Specific Process Knowledge/Wafer cleaning/IMEC

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Please note: This elaborate cleaning method is only used very rarely. It has turned out that at DTU Nanolab an 'RCA clean' prior to bonding (and do the cleaning and bonding very early in the morning with few people and thus lower particle level in the cleanroom) gives the best results. If you for some reason still prefer to do the IMEC clean described below, please contact DTU Nanolab to make arrangements. We do not have dedicated IMEC equipment which is immediately ready for use.

The IMEC process: Cleaning of wafers prior to fusion bonding

The IMEC cleaning process is used in circumstances where extraordinary clean wafers are required. It is primarily intended for cleaning wafers prior to fusion bonding. This procedure is based on the IMEC cleaning process: M. Meuris et al. "The IMEC clean: A new concept for particle and metal removal on Si surfaces.", Solid state Technology, Vol. 38, Issue 7, pp 109-113, 1995. Has been slightly modified by Karen Birkelund.

Information about equipment relevant to this procedure can be found in LabManager:

Info page for 'Fume hood 01: Acids/bases'
Info page for 'Fume hood 02: Acids/bases'
Info page for 'Wet bench 03: Wafer and mask cleaning'
Info page for 'Wet bench 05: Al etch'
Info page for 'Wafer Cleaning'
Info page for 'Optional Bath (Currently not in operation!)'

Step	Process	Details	Comments	Comments
1	Pre-bond cleaning of Si wafers prior to fusion bonding.	.	Takes approximately 1,5 hours Orient flat to minimize handling Preferably do the cleaning just before bonding to maintain cleanliness!	Get CLEAN box for wafers!!!
2	Piranha	Mixture: H2SO4:H2O2 (4:1) Temp: 80oC Time: 5 min	You can use the 'Mask Clean' bath in Wet Bench 04 (in cleanroom D-3). However, this requires planning at least a couple of days in advance, since the bath is primarily used for other purposes! Alternatively use a very clean glass beaker. The recommended procedure is: Pour H2SO4 into bath/beaker Place wafers in clean carrier (USE this in steps 2-7) Add H2O2 to the beaker that already contains H2SO4 Wait 30 sec to ensure mixing of chemicals, then dip wafers.	Maybe clean the tank the day before!
3	Rinse	2 min. rinse	Rinse you wafers with DI-water.	Put into dedicated wet box for IMEC
4	IMEC	Mixture: DI water:5% HF:Isopropanol (100:10:1) Temp: 25oC Time: 100 sec	Make an appointment some days in advance with a Nanolab employee to help you with this step! Clean tank (Cleanroom D-3, the 'Optional Bath' inside Wet Bench 05: Al etch) Mix your IMEC solution in dedicated bottle (IMEC) inside a fume hood Ask a Nanolab employee to help you filling the solution into the 'Optional Bath' tank!	.
5	Rinse	2 min. rinse	Put into dedicated wet box for IMEC	.
6	Piranha	Not nitride wafers! Mixture: H2SO4:H2O2 (4:1) Temp: 80oC Time: 20 min	Re-use piranha previously made in step 2 Makes wafers hydrophilic	.
7	Rinse & spin dry	5 min rinse	.	.
8	Put wafers in new clean carrier box	.	.	.