STANDARD PRE-LPCVD OR PRE-METAL CLEAN INFORMATION

WHO NEEDS IT?

1. Wafers should not have metal on them when getting this clean. Depending on where the clean will be done and where the wafers are going after, the wafers could have had the metal removed or had it turned to silicide prior to this clean (see section below "Where should I do it?" for details).
2. Standard pre-LPCVD clean should be done on wafers that are going into furnaces, LPCVD systems or metal deposition.
3. Wafers should be loaded into the furnace or deposition within one hour of the clean process. If they sit longer than one hour they MUST be RECLEANED.
4. Wafers with resist on them should get resist strip before going into prediffusion clean.

WHAT IS THE PROCESS

• 4:1 H₂SO₄:H₂O₂ @90C for 10 minutes.
• Dump Rinse (std 6 cycles) OR overflow rinse for 5 minutes (if at wbgeneral)
• 5:1:1 H₂O:H₂O₂:HCl @70C for 10 minutes.
• Dump Rinse (std 6 cycles) OR overflow rinse for 5 minutes (if at wbgeneral)
• 50:1 HF dip for 15 - 30 seconds
• Dump Rinse (std 6 cycles) OR overflow rinse for 5 minute (if at wbgeneral)
• Spin Dry (280 seconds rinse; 120 seconds spin dry; Auto Mode; >16 ohm-cm Rs on DI H₂O) OR if you are using wafers that do not fit into a spin dryer or a wetbench that does not have one blow dry the wafers on clean room lint free papers using a N2 gun.
  

VARIATIONS?

1. If you are going to thermal oxidation you should do the HF dip between the 4:1 H2SO4:H2O2 and the 5:1:1 H₂O:H₂O₂:HCl. This removes any chemical oxide and allows the HCl solution to remove any metal contaminants from the surface.
2. When cleaning thin very thin gate oxides, you may want to minimize or eliminate the HF dip step (to preserve the oxide), but keep in mind the possibility of bad contact to metal layers or hazy depositions.
   

HOW DOES IT WORK?

1. The H₂SO₄:H₂O₂ (Sulfuric Peroxide) solution removes the organic contaminants from the wafers.
2. The H₂O:HCl:H₂O₂ removes any metal contaminants that might be on the wafer (it is most effective if done after stripping off the chemical oxide).
3. When an HF dip is done last it removes the chemical oxide put on by the previous clean steps.

WHERE SHOULD I DO IT?

1. The process is used to clean wafers that do not have metal on them.
2. If the wafers have never had metal on them or been in any metal contaminated equipment the clean would be done at the wbdiff (,4", 3", 2" wafers) OR at wbgeneral in designated nonmetal quartz beakers (nonstandard sized wafers or pieces of wafers). Wafers cleaned this way could go into nonmetal furnaces (i.e. tylan1-6, tylanbpsg (nonmetal side), tylanpoly, tylannitride).
3. If they had "standard metals" on them but it was stripped off, the wafers would get cleaned at the wbsilicide. (4", 3", 2" wafers) OR wbgeneral in designated std metal ONLY quartz beakers (nonstandard sized wafers or pieces of wafers). NOTE: "standard metals" are Al, W and Ti. Wafers cleaned this way could go into "standard metal" furnaces ONLY (i.e. tylan7, tylanfga, tylanbpsg (metal side only).
4. NOTE: There is a cassette available at wgdiff, wbsilicide, wbnonmetal and wbmetal for cleaning 6 " wafers.