Electronic devices are getting smaller and flatter – one of the most obvious examples is the smartphone. This in turn requires microelectronic components and modules that are as spacesaving and as flat as possible. For this reason, wafers and chips (ICs) are being made that are increasingly thin so as to enable integration in electronic systems. Very thin semiconductor wafers are highly fragile, however, and their damage or destruction would mean a significant loss in value, so these sensitive items have to be handled with enormous care. Existing carrier techniques for fragile wafers are based on the use of removable adhesives. This method has its drawbacks, however: the thin wafer has to be detached and the polymer residue also has to be removed.
By contrast, electrostatic carrier techniques offer the advantage of adhesive-free, reversible attachment. In the project E-Foil, Fraunhofer EMFT researchers are working on a cost-effective method of making electrode structures – mounted on foil substrates (e.g. polyimide foils) – which can be electrostatically activated. The e-foil itself is approx. 50 μm thick and contains an electrode structure on the inside which is connected to contact points on the outside. By applying an electric potential to the electrode contacts, an electrostatic field can be switched on or off.
In the application, the e-foils are used as retention force agents between a substrate on the top (e.g. wafer, foil, chip) and the carrier plate underneath. The e-foil can also be used as a replaceable and reusable electrostatic carrier foil, or optionally also permanently affixed to a rigid carrier substrate (e.g. ceramic, glass, silicon wafer).
The project »Electrostatic foil carrier for the processing of fragile and flexible substrates« is being funded under the internal Fraunhofer program MEF (Application 115.27/01).