Many of today’s technological applications, such as solar cells, light-emitting diodes, displays, and touch screens, require materials that are simultaneously optically transparent and electrically conducting. Here we explore transparent conductors based on the excitation of surface plasmons in nanostructured metal films. We measure both the optical and electrical properties of films perforated with nanometer-scale features and optimize the design parameters in order to maximize optical transmission without sacrificing electrical conductivity. We demonstrate that plasmonic transparent conductors can out-perform indium tin oxide in terms of both their transparency and their conductivity.
Block copolymer thin films provide a robust method for generating regular, uniform patterns with sub-100 nanometer length scales over arbitrarily large areas. A significant advantage of such block copolymer-based patterning is its ease of integration with all other aspects of traditional thin-film processing, including plasma-based etching and metallization. Such process compatibility ensures a host of application opportunities in designing material properties through control of their nanostructure. Here, we describe our use of block copolymer self assembly for design and vapor phase synthesis of quasi one-dimensional nanostructured materials made of metals, semiconductors, and insulators. The precise control of surface texture afforded by block copolymer-based patterning can influence macroscopic materials properties such as optical reflectance and hydrophobicity.
Self-organizing block copolymer thin films hold promise as a photolithography enhancement material for the 22-nm microelectronics technology generation and beyond, primarily because of their ability to form highly uniform patterns at the relevant nm scale dimensions. Importantly, the materials are chemically similar to photoresist and can be implemented in synergy with photolithography. Beyond the challenges of achieving sufficient control of self-assembled pattern defects and feature roughness, block copolymer-based patterning requires creation of robust processes for transferring the polymer patterns into underlying electronic materials. Here, we describe research efforts in hardening block copolymer resist patterns using inorganic materials and high aspect ratio plasma etch transfer of self-assembled patterns to silicon using fluorine-based etch chemistries.
Self-organizing block copolymer thin films hold promise as a photolithography enhancement material for the 22-nm
microelectronics technology generation and beyond, primarily because of their ability to form highly uniform patterns at
the relevant nanometer-scale dimensions. Importantly, the materials are chemically similar to photoresists and can be
implemented in synergy with photolithography. Beyond the challenges of achieving sufficient control of self-assembled
pattern defectivity and feature roughness, block copolymer-based patterning requires creation of robust processes for
transferring the polymer patterns into underlying electronic materials. Here, we describe research efforts in hardening
block copolymer resist patterns using inorganic materials and high aspect ratio plasma etch transfer of self-assembled
patterns to silicon using fluorine-based etch chemistries.
We discuss fabrication processes for implementing nanometer scale confinement in an organic bulk heterojunction device architecture, including formation and integration of the confining self-assembled template. Such confinement has a beneficial influence on the electrical properties of blended poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester organic solar cell active layers. Crystallization of the blend upon annealing is inhibited by the confining template, which we understand through analysis of x-ray scattering measurements.
Material properties and directed self-assembly of a block copolymer containing hybrid material are presented in this
paper. The hybrid material, which is a mixture of poly(styrene-b-ethylene oxide) (PS-b-PEO) and organosilicate (OS),
shows morphologies of microdomains similar to those of organic diblock copolymers depending on the fraction of each
phase, i.e. PS and PEO+OS. This material system shows very strong segregation between phases, which provides well
defined microdomains in thin films even right after spin coating. The strong segregation also makes it possible to
generate microdomains of sub-10 nm length scale regime. The hybrid is found to be directed self-assembly (DSA)-
friendly, thus typical topographic and/or chemical guiding patterns can be used for DSA of the hybrid.
Self-assembling diblock copolymer thin films are an intriguing possible photolithography alternative for high-resolution patterning of advanced integrated circuit device elements. Cylindrical- and lamellar-phase materials spontaneously form patterns suggestive of contact-hole arrays and transistor gates at critical dimensions below 20nm. Besides high resolution, any serious lithographic process requires a means of pattern registration, and we discuss our efforts to develop self-aligned self assembly techniques using diblock copolymer materials. We describe the critical role of polymer surface interactions in affecting self-assembled pattern orientations. Control and design of surface properties allow precise registration of sub-20nm polymer domains to larger-scale lithographic layers.
KEYWORDS: Line edge roughness, Copper, Transistors, Atomic layer deposition, Silicon, Back end of line, Surface roughness, Tantalum, Front end of line, Plasma
Line edge roughness (LER) has been widely perceived to be one of the roadblocks to the continuing scaling of semiconductor devices. However, little evidence has been published on the impact of LER on device performance, particularly on the performance and the reliability of advanced interconnects. In this paper, we present such evidence from both the Front-End-Of-Line (FEOL) and Back-End-Of-Line (BEOL) standpoints. In the FEOL, we employed computer simulations to estimate the effects of LER on a number of performance parameters of sub-100nm transistors based on 2-dimensional and 3-dimensional device models. LER has been shown to affect both the average value and the variance of key device performance parameters for sub-100nm transistors. In the BEOL, we investigated the impact of LER on the performance of barrier layers in dual damascene copper interconnects. To this end, we emulated LER by roughening Si surfaces with controlled patterning by self-assembled diblock copolymers and reactive ion etching. In-situ time-resolved X-ray diffraction was used to study Cu diffusion through about 5nm Ta and TaN barrier layers deposited by plasma enhanced-atomic layer deposition (PE-ALD) on both smooth and rough surfaces. The X-ray diffraction results indicated that the surface roughness does not degrade barrier performance of the ALD Cu barriers. Mechanism of the roughness effects is also discussed. Line edge roughness is, however, expected to degrade copper interconnect performance by increasing copper electrical resistivity through enhanced electron surface scattering.
This paper describes the formation of nanometer-scale features in gold and silicon substrates. The features in gold were made by using a self-assembled monolayer (SAM) of nonanethiolate on gold as a resist damaged by neutral cesium atoms. A SAM resist of octyltrichlorosilane on silicon dioxide was used as a resist sensitive to cesium atoms in order to fabricate features in silicon. A silicon nitride membrane perforated with nm- and micrometers -scale holes was used to pattern the atomic beam. Etching transferred the pattern formed in the SAM layer into the underlying substrate. Features of < 100-nm size were etched into the gold and silicon substrates. Investigations of the reflectivity of samples of nonanethiolate on gold, exposed to the atomic beam without a mask and subsequently etched, revealed that the resist-etch system exhibited a minimum threshold dose of cesium for damage; at doses lower than approximately 3 monolayers, the damage was insufficient to allow penetration of the SAM by the etching solution. The threshold dose for damage of the octyltrichlorosilane SAM on silicon dioxide is under investigation.
Kent Johnson, Karl Berggren, Andrew Black, Charles Black, Arthur Chu, Nynke Dekker, D. Ralph, Joseph Thywissen, Rebecca Younkin, Mara Goff Prentiss, Michael Tinkham, George Whitesides
We describe the fabrication of approximately 70-nm structures in silicon, silicon dioxide, and gold substrates by the exposure of the substrates to a beam of metastable argon atoms in the presence of dilute vapors of trimethylpentaphenyltrisiloxane, the dominant constituent of the diffusion pump oil used in these experiments. The atoms release their internal energy upon contacting the siloxanes physisorbed on the surface of the substrate, and this release causes the formation of a predominantly carbon-based resist. To demonstrate the resolution of the resist formation process, the atomic beam was patterned by a silicon nitride membrane, and the pattern formed in the resist material was transferred to the substrates by chemical etching. Simultaneous exposure of large areas (44 cm2) was also demonstrated. The sensitivity of the resist formation to the internal energy stored in the atom allows a new pattern formation technique based on spatially dependent optical de-excitation of the metastable atoms.
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