Haruyuki Okamura

A UV curable resin with reworkable properties: application to imprint lithography

Difunctional methacrylate monomers having a hemiacetal ester moiety in the molecule were used to prepare a plastic replica of an original mold for imprint lithography. UV curing of the monomers was performed with 365 nm light and photo-induced degradation of the cured resins was performed using 254 nm light.

Reworkable dimethacrylates with low shrinkage and their application to UV nanoimprint lithography

Four types of reworkable dimethacrylates bearing hemiacetal ester groups were synthesized and the UV curing and degradation were studied. UV nanoimprint lithography (UV-NIL) using these monomers was performed and fine line/space patterns were obtained. The shrinkage in height of the UV imprinted pattern was studied in relation to the monomer structure and UV imprint conditions such as light intensity and concentrations of photoradical initiator and chain transfer reagent. The effect of UV imprint conditions on the kinetic chain length of UV cured networks was investigated using size exclusion chromatography of the linear polymers obtained from the degradation of the UV imprinted patterns. A relationship between the kinetic chain length and shrinkage of the UV imprinted patterns was discussed.

EUV resist based on low molecular weight PHS

Two types of EUV resists based on poly(4-hyrdoxystyrene) (PHS) were designed, i.e., PHS-bound sensitizer (PHS-FISS) and PHS/sensitizer blend (PHS/FITS). Imino sulfonate compounds were used as a photosensitizer. A PHS-bound sensitizer resist was prepared by the conventional radical copolymerization of 4-(tertbutyldimethylsilyl)oxystyrene (MSOST) and 9-fluorenilideneimino p-styrenesulfonate (FISS) and subsequent de-silylation of the copolymer. PHS with low molecular weight distribution was obtained by the anionic polymerization of MSOST and followed by de-silylation of the polymer. It was found that both types of resist were negative type and highly sensitive ( 10-20 mJ/cm2 ) on exposure at 254 nm and 13.5 nm. In the case of blended resist, the sensitivity was dependent on the amounts of sensitizer added and molecular weight of PHS. Outgassing from the present resists on EUV exposure was lower than that observed for MET-2D resist.

EUV negative-resist based on thiol-yne system

Non-conventional chemically amplified (CA) negative resist for EUV lithography was studied. We have designed negative-tone EUV resist based on thiol-yne stepwise radical reactions. OH groups of poly(4-hydroxystyrene) (PHS) were modified with functional units bearing C-C triple bond structure. Resist was formulated as a mixture of modified-PHS, multifunctional thiol compound, and photoradical generator. The present resist was developable with standard 2.38 wt% TMAH aq. solution. Photo-sensitivity of the resist was obtained on irradiation at 254 nm and 13.5 nm. The resist was highly sensitive to EUV exposure. The sensitivity and the contrast were affected by the structure of modified-PHS and process conditions.

Highly sensitive EUV-resist based on thiol-ene radical reaction

Non-conventional chemically amplified (CA) resist was designed. Photo-induced thiol/ene radical reaction was used to insolubilize the resist based on multifunctional thiol and poly(4-hydroxystyrene) (PHS) derivatives. Hydroxy groups of PHS were modified with allyl or propargyl moiety. Dissolution property of the modified-PHS in TMAHaq solution was affected by the modification degree. Resist was prepared by mixing the modified-PHS, multifunctional thiol compound, and photoradical generator. Photosensitivity of the resist was studied at 254 and 13.5 nm. The sensitivity was strongly affected by the modification degree of PHS, molecular weight of PHS, molecular weight distribution of PHS, amounts of thiol compound and photoradical generator added. It was found that the present resist system was highly sensitive to EUV exposure.

Novel resist for replica preparation of mold for imprint lithography

Two types of dimethacrylate which have hemiacetal ester moiety in a molecule were synthesized from difunctional vinyl ethers and methacrylic acid. UV curing of the monomers and photo-induced degradation of the UV cured resins were investigated. On UV irradiation at 365 nm under N2 atmosphere, these dimethacrylates containing 2,2-dimethoxy-2-phenylacetophenone and triphenylsulfonium triflate became insoluble in methanol. The UV cured resins degraded if acids were generated in the system. Present resins were applied to make a plastic replica of mold for imprint lithography and the plastic replica was prepared in good form. The effect of imprint conditions on volume shrinkage of methacrylates was investigated. Dimethacrylate that has adamantyl unit showed a low-shrinkage property.

Non-Chemically Amplified Negative Resist for EUV Lithography

Non-chemically amplified (CA) negative resist for EUV lithography was studied. Photo-induced thiol/ene radical reaction was used to insolubilize the resist based on poly(4-hydroxystyrene) (PHS) derivatives. Hydroxy groups of PHS were modified with allyl, norbornen, or methacrylate moiety. Dissolution property of the modified-PHS in TMAHaq solution was studied. The degree of the modification of PHS strongly affected the solubility in TMAHaq. Resist was a mixture of modified-PHS, multifunctional thiol compound, and photo-radical generator. Photo-sensitivity of the resist was studied at 254 nm and 13.5 nm. The sensitivity was affected the concentration of thiol compound added. It was found that the present resist system was highly sensitive (5~6 mJ/cm2) to EUV exposure.

Control of adhesive strength of acrylate polymers containing 1-isobutoxyethyl and isobornyl esters in response to dual stimuli for dismantlable adhesion

BackgroundTo develop an adhesion system satisfying both constant adhesion strength during use and quick debonding ability during a dismantling process.MethodsAdhesive properties were investigated for the random and block copolymers consisting of 1-isobutoxyethyl acrylate (iBEA), 2-ethylhexyl acrylate (2EHA), and 2-hydroxyethyl acrylate (HEA) as the dismantlable pressure-sensitive adhesives in the presence of a photoacid generator in response to dual external stimuli of photoirradiation and post baking.ResultsThe use of LED combined with a new photoacid generator SIN-11 was enable us to achieve a rapid dismantling process during UV irradiation within several minutes. The protection of the ester alkyl group in the iBEA repeating unit to give an acrylic acid unit was suppressed by the introduction of isobornyl acrylate (IBoA) as the additional unit into the copolymer of iBEA, 2EHA, and HEA. While IBoA‐containing block copolymer showed a constant adhesive strength during photoirradiation as the single external stimulus, deprotection was immediately induced by the subsequent heating, leading to a significant decrease in the adhesive strength.ConclusionThe copolymer including the iBEA and IBoA units was revealed to function as the highly sensitive adhesive materials for dual-locked dismantlable adhesion.

Diffusion of acid from resist to Si-hardmask layer

In a chemically amplified (CA) resist process, photochemically generated acid can diffuse in the resist matrix, inducing the de-protection reactions. The concentration of acid in resist matrix should be constant during the post-exposure-bake (PEB) treatment. In the practical resist processes, bottom anti-reflective coating (BARC) is essentially important to provide reflectivity control for resist patterning. In some cases, however, the photochemically generated acid in resist layer can diffuse into BARC layer, which causes the footing for resist patterns. In this work, we have studied the diffusion of acid from CA resist layer to Si-hardmask (Si-HM) layer. The Si-HM is essential for the multi-layer patterning process. The acid concentration in the resist layer was estimated based on the de-protection reaction kinetics for the CA resist using rapid scan FT-IR spectroscopy. It was found that the acid in resist layer diffused into the Si-HM layer. The diffusion efficiency of the acid was dependent on the crosslinking density of the Si-HM and the chemical structure of the resist.

Diffusion of amines from resist to BARC layer

In chemically amplified (CA) resist systems, photo-chemically generated acid can diffuse in resist matrix and the acid induces the de-protection reaction of resists. To control the rate of the de-protection reaction, small amounts of amines must be added as a quencher. The concentration of amines in resist matrix should be constant during the post-exposure-bake (PEB) treatment. In the practical resist processes, organic bottom anti-reflective coating (BARC) is essentially important to provide reflectivity control for resist patterning. In this study, we have studied the diffusion characteristics of amines from resist layer to BARC layer by bake treatment. The amine concentration in resist layer was estimated using the rate of de-protection reaction of conventional CA resist. It was found that the diffusion rate of amines from resist layer to BARC layer was negligibly low.