Low-Energy E-Beam Proximity Lithography (LEEPL): Is the Simplest the Best?

Abstract

Low-energy e-beam proximity lithography (LEEPL) is proposed as the simplest integrated circuit lithography for minimum feature sizes ≤0.1 µm. This new e-beam lithography is similar to 1× X-ray proximity lithography except that the X-ray beam is replaced with a beam of low-energy electrons of 2 kV. This low e-beam energy permits the use of single-crystal 0.5-µm-thick silicon stencil 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 ≤0.1 µm. Mask distortion caused by fabrication can be corrected by a fine-tuning deflector. Therefore, a mask with a residual distortion of more than 100 nm is acceptable. This eliminates the main difficulty of X-ray proximity lithography. The proposed system is not affected by a space-charge effect in the electron optics column, and a proximity effect with respect to both wafer and mask writings, and it is fundamentally 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 such as the chemical amplification of resist lines (CARL) process which consists of a chemically amplified thin deep ultraviolet (DUV) photoresist and a thick planarizing layer as a starting point. We estimated a throughput of about 40 12 inch wafers per hour and a resolution of a significantly less than 50 nm.