Azide resists

In experiments where relatively small volumes of sediment suspensions are employed, autoclaving may significantly alter the structure of the sediment as well as introducing possibly severe analytical difficulties. In such circumstances, there are few alternatives to incubation in the presence of toxic agents such as NaNj, which has been used at a concentration of 2g/L. There remains, of course, the possibility that azide-resistant strains could emerge during prolonged incubation, and the possible occurrence of reactions between the substrate and azide must also be taken into consideration. 

Figure 3.33. Schematic and mechanistic representation of plasma development of a PMIPK-azide resist.

Other approaches that have been exploited in azide resist compositions include directly attaching the azido groups to a polymer chain as shown in structures (IX) and (X). ... 

The most commonly used resin in his-azide resists is poly(c/5-isoprene), which is cyclized hy treatment with a mineral acid (Scheme 6.7). The cyclization reaction is quite similar to cationic polymerization. In the first reaction step, the acid cation adds to a double bond, producing a carbocation. The reaction of a nearby double bond with this ion leads to cyclization. ... 

Although the original KTFR resist based on 2,6-bis(4-azidobenzal)-4-methyl-cyclohexanone in poly(cA-isoprene) rubber resin that dominated the IC industry between 1957 and 1972 was organic solvent developed, in the 1980s, water-processable azide resists were described by Nonogaki and co-workers. These... 

It should be mentioned that the reaction of nitrenes with oxygen is a very important reaction that competes with cross-link formation in azide resists. ... 

The diazoquinone-novolac positive plates were only a moderate commercial success, but interest in the diazoqunone-novolac systems was revived in the 1970s when the resolution requirements of the semiconductor industry outpaced the capabilities of the negative bis-azide resists then in use. It was during this time that the diazoquinone resists established themselves as nonswelling, high-resolution imaging materials in the semiconductor industry. 

Upon exposure to u.v., azides decompose with the formation of a very reactive species nitrenes, which can be in singlet or in triplet state. Further reactions of nitrenes include hydrogen abstraction. Diets Alders reactions at the double bond and dimerization to azo dyes. Unfavorable reaction is with atmospheric oxygen which deactivates light sensitivity of the system (Figure 3). It is the second reaction that is important in the negative rubber-azide resists. 

The Curtms rearrangement has been used to prepare 5-aminothiazole (11) (60.61), 4-methyl-5-aminothiazole. 2-chloro-5-aminothiazole (58), and 2.4-dimethyl-5-aminothiazole (62) (Scheme 11). Heating the corresponding azides yield carbamates that resist hydrolysis but react with acetic anhydride to give the 5-acetylaminothiazoles. 

L First manufacturing use of chemically amplified resists Plasma-developed resist first described X-ray proximity lithography demonstrated Bis-azide rubber resists introduced DNO-novolac resist for microelectronics introduced Photoresist technology first applied to transistor fabrication DNO-novolac resist patented by Kalle... 

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. 

Neopentyl (2,2-dimethylpropyl) systems are resistant to nucleo diilic substitution reactions. They are primary and do not form caibocation intermediates, but the /-butyl substituent efiTectively hinders back-side attack. The rate of reaction of neopent>i bromide with iodide ion is 470 times slower than that of n-butyl bromide. Usually, tiie ner rentyl system reacts with rearrangement to the /-pentyl system, aldiough use of good nucleophiles in polar aprotic solvents permits direct displacement to occur. Entry 2 shows that such a reaction with azide ion as the nucleophile proceeds with complete inversion of configuration. The primary beiuyl system in entry 3 exhibits high, but not complete, inversiotL This is attributed to racemization of the reactant by ionization and internal return. 

The properties of chlorine azide resemble those of bromine azide. Pon-sold has taken advantage of the stronger carbon-chlorine bond, i.e., the resistance to elimination, in the chloro azide adducts and thus synthesized several steroidal aziridines. 5a-Chloro-6 -azidocholestan-3 -ol (101) can be converted into 5, 6 -iminocholestan-3l -ol (102) in almost quantitative yield with lithium aluminum hydride. It is noteworthy that this aziridine cannot be synthesized by the more general mesyloxyazide route. Addition of chlorine azide to testosterone followed by acetylation gives both a cis- and a trans-2iddMct from which 4/S-chloro-17/S-hydroxy-5a-azidoandrostan-3-one acetate (104) is obtained by fractional crystallization. In this case, sodium borohydride is used for the stereoselective reduction of the 3-ketone... 

Aminodebromination of 4-bromo-l//-3-benzazepin-2-amine (25) with triethylamine occurs readily and results in formation of the quaternary salt 26 (see also Section 3.2.1.5.6.), whereas attempts to effect nucleophilic substitution of bromide with primary or secondary amines gives only tarry mixtures.41 The bromo group is also resistant to displacement by azide and benz-cncthiolate but undergoes substitution with thiocyanate ion in hot dimethylformamide to give the 4-thiocyanato derivative 27 rather than the thiourea by addition at the amine function. 

On the other hand, for low shock-resistant expls such as Pb Azide, Mercury Fulminate or... 

Two other results will now be pointed out which presumably also require reinterpretation in the light of the reaction behavior of iminooxophosphoranes. Thus the gas phase pyrolysis of diphenylphosphoryl azide is reported to give monomeric 92 50) and the dehydrohalogenation of phenylphosphoric adamantylamidic chloride with methylhydrazine the heterocumulene 93 51), which is even considered resistant to water. Since partly correct analytical values are available, 92 and 93 may well be oligomers. 

A rather complex microwave-assisted ring-opening of chiral difluorinated epoxy-cyclooctenones has been studied by Percy and coworkers (Scheme 6.131) [265]. The epoxide resisted conventional hydrolysis, but reacted smoothly in basic aqueous media (ammonia or N-methylimidazole) under microwave irradiation at 100 °C for 10 min to afford unique hemiacetals and hemiaminals in good yields. Other nitrogen nucleophiles, such as sodium azide or imidazole, failed to trigger the reaction. The reaction with sodium hydroxide led to much poorer conversion of the starting material. 

Bis(azide)—rubber resists, 15 157 Bis-(P-hydroxyethyl) terephthalate, 10 487 Bis(biphenyl) chromium(I) iodide, physical properties, 6 528t Bis(carbamoyl) peroxides, 18 477 Biscarbonato uraniumfVI) complexes, 25 431... 

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. 

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. 

When the concentration of the azide exceeds 30 wt%, sensitivity decreases (Figure 2) and the contrast becomes worse (Figure 3). This is due to the increase of the optical density of the resist. Large optical density prevents the light from penetrating into the resist (3,11). Also, the resist thickness remainig after development is maximum at the 30 wt% azide concentration (Figure 2). From these results, it was concluded that the azide-styrene resin resist which contains 30 wt%... 

Figure 2. Effect of azide concentration on exposure characteristics for azide-styrene resin resist of 1.0 micron film thickness.

This indicates that the prebaking temperature higher than the melting point of the azide decomposes the azide (50%) and it totally decomposes upto 100 mJ/cm2 irradiation. It is possible that subsequent reactions of the nitrene, generated from the azide thermolysis and photolysis, with the styrene resin could be responsible for solubility modulation of this type resist (16). 

The UV spectra for this resist film, before and after exposure to KrF excimer laser irradiation for 100 mJ/cm2, are shown in Figure 6. The absorbance of the azide renders the reist film of l.o micron thickness essentially opaque at 248 nm. After exposure of 100 mJ/cm2, the absorbance bleaches from 0.5 to 6.0% at 248 nm. Intense absorption by this resist at 248 nm closely relates to the pattern profile of the resist, which will be discussed in the last section. 

As shown in Figure 6, the resist film strongly absorbs KrF excimer laser light. In the KrF excimer laser exposure of the resist, photon energy absorption is highest at the top of the resist film and lowest at the interface between the resist and substrate. This is due to the attenuation of the irradiation in the resist layer. Decreases in solubility followed by such photochemical reaction occur to a much greater extent in the vicinity of the resist film surface. Moreover, the thermally decomposed azide decreases solubility of the unexposed and exposed resist film (Figure 7). 

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