2 - Technologies

Cross-linking of highly oriented monomer films made by Langmuir-Blodgett method can simply be achieved by UV irradiation or by chemically initialized reactions. A small amount of a high-molecular-weight substance, which has polar molecules possessing hydrophobic tails and hydrophilic heads (e.g., fatty acids or higher alcohols), is dissolved in a volatile solvent, and one drop of the solution is sprinkled on the surface of the water. The solvent evaporates, and the molecules of the substance diffuse over the surface of the water, all orientated in the same manner due to their polarity. According to their concentration, either a "two-dimensional gas" is formed or a monomolecular film of liquid or solid. Such a film can be lifted up and put upon a plate or directly deposited onto the surface of a plate-shaped substrate using dipping. Several such films can be applied on top of each other, and in this way even films of several hundreds of nanometer thickness can be built up gradually, and finally cross-linked to form a polymer film.

Spinning, casting and photolitography

For applications in microelectronics and sensorics, it is necessary to form the films in specific, sometimes complicated patterns. For this purpose, a suitable mask is used to prevent condensation on the areas that we desire to keep clean. The mask is usually formed from a metal and is placed in the vapor stream as close as possible to the substrate on which the film is to be deposited. This is the so-called noncontact or masking through-mask-deposition method. There are several technologies for preparation of "in contact" masks, which are deposited directly onto the substrate. The most widely used type is the photolithographic one combined with selective etching of different layers, similarly to the silicon photolithography process. Another often-used technique is the so-called "lift-off" technique. In this method, the deposition of the film is carried out on a substrate that is covered previously with a photolithographically patterned mask. After the deposition, the latter one will be removed by etching or stripping from the unnecessary areas, together with the deposited film.