This process is to be done at the wbgeneral. There is a temperature controlled water bath set up.

1) Fill it with water (a couple of inches from the top so that it does not overflow when the beaker is in it).

2) Turn it on with the on off toggle and set the temp to 80C. Set the Limit Adjust knob at about 130C (if it is too low it will trip the breaker and cool down the bath. After about 3 hours check the water level and add water to the bath if needed.

3) The KOH beaker with your desired percentage of KOH should be immersed into the temperature controlled bath. Place your wafers in either the designated Teflon boat or single wafer Teflon holder and put them in the solution.

4) Place the condensing unit on top of the beaker with the lower hose connected to the industrial water connection and the upper hose going down the drain. Turn on the water (slow steady flow). A thermometer can be placed in the top to monitor the temperature of the bath.

NOTE: Most people use 30% KOH (dilute the 45% solution that we buy to be 30%). It etches at ~60 microns per hour.

I. LONG ETCHES

• DO NOT LEAVE THE BATH for more than 4 hours (NOT OVERNIGHT!!) It will boil dry.
  

II. PATTERNING

• Resist should NOT be put in the KOH (it will just lift off). You need to use nitride (as little as 250A will hold up for etching completely through a wafer). Oxide can be used for short etches, but is not recommended because it etches fast in KOH (rate unknown). If you want to use oxide as a mask, TMAH is recommended instead of KOH.
  

III. STORAGE and REUSE

• You may save your solution in in a plastic bottle (cool it first) as long as it is properly labeled and in a secondary containment (i.e. the bottom of the cart).
  

IV. DESIGNATED KOH BEAKERS and HOLDERS

If you plan to do processing in mainline equipment (i.e.: tylan 1-4, tylanpoly, tylannitride, tylanbpsg (LTO), drytek2, amtetcher, P5000, lampoly, etc) you MUST CLEAN your wafers first to remove all KOH contamination.

You MUST have used the designated quartz KOH etch beaker and the designated "clean" Pyrex rinse beaker. If you have used any other labware, you may NOT follow this procedure and your wafers may NOT go in any mainline equipment. If your wafers have ever had metal on them , they may not go into the designated quartz ware or into mainline equipment.

KOH contamination ruins devices (it is a lifetime killer). Other lab users may have spent months working on their device wafers. Their work may be ruined if you do not carefully follow these procedures.

• USE DESIGNATED KOH quartzware and Teflon holder ONLY.
  
• If they need to be cleaned, use room temperature solution of 1:1:1
• H₂O:H₂O₂:HCl for 20 minutes and then rinse well.
  
• The KOH quartzware is not to be used with metals or nonstandard materials because wafers that get KOH etched often go back into the main stream processing equipment. BEFORE THEY DO they MUST get a SPECIAL KOH REMOVAL step(see below)
  
• DO NOT USE GENERAL WETBENCH beakers and holders etc... because if they are not designated for KOH they could have been used for anything -- including gold.
  

V. KOH CLEANUP (removal of KOH contamination)

If you have used designated KOH beakers and want to do standard processing in mainline equipment (i.e. tylan 1-4 and poly and nitride and lto, etc..) you MUST clean your wafers first to remove KOH contamination.

This may be done in your own nonmetal contaminated quartzware (specifically used for this clean step OR with permission you may use the silicide wetbench) (see Process Staff before doing this).

Procedure at wbsilicide:

Do not start this procedure unless you have enough time to completely finish it in one session, read the whole procedure before you start.

Put a note on the splash shield that states:

• "KOH Contamination clean-up in progress in the HCl hot pot"
• your name
• the date
• the time
• the time you expect to be finished using the wetbench

Be sure to log the clean-up on the chemical change sheet. Note the fact that the silicide cassette and handle were both cleaned, too.

CLEAN THE WAFERS:

1. Aspirate the current HCL solution. If the current solution is hot, you must wait until it has cooled to 50C before aspirating.
2. Pour fresh 5:1:1 (H₂0:H₂O₂:HCl) solution
3. Heat the fresh solution to 70C
4. Use your KOH contaminated tweezers, to put the wafers in a silicide cassette. Put the KOH tweezers in the KOH tweezer box. Put the box away. You will not use the KOH tweezers after this point in the clean. Put the KOH contaminated cassette away also.
5. Do NOT put the silicide cassette , with the KOH contaminated wafers, in any dump rinser or hot pot before going in the 5:1:1 (H2O:H2O2:HCl) bath! (DO NOT DI RINSE FIRST -- that would contaminate the dump rinser!!)
6. Immerse wafers in a silicide cassette into the 5:1:1 (H₂0:H₂O₂:HCl) for at least 20 minutes heated to 70C.
7. After the 5:1:1 step, Dump rinse the wafers and spin them dry.
8. Use non-metal photoresist tweezers to remove the wafers from the silicide cassette.
9. Store the wafers in a non-metal, non-KOH, contaminated storage box.
10. The wafers are now clean enough to go to wbnonmetal, then wbdiff.

CLEAN THE HOT POT, CASSETTE, and HANDLE (you must do this immediately after cleaning your wafers...you may not come back later and clean the wbsilicide equipment!):

1. Aspirate the KOH contaminated 5:1:1 (H2O:H2O2:HCl). Remember, the solution must be cooled to 50C before aspirating.
2. Fill the hot pot (nearly to the top, so the whole pot is cleaned) with 1:1:1 (H2O:H2O2:HCl).
3. DO NOT HEAT the solution (it will heat up on its own).
4. Put the cassette and handle you used in the solution so that it will will be cleaned at the same time. Let the solution sit for at least 30 minutes.
5. After the 30 minutes, allow the solution to cool to 50C, then aspirate.
6. Rinse the hot pot thoroughly:
   1. fill the hot pot to the top with DI water
   2. aspirate
   3. fill the hot pot to the top with DI water
   4. aspirate
   5. fill the hot pot to the top with DI water, let it overflow for 2 minutes
   6. aspirate
   7. fill the hot pot to the top with DI water, lit it overflow for 2 minutes
   8. aspirate
7. Dump rinse and spin dry the cassette
8. Put the cassette handle in with the other handles
9. Pour fresh 5:1:1 (H2O:H2O2:HCl) solution in the hot pot..

VI. KOH NOTES

• 30% KOH etches at ~1u/min
  
• Openings >1mm will allow the KOH V etch to go all the way through a wafer of standard thickness.