Matrices azides

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Photolysis (254 nm) of this azide in an isopentane/methylcyclohexane matrix at 77 K produced an orange color, with the appearance of two bands at 272 nm and 474 nm in the UV/visible-spectrum. Irradiation in an argon matrix at 20 K gave the same results.3... 

Schel, S. A. etal., J. Mol. Struct., 1986, 147(3 -4), 203 -215 Although it is highly explosive, like other polyunsaturated azides, it was possible to record spectral data under the following conditions gaseous electron diffraction IR spectra of matrix-isolated species in argon at 15°K of amorphous and crystalline solids at 90°K and Raman spectra of the liquid at 240°K. 

An alternative explanation, based on a spectroscopic study involving an argon matrix, has been advanced to account for the singlet photochemistry of phenyl azide (457).381 The primary photoproduct is believed to be 1-azacyclohepta-l,2,4,6-tetraene (458). A separate but later study suggests that... 

Milligan and Jacox 44 have recently reported an elegant synthesis of CF2 in an argon matrix. Carbon atoms, produced from the photolysis of cyanogen azide, were allowed to react with molecular fluorine, and the presence of CF2 was demonstrated from infrared spectra. Use of radiation effective in photolyzing F2 produced CF3 from the reaction of the CF2 with atomic fluorine. 

A photosensitive composition, consisting of an aromatic azide compound (4,4 -diazidodi-phenyl methane) and a resin matrix (poly (styrene-co-maleic acid half ester)), has been developed and evaluated as a negative deep UV resist for high resolution KrF excimer laser lithography. Solubility of this resist in aqueous alkaline developer decreases upon exposure to KrF excimer laser irradiation. The alkaline developer removes the unexposed areas of this resist. 

The photosensitive azide compound was 4,4 -diazidodiphenyl methane (m.p. 44.0 t). The poly(styrene-co-maleic acid half ester) was used as a resin matrix. 

Figure 2 shows the exposure characteristics for azide-styrene resin resist film with an azide concentration from 10 to 40 wt% (based on the styrene resin weight) and Figure 3 shows the contrast of the resist films as a function of the azide concentration. Development was done with a 60s immersion in 0.83% TMAH solution. The styrene resin matrix alone has been found to be a negative deep UV resist. However, rather low contrast (1.48) and low sensitivity (2.5 J/cm2) are observed. The contrast and the sensitivity of the styrene resin is remarkedly increased by adding the azide, as shown in Figures 2 and 3. 

The UV spectra for the azide in a diethylene glycol dimethyl ether solution and for the styrene resin film with 1.0 micron thickness are shown in Figure 5. The azide has an intense absorption at around 248 nm (molar extinction coefficient at 248 nm = 3.0xl04 1/M cm). The syrene resin used as matrix polymer exhibits a significant transparency at 248 nm (70%). 

PI 2A. IR studies of N labeled azide la. We are concerned with providing further evidence that nitrene 2a was formed upon the photolysis of azide la. To this end, we plan to synthesize azide la as an isotope labeled in the N1 position (see Figure 15), obtain IR spectra before and after irradiation in an argon matrix, and compare the calculated shift for the C-N band in nitrene 2a with the experimental value. Because isotope shifts in IR bands can be calculated very accurately, this will be an excellent proof of the formation of a nitrene intermediate. (From Gudmundsdottir, 2001)... 

Store the obtained affinity matrix in a buffer stabilizing the ligand properties, supplement with a biocide, e.g., 0.02% sodium azide or 0.1% Thimerosal or some drops of chloroform. 

The photochemistry of ferf-butylazide in a nitrogen matrix at 12 K was followed by IR spectroscopy. Only one product, trimethyhmine, was observed. Thus, the removal of alpha hydrogen from the alkyl azide does not suppress 1,2-migration reactions. 

However, in 1978, Chapman and LeRoux discovered that photolysis of phenyl azide, matrix isolated in argon at 10 K, produces a persistent species with a strong vibrational band at 1880 10 cm . The carrier of this species was most reasonably assigned to ketenimine 30 rather than benzazitine 29 or triplet phenylnitrene. This result imphes that it is the ketenimine 30 and not benzazirine 29 that is trapped with amines to form the 37/-azepines (27) that had been isolated earher. It does, however, raise the question as to why two groups observed triplet phenylnitrene by low temperature spectroscopy while a third observed ketenimine 30. 

The great majority of matrix isolation studies of carbenes and nitrenes have employed their formal adducts with molecular nitrogen, that is, diazo compounds or diazirines in the case of carbenes, azides in the case of nitrenes, as precursors for their in situ generation. Usually, these compounds will readily release N2 on irradiation with a low-pressure mercury lamp (254 nm), and this fragment has the advantage that it will usually not react with or perturb the targeted reactive intermediate (see Scheme 17.2). 

Azides are virmally the only nitrene precursors that have been used in matrix isolation studies. They are usually easily accessible, but should only be made and handled in very small quantities because certain azides can be violently explosive. 

Confusion over the matrix and gas-phase optical spectroscopy of PN spilled over to the liquid phase. Initial flash photolysis experiments involving phenyl azide gave conflicting results, with different authors favoring the presence of triplet phenylnitrene, " benzazirine BZ, or cyclic ketenimine as the carrier of the transient spectra. 

This hypothesis was supported by analysis of the transient spectrum obtained upon LFP of 2-fluorophenyl azide, which reveals the presence of triplet nitrene 20a despite the small ratio of kisc/koss- This is clearly evident in Fig. 16 (Insert Spectrum 1), which presents the spectrum of the products formed from the decay of singlet nitrene 16a at room temperature. This spectrum is the sum of the spectrum of triplet nitrene 20a (narrow band at 303 nm and weak absorption below 450 nm) and ketenimine 18a (broad band at 350 nm). This complicated spectrum can be eompared with the simpler spectrum of ketenimine 18b (Spectrum 2) and the spectrum of triplet nitrene 20a observed as a persistent species in a low-temperature matrix (Spectrum 3). It is clear that the yield of triplet nitrene 20a is significant at room temperature. However, if one postulates that azirine 17a does not inter-eonvert with singlet nitrene 16a (Scheme 6, -r). then the yield of... 

Chapman and coworkers (79RTC334) from studies on the low temperature photolysis of phenyl azide in an argon matrix at 8 K produced convincing IR spectroscopic evidence for the formation of l-aza-l,2,4,6-cycloheptatetraene (217), rather than a benzazirine intermediate. In fact, these workers have reinterpreted the formation of 2-alkylamino-3ff-azepines on the basis of amine addition to the cumulated system (217) rather than the benzazirine. 

The problem, however, is not yet settled as contemporary studies on the photolysis of bicyclic azides, e.g. 1-naphthylazide, in an argon matrix at 12 K demonstrate clearly the existence of two transient species, the IR spectra of which correspond in one case to the cumulated system analogous to (217) and in the other, which absorbs strongly at 1708-1736 cm-1, to the azirine structure (218) (80CC499). 

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