Specific Process Knowledge/Wafer cleaning

Feedback to this page: click here == Cleaning of wafers ==During processing it is sometimes mandatory, necessary or just recommended to clean the wafers or the photo lithographic masks. This can be done by different cleaning procedures depending on what the wafers have been exposed to and where they are going to be further processed. In the comparison table below is listed different cleaning procedures available at nanolab.===Wafers that go into the high temperature furnaces===As a general rule all wafers that go into the high temperature furnaces need a full RCA clean directly before the furnace step.

===Wafers that have been in KOH baths (Si Etch 1, 2 and 3), KOH BHF baths or 'Nitride etch: H3PO4' (warm phosphoric acid)===Wafers that have been etched in KOH are often etched in warm phosphoric acid afterwards to strip the silicon nitride etch mask. Therefore, wafers that have been processed in KOH baths, KOH BHF baths or phosphoric acid nitride etch baths often need at minimum a 7-up or Piranha clean before they can be further processed (in order to remove KOH etch residuals and metal ions).

===Items that have been outside the cleanroom===Before bringing samples into the cleanroom you have to get approval from nanolab. Send an e-mail to danchipsupport@nanolab.dtu.dk. When you have an approval the items that have been outside the cleanroom should always be cleaned in soap and ultra sound followed by a 7-up or Piranha clean before entering the cleanroom.

===Masks===Masks that have become dirty by dust particles or resist residues have to be cleaned in the 7-up (mask) bath before use.

===Before entering specific process equipment===Sometimes the wafers need a certain cleaning process before they can enter specific process equipments due to the risk of cross contamination. Please consult the cross contamination scheme to see whether your wafers need a cleaning before the next processing sequence.


==Comparison of Wafer Cleaning Methods=={|border="1" cellspacing="1" cellpadding="3" style="text-align:left;" |-|-|-style="background:silver; color:black"!!RCA!Wafer/Mask Clean baths & Piranha!5% HF!IMEC!Soap Sonic!Post CMP Cleaner|-|-|-style="background:WhiteSmoke; color:black"!Generel description|Two step process to remove traces of organics and metals|Removes traces of organics and alkali ions|Removing native oxide|Removing dust, traces of organics and alkali ions and slightly polish the surface.Make the surface hydrophillic |Removing dust and particles||-|-|-style="background:LightGrey; color:black"!Purpose|Mandatory prior furnace processes |When needed and always after KOH etch and Nitride etch in Phosphoric acid. Sometimes mandatory before next processing step.|Optional during RCA cleaning|Recommended cleaning and treatment before wafer bonding |Mandatory cleaning of very dirty items that enters the cleanroom. Should always be followed by a piranha clean.||-|-|-style="background:WhiteSmoke; color:black"!Substrate size|*#1-25 2", 4" and 6" wafers|*#1-25 2", 4" and 6" wafers|*#1-25 2", 4" and 6" wafers|*#1-25 2" and 4" wafers|*All sizes that can go into the bath||-|-|-style="background:LightGrey; color:black"!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, other glass and Silicon wafers with Cr ONLY allowed in Mask Cleaning bath or beaker in fumehood|*Silicon*Poly Silicon*Silicon Oxide*Silicon Nitride*Silicon Oxy-nitride*Quartz/fused silica *Resists (depending on bath)*Pyrex (depending on bath)|*Silicon*Poly Silicon*Silicon Oxide*Silicon Nitride*Silicon Oxynitride*Quartz/fused silica *Pyrex|*All materials||-|}