Advancements in optical lithography tools, processes, and patterning materials have been critical to the continued performance increases of semiconductor devices as well as to the overall economics of the semiconductor industry.1 Reducing the wavelength of the source radiation has been a traditional pathway to increase resolution in optical lithography.1-3 In recent years, the technological challenges and the soaring costs associated with developing new exposure tools and new imaging materials have slowed the progress of wavelength scaling, evidenced by the decision not to commercialize 157 nm (F2 excimer) lithography in 2004.4 Rather than reducing the vacuum wavelength of the illumination, the semiconductor industry instead turned to scaling the effective wavelength via immersion lithography to extend the resolution capabilities of 193 nm lithography. Immersion lithography, which utilizes a coupling medium with a refractive index greater than that of air between the last lens element (LLE) and the photoresist, provides an increased depth-of-focus (DOF) and enables imaging systems with numerical apertures greater than one.5-13 This approach is economically attractive since it continues to use large amounts of the existing lithographic tooling infrastructure and patterning materials. In particular, the rapid development and commercialization of 193 nm water immersion lithography helped seal the fate of 157 nm lithography.

Advances in patterning materials for 193 nm immersion lithography.

Over the past three decades, the combination of inorganic-nanoparticles and organic-polymers has led to a wide variety of advanced materials, including polymer nanocomposites (PNCs). Recently, synthetic innovations for attaching polymers to nanoparticles to create “hairy nanoparticles” (HNPs) has expanded opportunities in this field. In addition to nanoparticle compatibilization for traditional particle–matrix blending, neat-HNPs afford one-component hybrids, both in composition and properties, which avoids issues of mixing that plague traditional PNCs. Continuous improvements in purity, scalability, and theoretical foundations of structure–performance relationships are critical to achieving design control of neat-HNPs necessary for future applications, ranging from optical, energy, and sensor devices to lubricants, green-bodies, and structures.

Hairy nanoparticle assemblies as one-component functional polymer nanocomposites: opportunities and challenges

Electrospinning: A versatile technique for making of 1D growth of nanostructured nanofibers and its applications: an experimental approach

Low toxicity of HfO2, SiO2, Al2O3 and CeO2 nanoparticles to the yeast, Saccharomyces cerevisiae

Photolithographic properties of tin-oxo clusters using extreme ultraviolet light (13.5 nm)

HfO2 nanoparticles stabilized with selected ligands possess high refractive index and low absorbance under 193 nm radiation. These materials combined with an appropriate photopolymer were used as a nanocomposite photoresist. The resulting nanocomposite materials were used successfully for high resolution patterning.

High refractive index and high transparency HfO2 nanocomposites for next generation lithography

The trend of ever decreasing feature sizes in subsequent lithography generations is paralleled by the need to reduce resist
thickness to prevent pattern collapse. Thinner films limit the ability to transfer the pattern to the substrate during etch
steps, obviating the need for a hardmask layer and thus increasing processing costs. For the 22 nm node, the critical
aspect ratio will be less than 2:1, meaning 40-45 nm thick resists will be commonplace. To address this problem, we
have developed new inorganic nanocomposite photoresists with significantly higher etch resistance than the usual
polymer-based photoresists. Hafnium oxide nanoparticles are used as a core to build the inorganic nanocomposite into an
imageable photoresist. During the sol-gel processing of nanoparticles, a variety of organic ligands can be used to control
the surface chemistry of the final product. The different ligands on the surface of the nanoparticles give them unique
properties, allowing these films to act as positive or negative tone photoresists for 193 nm or electron beam lithography.
The development of such an inorganic resist can provide several advantages to conventional chemically amplified resist
(CAR) systems. Beyond the etch resistance of the material, several other advantages exist, including improved depth of
focus (DOF) and reduced line edge roughness (LER). This work will show etch data on a material that is ~3 times more
etch-resistant than a PHOST standard. The refractive index of the resist at 193 nm is about 2.0, significantly improving
the DOF. Imaging data, including cross-sections, will be shown for 60 nm lines/spaces (l/s) for 193 nm and e-beam
lithography. Further, images and physical characteristics of the materials will be provided in both positive and negative
tones for 193 nm and e-beam lithography.

Development of an inorganic photoresist for DUV, EUV, and electron beam imaging

New organic−inorganic hybrid fibers (polyvinyl alcohol (PVA)/HfO2) were prepared by an electrospinning method using DI water as a solvent. The HfO2−acetate nanoparticles could be loaded up to 80% by weight in PVA polymer to fabricate uniform PVA/HfO2 electrospun hybrid fibers. After annealing at 140 °C for 12 h, electrospun PVA/HfO2 fibers were stable when soaked in water. Calcination of these hybrid fibers at temperatures ranging from 450 to 700 °C resulted in the formation of pure inorganic HfO2 fibers with diameters ranging from 0.1 to 0.8 μm depending on the concentration of HfO2−acetate nanoparticles in the spinning dope. Fourier transform infrared spectroscopy and Raman spectroscopy techniques were used to investigate the crystal structures of the HfO2 fibers, which were confirmed by X-ray diffraction (XRD) results. XRD results showed the presence of both monoclinic and tetragonal crystal structures in the HfO2 fibers. The type and size of the crystals formed depended on the concentration of HfO2−ac...

Properties of PVA/HfO2 Hybrid Electrospun Fibers and Calcined Inorganic HfO2 Fibers

A critical issue preventing the implementation of 193nm immersion lithography (193i) to the 32nm node is the
availability of high refractive index (n > 1.8) and low optical absorption fluids. To overcome these issues, we have
synthesized high refractive index nanoparticles and introduced them into the immersion fluid to increase the refractive
index. Hydrolysis and sol-gel methods have been implemented to grow high refractive index nanoparticles with diameters of 3-4nm. Depending on the synthetic route, it is possible to produce stable suspensions of nanoparticles in either aqueous or organic solvents, making it possible to synthesize a stable high-index immersion fluid.

Woo Jin Bae

Papers

High refractive index and high transparency HfO2 nanocomposites for next generation lithography

Development of an inorganic photoresist for DUV, EUV, and electron beam imaging

Properties of PVA/HfO2 Hybrid Electrospun Fibers and Calcined Inorganic HfO2 Fibers

High refractive index nanoparticle fluids for 193-nm immersion lithography

The use of nanocomposite materials for high refractive index immersion lithography