• Universitat de València

• Rafael Abargues López
• José Luis Valdés Navarro

The formation of conductive metallic layers and the possibility to structure them are fundamental aspects in the fabrication of semiconductor devices. The two most common methods for forming such metallic layers are based on etching techniques (dry or wet) and the lift-off technique. The lift-off technique is the most commonly used because the solvents required for resin removal cause less damage to the substrate, and also minimises the problems of subsequent metal layer deposition. However, one of the most important problems with this technology is associated with metal deposition, as the metal atoms are not deposited exclusively in a vertical direction to the substrate, but partial metal deposition occurs on the inner walls of the lithography-generated structure. This has a negative impact on the removal processes of the resin underneath the metal as it cannot be completely removed. These disadvantages are accentuated when the size of the structures decreases, especially for sub-micrometre sizes. This leads to limitations when it comes to generating micro- or nanostructures with a high fill factor or even fully metallic ones, since, as the amount of metal salts precursors of the nanoparticles increases, the lithographic properties of the material are drastically reduced.  There is therefore an objective technical problem in the state of the art concerning how to increase the fill factor of metallic nanoparticles embedded in a nanocomposite without losing its physico-chemical, i.e. lithographic, properties.

Researchers at the Institut Universitari de Ciència dels Materials de la Universitat de València (ICMUV) have developed a new method to obtain nano and micrometric metallic structures from a nanocomposite, where the nanocomposite is formed by a polymer with metal nanoparticles (such as Au, Ag, Pt, Pd, Ir, Ru, etc.) embedded in it. ) embedded in it, which allows to increase the filling factor of the polymer with said metallic nanoparticles, by means of a selective process of non-electrochemical metallic growth, and maintaining its physico-chemical properties.

The main applications of the technology are as follows:

• In the detection of chemical and/or biological molecules, in plasmonic or photonic devices, in light-guiding circuits, in electronic and/or photonic and/or opto-electronic chips and/or opto-electronics.

The main advantages provided by the invention are:

• Simplification of the manufacturing process of metal structures with respect to conventional technologies, by reducing the number of manufacturing steps.
• Problems with the removal of the resin underneath the metal are avoided by eliminating the lift-off step from the process.
• Metal deposition outside unwanted areas is completely reduced because nanoparticle growth and subsequent metallisation of the micro/nano-structure is selective, as it occurs only where the nanoparticles are located.
• Low cost.

• Patent granted