Michele Laus

Rapid thermal processing of self-assembling block copolymer thin films

Self-assembling block copolymers generate nanostructured patterns which are useful for a wide range of applications. In this paper we demonstrate the capability to control the morphology of the self-assembling process of PS-b-PMMA diblock copolymer thin films on unpatterned surfaces by means of fast thermal treatment performed in a rapid thermal processing machine. The methodology involves the use of radiation sources in order to rapidly drive the polymeric film above the glass transition temperature. Highly ordered patterns were obtained for perpendicular-oriented cylindrical and lamellar PS-b-PMMA block copolymers in less than 60xa0s. This approach offers the unprecedented opportunity to investigate in detail the kinetics of the block copolymer self-assembly during the early stages of the process, providing a much deeper understanding of the chemical and physical phenomena governing these processes.

Flash grafting of functional random copolymers for surface neutralization

Tailoring surface energies is the key factor to control the orientation of nanoscopic structures in thin block copolymer (BCP) films. In the general frame of the “grafting to” approach, this paper reports on the use of Rapid Thermal Processing (RTP) technology to perform flash grafting reactions of a hydroxyl terminated poly(styrene-r-methylmethacrylate) random copolymer to the activated silicon wafer surface. The perpendicular orientation of the cylindrical morphology of an asymmetric PS-b-PMMA block copolymer is achieved when the thickness of the random copolymer layer is higher than 6.0 nm. The grafting time to achieve this thickness reduces from about 750 s, when the RTP grafting process is performed at 230 °C, to 15 s at 310 °C. For a symmetric PS-b-PMMA block copolymer, the perpendicularly oriented lamellar morphology is obtained when the random layer thickness is higher than 3.5 nm, that is after 60 s RTP grafting time at 250 °C. In addition, TGA-GC-MS analysis indicates that a chain structural reorganization, which occurs during the RTP treatment at high temperature, affords a more stable film structure without changing its surface characteristics. In conclusion, the RTP technology allows the “grafting to” approach to be successfully integrated into the next generation lithographic processes and affords the unprecedented opportunity to study the grafting of macromolecules on time scales and in temperature ranges that have never been explored before, shedding new light on the early stages and on the dynamics of these processes.

Bessel-like photonic nanojets from core-shell sub-wavelength spheres.

It is accepted so far that the formation of photonic nanojets requires the use of large dielectric spheres (several wavelengths in diameter). Here we show both numerically and experimentally that similar effects can be obtained with properly engineered sub-wavelength core-shell colloids. The design of the spheres is strongly inspired by a far-field approach for the generation of Bessel beams.

High Aspect Ratio PS‑b‑PMMA Block Copolymer Masks for Lithographic Applications

The control of the self-assembly (SA) process and nanostructure orientation in diblock copolymer (DBC) thick films is a crucial technological issue. Perpendicular orientation of the nanostructures in symmetric and asymmetric poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films obtained by means of simple thermal treatments was demonstrated to occur in well-defined thickness windows featuring modest maximum values, thus resulting in low aspect ratio (h/d < 2) of the final lithographic mask. In this manuscript, the thickness window corresponding to the perpendicular orientation of the cylindrical structures in asymmetric DBC is investigated at high temperatures (190 °C ≤ T ≤ 310 °C) using a rapid thermal processing machine. A systematic study of the annealing conditions (temperature and time) of asymmetric PS-b-PMMA (Mn = 67.1, polydispersity index = 1.09) films, with thicknesses ranging from 10 to 400 nm, allowed ordered patterns, with a maximum value of orientational correlation length of 350 nm, to be obtained for film thicknesses up to 200 nm. The complete propagation of the cylindrical structures through the whole film thickness in a high aspect ratio PS template (h/d ≈ 7) is probed by lift-off process. Si nanopillars are obtained having the same lateral ordering and characteristic dimensions of the DBC lithographic mask as further confirmed by grazing-incidence small-angle X-ray scattering experiments.

Assessment of the In Vivo Antiproliferative Activity of a Novel Platinum Particulate Pharmacophore

The development of synthetic polymer drug-delivery systems is a promising strategy to improve the therapeutic index of effective but highly toxic anticancer agents, such as cisplatin, by taking advantage of the peculiar characteristics of tumor blood and lymphatic circulation, often referred to as the enhanced perme ability and retention (EPR) effect. In the present study, water-soluble, biocompatible core-shell nanospheres (ZN2) obtained from polymethylmethacrylate (PMMA), with a shell featuring positively charged quaternary ammonium groups, were used as noncovalently linked pharmacophores for the anionic platinum-containing moiety, [PtCl3NH3]- (PtA). The resulting adduct (PtA-ZN2), at the estimated maximum tolerated dose (MTD) of 25 mg Pt/kg/day for 5 consecutive days was significantly more effective than cisplatin, also at the MTD of 3.25 mg Pt/kg/day ×5, in inhibiting the growth of B16 murine melanoma in mice, in the absence of signs of general toxicity. In contrast, treatment with free PtA did not significantly affect tumor growth as compared to control mice. In vivo efficacy of the three Pt-containing species was found to correlate with Pt intratumor accumulation, as evaluated by ICP-MS following tumor tissue mineralization. PtA-ZN2 was also found to be superior to PtA in the in vitro cytotoxicity assays on cultured B16 cells (IC50 values at 5 days: 1.78 ± 0.79 |Lμg Pt/ml for PtA-ZN2 and 10.47 |Lμg Pt/ml for PtA), where the EPR effect is not an issue. This suggests that polymer conjugation can also enhance Pt efficacy at the single-cell level, possibly by facilitating Pt uptake; determinations of intracellular Pt levels following in vitro incubation of B16 cells with PtA and PtAZN2 and of internalization of fluorescent ZN2 nanospheres seem to support this hypothesis.

From grafting to to grafting from

The aim of this work is to obtain block copolymer brushes by a combined grafting to and grafting from approach. A new strategy was employed in which the second block re-growths starting from a homopolymer brush layer obtained by the grafting to approach. In detail, polystyrene samples with molecular weight ranging from 2.5 to 13u2005kg/mol and narrow molar mass distribution were synthesized by nitroxide-mediated-polymerization (NMP) using N-tert-butyl-N-[1-diethylphosphono(2,2-dimetylpropyl)] nitroxide (SG1/DEPN) as polymerization controller. Such polymers were grafted onto a silicon oxide surface by Rapid Thermal Processing (RTP) at different temperatures. As thermolabile groups deriving from the terminal SG1 are located at the silica surface, they could allow a synthesis of block copolymers via the grafting from approach by surface initiated NMP. Preliminary experiments of regrowth from surface were conducted with deuterated styrene and 4-vinylpyridine. The corresponding block copolymer brushes were obtained and their characteristics discussed as a function of the relevant reaction parameter.The aim of this work is to obtain block copolymer brushes by a combined grafting to and grafting from approach. A new strategy was employed in which the second block re-growths starting from a homopolymer brush layer obtained by the grafting to approach. In detail, polystyrene samples with molecular weight ranging from 2.5 to 13u2005kg/mol and narrow molar mass distribution were synthesized by nitroxide-mediated-polymerization (NMP) using N-tert-butyl-N-[1-diethylphosphono(2,2-dimetylpropyl)] nitroxide (SG1/DEPN) as polymerization controller. Such polymers were grafted onto a silicon oxide surface by Rapid Thermal Processing (RTP) at different temperatures. As thermolabile groups deriving from the terminal SG1 are located at the silica surface, they could allow a synthesis of block copolymers via the grafting from approach by surface initiated NMP. Preliminary experiments of regrowth from surface were conducted with deuterated styrene and 4-vinylpyridine. The corresponding block copolymer brushes were obtaine...

Deterministic doping via self-limited grafting of phosphorus end-terminated polymers

Phosphorus terminated polystyrene polymers with molar mass ranging from 2 to 25u2005kg/mol and narrow molar mass distribution were synthesized by Atom Transfer Radical Polymerization (ATRP) followed by phosphorylation reaction. Polymers were grafted onto a native silicon oxide surfaces of a silicon wafers by Rapid Thermal Processing (RTP). The self-limiting nature of the grafting to reaction provides an accurate control of the surface density of P atoms as a function of the molar mass of the polymer grafted. After removing the polymeric part of the grafted layer with by O2 plasma hashing, the phosphorus diffusion in the silicon substrate was promoted by high temperature thermal treatments.Phosphorus terminated polystyrene polymers with molar mass ranging from 2 to 25u2005kg/mol and narrow molar mass distribution were synthesized by Atom Transfer Radical Polymerization (ATRP) followed by phosphorylation reaction. Polymers were grafted onto a native silicon oxide surfaces of a silicon wafers by Rapid Thermal Processing (RTP). The self-limiting nature of the grafting to reaction provides an accurate control of the surface density of P atoms as a function of the molar mass of the polymer grafted. After removing the polymeric part of the grafted layer with by O2 plasma hashing, the phosphorus diffusion in the silicon substrate was promoted by high temperature thermal treatments.

Boron-terminated polystyrene as potential spin-on dopant for microelectronic applications

Boron-terminated polystyrene with molecular weight ranging from 1800 to 18000u2005g/mol were synthesized for p-type doping of silicon substrates through spin-on technique. Several polymers were prepared using the ARGET-ATRP method using tert-butyl 2-bromoisobutyrate as initiator, changing monomer to initiator ratio and the reaction time. After polymerization, polystyrene samples were functionalized in order to end-cap the chains with a boron-containing molecule. Various polymers were characterized by SEC, to estimate Mn, Mw and PDI, by NMR (1H and 13C) in order to investigate the correct structure of the molecules and by TGA-GC-MS for knowing the thermal behavior and the amount of boron into the polymers.

Analysis of phosphorus-end capped functionalpolymers, from bulk to ultrathin films

A fully calibrated and validated TGA-GC–MS is proposed for the quantitative analysis of diethylphosphate- end capped polymers. It allows the determination of the amount of phosphorous in polymeric samples and also thedetermination of the number of repeating units per chain end. Since no sample pretreatments are required polymeric films supported on inert substrates can be directly analyzed even in ultrathinfilms with thickness of few tens of nanometers. Finally, the chromatographic profile of the species evolving during the thermal degradation depend on the polymeric film thickness allowing that information concerning the polymer stability anddegradation mechanism at different size scale can be obtained. Considering the widespread interest for thin and ultrathin films of polymers containing phosphorous groupsfor brush-based technologies, the proposed method can be helpful in various areas, including flame retardantmaterial, healthcare and medicine, microelectronic, for facile and precise characterization ...

Technological strategies for self-assembly of PS-b-PDMS in cylindrical sub-10 nm nanostructures for lithographic applications

Abstract The continuous demand for small portable electronics is pushing the semiconductor industry to develop novel lithographic methods to fabricate the elementary structures for microelectronics devices with dimensions below 10 nm. Top-down strategies include multiple patterning photolithography, extreme ultraviolet lithography (EUVL), electron beam lithography (EBL), and nanoimprint lithography. Bottom-up approaches mainly rely on block copolymers (BCPs) self-assembly (SA). SA of BCPs is extremely appealing due to its excellent compatibility with conventional photolithographic processes, high-resolution patterns, and low process costs. Among the various BCPs, the polystyrene-b-polydimethylsiloxane (PS-b-PDMS) represents the most investigated material for the fabrication of sub-10 nm structures. However, PS-b-PDMS cannot be easily processed by conventional thermal treatments due to its slow SA kinetic coupled with a relatively low thermal stability. This review focuses on the available annealing methods to promote the SA PS-b-PDMS in parallel-oriented cylindrical sub-10 nm structures. Moreover, literature data regarding the annealing time, defects density, line edge roughness (LER) and line width roughness ( LWR) are discussed with reference to the stringent requirements of semiconductor technology.