Extreme ultraviolet lithography C. W. Gwyn, R. Stulen, D. Sweeney, and D. Attwood Citation: Journal of Vacuum Science & Technology B 16, 3142 (1998); doi: 10.1116/1.590453 View online: http://dx.doi.org/10.1116/1.590453 View Table of Contents: http://scitation.aip.org/content/avs/journal/jvstb/16/6?ver=pdfcov Published by the AVS: Science & Technology of Materials, Interfaces, and Processing Articles you may be interested in Characterization of multilayer reflective coatings for extreme ultraviolet lithography AIP Conf. Proc. 521, 108 (2000); 10.1063/1.1291768 Rigorous simulation of mask corner effects in extreme ultraviolet lithography J. Vac. Sci. Technol. B 16, 3449 (1998); 10.1116/1.590476 At-wavelength detection of extreme ultraviolet lithography mask blank defects J. Vac. Sci. Technol. B 16, 3430 (1998); 10.1116/1.590473 At-wavelength interferometry for extreme ultraviolet lithography J. Vac. Sci. Technol. B 15, 2455 (1997); 10.1116/1.589666 Use of attenuated phase masks in extreme ultraviolet lithography J. Vac. Sci. Technol. B 15, 2448 (1997); 10.1116/1.589664 Redistribution subject to AVS license or copyright; see http://scitation.aip.org/termsconditions. Download to IP: 193.0.65.67 On: Sat, 10 Jan 2015 13:09:33 Extreme ultraviolet lithography C. W. Gwyna) EUV LLC, Livermore, California 94551-0960 R. Stulen, D. Sweeney, and D. Attwood VNL, Livermore, California 94551-0960 ~Received 29 May 1998; accepted 16 September 1998! An extreme ultraviolet ~EUV! lithography tool using 13.4 nm radiation is being developed by a consortium of integrated circuit ~IC! manufacturers to support 100 nm imaging for integrated circuit production. The 43, 0.1 NA alpha tool has a .1 mm depth of focus, all reflective optics, a xenon laser plasma source, and robust reflective masks. The technology is expected to support feature scaling down to 30 nm. © 1998 American Vacuum Society. @S0734-211X~98!12006-1# I. INTRODUCTION Equations ~1! and ~2! demonstrate that improvements in resolution achieved by incremental decreases in wavelength Although the first papers proposing the use of extreme and increases in NA result in a decrease in DOF and corre- ultraviolet ~EUV! or soft x-ray radiation ~wavelengths from 2–50 nm! for projection lithography were published in the sponding decrease in the process window. EUVL extends late 1980’s,1–4 extensions of conventional optical lithogra- optical lithography by using much shorter wavelengths rather phy have continued to dominate semiconductor device than increasing NA to achieve better resolution. As a result, manufacturing. These extensions have relied on incremental it is possible to simultaneously achieve a resolution of 100 decreases in illumination wavelength and increases in optical nm or smaller and a DOF of 1 mm or larger by operating numerical aperture ~NA! for the system. While 248 and 193 with a wavelength of 20 nm or less using a camera having a nm optical lithography can be extended to support integrated NA of 0.1 or less. circuit ~IC! manufacturing for 130 nm and perhaps 100 nm, a Despite the potential advantages of shorter EUV wave- next generation lithography technology will be required for lengths, the continued extension of optical lithography and printing ,100 nm features. Extreme ultraviolet lithography the technical challenges associated with using EUV radiation ~EUVL!, using 10–14 nm extreme ultraviolet light, is one of as a light source have delayed industry acceptance and in- the most promising technologies. This technology builds on vestment in the technology. Most of the research and devel- the industrial optical experience, uses an EUV light source, opment in the US during the early 1990’s were performed by and is initially expected to support IC fabrication at 100 nm; the Department of Energy and AT&T Laboratories. In 1996, scaling is expected to support several technology generations changes in government funding priorities resulted in reduced down to possibly 30 nm. The two fundamental relationships describing a lithogra- support for the Department of Energy ~DOE! EUV program phy imaging system, resolution ~RES! and depth of focus at Lawrence Livermore National Laboratory and Sandia Na- ~DOF!, are given by tional Laboratories. Based on the technical success of the DOE program and RES5k1l/NA ~1! the potential of EUV lithography to be scaled to small ge- ometries, a consortium of semiconductor manufacturers, the and EUV LLC, was formed in 1997 to provide funding and guid- 2 ance for the commercialization of EUVL. The EUV LLC DOF5k2l/~NA! , ~2! consortium is composed of Advanced Micro Devices, Intel, where l is the wavelength of the radiation used for imaging and Motorola. The program goal is to facilitate the research, and NA is the numerical aperture of the camera. The param- development and engineering to enable the Semiconductor eters k1 and k2 are empirically determined and correspond to Equipment Companies ~SEMs! to provide production quan- those values that yield the desired critical dimension CD ~ ! tities of 100-nm-EUV exposure tools for IC manufacturing control within an acceptable IC manufacturing process win- by 2004.5 Funding is provided by the EUV LLC to the dow. Values for k and k of 0.6 and greater have been used 1 2 ~DOE! Virtual National Laboratory ~VNL! composed of in high volume manufacturing, however, a given lithographic Lawrence Berkeley National Laboratory ~LBNL!, Lawrence technology can be extended further for smaller values for k1 by optimizing the IC fabrication process at the cost of tighter Livermore National Laboratory ~LLNL!, and Sandia Na- tional Laboratories ~SNL! to perform the required research process control. Setting k1 and k2 equal to 0.5 corresponds to the theoretical values ~Rayleigh criteria! for resolution and and engineering. Joint development programs support key DOF. EUV component technologies with industry partners. The LLC members are also investing resources within their own a!Electronic mail: [email protected] companies to support mask and resist development. 3142 J. Vac. Sci. Technol. B 16„6…, Nov/Dec 1998 0734-211X/98/16„6…/3142/8/$15.00 ©1998 American Vacuum Society 3142 Redistribution subject to AVS license or copyright; see http://scitation.aip.org/termsconditions. Download to IP: 193.0.65.67 On: Sat, 10 Jan 2015 13:09:33 3143 Gwyn et al.: Extreme ultraviolet lithography 3143 FIG. 1. Parallel development accelerates learning for SEM tool develop- ment. II. OBJECTIVES FIG. 2. Schematic representation of the EUV lithography system. The objectives of the EUV LLC program are to extend and apply the basic technology to the design, fabrication, and handling, and a simplified software and user interface. It will testing of an alpha-like tool denoted as the Engineering Test be heavily instrumented with diagnostics to provide as much Stand ~ETS! and to transfer learning to the SEMs for the performance learning data as possible. development of beta tools. The beta tools are expected to A schematic representation of an EUV lithography tool is result in production tools for 100 nm geometries by 2004. shown in Fig. 2. The key EUV technologies include: ~1! an The EUV program represents a highly parallelized pro- EUV illumination system consisting of a radiation source gram focused on the phased development of the ~1! alpha, and a condenser system to collect the light and to provide ~2! beta, ~3! production tools, ~4! simultaneous support for proper ring field illumination, ~2! a patterned reflective mask, masks and resists, and ~5! establishment of an industry infra- ~3! a43reduction camera using four mirrors, ~4! multilayer structure for EUV specific component development. The coatings for optical elements and masks, ~5! an EUV sensi- program relationships are shown in Fig. 1. tive resist, and ~6! metrology to support manufacturing and The following discussion outlines the ETS tool design inspection of reticles. Non-EUV specific subsystems consist development approach, some of the specifications associated of the focus and overlay systems, scanning mask and wafer with the subsystems, and technology and component devel- stages, optics housing, and wafer and reticle handling inter- opment status. Early EUV printing results are obtained using faces and robotics. A preliminary structural and mechanical existing 103 microsteppers. Finally, a few of the potential design based on CAD drawings is shown in Fig. 3. advantages of the EUV technology for the next generation The ETS is based on a laser plasma point source and a lithography applications are listed. four mirror, ring-field imaging system. A single membrane filter separates the condenser from the mask and projection III. TOOL DEVELOPMENT STRATEGY: optics. With four mirrors, the reticle and wafer stages can be ENGINEERING TEST STAND located on either side of the projection optics box, eliminat- The goals for the ETS are focused on continued technol- ing interference problems associated with mechanical scan- ogy development, integration of the technology into a tool, ning. EUV flux to the wafer will support a throughput of and transfer of the technology and learning to the stepper companies for the beta tool development. The program is not focusing on demonstrating technology elements, which are extensions of current optical lithography steppers, such as precision alignment and wafer handling, which are expected to be implemented in a commercial EUVL tool. With input from the end users including both the semiconductor manu- facturers and the stepper companies, the ETS will serve to significantly lower risk in EUV-specific areas including source, condenser, reticle, projection optics, environmental system, and methods for isolating the environments and eliminating contamination. The ETS development will provide a flexible test stand for EUV-specific system, subsystem, and component learn- ing. This machine will initially emphasize EUV flux throughput, not wafer throughput, will have simplified wafer FIG. 3. Preliminary implementation of ETS using CAD system drawings. JVST B - Microelectronics and Nanometer Structures Redistribution subject to AVS license or copyright; see http://scitation.aip.org/termsconditions.