Equipment and prep

• for future improvement

  • large plastic tongs and tweezers

  • plastic HF compatible dipping basket that fits our HF beakers

  • 2 metal tweezer set for pre-air fire and post-oven bake. i.e. 4 tweezers total

  • wider Pyrex container for oven bake so the crucible will remain tilted

Note: there should be a bin in the MBE workroom that has most of the equipment (minus appliances, like furnaces)

• Air Fire

  • Tube furnace, see Terry's office

  • Quartz tube that is ~1-2 inches longer on each end of the furnace, e.g. a 16 inch furnace needs a tube that is 18 to 20 inches long

    • Tube needs to fit in the furnace. This sounds obvious, but you need to measure both the opening and the coils inside the furnace (coils often have a smaller diameter than the openings)

    • Example of tube specs for a 16 inch furnace: 18 inches overall length, open ends ground smooth, ~32 mm ID, and no more than ~35 mm OD. The ID can be flexible based on the OD

    • Clean the tube using a solvent clean of acetone, IPA, and water before every use except if you used the tube very recently, e.g. yesterday

      • There are tall treatment containers in the batcave. Fill them over half way up the length of the quartz tube. Dip each half of the tube multiple times in each solvent. Rinse with DI-H2O and allow to dry

    • Bake the tube at ~5-10% higher output power on the variac than the temp you plan to use for the crucible. This way any extra junk is desorbed. Regardless of when you used the tube last, bake it before use.

  • Variac power supply to control the furnace temperature

    • Use a thermometer to derive a temp vs. output power curve before using the furnace for crucibles

    • Different sizes of Variacs will produce different temp vs. power curves

  • Cleaned push rod used for inserting/removing the crucible from the furnace

    • Glass/quartz is probably easiest, but whatever you use will handle the crucible at room temp

  • Perform treatment on 2 pairs of metal tweezers that will be used when handling the crucible.

• HF etch

  • Get new rubber chemical gloves before each use (supplied by cleanroom). You will use a large amount of concentrated HF. Safety if important, so check for any holes or tears in the gloves before using

  • Will use ~ 2 L of HF. If you need more, check the acid cabinets in the main cleanroom

  • You will need at least 2 waste bottles for the HF dip due to the large volume of liquid that will be disposed. Label each one "50% hydrofluoric acid, 50% DI-water

  • Need to perform ultra clean treatment on:

    • 2x large HF compatible containers, e.g. 2 L HDPE.

      • The first container is for HF. It needs to hold enough HF to submerse the crucible AND to maneuver with your tools, e.g. basket and tipping the crucible to remove all HF

      • The second container is for the water rinse following the HF dip, so it needs to also be larger enough for the crucible submersion and any tool maneuvering

      • Clean these containers using HF

        • Put pure HF (49%) into a small plastic beaker and pour down the sides

        • Collect the HF waste into an appropriate container

        • Spray down the side walls of the containers using the DI water gun

        • Collect the water into an appropriate waste container

        • Cascade rinse with DI-H2O in plastic sink for each HF-treated container for 15-20 minutes

    • 1x Pyrex container that is large enough to hold the crucible for oven baking

      • Perform regular ultra clean treatment (i.e. micro 90, acetone, IPA)

    • 1x dipper basket that is large enough for the large for use in the HF compatible containers mentioned above

    • 2x plastic tweezers that will be used for HF cleaning

      • Make sure the tweezers are HF compatible! Teflon is recommended. The grey Delrin tweezers are made of acetal and will disolve in HF!

• Post-etch oven bake

  • Do not use the ovens in the main clean room, because those are used to cure plastic-based polymers (e.g. PR processing)

  • Terry has a large oven in his office, check that it is plugged in and the oven racks are positioned so the Pyrex container and crucible will fit

  • The day before you plan to use the oven, turn it on to a temp that is ~ 10-20% higher than what will be used for a few hours. This will desorb any extra contaminates

Procedure for cleaning crucibles

This is a combination of cleaning tips from the "Notes from others" section and from talking to Terry about what he has done.

General notes:

• Handle with clean gloves (even though the crucible may be dirty, just try to keep it clean). After each step of the cleaning process, tools used previously are now "dirty". If you need to reuse them, clean appropriately (i.e. ultra clean using treatment or HF dip)

• Don't use HF or let any tools come into contact with HF if they are glass or metal. Only use HF-compatible materials. Teflon is the best way to go if you need to order more parts

• Don't trust the cleanliness of the ultra clean opening tools. They may have shmootz or arsenic on them. It's better to use a separate ultra clean pair of tools

• Be careful when handling the crucible. The lip may be flimsy and is susceptible to cracking or warping. Grab and handle the crucible by the neck and base. For the 200 g Al SUMO, grabbing around the neck is very secure and should be used for all dipping and transporting

1. Use a high-intensity light or LED to inspect the crucible before starting

   1. Treat as ultra clean, which will make the inspection process admittedly difficult

   2. Looking for cracks or nodules from non-uniformities. With a bright enough light, the crucible will be transparent and allow you to see any problematic features

   3. Once finished, put it in a kimwipe-lined clean foil pouch, and label accordingly, e.g. "pre-air fire"

2. Air fire at 700 to 800 C for at least 1 hour using quartz tube furnace. Ask Terry to use his furnace

   1. This step oxidizes any carbon-based contaminates

   2. Leave a new bag of nitrile gloves near the furnace, because you will use a bunch of them

   3. Make sure the quartz tube was pre-baked (see instructions in the prep section)

   4. At room temperature and using the pre-air fire metal tweezers, insert the crucible into the tube with the opening of the crucible facing the opposite direction it is getting pushed. Insert the crucible into the end of the tube furnance that was highest when originally putting the tube into the furnance. This is because the opening that was lower is more likely to have dragged along the inside of the furnance and got dirty -- the higher end should be clean of debris

   5. Push the crucible so it is centered inside the furnace using the push rod

   6. Turn on variac to the correct baking temperature/power percentage. You can turn the variac directly to the value, i.e. no need to use a slower ramp rate. Takes ~ 20 to 30 minutes to reach temperature

   7. Bake for at least an hour

   8. Let it cool down for at least 1.5 hours once finished

   9. Crucible does not need to receive the HF dip in the next step immediately, so do not feel the need to rush

   10. Use the push rod to push the crucible out of the furnance, such that it leaves the same way it entered.

   11. Once finished, put it in a new kimwipe-lined clean foil pouch, and label accordingly, e.g. "post-air fire, pre-etch"

   12. Once cool, gently remove the quartz tube

       1. Treat as very clean

       2. Tilt the furnace to prevent any extra junk on the furnace from falling into the tube

       3. Store using ultra clean procedures

3. Buffered HF oxide etch

   1. Use HF straight from the bottle, i.e. 49% HF by volume

   2. Goal is to clean out the inside and outside of crucible to remove the oxidized stuff generated from the air fire

   3. Need to slowly/gently agitate HF solution. Dip the crucible in and out of the solution for 5-10 minutes. Use some sort of plastic holder or basket with tweezers to do it. Make sure all parts are HF-compatible!!

4. Rinse and soak using pure H2O

   1. Same dipping process as for the HF

   2. Use a large plastic container to do a H2O dip, then dispose of the waste. Repeat this 3 times

   3. Using the same container, perform a cascade rinse for 5 minutes

   4. Move the rinsed crucible to the ultra clean Pyrex container

   5. Immediately move the crucible to the oven bake in the next step

5. Bake using lab oven at 150 C for at least 1 hour to remove water

   1. Make sure the oven was pre-baked and the oven rack is correctly positioned (see prep steps above)

   2. Need to turn the oven on a few hours in advance so it can reach and stabilize at temperature

   3. Transport to the oven with the ultra clean foil cover over the top of the container

   4. Cover the top of the Pyrex container loosely with ultra clean foil to prevent and large particles from falling into the crucible but still allow water vapor to leave

   5. Turn down the oven and turn off after bake is finished

   6. Remove from oven when cool (~ 45-60 minutes, can speed up to ~30 minutes by leaving the oven door cracked open)

   7. Transport back to the lab with the ultra clean foil cover over the top of the container

   8. From this point on, you can use the post-oven bake ultra clean metal tweezers when handling the crucible

6. Inspect using an intense lamp/light. Look for:

   1. Cracks or voids in the PBN

   2. Trapped water

   3. Any nonuniformities

   4. The more uniform the color, the more uniform the wall thickness

7. Store in a desiccator and treat as ultra clean until ready for vacuum firing on the BOS (could be a few days or several months)

   1. Put it in a new kimwipe-lined clean foil pouch, and label accordingly, e.g. "air-fired, etched, baked, and inspected"

8. Vacuum fire

   1. This is the standard vacuum bake we perform on the BOS

   2. Monitor the RGA during the bake

9. Inspect the crucible vacuum fire for any contaminates

   1. Should be fine because of the air fire and HF dip, but still check

   2. Terry said to keep an eye out for black marks or smudges, e.g. finger prints

Notes from others

Veeco

Before shipping us a new crucible: "The crucible are air baked at 600C" - Ken Kohler

Historically, we put these crucibles straight onto the BOS then bake them before loading source material.

Momentive

Updated Momentive Al Crucible Cleaning Procedure (1/17/2022 - AFR)

Supplies needed:

• Crucibles

• Ultraclean pliers (x2)

• Scissors

• Clean foil boat

• Clean gloves

Bake

• Turn on the furnace

  • Go in the maintenance room behind the furnaces

  • Flip the switch “on” for the furnace (3rd from the right)

  • Watch to see that the power increases

  • Wait for the furnace to heat up for 1 hour

• Pull the furnace tube cap out with the high temperature glove

• Pull out the furnace tube and place on the table

• Pull out the furnace tray ~halfway with glass rod and let hover over foil tray

• Cut and drop crucibles onto the foil, use UHV pliers to gently place on the tray

• Push tray back into the furnace tube with the glass rod

• Line up the furnace tube with the furnace opening

• Push the furnace tray into the furnace with the glass road

• Pull out the furnace tube and set aside, replace the furnace cap with high temperature glove

• Let bake for 1-1.5 hours

Etch

• Fill bucket for DI rinse with DI water in the acid bench sink

• Fill bucket for HF with HF in the acid bench sink

• Soak the crucible in HF

  • Place crucible in dipper with pliers

  • Place dipper + crucible in HF beaker

  • Use acid safe tweezers to push down the floating crucible and fill with HF

  • Set timer for 10 minutes

• Carefully remove the dipper and dump out HF from crucible using tweezers to brace the crucible to the dipper

• Soak crucible in water

  • Place dipper + crucible in water beaker

  • Use acid safe tweezers to push down the floating crucible and fill with water

  • Set timer for 3 minutes

• Carefully remove the dipper and dump out water from crucible using tweezers to brace the crucible to the dipper

• Grasp the crucible neck gently with the pliers and spray with nitrogen to dry

• Place dried crucible in clean foil tray

• Use the aspirator to empty used HF from beaker

• Cascade rinse the acid beaker for several minutes

• Triple rinse the water beaker

Finishing up

• Prepare a clean foil packet for the crucible

• Weigh the cleaned crucible and mark down the starting weight

• Store and label the baked + etched crucible in the foil packet, it is ready for BOS
  
  

Custom ordered crucibles from Momentive are: "There are mainly two step in the cleaning procedure: (1) Ultrasonic cleaning with Pure water for 2 min. (2) Heating treatment at 800C for 15 min in air." - Roland McGoodwin

NOTE Terry said not to use the sonicator because it is more likely to harm than help, e.g. delamination. We suspect that Momentive has some sort of safe set-up to sonicate -- let's not invent that wheel...