Ultrathin random copolymer-grafted layers for block copolymer self-assembly

Hydroxyl-terminated P(S-r-MMA) random copolymers (RCPs) with molecular weights (Mn) from 1700 to 69000 and a styrene unit fraction of approximately 61% were grafted onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder-forming PS-b-PMMA block copolymer (BCP) thin films. When the thickness (H) of the grafted layer is greater than 5-6 nm, a perpendicular orientation is always observed because of the efficient decoupling of the BCP film from the polar SiO2 surface. Conversely, if H is less than 5 nm, the critical thickness of the grafted layer, which allows the neutralization of the substrate and promotion of the perpendicular orientation of the nanodomains in the BCP film, is found to depend on the Mn of the RCP. In particular, when Mn = 1700, a 2.0 nm thick grafted layer is sufficient to promote the perpendicular orientation of the PMMA cylinders in the PS-b-PMMA BCP film. A proximity shielding mechanism of the BCP molecules from the polar substrate surface, driven by chain stretching of the grafted RCP molecules, is proposed

Self-Assembly of Cylinder-Forming Block Copolymers by Means of High-Temperature Thermal Treatments

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 reduced size. Self-Assembly of Block copolymers is extremely appealing due to its excellent compatibility with conventional photolithographic processes, high-resolution patterns and low process costs. This thesis work will focus on the Self-Assembly of cylinderforming Block copolymers as promising next-generation technology for the fabrication of sub-20 nm structures. Two different BCPs were investigated: polystyrene-b- polymethylmethacrylate (PSb-PMMA) and Polystyrene-block- poly(dimethylsiloxane-random-vinylmethylsiloxane) (PS-b-P(DMS-r-VMS))

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

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

Molar Mass and Composition Effects on the Thermal Stability of Functional P(S-r-MMA) Random Copolymers for Nanolithographic Applications

The thermal stability of P(S-r-MMA) random copolymers for BCP-based nanolithography is discussed with reference to molar mass and composition.</p

GISAXS Analysis of the In-Depth Morphology of Thick PS-b-PMMA Films

The morphological evolution of cylinder-forming poly(styrene)-b-poly(methyl methacrylate) block copolymer (BCP) thick films treated at high temperatures in the rapid thermal processing (RTP) machine was monitored by means of in-depth grazing-incidence small-angle X-ray scattering (GISAXS). The use of this nondisruptive technique allowed one to reveal the formation of buried layers composed of both parallel- and perpendicular-oriented cylinders as a function of the film thickness (24 ≤ h ≤ 840 nm) and annealing time (0 ≤ t ≤ 900 s). Three distinct behaviors were observed depending on the film thickness. Up to h ≤ 160 nm, a homogeneous film consisting of perpendicular-oriented cylinders is observed. When h is between 160 and 700 nm, a decoupling process between both the air-BCP and substrate-BCP interfaces takes place, leading to the formation of mixed orientations (parallel and perpendicular) of the cylinders. Finally, for h > 700 nm, the two interfaces are completely decoupled, and the formation of a superficial layer of about 50 nm composed of perpendicular cylinders is observed. Furthermore, the through-film morphology affects the nanodomain long-range order, which substantially decreases in correspondence with the beginning of the decoupling process. When the thick samples are exposed to longer thermal treatments, an increase in the long-range order of the nanodomains occurs, without any sensible variation of the thickness of the superficial layer

Effect of Entrapped Solvent on the Evolution of Lateral Order in Self-Assembled P(S-r-MMA)/PS-b-PMMA Systems with Different Thicknesses

Block copolymers (BCPs) are emerging as a cost-effective nanofabrication tool to complement conventional optical lithography because they self-assemble in highly ordered polymeric templates with well-defined sub-20-nm periodic features. In this context, cylinder-forming polystyrene-block-poly(methyl methacrylate) BCPs are revealed as an interesting material of choice because the orientation of the nanostructures with respect to the underlying substrate can be effectively controlled by a poly(styrene-random-methyl methacrylate) random copolymer (RCP) brush layer grafted to the substrate prior to BCP deposition. In this work, we investigate the self-assembly process and lateral order evolution in RCP + BCP systems consisting of cylinder-forming PS-b-PMMA (67 kg mol(-1), PS fraction of 3c70%) films with thicknesses of 30, 70, 100, and 130 nm deposited on RCP brush layers having thicknesses ranging from 2 to 20 nm. The self-assembly process is promoted by a rapid thermal processing machine operating at 250 \ub0C for 300 s. The level of lateral order is determined by measuring the correlation length (\u3be) in the self-assembled BCP films. Moreover, the amount of solvent (\u3a6) retained in the RCP + BCP systems is measured as a function of the thicknesses of the RCP and BCP layers, respectively. In the 30-nm-thick BCP films, an increase in \u3a6 as a function of the thickness of the RCP brush layer significantly affects the self-assembly kinetics and the final extent of the lateral order in the BCP films. Conversely, no significant variations of \u3be are observed in the 70-, 100-, and 130-nm-thick BCP films with increasing \u3a6

Characterization of ultra-thin polymeric films by Gas chromatography-Mass spectrometry hyphenated to thermogravimetry

Polymeric materials are widely employed to build up tunable nanomasks for nano-patterning technologies. Ultrathin polymer layers are involved in this process. A Thermo Gravimetric Analysis-Mass Spectrometry (TGA-GC-MS) method was optimised, validated and successfully applied to investigate the thermal behavior of ultrathin poly(styrene-r-methylmethacrylate) random copolymer layers P(S-r-MMA) grafted to a silicon wafer surface. The interface between TGA and MS is highly versatile since many instrumental parameters (i.e. loop volumes, pulsed sampling frequencies, acquisition modalities, carrier gases, flow rates) can be easily tuned. Samples featuring substantial scale difference, i.e. bulk materials, thick films (few μm thickness), thin and ultrathin films (few nm thickness) can be analyzed without any instrumental modification or sample pretreatments. The TGA-GC-MS analysis was used to highlight subtle differences in samples featuring different thicknesses, in the 2-6 nm range, and subjected to various thermal treatments, thus indicating that this hyphenated technique could be successfully applied to the investigation of ultrathin polymer films

Composition of ultrathin binary polymer brushes by thermogravimetry-gas chromatography-mass spectrometry

In the present paper, a reliable and rugged thermogravimetry-gas chromatography-mass spectrometry (TGA-GC-MS) method was developed to determine the composition of ultrathin films consisting of binary blends of functional polystyrene (PS) and polymethylmethacrylate (PMMA) grafted to a silicon wafer. A general methodology will be given to address the composition determination problem for binary or even multicomponent polymer brush systems using the PS/PMMA-based samples as a paradigmatic example. In this respect, several distinct tailor-made materials were developed to ensure reliable calibration and validation stages. The analytical method was tested on unknown samples to follow the composition evolution in PS/PMMA brushes during the grafting reaction. A preferential grafting of the PMMA was revealed in full agreement with its preferential interaction with the SiO2 polar surface