Etching

Bromine-Methanol works very well for etching III-V material off of the molybdenum Uni-blocks and Faceplates. Our standard procedure is as follows:

1. Gather materials and equipment

   1. Uni-block pieces to be etched

      1. Faceplates

      2. Blocks

      3. Spring clips

   2. Several 18+ inch lengths of tantalum (Ta) wire (wipe clean with IPA)

   3. 2x (1000 to 2000 mL) teflon or borosilicate Glass Beakers

   4. 1x teflon or borosilicate glass stirring rod

   5. 1x teflon or borosilicate glass funnel

   6. 1x borosilicate glass graduated cylinder (~100 mL) or pipette.

      • We historically use a graduated cylinder, but a pipette would likely be easier for such small volumes

      • Polyethylene is not bromine resistant (check the pipette material before using one)

   7. Borosilicate glass waste containers (preferably with teflon-inserts in the cap)

      1. Look in fume hood for large brown glass jugs that may be used for fluid waste collection. Put a waste label on the jugs (Room: 1.710A, Methanol >= 97%, Bromine <= 3%, Arsenic <= 1%)

         1. Will need ~4 L of free fluid space, so budget accordingly

         2. Check batcave for any extra brown glass jugs

         3. Ask Darren for brown jugs as needed. Warning: he has a limited supply, so he might not be willing to give us any.

         4. Buy more jugs if none are available.

   8. Label waste bag for Br trash in the fume hood (write in sharpie Bromine contaminated waste)

   9. Liquid Bromine (Br2). Note: New bottle of Br2 only contain ~30 mL of fluid. Realistically, you need 50 - 60 mL, so make sure we have enough in stock! Updated Note: New bottles of the bromine we bought had ~100ml - JAM 230106

   10. Methanol

   11. Acid gloves and apron

   12. Kimwipes (for absorbing spilled solution)

2. Prepare the blocks and/or faceplates

   1. Wearing clean gloves, wrap the tantalum wire around each block and faceplate, separating them with a loop

   2. Leave enough extra wire to hang over the side of the beaker

   3. Wiring up all the faceplates, spring clips, and blocks takes ~1 hr. You could wire and start the etch for the first set of pieces then wire together the next set, if you're pressed for time. It might also work to wire the pieces together the day before.

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Wiring up pre-etched faceplates, step 1

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Wiring up pre-etched faceplates, step 4. Note: make sure you leave enough wire so it can comfortably stick out of the top of the etch container

4. Prepare the etch solution and methanol rinse

   1. Wearing acid gloves and apron, in an acid hood:

   2. In the dedicated rinse beaker:

      1. Pour enough methanol to completely submerge the blocks and faceplates (don't actually add them yet), plus an extra ~100 mL

   3. In the dedicated etch beaker:

      1. Pour enough methanol to completely submerge the blocks and faceplates (don't actually add them yet),

      2. Using the graduated cylinder or pipette, measure out and add 3% bromine (by volume) to the methanol (1000 mL of methanol => 30 mL bromine). White etch and rinse containers are 2 L in size and you don't fill them up all the way, so 50 - 55 mL of Br is sufficient

      3. Its worth noting that even though the PTFE beakers are 2 L it is probably safest to only fill them with 1 L of methanol. Pouring our of these beakers is difficult (the spout of the beaker is too small) and the surface tension of the liquid causes it to drip down the beaker as you pour, which is dangerous. With less liquid you will be able to pour at a steeper angle which will help fight the surface tension issue. -AFB 191105

      4. Stir the solution with the stirring rod, thoroughly rinse it in the rinse beaker, then set it on kimwipes to dry.

      5. Also rinse the graduated cylinder or pipette with methanol, reclaim any waste in a borosilicate glass waste bottle, and then set on kimwipes to dry

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Measuring out Br to 3% by volume in graduated cylinder before pouring it into etching container that's already full of methanol

5. Etching

   1. Using the tantalum wire, lower the blocks into the etch solution, and leave part of the wire hanging over the edge. An hour or two is typically adequate. Bromine etches Ta wire. If you leave the solution overnight the Ta wire might be etched away. Gentle agitation can be used to help remove large particles.

      • Note: Rare-earth films form black bromide salt films which are not etched. However, these films are very stable, and should not cause issues with vacuum or subsequent growth.

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   Submerging unetched blocks into the methanol and Br bath. Note: bend the Ta wire over the edge of the container to secure the pieces in place

   1. Once the blocks appear thoroughly etched, use the tantalum wire to remove them, then lower them into the rinsing beaker. Gently agitate to thoroughly rinse, then place on kimwipes.

6. Cleanup

   1. Use the borosilicate glass funnel to pour the waste into the borosilicate glass waste bottles.

   2. A base layer of kimwipes should be used to absorb any solution that may be spilt in the process. These should be collected in a ziplock-bag and later disposed of in an acid waste bin.

   3. After all Br waste (kimwipes, contaminated stir bars, bottles) are placed in the ziplock-bag, double bag that ziplock-bag in two black trashbags (similar to how we take out the arsenic trash) and place a waste label on the outermost bag that says "Bromine contaminate waste"

   4. Put any full methanol and bromine solution brown bottles into the fumehood sink with the trash bagged waste

   5. Alert Darren that we have bromine waste in our fumehood, because he will come to pick up the waste. Ask him if there are any special labelings he wants for it.

7. Cleaning blocks

   1. Follow the standard ultra-clean procedure, but skip the DI-water and Micro-90 step (only use acetone and IPA).

      1. Use standard acetone and IPA beakers with 1500-1600 mL of fluid in each

      2. Put beakers on a hotpate with magnetic stir capabilities. Find magnetic stir bars and place them in each beaker (there should be magnetic stir bars labeled for acetone and IPA in the batcave).

   2. Once ultra-clean, use ultra-clean wire cutters to remove the tantalum wire. Put the clean and unwired pieces into a kimwipe-lined piece of clean foil. Store in desiccator until ready for baking.

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Uniblock treatment set-up with IPA and acetone containers on hotplates using magnetic stirbars

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Example of performing the treatment with multiple sets of faceplate groupings in at once

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Removing the wire from the blocks using ultra clean tools following the treatment

Baking

Winter 2017

Bake on the buffer heater station:

• When loading wafers in LC, use safe LC bake procedure since the unbaked block parts are probably gassy

• Depending on the growth calendar, could use both Bravo and Echo's buffer heater stations

• The heater stations may have an upper temperature limit and need adjusting in AMBER or on the Eurotherms

• Bravo's heater station may be in set point 2 because the water that is supplied to the atomic hydrogen station comes from the same water manifold as the sources. Since the AHS needs less water but the interlock logic is designed for sources, it will trigger the heater station to be in set point 2. Again, might need to adjust the maximum temperature on the Eurotherm for set point 2.

• Put the trolley in a chamber that is not the same as the buffer heater station(s) in use, e.g. LC. This prevents the material that is outgassed from the block being baked from landing on blocks on the trolley

• Point a fan at the viewport closest to the heater station to mitigate thermal stress

• Turn off viewport lights/lamps

• Perform bake as 100 deg C steps from room temp to 800 C. Wait for the heater station to reach the current step's temp, wait for 1 minute, then wait for the pressure to drop below 1E-7. For the last one or two steps, wait on the step for 5 minutes, then wait for the pressure to drop below 1E-7. Once 800 C is reached, wait for 10 minutes, then wait for the pressure to drop below 1E-7.

  • See bakes from early January 2018 on Bravo and Echo as examples

Bake in the following order (unloading and reloading between steps):

1. Uniblock ring + 8x new Si backing wafers (Ring+Backing Wafer - RBW)

   1. Si wafers should all be the same direction crystallographic direction (e.g. (100)) and doping for consistent heating between growths

   2. Load wafers with polish side epi-up during loading, i.e. away from growth direction and toward the heater element

   3. In a pinch, can use another Si wafer type temporarily to complete the block bakes, but should bake a new set of Si wafers when possible after a new order of backing wafers arrives

2. One face plate + once baked RBW

3. The other face plate + twice baked RBW

4. Pair up the once baked face plate pieces + thrice baked RBW

5. Because sapphire is transparent to IR, it requires faceplates to conductivity heat the backing wafer. Use a fully baked pair of faceplates with a fresh sapphire wafer.

6. Blocks, backing wafers, and faceplates should now be ready for MBE growth

7. Set all Eurotherms and AMBER set points to their original values, if you changed them to make the heater station(s) reach 800 C.

Summer 2016

1. Load and bake the blocks in the buffer chamber.

2. The bake proceeds with the following steps:

   1. Freshly etched blocks alone with a new backing wafer

      1. Throw old backing wafers into the wafer trash

      2. 8x Si (100) wafers and 4x Sapphire wafers

      3. Matted side of the new backing wafers needs to face in the epi direction

   2. Once-baked blocks and backing wafers again, adding a single face plate.

   3. Twice-baked blocks and backing wafers with the other half of the face plate pair.

   4. Thrice-baked blocks and backing wafers again, pairing up already-baked face plates.

   5. The blocks and faceplates should now be ready for MBE growth.