Summary

Day 1 Review Maintenance plan with other lab members. Make sure the order of operations and timeline makes sense. Prepare any parts that need to be etched or baked. Etch and Bake some of those parts so maintenance can start without delay. Cool the As and Sb sublimators and crackers using a recipe. Cool the other cells to a very low idle temperature (150 C). Day 2 Freeze Al using a recipe, per the combined instructions of the relevant Wiki page (Melting and Freezing Aluminum) and the last Al freezing recipe. Day 3 Turn off the LN2. When the LN2 is gone, we can turn all of the cells off (except Ga). Take off the shutter wheel. It is important to disconnect the supply to shutter wheel connection (input pressurized air line and electronic control cable), as well as shutter wheel to GC connections. The shutter wheel to GC connections are: pneumatic (supply the air for shutter operation), electronic (controls the pneumatic), and mechanical (move the physical shutter). Tape down the shutters carefully and securely in a neutral/floating position using kapton, and avoid taping on the bellows welds. Once the LN2 had evaporated out quite a bit, turn the cells (except for Ga) off. Let the GC pressure stabilize before proceeding. Day 4 - Draining Day Turn down all of the cells to 0 output power (except for Ga). The substrate heater is also lowered to 10 and put into manual. We keep Ga warm (at 100 C), we have an interlock override connector. We insert the overrides into the Ga Base and Ga Tip Eurotherms. Drain Sources Cooling Water Drain SF Water Remove N2 station. I will refer you to the wiki page: Removing the Bravo Nitrogen System. Day 5 - Prep SF and Glovebag Prep SF for Glovebag Here's an Outline, details will go onto an existing or new Wiki page, TBD. Open As and Sb valves and remove valve motors. Tape down so valves stay open. Disconnect power lines besides Ga. Thermocouples then power lines (all cells are in manual receiving 0% power, but double check). Zip tie down thermocouples and power feedthroughs, prevents extra loose things in the glovebag. Double check all shutter tape jobs, fix as needed. Cover pointy parts of system and surroundings with kimwipes (taped-on) to prevent sharp edges contacting the glovebag. Also cover the As sublimator top. Close the GC to BC gate valve completely. Prep Glovebag Put up the glovebags. We did both the BOS and GC glovebag. There are two tables to support glovebag setup and work. As of now, we use the GC table as just a tabletop and blue bins (three stacked upside down) and the Bravo frame as the legs. Begin pre-purge with UHP N2. Fill up the bag and make sure it inflates and the tape job is good. Prep tool bins for opening, the list of what to pack is on the Wiki under the opening checklist. Prep glovebags for opening: put in other things that don't fit in tool bin, or are needed but not on opening checklist and not in a desiccator. Misc We need to cap off the cell water feedthroughs before venting. Hopefully they arrive during meeting and we can cap right after. Normally we would've capped days ago when we disconnected and dried out the lines. The transit case for the HVP and Al cell is in the front desiccator. Ultra clean tools will be loaded for desiccation tomorrow before meeting. Always monitor Ga during GC openings. 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. We strike a balance by turning the power to 0%, and raising it slightly as needed during opening to keep the Ga molten. Recall it idles at 100 C for maintenance. Review how to pump down the growth chamber with the new turbo pumps.

Day 1

I have spent time the last two days reviewing this plan with Kyle and Siff while getting started to make sure the order of operations and timeline makes sense. AK and Kyle started the peroxide etch on the zero-length 6" to 4.5" reducer we will use on top of the growth chamber (GC) for the 4.5" viewport we are installing there. I cooled the As and Sb sublimators and crackers using a recipe, then cooled the other cells to a very low idle temperature. We cannot yet cool the cells all the way because the LN2 in the cryoshroud could cool the source flange (SF) cooling water enough to freeze it, creating major issues. See this page (which will be updated) for more info: Idling Cells for Opening

Day 2

Freeze Al using a recipe, per the combined instructions of the relevant Wiki page (Melting and Freezing Aluminum) and the last Al freezing recipe. The recipe is a loop that decreases the power to the Al cell by 0.1% and waits 10 minutes to repeat. (It lowers the temperature 1 C every ~2.5 minutes.) I will update the Wiki soon. We also put the 2.75" viewports and new sapphire HVP on the BOS and will bake them tomorrow. This is a good activity for new students.

Day 3

The Al cell will be cold, other cells are still warm, we can now turn off the LN2. We will bake the viewports on the BOS so they are ready for the GC when we get to that point. By baking them now, we won't have to bake them when we put the Al cell on the BOS, potentially mitigating baking any crud from them onto the Al cell. When the LN2 is gone, we can turn all of the cells off (except Ga). We plan to remove the shutter wheel as well.

LN2 supply was turned off. As the remaining LN2 in the cryoshroud warms up, it evaporates out of the shroud via the Return line. As the shroud warms, it no long freezes molecules onto it, and we lose its effective pumping ability. More importantly, everything that was cryo-adsorbed onto it will warm up, and effectively come off (at well below room temperature). During this process, the growth chamber pressure will rise.

We took off the shutter wheel. It is important to disconnect the supply to shutter wheel connection (input pressurized air line and electronic control cable), as well as shutter wheel to GC connections. The shutter wheel to GC connections are: pneumatic (supply the air for shutter operation), electronic (controls the pneumatic), and mechanical (move the physical shutter). The pneumatic connections for most cells are self-contained on the shutter wheel, but the connections with non-SF components extend beyond. These are the deep upward looking (DUL) dopant cells, and RHEED screen. The electronic connections are similarly mostly self-contained, but again the DUL dopant cells and RHEED are off the shutter wheel. The mechanical connections are the physical shutter rods and where they attach to the shutters. The off-shutter wheel shutters are self-contained for this part. The other cells on the SF itself have shutter rods that must be carefully disconnected at the shutter. They are joined by a pin and eye socket type connection. The shutter must not be allowed to move while disconnecting, lest the shutter moves and smacks into a full open or close position, which could potentially damage it. The shutter wheel also has four posts which attach it to the SF, each with one set screw. The set screw must be loosened to pull it off. Once everything is disconnected (and double checked), you can pull off the shutter wheel (2-4 people recommended). You want at least one person pulling it off and one person keep lines and tubes out of the way. Use two and two for extra eyes and ease. Tape down the shutters carefully and securely in a neutral/floating position using kapton, and avoid taping on the bellows welds.

Once the LN2 had evaporated out quite a bit, we could turn the cells (except for Ga) off. Right now we are letting the GC pressure stabilize before proceeding.

Day 4 - Draining Day

LN2/Chamber Pressure and Cells
After turning off the LN2 yesterday, we had to wait for the growth chamber pressure to rollover and stabilize. It did so this morning. We could then turn down all of the cells to 0 output power (except for Ga), as the (soon-to-be-drained) SF water was no longer at risk to freeze. The cell setpoints are set to 10 C (below room temperature) so the output power will drop to 0 (if the Eurotherms are put into auto the cells won't re-heat) and the Eurotherms are put into manual (prevents accidental re-heating via Amber). The substrate heater is also lowered to 10 and put into manual. We keep Ga warm (at 100 C), we have an interlock override connector. We insert the overrides into the Ga Base and Ga Tip Eurotherms.

Drain Sources Cooling Water
The hardware for water draining is kept in the white cabinet by the fume hood (tubing, caps, quick-disconnect fittings). By stopping the flow of the source cooling water, we will trip the associated interlock. All of the cells (except Ga) and substrate heater are already cold and in manual (or overridden), so this has no effect. The sources cooling water comes from a manifold near the ceiling equipped with self-sealing quick-disconnect fittings. We can disconnect the Supply and Return line from the manifold, and only a few drops of water might drip out. Each line is now a tube connected to the appropriate cell water feedthroughs. Some lines have multiple cells on the same line (a Cell Group), that are interconnected in series with short lines between cells. An example is Ga, In, Er, Bi. We can then connect a quick-disconnect fitting to the Supply end of the water line and put it into a milk jug (our receptacle of choice) to contain draining water. It won't drain til we open up the other end though, because it is sealed and draining water would create a vacuum in one end. We connect a Clean Dry Air (CDA) line to the Return end of the water line and water will start draining out of the Supply into the milk jug. The logic behind draining out of the Supply is below. Let the air run for three minutes per cell to dry it out nicely. Disconnect the tubing from the cell water feedthroughs. Cap the cell and nipple water feedthroughs to keep them sealed during glovebagging. We can coil up the water line and put it aside. We repeat this for each Cell Group. The As and Sb sublimators are different, they have to be blown out for ten minutes. All of the drained water should be put back into the proper chiller for re-circulation before bringing the system back up.

Drain SF Water By stopping the flow of the SF water, we will trip the associated interlock. The cells and substrate heater are already cold, and Ga is interlock overriden, so we are fine. First, look at the water flow level for the Echo SF, there is a gauge located at ceiling level near the middle of lab-- we will need to set it back to that level shortly. Echo and Bravo share a SF water chiller in the mezzanine, turning one on or off will affect the other's flow. The valves to turn the SF water on or off are located at ceiling level near the middle of lab and are labeled. Turn off the Bravo flow of water, first the Supply, then the Return. We always turn off Supply first, then Return, to prevent a pressure build up (to turn flow on, open Return first, then Supply). Adjust the Echo flow back to the proper operation level by adjusting the valve handle on the ceiling labeled Echo supply. Uncap the Bravo Drain line while someone holds a water catching bin (drip bin) underneath the Drain line connection (to catch and water that will drip out). The water shouldn't spray or splash out (that would create a vacuum up the line), but I've seen things, so use the bin and have cleanroom wipes on hand. Attach draining tubing and put the tubing end into a carboy to collect the SF water. Loosen the Return line (at SF top) to let some air leak in and get the draining flow started. Wait for the Return line to be empty, then Unscrew the Return line with a drip bin underneath. Cap the Return tubing and leave the metal pipe open. Let the water drain, it looked like 3/4 gallon. When the water is drained, unscrew the Supply line (at bottom), cap the tubing, and leave the metal pipe open for a minute. Cap the Return metal pipe and then the Supply metal pipe. Disconnect the Drain line tubing, and cap the Drain metal pipe. All of the drained water should be disposed of, it has glycol in it. We must top off the SF chiller before bringing Bravo back up.

Water Supply vs Return
New students, there are crucial differences between Supply and Return water lines.There is logic behind which line is which, and from which line we fill or drain water. If you want to ensure that a cup with a hole at the bottom is completely full, how should you fill it? Why should you care it is completely full? Our cup is the Cell water feedthroughs and in Cell cooling. By having a full "cup," we avoid air pockets, hotspots, and areas with very different temperatures. We fill that "cup" from the hole at the bottom. Filling it from the top would cause the water to just go in and seek the drain hole without filling the volume and effectively cooling the cell. By filling from the bottom, we ensure that the whole volume is full before the water finds the drain hole at top. Thus, each Supply water feedthrough is at the lowest point of the cell, and each Return is at the highest point. Because the Supply is the low point, it is the best water line to drain, making the Return better suited for a CDA line to push water out and dry the lines.

Remove N2 station. I will forego detail in this email and refer you to the wiki page: Removing the Bravo Nitrogen System

Day 5 - Prep SF and Glovebag

Prep SF Here's an Outline, details will go onto an existing or new Wiki page, TBD.

1. Open As and Sb valves and remove valve motors. Tape down so valves stay open. [This was done Friday, but is noted here for completeness.]

2. Disconnect power lines except Ga. Thermocouples then power lines (all cells are in manual receiving 0% power, but double check).

3. Zip tie down thermocouples and power feedthroughs, prevents extra loose things in the glovebag.

4. Double check all shutter tape jobs, fix as needed.

5. Cover pointy parts of system and surroundings with kimwipes (taped-on) to prevent sharp edges contacting the glovebag.

6. Close the GC to BC gate valve completely. [This better fits in the Prep GC for Opening, part of tomorrow's email, but we did it today so we wouldn't forget.]

Prep Glovebag

1. Put up the glovebags. We did both the BOS and GC glovebag. There are two tables to support glovebag setup and work. As of now, we use the GC table as just a tabletop and blue bins (three stacked upside down) and the Bravo frame as the legs.

2. Begin pre-purge with UHP N2. Fill up the bag and make sure it inflates and the tape job is good.

3. Prep tool bins for opening, the list of what to pack is on the Wiki under the opening checklist.

10. Prep glovebags for opening: put in other things that don't fit in tool bin, or are needed but not on opening checklist and not in a desiccator.

Misc.
---The transit case for the HVP and Al cell is in the front desiccator.
---Ultra clean tools will be loaded for desiccation tomorrow morning.
---Monitor the Ga temperature and power during opening. 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. We strike a balance by turning the power to 0%, and raising it slightly as needed during opening to keep the Ga molten. We want to keep the tip warmer than the base, and not exceed 1 A to either filament. Recall it idles at 100-150 C for maintenance.
---I reviewed how to pump down the growth chamber with the new turbo pumps.
---Remember to override cryopump interlocks for GC IG after pumping down GC after venting.