Membrane Transfer Solder Process

NTS, 03/18/2015, Seth’s recent idea. Fernie worked on it Summer 2015. Ashley worked on it Summer 2016. Updated NTS 20160728

[Note: Be mindful of the gear you use for this process, and when and where you do it. HF is involved, as is grown III-As, and the etch can take a long time.]

Grow Samples with AlAs release layer

• This process requires an AlAs etch release layer, so there is no easy way to make dummy samples— they must be grown.

• Our successful samples have a 5000 A (or 3000 A) layer, but Yablonovitch had success at 50 A

Joining Membrane Sample to Carrier Wafer

Prep

• Prep clean tools and container for samples and UHP indium nugget

  • Do The Treatment on indium-free tools as needed, or once every 3-4 weeks while active

  • Pyrex petri dish for indium, only needs to be replaced and cleaned on as needed basis

  • Let tools dry overnight in a giant closed but vented UHV foil boat

• Cleave 10 x 10 mm membrane and carrier samples with ultraclean (UC) tools for this project

  • Can put back in mailer when done

  • We used a p silicon SSP carrier for our first bonder exploration

• Prep In, Soldering Iron, and hot plate

  • UC gloves needed

  • Get enough UHV foil to double layer cover our hotplate and double layer cover hotplate

    • Get it tight but minimize glove (ultraclean) touching of foil

  • Use UC razor blades to cut TINY, THIN indium flakes in the petri dish

    • A thin flake should be ~1/3 the area of the sample being joined. Thicker flakes or tiny nuggets need to be smaller. We’re talking grain of sand sized

    • Working with indium is hard as it is sticky, so practice this and be careful

    • Only use appropriate tweezers when working with or near In. In can’t be cleaned off

• Make foil boat for samples and put them in it (for ease of handling)

  • Setup Soldering iron foil area and stand, check tip is secure, and plug in

  • Turn hot plate up to 220 C, wait

Soldering

• This is UC work, use proper UC gloves, tweezers, etc. Use In/semi-In tweezers with/near In

• Put one carrier sample face UP onto hot plate using ultraclean In-free metal tweezers, wait

• Put flake of indium onto the carrier carefully, it will stick to tweezer tips

• Using soldering iron to paint In around most of carrier (not to edges) while holding at a corner

• You don’t want perfect coverage at all edges and corners! If any indium flows out later on, it can flow up and cover our etch release layer, and we can’t undo the indium

• Once applied, you can carefully remove the carrier to a UC foil boat to cool, repeat as needed

• When done, turn down the hot plate, unplug the soldering iron, and put away when cool

• Put indium petri dish into rear of a front desiccator, nugget is good for X months after opening

Wafer Bonder

• See Wafer Bonder Procedure, make sure samples are properly layered, oriented and aligned

• Use 260 C, 1600 N, 11 minutes

• Record the approximate temperature, force, time, and the under-stage gauge and computer micrometer distance before platens are in contact and again when at target force

Release epitaxial membrane from substrate

• Takes Overnight (18+ hours), leave a proper note x2: HF, Name, PI, phone number, date, time

• Setup acid bench, put dipper in bench, and place samples carrier DOWN into dipper

• Pour 49% HF into HF Etch beaker, carefully

  • MRC provides HF at 49% (~50%)

• Put dipper into Etch beaker with 49% HF solution

  • The lateral etch rate of AlAs in 10% HF is ~1 mm per hour supposedly, so a 1 cm^2 sample should take 5-6 hours to etch in 10% HF, but it takes ~18 hours in 49%

• Ideally, after the etch is complete, the target substrate and membrane will float to the surface and you can handle it carefully with tweezers

• Usually, you will have to jiggle the dipper in the acid after leaving it overnight, and then the membrane will release (if the etch is done) and float

• Once the membrane is released, prepare the Rinse beaker with water about 6-10 mm from the brim and carefully move the dipper from the Etch to the Rinse beaker, capturing the membrane in the dipper and letting it float on the Rinse water.

• After a minute use tweezers to take the membrane out, dunk it 3x, and put it on wipes.

• Flip it over. This lets the wipes absorb-dry the sample. Repeat flipping it over if needed.

• Repeat above two steps if needed and membrane isn’t drying (dunk 3x and flipping over to dry).

• Put it into your sample holder. Repeat as needed for liftoff samples.

  • Use a very light N2 spray on each side of it if desired.

• Rinse the substrates and gear to clean up.

• If it doesn't release and float to the surface, give it more time. If it has been a long time (~72 hours), the wax layer can be removed from the substrate using a pair of tweezers after removing it from the HF.

  • Work a pair of Delrin tweezers under a receptive corner and move the tweezer tip around the edges. Work on getting the tweezer further under the membrane, and so on. Be careful.

• Carefully rinse sample and substrate to remove HF (as well as tweezers and gear).

  • Your best option is probably keeping the sample and substrate in the dipper and doing a dunk rinse, or light cascade rinse or spray. A normal sprayer is probably too forceful.

Regrowth

• Grow