February 21, 2006, San Jose, CA--Researchers at IBM have shrunk the minimum size of features produced by deep-ultraviolet (DUV) lithography down to just under 30 nm. They have done it by raising the refractive index of the fluid used in the immersion-lithography process; this change will allow the creation of lens designs that reach higher resolution.
The achievement may further extend the decades-long reign of refractive optical lithography, postponing the need to switch to the radically different and expensive extreme-ultraviolet (EUV) lithography technique, which has been considered necessary to reach these small feature sizes. While DUV lithography uses 193-nm light and relatively conventional (although extremely sophisticated) refractive lenses, EUV lithography relies on light of a much-shorter wavelength (13 nm) produced by exotic light sources, and requires extremely difficult-to-manufacture precision off-axis mirror optical systems.
The features produced by the IBM researchers are well-defined and equally spaced 29.9 nm lines and spaces. Producing equal-sized lines and spaces of this size is quite an achievement: while there are other ways to optically produce 30-nm (and even smaller) isolated features, creating "dense" lines and spaces is the true test of an optical system's ability.
The 29.9-nm size is less than one-third the size of the 90-nm features now in mass production and just below the 32 nm that industry consensus has held as the limit for optical lithography techniques.
"Our goal is to push optical lithography as far as we can so the industry does not have to move to any expensive alternatives until absolutely necessary," said Robert Allen, manager of lithography materials at IBM's Almaden Research Center. "This result is the strongest evidence to date that the industry may have at least seven years of breathing room before any radical changes in chip-making techniques would be needed."
The 29.9-nm lines and spaces were created on a lithography test apparatus designed and built at IBM Almaden, using new materials developed by its collaborator, JSR Micro (Sunnyvale, CA). The first technical details are to be presented this week (Monday, Feb 20, 2006) at the SPIE Microlithography 2006 conference being held in San Jose, California.
"We believe that high-index liquid imaging will enable the extension of today's optical lithography through the 45- and 32-nm technology nodes," said Mark Slezak, technical manager of JSR Micro, Inc. "Our industry faces tough questions about which lithography technology will allow us to be successful below 32 nm. This new result gives us another data point favoring the continuation of optical immersion lithography."
For its research, IBM developed an interference immersion-lithography test apparatus, called NEMO. IBM's NEMO tool uses two intersecting laser beams to create light-and-dark interference patterns with spacings closer than can be made with current chip-making apparatus. As a result, NEMO is ideal for researching, testing and optimizing the various high-index fluids and photoresists being considered for use in those future DUV systems that would create such fine features. Now that IBM's new result shows a path for extending optical lithography, high-index lens materials must be developed to enable its commercial viability.
Resolution in immersion lithography is limited by the lowest refractive index of the final lens, fluid, and photoresist materials. In IBM's NEMO experiments, the lens and fluid had indices of about 1.6, and the photoresist's index of refraction was 1.7. Future research is aimed at developing lens, fluid, and photoresist materials with indices of refraction of 1.9, which would enable even smaller features to be imaged.