ABSTRACT
This paper discusses the basic concepts and current state of development of 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 2008, so-called Next-Generation Lithographys will be required. EUVL is one such technology vying to become the successor to optical lithography. This paper 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.
INTRODUCTION
Microprocessors, also called computer chips, are made using a process called lithography. Specifically, deep-ultraviolet lithography is used to make the current breed of microchips and was most likely used to make the chip that is inside your computer.
Lithography is akin to photography in that it uses light to transfer images onto a substrate. Silicon is the traditional substrate used in chip making. To create the integrated circuit design that?s on a microprocessor, light is directed onto a mask. A mask is like a stencil of the circuit pattern. The light shines through the mask and then through a series of optical lenses that shrink the image down. This small image is then projected onto a silicon, or semiconductor, wafer. The wafer is covered with a light-sensitive, liquid plastic called photoresist.The mask is placed over the wafer, and when light shines through the mask and hits the silicon wafer, it hardens the photoresist that isn?t covered by the mask. The photoresist that is not exposed to light remains somewhat gooey and is chemically washed away, leaving only the hardened photoresist and exposed silicon wafer. The key to creating more powerful microprocessors is the size of the light?s wavelength. The shorter the wavelength, the more transistors can be etched onto the silicon wafer. More transistors equal a more powerful, faster microprocessor.
DUVL uses a wavelength of 240 nanometers As chipmakers reduce to smaller wavelengths, they will need a new chip making technology. The problem posed by using deep-ultraviolet lithography is that as the light?s wavelengths get smaller, the light gets absorbed by the glass lenses that are intended to focus it. The result is that the light doesn?t make it to the silicon, so no circuit pattern is created on the wafer. This is where EUVL will take over. In EUVL, glass lenses will be replaced by mirrors to focus light and thus EUV lithography can make use of smaller wave lengths. Hence more and more transistors can be packed into the chip. The result is that using EUVL, we can make chips that are upto 100 times faster than today?s chips with similar increase in storage capacity.
