Electron-Beam Lithography is one of the most widely used patterning technologies to realize sub-micrometer and, in particular, sub-100 nm features on planar surfaces, although the long exposure times somehow limit its applicability for high-volume manufacturing. The operation principle of an electron-beam lithography system is the acceleration of an electron-beam onto an electronic resist in order to expose features previously generated by computer-aided design.

Fabrication of masters for Soft Lithographies. We generally use electron-beam lithography to realise silicon master templates with high lateral resolution (features in the range from tens to hundreds of nanometers) to be used for Soft Lithography. The electron-beam exposure is followed by a series of processes (development, metal evaporation, lift-off and reactive ion etching). In Electron-Beam Lithography, the achieved lateral resolution is not limited by optical diffraction, but it is set by the contribution of backscattered electrons far from the actual position of the e-beam (proximity effect). The correction of proximity effect and the achievement of well-vertical walls in the resulting etched features are crucial for further replication by Soft Lithographies.

In particular we have realized large-area (many mm2) 1D and 2D photonic crystals on silicon, with specific features periods from 200 nm to 700 nm and an aspect ratio in the range 2-5 (Fig. 1).

 

Fig. 1 Cross-sectional view of a one-dimensional grating realized on silicon. Feature size and period of 70 and 200 nm, respectively, aspect ratio  about 5. The grating is obtained by a well-defined sequence of processes, including spin-coating, electron-beam exposure of the electronic resist, development, thermal evaporation of chromium, lift-off and Ar/CF4 reactive ion etching. These kind of patterns are very suitable as master for subsequent soft and nanoimprint lithographies.

 

Direct Electron-Beam Writing on Active, Light-Emitting Materials. Conjugated polymers are an important class of materials exhibiting good optical gain and waveguiding properties. We have demonstrated a straightforward and high-resolution patterning route on conjugated polymers, not followed by developing/etching processes. The interaction of the e-beam with conjugated materials affects both the morphology and the opto-electronic properties of the film (Fig. 2). The resulting gain modulation in the active layer could be employed for the fabrication of nanopatterned photonic devices such as directly written polymer distributed feedback (DFB) lasers.

 

Fig. 2 The figure shows the surface morphology, investigated by AFM, of a thin film (~240 nm) of a conjugated polymer textured with a 610 nm period grating by electron-beam lithography. We used an area e-dose of 150 µC/cm2. It is possible to appreciate a slight, periodic morphological modulation with 350 nm features, corresponding to a 0.5-1.0 nm reduction in the exposed polymer regions.

 

 

For more information, please contact: Dr. Dario Pisignano ( This e-mail address is being protected from spam bots, you need JavaScript enabled to view it )

Publications:

[1] E. Mele, A. Camposeo, R. Stabile, P. Del Carro, F. Di Benedetto, L. Persano, R. Cingolani, D. Pisignano
Appl. Phys. Lett. 89, 131109 (2006).

 

[2] P. Del Carro, A. Camposeo, R. Stabile, E. Mele, L. Persano, R. Cingolani, D. Pisignano
Appl. Phys. Lett. 89, 201105 (2006).

[3] R. Stabile, A. Camposeo, L. Persano, S. Tavazzi, R. Cingolani, D. Pisignano
Appl. Phys. Lett. 91, 101110 (2007).