RCA Clean Notes

I removed 2 fresh disks from the large wafer cassette and labelled them with today's date, "sym flats", and 280um.

I performed a solvent wash in acetone then methanol, followed by the base wash RCA1, followed by 2 minutes HF etch with 2.5% buffered HF solution, followed by acid wash RCA2. The solvent wash procedure also called for an initial wash in tetrachloride ethanol, but this was not available so I skipped this washing step. Bert advised that he has not heard of this step in the RCA procedure, so it is probably not standard.

I was using the RCA 1 and 2 procedures attached. Bert also advised that when he plans to put the disk in the furnace or PECVD immediately after cleaning, he typically does the HF step last (after RCA2).

The cryostat is still cold (-83C), so I have placed the wafers back in the desiccator. One of the wafers (labelled) has been RCA-cleaned, the other has not.

Bert also recommended some wafer handling tools that will help avoid scratching the surface of the wafer on glassware.

Step by step

In practice, due to wait times, it is clear that the RCA procedures should be in a slightly different order. I've also included 

1. Before getting started, login to the PECVD and do the initial setup steps.
2. Decant NH4OH and water into a beaker, start heating it
   1. Takes about 10 minutes to heat up
3. Decant the acetone, and soak the wafer for 3 min
4. While the wafer soaks, decant the methanol and H2O2 (part 1)
   1. Keep an ear out for the timers on the solvent soaks--swap the wafer to methanol for 3 min then H20 for 3 min
5. At this point the NH4OH should be hot. Mix in the H2O2, and once it starts bubbling add the wafer.
   1. This solution sits for 15 min.
6. While the RCA1 soak proceeds, decant and begin heating the HCl and H2O2 for the RCA2 clean.
7. Decant and dilute the buffered HF to 2.5%.
8. HF etch the wafer for 2 minutes, then rinse for 1-2 min.
9. While the wafer rinses, check on the RCA2 bath. It should be getting hot by now, remove it and add the HCl to H2O2. 
10. Remove the wafer from the HF rinse water, blow dry with nitrogen, and transfer over to the RCA2 bath.
11. While the RCA2 bath soaks for 15 min, clean up the workbench and check on the PECVD. Get the PECVD completely ready to load a wafer.
12. Remove the wafer from RCA2, blow until dry with nitrogen. Immediately transfer to the PECVD and begin recipe.

Bert suggested that the HF etch should be the final step if we want a fresh surface for PECVD deposition. The RCA2 clean does introduce a (high purity) oxide layer, which is why the wafer surface is hydrophilic following this cleaning step. If PECVD is to be used, simply move item 8 to the end of the list, and transfer the wafer from the post-HF rinse directly to the PECVD. During the extra wait time you can always clean up one of the benches.