Mathies:Wafers Cleaning and Deposition

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Cleaning Wafers

Cleaning in preparation for LPCVD poly-Si deposition (Tystar16), sputter coating, or wafer bonding:

1. Wafer cleaning is done in sink 432c, in the old lab.

2. Quick DI water rinse. (15-30 sec)

3. Brush clean with NovaClean to remove grease, particles, etc.

  • Use the shallow pyrex pie dish for the NovaClean wash.
  • Brush both sides of the wafer vigorously; rinse in the NovaClean solution repeatedly.

4. Longer DI water rinse, in large tank under running water (1-3 min).

5. Blow dry w/ N2 gun. (Skip this step if going straight to the acetone sonication.)

6. Acetone sonication, 5-10 min.

  • Set wafers with the etched side facing down.

7. Rinse wafers with acetone, IPA, & DI H20. (Note: rinse the acetone off with IPA before it evaporates, and rinse the IPA off with H2O before the IPA evaporates.)

8. Blow dry w/ N2 gun. Inspect for particles, etc.

9. Strip Si off front side at this stage if necessary (for bonding, etc).

10. Piranha clean at sink8, 10 min.

11. Quick-dump rinse at sink8, 2+ cycles.

12. Spin-rinse dry - top SRD is for 6" wafers, bottom SRD for 4".


If you are cleaning a wafer after holes have been drilled, it may be helpful to do an acetone sonication & rinse before the NovaClean scrub, then sonicate afterwards again with fresh acetone.

Notes on wafer handling (general):

1. Always wear gloves

2. Touch wafer only at the edges, use tweezers or vacuum wand if appropriate

3. When transferring wafers between two cassettes, lock the cassettes together and flip to transfer. (This is cleaner than touching the wafers with gloves/tweezers/vacuum wand.)

4. When drying wafers with the N2 gun, first blow-dry the back side, then lay the wafer dry-side down on a technicloth to blow-dry the front side from center to edge. The idea here is to blow the water off the edge of the wafer onto the technicloth.

5. Do not put your hands, face etc directly over a wafer, especially when under a laminar flow hood. Also try not to talk over or breathe onto the wafer when you are working.


LPCVD preparation

Note:

At present, we can use the tystar16 LPCVD system in the Microlab for depositing Si on borofloat and pyrex wafers, but not for D263 wafers. D263 wafers should be cleaned, then sealed in shipping boxes and sent to UHV Sputtering to have a layer of Si (or Ti/Pt, as needed) sputtered on one side.

1. Select wafers without scratches or chips. The tystar boat holds 25 wafers.

2. Make sure all of the wafers are very clean. NovaClean and acetone sonicate (this can be done ahead of time), then piranha clean immediately before loading wafers into furnace. (See Wafer Cleaning for more details.)

3. Piranha-clean step: 10 min in piranha tank, at least 2 cycles in the QDR, then dry in the spin-rinse dryer.

  • Make sure that once the wafers have been piranha-cleaned they are kept under laminar flow hoods, and use proper cleanroom technique to avoid getting particles on the clean wafers.

LPCVD process and recipe

Note:

There are two boats available, for two wafer sizes. We use the shared 4" boat for the tystar16, located in the rack to the right of the furnace area. If necessary, we can borrow another 4" boat from the Microlab to do do a run with two 4" boats (50 wafers). (Talk to Sia Parsa to get the second boat.) For 6" wafers, we have our own 6" quartz wafer boat, which is kept wrapped in padding when not in use and stored in one of the Microlab lockers.

1. Check the furnace control panel. The recipe running should be the standby recipe (16STNBYA) and the program should be on STEP 035, meaning that the furnace tube is under vacuum and at temperature. If another recipe is loaded or running, do not try to open the furnace.

2. If 16STNBYA is running, press the ALM/ACK button on the furnace control panel to begin the backfill process. Backfilling is a 2-step process, takes 12 min total.

3. Once 16STNBYA reaches the end of the program, press ALM/ACK to silence the alarm, then load your deposition recipe.

  • To load a recipe, make sure the TYSTAR16 disk is in the tycom computer, then type LO *recipename* *tube#* at the tycom terminal. (eg, LO 16VTPLYA 16 or LO 16STNBYA 16.)
  • The current deposition recipe is 16VTPLYA, with deposition parameters as follows:
           Temperature = 525°C for all variables
           Gas Flow (SiH4) = 100 scc/min
           Gas Flow (PH3 hi/lo) = 0 scc/min
           Process pressure (PRCPR) = 300 mtorr
           Time = 02:20:00 (2hr 20min)
  

4. After the deposition recipe is loaded properly, press RUN on the furnace control panel to start the program. This should cause the furnace tube to open so that the wafers can be loaded.

5. Remove the center dummy boat using the larger boat-carrier. Set this aside (very carefully) on the rack at the top of the furnace area.

6. Using the smaller boat-carrier, transfer the wafer-deposition boat to the tube supports. Make sure the boat is level and balanced.

7. Transfer wafers to boat using vacuum wand.

8. Press ALM/ACK to return tube to furnace & continue deposition program.

9. Once deposition is finished, proceed through backfill steps to end of deposition program.

  • For 16VTPLYA, the program will hold at STEP 130 once the deposition is finished. Press ALM/ACK twice at this step to exit out of standby subroutine and continue to backfill steps (STEP 150 & 155).

10. When the program ends, the furnace control panel will beep and read END. Press ALM/ACK, then press RUN again to unload the furnace tube.

11. Using the smaller boat-carrier, remove wafer deposition boat (with wafers) from tube supports, then set aside (very carefully) on the rack at the top of the furnace area to cool for 5-10 min.

12. Return the center closed dummy boat to tube, then press ALM/ACK to return tube to furnace.

13. Once the furnace is sealed, press ABORT to end that program so that the standby recipe can be loaded.

14. Load the standby recipe (type LO 16STNBYA 16) at the tycom, then press RUN at the furnace control panel to start the standby program.

15. Once the wafers have cooled enough, transfer them back to the wafer box using a vacuum wand. When the boat is cool, return it to the appropriate storage location.

Contact

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