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

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 fumehood in a beaker "Piranha" Both 7-up and Piranha removes heavy organics. Always use one of these after KOH to remove alkali ions before further processing. 7-up and Piranha are also used as cleaning solutions after stripping resist.

Comparing data for 7-up and Piranha

	7-up	Piranha
General description	Cleaning of wafers or masks using the dedicated tanks. There are one tank for masks and glasswafers and one for 4-6" Si wafers in cleanroom 4 and one tank in cleanroom 3 for 4" Si wafers only.	Cleaning of wafers using a beaker in the fumehood in cleanroom 2.Used for glass wafers or wafers with metal or other materials that you are not allowed to put in the 7-up for wafers.
Chemical solution	98% Sulfuricacid and Ammoniumsulfat	98% Sulfuricacid and Hydrogenperoxide 4:1 add H $_{2}$ O $_{2}$ to H $_{2}$ SO $_{4}$
Process temperature	80 ^oC	~70 ^oC the chemicals will heat up to working temperature during mixing, therefore be carefull!
Process time	10 min.	10 min.
Allowed materials	Dependent on which bath is used, look at the text in the pictures.	All materials (in beaker).
Batch size	1-19/25 4" wafers or 5 masks at a time	1-5 4" wafer at a time
Size of substrate	4-6" wafers	2-4" wafers