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

The APV for working with piranha in fumehood can be found by clicking here

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	Sulfuric acid (98%) and Ammonium persulfate	Sulfuric acid (98%) and Ammonium persulfate	Sulfuric acid (98%) and Hydrogen peroxide (30%) in the ratio 4:1. First add H2SO4 into a glass beaker then add H2O21.
Process temperature	80 oC	80 oC	~70 oC the chemicals will heat up to working temperature during mixing, therefore be careful! First add H2SO4 into a glass beaker then add 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 H₂O₂, which is a very strong oxidant, to H₂SO₄, which is a very strong acid. This is done because it is potentially explosive and at the very least will cause the solution to become very warm.