Specific Process Knowledge/Wafer cleaning/7-up & Piranha

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Cleaning of wafers or masks

Cleaning of wafers or masks with sulphuric acid can be done either in a dedicated tank "7-up" or in the fume hood in a beaker "Piranha". Both 7-up and Piranha removes heavy organics. Always use one of these after KOH etch or hot phosphoric acid etch to remove alkali ions before further processing. 7-up and Piranha are also used as cleaning solutions after stripping resist.

7-up 6" in cleanroom D3. <br\> -Up to 25 wafers of 4" or 6" at a time.<br\> -Materials allowed: Silicon, Poly Silicon, Silicon Oxide, Silicon Nitride, Silicon Oxynitride,Quartz/fused silica

7-up for masks and glass wafers positioned in cleanroom D3:<br\> -Up to 25 glass wafers of 4" at a time or 4 masks.<br\> -Materials allowed: Silicon, Poly Silicon, Silicon Oxide, Silicon Nitride, Silicon Oxynitride, Quartz/fused silica, glass (Pyrex and Soda Lime), chromium

The user manual, user APV and contact information can be found in LabManager: 7-up 6" info page in LabManager or 7-up (masks) info page in LabManager

Comparing the 7-up cleans and Piranha clean

	7-up wafers	7-up Masks	Piranha
General description	Cleaning of wafers using the dedicated tank in cleanroom D3.	Cleaning of masks using the dedicated tank in cleanroom D3.	Cleaning of wafers using a beaker in the fumehood in cleanroom B1. Used for glass wafers or wafers with metal or other materials that you are not allowed to put in the 7-up for wafers or masks.
Chemical solution	98% Sulfuric acid and Ammonium sulfate	98% Sulfuric acid and Ammonium sulfate	98% Sulfuric acid and Hydrogen peroxide 4:1 add H2O2 to H2SO4
Process temperature	80 oC	80 oC	~70 oC the chemicals will heat up to working temperature during mixing, therefore be careful! First ad H2SO4 then H2O21
Process time	10 min.	10 min.	10 min.
Allowed materials	Silicon Poly Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Quartz/fused silica	Silicon Poly Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Quartz/fused silica Pyrex Soda lime glass Wafers with Cr	All materials (in beaker).
Batch size	1-25 4" or 6" wafers	1-25 4" or 6" wafers or 1-4 5" masks	1-5 4" wafer at a time
Size of substrate	4-6" wafers	4-6" wafers or 5" masks	All sizes that can fit into the beaker in a dedicated holder

Note 1: In preparing a solution involving an acid, always add the acid last. The exception to this rule is Piranha, in which case you add hydrogen peroxide (H2O2), a very strong base, to sulfuric acid (H2SO4), a very strong acid. Why? Because it is potentially explosive and at the very least will cause the solution to become very warm. Picking up a beaker that is this hot will be very painful, might melt your gloves, and may cause you to spill it.