Directed self-assembly lithography

Chemically amplified resists are quite effective in improving pattern sizes in photofabrication. However, optical limitations in resolution must be overcome to improve further progress. Several processes contribute to improving the resolution of photofabrication. In this chapter, immersion, double-patterning, multipatterning maskless, multielectron beam, and direct self-assembly lithography processes are introduced. 

Imm Immersion,DP DoublePatteming, MP Multi Patterning, ML2 MaskLes Lithography, Imprint Nanoimprint, MEB Multi Electron Beam, DSA Direct Self Assembly... 

Direct self-assembly (DSA) pays attention to pattern formation in materials smaller than 20 nm in size. DSA does not require special equipment for patterning, which is different from immersion lithography and nanoimprint. Pattern formation is performed by microphase separation in the DSA process. DSA patterning is quite different from conventional patterning. Diblock polymers composed of hydrophilic and hydrophobic polymer units are applied for DSA materials. Diblock polymers of the A-B type, where the A block is reciprocal to the B-block, accelerate to concentrate in the same block. A diblock polymer produces self-assembly and microphase separation by formation of a sphere, cylinder, and lamellar, which are controlled by product P of the % parameter (Flory interaction parameter) and degree of polymerization N siP = Z ab)- Classical structures of phases are shown in Figure 3.20. 

Directed self-assembly shows promise in advanced lithography and a variety of other applications that have less complex requirements. For example, directed self-assembly could be used for enhancing etch selectivity, placing dopants in ordered arrays, or generating high-density, close-packed electrodes in capacitor arrays [6]. Additionally, the assembled nanostructures could be used for fabricating densely packed porous templates [12-14] or membranes [15, 16] at the nanoscale. Other potential applications of assembled block copolymer thin films include the fabrication of MOSFETs (metal-oxide-semiconductor field-effect transistors) [17], quantum dots [18], high surface area devices [19, 20], photovoltaic devices [21], and bit patterned media [22-24]. 

Gamer, C.M., Herr, D., and Krautschik, C.Directed self-assembly requirements for sub-20nm lithography, www.itrs. 

Nealey and coworkers [75,76,146] took a similar approach and applied lithographically defined self-assembled monolayers as substrates to direct the orientation of block copolymer thin films. After EUV interferometic lithography on octadecyltrichlorosilane (OTS) or phenylethyltrichlorosilane (PETS) monolayers, PS-fr-PMMA block copolymers were deposited and annealed on the substrates. Due to the selective wetting of PS and PMMA on the unexposed and exposed regions, respectively, they were able to obtain large areas of perpendicular lamella when the commensurate condition was fulfilled. 

Fig. 14 Graphoepitaxy vs epitaxial self-assembly, (a) Graphoepitaxy utilizes topographic substrate pattern for directed block copolymer assembly. The substrate pattern remains in the finally formed nanopattemed morphology, (b) Epitaxial self-assembly utilizes nanoscale chemical pattern to register block copolymer assembly. Ultrafine chemical patterning requires e-beam lithography or other high-cost lithography such as EUV. Reprinted with permission from Jeong et al. [153]. Copyright 2010 American Chemical Society...

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