Soft stamp imprint

Several ETFE soft stamps are then transferred on to a tensioned belt, which loops continuously over two rollers. The soft stamp imprints the nanoscale pattern onto the conveying coated substrate (Fig. 13.9). Continuous roU-to-roU imprinting has been demonstrated using a 10 cm wide pattern. The polymer-coated substrate is imprinted and simultaneously UV cured, before the rolling stamp detaches from the imprinted polymer. The UV-curable polymer resist used is low viscosity liquid epoxysilicone [62]. 

Substrate Conformal Imprint Lithography (SCIL) is a relatively new technique developed jointly by Philhps and Suss Microtec AG [57, 58]. It uses flexible soft stamp technology combined with an elegant vacuum controlled technique for the stamp imprint and retraction process. 

Soft imprinting using flexible stamp has ample potential to be applied for reel-to-reel process [54, 55]. To achieve fast process in reel-to-reel device fabrication, passive alignment process between flexible stamp and substrate is needed rather than active optical alignment procedure. As a passive alignment process, lock and key mechanism was studied between flexible stamp and substrate in soft imprinting. 

While imprint lithography does not involve the use of an elastomeric stamp and hence is not a soft lithography technique, it is a next-generation patterning technique that has gained tremendous attention for generating nanoscale features, which is... 

The nanoimprint process utilises a patterned, 3D mould (template or stamp) to define patterns by embossing a soft polymer or liquid material. Once the material has completely filled the template cavities, it is hardened, using either a thermal or photochemical process, and the template is removed. The hardened imprinted polymer is an inverse 3D replication of the template mould. NIL uses a stamp or template to imprint or emboss a pattern into a polymer. The 3D polymer structures themselves may be used to create the desired nanostructures or alternatively, the polymer structures may be used as a protective mask to selectively protect a substrate during a subsequent process e.g. etching or deposition. 

Hot embossing is perhaps the most simple NIL technique, where the master stamp is imprinted into a soft polymer layer on a substrate (Fig. 13.6) [50]. The polymer and substrate are then heated, curing the polymer to form rigid polymer structures— the inverse of the structures on the master stamp. Once the polymer has been cured sufficiently, the master stamp is retracted, leaving the patterned polymer layer on the wafer substrate. 

The soft PDMS stamp allows large area imprinting and can lower the stamp fabrication cost, since thousands of copies can be reproduced from one master stamp. In addition, lateral stamp distortion and structure deformation caused by backside pressure during standard imprinting processes, which often restricts the resolution of UV-NIL using PDMS stamps to several hundreds of nanometres, can be minimised using the SCIL process [59]. 

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