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As the critical path to increasing circuit density, deep-ultraviolet (DUV) lithography has played a key role in the development of new semiconductor products. At present, DUV refers to imagery at the 248-nm wavelength, with the introduction of 193-nm photolithographic systems anticipated in the next few years. This paper presents an overview of DUV lithography applications in the IBM Advanced Semiconductor Technology Center (ASTC). Since 1990, we have used DUV lithography for critical levels of advanced generations of DRAM (64Mb, 256Mb, and 1Gb) and associated families of logic products. We describe the means by which DUV capability and productivity have increased in a decreasing process window environment. Tooling, processes, and process control systems have undergone continuous improvement to accommodate increasing wafer starts and the rapid introduction of new products.
Introduction
The IBM Advanced Semiconductor Technology Center (ASTC) is a pilot line created in 1989 for the development and early manufacture of all advanced IBM semiconductor products. It has also been the site of recent development alliances among IBM, Siemens, and Toshiba, and is currently in the process of transferring products to manufacturing sites throughout the world. ASTC acts as the common foundry for future generations of DRAM (64Mb, 256Mb, and 1Gb), associated CMOS logic, and various experimental chip designs and processes. The need to process a wide spectrum of products, spanning all stages from early exploration to fully qualified manufacturing, poses a unique challenge to the efficient operation of a lithography sector at ASTC.
Deep-ultraviolet (DUV) lithography has enabled ASTC to pursue aggressive circuit ground-rule migration in the early 1990s; it has been the primary means of reducing the minimum ground rule (Gmin), as illustrated in Figure 1. The actual minimum ground rules achieved during the first half of the decade are displayed in two ways: 1) the lower, dashed curve shows the minimum ground rule processed successfully on integrated hardware in a given year, and 2) the upper, solid curve shows the weighted average ground rule across all hardware programs and DUV exposure levels processed successfully in a given year. The weighted average minimum ground rule processed in the ASTC DUV sector is projected to fall below 0.2 ym by the year 2000.
Also indicated in Figure 1 are key DUV lithography milestones associated...