Yu-Chih Tseng

Nanoscopic Patterned Materials with Tunable Dimensions via Atomic Layer Deposition on Block Copolymers

Selective self-limited interaction of metal precursors with self-assembled block copolymer substrates, combined with the unique molecular-level management of reactions enabled by the atomic layer deposition process, is presented as a promising controllable way to synthesize patterned nanomaterials (e.g., Al{sub 2}O{sub 3} see Figure, TiO{sub 2}, etc.) with uniform and tunable dimensions.

A route to nanoscopic materials via sequential infiltration synthesis on block copolymer templates.

Sequential infiltration synthesis (SIS), combining stepwise molecular assembly reactions with self-assembled block copolymer (BCP) substrates, provides a new strategy to pattern nanoscopic materials in a controllable way. The selective reaction of a metal precursor with one of the pristine BCP domains is the key step in the SIS process. Here we present a straightforward strategy to selectively modify self-assembled polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) BCP thin films to enable the SIS of a variety of materials including SiO(2), ZnO, and W. The selective and controlled interaction of trimethyl aluminum with carbonyl groups in the PMMA polymer domains generates Al-CH(3)/Al-OH sites inside the BCP scaffold which can seed the subsequent growth of a diverse range of materials without requiring complex block copolymer design and synthesis.

Enhanced lithographic imaging layer meets semiconductor manufacturing specification a decade early.

IO N Lithography followed by plasma etching is the standard method for manufacturing microelectronics. Requirements on lateral resolution and vertical dimensions translate into signifi cant engineering challenges for the lithographic imaging layer (resist). The resist needs to have high resolution, little line-edge roughness, high resistance to plasma etching, and signifi cant mechanical stiffness to prevent pattern collapse during wet development. Presently, no resist material satisfi es all these requirements simultaneously. We show that many of the qualities of an ideal resist layer can be achieved by improving plasma etch resistance of poly(methyl methacrylate) (PMMA). PMMA treated with aluminum oxide sequential infi ltration synthesis (SIS) allows dense high-resolution (sub-20 nm) patterns to be defi ned and transferred deeply into silicon without an intermediate hard mask. The improved etch resistance of the SISPMMA also allows the aspect-ratio of the resist structures to be decreased below the limit of wet collapse, thereby meeting the requirements of the International Technology Roadmap for Semiconductors up to year 2022. Lithography and plasma etching form the cornerstones of nanoscale manufacturing. Initially developed for the microelectronics industry, these techniques are also essential to other technologies, such as micro-electro-mechanical and microfl uidic systems. Indeed, the physical realization of any system with nanoscale components requires a certain degree of topdown patterning. In lithography, an imaging layer (resist) sensitive to light or electrons is exposed to the image of a fi ne pattern and developed in wet chemicals. Plasma etching is then used to transfer the pattern in the imaging layer to a material of interest. These procedures are then repeated many times to complete a functional system. Central to the success of these top-down manufacturing methods is the ability of the imaging layer to capture fi ne features with high fi delity. In addition, the imaging layer needs to play the role of etch mask. It needs to be resistant to plasma etching to allow pattern transfer into the underlying material. The imaging layer, however, is usually carbon-based and has little resistance to plasma etching. This non-ideality is

Enhanced polymeric lithography resists via sequential infiltration synthesis

Etch resistance of two commonly used lithography resists is increased significantly by sequential infiltration synthesis (SIS). Exposing films to trimethyl-aluminum and water with long dosage times infiltrates the bulk of the film with alumina, which renders them dramatically more resistant to plasma etching with no degradation to the patterns. Enhanced etch resistance eliminates the need for an intermediate hard mask and the concomitant costs and pattern fidelity losses. Moreover, by allowing for thinner resist films, this approach can improve the final pattern resolution.

Etch properties of resists modified by sequential infiltration synthesis

The etch resistance of electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and ZEP520A, is increased significantly by sequential infiltration synthesis (SIS). This process infiltrates the bulk of the resist film with alumina, rendering it resistant to plasma etching. The enhanced etch resistance eliminates the need for an intermediate hard mask and the associated process costs and pattern fidelity losses. Furthermore, the improvement is realized with no degradation to the line-edge roughness of lithographically defined patterns. The enhancement in etch resistance is especially strong at the edges of the printed lines, owing to diffusion of the SIS precursors from the resist sidewalls. These improvements enable the anisotropic transfer of sub-100 nm patterns deeply into silicon without the need for an intermediate hard mask.

Making complex nanomaterials with molecular stencils

Nanomaterials can impact innumerable applications ranging from high-performance composites to energy-conversion technologies. The challenge lies in finding ways of efficiently fabricating these nanomaterials. One approach consists of starting with a large object and carefully removing material until the required structure is obtained. But as features become smaller, this approach becomes prohibitively slow or expensive. Alternatively, we can work from the bottom up using building blocks to assemble—or ideally self-assemble—the desired nanostructure. This method can be powerful but, in many cases, the most effective self-assembly materials do not have the properties desired for target applications, such as magnetic or metallic behavior. Many different approaches to making nanomaterials have been demonstrated. These include lithographic techniques such as electron beam lithography and nanoimprint lithography,1 as well as bottom-up techniques such as DNA origami2 and block copolymer self-assembly.3 In many cases, however, these approaches are either costly or do not exhibit functional properties of interest. Electron beam lithography, for example, is serial in nature, meaning that each piece of the pattern is written one at a time. This makes the process slow and, therefore,