November 17, 1997
Hitachi Develops Direct-write EB Lithography System for Volume Fabrication Applications Offering Major Boost in Throughput- Enhanced cell-projection system more than triples writing speed -Nowadays PCs and other information devices, as well as consumer appliances, make extensive use of semiconductor products such as microprocessors, microcontrollers and memory chips. The circuits of such devices are produced by using photolithography techniques to draw the circuit patterns on the semiconductor wafers. As the size of semiconductor devices continues to decrease, the dimensions of the circuit pattern features have shrunk to less than 0.25 micrometer. Below that level, circuit dimensions start to get smaller than the wavelength of the light beams used to draw the patterns. At such sub-quarter-micron levels, forming patterns with the required degree of precision therefore involves complicated processes, which poses a major obstacle to improved throughput. Instead of a light beam, an EB lithography machine uses a tightly-focused beam of electrons to draw the circuit patterns on the semiconductor wafers. With electron-beam technology, it is possible to draw patterns at a dimensional resolution of 0.15 micrometer or above. A problem with existing EB lithography systems has been a lack of sufficient throughput to handle high-speed, high-volume fabrication tasks. This has effectively limited the use of such systems to research and development of advanced devices, and low-volume fabrication of diverse items, such as ASICs. Hitachi started research and development work on EB lithography systems in 1970, and in 1981 released a high-speed system that used variable-shaped-beam technology. The company went on to develop technology that enabled groups of cells to be exposed by cell-projection. This enabled high-speed drawing of LSI circuit patterns, and was incorporated in a system marketed in 1992. Today that system is widely used in the development of next-generation LSIs and the fabrication of ASICs, and is the market leader in direct-write systems. Hitachi also produces high-throughput mask-and-reticule lithography systems that use variable-shaped-beam technology. The new system uses transfer deflection technology for high-precision, wide-angle deflection of the electron beam and, for circuits that include repetitive pattern segments, is able to form up to 21 circuit patterns by cell-projection, compared to just five at present. Cell-projection capabilities are further enhanced by the ability to automatically set approximately 2,000 types of repetitive circuit patterns. In another improvement, the speed of the beam computation and deflection control circuitry is some 1.4 times higher. The overall result is that compared to existing systems, drawing speed is some three times higher, providing a major improvement in throughput. To ensure stability of drawing precision, a light, highly rigid electron-beam column is used that offers excellent resistance to vibration. The integrated structure used for the control system has enabled the overall size of the system to be reduced to around 70% the size of the existing system, so it takes up less space. In addition, productivity can be further improved by integration of coating and development system units. Under a commission from the Ministry of International Trade and Industry's New Energy and Industrial Technology Development Organization (NEDO), the results of research into single-column electron-beam lithography systems conducted by the Association of Super-advanced Electronics Technologies (ASET) was incorporated to achieve the system technology. Further details of the new system will be presented at the Semicon Japan exhibition on December 3 to 5 at Makuhari Messe. Basic specifications
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