Photoactive compounds

Instead of using thermal energy to trigger the hydrogen abstraction mechanism, photo-induced reactions can be also be used to successfully crosslink acrylic PSAs [74-76], In this case, photoactive compounds, such as for example those containing benzophenone, anthraquinone or triazine nuclei are compounded with the polymer or copolymerized as one of the monomers. After drying, the adhesive... 

Figure 17 shows the sensitivity curves of the resist containing PM-5(run-6)(75 weight%) and 5-naphthoquinone diazide sulfonate of 2,3,4-trihydroxybenzophenone(25 weight%). The average esterification ratio of the photoactive compound was 2.5 units per three OHs in the benzophenone. The y value was 1.6 and the sensitivity was 90mJ/cm2 when developed with 0.34% TMAH aqueous solution for 120 sec at 20°C. The resist containing M-5(run 3)... 

HPR-206 Positive Photoresist (Olin-Hunt) Mixed Isomer Novolac + Diazonaphthoquinone Photoactive Compounds 120-140... 

The glycosylated derivatives 51A-D were tested against the yeast Saccharomyces cerevisiae and displayed different photoactivities.24 In this case, the most photoactive compounds were the mono-glycosylated 51A and... 

The positive resist materials evolved from discoveries made by the Kalle Corporation in Germany who developed the first positive-acting photoresist based on the use of a novolac matrix resin and a diazoquinone photoactive compound or sensitizer. The original materials were designed to produce photoplates used in the printing industry. These same materials have been adopted by semi-conductor fabrication engineers and continue to function effectively in that more demanding application. 

The photoactive compounds, or sensitizers, that are used in the formulation of positive photoresists, are substituted diazonaphthoquinones shown in Figure 17. The substituent, shown as R in Figure 17, is generally an aryl sulfonate. The nature of the substituent influences the solubility characteristics of the sensitizer molecule and also influences the absorption characteristics of the chromophor (79). The diazonaphthoquinone sulfonates are soluble in common organic solvents but are insoluble in aqueous base. Upon exposure to light, these substances undergo a series of reactions that culminate in the formation of an indene carboxylic acid as depicted in Figure 17. The photoproduct, unlike its precursor, is extremely soluble in aqueous base by virtue of the carboxylic acid functionality. 

Such a pinhole density test was performed on the AZ/PMMA two-layer deep-UV PCM system (26). The result is shown in Table IX where a pinhole density of 8 and 6 per cm was obtained for the capped (A) and uncapped (B) systems. Because only three wafers were used for each test, the result should be taken only qualitatively and the numerical difference between 6 and 8 pinholes/cm should be taken as being indicative of measurement fluctuations only. It should not be attributed to the use of different developers or O2 plasma because in the subsequent tests of batches C and D in which the DUV exposure was omitted, the numbers were 0 and 1 pinhole/cm with the capped system giving the smaller pinhole density. The low pinhole density in batch E in which the AZ development step was omitted suggests that the pinholes arise during the development of the AZ layer. Presumably, a small portion of the AZ base resin molecules were not linked up with the photoactive compound and therefore still exhibited their intrinsic high solubility in the AZ developer. After development, these high solubility spots became pinholes. These pinholes are apparently larger than the diffraction - limited sizes so that they can be transferred into the PMMA film by deep-UV exposure. 

At the present time, most of the positive photoresists used in the manufacture of microcircuits consist of a low molecular weight phenolic resin and a photoactive dissolution inhibitor. This composite system is not readily soluble in aqueous base but becomes so upon irradiation with ultraviolet light. When this resist is exposed, the dissolution inhibitor, a diazoketone, undergoes a Wolff rearrangement followed by reaction with ambient water to produce a substituted indene carboxylic acid. This photoinduced transformation of the photoactive compound from a hydrophobic molecule to a hydrophillic carboxylic acid allows the resin to be rapidly dissolved by the developer. (L2,3)... 

The most popular positive resists are referred to as DQN, corresponding to then-photoactive compound (DQ) and base material (N), respectively. DQ stands for diazo-quinone, and N stands for novolac resin. The repeat unit of a novolac resin is shown in Figure 7.47. Novolacs normally dissolve in aqueous solutions, but combinations of... 

Apart from multi-level layer resist systems, conventional positive-tone resists can be classified into two categories one-component and two-component systems. Classical examples of the former systems are polyfmethyl methacrylate), and poly (butene-1-sulfone) (2,3). Typical examples of the latter system are AZ-type photoresists, which are mixtures of cresol-formaldehyde-Novolak resins and a photoactive compound acting as a dissolution inhibitor... 

The most popular photoactive compound, 1, is a substituted diazonaphthoquinone shown below together with a cresol-formaldehyde Novolak resin, 2 (5). There are many varieties of photoactive compounds that generate... 

A mixture of three isomeric cresols is used in a commercially available cresol-formaldehyde Novolak resin. This mixed Novolak resin, Varcum resin (12), provides adequate properties as a host resin for near-UV- and mid-UV-photoresist applications. Gipstein and his co-workers prepared pure cresol-formaldehyde Novolak resin from each isomeric cresol and compared their spectroscopic and resist characteristics (13). Their data on the UV-absorption spectra of each cresol-formaldehyde Novolak resin together with the commercially available Varcum resin are as follows the absorbances of 0.2 jim thick Novolak films at 250 nm are 0.165(Varcum), 0.096(o-cresol), 0.092(m-cresol), and 0.055(p-cresol). The so-called "window" in the UV absorption at around 250 nm is a maximum with the p-cresol-formaldehyde Novolak resin, while the other isomeric cresol and formaldehyde Novolak resins yielded similar UV absorptions at this wavelength. The smallest UV absorption at 254 nm is an advantage for the p-cresol-formaldehyde Novolak when the resin is used for a deep UV photoresist with a suitable photoactive compound (14). 

The structural variations of Novolak resins also influence how well they mix or form solid solutions with a dissolution inhibitor when resist films are cast onto substrates. This is a crucial problem for resist formulation. Usually, cresol-formaldehyde Novolak resins mix well with photoactive compounds like a... 

Chlorinated Novolak Resins. Mixtures of a cresol formaldehyde Novolak resin and a photoactive compound cross-link at electron doses far smaller than the dose required for the Novolak resin alone (11). The reason for this accelerated cross-linking is the reactions between the ketene (an intermediate formed from the photoactive compound upon irradiation) and the Novolak resin. This reaction may be reduced by using a Novolak resin modified for this purpose, or by using certain additives. The rationale for developing a halogen-substituted Novolak resin is the control of the reaction between the intermediate ketene and the Novolak. 

Many halogen-substituted cresol/phenol-formaldehyde Novolak resins were prepared and tested for their electron beam sensitivity when mixed together with a photoactive compound. The following halogen-substituted phenols and cresols were used as starting materials o-, m-, p-chlorophenols o-,... 

Formulation of Resist Solutions. Forty grams of a Novolak resin was mixed with 10 g of the photoactive compound, and dissolved in 100 g of bis-2-methoxy-ethylether. After wafers were spin-coated, the samples were immediately placed on a hot plate at 82 C for 14 min. The formulation procedure of a composite resist of poly (2-methyl-1-pentene sulfone) in the Novolak resin is as follows the polysulfone was mixed with the resin (13 wt% solid), and then dissolved in 2-methoxyethyl acetate the films were spin-coated onto silicon wafers, and then baked at 100°C for 20 min prior to electron beam exposure. 

The preparation method is similar to that for the cresol-formaldehyde Novolak resin with a molar ratio of cresol/benzaldehyde = 1.1 in acidic conditions. We have prepared varieties of substituted m-cresol-benzaldehyde Novolak resins, and 1-, and 2-naphthol-4-hydroxybenzaldehyde Novolak resins in the same manner. Almost all of these benzaldehyde Novolak resins give excellent resist films when spin-coated onto silicon or silicon dioxide substrates after being dissolved, together with a photoactive compound, in a solvent like 2-... 

Typical resist images obtained after a mid UV-exposure with an UV3 Perkin Elmer Exposure System are shown in Figure 5 using the m-c resol-benzaldehyde Novolak and the diester photoactive compound. The experiments were not carried out under optimum conditions, and the exposure dose at 313 nm was 500 mJ/cm2. Although this resist system was not the fastest one at this wavelength region, it clearly provides usable patterns. 

Figure 5. Resist images made of m-cresol-benzaldehyde Novolak resin with a photoactive compound (15 wt%) 500 mJ/cm2 at 313 nm, and 70 sec in (1 4.5)...

Other modifications to the [ . . ] cryptands include replacing one or more of the polyether chains by o-phenanthroline and/or bipyridine, as in (46), to obtain photoactive compounds.165... 

The incorporation of photoactive compounds into organized supramolecular assemblies allows the induction of specific reactions and structural changes such as, for instance, in the photocrosslinking of photopolymerizable components in lipid vesicles, a powerful approach to the control of polymolecular architectures [7.10, 8.78]. 

In a more general sense, these observations show that upon immobilization of photoactive compounds onto a solid substrate a substantial difference is detected between the photophysical processes observed for the heterotriad and the dyad in solution. More importantly, direct injection from those moieties not directly bound to the oxide surface can be efficient - this is always fully realized and such an observation is important for the further development of real devices. As a result of this through-space interaction, no osmium-based emission is observed and injection from both the ruthenium and the osmium centers is faster than the laser pulse. An interesting observation is also that upon irradiation of the heterotriad Ti02-Ru-0s, only one final product, i.e. Ti02(e)-Ru(ll)0s(lll), is obtained. In view of the potential of these modified surfaces as potential molecular devices, this is an important feature. The presence of a rigid structure rather than a flexible one, as observed in the Ru-Rh case, clearly leads to a more uniform behavior. 

Cameron, J.F., Willson, C.G. and Frechet, J.M.J. (1997) Photogeneration of amines from a-keto carbamates design and preparation of photoactive compounds. Journal of the Chemical Society, Perkin Transactions 1, 2429-2442. 

Thioxopteridines are also an interesting class of photoactive compounds. Under aerobic conditions, various types of photooxidations take place. l,3,5-Trimethyl-6(5//)-lumazinethione... 

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