To make smaller transistors so chips can pack more gates and deliver higher performance, lithography must use shorter light wavelengths to form the smaller features. To that end, developments to extend the use of 193-nm lithography have turned to water. Immersion lithography uses a transparent liquid to fill the space between the projection lens of the step-and-repeat lithography system and the wafer surface.
For a 193-nm exposure wavelength, researchers prefer to use water. This scheme appears to offer better resolution enhancement over conventional projection lithography because the lens can be designed with numerical apertures higher than one. That would allow the lithography system to produce smaller images and thereby shrink the transistor dimensions.
According to International Sematech (ISMT), Austin, Texas, a few researchers have investigated the technology's potential to extend optical lithography over the last two years. But over the last few months, it has piqued more general interest among tool manufacturers and device makers as a way to extend the life of 193-nm systems.
The organization recently held a forum to determine the critical areas that should be addressed to improve the understanding of fundamental characteristics and properties of materials involved in immersion lithography. According to Tony Yen, codirector of Lithography at ISMT and an assignee from TSMC, it will also determine if new materials, like photoresists, need to be developed.
For details, see www.sematech.org.
Reprints
