Luciana Meli

Aggregation and Coarsening of Ligand-Stabilized Gold Nanoparticles in Poly(methyl methacrylate) Thin Films

Dodecanethiol-stabilized gold nanoparticles (5 nm diameter) are shown to self-organize to form a two-dimensional hexagonal structure in poly(methyl methacrylate) films upon spin-casting from solution onto a substrate, using high-angle annular dark-field scanning transmission electron microscopy. Through use of the distribution functions describing particle distributions, we show that the particle coarsening dynamics is self-similar, characterized by two distinct growth stages. During the initial stage, coarsening occurs via simultaneous Ostwald ripening and coalescence mechanisms, whereas during the second stage, the dominant coarsening mechanism is coalescence.

Control of the entropic interactions and phase behavior of athermal nanoparticle/homopolymer thin film mixtures

It is shown that the phase behavior of an athermal thin film nanoparticle/polymer hybrid material of polystyrene (PS) with PS-grafted gold nanoparticles is readily tailored through control of the degrees of polymerization, N and P, of the grafted and the free chains, respectively, and the relative size of the nanoparticle to the average dimensions of both the grafted and the host chains. Complete miscibility or a surface-induced phase transition, leading to segregation of the particles to an interface, is readily achieved in this system.

Glass transition of polymer-nanocrystal thin film mixtures: Role of entropically directed forces on nanocrystal distribution

The connection between the average properties of a polymer/nanocrystal hybrid material and the nanocrystal spatial distribution is shown. Specifically, a property such as the glass transition temperature, Tg, is shown to vary by as much as 65 degrees C through only changes in the spatial distribution of the nanocrystals. Considerable control can be exercised over the nanoparticle spatial distribution. In addition, we show that while the Tg of a thin film hybrid material may be enhanced in relation to the pure bulk system, the bulk nanocomposite analog shows a reduction in Tg. These findings have broad implications with regard to the design of materials with required properties.

Study of alternate hardmasks for extreme ultraviolet patterning

Traditional patterning stacks for deep ultraviolet patterning have been based on a trilayer scheme with an organic planarizing layer, silicon antireflective coating or organic bottom antireflective coating, and photoresist. At an extreme ultraviolet (EUV) wavelength, there is no longer a need for reflectivity control. This offers an opportunity to look at different types of underlayers for patterning at sub-36 nm pitch length scales. An alternate hardmask can be used to develop a low aspect ratio patterning stack that can enable a larger process window at sub-36 nm pitch resolution. The hardmask layer under the resist has the potential for secondary electron generation at the resist/hardmask interface to improve resist sensitivity. This work explores EUV patterning on deposited hardmasks of various types such as silicon oxides and metal hardmasks. It also details the challenges of patterning directly on an alternate underlayer and approaches for improving patterning performance on such layers.

Successes and frontiers in extreme UV patterning

As a semiconductor patterning technique, extreme UV (EUV) lithography has stood at the cusp of viability for over a decade. In this technique, simple single-level patterning is conducted at an exposure wavelength of 13.5nm. EUV lithography brings the promise of delivering the node-by-node feature scaling that is required by the semiconductor industry, but the delay in its implementation has necessitated the adoption of 193nm immersion (193i) multi-patterning techniques to deliver the same scaling, albeit at obvious extra cost and complexity. While the industry has been stuck at 193i-based patterning, the initial lithography and etch steps have remained at relatively unchanged dimensions and have used well-known (and optimized) materials. The step down to EUV-based lithography (i.e., from about 80nm pitch for 193i to about 30nm pitch) therefore brings the need for much thinner, and potentially more etch-selective, patterning materials in the trilayer lithography stack so that the dimensions and aspect ratios required for etch transfer can be achieved. In other words, to meet high-volume manufacturing (HVM) needs, a decade’s worth of industry yield learning must be revised in less than five years (see Figure 1). Over the last couple of years, the industry has made significant progress in tackling many of the main impediments to the adoption of EUV in HVM. Most notably, there have been significant improvements to exposure tool throughput, reliability, and variance control,1 as well as patterning materials with which it is possible to achieve the small dimensions required.2 In addition, we have demonstrated key aspects of EUV mask infrastructure that provide further confidence in the technology as an HVM solution.3, 4 Nevertheless, the implementation of EUV as part of the integrated patterning process is still a remaining challenge. Figure 1. Moving from 193nm immersion (193i) to extreme UV (EUV) lithography (litho) involves a large step down in aspect ratios and pitch size. The change in patterning technique also brings a number of ‘unknowns’ that are related to the materials and processes involved. Cartoons are shown to scale.