4- -2,6-dinitrobenzyl tosylate

The polymer TBSS is known to undergo radiation induced chain scission and provides an improvement in the sensitivity compared to resists formulated with polymers which do not undergo chain scission. The lithographic performance of a resist formulated from this polymer and 2,6-dinitrobenzyl tosylate acid generator is reported. 

A nonionic, non-volatile photoactive acid generator, 2,6-dinitrobenzyl tosylate has been recently reported and shown to be effective in chemically amplified resist systems (10). This ester is a nonionic compound that has a much wider range of solubility in matrix polymers and does not contain undesirable inorganic elements. While it is known to exhibit a lower sensitivity to irradiation than the onium salt materials, many structural variations can be produced to precisely vary the acid properties of the molecule and to control the diffusion of the AG in the polymer matrix (11). 

Much less work has been focused on the effect of polymer structure on the resist performance in these systems. This paper will describe and evaluate the chemistry and resist performance of several systems based on three matrix polymers poly(4-t-butoxycarbonyloxy-a-methylstyrene) (TBMS) (12), poly(4-t-butoxycarbonyloxystyrene-sulfone) (TBSS) (13) and TBS (14) when used in conjunction with the dinitrobenzyl tosylate (Ts), triphenylsulfonium hexafluoroarsenate (As) and triphenylsulfonium triflate (Tf) acid generators. Gas chromatography coupled with mass spectroscopy (GC/MS) has been used to study the detailed chemical reactions of these systems in both solution and the solid-state. These results are used to understand the lithographic performance of several systems. 

The dinitrobenzyl tosylate, (15) triphenylsulfonium hexafluoroarsenate (16), and triphenylsulfonium triflate (17) were prepared as described in the literature. The monomers, 4-t-butoxycarbonyloxy-a-methylstyene (t-BOC-a-methylstyrene), and 4-t-butoxycarbonyloxystyrene (t-BOC-styrene) and their respective homopolymers, TBS and TBMS were prepared as described in the literature (12,14). TBSS was prepared by conventional, free-radical methods (13,18). The composition of this polymer (ratio of SO2 to t-BOC styrene) is controlled by changing the polymerization temperature and/or initiator concentration (Table II). 

Samples for analysis were prepared by spin-coating Si substrates from cyclohexanone solutions of 2,6-dinitrobenzyl tosylate and TBMS or TBS. The samples were prebaked at 90 C for 15 min in a convection oven, and analyzed after exposure and heating at 120 C for 30 min. The films on each substrate were dissolved with 5 ml of THF and a 1 ml aliquot of 0.1 vol % benzene in THF added. Finally, the solutions were diluted to 10 ml with THF, and IOOjj.1 injected onto the GPC for analysis. 

Having established the tendency of TBMS to undergo acid catalyzed depolymerization, the propensity for photochemically generated acid to effect the same phenomenon was evaluated. The resistance of TBS and TBSS to acid catalyzed depolymerization was also evaluated. Onium salts are well known photogenerators of acid, (16,17) while 2,6-dinitrobenzyl tosylate has been shown recently (15) to efficiently generate acid upon irradiation. Unirradiated samples of all the polymers... 

The triphenylsulfonium trifluoromethanesulfonate (Tf) photoactive acid generator affords the highest sensitivity (3-5 mJ cm-2) for all polymer systems studied. The contrast for these systems ranged between 2 and 6 and sub-micron resolution was obtained with all the materials. Resist systems using the triphenylsulfonium hexafluoroarsenate (Ar) precursor exhibited slightly lower sensitivities (16-20 mJ cm-2) while contrast values were similar, i.e., 2-6. Upon formulation with 5 wt% 2,6-dinitrobenzyl tosylate (Ts) the substituted styrenes exhibited still lower sensitivities (65-170 mJ cm2) and contrast remained in the range of 2-6. 

Deep-UV resists comprised of matrix polymers and a 2,6-dinitrobenzyl tosylate photoactive acid generator have been described and compared to previously reported onium salt systems. Although these resists exhibited lower sensitivity than onium salt-based materials, the contrast and processibility are superior. The use of a matrix polymer capable of radiation-induced chain scission improves the sensitivity and allows the 2,6-dinitrobenzyl tosylate acid generator to more nearly... 

Also, it will be shown that the absorbance and lithographic sensitivity engendered in a typical t-BOC based resist by 1 and that of a model compound without the DISCA feature, 4-(methotycarbonyI)-2,6-dinitrobentyl totylate 2, are comparable to that found when using 2,6-dinitrobenzyl tosylate 3. 

Figure 2. Comparative DSC s of 4-(/-but03Q carbonyl)-2,6-dinitrobenzyl tosylate 1, 4-methoi carbon -2,6-dinitrobeii l to late 2, and 2,6-dinitroben l tosylate 3.

Figure 5. DSC and TGA of a 50/50 mixture of the r-butyl ester of 3 -di-nitrotoluic acid 4 and 2,6-dinitrobenzyl tosylate 3.

It has been found that 4-(t-butffl carbonyl)-2,6-dinitrobenzyl tosylate 1 can be thesized from a inexpensive and readily available commerdal starting mate-... 

Poly((4-t-butylo] carbonylo 7)styrene sulfone) (PTBSS) was synthesized as previous described (19). A research sample of pofy(4-hydro ene) (PHS) (M,y 12300) was obtained from the Hoechst chemical company. 2,6-Dinitro-ben l tosylate and 2,6-dinitrobenzyl 4-nitrobenzenesulfonate were made as previously described (Z 8, 9). All other diemicals were obtained from the Aldrich Oiemical Company. 

Since thermal elimination of isobutene occurs at 163 the Tmin measured for 1 really corresponds to that of 4-carboityl-2,6-dinitrobemtyl tosylate. However, the predicted for this compound should have been 238 °C and not the 204 value found. A DSC experiment with a 50/50 mixture of 34-dinitrotoluic add and 2,6-dinitrobenzyl totylate shows that the temperature of is lowered to 192 ° from 200 C (Figure 6). A possible ei lanation for the lower measured value of T i is that the more polar matrix containing carboxylic acid moieties has lowered slightly the transition state for thermal generation of tosic add. 

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