1 Echo Bake (7/1/10, v1)
- 1.1 !State of MBE:
- 1.2 !Baking Procedure:
- 1.3 !After Baking
- 1.4 !Important things to watch:
2 Unmodified (and unparsed) from Stanford MBE lab... Please modify

Echo Bake (7/1/10, v1)

!State of MBE:

Magnets off of buffer ion pump
Transfer arm magnets off (and anything else that isn‚Äôt bakeable). E.g. is the new ion pump cable bakeable? If not, replace with an older one and you can use one of the old-style controllers.
GC gate valve open
GC ion pump gate valve open
Buffer/LC gate valve open
Monitor GC pressure with growth chamber ion gauge (w/bakeable cable)
Bakeable TC on CAR, but not heater cable (this is our internal thermometer). Make a TC cable for this, don‚Äôt shorten the life of the normal CAR TC
Do NOT run the heated viewport or the CAR heater as we don‚Äôt want to shorten the life of the filaments (this contradicts what I said earlier)
Important: set bake interlock to ~5e-6 so it doesn‚Äôt trip unless something very bad happens (want to avoid thermal cycling). You might need to disable the system interlock off the buffer ion pump since the buffer ion pump will be off?

!Baking Procedure:

Begin baking top half of MBE first [Max=190C (external TC)]

0.2C/min, 20C steps, use a waituntil pressure <1e-6 pause between 20C steps
Slowly start heating the heater tape on the buffer. Heat to normal buffer bake temperatures‚Ä¶
Get top half up to 190C (external TC) and wait until pressure stabilizes and is falling nicely

Begin ramping sump [Max=190C (external TC)] ~12 hours into bake

0.2C/min, 20C steps, use a waituntil pressure <1e-6 pause between 20C steps

When sump = ~60C:

Begin ramping GC ion pump [Max = 150C] 0.2C/min, 20C steps, use a waituntil pressure <1e-6 pause between 20C steps

Hold until point of diminishing returns‚Ä¶ the linear regime‚Ä¶

!After Baking

Lubricate all metal valves. (RTFM, and also read AllMetalValveMaintenance)
Lubricate gate valves (if necessary - RTFM)

!Important things to watch:

Pressure ‚Äì avoid tripping the pressure interlock! If possible‚Ä¶
Cryo temperature ‚Äì you‚Äôll likely need to keep turning up the cryo GV interlock temperature as the sump heats. This is OK, but you want to make sure that the cryo isn‚Äôt dumping (thermally shorting because it‚Äôs filled with gas)
Temperatures ‚Äì want to ensure that the bake is uniform, so watch the various TCs around the machine (note: there is some TC to TC variation, so note the various TC readings before the bake starts; hopefully their relative readings don‚Äôt change much).

Unmodified (and unparsed) from Stanford MBE lab... Please modify

Before bake...

Leak check.
Cover counters with foil.
Heat sources. Typical temperatures... Sb:125, Si:400, Be:400, In:300, Ga:300, Al:300, As:85 (if valve is closed, which it should be for most of bake).
Turn up heated viewport to 1, then 2 at least half an hour later.
Check for unbakeable items and any foreign plastic. In particular, make sure the substrate rotation magnet is removed.
Leave GC/TT gate valve cracked open. (Can't bake it closed.) Monitor TT pressure during bake.
Disconnect ion gauges and remove cables. (They're bakeable, but the cables last longer this way.)
If you're not flowing cooling water through sources, remove water line(s).
Tape all shutters closed.
Set up bake shrouds and seal all openings & cracks with foil & bakeable tape.
Remove CAR cables. Substitute a bakeable thermocouple cable if you want to monitor bake temperature. (A good idea.)
Turn CAR so substrate is facing upward, beam flux facing downward.
Mostly close the ion pump gate valve for initial part of bake. The junk coming off the walls is cryo-pumpable, and the cryo pumps it better anyway. But don't close the gate valve all the way, because the ion pump limits the temperature of the bake if the pressure gets too high.

The System 5 shroud wiring is as follows... If you're facing the TT with the growth chambers behind it...

One GC plug on breaker panel goes to GC left panel (Auger side), then dividing wall between GC & LC. The other GC plug goes to LC front panel (which also has a stubby extension for the transfer arm), LC right panel, and ends at LC rear panel. If the sump and/or GC bakes won't turn on, check the pressure relay and the connected ion pump.

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Gate valves should be open or partially open during bake, or else wrapped in layers of foil to keep them cool, to avoid softening the gasket. Fans help.