Character Projection Lithography for Application-Specific Integrated Circuits

In the recent fabrication of semiconductor devices, quite various devices are produced while most of them result in small production volumes. A small production volume of ICs leads to a rise of the price of an IC because the expensive investment made in its photomask set must be redeemed by passing on the price. The price of photomasks increases rapidly as the transistor integration advances. The price of photomasks has a great impact on the price of semiconductor devices. Electron beam direct writing (EBDW) is a solution to fabricating small-lot ICs at a cheap cost. The EBDW can draw patterns onto silicon wafers masklessly or quasi-masklessly (Inanami, 2000; Pfeiffer, 1979). The throughput of the conventional EBDW equipment which adopts the variable shaped beam (VSB) method (Pfeiffer, 1978) is, however, extremely low. In the VSB method, exposed patterns are divided into a large number of small rectangular and triangular shapes to draw them as shown in the left of Fig. 1. In this figure Letter “E” is divided into four rectangles and consequently needs four “EB shots” to be drawn. The conventional VSB equipment shoots rectangular and triangular shapes onto silicon wafers and results in a lot of EB shots, which deteriorate the throughput of the equipment.