Base quenchers

The addition of base quenchers to resists has been shown to improve LER at the expense of photospeed (see Fig. 17.28). This stems from the neutralization reaction between the photoacid and the base quencher within the exposed area, resulting in the increase in the photogenerated acid concentration gradient, as well as chemical contrast at the feature edge. The enhanced chemical contrast at the feature edge translates into enhanced development contrast between the exposed and the unexposed areas of the film the result is a much sharper edge (lower LER) than would otherwise be the case. 

He and F. Cerrina, Process dependence of roughness in a positive tone chemically amplified resist, J. Vac. Sci. Technol. B. 16(6), 3748 (1998). 

Yoshino, S. Hashimoto, M. Yamana, N. Samoto, and K. Kasama, Acid and base diffu sion in chemically amplified DUV resists, Microelectron. Eng. 35, 149 (1997) T. Itani, H. Yoshino, and S. Hashimoto, Photoacid hulkiness effect on dissolution kinetics in chemically amplified deep ultraviolet resists, J. Vac. Sci. Technol. B. 13(6), 3026 (1995). 

Hutchinson, Shot noise impact on resist roughness in EUV lithography, Proc. SPIE 3331, 531 (1998) N. Rau, F. Stratton, C. Fields, T. Ogawa, A. Neureuther, R. Kubena, and G. Willson, Shot noise and edge roughness effects in resists patterned at 10 nm exposure, J. Vac. Sci. Technol. B. 16(6), 3784 (1998). 

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The copper(I) complex Cu(dmp)2 (dmp = 2,9-dimethyl-l,10-phenanthroline) displays MLCT luminescence in ambient temperature CH2CI2 solutions [85]. This emission has been shown to be quenched by various Lewis bases (B), and the mechanism proposed is addition of B to the MLCT state at the metal center to give an exciplex which decays rapidly (Eq. 6.39). The validity of this mechanism was tested by comparing, in the presence and absence of Lewis base quenchers, the pressure effects on the emission lifetimes of Cu(dmp)2 vvith those on the emission lifetimes of the bulkier 2,9-diphenyl-phen analog Cu(dpp) [86]. The lattice ions should not be as susceptible to reaction of the copper center with B. For both ions, emission quantum yields are small (<10 ) at ambient T and unimolecular photoreactions are not observed, so the pressure sensitivity of x reflects non-radiative deactivation mechanisms. 

Figure 17.28 LER versus l/ Esize for DUV 248-nm and EUV 13.4-nm exposure of EUV 2D resists formulated with seven different concentrations of base quencher. ...

Activation parameters for the quenching of Cu(2,9-Me2-phen)2 by a series of Lewis base donors have provided support for exciplex formation in these reactions of Cu(I) complexes. The data for a series of Lewis base quenchers are collected in Table 2.11. These data show that the fastest quenching rates are found for strong donor ligands such as DMF and DMSO. It is also apparent that the activation... 

Fig. 5 Tuning the absorbance wavelength of azulene-based quenchers...

CAR materials based on blends of protected polymers, PAGs, and base quenchers that have been tested, the basic trade-off between the achievable resolution, sensitivity, and LER in a given resist material design (i.e., a particrrlar positive-tone CAR polymer platform) can be expressed as shown in eqn [4], Given the rough scaling shown in the equation, attempts to increase resolution or... 

For example, in three-component blended, positive-tone CAR systems, one can increase the amount of base quencher to achieve improvements in resolution and edge roughness but with an associated loss in resist sensitivity due to photoacid quenching in the exposed region by the base quencher as well. 

Meta.1 Complexes. The importance of Ni complexes is based on their effectiveness as quenchers for singlet oxygen. Of disadvantage is their low colorfastness and their lower ir-reflectance compared to cyanine dyes (qv) therefore they are used in combination with suitable dyes. Numerous complexes are described in the Hterature, primarily tetrathiolate complexes of Pt or Ni, eg, dithiolatonickel complexes (3). Well known is the practical use of a combination of ben2othia2ole dyes with nickel thiol complexes in WORM disks (Ricoh, TDK) (17). 

Fatty Acid Transporters. Figure 2 Quencher-based real-time fatty acid uptake assay with a fluorescently labeled FFA analogue (C1-Bodipy-C12). Predominantly protein-mediated fatty acid uptake by 3T3-L1 adipocytes (diamonds) was compared with diffusion-driven uptake by fibroblasts (squares) using the QBT Fatty Acid Uptake reagent (Molecular Devices Corp., CA, USA), which contains C1-Bodipy-C12 as substrate in conjunction with a cell impermeable quencher. Uptake kinetics was recorded using a Gemini fluorescence plate reader. Error bars indicate the standard deviations from 12 independent wells. RFU relative fluorescence units. 

As just mentioned, phosphorus porphyrins have unique photochemical properties. Their photophysics is also interesting. Emitter-quencher assemblies based on porphyrin building blocks have attracted attention due to their potential to serve as models in photosynthetic research (see [90] for an example) or for the development of photoswitches that could be used for the fabrication of molecular electronic/optical devices. In this context, Maiya and coworkers constructed a P(VI) porphyrin system 59b with two switchable azobenzene groups positioned in the apical positions of the pseudo-octahedral phosphorus atom [92]. Photoswitch ability (luminescence on/off) was demonstrated as... 

Time-resolved luminescence quenching measurements using the probe Tb(pyridine-2,6-dicarboxylic acid)i and the quencher bromophenol blue show the existence of micellar clusters in AOT-based w/o microemulsions. The fast exchange appearing over several microseconds was attributed to intracluster quenching, whereas the slow exchange on the millisecond time scale was attributed to intercluster exchange [243]. 

Alternatively, the quencher can be directly connected to the dendrimer structure. The photophysical behavior of generation 1,2 (compound 29), and 3 dendrimers containing a free-base porphyrin core and 12, 36, and 108 peripheral anthraquinone units, respectively, was studied in chloroform and dimethylac-... 

Considerable amounts of quenching of the acridone emissions by guanine in the DNA occurred when guanine was close to acridone, which can be applied as a quencher-free probe (no additional quencher is required) for the detection of a special sequence of DNA. The DNA bearing acridone at the C5 position of inner thymidine could distinguish the opposite T-T base mismatch, while enhancement of discrimination ability is needed for the practical use of single nucleotide polymorphism (SNP) typing. 

A significant number of fluorogenic sensors are based purely on an increase or decrease of fluorescence. As discussed above, these probes, though often very useful, lack the internal reference that ratiometric sensors provide and require therefore difficult calibration. Especially hydrolytic enzymes are easily monitored by a fluor-ophore that is held in a non-fluorescent stage until the enzyme of interest removes the quencher. Certainly, it is beneficial if the... 

Fig. 6.14. Quenched activity based probe for the imaging of cathepsins. Upon covalent binding of the sensor to histidine and serine residues in the active site of the enzyme, the quencher is released and increased fluorescence indicates the now covalently labeled enzyme of interest. 

The Stem-Volmer equations discussed so far apply to solutions of the luminophore and the quencher, where both species are homogeneously distributed and Fick diffusion laws in a 3-D space apply. Nevertheless, this is a quite unusual situation in fluorescent dye-based chemical sensors where a number of factors provoke strong departure from the linearity given by equation 2. A detailed discussion of such situations is beyond the scope of this chapter however, the optosensor researcher must take into account the following effects (where applicable) ... 

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