Patterning of Nanostructures

With laser interference lithography it is easily possible to reduce pore sizesa in microsieves to the nanometer regime, herewith giving birth to "nanosieves" [74]. A known technique to pattern surfaces on a substrate is to evaporate a material through a thin membrane (shadow mask) with well-defined openings [90] (see Figs. 42 and 43). It is also well known to use such shadow masks as a poor man's technique to make patterns on a substrate if photolacquer patterned layers are too elaborate or not wanted. Shadow masks with nanosized perforations may therefore be used in applications such as ion beam etching [91], electron beam patterning, near field optics, etc. Reactive ion etching through a shadow mask can be used for direct etching [3] of a (nano)pattern in a substrate (for example metal or polymeric foils).

Self-assembly (Nano)mask Preparation The micro/ nanopattern may for instance be formed by using particles with a uniform size, for example a silica dispersion or a latex suspension, with particle sizes ranging from 5 nm to 5 /m.

Figure 40. High-porosity microsieve fabricated on a (110) silicon wafer. Through the slit-shaped pores some typical etch angles can be recognized. Courtesy of Aquamarijn Research.

This suspensions may directly be formed on a substrate with use of a spin coating or evaporation technique. A more or less ordered distribution of particles will then be found in the pattern forming layer on the support. After the evaporation of the solvent of the suspension a very thin metal layer (e.g., a 10 nm chromium layer) may be deposited (e.g., by means of vapor deposition, i.e., sputtering or evaporation) on the substrate and on top of the particles, for example silica particles with a diameter of 30 nm. The silica particles are then solved in a buffered HF solution and a perforated chromium layer remains with perforations of approximately 20-30 nm in diameter depending on the chromium deposition conditions (correction for shadow effect of deposition). The chromium layer may be used as a membrane layer or alternatively as a mask layer for the (dry) etching of a membrane layer underneath the chromium layer (see Fig. 41).

Figure 42. A nanosieve may be used as a shadow mask (nanostencil) for evaporation of material (e.g. gold) through the pores of the nanosieve. Reprinted with permission from [92], J. Brugger et al., Microelectron. Eng. 53, 403 (2000). © 2000, Elsevier Science.

Was this article helpful?

0 0

Post a comment