ELECTRON-BEAM LITHOGRAPHY FOR 0.13 MU-M MANUFACTURING

General requirements for the use of electron beam lithography in direc t write manufacturing of silicon integrated circuits are discussed. 50 keV is suggested as an optimum beam energy, since this is the minimum beam energy that can achieve high aspect ratio structures (4:1) in si ngle layer resists in a manufacturing environment. Higher beam energie s result in an inefficient exposure process requiring larger currents; this combination will lead to excessive resist and wafer heating. Low er voltages will require the use of top surface imaging or multilayer resists, which have concerns of processing complexity, resist charging , and defects. At 50 keV, some form of proximity correction is require d to achieve reasonable control of critical dimensions. While one of t he principle arguments for low voltage lithography is that it avoids t he need for proximity correction, proximity correction is a solvable p roblem for large chips and is therefore a less risky approach than dev eloping a reliable surface imaging resist technology. From a quick rev iew of available resists and recent resist progress, it appears that a sensitivity of 5 mu C/cm(2) at 50 kV is the best that will be achieve d in the next several years. Neglecting overheads, for a design point of 40 8 in. wafers/h, a peak beam current of 13 mu A for a raster scan or projection tool is required. One of the major challenges of design ing a tool with such high beam currents is controlling space charge ef fects so that there is minimal impact on lithographic quality. After d iscussing the characteristics of various high speed electron beam writ ers that have been made to date, it will be concluded that there are t wo types of systems that have the best chance of meeting all of the re quirements-a projection system such as SCALPEL, and a multibeam system with hundreds of independently blanked beamlets. These systems minimi ze space charge effects by spreading out the electrons through a large r volume of space, allowing a larger total beam current. However, in o rder to make these systems a commercial reality, a great deal of innov ation, research, and development are still required. (C) 1997 American Vacuum Society.