Microstructures can be realized without adhesive masks, when a pattern transfer from an external source is directly coupled with a local ablation or the removal of a functional material. Therefore, high energies have to be applied locally on the substrate surface, which is not really possible for larger areas. The primary limitation is not the power of the external source, but rather problems with both energy dissipation and the chemical temperature plus the stability ofthe shape ofthe substrate. These disadvantages usually exclude group transfer processes from maskless structure generation.
A simple implementation for maskless techniques is a local removal process induced by an intensive beam of either laser, electrons, ions or nanoparticles. Because a local removal of material requires high power densities, focused beams are preferred. A suitable process is the direct-writing lithographic technique in a serial approach. The removal usually occurs as a result ofa combination ofmechanical impulse transfer and local thermal effects. Specific chemical processes play only a minor role. As the diameter of the probe and the lateral radius of its expansion determine the resolution of direct writing procedures, use of such procedures with particle beams can be utilized for the fabrication of nanostructures. For light-optical procedures, e. g., by the use of lasers, application is limited to the micrometer and sub-micrometer range.
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