Jae-Hak Choi

Simple micropatterning of biomolecules on a diazoketo-functionalized photoresist

A simple strategy for the patterning of cells and biomolecules including DNA and protein was developed, employing novel diazoketo-functionalized photoresists in conjunction with a simplified lithographic process that does not require photoacid generator, post-exposure bake or development steps. The diazoketo functional groups present in the polymers undergo Wolff rearrangement upon UV light irradiation to generate carboxylic groups. This chemistry was used to create patterns of alternate hydrophilic/hydrophobic regions on the surface of diazoketo-functionalized polymers. The in vitro cell culture on the patterned surfaces of the polymer showed good alignment of cells on the UV-exposed regions, where carboxylic groups were predominant. Furthermore, cells were found to maintain their alignment during proliferation. In addition to this, the photogeneration of carboxylic groups by diazoketo functional groups was exploited for DNA and streptavidin patterning. For DNA patterning, amine-modified probe DNA was successfully immobilized on the photopatterned regions of the polymer by amide bond formation using EDC/NHS coupling chemistry. Successful hybridization with complementary DNA proved the selectivity and functionality of the immobilized probe DNA. Biotin-amine was also immobilized on the photopatterned regions of the diazoketo-functionalized polymer in a similar manner to that of probe DNA to study streptavidin patterning. Biotin-specific streptavidin binding proved the successful patterning of biotin-amine by amide bond formation. These results showed that diazoketo-functionalized photoresist is biocompatible and simple to use for biomolecular patterning, which can be used in further approaches for high-throughput screening assays.

Photobleachable silicon-containing molecular resist for deep UV lithography

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.

Synthesis of poly(2-trimethylsilyl-2-propyl methacrylate) and their application as a dry-developable chemically amplified photoresist

Poly(2-trimethylsilyl-2-propyl methacrylate) was synthesized and evaluated as a potential dry-developable chemically amplified photoresist. The deprotection of 2-trimethylsilyl-2-propyl group of the polymer takes place in the exposed region after post-exposure bake. The difference of silicon content between the unexposed region and exposed regions is large enough to form patterns using oxygen reactive-ion etching. The etching selectivity of the unexposed region to the exposed region was 142.

Water-developable resists based on glyceryl methacrylate for 193-nm lithography

Novel water-developable negative resists were designed to induce both cross-linking and polarity change upon exposure and bake. The matrix polymers were synthesized by copolymerization of glyceryl methacrylate and methacrolein. The acid-catalyzed acetalization of the polymer induced cross-linking, polarity change, and increase in dry-etch resistance. The resist formulated with this polymer and cast in a water-ethanol mixture, showed 0.7 μm line and space patterns using a mercury-xenone lamp in a contact printing mode and pure water as a developer.

Acid diffusion control in chemically amplified resists

Abstract A new chemically amplified resist containing a basic monomer, 3-(t-butoxycarbonyl)-1-vinylcaprolactam, in the matrix polymer was prepared for post-exposure delay stability. Poly(3-(t-butoxycarbonyl)-1-vinylcaprolactam-co-t-butyl methacrylate) was synthesized and evaluated as a new matrix resin. The diffusion lengths of photogenerated acid in the resist films were studied for various fractions of the basic monomer in the copolymers. The results show the copolymer with a basic monomer can control the acid diffusion without a severe decrease in sensitivity. This new resist system enables us to form fine patterns and attain 2xa0h post-exposure delay stability without any additional treatment.

Nonshrinkable photoresists for ArF lithography

Outgassing from the resist causes volume shrinkage of the resist film and extensive damage to optical lenses of exposure tools. Image distortion and throughput loss can take place due to the outgassing. In this study, we designed and synthesized a new acid labile group, 7,7-dimethyloxepan-2-one, which was introduced into the matrix polymers for ArF chemically amplified resists. The 7,7-dimethyloxepan-2-one group was readily cleaved and the carboxylic acid functionality was formed by acid-catalyzed ring-opening reaction in the exposed region after post-exposure bake. The resist patterns of 0.22 μm feature size were obtained with a conventional developer using an ArF exposure tool.

Novel molecular resists based on inclusion complex of cyclodextrin

A positive working molecular photoresist based on (beta) -cyclodextrin ((beta) -CD) and its inclusion complex ((beta) -CD-IC) has been developed. Cyclodextrin is one of the most important host molecules in supramolecular systems. 1-Adamantanecarboxylic acid (Ad-COOH) is employed as a guest molecule to increase the dry etch resistance. (beta) -CD and (beta) -CD-IC were protected with t-BOC to control the dissolution rate with various feed ratios of di-t-butyl dicarbonate. The t-BOC protecting ratio turns out about 34 mol% which corresponds to the protection of primary hydroxyl groups on the upper rim of (beta) -CD. The t-BOC-protected (beta) -CD has low absorbances at 248 and 193 nm, and good film forming property. Using t-BOC-protected (beta) -CD and (beta) -CD-IC, submicron patterns were delineated when it was exposed to a KrF stepper and developed with a 2.38 wt% aqueous TMAH solution.

Bilayer resists based on polyhedral oligomeric silsesquioxane for 193-nm lithography

A novel nanomolecular resist based on POSS substituted with diazodiketo-functionalized cholate derivatives was successfully synthesized as a candidate for 193-nm lithography. The diazodiketo group was introduced into the cholate derivatives to provide the solubility change and to eliminate the problems of chemically amplified resists. The decomposition temperature of the resist was found to be 130°C. The initial lithographic studies showed the feasibility of the resist to be used as a candidate for 193-nm lithography.

Acid diffusion and evaporation in chemically amplified resists

A chemically amplified resist containing a basic monomer, 3- (t-butoxycarbonyl)-1-vinylcaprolactam (BCVC), in the matrix polymer was synthesized with various monomer feed ratios. Diffusion and evaporation of photogenerated acid in the copolymer films were investigate for various fractions of the basic units in copolymers. It is found that only acid surviving deactivation by the BCVC units diffuses into unexposed areas and evaporates for the copolymer film to bleach the indicator film. Evaporation of a low molecular weight basic additive is also examined. Whereas the low molecular weight basic additive evaporated during baking, the basic monomer units in the copolymer did not evaporate at all due to covalent bonding to polymer backbone chain. Thus, the copolymer with the basic monomer can control the acid diffusion and evaporation effectively. The new resists system enables us to form fine patterns even after post- exposure delay of 2 h without any additional treatment.

Control of photogenerated acid diffusion and evaporation by copolymerization with a basic monomer

Copolymers of t-butyl methacrylate and 3-(t-butoxycarbonyl)-1-vinylcaprolactam (BCVC) were synthesized with various monomer feed ratios. Diffusion of photogenerated acid in the copolymer films and the acid trapping capability of the basic BCVC units were investigated. The evaporation of acid was also studied by a spectral change of an indicator film that consisted of poly(vinyl alcohol) and tetrabromophenol blue sodium salt. It is found that only acid surviving deactivation by the BCVC units diffuses into unexposed areas and evaporates from the copolymer film. The evaporation of a low molecular weight basic additive is also examined. Whereas the low molecular weight basic additive is evaporated during baking, the basic monomer units in the copolymer are not evaporated at all. Thus, the copolymer with the basic monomer can control the acid diffusion and evaporation effectively. The new resist system enables us to form fine patterns even after a 2 h postexposure delay without any additional treatment.