A polymer obtained through copolymerization of a monomer having a hexafluoroalcohol pendant whose hydroxyl moiety has been protected and a monomer having an acid labile group is useful as an additive to a photoresist composition for immersion lithography. When processed by immersion lithography, the resist composition exhibits good water repellency and water slip and produces few development defects.

Polymer, resist composition and patterning process

A resist composition is provided comprising a silicone resin, a photoacid generator, a nitrogen-containing organic compound, and a solvent. The silicone resin is obtained through cohydrolytic condensation of a mixture of three silane monomers containing an organic group having a hydroxyl group and having at least 3 fluorine atoms, in total, on a proximate carbon atom, an organic group having a carboxyl group protected with an acid labile group, and a lactone ring-bearing organic group, respectively. The resist composition has satisfactory resolution and overcomes the problem of a low selective etching ratio between resist film and organic film during oxygen reactive etching.

Resist composition and patterning process

A resist composition comprising a polymer containing vinyl sulfonate units having fluorinated hydrophilic groups as a base resin has excellent transparency, substrate adhesion and developer penetrability as well as plasma etching resistance, and is suited for lithographic microprocessing.

Polymers, resist compositions and patterning process

Advancements in optical lithography tools, processes, and patterning materials have been critical to the continued performance increases of semiconductor devices as well as to the overall economics of the semiconductor industry.1 Reducing the wavelength of the source radiation has been a traditional pathway to increase resolution in optical lithography.1-3 In recent years, the technological challenges and the soaring costs associated with developing new exposure tools and new imaging materials have slowed the progress of wavelength scaling, evidenced by the decision not to commercialize 157 nm (F2 excimer) lithography in 2004.4 Rather than reducing the vacuum wavelength of the illumination, the semiconductor industry instead turned to scaling the effective wavelength via immersion lithography to extend the resolution capabilities of 193 nm lithography. Immersion lithography, which utilizes a coupling medium with a refractive index greater than that of air between the last lens element (LLE) and the photoresist, provides an increased depth-of-focus (DOF) and enables imaging systems with numerical apertures greater than one.5-13 This approach is economically attractive since it continues to use large amounts of the existing lithographic tooling infrastructure and patterning materials. In particular, the rapid development and commercialization of 193 nm water immersion lithography helped seal the fate of 157 nm lithography.

Advances in patterning materials for 193 nm immersion lithography.

Over the last three decades, my engagement in "fluorine chemistry" has evolved substantially because of the multidisciplinary nature of the research programs. I began my research career as a synthetic chemist in organometallic chemistry and homogeneous catalysis directed toward organic synthesis. Then, I was brought into a very unique world of "fluorine chemistry" in the end of 1970s. I started exploring the interface of fluorine chemistry and transition metal homogeneous catalysis first, which was followed by amino acids, peptides, and peptidomimetics for medicinal chemistry. Since then, I have been exploring the interfaces of fluorine chemistry and multidisciplinary fields of research involving medicinal chemistry, chemical biology, cancer biology, and molecular imaging. This perspective intends to cover my fruitful endeavor in the exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology in a chronological order to show the evolution of my research interest and strategy.

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Exploration of Fluorine Chemistry at the Multidisciplinary Interface of Chemistry and Biology

Based on UV measurements at 157nm of in-house fluoropolymers we have selected (alpha) -trifluoromethylacrylate and norbornene bearing a pendant hexafluoroisopropanol group as our building blocks for 157nm resist polymers. Polymers consisting of these repeat units have an optical density/micrometers of 3 or below at 157nm. We have found that the (alpha) -trifluoromethylacrylate derivatives conveniently undergo radical copolymerization with norornenes, which has provided a breakthrough in preparation of our 157nm resist polymers. This approach offers flexibility and versatility because an acidic moiety or acid-labile group can be placed in either acrylate or norbornene repeat unit. Other platforms of interest include all acrylic, all-norbornene, and acrylic-styrenic polymers.

Polymer design for 157 nm chemically amplified resists

Unexpectedly good UV transmittance at 157nm of poly(norbornene sulfone) bearing a pendant hexafluoroisopropanol functionality has prompted us to employ this fluoroalcohol as an acid group for the design of chemical amplification resists for use in 157nm lithography. The backbone structures to which the hexafluoroalcohol group is attached are polynorbornene and polystyrene. Furthermore, our discovery that poly(methyl α-trifluoromethylacrylate) is adequately transparent at 157nm has led us to incorporate the α-trifluoromethylacrylic unit in the polymer backbone by radical copolymerization with styrenes and norbornenes. Thus, four platforms are currently available to us in preparation of 157nm resist polymers; 1) all-acrylic, 2) all-norbornene, 3) acrylic-norbornene, and 4) acrylic-styrenic systems.

Novel Fluoropolymers for Use in 157nm Lithography

For adequate transparency we have selected hexafluoroisopropanol as an acid group and an α-trifluoromethylacrylic moiety as a repeat unit of our 157 nm resist polymers. The hexafluoroalcohol group is bound to norbornene or styrene. Four platforms are currently available to us: (1) all-acrylic, (2) all-alicyclic, (3) acrylic-alicyclic, and (4) acrylic-aromatic systems. While the all-alicyclic (all-norbornene) polymers are synthesized by transition-metal-initiated addition polymerization, all other polymers involving α-trifluoromethylacrylic monomers are prepared by conventional radical copolymerization. Characterization of the polymers and preliminary lithographic evaluation are reported.

Development of 157 nm positive resists

A copolymer of t-butyl 2-trifluoromethylacrylate (TBTFMA) and norbornene bearing hexafluoroisopropanol (NBHFA) as an acid group, which is prepared by radical copolymerization, is employed in our 157nm resist. The radical copolymerization of 2-trifluoromethylacrylic monomers with norbornene derivatives has been shown to follow the penultimate model much better than the commonly employed terminal model. These copolymers (containing >50mol% TBTFMA) are too lipophilic to provide good imaging. Blending a NBHFA homopolymer with an optical density (OD) of 1.7/μm at 157nm into the copolymers (OD=2.5-2.7/μm) results in increased hydrophilicity and reduced OD (2.2-2.0/μm) and provides high resolution images. A copolymer of TBTFMA with vinyl ethers has been identified as a new platform, which can be prepared facilely by common radical polymerization. Certain vinyl ether copolymers are also compatible with the NBHFA homopolymer and thus blending improves their OD and aqueous base development. Because these fluoropolymers are highly transparent at 193nm as well, they are evaluated as 157/193 dual wavelength resists.

Fluoropolymers for 157/193nm Lithography: Chemistry, New Platform, Formulation Strategy, and Lithographic Evaluation

Our primary platform for 157 nm positive resists is built on a copolymer of t-butyl 2-trifluoromethylacrylate (TBTFMA) andnorbornene bearing hexafluoroisopropanol (NBHFA) as an acid group, which is prepared by radical copolymerization. Theradical copolymerization of 2-trifluoromethylacrylic monomers with norbornene derivatives has been found throughreactivity ratio determination and in situ 1 H NMR analysis of kinetics to deviate from the terminal model but to follow thepenultimate model. These copolymers typically contain >50 mol% TBTFMA, are lipophilic, and fail to provide goodimaging due to poor wettability. Blending a homopolymer of NBHFA (optical density (OD)=1.7/ m at 157 nm) into thecopolymers (OD=2.5-2.7/ m) increases the hydrophilicity and reduces OD to 2.2-2.0/ m, providing high resolution images.Another platform we have identified is a copolymer of TBTFMA with vinyl ethers, which can be prepared by using acommon radical initiator. Some of the vinyl ether copolymers are also homogeneously miscible with the NBHFAhomopolymer and thus their OD and aqueous base development can be improved by blending.Keywords: 2-trifluoromethylacrylate, hexafluoroisopropanol, radical copolymerization, reactivity ratios, copolymerizationkinetics, terminal model, penultimate model, dissolution kinetics, quartz crystal microbalance, chemical amplification, 157nm lithography

Nicolette Fender

Papers

Polymer design for 157 nm chemically amplified resists

Novel Fluoropolymers for Use in 157nm Lithography

Development of 157 nm positive resists

Fluoropolymers for 157/193nm Lithography: Chemistry, New Platform, Formulation Strategy, and Lithographic Evaluation

Aliphatic platforms for the design of 157-nm chemically amplified resists