Hocheng, H; Jadhav, UU; Lin, TC; Tsai, HY; Wang, KY
In recent years, intensive efforts in the development of direct surface patterning techniques for new products have taken place as a result of the convergence of different fields of science and technology. Laser methods open a way of fabrication of the low-dimensional structures, modification of the optical properties of the materials, and high precision surface processing. Such techniques are mainly used in the microelectronics industry for the creation of sensors, multifunctional microsystems, hybrid electronics and optics, interconnections between integrated circuit structures, and so on. This chapter describes both machining-based and deposition-based surface patterning using lasers. Laser machining with high intensity laser beams of varying widths is used for a variety of applications such as cutting and creating holes. Different types of materials such as metals, plastics, glass, and metal oxides can be fabricated by laser machining. Laser machining processes involve the use of conventional and fiber optic beam delivery systems, which allow precision positioning while ablating/cutting materials. They are used to cut burr-free parts that are required in a number of industries. The process is efficient and fast. It can be repeated any number of times depending on production volumes. It is also used to create grooves with a specific depth by one pass of a laser beam without severing any material from the workpiece. Laser machining is used for producing a knurled or roughened surface on hard materials such as ceramics, glass, and metals. The technology is also used for marking/patterning material surfaces by Nd:YAG, excimer, or femtosecond laser without mask. The current chapter also introduces the techniques of mask-based laser machining. A mathematical model of the ablation profile on polymer surface by excimer laser-dragging is presented as an example. The proposed model describes the machined profile as a function of the shape of the mask and the operating parameters. The profile of groove pattern obtained by single dragging and complex three-dimensional structures obtained by cross-dragging with varying mask parameters and laser operating parameters are simulated. A maskless fabrication process by deposition has been developed, on the other hand. The designed micropatterns are written on the specimen by laser guiding to build or repair microstructure rapidly rather than using the mask fabrication process requiring a long lead time. This chapter provides a review of the technique of laser-guided deposition and patterning. The most widespread metals deposited by laser methods are copper (Cu), nickel (Ni), palladium (Pd), and silver (Ag). The low electrical resistivity of the copper and its availability makes it the most attractive among the other metals for the on-chip metallization or creation of ultra-large-scale integrated devices. The choice of the substrate for the metal precipitation is mainly determined by the application domain, but the most popular for industrial use are polymers (polyimide, Mylar, Teflon) or several kinds of semiconductors and insulators such as Si, Ge, GaAs, SiO2, and so on. This chapter also presents the particular development of a micropatterning technique based on the direct laser-writing of metal tracks on silicon oxide. It demonstrates the feasibility of laser-assisted deposition of copper patterns using Thiobacillus ferrooxidans (T. ferrooxidans) culture supernatant as working medium. This is a new approach instead of chemical deposits. This laser-assisted deposited copper pattern process is a photothermal reaction in which the copper ions (Cu2+) oxidized from the substrate surface by T. ferrooxidans culture supernatant are reduced and deposited along the laser scanning trajectory on substrate. Combining the etching and the laser-guided writing through T. ferrooxidans culture supernatant reveals an innovative way of producing metallic microstructures. In the previously reported methods, the use of formaldehyde for laser deposition is necessary, which may create pollution probl ms and also may have adverse effects on living systems. The use of T. ferrooxidans culture supernatant not only overcomes this problem but also opens new paradigms in the metal deposition on the substrate surface.
