Laser Fabrication of Sharp Conical Microstructures on Si Thin Films by Nd:YAG Laser Single Pulse Irradiation
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Laser Fabrication of Sharp Conical Microstructures on Si Thin Films by Nd:YAG Laser Single Pulse Irradiation Joe Moening, and Daniel Georgiev University of Toledo, Department of Electrical Engineering and Computer Science, Mail Stop 308, Toledo, OH, 43606 ABSTRACT Conical microstructures with nanoscale sharpness form on silicon films as a result of single-pulse, localized UV irradiation using a solid-state, Q-switched Nd:YAG laser. Projection imaging of pinhole apertures was employed to obtain micron-sized irradiation spots on the surface of silicon-on-insulator samples. The formation of these structures requires melting of the silicon film and was followed at different laser fluence levels and irradiation spot sizes. Atomic force microscopy (AFM) was used to characterize the structures. After fabricating small arrays of such micro-cones, the silicon top layer was selectively etched away in order to understand the role of the underlying silicon oxide. AFM images of such etched samples revealed that the topography of the oxide material below the cones had been significantly modified: bumps with heights that represent a significant fraction of the original Si cone height have formed. This suggests that substrate melting plays an important role in the mechanism of formation of the silicon cones. INTRODUCTION Reliable, simple and low-cost techniques for fabrication of sharp micro- and nanotips of silicon and other semiconductor and metal materials, as well as large, high-density arrays of such tips, are desirable in technological applications. Such applications include emitters for fieldemission-based devices such as high-definition displays [1,2] and other vacuum microelectronics devices and systems [3], probes for scanning probe microscopy techniques, and novel designs of high-density nonvolatile phase-change memory devices . There is also a considerable amount of ongoing research on surface patterning of materials for biomedical applications [4-6], which could benefit from new developments in the area of materials surface micro- and nanostructuring. High-intensity pulsed laser radiation can be used to modify surfaces of materials and fabricate technologically desirable structures on a micrometer and sub-micrometer level. The processes involved in such radiation/matter interactions are complex and usually non-equilibrium due to high heating and cooling rates, large temperature gradients and a variety of chemical and photochemical transformations. These processes and their interplay are not well understood, and therefore systematic studies of laser irradiation of materials as a function of a certain set of parameters are essential. Laser fabrication techniques that utilize high-energy pusled lasers with large-area homogenized beam cross-sections can provide the advantages of high-resolution, high throughput, uniformity, highly localized heating, simplicity and reproducibility. In addition, combinations of laser techniques with other established technological steps could evolve into new, more flexible techn
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