Future electron-beam lithography and implications on design and CAD tools

Summary form only given. The steeply increasing price and difficulty of masks make the mask-based optical lithography, such as ArF immersion lithography and extreme ultra-violet lithography (EUVL), unaffordable when going beyond the 32-nm half-pitch (HP) node. Electron beam direct writing (EBDW), so called maskless lithography (ML2), provides an ultimate resolution without jeopardy from masks, but the extremely low productivity of the traditional single beam systems made it very laborious for mass manufacturing after over 3 decades of development. Although electron beam lithography has been long used for mask writing, it is yet very slow and typically takes from hours to days to write a complete 6-inch high-end mask. Direct writing a 300-mm wafer definitely would take much longer. Considering production efficiency in the cleanroom, the throughput of lithography tools should be in the order of 10 wafers per hour (WPH) per square meter as compared to that of an ArF scanner. To achieve such a throughput per e-beam column requires an improvement of more than 3-order. Increasing the beam current in the conventional single beam system would induce the space charge effect and thus is not a solution. Several groups have proposed different multiple electron beam maskless lithography (MEBML2) approaches, by multiplying either Gaussian beams, variable shape beams or by using cell projections, to increase the throughput. The maturing MEMS technology and electronic control technology enable precise control of more than ten thousands or even millions of electron beamlets, writing in parallel. Without the mask constraint, the exposure can be made by continuously scanning across the entire wafer diameter as long as the ultra-high speed data rate can be supported. Hence a much slower scan speed is required and therefore a small tool footprint is achievable.