In order to improve EUVL resist characteristics, especially sensitivity, we have investigated two types of partially
fluorinated resist polymers. The one was side chain fluorinated PHS type resist polymers. The other was main chain
fluorinated resist polymers. Poly (p-hydroxystyrene) (PHS) type polymers with trifluorostyrene (TFSt) were synthesized
and characterized their sensitivity behavior. From this evaluation, we found that PHS contained TFSt unit had a high
sensitivity, keeping their etching durability. We expect that TFSt unit can work to enhance the resist sensitivity in PHS
based EUVL resist polymers. Main chain fluorinated polymers based FIT unit (FITMAd and FITAdOM) were
synthesized. FITMAd and FITAdOM showed high sensitivity compared to non fluorinated reference sample. From
molecular weight measurement, we infer that the polymer main chain of FITMAd can be decomposed by irradiating with
EUV light. The outgassing of FITMAd and FITAdoM were measured. There is no big difference between the total
outgassing of FIT polymers and that of non fluorinated acrylic sample. And small amount of Hydrogen fluoride (HF)
were detected. We infer that FITMAd and FITAdOM are decomposed then HF is generated under EUV exposure. From
these results, we expect that FIT unit can work to enhance the resist sensitivity and can act main chain decomposed resist
unit in EUVL resist polymers.
In immersion lithography, the impact of water on resist performance and the possibility of damage to the lens by the
components eluted from the resist material are seriously concern. And much work has shown that controlling the water-resist
interface is critical to enabling high scan rates. Many topcoat materials have been developed to control the
aforementioned interfacial properties. Developable topcoats have been particularly investigated as suitable candidates for
its applicability to the resist developing process. Achieving the balance between the low surface energy required for
higher receding contact angle and the base solubility for topcoat removal is challenging. We have already reported
FUGU polymer which have partially fluorinated monocyclic structure and hexafluoroalcohol(HFA) group and showed
that its developer solubility was excellent but hydrophobicity was insufficient for high scan rate. We have also reported
that co-polymers of FUGU and highly fluorinated monomers which have perfluorinated cyclic structure had sufficient
hydrophobicity but lower developer solubility. We have found that it was difficult to use these copolymers in themselves
as topcoat. But by blending of moderate amount of these copolymers into FUGU polymer, we have finally obtained
highly hydrophobic developer-soluble topcoat. Hydrophobicity can be controlled by blending ratio. Furthermore we have
newly successfully synthesized a series of fluoropolymers, FIT polymer partially fluorinated monocyclic structure and
having carboxylic acid group as developer-soluble unit. When FIT polymer as well as FUGU polymer, was blended to
highly hydrophobic copolymer, the blended polymer also showed higher hydrophobicity keeping sufficient developer
We have investigated higher hydrophobic developer-soluble topcoat by combination of developer-soluble unit with
higher hydrophobic unit. We have already reported a series of fluoropolymers, FUGU having a partially fluorinated
monocyclic structure and having acidic hydroxyl group which act as dissolution unit into alkaline solution. In
addition, recently we have developed new series of highly fluorinated monomers which was expected to act as
hydrophobic unit. In this paper, we describe results of co-polymersization of FUGU with these hydrophobic monomers
and evaluation of them. Some of them showed good hydrophobicity keeping moderate developer solubility.
Furthermore, we found that higher hydrophobic developer-soluble materials were achieved by adding small amount
of highly hydrophobic polymer to developer-soluble polymer, for example FUGU, and in fact this type of blending
polymer showed high hydrophobicity keeping high dissolution. We have obtained various kind of new type of topcoat
materials whose receding angle varied from 70-90 degree and patterning profile without dissolution residue could be
obtained by using two beam interference.
Recently it is known well that blending hydrophobic additives into conventional resist polymer drastically improve its
film surface hydrophobicity. So we thought that this approach was one of candidates and most promising to
achieve a non-topcoat resist process for immersion lithography. And it would be able to maintain original resist
performance because only a small amount of additives were added into conventional resist. Then we have investigated
hydrophobic polymers for use as additives of non-topcoat resists.
We have newly successfully synthesized various new highly fluorinated monomers by our peculiar fluorination
process. We found that some specific methacrylate ,which have perfluorinated cyclic structure, showed excellent
hydrophobicity. The other hydrophobic candidates is our fluoropolymer, FUGU, which had already developed, having
partially fluorinated monocyclic structure. However its hydrophobicity is insufficient due to presence of acidic
hydroxyl group which act as dissolution unit into the developer. To improve the its hydrophobicity, we protected all or a
part of its hydroxyl group. The protected FUGU polymer provide good hydrophobicity whose sliding angle (S.A.) and
receding angle (R.A.) were 7 degree and 90 degree respectively , compared to original polymer, FUGU.
In this paper, we describe a characteristics and evaluation of these our hydrophobic polymers to apply to additives for
We have optimized these polymers to apply to additive for conventional resist. As a result, various kinds of additives
were obtained. For example, some of them dissolve in developer due to the presence of alkali soluble group in the
polymer, the others are soluble in developer after deprotection reaction by post exposure bake. We call the former one is
'top-coat type', the latter is 'resist type'. Two type additives were investigated to give the hydrophobicity and to depress
the leaching amount to conventional resist.
We earlier developed new monocyclic fluoropolymers (FUGU) for F2 resist materials. But, it is necessary for FUGU to improve of their characteristics, especially the dry-etching resistance, in order to apply for ArF lithography at fine design rules. We have tried to combine FUGUs with Adamntyl methacrylates based conventional ArF resist polymer. In this paper, we have investigated the role of cyclic fluorinated unit, FUGU, in 193 nm resist polymers by analyzing the dissolution behavior. We found that FGEAM showed high sensitivity and good dissolution contrast, compared with acrylate based conventional samples at low PEB temperature (100oC). And this difference of sensitivity was clearly found when weak acidity PAGs were used. From the dissolution behaviors of FGEAM, FUGU unit can work to improve the resist sensitivity in acrylate based ArF resist polymers. And we also found that FGEAM showed long acid diffusion length on PEB process, compared with Conventional samples. These result show that FUGU unit has a unique characteristics of the sensitivity with 193nm exposure and the acid diffusion behavior. We also investigated a new series of fluorinated copolymers for 193-nm lithography, combination of FUGU monomer and acrylate units which are used in conventional ArF resist. Six ter-polymers of FUGU, combination of FUGU monomers and EAdMA, GBLMA and HAdMA were prepared. We found that FUGU ter-polymers had a good dry etching resistance keeping high transparency at 193nm. And FUGU ter-polymers showed high sensitivity toward 193nm exposure. FUGU ter-polymers also had a high hydrophobic properties compared conventional type ArF resist polymers. So we also expect FUGU ter-polymers to be useful for ArF dry and immersion lithography.
We had already developed several series of fluoropolymers, FPRs and FUGUs, having a partially fluorinated monocyclic structure and having acidic hydroxyl group, which acts as dissolution unit into alkaline solution. Then we have optimized these polymers for top-coat as the developer-soluble type in the 193nm immersion lithography. However the hydrophobicity of these polymers were a little poor due to its hydroxyl group. So we thought that the introduction of water repellent moiety into the these polymers structure is effective to improve the their hydrophobicity though the increase of water repellent unit in the polymer leads to lower dissolution rate in developer. To introduce as much as possible of hydrophobicity unit, we selected FUGU as platform, which has larger dissolution rate in developer than that of FPRs, We copolymerized FUGU with higher water-repellent component and obtained three copolymers, FUGU-CoA, FUGU-CoB, and FUGU-CoC. In this paper, we described characteristics and evaluation of these polymers. Most of these polymer showed an improvement of hydrophobicity, in particular FUGU-CoB had excellent hydrophobicity due to introduction bulky containing-fluorine group. In this study, we also investigated the interaction between the water and various polymers by using QCM method. The difference between FUGU and water repellent polymers for swelling behavior to water became clear by analysis of diffusion coefficient. We found that our new co-polymers have excellent diffusion coefficient than FUGU which was confirmed by QCM method used to evaluate water permeability and water diffusion in the materials.
We earlier developed new monocyclic fluoropolymers (ASF-2) for F2 resist materials. But, it is necessary for ASF-2 to improve of their characteristics, especially the dry-etching resistance, in order to apply for ArF and F2 lithography at fine design rules. In this study, to improve the dry-etching resistance keeping good characteristics of ASF-2, we examined using two methods. The one is to co-polymerize with ASF-2; the other is to introduce protective groups. We synthesized a new series of fluorinated co-polymers (ASF-2 with various monomers, e.g., methacrylate derivatives and vinyl ester derivatives). We found that the dry-etching resistance was improved by co-polymerization. Especially, the co-polymer with methacrylates containing an adamantyl moiety had a good dry-etching resistance, 1.45 vs. conventional KrF resist. This co-polymer also kept a good transparency at 193 nm. The introduction of various protective groups to the hydroxyl group of ASF-2 was also investigated. As the result of the optimization of protective groups and a protecting ratio, the partially protected ASF-2 with CCOM protecting groups had a good transparency at 157 nm and a good etching resistance (1.42 vs. conventional KrF resist). Using partially CCOM protected ASF-2 with an appropriate protecting ratio, sub-60 nm line and space pattern in 150 nm-thick film was obtained.
For 157-nm single-layer resists, dry etching resistance is an important issue because of the difficulty of striking a balance between 157-nm transparency and an acceptable level of dry etching resistance. To achieve an acceptable trade-off, the fluorine atom can be introduced into the resist polymer structure to obtain higher transparency, despite the fluorine atom’s high reactivity in the plasma etching process. We recently proposed a model for estimating dry-etching-resistance (the KI-model) and have shown that it can be effectively applied to the design of new fluoropolymer structures. Through simulation based on the KI-model, we were able to develop a new fluoropolymer with good dry etching resistance and high transparency. We found that a new protective group, 2-cyclohexylcyclohexanoxymethyl (CCOM), improved the characteristics of our novel fluoropolymer, compared with use of a MOM group, when used in the base resin of the resist. In this paper, we report on the usefulness of the KI-model for developing new fluorinated protective groups and new base polymers. Moreover, we have developed a new base fluoropolymer which has higher transparency and a similar degree of dry etching resistance as a monocyclic fluoropolymer with a CCOM protective group.