The nanotechnology revolution of the past decade owes much to the science of lithography, an umbrella term which encompasses everything from conventional photolithography to “unconventional” soft lithography and the self-assembly of block polymers. In this review, some of the recent advances in lithography are summarized with special reference to the microelectronics industry. The next generation photolithography, two-photon lithography, step-and-flash imprint lithography and nanofabrication using block copolymers are covered, in an attempt to describe more recent work in this vibrant and active field of research. Copyright © 2006 John Wiley & Sons, Ltd.

Recent progress in high resolution lithography

The search for advanced, high performance, high temperature resistant polymers is on the rise in view of the growing demand for polymer matrix composites that are to meet stringent functional requirements for use in the rapidly evolving high-tech area of aerospace. Cyanate esters (CEs) form a family of new generation thermosetting resins whose performance characteristics make them attractive competitors to many current commercial polymer materials for such applications. The chemistry and technology of CEs are relatively new and continue to evolve and enthuse researchers. The CEs are gifted with many attractive physical, electrical, thermal, and processing properties required of an ideal matrix resin. These properties are further tunable through backbone structure and by blending with other polymer systems. The structure-property correlation is quite well established. Several new monomers have been reported while some are commercially available. The synthesis of new monomers has come to a stage of stagnation and the present attention is on evolving new formulations and processing techniques. The blends with epoxy and bismaleimide have attracted a lot of research attention and achieved commercial success. While the latter is now known to form an IPN, the reaction mechanism with epoxy is still intriguing. Extensive research in blending with conventional and high performance thermoplastics has led to the generation of key information on morphological features and toughening mechanisms, to the extent that even simulation of morphology and property has now become possible. Despite the fact that the resin and its technology are nearly two decades old, the fundamental aspects related to curing, cure kinetics, reaction modeling, etc. still evince immense research interest and new hypotheses continue to emerge.

Cyanate Ester Resins, Recent Developments

We report the self-assembly of organic-inorganic block copolymers (BCP) in thin-films by simple solvent annealing on unmodified substrates. The resulting vertically oriented lamellae and cylinders are converted to a hard silica mask by a single step highly selective oxygen plasma etching. The size of the resulting nanostructures in the case of cylinders is less than 10 nm.

One‐Step Direct‐Patterning Template Utilizing Self‐Assembly of POSS‐Containing Block Copolymers

Silicate nanorods (attapulgite, ATT) were organically modified and homogeneously dispersed in a cyanate ester (CE) resin. ATT dispersions and networks were characterized by rheological and microscopic measurements. Amine groups grafted onto the particle surface catalyzed the cyclotrimerization of the CE monomers and enabled the CE monomers to enter the inter-rod spacing of loose aggregates easily, resulting in homogenization of the particle size distribution in the nanocomposites. The addition of nanorods decreased the density of organic networks and increased intracyclizations. Covalent bonding at the interface was confirmed by Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA), which establishes a basis for enhancing/ optimizing mechanical properties of CE resins. Nanocomposite modulus, strength, and toughness increased 40, 42, and 55%, respectively, relative to the neat resin, although high nanorod loadings (e.g., 8 wt %) showed negligible benefit. The interplay between nanorod and resin networks governed the mechanical properties of the nanocomposites. The curing reaction decreased the size of particle aggregates and thus reduced the percolation threshold of particle networks. Particle networks induced the formation of more linear or branching polymer molecular structures, resulting in weaker particle-matrix interactions. These factors reduced the stress transfer efficiency and crack propagation resistance, impairing the extent of reinforcing at high particle loadings.

Hybrid Network Structure and Mechanical Properties of Rodlike Silicate/Cyanate Ester Nanocomposites

PROBLEM TO BE SOLVED: To provide a positive resist material using a high molecular compound suitable for a base resin of a chemically amplified positive resist material, and to provide a pattern forming method. SOLUTION: In the positive resist material, a resin formed by substituting a hydrogen atom in a carboxyl group with an acid-labile group shown by a general formula (1) is used as the base resin. In the general formula (1), R 1 , R 2 are an alkyl group, an alkoxy group, an alkanoyl group, an alkoxycarbonyl group, a hydroxy group, an aryl group, a halogen atom or a cyano group; R is a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group or an aryl group; m, n are an integer of 1-4, respectively, and G is a methylene group, an ethylene group, a vinylene group or -CH 2 -S-. The positive resist material is extremely high in alkaline dissolution rate contrast before and after exposure, has a high resolution, and is excellent in pattern shape and edge roughness after exposure, suppressed in acid diffusion velocity, and exhibits excellent etching resistance. COPYRIGHT: (C)2011,JPO&INPIT

Positive resist material and pattern forming method using the same

Toughening of cyanate ester resins with cyanated polysulfones

A novel molecular resist material based on polyhedral oligomeric silsesquioxane, possessing diazoketo groups, was successfully synthesized for deep UV lithography. The initial lithographic evaluation of the molecular resist shows the potential of the new platform for the next generation resists.

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Photobleachable silicon-containing molecular resist for deep UV lithography

Synthesis and lithographic evaluation of poly[(methacrylic acid tert-butyl cholate ester)-co-(γ-butyrolactone-2-yl methacrylate)]

Negative working nanomolecular resists based on fully epoxy-protected tetra-Cmethylcalix[4]resorcinarene (epoxy C-4-R) and oxetanyl-protected tetra-methylcalix[4]resocinarene (oxetanyl C-4-R) have been developed. They were prepared by the reaction of C-4-R with epichlorohydrin or in the presence of trimethylamine. They can be coated on the silicon wafer by spin-coating method. A clear film cast from a 20 wt% epoxy C-4-R solution in chloroform showed high transparency to UV above 300 nm. A fine negative image featuring 0.8 μm of minimum line and space patterns was observed on the film of the photoresist exposed to 40 mJ/ cm2 of Near UV-light by the contact mode.

Negative nanomolecular resists based on Calix[4]resorcinarene

To satisfy the upcoming demand of next generation lithography, new chemically amplified resist materials should be developed that can perform at the limit where the image feature size is on the order of molecular dimensions. Amorphous low-molecular-weight materials have several advantages over conventional polymeric systems. First, the limit of resolution can be enhanced since the building block of the image feature shrinks to the small molecule. Second, nanomolecular materials do not have chain entanglement due to the short chain length. Third, resist molecules that are free of intermolecular chain entanglement may decrease line edge roughness at very small feature sizes. Fourth, they can be coated on the silicon substrate by spin coating method because of their amorphous properties. Herein we studied several nanomolecular resists for 193-nm lithography. Adamantane was used as a core and two cholate derivatives were attached to adamantane.

Tae-Hwan Oh

Papers

Toughening of cyanate ester resins with cyanated polysulfones

Photobleachable silicon-containing molecular resist for deep UV lithography

Synthesis and lithographic evaluation of poly[(methacrylic acid tert-butyl cholate ester)-co-(γ-butyrolactone-2-yl methacrylate)]

Negative nanomolecular resists based on Calix[4]resorcinarene

Nanomolecular resists with adamantane core for 193-nm lithography