Direct patterning processes

Direct patterning processes are extremely interesting for many aspects such as low costs, ease of fabrication, good quality, etc. and surely they will receive an even stronger attention in the next future. 

Although e-beam lithography can give excellent spatial control of functional microdomains, this direct-write patterning process is not time-efficient for large-area integration of functional devices. Techniques for rapid patterning of functional nanostructures are thus needed for real-time applications. Ober et al. [106-108] have successfully developed a novel block copolymer... 

Once the resist has been patterned, the selected regions of material not protected by photoresist are removed by specially designed etchants, creating the resonator pattern in the wafer. Several isotropic (etching occurs in all directions at the same etch rate) and anisotropic (directional) etching processes are available. Wet chemical etching is an isotropic process that... 

A recently reported alternative to spin or spray coating is screen printing of polyimide solutions (82, 85, 90). Screen printing is a low-cost, high-throughput process capable of directly patterning the polyimide films as they are deposited. Another alternative is the vapor deposition of polyimides, which was reported by researchers who co-evaporated the diamine and dianhydride monomers at stoichiometric rates (140). The evaporated films had better adhesion, a lower dielectric constant, and a lower dissipation factor compared with spin-coated polyimides. With this process, uniform, defect-free, conformal films can be cured in situ during deposition. 

As shown in Fig. 13.1, a CMP step is required in the STI process. There are two possible approaches to implementing the CMP step STI—direct and indirect. In a direct STI process, the CMP process is applied directly on a wafer right after the trench oxide deposition (Fig. 13.1). The CMP process removes the overburden oxide as well as the topography created during trench oxide deposition over the features with various pattern densities across the dies and the wafer. For some slurries, especially the conventional oxide slurries, these topographies are a challenge. To overcome this difficulty, a pre-CMP step is sometimes implemented in which a reverse mask is applied onto the film and the oxide in the raised area is preferentially etched. After the etching step, the... 

This mode of operation was primarily developed by Bard and coworkers in the early days of SECM. The direct mode is based on approaching a conducting substrate with a biased UME. The substrate acts as the auxiliary electrode, which means that if a reduction process occurs at the UME, an oxidation reaction must take place at the substrate. The latter reduction is the driving force for the patterning process. Because the whole substrate is biased, localization of the process on the substrate is caused by the distribution of the electrical field between the UME and the substrate (2). Accordingly, the resolution of the patterns chiefly depends on the distance between the UME and the substrate. Therefore, in most cases where the direct mode has been applied, care has been taken to minimize the distance between the UME and the substrate. 

On the other hand, there are many cases where the chemical or electrochemical reactions taking place on the surface are the rate-limiting steps in the patterning process. This will limit the patterning rate or will require development of other approaches whereby the whole pattern is made at the same time. At present, the common approaches used in SECM, i.e., the direct and feedback modes, cannot compete with the conventional photolithography methods. Nonetheless, future approaches such as multitip configuration may dramatically enhance the SECM capabilities in terms of speed of surface modification. 

Figure 15.13 SEM image of directly patterned cone structures (formed by redeposition processes at the lens edges following prolonged sputtering GaAs substrate) with maskless Ion projection lithography system, using 250,000 parallel 10-keV argon...

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