Bisazides

These polymers need to be made photosensitive for use as photoresists and this is achieved by the incorporation of bisazide sensitisers. On exposure to light the photochemical reaction induced by the bisazide results in rapid crosslinking of the polymer rendering it insoluble in the developing solvent. 

Scheme 13. Formation of the bislactam 53 by reaction of bisazide 49 with C60-...

The use of phenolic polymers in photocrosslinkable systems usually involves multicomponent systems which incorporate polyfunctional low molecular weight crosslinkers. For example, Feely et al. [9] have used hydroxymethyl melamine in combination with a photoactive diazonaphthoquinone which produces an indene carboxylic acid upon irradiation to crosslink a novolac resin. Similarly, Iwayanagi et al. [10] have used photoactive bisazides in combination with poly(p-hydroxy-sty-rene) to afford a negative-tone resist material which does not swell upon development in aqueous base. 

Cyclized polyisoprene has been used as a photoresist by being sensitized with bisazides(1-3). Recently, H.Harada et al. have reported that a partially cyclized 1,2-polybutadiene showed good properties as a practical photoresist material in reproducing submicron patterns (U ). S.Shimazu et al, have studied the photochemical cleavage of 2,6-di(h -azidobenzal)cyclohexanone in a cyclized polyisoprene rubber matrix, and have reported that the principal photoreaction is the simultaneous cleavage of the both azido groups by absorption of a single photon with a U3% quantum yield(5 ). Their result does not support the biphotonic process in the photolysis of bisazide proposed by A.Reiser et al.(6 ). 

Based on these results and the reaction mode of phenylazide with unsaturated olefine monomers as the model compound of the polymer, mechanisms [i] - [ill] are proposed for the crosslinking of 1,2-polybutadiene by bisazide. 

Phenylenebisnitrene (43) has been generated at low temperatures [107,108] from the corresponding bisazide (43-N2) and characterized by IR spectroscopy (Scheme 9). No intermediates, resulting from elimination of one nitrogen molecule, were observed under these conditions. Thus, no IR bands attributable to nitrene 45 (Structures 45 and 46), which was suggested as an intermediate in the formation of dicyanobutadiene 44 (mucononitrile) from the thermolysis of bisazide 43-N2 [109] or the oxidation of 46 [110], were observed. 

Lull and co-workers showed that the tethered bisazides such as 2,2-dibenzyl-l,3-diazidopropane (124) undergo [3-t2] cycloadditions to adjacent [6 6]-bonds (cis-l addition). Thermal extrusion of N2 afforded a mixture of the corresponding cis-1-1,2,3,4-bisimino[60]fullerenes and twofold cluster-opened 2,3,4,5-bis-aza-homo[60]-fullerenes [36, 37, 111]. The reaction of with optically active bisazides yielded enantiomerically pure bis-azafullerenes with the same addition pattern [111]. 

Miura and Kobayashi studied the photochemistry of 4,4-biphenyl bisazide. They concluded that photolysis of this diazide leads to extrusion of a single molecule of nitrogen with the formation of a singlet state species, X , with a lifetime of 19 ns. Miura and Kobayashi did not specify the nature of X. This species absorbs at 380 nm and its spectrum and lifetime are similar to our results with singlet para-biphenylnitrene. Therefore we conclude that X is singlet 4 -azido-4-biphenylnitrene. 

Figure 9. Photochemical transformations of a bisazide sensitizer in negative photoresists based on cyclized polyisoprene.

Negative Resists for Deep UV. There has been considerable effort recently devoted to the design of negative resists for deep-UV application. Iwayanagi and co-workers (37) have reported on the properties of resists composed of cyclized polyisoprene and several bisazides whose absorption maxima lie within the deep-UV region. Since the sensitizers do not absorb in the visible region they are referred to as "white resists" and are claimed to be 60-450 times more sensitive than PMMA. One of these resist is available commercially as... 

Iwayanagi (40) recently extended this system into the mid-UV range by changing the sensitizer to an aromatic monoazide compound (4-azidochalcone). Insolubilization of this mid-UV resist does not result in a cross-linked matrix as occurs with the bisazide sensitized MRS. The primary reaction appears to be insertion of the reactive nitrene into a C-H bond on the ring, forming a secondary amine. 

A modification of these systems involving replacement of poly (4-vinylphenol) with poly(methyl isopropenyl ketone) (PMIPK) was reported by Nakane and co-workers (41). Although PMIPK is a positive-acting singlecomponent resist in the deep UV, it functions as a negative resist when mixed with an aromatic bisazide such as 2,6 di(4-azidobenzylidene)-4-... 

A different approach has been used by Tsuda, Nakane and their collaborators (138,139) who showed that mixtures of poly(methylisopropenyl ketone) (PMIPK) containing a bisazide sensitizer such as 4,4 -diazodiphenyl sulfide or 4-methyl-2,6-di(4-azidobenzylidene) cyclohexanone function as negative dry-developable resists. It is claimed that the bisazide... 

Stable triazolines are obtained from aryl azides and V-alkyl and N-aryl maleimides (Scheme 81 )307-309a the reaction succeeds with silyl azides310 and is utilized in the synthesis of polymers from bisazides and bismaleimides.311 312 Unlike maleimides, maleic anhydrides do not yield stable triazolines with trimethylsilyl azide the reaction products are oxazinediones (Section IV,A).310,313,314... 

Several bisazides with absorption maxima between 240 and 290 nm have been examined as DUV sensitizers for cyclized polyisoprene (76). The sensitivity of DUV resist formulated with cyclized polyisoprene and 1 wt % of 3,3 -bisazidophenyl sulfone (structure 3.10) is 75 times higher than that of PMMA. These azide DUV resists suffer from the resolution limit imposed by low contrast and the swelling phenomenon, which is as expected from the preceding discussion. 

Taylor et al. (124) described a process in which a bisazide-polyisoprene resist is exposed to UV light and, in a subsequent step, treated with an... 

Typical resists include cyclized polyisoprene with a photosensitive crosslinking agent (ex bisazide) used in many negative photoresists, novolac resins with diazoquinone sensitizers and imidazole catalysts for positive photoresists, poly(oxystyrenes) with photosensitizers for UV resists, polysilanes for UV and X-ray resists, and polymethacrylates and methacrylate-styrenes for electron-beam resists (Clegg and Collyer, 1991). Also note the more recent use of novolac/diazonaphthoquinone photoresists for mid-UV resists for DRAM memory chips and chemically amplified photoacid-catalysed hydroxystyrene and acrylic resists for deep-UV lithography (Choudhury, 1997). 

Fig. 13 SEM photographs showing wall profiles obtained by surface crosstinkages (a) no UV-flood exposure, (b) 10 mJ/cm exposure at 300 nm, (c) 15 mJ/cm exposure at 300 nm. The resist was a bisazide-added Shipley 1450J.

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