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Si Wafer Polishing

Si Wafer Polishing

This procedure is an adaptation of Laser thinning procedures

Last Updated: April 2017, SDM

Special Notes

  • DO NOT use any of the cleaving tools (tweezers etc.) to handle samples exposed to polishing materials (e.g crystal bond or micropolish alumina )

  • Use only the dishes and lapping tools that are designated for your sample type. For example, don't use III-V dishes when polishing Si and vice versa

Procedure

  1. Cleave samples to ~13x13 mm square size (limited by the size of the chuck)

  2. Attach sample to chuck using crystal bond

    1. Turn on foil-covered hotplate to level 4 or 5 heat. Let sit for 5 min to warm up

    2. Put chuck on hotplate and wait ~ 1-2 minutes for the chuck to get warm

    3. Place a small piece of crystal bond on the chuck and wait for it to melt (~1 min)

    4. Using metal tweezers (plastic will melt) hold the chuck in place on the hotplate and use a razor blade to smooth out the melted crystal bond so that it uniformly covers the chuck

    5. While the chuck is still on the hotplate, place the sample on the crystal bond with the side to be polished facing up (i.e. the side to be polished should not contact the crystal bond)

    6. Center the sample on the chuck. Not centering will result in non-uniform polishing

    7. Remove chuck/sample from hotplate and allow it to cool so the crystal bond hardens

      1. Can use N2 gun and DI-H2O to cool sample, just make sure it is dry before moving on

  1. Prep polish dish

    1. Get the first polish dish

      1. For Si polishing, use the labeled "1 um Alumina on Trident Pad" dish. Dish should be black plastic

    2. Remove the circular glass slide in the dish (forcefully/gently shake it out)

    3. Apply a TexMet C Lappying pad to the glass slide

      1. The pad has an adhesive backside, sick a sticker

      2. These pads are in the Laser Lapping Step 2 box

  1. Add nickle- or dime-sized puddle of the first step of polishing slurry to the polishing dish

  2. Put sample/chuck (sample first orientation) into the slurry

  1. Put dish and sample/chuck on the polishing machine

    1. There's a square on the bottom of the dish that shold fit on a square on the polishing machine

  1. Perform polish

    1. On the machine, adjust the time, speed, strength, and softstop

      1. These are recommended values

        1. Time --> 30

        2. Speed --> 20 (doesn't really make a difference what the speed is)

        3. Strength --> 10 for III-V, 10 for Si

        4. Softstop --> On

  2. Wait for Polish to finish

  1. Clean up and prep for next step of polish

    1. Clean up is important because you don't want cross contamination between steps!!!

    2. Remove polishing dish with sample from the polishing machine

    3. Grab sample/chuck and wash it off using DI-H2O. Dry with the N2 gun

      1. If the sample looks sufficiently polished, it is ready for the next stage

      2. If the sample does not look sufficiently polished, use the same/used TexMet lapping pad and add more step 1 slurry. Put it back on the polishing machine and polish for more time and/or higher strength

      3. "Sufficiently polished" is relative to the user. A rule of thumb is when you can see your eye or glasses when looking at the sample

    4. Clean off the rest of the slurry and dry sample/chuck using N2 gun

    5. Place down 2 cloth kimwipes

    6. Remove circular glass slide onto the first kimwipe

    7. Use a razor to remove the TexMet pad

    8. Throw the first kimwipe and TexMet pad into the arsenic trash

    9. Apply a Micocloth lappying pad to the glass slide

    10. Add a quarter-sized drop of 0.3 micropolish alumina

    11. Put sample/chuck into the slurry

  1. Start next polish step

    1. Place dish with sample/chuck onto the polishing machine

    2. Start polish

      1. Recommended values

        1. Time --> 30

        2. Speed --> 20 (doesn't really make a difference what the speed is)

        3. Strength --> 5 for III-V, 5 for Si

        4. Softstop --> On

  2. Wait for Polish to finish

  1. Remove sample from chuck

    1. Heat up hotplate at level 4 or 5 for 5 min

    2. Put sample/chuck on the hotplate and allow the crystal bond to melt

    3. Using tweezers, pull and push sample off the chuck

  1. Clean sample

    1. Put sample into acetone, IPA, DI-H2O rinse for 2 min in each solution

      1. The acetone desolves crystal bond

      2. Use a wire basket

      3. Adgitate the solution

    2. When finished, dry off sample using N2 gun

    3. Dispose of solution waste in the side sink of the fumehood

  1. Cleanup set-up

    1. Remove the TexMet pad that remains on the circular glass slide. Put in arsensic trash

    2. Return any acetone, IPA, and H2O dishes to their homes

    3. Fill a spare dish with acetone such that it will totally submerse the sample chuck. Put chuck into this solution and let it sit overnight to remove remaining crystal bond

    4. Turn off hotplates and polisher machine

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