Hybrid Lithography Approach

Hybrid lithography approaches are emerging as a class of fabrication methods that could potentially yield structures and devices with vastly complex 3D geometries, improved mechanical performance, and enhanced functionality. Hybrid approaches exploit the unique or most of the advantages and properties inherited by individual fabrication methodology. Particular promise is seen for fabrication methods that yield hybrid nanostructures akin to approaches that are commercially and clinically relevant.

4.4.1. X-ray and Nanoimprint Lithography for 3D Patterning

Most of the excellent characteristics that nanoimprint lithography (NIL) has shown as a two-dimensional patterning technique, such as high resolution, high throughput and low cost, do apply also to its three-dimensional structuring capabilities. Nevertheless, the potential of NIL for 3D remains largely unexplored and unexploited, hindered by the difficulties in the fabrication of high quality masters at the wafer scale level. This fact is due to the need of using advanced techniques such as Focused Ion Beam (FIB), or gray-tone Electron Beam (EB) lithography, that are intrinsically slow or require special know-how to be

FIGURE 4.23. Example of device three-dimensional structures fabricated using a Focused Ion Beam Induced Deposition: (a) wineglass, (b) coil, (c) micro-crown (courtesy by J. Fujita et al. [99]), (d) SiO2 micro box to hold cells, (e) an array of metallic pins for capturing particles.

performed. In order to solve this difficulties we have developed a method for 3D patterning using nanoimprint, in combination with other techniques. Our aim is to demonstrate that there is a number of possibilities for fabricating complex 3D masters, using simple, robust and fast processes, offering a tight control on three-dimensional profiles in the scales from sub-100 nm to above 100 mm.

We present the results about an innovative lithographic approach (see figure 4.24) that combines nanoimprint (NIL) and X-ray lithography (XRL) for fabricating unconventional three-dimensional (3D) polymer structures [100]. The use of XRL for structuring a pre-patterned resist by NIL gives rise to high-resolution high-aspect-ratio structures whose overall profile is enveloped by the original 3D imprinted profile. The technological potential of this method has been demonstrated by patterning several different types of structures with

Master with generic 3D profile

Thermoplastic acting as positive ^ tone x-ray resist

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