Optimization of PHS-based chemically amplified negative resist for 100-kV electron-beam projection lithography (EPL)

Electron beam (EB) lithography has often been used for fabricating advanced ULSIs. Recently, to increase the throughput, EB projection lithography (EPL) has been proposed. If 100 kV acceleration voltage and 20 to 30 mu A beam current are to be adopted in this technology, a high sensitivity resist will have to be developed to achieve a throughput of more than 30 wafers/hour (8 "phi). In this paper, we show the photoacid generator (PAG) optimization of a polyhydroxysterene (PHS)-based chemically amplified negative resist for EPL. To evaluate the resist sensitivity and the resolution, we prepared the PHS-based negative resists with PAGs of various quantum yields of acid generation, which were the onium-salt-type PAG, the imide-type PAG, and the alkylbenzene-type PAG. The cross-linker was the melamine-type one. To simultaneously obtain a high sensitivity of less than 10.0 mu C/cm(2) and a high resolution of less than 0.10 mu m, a PHS-based negative resist with the imide-type PAG was most preferable. With this resist, we successfully obtained 0.08-mu m gate line patterns (128K sub-array of DRAM), exposed by one 250x250 mu m(2) EB shot using a 100-kV EB projection experimental column. In addition, the throughput was estimated to be 30 wafers/hour (8 "phi) or more.