Mass Production of Large-Format Micro-/Nanostructure-Based Optical Devices

Abstract

The ability of micro- to nanometer-scale structure patterning on large-area flexible substrates can enable many new applications in the fields of photonics and electro-optics. Among the emerging techniques, nanoimprinting lithography (NIL) clearly stands out as a promising technology for high throughput and high resolution beyond the limitations set by light diffraction or beam scattering that are encountered in traditional techniques. The major roadblock for large-format NIL is how to obtain the imprinting mold. In this chapter, we introduce two adopted techniques to fabricate large-format master mold: interference lithography and spatial light modulator-based lithography. The former method, periodic feature size of which is about 300 nm under 405 nm semiconductor laser, can get a format with the size of 600 × 800 mm in several hours. The latter is a maskless parallel pattern technique, in which arbitrary pattern can be input from a personal computer with high resolution (~280 nm in our system). After exposure and development, the micro- and nanostructures on the photosensitive layer are transferred to metal (Ni, Cu, etc.) using a quasi-LIGA process. We call it “quasi” because not X-ray lithography but blue or UV laser source is used unlike usual LIGA. The process involves electrodeposition filling the resist mold with a metal and, after resist removal, a freestanding metal structure results. The quasi-LIGA bandwidth of possible sizes in three dimensions makes it potentially useful, not only for microstructure manufacture itself but also for the manufacture of microstructure packages. A brief introduction to NIL is followed. The obtained metal mold with surface relief structure is wrapped onto a roller as master mold. The concept of roller imprinting is being pursued by many investigators as means to increase throughput and achieve high resolution. Several types of flexible roll-to-roll nanoimprinting (UV, thermal-embossing, roll-to-roll seamless nanoimprinting lithography) are detailed discussed in this chapter. We will also investigate several key issues in R2R NIL process, such as imprinting resist, mold–sample separation, fidelity, and resolution. Finally, potential applications of our techniques are briefly reviewed.