Multilayer microstructures and laser based method for precision and reduced damage patterning of such structures

#The invention resides in the field of direct laser ablation of material. In particular, it relates to laser patterning of layers in the manufacturing of integrated semiconductor circuits and to such circuits made thereby. In more specific applications, the invention is a technique of patterning a metallic layer on an organic sublayer with minimal ablation or damage due to melt and/or carbonization of the underlying organic sublayer during processing of the metallic layer.

#Manufacture of integrated circuits involves deposition of a layer or layers on a substrate and etching parts of the layer or layers in desired patterns. Often theses steps are repeated to produce a stacked structure. A variety of materials are used as layer and equally a variety of etching techniques are used for production of desired patterns. Direct laser etching or patterning is gaining wide acceptance in the field of IC (integrated circuits) manufacture.

#The demand for low-cost and lower power small displays, digital projection and other personalized applications, has created a steady growing interest in organic light emitting materials that can be deposited using relatively inexpensive processes, such as spin-coating. However, organic materials are extremely sensitive to environmental conditions such as oxygen and moisture and to the chemical treatment used in the processing of photosensitive resins. As a result, pattering of organic-based devices cannot be easily realized with conventional methods of micro-fabrication since all-dry etching processing is required.

#FIG. 1 is a curve showing the reflectivity coefficient of silver in relation to the energy of laser beam.

#FIG. 2 is a curve showing the reflectivity coefficient of aluminum in relation to the energy of laser beam.

#FIG. 3 shows schematically a set-up of direct laser ablation according to one embodiment of the invention.

#Among many possible ways, an increased level of the vertical resolution in the laser-based patterning is achieved by applying laser beams of very short wavelengths, e.g. 193 or 157 nm. At these wavelengths the beam absorption depth is drastically reduced and the ablation process is confined to a shallow depth. Improvements to the method are achieved by applying sophisticated methods for in-situ monitoring of the ablation process.

#The deposition methods to achieve patterned structures, such as the separator technique, have not been commercially established, they are complicated, thus potentially they will be expensive. The use of shorter laser wavelengths (193 or 157 nm) for patterning requires a special processing environment due to the strong absorption of these wavelengths in air, and in case of 157 nm the vacuum-processing environment is required. This results in high processing costs, especially if patterning is carried out for large size wafers.

#Applying a laser-based patterning technology in combination with a special low- or anti-reflection layer deposited on top of the workpiece dramatically enhances the coupling of the laser beam with the processed surface of the workpiece. This results in a large reduction of the requirement for the level of the laser fluence. A method that makes possible laser patterning of conductive metal electrode deposited on top of an organic material without significant ablation of the organic material is based on the application of a thin layer of an inexpensive anti- (or low) reflector deposited on top of the desired metal electrode. In case of a XeCl excimer laser that operates at λ=308 nm (EXeCl=4.02 eV), this can be achieved with a thin layer of Ag (silver) as an anti-reflector on top of an electrode layer of aluminum. FIGS. 1 and 2 are relationship curves between reflectivity coefficient and energy of laser beam at wavelength of λ=308 nm. As seen in the figures, for such wavelength, silver's reflectivity coefficient is about R=0.08, which compares with R=0.92 for Al (aluminum). Al is a material which is frequently used as a cathode for passive matrix organic devices. Other materials with large difference in reflectivity to a specific wavelength of a laser beam can be used for this purpose, provided other characteristics are favourable, e.g., electrical conductivity, resistivity, ease of applying coatings, etc.