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Au films for biology, surface chemistry and interface characterization
Introduction
The capability for Au deposition over large area wafers (up to 150mm diameter, using the Ion Beam system Nordiko 3000) has been used for the deposition of test samples for several groups. The gold surface is used to promote the formation of self-assembled monolayers of several molecule types, so that its surface chemistry and functionalization is characterized. Another application is for neutron reflectometry measurements (ISIS, UK).
Main Results
Typically twice a year, batches of 15-20 wafers (150mm diameter) are deposited with Cr 5nm/Au 25-40nm and then diced into smaller sizes (Figure 3), according to the request. The Au surface is protected by photoresist for the dicing and transportation.
Figure 3- Dicing schemes for the 150mm wafers Si/Cr/Au (Photoresist)
Another application started successfully in 2005 (Rutherford Laboratory, UK), consisting on Fe/Au and NiFe/Au film deposition by Ion beam on 10mm thick Si wafers (100mm diameter). The wafers are used as substrates for neutron reflectometry measurements in the UK. In these experiments the neutron beam travels through the silicon and is reflected from the gold/solution interface. For this particular series of experiments they have membrane proteins that have been modified with a cysteine residue to bind to the gold giving a controlled orientation of the protein at the interface. The beam needs to come in through the side of the silicon for geometric reasons. The incident angle ranges from 0.35 to 1.8 degrees and the beam is up to 3.5 mm high. Therefore the minimum silicon thickness possible is about 5 mm.
The main issues are very flat interfaces, and very good film thickness uniformity over the wafer (which are +-2% over 150mm areas, in the Nordiko3000 system). Due to the high thickness of the wafers, the loading from the loadlock into the deposition chamber (Nordiko3000) is impossible, and each weafer has to be mounted individually on the substrate tabel after venting the deposition chamber.
Projects and Collaborations 2004 - present
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INEB – Inst.Engenharia Biomédica (Porto)
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BERG - Inst. Superior Técnico (Lisbon)
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ISIS - Rutherford Appleton Laboratory (UK)