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Old GaSb based MQW laser

Old GaSb based MQW laser

Old Process Flow for GaSb based laser

Adopted from Process Flow for Tunnel Junctions and TLM Written by Adam Crook July 1, 2010. Modified by Thien-An Nguyen August 10, 2010. Modified by Rodolfo Salas 9/15/11. Modified by NTS 08/07/13

[Note: Sample must be cleaved and in sample holders to begin.]

Silicon Nitride Deposition

  • Refer to PECVD procedure

    • O2 clean chamber for 30 minutes (Full Recipe on Wiki)

    • Prime chamber: Recipe AMC_SIN for 3 minutes (Full Recipe on Wiki)

  • Deposit ~200 nm of SiNx onto sample: run AMC_SIN for 10 minutes

Laser Stripe Lithography

  • Solvent Clean (ACE, IPA, DI: 2 min)

    • Take photoresist out of the refrigerator because it needs to be at room temp

      • Crack PR fridge to let fumes get vacuumed up, then open.

      • AZ 5214E-IR

    • Create a clean workstation before beginning.

      • Spray bench with IPA if needed, then wipe clean

      • Do this by getting clean wipes from the dispenser and lay them down anywhere you plan to work.

      • For Regrowth, layer wipes from back to front, and right to left, and go up to/over lip of bench

    • Setup solvent beakers and dipper basket

    • Note: The dipper baskets are labeled. Only use those that are appropriate for your immediate task. Otherwise, keep them in the box and close the box to prevent any contamination.

    • Always fill each subsequent beaker higher than the previous

    • Note: Gentle agitation during cleaning process is recommended

    • Acetone: 2 min

    • 2-propanol: 2 min

      • Go get UHV foil for boat

      • Scrap UHV foil is ideal, never trust another person’s boat

    • DI water cascade rinse: 2 min

    • Make foil boat

      • Scrap UHV foil is ideal, never trust other person’s boat

    • N2 blow dry

    • Put samples in boat

  • Dehydration bake

    • 150C oven: 5 min

    • Let Samples cool in boat

  • Spinner Prep

    • Make sure spinner chuck is clean

      • Spray wipe with IPA and wipe chuck off

      • N2 dry chuck

      • If chuck is not at spinner you want it at, assume it’s dirty

    • Make sure you have pipettes for PR

    • Note: Set spinner to max time, always use your timer!

    • Check the spinner by placing a junk wafer piece on it. Make sure it spins correctly and at the correct RPM (4k) before placing on your actual wafer.

  • Spin on resist (AZ 5214E-IR, 4k rpm, 40 sec)

    • Check Sample 1 and N2 blow

    • Put Sample 1 on chuck and center

    • Check centering and RPM

    • Note: When putting PR onto the wafer, try not to put on so much that it leaks off the sides because this can get into the vacuum and mess things up. Also, make sure that there is an adequate amount, as to completely coat the wafer with an even amount.

    • Put PR (AZ 5214E-IR) in pipette carefully and drop a drop out on spinner wipes (to eliminate air)

    • Drop on PR, no bubbles, and Spin

    • 4k rpm

    • 40 sec

    • Check wafer when done. No streaks.

    • Repeat as needed

    • When done, empty pipette back into PR container and return to fridge

  • Pre-Bake (evaporate solvents before lithography)

    • 90C oven: 10 min

    • Let samples cool in boat while you prep aligner

  • First exposure (Laser 2013 Mask 1, 13 sec)

    • Note: Remember to sign on/off machine

    • Note: When placing mask onto the holder, place it so that the chrome side of the mask faces away from the holder. (Brown side faces sample after placement)

    • Put Laser 2013 Mask 1 (laser lines) onto holder, turn on vacuum, slide into aligner, and tighten screws

    • Choose stage for your sample and load sample

    • Prepare height of aligner stage to be close to what you will want with the sample.

    • Lower stage (turn the knob in front after putting mask into aligner)

    • While looking from the front of the aligner at the sample (between the mask and stage), rotate contact lever, and then raise the stage til it looks like the sample and its reflection on the mask are about to touch.

    • Align features, then raise stage til contact. The best way to tell contact is by looking (through the microscope) for rings to appear at a corner of the sample.

    • Note: Will feel a noticeable increase in resistance of the knob

    • Parameters

      • Align + expose

      • Hard contact: 1 sec

      • 13 sec on MJB4 contact aligner

    • Note: Do not face the aligner when the wafer is being exposed. Also, make sure to move your other samples away from the aligner, as not to ruin them from scattered UV light.

  • IR bake (Image Reversal Bake)

    • 110C oven: 2 min 15 sec

    • Note: Very important step, do not over/under bake

    • Remove mask from aligner

  • Second exposure (Flood exposure = w/o mask)

    • 30 sec on MJB4 aligner

    • Do not use hard contact

    • Note: Only put one wafer on at a time so as to not ruin wafers with scattered UV light.

  • Develop with AZ 726 mif

    • 60 sec followed immediately by DI cascade rinse: 2min

    • Note: Gentle agitation the whole time.

    • Note: Does not stop developing after you take the wafer basket out of the developer solution, make sure to immediately dunk into DI water and rinse

    • N2 blow dry

    • Put stuff away and clean up bench

    • Inspect Pattern

Note: The key parameter for this process is the bake. If the pattern looks like its features are way to big then the sample was under baked. If the features look too small then it was over baked.

SiNx etch

  • Refer to PT1 RIE procedure

    • O2 clean chamber for 20 minutes (Full Recipe on Wiki)

    • Prime chamber: Recipe SIN_CF4 for 3 minutes (Full Recipe on Wiki)

      • P = 75 mT (normally runs at 80 +/- 2 mT)

      • RF = 50 W (normally runs at 48 W)

      • CF4 = 40 sccm

  • Etch: Run SIN_CF4 for 16 minutes

  • Kwikstrip PR for X minutes (3<X<3000, this seems to vary based on PR toughness)

++++++++++++++++++++++++++++ Everything after here is questionable ++++++++++++++++++++++++++++

Dividing Line Lithography

Same as laser line litho except for using the other mask, I assume.

Bottom Contact Metallization

  • Start vent of CHA#1 (takes about 12 min)

  • Go to acid hood and prepare surface cleaning solution

    • HCL:DI (1:10)

  • Once bell jar lifts on CHA #1 – This part takes a few minutes (~10), so start it once you vent CHA #1.

    • Dip samples for 15 sec in solution (precision is not needed here)

    • Rinse for 30 sec in DI

    • Blow dry with N2

  • Take samples immediately to CHA #1

    • Vacuum and clean sealing surface

    • Load metals (vacuum hearth if dirty)

    • Load samples

    • Pump down

  • Deposit contact metal (for bottom contact near epilayer we contact p-GaSb)

    • pGaSb: Ti/Pt/Au (100/100/2000 A) – These numbers are probably very wrong

    • nGaSb: Au/Sn/Au (50/50/1000 A)

  • Lift off metal in Acetone or Kwik Strip

    • 20-40 min in Acetone or 40-60 min 90C Kwik Strip

    • Gentle spray with Acetone or Kwik Strip if possible

    • 2-propanol

    • DI rinse

    • Blow dry with N2

Lap Substrate

  • Cleave laser and crystal bond pieces to holder as needed (forget what this holder is)

  • Lap laser pieces as needed

  • Release laser pieces from crystal bond using acetone

  • Bond pieces to glass slides

Top Contact

  • See Bottom Contact and use appropriate metallization on laser pieces mounted on glass slides

Final Packaging

  • Release piece from glass slide and cleave into individual lasers

  • Indium mount bottom contact (SiNx side) to copper piece

 

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