Solubility Switch Research Articles

Influence of solubility switching mechanism on resist performance in molecular glass resists

Five different molecular glass chemically amplified photoresists which utilized different solubility switching mechanisms and chemistries, based on a tris(4-hydroxyphenyl)ethane (THPE) core, were synthesized and their performance compared. Three different positive tone systems were designed based on acid catalyzed deprotection of a phenolic hydroxyl group protected with one of the following groups: tert-butoxycarbonyl (tBoc), tetrahydropyranyl, or ethoxyethyl. Two negative tone systems were designed; one using cationic epoxide polymerization of pendant epoxides and one using condensation of the unprotected THPE with a multifunctional cross-linking additive. The tBoc system and negative tone systems showed good performance under deep UV and large field e-beam patterning, but the epoxide system showed far superior performance for high resolution electron beam patterning. It was able to produce 50nm 1:1 line/space patterns and 30nm lines on 1:3 line/space patterns with high sensitivity, good contrast, and a very low line edge roughness (3σ) of 2.3nm using 100keV electron beam patterning.

Tyrosine-Selective Protein Alkylation Using π-Allylpalladium Complexes

A new protein modification reaction has been developed based on a palladium-catalyzed allylic alkylation of tyrosine residues. This technique employs electrophilic pi-allyl intermediates derived from allylic acetate and carbamate precursors and can be used to modify proteins in aqueous solution at room temperature. To facilitate the detection of modified proteins using SDS-PAGE analysis, a fluorescent allyl acetate was synthesized and coupled to chymotrypsinogen A and bacteriophage MS2. The tyrosine selectivity of the reaction was confirmed through trypsin digest analysis. The utility of the reaction was demonstrated by using taurine-derived carbamates as water solubilizing groups that are cleaved upon protein functionalization. This solubility switching technique was used to install hydrophobic farnesyl and C(17) chains on chymotrypsinogen A in water using little or no cosolvent. Following this, the C(17) alkylated proteins were found to associate with lipid vesicles. In addition to providing a new protein modification strategy targeting an under-utilized amino acid side chain, this method provides convenient access to synthetic lipoproteins.

The Impact of Fluoropolymers on Line Edge Roughness in 193nm Imaging

We report here a family of tetrafluoroethylene (TFE) based photoresist polymers that image at 193 nm with low line edge roughness relative to other candidate polymers, while also demonstrating good resolution, high contrast, high transparency at the imaging wavelength and widely tuneable dissolution rates. These polymers are typically composed of (TFE), cyclo-olefins such as norbornene with one or two pendant hexafluorisopropanol groups per monomer and various acrylates. A solubility switch is incorporated into either the cyclo-olefin or the acrylate monomers. These polymers have the flexibility to easily incorporate a wide range of monomers to enhance properties such as solubility and adhesion. Imaging using Lucent's 0.6 NA SVGL stepper with an altPSM is shown. Contrast, optical absorption and dissolution data are also discussed. We have demonstrated a process for manufacture of these polymers that is scaleable to commercial volumes and which results in exceptional compositional uniformity and acceptably low levels of impurities.

Silicon Containing Organic-Inorganic Hybrid Materials as EUV Photoresists

The opportunities posed by extreme ultraviolet (EUV) lithography are encouraging the development of new resist platforms. The absorbance characteristic of materials required for the EUV lithography demands the use of polymers containing highly transparent silicon atoms. At the same time, very low levels of outgassing of silicon containing fragments are required due to the vacuum environment present during exposure and the extremely high cost of the EUV tools. These two contradictory requirements have led us to pursue new types of silicon containing hybrid materials as a resist platform; chemically amplifiable polysilanes and silsesquiazanes. In the former case, the direct incorporation of acid sensitive groups into the polymer backbone allows for a solubility switch upon exposure. In the later system, a silicon-nitrogen backbone structure can be cleaved upon exposure to induce a solubility switch. These hybrid materials possess many useful properties including low absorbance, low outgassing, and high sensitivity. Silsesquiazanes having different substituents and branching ratios were synthesized. The properties of the polymers will be discussed in the context of their lithographic performance.

Patternable block copolymers with high transparency at 157 nm: Fluorocarbinol functionalized poly(isoprene-b-cyclohexane)

A three-step polymer modification reaction was developed to prepare polydiene-based patternable block copolymers with high transparency at 157 nm wavelength. In the first step, the ene reaction of poly(isoprene-b-cyclohexadiene) with hexafluoroacetone was carried out to incorporate a pendent hexafluoro-2-hydroxy-2-propyl functional group in the polyisoprene block. Subsequently, the hexafluorocarbinol functionalized block copolymer was hydrogenated to enhance transparency at 157 nm and finally the fluorocarbinol was protected with an ethoxymethyl group to induce a solubility switch after exposure. The final block copolymer exhibited an absorption coefficient of 3.30 μm-1 at 157 nm. Exposure was carried out on a 248 nm stepper and feature sizes down to 0.5 μm were resolved prior to optimization of exposure and formulation conditions.

New Strategies for High Resolution Photoresists.

2-[4-(2-hydroxyhexafluoro isopropyl)cyclohexane]hexafluoroisopropyl acrylate (AF) was prepared as a key monomer for 157nm photoresist platforms. In order to balance transparency with other desirable traits such as etch resistance, new strategies for high resolution photoresists were developed and are discussed. (1) The α-trifluoromethyl group was introduced on the polymer backbone and the resulting polymer showed unexpectedly high transparency at 157nm (A=1.6μm-1) despite a carbonyl group in all the monomers. A new 157nm transparent monomer that will provide a solubility switch necessary for base solubility was designed. (2) p-t-Butoxy-tetrafluorostyrene was copolymerized with AF. The high acidity of p-hydroxy-tetrafluorostyrene allowed us to increase the content of the monomer in the system to produce a novel polymer that is highly transparent at 157nm (A=2.1μm-1). The polymer showed good 248nm lithographic performances. (3) Introduction of fluorine on the polymer backbone was carried out. Due to a lower electron density of the vinyl groups with fluorine, these vinyl monomers can be copolymerized with electron-rich vinyl monomers such as norbornene using radical initiators. 2-Methyl-2-adamantyl trifluoroacrylate (MAdTFA) was synthesized. An alternating copolymer with a norbornene derivative was found to have high Tg and gave clear images using 248nm imaging.