Chapter 10
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Highly Photosensitive Diazo Compounds as Photoacid Generators for Chemically Amplified Resists 1
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Kieko Harada , Masahito Kushida , Kyoichi Saito , Kazuyuki Sugita , and Hirotada Iida 2
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Department of Specialty Materials, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263, Japan Toyo Goshei Kogyo Company, Research Center, 563 Komegasaki, Funabashi-shi, Chiba 273, Japan
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Diazo compounds are the photosensitive components for the contrast enhanced lithography (CEL) materials and the photoacid generator(PAG) for PS printing plates based on thermal crosslinking. This paper reports on PAG performance of p-benzoylamino-2,5ethoxybenzenediazonium triflate (BTf) for microlithography resists. The rate of acid generation from BTf was larger than that of diphenyliodonium triflate(ITf). Deprotection of poly(tertbutyloxycarbonyloxystyrene) (tBOCHS) with BTf was 3 times faster than that with ITf after postexposure bake at same temperature. BTf with higher sensitivity and thermal stability may be expected to be PAG of diazo compounds applicable to microlithography resists. Diazo compounds are the photosensitive components for copying o f the diazo-type and vesicular processes, the contrast enhancement lithography ( C E L ) materials and the photoacid generator ( P A G ) for thermal-crosslinking type P S printing plates (1). Diazo compounds substituted with chlorine atom were used for thermal ring-opening polymerization o f tetrahydrofuran (2). 2,5-Diethoxy-4-tolylthiobenzenediazonium ion coupled with various Lewis acids ( S b F — , P F — , B F — etc.) was used for ringopening photopolymerization o f 1,2-epoxypropane (3). 4-(4-Methoxyanilino)benzenediazonium hexafluorophosphate with an absorption at long wavelengths was an initiator for cationic polymerization o f poly(2,3-epoxypropyl methacrylate) by argon ion laser (4). Diazo compounds substituted with dialkylamino groups showed high photosensitivity and thermal stability, but they can not be used as P A G (5). The acid generated was trapped by coodination to lone-pair electrons on the nitrogen o f the dimethyl amino group (6), but the coodinated acid was reported to dissociate from the nitrogen by heating (7). 6
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Diazo compounds substituted with a benzoylamino group have been used for wet diazo-type copying process, which offer high sensitivity and thermal stability. This paper will report on P A G performance o f these compounds for microlithography resists. 126
© 1 9 9 8 American Chemical Society Ito et al.; Micro- and Nanopatterning Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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Experimental Materials. 4-Benzoylamino-2,5-ethoxybenzenediazonium hexafluorophosphate (BP), was obtained by adding ammonium hexafluorophosphate to an aqueous solution o f 4benzoylamino -2,5-ethoxybenzenediazonium zinc chloride. The crude solids were recrystallized from methanol. 4-Benzoylamino-2,5-ethoxybenzenediazonium trifluoromethanesulfonate (triflate) (BTf) was prepared by diazotizing the corresponding amino compound with isopentyl nitrite in acetic acid containing trifluoromethanesulfonic acid (4). After completion o f diazotization, the precipitated crystals were filtered and dried. p-Phenylaminobenzenediazonium hexafluoro phosphate ( D P D ) and pdimethylaminobenzenediazonium hexafluorophosphate ( D E D ) were prepared similarly to B P . The matrix polymers, poly(p-hydroxystyrene)(PHS) and P H S partially protected with a t-butoxycarbonyl (tBOC) group (20% protected, M w . = 8,000) ( t B O C H S ) , were purchased from Aldrich Chemical C o . Inc. and Iweiss Chemical C o . respectively. Diphenyliodonium hexafluorophosphate (IP) and diphenyliodonium triflate(ITf), were obtained from M i d o r i Chemical C o . Tetrabromophenol Blue ( T B P B ) indicator was obtained from Aldrich C o . Inc. Diethylene glycol dimethyl ether ( D G D E ) was used as the coating solvent. The P H S film (thickness : 4 / / m ) was formed on a glass plate by spin-coating a polymer solution containing a matrix polymer P H S , T B P B indicator, acid generator, and D G D E , (0.5g: 0.03g: 5 . 8 X 1 0 M : 1.0 ml). The t B O C H S film was formed from a polymer solution containing t B O C H S , acid generator and D G D E (0.5g: 5 . 8 X 1 0 " M : 1.0 ml). _5
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Measurements. The B P and B T f in methanol were exposed to a super-high pressure mercury lamp, Toshiba S H L - 1 0 0 - U V - 2 (100W) with a Matsuda U V - D 2 (Transparency:300-400 nm) filter. The polymer layers containinng B P or B T f were exposed to a super-high pressure mercury lamp, Toshiba S H L - 1 0 0 - U V - 2 (100W). The resist films containing IP or I T f were exposed to a low pressure mercury lamp ( L P L ) , Toshiba G L - 8 (8W). The incident energies o f the high and l o w pressure mercury lamps were 3.83 and 0.42 mW/cm , respectively. Absorption spectra were measured with a Shimazu U V - 1 8 0 spectrophotometer. Thermal analysis were performed by M a c Science 001 Thermal Analyzing System at a heating rate o f 5°C/min for T G A and D T A under N atmosphere. F T I R spectra o f the films on an I T O glass were measured with a Perkin Elmer 1600 spectrophotometer. I R spectra o f the film on a N a C l plate were measured with a Hitachi 1-2000 spectrophotometer. 2
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Results and Discussion Photolysis and Thermolysis. The absorption maxima o f diazo compounds B T f and B P in methanol were at 396 nm and 392 nm as shown in Table 1. After U V irradiation o f the methanol solution, the concentrations o f the remaining diazo compounds were calculated from the absorbance at X max and are plotted against irradiation time as shown in F i g . l The absorbed photon numbers (4.36X10" einstein/cm ) were measured by potassium ferrioxalate actinometry. The quantum yields for photodecomposition,
