EXTREME ULTRAVIOLET LITHOGRAPHY

EXTREME ULTRAVIOLET LITHOGRAPHY

Abstract:

EUV lithography (EUVL), a relatively new form of lithography that uses extreme ultraviolet (EUV) radiation with a wavelength in the range of 10 to 14 nanometers (nm) to carry out projection imaging.
Currently, and for the last several decades, optical projection lithography has been the lithographic technique used in the high-volume manufacture of integrated circuits. It is widely anticipated that improvements in this technology will allow it to remain the semiconductor industry's workhorse through the 100 nm generation of devices. However, some time around the year 2005, so-called Next-Generation Lithographies will be required. EUVL is one such technology vying to become the successor to optical lithography. This topic provides an overview of the capabilities of EUVL, and explains how EUVL might be implemented. The challenges that must be overcome in order for EUVL to qualify for high-volume manufacture are also discussed.

Optical projection lithography is the technology used to print the intricate patterns that define integrated circuits onto semiconductor wafers. Typically, a pattern on a mask is imaged, with a reduction of 4:1, by a highly accurate camera onto a silicon wafer coated with photoresist. Continued improvements in optical projection lithography have enabled the printing of ever finer features, the smallest feature size decreasing by about 30% every two years. This, in turn, has allowed the integrated circuit industry to produce ever more powerful and cost-effective semiconductor devices. On average, the number of transistors in a state-of-the-art integrated circuit has doubled every 18 months.
Currently, the most advanced lithographic tools used in high-volume manufacture employ deep-ultraviolet (DUV) radiation with a wavelength of 248 nm to print features that have line widths as small as 200 nm. It is believed that new DUV tools, presently in advanced development, that employ radiation that has a wavelength of 193 nm, will enable optical lithography to print features as small as 100 nm, but only with very great difficulty for high-volume manufacture.
Over the next several years it will be necessary for the semiconductor industry to identify a new lithographic technology that will carry it into the future, eventually enabling the printing of lines as small as 30 nm. Potential successors to optical projection lithography are being aggressively developed. These are known as "Next-Generation Lithographies" (NGL's). EUV lithography (EUVL) is one of the leading NGL technologies; others include x-ray lithography, ion-beam projection lithography, and electron-beam projection lithography.
In many respects, EUVL may be viewed as a natural extension of optical projection lithography since it uses short wavelength radiation (light) to carry out projection imaging. In spite of this similarity, there are major differences between the two technologies. Most of these differences occur because the properties of materials in the EUV portion of the electromagnetic spectrum are very different from those in the visible and UV wavelength ranges., and to provide the reader with an understanding of the challenges that must be overcome if EUVL is to fulfill its promise in high-volume manufacture.