Low energy electron-beam proximity projection lithography: Discovery of a missing link

Low energy electron(e)-beam proximity projection lithography is proposed for integrated circuit lithography for minimum feature sizes less than or equal to 0.1 mu m. This new e-beam lithography is similar to optical projection lithography except that photons are replaced by low energy electrons of 2 kV. The low e-beam energy permits the use of single crystal 0.5 mu m thick silicon membrane masks without an absorbing metal layer of high atomic number. This membrane mask is thick enough for good heat conduction and thin enough for feature sizes less than or equal to 0.1 mu m. The mask distortion caused by the fabrication can be corrected by a fine-tuning deflector. Therefore the mask is allowed to have a residual distortion of more than 100 nm. The proposed system does not suffer from the space charge effect in the electron optics column nor the proximity effect with respect to both the wafer and mask writings, and it is fundamentally a low power lithography which needs no special cooling system. The analysis shows that the e-beam column can be made entirely of electrostatic components to achieve sufficient resolution. For an appropriate resist process for this low energy e-beam we propose a bilayer process which consists of a chemically amplified thin deep ultraviolet photoresist and a thick antireflective layer. We estimated a throughput of 30 12 in. wafers per hour and a resolution of less than 50 nm. (C) 1999 American Vacuum Society. [S0734-211X(99)17806-5].