Photo Reactive Gas Generation System

As resist feature sizes and film thicknesses continue to shrink in dimension, a number of resist feature size and film thickness dependent effects are being observed in the lithographic performance of high resolution photoresists. In order to understand these phenomena, a better understanding of the physiochemical behavior of complex multi-component organic resist thin films is needed. As a first step in that direction, a series of model photoresists were studied in an effort to begin to understand the thermophysical properties of such multi-component thin films. The influence of photoacid generator (PAG) loading and PAG chemistry on the glass transition behavior using the model photoresists was studied. A thermal flow experiment was used to characterize an "apparent glass transition temperature" of the resist thin films as a function of PAG type and loading. These results were compared to traditional glass transition measurements made on the same resist compositions using differential scanning calorimetry (DSC). The two methods, namely DSC and the thermal flow measurement, yielded very different results depending on the type of PAG used. Further studies using ToF SIMS to profile the distribution of PAG in the resist thin films revealed that the two PAGs focused on in this work, a triphenylsulfonium triflate (TPS.OTF) and a triphenylsulfonium nonaflate (TPS.ONF), exhibited very different distribution behavior in resist thin films. In the case of TPS.OTF, the PAG was observed to show a depletion region near the resistsubstrate interface while the TPS.ONF PAG was relatively homogeneously distributed in the resist thin films. In the case of TPS.ONF, it was also the resist system which showed very different thermophysical behavior when comparing the glass transition temperature measured using DSC to the thermal flow temperature measurement. This work points out the fact that component distribution and thin film effects must be carefully considered in interpreting and analyzing the behavior of multi-component thin films.

We describe new sulfonium salts incorporating semifluorinated sulfonate anions and their successful application as photoacid generators (PAGs) intended to solve the environmental problems caused by perfluorooctyl sulfonate (PFOS). By utilizing simple and unique chemistries based on 5-iodooctafluoro-3-oxapentanesulfonyl fluoride, a series of alicyclic-group functionalized octafluoro-3-oxapentane-sulfonate anions were prepared in high purity and high yield. Triphenylsulfonium (TPS) salts of norbornyl and γ-butyrolactone groups functionalized octafluoro-3-oxapentanesulfonates were extensively studied. They have excellent thermal stability and good solubility in various polar solvents. Their optical and thermal properties were thoroughly investigated. Angle resolved X-ray photoelectron spectroscopy (XPS) analysis confirmed that the new TPS salts are uniformly distributed in polymer films, whereas TPS PFOS is heavily segregated to a polymer film surface. Lithographic performance of the new salts together with TPS PFOS and triphenylsulfonium perfluorobutyl sulfonate (TPS PFBS) in model positive tone resists was evaluated and compared at 193 nm (both dry and immersion) and extreme ultraviolet (EUV) wavelengths. Resist compositions containing the new salts are capable of resolving sub-100 nm dense lines and spaces at both tested wavelengths. Especially, a pattern of 42 nm dense lines was successfully demonstrated in 193 nm immersion exposures. A specific TPS salt of monosaccharide-functionalized octafluoro-3-oxapentanesulfonate, a “sweet” PAG, was also synthesized and studied. This PAG is capable of resolving 90 nm lines in 193 nm lithography. These new PAGs show comparable performance with TPS PFBS and better performance than TPS PFOS, which makes them very promising environmentally friendly candidates for high resolution lithography applications.

Atom transfer radical polymerization (ATRP) was used to prepare poly(acetoxystyrene) (PAS) with a controlled molecular weight and narrow polydispersity. Using 1‐phenylethylbromide (PEBr)/CuBr/Cu(0)/2,2′‐bipyridine as an initiating system, the heterogeneous ATRP of 4‐acetoxystyrene was carried out to form PAS as a precursor polymer. The reaction follows the first‐order kinetics with respect to the conversion of monomer. A linear molecular weight (polydispersities Mw/Mn = 1.07–1.27) indicates the “living”/controlled nature of polymerization. The obtained PAS was chemically modified to obtain succinylated poly(hydroxystyrene) (Succ‐PHS). The formulation of Succ‐PHS, crosslinker (benzoguanamine‐formaldehyde), and triphenylsulfonium triflate (TPST) as a photo acid generator (PAG) was carried out by UV irradiation using an i‐line tool. The performance of the resultant polymer as the negative resist pattern photoresist for photolithography was studied with instrumental techniques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3560–3566, 2007

Cadmium selenide quantum dots: synthesis, characterization, and dye removal ability with UV irradiation

A new class of compounds, (5-alkylsulfonyloxyimino-5H-thiophen-2-ylidene)-2-methylphen yl-acetonitriles, characterized as non-ionic and halogen-free photoacid generators (PAG's) was developed. The compounds generate various kinds of sulfonic acids, such as methane, n-propane and camphor sulfonic acid under the g-line (436nm), i-line (365 nm) and Deep UV (DUV, 248 nm or shorter) exposure and are applicable for chemically amplified (CA) photoresists. The application-relevant properties of the compounds such as solubility in propylene glycol monomethyl ether acetate (PGMEA), UV absorption, thermal stability with or without poly(4-hydroxystyrene), storage stability in a neat form, sensitivity in some model resist formulations and dissolution inhibition efficiency during development process were evaluated. The compounds exhibit enough solubility in PGMEA, red-shifted UV absorption ($lamdamax: 405 nm), good thermal stability up to 140 C in a phenolic matrix, effective acid generation in terms of quantum yield in an acetonitrile solution and high sensitivity in negative tone and positive tone CA resist formulations, such as tert-butyl ester type and t-BOC type formulations, with g-line, i-line and DUV exposure. The photochemical decomposition reaction of the compound was also studied. Additionally a scanning electron microscope (SEM) photography as an application example of microlithography by the CA negative tone resist with the PAG is presented.

This report will introduce novel resist materials including specific photo acid generator (PAG) to improve flare issue from the resist standpoint. We have developed a method to control the acid diffusion length from the PAG. It previously reported that acid diffusion length can be altered by the PAG anion size. In this report, we focused on the effect of the Tg of a resist film. The thermal flow rate of a resist film can suggest the approximate resist Tg. Therefore, we measured the thermal flow rate of the resist. And we found out passivity of acid diffusion control by changing PAG species and volume. Moreover, newly designed PAG tested was confirmed to have uniform distribution in the resist film with no PAG clustering at the resist surface at compared to our conventional PAG. This new positive tone resist formulation shows good performance under flare condition. In addition, we focused on the pattern density variation as one of the key parameters for flare value. Low pattern density indicated less flare value. It is considered that negative tone resist to have advantage for isolated line type features. Novel positive and negative tone type resists were compared side-by-side and discussed for its advantages at varying pattern densities.

For designing high-resolution integrated circuits, extreme ultraviolet (EUV) lithography using 13.5-nm light is indispensable; however, stochastic issues which can result in pattern roughness and stochastic defects have yet to be resolved. Many of these issues can relate to the low photon density when compared to DUV lithography. To resolve stochastic concerns in chemically amplified (CA) photoresists, it is important to use appropriate photoacid generator (PAG). EUV PAGs are designed to capture secondary electrons that originate from EUV irradiation to the photoresists. Herein, we focused on in silico analysis of C-S bond cleavage of sulfonium cation series, which is a well-known mechanism in production of photogenerated acids. Change in cation types or substituted functional groups directly affect electron affinities of PAG cations, as well as the efficiency of C-S bond cleavage reaction. Finally, the correlation between actual lithographic performance and calculated properties was carried out to understand the factors that influence efficiency of photoacid generation.

In this work, the feasibility of using interdigitated electrodes to measure the kinetics of photoacid generation in a resist film has been examined. Interdigitated electrodes provide a quick, noninvasive, nondestructive alternative to traditional Dill C measurement techniques and unlike traditional techniques is easily performed in a wafer fab environment. The initial results indicate that the interdigitated electrodes (IDEs) used in this work are capable of both detecting the small quantities of acid generated by photoacid generators (PAGs) at loadings typical of those found in chemically amplified resists and quantifying the amount of acid generated during exposure. In addition, a linear relationship has been observed between measured IDE capacitance and both PAG and photoacid content. This relationship has been utilized to determine the Dill C parameter from the measured IDE capacitance response vs. exposure dose for films consisting of triphenylsulfonium triflate (TPS-Tf) in a poly(hydroxystyrene) (PHOST) matrix. A Dill C value of 0.0445 cm2/mJ was measured for TPS-Tf in PHOST, which is in agreement with literature values for similar PAG-polymer systems. © 2004 The Electrochemical Society. All rights reserved.

Biopolymers such as alginate and pectin are well known for their ability to undergo gelation upon addition of multivalent cations such as calcium (Ca(2+)). Here, we report a simple way to activate such ionic gelation by UV irradiation. Our approach involves combining an insoluble salt of the cation (e.g., calcium carbonate, CaCO(3)) with an aqueous solution of the polymer (e.g., alginate) along with a third component, a photoacid generator (PAG). Upon UV irradiation, the PAG dissociates to release H(+) ions, which react with the CaCO(3) to generate free Ca(2+). In turn, the Ca(2+) ions cross-link the alginate chains into a physical network, thereby resulting in a hydrogel. Dynamic rheological experiments confirm the elastic character of the alginate gel, and the gel modulus is shown to be tunable via the irradiation time as well as the PAG and alginate concentrations. The above approach is easily extended to other biopolymers such as pectin. Using this approach, a photoresponse can be imparted to conventional biopolymers without the need for any chemical modification of the molecules. Photoresponsive alginate gels may be useful in creating biomaterials or tissue mimics. As a step toward potential applications, we demonstrate the ability to photopattern a thin film of alginate gel onto a glass substrate under mild conditions.

Kinetics and products of HONO interaction with TiO2 surface under UV irradiation

This paper presents an experimental study about the effects of UV irradiation on polyether polyurethane (PU) fibers investigated by FTIR, SAXS and AFM, and the multiple mechanism is finally proposed.The results show that, at low UV irradiation (0.6W/m2, 0.9W/m2), the mechanism responsible for UV degradation of polyether PU fibers could be described as a primary reaction causing the break up of chemical bonds and forming the new quinone structure, along with a secondary reaction to explain hydrogen peroxide formed in the presence of UV irradiation, water and oxygen environment which promotes QUV aging by providing loose structure of polyether PU fibers. Moreover, the micro phase separation is promoted for a parallel reaction occurred to produce new polyether PUs and more compact micro domains by the residual isocyanate in pre-polymerization stage and alcohols formed under QUV aging. Under higher UV irradiation (1.2W/m2, 1.5W/m2), in addition to the primary reaction, a tertiary reaction showing the re-polymerization occurred under accumulation of aging products (carboxylic acids and alcohols) is also considered as the mechanism, while the secondary reaction would be inhibited for the peak assigned to H2O2 is not observed. Also, this decreases micro phase separation of polyether PU fibers for the primary reaction is dominant.

One of some critical issues for ArF immersion lithography was leaching of resist components to water fluid. To decrease the leaching amount, increase hydrophobicity of Photo Acid Generator (PAG) was one of the most effective methods. The hydrophobicity of PAG was detected by simulating Log-P value and measuring Retention Time (RT) on reversed phase chromatography. However, simple high hydrophobic PAG indicated high defect number. The improvement of this issue was achieved by introducing acid cleavable group into PAG cation frame. It may suggest that PAG material proposed on this study showed low leaching amount and low defect risk as new concept for ArF immersion resist.

We have examined four molecular glasses (MGs) which are candidates for EUV photoresist formulations. These derivatized glasses, and their unprotected precursors, were investigated by both proton and ¹³C solid state NMR techniques in the bulk state as pure materials and as mixtures with 5 or 10 % by mass of the photoacid generator (PAG), triphenyl sulfonium perfluorobutanesulfonate. The ¹³C techniques gave information about crystallinity, purity, and the presence of the PAG. This paper characterizes the intimacy of mixing of the PAG and the MGs using proton spin diffusion methods. Phase separation of the PAG into PAG-rich larger domains was never seen; the PAG was always finely distributed. A maximum diameter for any PAG clustered into spherical domains was estimated to be 3.8 nm, which is too small to reflect thermodynamic incompatibility as the driving force during relatively slow removal of solvent. Hence, PAG blended samples are deduced to be thermodynamically compatible, with differential solubility in the preparation solvent the most likely candidate for producing the significant inhomogeneities in PAG concentration observed in a few samples. For one of the unprotected crystalline calix[4]resorcinarenes precursor materials, the solvent, N-methyl 2-pyrrolidinone (NMP) was used. The resulting solid was crystalline with a segregation of isomers, one of which formed a solid adduct with a 1:1 molecular ratio with NMP. Qualitatively, the strong NMP affinity for the calix[4]resorcinarenes is also evident in a) the immobility of the NMP, b) the fact that the ¹⁴N quadrupolar interaction changes when NMP goes from the crystalline, unprotected host to a glassy, protected host, and c) that NMP tends to remain as a significant residue. Only the underivatized materials display crystallinity implying that the mixing of the PAG with any derivatized MG is not restricted by crystallization, at least not before the post-exposure bake step. As a final note, very strong hydrogen bonds exist in three underivatized materials which is reduced or eliminated with partial protection with t-BOC.

New negative tone resists for sub-quarter micron lithography

t-BOC protected hexakis(4-t-BOC-phenoxy)cyclotriphosphazene, TBP, was synthesized from a semiinorganic phosphazene compound and its acid-catalyzed thermal deprotection was utilized in the design of a three-component positive resist system based on the combined principles of chemical amplification and dissolution inhibition. The new resist system, PTPNS(NR/TBP/PAG), is formulated with novolac resin (NR), TBP and a photoacid generator (PAG). The dissolution characteristics of PTPNS in alkaline development are ideally suited for application to positive type resists which are based on a dissolution inhibition mechanism. The t-BOC protected TBP of the PTPNS resist system effectively acts as an acid-labile dissolution inhibitor of novolac resin when TBP concentration is more than 10% by weight. As a representative, PTPNS(100/15/5) (by weight parts) exhibited high sensitivity in the range of 20 to 25mJ/cm2 with contrast of 5 after exposure at 250nm light and PEB treatment at 100 to 130°C. Appropriately formulated PTPNS resist rendered positive-tone patterns down to sub-half micron with high sensitivity when the resist was exposed to KrF excimer laser or electron beam and developed with 2.38wt% tetramethylamonium hydroxide solution.