be in the high -7s
3. When it gets 2e-7 or lower, you can leak check with He
  1. The RGA should not be turned on above 2e-7
  2. The RGA should not have its com cable plugged in without the power cable (for grounding)
4. Monitor cryopump pump down of GC.
5. Turn off the Chamber N2
Leak Check
1. Leak Check all flanges and feedthroughs you worked with
2. Leak check all flanges and feedthroughs you worked near
3. Check shutters and viewports carefully if desired
Turn Ga power up manually to prevent freezing, or set to Auto.
1. Keep the cell between 100-150 C, and the tip warmer than the base.
2. Manual: Set the tip to 3.5% and base to 2%. This may need to be modified slightly based on how much Ga is in the cell.
3. Auto: Determine by setting to manual overnight and seeing at what temperature Ga cell stabilizes.
  1. Auto (full Ga): Tip: 139.8 C (~3.2% power); Base: 129.6 C (~2.2% power)
  2. Auto (low Ga): Tip: 135 C (~3.5% power); Base: 105 C (~1.0% power)
Turn down the glovebag air to 0-10 psi or off
The GC is isolated from the RM, and the RM and LC are connected and being pumped by the turbo. All are at UHV will all pumps on and pumping.