Development Of A High ThermoStability UV Positive Photoresist And A 248nm Deep-UV Photoresist

Photoresist is a key and foundmental material for the photolithographic technique in the microelectronics manufacturing system. It defines the development level of microelectronics technique. As a rule, photoresist is composed of matrix resin, photosensitizer (photoactive compound), solvent and other additives. At the present time, the research and development of photoresist in China is much behind the internationally leading level.By using novel methods, a series of monomers for the matrix resins of photoresist were synthesized, including N-phenyl-methacrylamide, N-(p-hydroxyphenyl) methacrylamide, N-(p-acetoxyphenyl)methacrylamide, p-tert-butoxycarbonyloxystyrene (PTBOCS), N-hydroxy-5-norbornene-2,3-dicarboximidomethacrylate and N-hydroxy-3,6- endo-oxo-4-cyclohexene-dicarboximidomethacrylate. Their FT-IR and 1H NMR spectra were measured for characterization.Two common photoacid generators(PAGs) triphenylsulfonoum tosylate and N-hydroxyphthalimidotosylate were prepared. They were characterized by FT-IR and 1H NMR, and tested by thermal property, UV absorbance and solubility. It showed that they could be used as the PAGs of deep-UV photoresist.Three copolymers were obtained from the solution free radical copolymerization of the above monomers and comonomer styrene, i.e. poly-styrene-co-N-(p-hydroxy phenyl)maleimide, poly-N-(p-hydroxyphenyl)methacrylamide-co-N-phenylmaleimide and poly-N-phenylmethacrylamide-co-N-(p-hydroxyphenyl)maleimide. The investigations of their properties showed that all of them had high glass transition temperatures(Tg>250℃), good solubilities, film forming characteristics and hydrophilicities, so they could be used as the matrix resins of high thermostability UV positive photoresist.A new copolymer poly-PTBOCS-co-N-hydroxy-5-norbornene-2,3-dicarboximido methacrylate was prepared from the above monomers PTBOCS and N-hydroxy-5- norbornene-2,3-dicarboximidomethacrylate. Its FT-IR spectrum, thermal property and UV transmittance were determined. A conclusion could be drawn that it had excellent solubility, film forming characteristic, thermostability(Tg=175℃),UV transmittance in 248nm wavelength and adhesiveness to the wafer substrates, so it could be a good matrix resin of deep-UV photoresist. But another new polymer poly-PTBOCS-co- N-hydroxy-5-norbornene-2,3-dicarboximidomethacrylate had poor solubility in organic solvent, so it was unfit for the matrix resin of deep-UV photoresist.For the first time, poly-N-(p-hydroxyphenyl)methacrylamide-co-N-phenyl maleimide and poly-N-penylmethacrylamide-co-N-(p-hydroxyphenyl)maleimide were used as the matrix resins of the high thermostability UV positive photoresist. The optimal formulation and photolithographic processing conditions of a new UV positive photoresist, which was a mixture of poly-N-(p-hydroxyphenyl)methacrylamide-co-N–phenylmaleimide, diazonaphthoquinone sulfochloride(DNS), benzophenone and solvent, were studied in detail. It was found that its imaging contrast was 3.001, its resolution was up to about 1μm and its plasma etching resistance was comparable to that of the novolak-diazonaphthoquinone(DNQ) system UV photoresist.A new single-layer 248nm deep-UV photoresist system was developed, whose matrix resin was the above poly-PTBOCS-co-N-hydroxy-3,6-endo-oxo-4-cyclohexene- dicarboximidomethacrylate, PAG was triphenylsulfonium tosylate, dissolution inhibitor was (4,4'-di-tert-butoxycarbonyloxy)diphenylpropane, solvent was 1:1(v/v) ethylene glycol monomethyl ether acetate(EGMEA) and ethyl lactate(EL), and developer was 2.38% tetramethylammonium hydroxide (TMAH) aqueous solution. Its optimal formulation and photolithographic processing conditions were explored. It showed that it was an environmentally stable chemically amplified photoresist(ESCAP), and it had the resolution of no less than 0.5μm, the plasma etching resistance comparable to that of the novolak-DNQ system photoresist, and the sensitivity of 22mJ/cm2.The development imaging mechanisms were simply explored for the high thermostability UV positive photoresist of poly-N-(p-hydroxyphenyl)methacrylamide -co-N-phenylmaleimid-DNS system and the 248nm deep-UV photoresist of poly-PTBOCS-co-N-hydroxy-3,6-endo-oxo-4-cyclohexene-dicarboximidomethacrylate-triphenylsulfonium tosylate system.