Bisazides poly

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. 

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... 

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). 

Even resists based on poly(4-hydroxyl styrene) have been shown to be cross-linked in the DUV using 3,3-diazodiphenylsulfone and other bisazides as the... 

Alternatively, bisazides, i.e. low molar mass compounds containing two azide groups, can be added to the polymer. Several commercially used bisazides are presented in Table 7.2. Many linear polymers can be photo-cross-linked with the aid of bisazides [17]. Of note in this context is poly(cis-isoprene), which contains some cyclized structures (Chart 7.7). It has been frequently applied as a resist material in photolithography applications. 

A water-soluble bisazide (see Chart 7.8) is applicable for the photo-cross-linking of water-processable polymeric systems containing polyacrylamide or poly(vi-nyl pyrrolidone). 

The earhest photoresists used in integrated circuit manufacture consisted of polymers that were rendered insoluble by photo-cross-linking and thus operated in the negative tone mode. For instance, partially cycUzed poly(cis-isoprene) containing a bisazide as additive served for a long time as the workhorse resist material in photohthography applications [15]. This system has already been described in Section 7.2.3. Subsequently, Novolak-based positively functioning sys-... 

A higher contrast material was described being a mixture of poly(methyl iso-propenyl ketone) and aromatic bisazides Exposure to UV light results in the formation of nitrenes, which insert into C—H bonds of the polymer. After exposure, a difference in etch rate in an oxygen plasma is observed but this difference increases considerably upon baking. The reported etch rates after baking are 100 nm/min for exposed material and 600 nm/min for unexposed material. 

This method is suited to large amounts of crosslinking and low swelling polymer gels. Examples are known of water soluble polymers, such as poly(vinyl alcohol) and poly(N-vinyl pyrrolidine), being photocrosslinked via diazo resins, bisazides, chromic acid, and photodimerization of polymers having photosensitivity, such as styrenebazolium salt, on the water soluble polymer main chain. 

A negative deep-UV resist composed of poly( p-vinylphenol) and a bisazide has been developed (5). A limitation has been that a high percentage of bisazide (20 wt%) to resin is required such that a resist film of 1 jam thickness is virtually opaque in the 200-300 nm region. Consequently, undercut profiles are typically observed after development and the processing conditions have to be carefully controlled to maintain line-width and reproducibility (2). Other negative resists such as novolac resin with a bisazide (15-20 wt%) (9), an acidic resin with a bisazide (30 wt%) 10) and poly(methyl methacrylate) with a bisazide (20-25 wt%) 11) also suffer because of the poor cross-linking efficiency of the bisazide. 

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