The Extreme Ultraviolet Lithography (EUVL) technology is transitioning from the basic research and technology demonstration phase into commercialization. All key EUVL system modules have been demonstrated with an Engineering Test Stand (ETS) and the system has been used to provide the basic learning for developing commercial EUVL tools. Full field scanned printing has been demonstrated. Full field masks have been produced and methods have been demonstrated for defect repair for both mask blanks and for patterned masks. Major European, Japanese, and US consortia in partnership with over 100 industrial companies are supporting the establishment of the EUVL infrastructure. The remaining challenges have been identified and laboratory and industrial support are continuing to reduce the risks for developing beta and production tools. Production tools are expected to be introduced in the 2007 time frame to support aggressively implementation of 45 nm node geometries with volume production support for the 32 nm node in 2009.
Static and scanned images of 100 nm dense features were successfully obtained with a developmental set of projection optics and a 500W drive laser laser-produced-plasma (LPP) source in the Engineering Test Stand (ETS). The ETS, configured with POB1, has been used to understand system performance and acquire lithographic learning which will be used in the development of EUV high volume manufacturing tools. The printed static images for dense features below 100 nm with the improved LPP source are comparable to those obtained with the low power LPP source, while the exposure time was decreased by more than 30x. Image quality comparisons between the static and scanned images with the improved LPP source are also presented. Lithographic evaluation of the ETS includes flare and contrast measurements. By using a resist clearing method, the flare and aerial image contrast of POB1 have been measured, and the results have been compared to analytical calculations and computer simulations.
While interferometry is routinely used for the characterization and alignment of lithographic optics, the ultimate performance metric for these optics is printing in photoresist. The comparison of lithographic imaging with that predicted from wavefront performance is also useful for verifying and improving the predictive power of wavefront metrology. To address these issues, static, small-field printing capabilities have been added to the EUV phase- shifting point diffraction interferometry implemented at the Advanced Light Source at Lawrence Berkeley National Laboratory. The combined system remains extremely flexible in that switching between interferometry and imaging modes can be accomplished in approximately two weeks.
The Engineering Test Stand (ETS) is an EUV lithography tool designed to demonstrate full-field EUV imaging and provide data required to accelerate production-tool development. Early lithographic results and progress on continuing functional upgrades are presented and discussed. In the ETS a source of 13.4 nm radiation is provided by a laser plasma source in which a Nd:YAG laser beam is focused onto a xenon- cluster target. A condenser system, comprised of multilayer-coated and grazing incidence mirrors, collects the EUV radiation and directs it onto a reflecting reticle. The resulting EUV illumination at the reticle and pupil has been measured and meets requirements for acquisition of first images. Tool setup experiments have been completed using a developmental projection system with (lambda) /14 wavefront error (WFE), while the assembly and alignment of the final projection system with (lambda) /24 WFE progresses in parallel. These experiments included identification of best focus at the central field point and characterization of imaging performance in static imaging mode. A small amount of astigmatism was observed and corrected in situ, as is routinely done in advanced optical lithographic tools. Pitch and roll corrections were made to achieve focus throughout the arc-shaped field of view. Scan parameters were identified by printing dense features with varying amounts of magnification and skew correction. Through-focus scanned imaging results, showing 100 nm isolated and dense features, will be presented. Phase 2 implementation goals for the ETS will also be discussed.
The Engineering Test Stand (ETS) is a developmental lithography tool designed to demonstrate full-field EUV imaging and provide data for commercial-tool development. In the first phase of integration, currently in progress, the ETS is configured using a developmental projection system, while fabrication of an improved projection system proceeds in parallel. The optics in the second projection system have been fabricated to tighter specifications for improved resolution and reduced flare. The projection system is a 4-mirror, 4x-reduction, ring-field design having a numeral aperture of 0.1, which supports 70 nm resolution at a k<SUB>1</SUB> of 0.52. The illuminator produces 13.4 nm radiation from a laser-produced plasma, directs the radiation onto an arc-shaped field of view, and provides an effective fill factor at the pupil plane of 0.7. The ETS is designed for full-field images in step-and-scan mode using vacuum-compatible, magnetically levitated, scanning stages. This paper describes system performance observed during the first phase of integration, including static resist images of 100 nm isolated and dense features.
A model has been developed to predict the cost of extreme ultraviolet lithography (EUVL) masks. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor and is coated with reflective Mo/Si multilayers. Absorber layers are deposited on the multilayer and patterned. EUVL mask patterning will use evolutionary improvements in mask patterning and repair equipment. One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. The model of mask cost assigns yield and time required for each of the steps in fabricating EUVL masks from purchase of a polished substrate to shipment of a patterned mask. Data from present multilayer coating processes and present mask patterning processes are used to estimate the future cost of EUVL masks. Several of the parameters that significantly influence predicted mask cost are discussed in detail. Future cost reduction of mask blanks is expected from learning on substrate fabrication, improvements in low defect multilayer coating to consistently obtain <0.005 defects cm-2, and demonstration of multilayer smoothing which reduces the printability of substrate defects. The model predicts that the price range for EUVL masks in production will be S30-40K, which is comparable to the price of complex phase shift masks needed to use optical lithography for 70 nm critical dimension patterning.