Microfabrication Technologies for Advanced VLSI Devices
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MICROFABRICATION TECHNOLOGIES FOR ADVANCED VLSI DEVICES Y. HORIIKE,
R. YOSHIKAWA, H. OKANO,
M. NAKASE,
H. KOMANO,
AND T. TAKIGAWA
TOSHIBA RESEARCH AND DEVELOPMENT CENTER, VLSI RESEARCH CENTER, KOMUKAI TOSHIBACHO 1, SAIWAIKU, KANAGAWA, JAPAN, 210. ABSTRACT Recent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 um patterns employing PMMA,high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 iimpatterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10-3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n' poly-Si with resist mask and with pattern transfer using an optics down to 0.5 Pm and 0.9 Pm resolutions respectively. 1. Introduction Progress in VLSI devices has been achieved by advances in a large number of technologies. Microfabrication technologies, such as lithography and etching, contributed substantially in these developments. Recent development of the optical reduction projection system, which is called "the stepper", enables the fabrication of 4MDRAM with 0.8 i'm feature size. Now, efforts are concentrated in 16MDRAM with 0.5 im minimum dimension. Over the past several years, optical, X-ray, and electron beam (EB) were the three potential candidates for practical submicron lithography. However, because of subsequent progress, 0.5 im patterning has been demonstrated using optical lithography [1], which clearly indicates optical lithography is the prime candidate for 0.5 im dimensions. In addition, directional etching of substrates, defined by finely delineated patterning, is also an important technology. However, RIE, which is widely used for VLSI processes, faces difficult problems in submicron microfabrication. These problems include uniformity and throughput for processing larger size wafer, etching of high aspect ratio features such as trench in silicon, etching with high selectivity to the underlying thin film, and serious radiation damages. Concerning the latter two items, low energy and neutral process, such as photochemical etching, should be studied. This paper reports lithographic and etching technologies for the fabrication of advanced devices such as 16M and 64MDRAM developed in our laboratory. Future trends in these technologies are also discussed.
Mat. Res. Soc. Symp. Proc. Vol. 75. 1 1987 Materials Research Society
18
2.
Lithography Technology
2-1
EB Lithograp
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