Combining directed self-assembly of block copolymers with soft lithography
Karjalainen, Hertta (2014)
Karjalainen, Hertta
2014
Teknis-luonnontieteellinen koulutusohjelma
Luonnontieteiden tiedekunta - Faculty of Natural Sciences
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Hyväksymispäivämäärä
2014-09-03
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201408271404
https://urn.fi/URN:NBN:fi:tty-201408271404
Tiivistelmä
Block copolymers (BCPs) are macromolecules consisting of two or more polymer blocks covalently joined together. These blocks may be thermodynamically incompatible, in which case the repulsive forces between the blocks initiate the formation of ordered structures at the molecular scale in dimensions of 5 – 50 nm. In thin films of block copolymers this phase separation behavior leads to nanoscale patterns of lamellae, cylinders or spheres depending on the composition and molecular weight of the block copolymer. These patterns can be guided by lithographically predefined structures that can be either topographic relief structures or chemically differentiated surface regions.
One application of BCPs in microfabrication is to combine block copolymer self-assembly with soft lithographic methods by using a block copolymer template as a master to fabricate an elastomeric stamp that can be used to transfer nanoscale patterns onto substrates. This stamp would have a high resolution pattern in dimensions unachievable by traditional lithographic methods that have commonly been used in stamp fabrication for soft lithography. Microcontact printing is one of the soft litho-graphic techniques in which the stamp is used to transfer monolayers of molecules onto a substrate. Using a stamp with nanoscale patterns to microcontact print a self-assembled monolayer (SAM) opens interesting prospects for arranging nanoparticles, such as quantum dots, in ordered manner on top of this SAM.
In this Thesis polystyrene-block-polymethyl metacrylate (PS-b-PMMA) block copolymer was used to fabricate PMMA cylinders in PS matrix ordered perpendicular to the supporting silicon substrates. Nanohole patterns of ~25 nm diameter were obtained after selective etching of the PMMA. It was found, that adding a thin silica layer on top of silicon substrates enhanced the quality of BCP assembly remarkably. Directed assembly of block copolymer domains on topographically pre-patterned substrates with various pattern shapes and dimensions was investigated. Nearly defect free assembly of PMMA cylinders in topographically defined trench patterns was obtained but the as-sembly in smaller square patterns was still found inadequate. Different dry etching methods for the BCP pattern transfer into the underlying substrates were tested and, consequently, the etching with CHF3/O2 plasmas was concluded to be the best etching recipe. The masters obtained were used to fabricate elastomeric h-PDMS stamps for microcontact printing. It was noted that the height of the patterns in the stamps is too low resulting from either too low etching of the masters or poor adjustment of the stamp material to the pattern. When investigating the microcontact printing with (3-Mercaptopropyl)trimethoxysilane (MPTMS) alkoxythiolate, the attachment of the mon-olayer with unpatterned stamp was confirmed by fluorescence lifetime microscopy but the stamping with patterned stamps still has to be developed further.
One application of BCPs in microfabrication is to combine block copolymer self-assembly with soft lithographic methods by using a block copolymer template as a master to fabricate an elastomeric stamp that can be used to transfer nanoscale patterns onto substrates. This stamp would have a high resolution pattern in dimensions unachievable by traditional lithographic methods that have commonly been used in stamp fabrication for soft lithography. Microcontact printing is one of the soft litho-graphic techniques in which the stamp is used to transfer monolayers of molecules onto a substrate. Using a stamp with nanoscale patterns to microcontact print a self-assembled monolayer (SAM) opens interesting prospects for arranging nanoparticles, such as quantum dots, in ordered manner on top of this SAM.
In this Thesis polystyrene-block-polymethyl metacrylate (PS-b-PMMA) block copolymer was used to fabricate PMMA cylinders in PS matrix ordered perpendicular to the supporting silicon substrates. Nanohole patterns of ~25 nm diameter were obtained after selective etching of the PMMA. It was found, that adding a thin silica layer on top of silicon substrates enhanced the quality of BCP assembly remarkably. Directed assembly of block copolymer domains on topographically pre-patterned substrates with various pattern shapes and dimensions was investigated. Nearly defect free assembly of PMMA cylinders in topographically defined trench patterns was obtained but the as-sembly in smaller square patterns was still found inadequate. Different dry etching methods for the BCP pattern transfer into the underlying substrates were tested and, consequently, the etching with CHF3/O2 plasmas was concluded to be the best etching recipe. The masters obtained were used to fabricate elastomeric h-PDMS stamps for microcontact printing. It was noted that the height of the patterns in the stamps is too low resulting from either too low etching of the masters or poor adjustment of the stamp material to the pattern. When investigating the microcontact printing with (3-Mercaptopropyl)trimethoxysilane (MPTMS) alkoxythiolate, the attachment of the mon-olayer with unpatterned stamp was confirmed by fluorescence lifetime microscopy but the stamping with patterned stamps still has to be developed further.