A novel class of low molecular-weight organic resist materials for nanometer lithography, 1,3,5-tris[4-(4-toluenesulfonyloxy)phenyl]benzene (TsOTPB) and 4,4′,4″-tris(allylsuccinimido) triphenylamine (ASITPA), was designed and synthesized. TsOTPB with a glass-transition temperature (Tg) of 64 °C and ASITPA with a Tg of 80 °C were found to function as positive and negative resists, respectively, enabling the fabrication of 150 and 70 nm line patterns on exposure to an electron beam at 50 keV.
The minimum feature size in semiconductor devices is becoming smaller and smaller. A 0.35 µm resolution is required for the fabrication of 64 Mbit DRAM, and nanometer-size lithographic patterns will be required in the future. One of the factors determining the resolution limit of the lithography process is the particle size of resist materials. In order to obtain nanometer-size lithographic patterns, it is desirable to reduce particle size of the resist materials. Organic polymers have been used as resist materials. The particle size of organic polymers with a degree of polymerization of 105 is roughly calculated to be 10 nm [1]. This means that there is more than 10 % fluctuation in 100 nm lithographic patterns. A breakthrough to achieve nanometer-size lithography is to develop lowmolecular-weight organic resist materials. However, low-molecular-weight organic compounds generally do not form uniform stable amorphous films, since they tend to crystallize readily. Very recently, an oligomer, a calixarene derivative [2], and a vacuum evaporated film of C60 [3] have been reported to function as negative electron-beam resists with high resolution.We report here a novel low-molecular-weight organic compound, 1,3,5-tris[4-(tert-butoxycarbonylmethoxy)phenyl]benzene(BCMTPB), which functions as a positive-type electron-beam resist material. The new compound BCMTPB was synthesized by the condensation reaction of 1,3,5-tris(4-hydroxyphenyl)benzene with chloroacetic acid tert-butyl ester and identified by various spectroscopies, mass spectrometry and elemental analysis.BCMTPB was found to form readily an amorphous glass, as evidenced by differential scanning calorimetry. When the crystalline sample of BCMTPB obtained by recrystallization from benzene/hexane was heated, an endothermic peak due to melting was observed at 141 °C. When the resulting isotropic liquid was cooled on standing in air, it formed an amorphous glass via a supercooled liquid. When the amorphous
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