The end of optical lithography has been so often predicted (incorrectly) that such predictions are now a running joke among lithographers. Yet optical lithography does have real, physical limitations and even more real economic limits, and an accurate estimation of these limits is essential for planning potential next generation lithography (NGL) efforts. This paper will review the two types of resolution limits in optical lithography: the pitch resolution, governed by the amount of spatial frequency information that can pass through an imaging lens, and the feature size resolution, limited by our ability to control feature size. Projecting the trends in these resolution limits, the capabilities of 193nm immersion lithography will be explored.

Electronics has been the nation’s largest and fastest growing manufacturing industry throughout the end of the last century. Semiconductors have fueled that growth , even with the downturn in the past two years. The US semiconductor industry now has the largest value-added of any US manufacturing sector, comprising almost 1 percent of US gross domestic product (GDP). In 2001 US-based firms accounted for approximately 52% of the $140-billion world semiconductor market, and the electronics industry employs more than 2 million Americans. This growth has been sustained through steady advancements in semiconductor manufacturing science and technology. These strategies have lead to increasingly cost effective advanced communications and information technologies.

Today in 2004, the areal density in magnetic recording systems stands at approximately 100 Gbit/in². It is projected to increase by 30-60% per year for the foreseeable future and reach 1 Tbit/in² around the end of the decade. The corresponding rapid reduction in bit dimension poses significant challenges for lithography, both now in the thin-film head, and in the future on the disk, with the possible transition to patterned media. In thin-film head production, the critical dimension is now less than 100 nm and by 2006 will be less than 50 nm. To meet these requirements, the magnetic recording industry in recent years has been turning to direct-write electron-beam lithography. However, advances in both electron-beam systems and chemically-amplified resists will be required as areal density approaches the Terabit per square inch regime. No lithography is presently used on the disk or media, but this could change within a few years if discrete track media or patterned media is introduced. The key challenge will be establishing a low cost manufacturing capability at the very high resolution bit dimensions required. One new technology that shows considerable potential is nanoimprint lithography, but significant tool development will be required to improve throughput and provide sufficiently low cost per disk. High-resolution electron-beam systems and advanced resists will also be required to fabricate the 1X master templates. Further in the future, a combination of lithography and self-assembly of magnetic nanoparticles may provide a path to areal densities as high as 40 Tbit/in².

ASML has continued to make significant investments in the development of extreme ultraviolet lithography (EUVL), addressing the critical challenges, including defect-free mask handling, reflective optics technology, environmental control, and source. We present updates in these key areas and in the realization of our process development exposure tool. This tool is used to minimize the risk of EUVL for the 45-nm technology node and below, and to support the development of the global infrastructure of masks, sources, and resist. Realization of the process development tool is well underway; most of the modules are in vacuum qualification and functional testing. From arial image simulations, we conclude that EUVL tools are particularly suited for contact printing, due to the use of dark-field masks, and hence, limited influence of flare.

We have exposed 10 wafers on the Engineering Test Stand (ETS), the 0.1 NA EUV scanner at Sandia National Laboratories in Livermore, CA. The EUV reflective mask was fabricated in-house using a Ta-based absorber stack on Mo/Si multilayers. The printed wafers contained different line sizes and pitches, line-end shortening measurement structures, contact holes, and patterns for estimating absorber defect printability. The depths of focus of each feature are typically 2 um due to the small NA of the scanner, and these should decrease by at least a factor of 6.25 as the NA's increase to 0.25. The data from measurements of line size through pitch and line-end shortening test structures indicate that both 1D and 2D optical proximity correction will be required. Defects that are either notches in or protrusions from absorber lines are the first to print, and they begin to print when they reach approximately 15~nm (1X) in size. This size threshold is in accordance with the 2003 ITRS specifications. We also report the first printing of SRAM bitcells with EUV lithography.

This work discusses the imaging properties of EUVL systems on the basis of an aerial image study in resist. A process window analysis for the lithographic structures which are driving the ITRS roadmap is presented. Here we cover the 45 nm and 32 nm node. In a first step we focus on the contribution of wavefront aberrations and flare effects to the imaging performance. In a second step we investigate the process latitude for different generic pattern of the above mentioned nodes. It becomes clear that EUVL tools are a very good choice for the printing of contact holes. Dense and semi-dense lines can be easily printed too, using a conventional illumination setting. From our current perspective, isolated features on bright field reticles are the most challenging structures for EUV imaging due to the flare impact on contrast and process latitude. Related to flare we discuss our progress in mirror surface manufacturing to reduce the overall flare level.

Extreme ultraviolet (EUV) interferometry has been successfully performed for the first time at 0.3 numerical aperture (NA). Extensive EUV “at-wavelength” testing including alignment, was performed on a newly created Micro Exposure Tool (MET) optic designed for sub-50-nm EUV lithographic imaging experiments. The two-mirror, 0.3 NA MET is ar-guably the highest resolution light-projection lithography tool ever made. Using both lateral shearing and phase-shifting point-diffraction interferometry, the wavefront was measured across the field of view, and the alignment was optimized in preparation for imaging. The wavefront quality reached 0.55 nm RMS (lambda[EUV]/24.5) in a 37-term annular Zernike poly-nomial series, dominated by higher-order spherical aberration. Measurements included calibrations of the interferometer accuracy, assessment of repeatability, and cross-comparisons of visible and EUV interferometric measurements. The comparisons and the final, measured wavefront quality were affected by an apparent alignment drift, several tenths of a nm in magnitude. Significant unresolved differences between testing strategies shows that continued work is needed to improve the measurement accuracy to levels required for EUV lithography.

The shot noise, line edge roughness (LER) and quantum efficiency of EUV interaction with seven resists related to EUV-2D (SP98248B) are studied. These resists were identical to EUV-2D except were prepared with seven levels of added base while keeping all other resist variables constant. These seven resists were patterned with EUV lithography, and LER was measured on 100-200 nm dense lines. Similarly, the resists were also imaged using DUV lithography and LER was determined for 300-500 nm dense lines. LER results for both wavelengths were plotted against E_size. Both curves show very similar LER behavior-the resists requiring low doses have poor LER, whereas the resists requiring high doses have good LER. One possible explanation for the observed LER response is that the added base improves LER by reacting with the photogenerated acid to control the lateral spread of acid, leading to better chemical contrast at the line edge. An alternative explanation to the observed relationship between LER and E_size is that shot-noise generated LER decreases as the number of photons absorbed at the line edge increases. We present an analytical model for the influence of shot noise based on Poisson statistics that preidicts that the LER is proportional to (E_size)^-1/2. Indeed, both sets of data give straight lines when plotted this way (DUV r² = 0.94; EUV r² = 0.97). We decided to further evaluate this interpretation by constructing a simulation model for shot noise resulting from exposure and acid diffusion at the mask edge. In order to acquire the data for this model, we used the base titration method developed by Szmanda et al. to determine C-parameters and hence the quantum efficiency for producing photogenerated acid. This information, together with film absorptivity, allows the calculation of number and location of acid molecules generated at the mask edgte by assuming a stochastic distribution of individual photons corresponding to the aerial image function. The edge "roughness" of the acid molecule distribution in the film at the mask edge is then simulated as a function of acid diffusion length and compared to the experimental data. In addition, comparisoins between of the number of acid molecules generated and photons consumed leads to values of quantum efficiencies for these EUV resists.

The minimum gate CD for the 32 nm node is 15 nm and the CD control requirement on the gate CD is < 2.5 nm 3σ. One of the major concerns for meeting these targets using EUV lithography is flare. Flare degrades the aerial image contrast which decreases the process window, and within-die chrome density variation results in local flare variation which worsens the CD control. Since mirror roughness contributes to flare, mirror polishing needs to be improved so that the Mid Spatial Frequency Roughness (MSFR) will be reduced to < 0.14 nm/mirror for 6 mirror imaging systems. In this paper, we will determine the minimum acceptable flare for the 32 nm node to meet the CD target and control requirements using modeling and present methods to meet them as demonstrated by experiments run on the Engineering Test Stand (ETS). Effectiveness of flare mitigation methods using chrome dummification and negative tone resists are quantified, and the capability of Flare Variation Compensation (FVC) to meet CD control targets are verified experimentally.

EUV substrate materials have to meet enhanced requirements with respect to extreme low thermal expansion, high homogeneity and superior surface quality. A SCHOTT R&D program aims at the development of advanced materials covering these various aspects. The glass-ceramic Zerodur (registered trademark) of SCHOTT represents a substrate material currently used for EUV masks and optics of first generation tools due to its extremely low coefficient of thermal expansion (CTE) and its excellent homogeneity. Zerodur(registered trademark) even allows continuous shifting of the position of zero crossing of the CTE-slope to control the thermal expansion behavior according to varying customer requirements: As a result of specifically adjusted process parameters, samples of Zerodur (registered trademark) exhibit a coefficient of thermal expansion CTE < 5 ppb/K corresponding to the lowest expansion class of the SEMI standard P37 (19 to 25°C) for EUV mask blanks. By further variation of process parameters, the position of zero crossing, e.g. at 22.5°C or 30°C, can be varied, revealing an attractive attribute feature of Zerodur (registered trademark). A new dilatometer type reveals an improved reproducibility of ~ 1ppb/K in the temperature range of 0 to 50°C. A series of CTE(0;50°C) measurements with a test-cube of Zerodur (registered trademark) provides information on CTE homogeneity on a cm-scale: no CTE variation was observed within the error of measurements (1ppb/K) for a block exhibiting ± 3.5*10^-6 variation in refractive index. CTE variation can cause surface deformations during changing temperature conditions. A Fizeau-Interferometer was used to record surface roughness at two different temperatures. This non- destructive metrology is regarded as a method to distinguish CTE variation < 1ppb/K. The surface deformation of Zerodur (registered trademark) due to elevated temperature was determined to be lower than the resolution. Both methods to analyze the CTE homogeneity of Zerodur (registered trademark) lead to the result of CTE variation below 1 ppb/K. Surface treatment of glass-ceramic material is a major challenge as final finishing of EUV substrates may increase roughness of super-polished surfaces significantly. Improved new glass-ceramic materials demonstrate optimization of glass-ceramic compositions to nearly meeting the specification of surface roughness after a standard finishing process. Recent achievements of material development reveal CTE-performance of this new glass-ceramic to also be adjustable to varying customer needs as already known for Zerodur (registered trademark). These results are regarded as a promising milestone to develop an optimized glass-ceramic material, because the features of the modified New-Glass Ceramic now better match the key requirements of EUVL substrate materials.

We fabricated molybdenum (Mo)/silicon (Si) multilayers with low-pressure rotary magnet cathode (RMC) sputtering, which can be performed at a lower gas pressure (about 0.1Pa) than conventional magnetron sputtering. We obtained high reflectivity at a wavelength of extreme ultraviolet (EUV) in Mo/Si multilayers sputtered with low-pressure xenon (Xe) gas. The measured maximum reflectivity was approximately 71%. We confirmed that the multilayers sputtered at a lower pressure exhibited higher reflectivity. From the transmission electron microscope (TEM) cross-sectional images we observed thinner interdiffusion layers between Mo and Si layers in multilayers sputtered by RMC sputtering than in those sputtered by ion-beam sputtering. The Mo single layer deposited by RMC sputtering had tensile stress and the Si single layer had compressive stress. By changing the Γ ratio (the fractional thickness ratio of a Mo layer to the total thickness of a Mo layer and a Si layer) of the multilayer coatings, the film stress was controlled from tensile to compressive. However, for large Γ ratios, the interface roughness was increased and the EUV reflectivity was reduced. We have developed a doubly stacked multilayer structure that can provide low stress and high EUV reflectivity simultaneously. By using this technique, the stress of multilayer coatings was reduced to -6MPa while maintaining the high EUV reflectivity of 69%.

In extreme ultraviolet lithography (EUVL) environments transient plasma dynamics dictate conditions for particle/surface interactions. A critical challenge facing EUVL development is optic component lifetime both in gas-discharge produced plasmas (GDPP) and laser-produced plasmas (LPP) devices. Optic components are exposed to impingent species, impurities (H,C,O,N) and debris leading to their degradation and consequently limiting 13.5 nm light reflection intensity. Experiments in the PRIME (Particles and Radiation Interaction with Matter Experiments) facility at the Argonne National Laboratory study the synergy between radiation-induced athermal and thermal mechanisms that influence the behavior of EUVL materials (electrodes and condenser optics) under irradiation conditions including: incident particle energy (50 eV - 5 keV), angle-of-incidence (near-normal to oblique), incident flux (10¹¹-10¹⁷ ions/cm²/s), surface coatings (impurity: C,O or capping layers: Ru, W), and surface temperature (100 - 1000 C). Results of electrode and optical component interaction with singly-charged inert gases (Xe) are presented. Critical issues under study include: radiation enhanced diffusion, radiation induced segregation, preferential sputtering, collisional mixing, surface segregation, surface amorphization, thermal diffusion and thermal spike evolution. Experiments in PRIME will be complemented with atomistic modeling to study how these mechanisms modify surfaces and how these mechanisms can work synergistically to introduce solutions to enhance component lifetime of electrode and condenser optic materials.

Small plasma-pinch devices operating at a gas mixture of Xe and He with a frequency of 5-10 kHz and pulsed energy of 1-100 J are very promising sources of EUV radiation for lithography. A key issue in design of EUV sources is erosion of the pinch facing material under the hot Xe plasma and electric currents. Material erosion limits the lifetime of device components and thereby reduces the economical feasibility of these devices. Selection of high-resistant materials is critically important for development of future commercial EUV sources. Experiments are being carried out at plasma gun facilities in well-diagnosed and controlled conditions. The plasma gun is applied as a source of pulsed energetic Xe plasma capable of generating Xe plasma streams with a velocity 4 10⁶ - 4 10⁷ cm/s and duration of the plasma pulse 10-40 microseconds. Xenon plasma stream velocity of 4-10 10⁶ is sufficient to obtain plasma temperture of 30-50 eV, i.e., typical for pinch EUV devices. The formation of plasma could makes possible to study erosion and surface damage induced by particles and radiation of Xe plasma at these temperatures. Initial results of material testing by Xe plasma particles are presented. Samples of copper and tungsten, which are currently being used as electrode materials in pinch devices, were exposed to multiple irradiations by pulsed energetic Xe plasma. Material erosion and surface damages are analyzed. Future results will permit identification of the erosion mechanisms induced by Xe plasma particles, plasma radiation, and electric currents and their contributions to the net material erosion. The experimental data are being used for validation of numerical models developed in the HEIGHTS-EUV package for evaluation of material erosion in EUV sources.

Semiconductor chip manufacturers are expecting to use extreme ultraviolet (EUV) lithography for high volume manufacturing of DRAMs and ICs starting by the end of this decade. Among all the technologies and modules which have to be developed EUV sources at 13.5 nm are considered to be the most critical issue. Specifically the required output power of 115 W at the entrance of the illuminator system in combination with the required lifetimes of source components and collector optics make the source technology critical for EUV lithography. The present paper gives an update of the development status of EUV light sources at XTREME technologies, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany. Results on both laser produced plasma (LPP) and gas discharge produced plasma (GDPP), the two major technologies in EUV sources, are given. The LPP EUV sources use xenon-jet target systems and pulsed lasers with 500 W average power at up to 10 kHz developed at XTREME technologies. The maximum conversion efficiency from laser power into EUV in-band power is 1.0 % into 2p solid angle. 2.0 W EUV radiation is generated at 13.5 nm in 2p sr solid angle. The small source volume of < 0.3 mm diameter will allow large collection angles of 5 sr. The intermediate focus power is estimated to 1 W. Collector mirror lifetime tests showed 5 million pulses lifetime without debris mitigation. With debris mitigation in place lifetimes of more than 1 billion pulses are estimated. For the next generation of higher power EUV LPP sources a laser driver has been tested at 1.3 kW average laser power. This will lead to 5 W EUV power in intermediate focus. The GDPP EUV sources use the Z-pinch principle with efficient sliding discharge pre-ionization. Prototype commercial gas discharge sources with an EUV power of 35W in 2p sr were already delivered for integration into EUV microsteppers. These sources are equipped with a debris-filter which results in an optics lifetime exceeding 100 million discharges at 1 kHz repetition frequency. The same lifetime was achieved for the components of the discharge system itself. The progress in the development of high-power discharge sources resulted in an EUV power of 150 W in continuous operation at 4.5 kHz repetition rate by implementation of porous metal cooling technology. The EUV plasma has a FWHM-diameter of 0.5 mm and a FWHM-length of 1.5 mm. The intermediate focus power is calculated to be in the range of 15 W - 20 W, depending somewhat on the transmission of the optical path to the intermediate focus and on the etendue specification. The typical fluctuations of the EUV energy are standard deviation s<5% without any active stabilization. Discharge sources with Sn as emitter were investigated as more efficient alternative to Xenon. Estimates regarding Sn sources reveal the potential of achieving 65 W intermediate focus power by using developed porous metal cooling technology. Improvement of cooling could open the path to 115 W of power for high volume manufacturing using EUV lithography. However, Sn-sources are technologically risky und much less advanced than Xe sources, since fuel-handling and debris mitigation is much more challenging in comparison to Xe-sources. GDPP and LPP sources still compete for the technology of high volume manufacturing sources for EUV lithography. Optimization potential of the etendue of the optical system of EUV scanners will certainly influence any technology decision for HVM sources.

We have recently made significant advances in the performance of our laser driver module employed in our laser produced plasma (LPP) EUV source. We increased the average power output from the laser whilst minimising the overall Cost of Ownership (CoO) and footprint of the system. In addition to minimising the CoO of the laser solution, it is necessary to choose an appropriate target that can attain the overall requirements of EUVL. We are currently investigating xenon in its various phases, as well as other target materials, in order to increase the conversion efficiency of the source and therefore further drive down its CoO. We have prepared a source roadmap in response to industry demands, and it shows that the combination of our demonstrated laser technology with available targets will meet the objectives for a production level source.

The paper describes progress of the Philips’ hollow cathode triggered (HCT) gas discharge EUV source. The program has been focussed on three major areas: (1) Studying the basic physics of ignition, pinch formation and EUV generation. The paper reports on progress in this area and particularly describes the underlying atomic physics both for Xe and Sn. (2) Discharge based on Sn. Results on overall efficiency more than 5 times the Xe efficiency are reported as well as high frequency operation up to 6.5 kHz. This system shows all the necessary ingredients for scaling to production power levels. (3) Integration of the Xe source in an alpha tool. Results on integration issues like electrode life time, collector life time and dose control will be presented.

The main technological challenge of a future extreme ultraviolet (EUV) light source is the required average power of 115W at the intermediate focus. High repetition rate laser produced plasma (LPP) sources are very promising to face this challenge. We report the current status of the laser produced light source system we started to develop in 2002. The system consists of the following main components: The plasma target is a liquid xenon jet with a maximum diameter of 50 micrometer and a velocity of more than 30 m/s. A Nd:YAG laser oscillating at 1064 nm produces the plasma. The laser is a master oscillator power amplifier (MOPA) configuration with a maximum repetition rate of 10 kHz and an average power of 1kW. The EUV system currently delivers an average EUV in-band power of 4 W (2% bandwidth, 2π sr) having a stability of 0.54 % (1σ, 50-pulse moving average). In order to evaluate a further increase of the repetition rate, xenon jet characteristics and EUV plasma images have been investigated at 10 kHz. In addition, a conversion efficiency of 0.67% (2% bw, 2π sr) has been obtained at low repetition rate operation. This paper presents the progress of our LPP light source development.

Over the past several years, a continuous improvement of the performance parameters of discharge produced plasmas as potential sources of 13.5 nm radiation for commercial EUV lithography systems has been achieved. At Cymer we have continued developing the dense plasma focus (DPF) discharge as an EUV source. The majority of the data presented here is focused on DPF operation with xenon gas. We have recently started investigating the DPF operation with Sn, as well. A significant improvement in conversion efficiency (CE) was observed. We have investigated DPF configurations with different polarity of the drive voltage. Central to both configurations is the pulsed power system, which is being developed to operate in continuous mode at 5 kHz while delivering approximately 10 J to the load. Significant differences have been observed for the energy deposition profiles in the positive and negative polarity systems. Calorimetric data show that the fraction of energy deposited into each discharge electrode depends on the polarity. The thermal engineering of the central electrode remains a major challenge. With the present generation DPF we have demonstrated operation at 5 kHz in burst mode and at 2.3 kHz in continuous mode, with 76 W of in-band energy generated at the source. We observed that certain transient effects in the EUV output were correlated with the degree of energy coupling during the burst. However, we found that the pulsed power system is well matched to the load with >90% of the stored energy coupled to the discharge and electrodes. The conversion efficiency of the DPF operated with Xe is near 0.5% for both polarities, while measurements with Sn show a CE ~1.7%. Plasma modeling supported the optimization of the pinch dynamics and electrodes. Debris mitigation studies were also carried out and the carbon contamination was reduced.

We have utilized the nanoimprint lithography process described this paper to fabricate a rewritable, nonvolatile memory cell with an equivalent density of 6.4 Gbits/cm². The architecture of the circuit was based on an 8x8 crossbar structure with an active molecular layer sandwiched between the top and bottom electrodes. A liftoff process was utilized to produce the top and bottom electrodes, made of Pt/Ti bilayers. The active molecular layer was deposited by the Languir-Blodgett technique. We proposed the use of a new class of nanoimprint resist formulated by dissolving a polymer in its monomer, such as poly(benzyl methacrylate) dissolved in benzyl methacrylate (~8%/92% wt). The new resist enabled us to achieve Pt /Ti lines of 40 nm in width and 130 nm in pitch, as described in this paper. Our overall nanofabrication process has the advantages of relatively low temperature (~70°C) and pressure (~500 psi or 4.5 MPa), both of which are critical to preserving the integrity of the molecular layer.

While researchers of ever more advanced NGL systems are still struggling to demonstrate the feasibility to manufacture features well below 100 nm at an affordable cost and a reasonable throughput, nanoimprint technologies are emerging as a possible answer to these challenges. 100 nm patterns are imprinted with a fully patterned 4 inch diameter stamp in a low-temperature embossing process. In low temperature imprinting processes with polymers having very low glass transition temperatures heating and cooling cycles are minimized. This enables to increase the throughput of a hot embossing process, which is important for potential industrial applications.

Photo-curable nanoimprint lithography (P-NIL), a low pressure and room temperature process, is developed on Nanonex NX-2000 nanoimprintor. The process is capable of achieving uniform imprinting over large area in less than 60 seconds, which is mainly attributed to the Nanonex patented air cushion press (ACP) technology. Nanostructures such as 200nm pitch grating have been successfully demonstrated on 4-inch wafer level using P-NIL on NX-2000 nanoimprintor.

Nanoimprint lithography (NIL) has the advantage of high-throughput, sub-10 nm resolution and low cost [1]. It has been included into 2003 ITRS as the Next Generation Lithography (NGL) for 45 nm node [2]. This paper summarized current status of Nanonex imprint technologies. Nanonex imprint process includes thermal nanoimprint (T-NIL) and photo-curable nanoimprint (P-NIL). Both T-NIL and P-NIL utilized a proprietary air cushion press (ACP), which has the advantage of ultra-uniformity, low lateral stress, less damage to the mold and substrate, and higher alignment accuracy. Nanonex Corporation delivers user-friendly nanoimprint lithography tools and solutions for both experts and non-experts of micro and nanofabrication. Nanoimprint machines, resists, molds and processes have been developed and are available today.

Step and Flash^TM Imprint Lithography (S-FIL^TM) process is a step and repeat nano-replication technique based on UV curable low viscosity liquids. Molecular Imprints, Inc. (MII) develops commercial tools that practice the S-FIL process. The current status of the S-FIL tool and process technology is presented in this paper. The specific topics that are covered include: • Residual layer control • Etch process development • Patterning of lines, contacts and posts • CD control • Defect and process life • Alignment and magnification control

The Step and Flash Imprint Lithography (S-FIL^TM) process is a step and repeat nano-replication technique based on UV curable low viscosity liquids. Molecular Imprints, Inc. (MII) develops commercial tools that practice the S-FIL process. This talk will present the imprint materials that have been developed to specifically address the issue of process life and defects. The S-FIL process involves field-to-field dispensing of low viscosity (<5 cps) UV cross-linkable monomer mixtures. The low viscosity liquid leads to important advantages that include: • Insensitivity to pattern density variations • Improved template life due to a lubricated template-wafer interface avoids “hard contact” between template and wafer • Possibility for lubricated (in-situ) high-resolution alignment corrections prior to UV exposure The materials that are optimal for use in the S-FIL process need to possess optimal wetting characteristics, low evaporation, no phase separation, excellent polymer mechanical properties to avoid cohesive failure in the cured material, low adhesion to the template, and high adhesion to the underlying substrate. Over 300 formulations of acrylate based monomer mixtures were developed and studied. The imprint materials were deemed satisfactory based on the process of surviving imprinting more than 1500 imprints without the imprints developing systematic or repeating defects. For the purpose of these process studies, printing of sub-100 nm pillars and contacts is used since they represent the two extreme cases of patterning challenge: pillars are most likely to lead to cohesive failure in the material; and contacts are most likely to lead to mechanical failure of the template structures.

Schott Lithotec has introduced all relevant technology steps to manufacture EUV mask blanks - ranging from Low Thermal Expansion Material (LTEM) via high quality substrate polishing to low defect blank manufacturing. New polishing and cleaning technologies, improved sputter technology and updated metrology enable us to routinely produce EUVL mask blanks meeting already many of the roadmap requirements. The goal is pilot production of EUV blanks for the 45 nm node end of 2005. There are several technology options for achieving the mechanical, optical and chemical specs for substrates and coatings. Some of them are already integrated in our processes. An important focus of this paper is the understanding of defect sources starting from the LTEM bulk material to the fully coated blanks with multilayer, buffer and absorber. We present details on some production steps controlling defect detection sensitivity dedicated to various layers and report on new results on defect reduction research after the different process steps.

One of the greatest challenges for extreme ultraviolet lithography (EUVL) technology is the development of a nearly defect-free mask blanks. For EUVL mask blanks with a few printable multi-layer (ML) defects, several defect mitigation methodologies have been proposed. It includes directly repairing small ML phase and amplitude defects,1-2 mask absorber pattern proximity repair,3 and using absorber pattern to cover the ML defects. In each case, the ML defects first need to be identified and located during the ML blank defect inspection. To precisely locate the ML defects on the blank, fiducial marks on the ML blank are needed for mask alignment and defect location identification. In this study, we have demonstrated that EUVL mask ML blank fiducial mark with 60nm trench depth, which is more than 10X the required minimum detectable height of the defect inspection tool, can be generated via local heating. No material removal occurs. Therefore, it is a very clean process. These fiducial marks work for many inspection tools such as optical inspection tool, e-beam inspection tool, and EUV Aerial Image Monitor (AIM) inspection tool. The fiducial marks generated in the experiment were realized via laser heating. The locally heated Mo/Si ML converts to molybdenum silicide that has a low volume than that of Mo/Si ML. As a result, a trench or a mark is generated. The process is expected to have large process margin as the depth of the mark is determined by completely silicide the ML. Additional heating will not be able to further deepen the trench. Therefore, the temperature and heating time control should be loose.

Phase Shift Masks (PSM) for Extreme Ultraviolet Lithography (EUVL) have the potential for extending the lithographic capability of EUVL beyond the 32-nm node. The concept of EUV PSM structures can be implemented either by adding absorber structures on top of the Mo/Si multilayers (additive approach) or by partial etching into the multilayers (subtractive approach). Among many technical challenges, evaluating optical constants of absorber materials is the most important issue particularly for PSM by the additive approach (PSM-ADD), while the etch stop capability and the etch selectivity with vertical sidewall profile are the main technical challenges for PSM fabricated by the subtractive method (PSM-SUB). For fast turn around of PSM development, the indirect optical constant evaluation through material analysis is a useful metrology technique. The optical constant of TaSiN extracted from Rutherford Backscattering Spectroscopy (RBS) data agrees well with that obtained from the direct measurement by transmission interferometric technique. For PSM-SUB, the concept of embedding B4C and NiFe etch stop layer (ESL) is verified by measuring reflectivity of the ESL embedded substrates and demonstrating good etch stop capability.

The development of defect-free mask blanks including inspection is one of the big challenges for the implementation of extreme ultraviolet lithography (EUVL), especially when the introduction of EUVL is rescheduled to a later technology node. Among others, inspection of multilayer coated mask blanks with no oversight of critical defects and with minimal detection of false defects is a challenging issue for providing mask blanks free of defects or with thorough characterization of any existing defects. MIRAI Project has been developing a novel actinic (at-wavelength) inspection tool for detecting critical multilayer defects using a dark-field imaging and a laser-produced plasma (LPP) light source, expecting better sensitivity and better correlation with printability. The first experimental set up is completed for proof-of-concept (POC) demonstration using 20x Schwarzschild imaging optics and a backsideilluminated CCD. An in-house LPP light source is integrated to optimally illuminate the area of interest by EUV with a wavelength of 13.5nm. For its illuminator, a multilayer-coated elliptical mirror is used to illuminate a mask blank with the EUV that is collected within a wide solid angle from the light source. The first EUV dark-field image is obtained from a mask blank with programmed multilayer defects which are manufactured by locating well-defined patterns before depositing Mo/Si multilayer on EUV mask substrate. All the fabricated multilayer defects down to 70nm in width and 3.5nm in height are detected as clear signals that are distinguishable from the background intensity arising from the scattering by the surface roughness of the multilayer-coated mask blank. We have also detected a phase defect as low as 2nm in height. False defect count was not only zero within the area of view but also statistically confirmed to be less than one within the whole area of a mask blank assuming the extrapolation of observed fluctuation of background intensity is applicable. EUV pulse energy measurements and a CCD speed scaling suggested that the inspection throughput of 2 hours per mask blank will be feasible. The actinic tool based on this scheme will, not only serve for benchmarking with non-actinic tools or support multilayer deposition process improvements, but also be a viable choice for qualification of premium EUV mask blanks.

The printability of a dense line pattern and a model pattern using two configurations of absorber and buffer materials for the mask were examined through simulations. An absorber material with a small extinction coefficient of 0.025 must be thicker than one with a large extinction coefficient fo 0.040 to ensure sufficient reflectance contrast. However, a thick absorber enhances the adverse influence of off-axis incidence on the critical dimensions and pattern fidelity of a dense pattern layout, and the influence increases markedly when the incident angle is over 6.2°. Thus, and absorber material with a large extinction coefficient is advantageous in reducing the influence of off-axis incidence because it allows the use of a thinner layer. Another approach to reducing this influence is mask pattern correction. A newly developed algorithm makes the mask near-field energy for off-axis incidence the same as that for normal incidence. This simple correction compensates effectively for the influence of off-axis incidence and provides excellent pattern fidelity. The algorithm enable the use of absorber and buffer materials with a small extinction coefficient and also a large incident angle of over 6.2°.

Photoresist patterning experiments on the EUVL Engineering Test Stand using two masks with different types of architecture indicate that etched-multilayer binary masks can provide larger process latitude than standard patterned absorber masks. The trends observed in the experimental data are confirmed by rigorous electromagnetic simulations taking into account the mask structure, the imaging optics characteristics and the illumination conditions.

The CNTech Advanced Lithography Toolset uses a beam propagation method to calculate the intensity profile as it propagates through the mask and into the photoresist. One can construct the membrane, absorber, gap, and resist, each as a series of n-slices to achieve unusually precise calculations. Here a clear X-ray phase mask is modeled with silicon nitride in a configuration called a Bright Peak Enhanced X-ray Phase Mask (BPEXPM). For the optimized structure of this mask, which relies on both diffraction and phase shifting to produce the reduced wafer image, four factors must be controlled; these are: absorber thickness - material and wavelength dependent, absorber wall slope, gap, and resist threshold. A central composite experimental design showed that a 100 nm mask would print a wafer at 35 nm CD using the 70% maximum intensity threshold when the wall slope was 0.5° from the vertical. Additionally: 1) a 100 nm increase in absorber thickness decreased the CD by 1.0 nm; 2) every 1.0 um increase in gap decreased the CD 0.8 nm; and 3) every 1.0 nm increase in mask CD increased the linewidth only 0.1 nm. Other mask processing materials were examined in addition to the 180° (π) phase-shift absorber thickness. Experimental verifications of the modeling results are in progress to demonstrate device construction for devices with lower wafer coverage than would be required for memory devices.

The paper describes the use of water-dissolvable masks, formed from a polyvinyl alcohol film forming solution, for high-resolution pattern definition and materials-transfer printing. The approach replicates surface patterns as water-soluble polymer masks (templates) by spin-casting the film-forming solution onto a master pattern. The water-soluble mask is coupled to a substrate by polymer adhesion to form a solid two-layer structure. Water is used to dissolve the mask layer to uncover the formed pattern in the adhesive layer, thereby providing a new release mechanism for contact-based methods of pattern formation. Moreover, the patterned polymer adhesion transfer process enables a large-area, conformable, single-use template addressed towards meeting registration and defect control challenges in contact printing. The process further incorporates the capability to replicate with loaded nanostructured materials to form a composite of nanoparticles in a soluble polymeric matrix with a patterned surface. The embedded particles are accessible at the surface of the template and thereby are concurrently transferred to the substrate through the polymer adhesion process and subsequently released from the soluble template after water-dissolution in a structured manner. The paper also describes applications of PVA in forming polymer masks as (a) suspended thin-film templates, (b) imprinting templates for repeated use, and (c) as templates for nanoparticle formation by collimated deposition. Polyvinyl alcohol thus provides an additional material for consideration as a mask (template) for nanofabrication, and would be an alternative to quartz, silicon, and polydimethylsiloxane (PDMS) in that regard. The class of printing techniques using PVA as a mask material is referred to as molecular transfer lithography (MxL).

Nanoimprint lithography (NIL) has been successfully employed in nanoscale patterning, however, it is known to have limitations in replicating large scale (hundreds of microns and larger) and nanoscale patterns simultaneously. We present a new lithographic technique that integrates photolithography into the NIL patterning process. This technique uses a hybrid mold that has large metal pads embedded in a transparent NIL mold. Such a hybrid mold allows both large and nanoscale patterns to be replicated in one step by a combination of imprinting and photolithography. In addition, this new technique offers the advantages of simplifying residual layer distribution and avoiding NIL failures resulting from insufficient polymer flow, and can also eliminate the oxygen plasmon etching process used in NIL to remove the residual polymers.

Step and Flash Imprint Lithography (SFIL) is a revolutionary next generation lithography option that has become increasingly attractive in recent years. Elimination of the costly optics of current step and scan imaging tools makes SFIL a serious candidate for large-scale commercial patterning of critical dimensions below ~50 nm. This work focuses on the kinetics of the UV curing of the liquid etch barrier and the resulting densification/contraction of the etch barrier as it solidifies during this step. Previous experimental work in our group has measured the bulk densification of several etch barrier formulations, typically about 9 % (v/v). It remains unknown, however, how much etch barrier contraction occurs during the formation of nano-scale features. Furthermore, it is of interest to examine how changes in monomer pendant group size impact imprinted feature profiles. This work provides answers to these questions through a combination of modeling and experimental efforts. Densification due to the photopolymerization reaction and the resulting shift from Van der Waals’ to covalent interactions is modeled using Monte-Carlo techniques. The model allows for determination of extent of reaction, degree of polymerization, and local density changes as a function of the etch barrier formulation and the interaction energies between molecules (including the quartz template). Experimental efforts focus on a new technique to examine trench profiles in the quartz template using TEM characterization. Additionally, SEM images of imprinted images from various etch barrier formulations were examined to determine local contraction of the etch barrier. Over a large range of etch barrier formulations, which range from 10 - 20 % volumetric contraction as bulk materials, it was found that dense 100 nm lines printed approximately the same size and shape.

Substantial recent interest in microelectronics manufacturing has motivated significant work on non-traditional processes such as embossing-based lithography. This work has been generally limited to manufacturing conventional microelectronics, producing two dimensional patterned surfaces and structures. To date, little work has been done to produce microelectromechanical systems (MEMS), which can require production of complex three-dimensional and possibly free standing structures. This paper reports a novel method for manufacturing three-dimensional microstructures that can be freely standing and/or fully released. The method involves the use of thermally sacrificial polymers, i.e. materials that can be cleanly decomposed to gaseous products upon heating at elevated temperatures. Such sacrificial polymers can be directly embossed and subsequently overcoated with a variety of materials including other polymers, dielectrics, semiconductors, and metals. Following the deposition of the overcoat layer, further processing can be performed on the overcoat layer (e.g. selective etching or deposition of additional materials). Finally, the entire structure is heated to the decomposition temperature of the sacrificial polymer which results in the “dry” removal of the sacrificial layer, thus releasing the desired structures. The various sacrificial materials that have been investigated are polynorbornenes and polycarbonates, and the overlayer materials include polyimides, silicon oxide, and metals. This paper discusses the various properties of these sacrificial materials, the printing and processing conditions for these materials, and the use of this method for the fabrication of a MEMS based microfluidic system with free standing and suspended obstructions. This novel manufacturing technique meets the needs of MEMS manufacturing in that it can produce three dimensional and free standing microstructures. It permits the fabrication of devices and systems in only a few process steps that would otherwise be either substantially more complicated or impossible to achieve. This process of coating, embossing, and overcoating can also be repeated to build-up complex multi-layered structures.

Recently, the International Roadmap for Semiconductors (ITRS) has included imprint lithography on its roadmap, to be ready for production use in 2013 at the 32 nm node. Step and Flash Imprint Lithography (S-FIL^TM) is one of the promising new methods of imprint lithography being actively developed. Since S-FIL is a 1X printing technique, fabrication of templates is especially critical. S-FIL has previously demonstrated the ability to reliably print high resolution line/space and contact hole features into a silicon-rich etch barrier material. Beyond printing with S-FIL however, there is the requirement to develop low or zero bias, high selectivity dry etch processes needed to transfer printed images into the substrate. In this study, the feasibility and methodology of imprinting sub-80 nm contacts, and pattern transferring this image into an underlying oxide layer is demonstrated. Critical parameters such as e-beam dose and etch biases associated with template pillar fabrication, and biases associated with pattern transfer processes for sub-80 nm 1:1 and 1:2 pitch contacts are discussed. Wafer imprinting was done on 200 mm wafers using Molecular Imprints Inc., Imprio 100^TM system.

Particle-cluster tin target is presented as the solution of a 100W EUV source for EUVL. Theory for maximizing conversion efficiency of a laser-produced plasma is derived and the theory is experimentally confirmed by using a dispersed SnO₂ particles. The EUV intensity 4 times higher than that from a plasma on a solid Sn plate target is observed at the optimized density. The achieved conversion efficiency for dispersed particles is estimated to be as high as 3%/(2π str 2%BW) or higher from the value for a Sn plate of 0.8% measured by using two multilayer mirrors and a calibrated photodiode. Theoretical consideration reveals that larger diameter plasma enables higher EUV power. The particle-cluster can be delivered at multi kHz rep-rate by using water droplet. Experimental confirmation of delivering particles by droplets is also reported.

A magnetohydrodynamic (MHD) model of gas discharges has been developed to accelerate the development of compact, intense sources of EUV radiation for microlithography. The model is an MHD numerical simulation with atomic and radiation physics. The plasma evolution is simulated with the MHRDR (Magneto-Hydro-Radiative-Dynamic-Research) 2D, three-temperature, MHD computer code. The MHD results are postrocessed witha code that caluculated the radiation spectrum from Xe ions, including 13.4-nm EUV output, based on a detailed collisional-radiative atomic kinetics model. A variety of gas discharges relevant to microlithography can be modeled with this new tool.

A possible design window for extreme ultraviolet (EUV) radiation source has been introduced, which is needed for its realistic use for next generation lithography. For this goal, we have prepared a set of numerical simulation codes to estimate the conversion efficiency from laser energy to radiation energy with a wavelength of 13.5 nm with 2 % bandwidth, which includes atomic structure, opacity and emissibity and hydro dynamics codes. The simulation explains well the observed conversion efficiency dependence of incident power using GEKKO XII laser system as well as spectral shapes. It is found that the conversion efficiency into 13.5 nm at 2% bandwidth has its maximum of a few percent at the laser intensity 1-2 x 10¹¹ W/cm².

Discharge produced plasma (DPP) devices are being used as a light source for Extreme Ultraviolet (EUV) Lithography. A key challenge for DPP is achieving sufficient brightness to support the throughput requirements of exposure tools for high-volume manufacturing lithography. An integrated model is being developed to simulate the environment of the EUV source and optimize the output of the source. The model describes the hydrodynamic and optical processes that occur in DPP devices. It takes into account plasma evolution and magnetohydrodynamic processes as well as detailed photon radiation transport. The total variation diminishing scheme in the Lax-Friedrich formulation for the description of magnetic compression and diffusion in a cylindrical geometry is used. Several models are being developed for opacity calculations: a collisional radiation equilibrium model, a self-consistent field model with Auger processes, and a non-stationary kinetic model. Radiation transport for both continuum and lines with detailed spectral profiles is taken into account. The developed models are being integrated into the HEIGHTS-EUV computer simulation package. Preliminary results of a numerical simulation of xenon gas hydrodynamics and EUV radiation output are presented for various plasma conditions.

At Laser-Laboratorium Goettingen different types of laser-plasma EUV sources based on gas and cluster targets were tested to optimize the spatially resolved EUV radiation with respect to maximum EUV intensities, small source diameters, and pointing stability. The EUV radiation is generated by focusing a Q-switched Nd:YAG laser at 1064nm into a pulsed gas puff target. By the use of different target gases, broad-band as well as narrow-band EUV radiation is obtained, respectively. The influence of the laser and target gas parameters on the plasma shape and EUV intensity was investigated by the help of specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. The properties of the gas jet determine crucial parameters of the source. A directed gas jet in vacuum with a high number density is needed for an optimal performance of the source. Therefore, conical nozzles with different cone angles were drilled with an excimer laser to produce a supersonic gas jet. The influence of the nozzle geometry on the gas jet was analyzed with a Hartmann-Shack wavefront senor, the first time to our knowledge. The deformation of a planar wavefront after passing the gas jet was analyzed with this sensor, out of which the gas density distribution was reconstructed. Thus, the gas jet was optimized resulting in an increase of EUV emission by a factor of two and decreasing the plasma size at the same time.

A commercial extreme ultraviolet (EUV) source for at-wavelength metrology is developed. The source concept is based on the transfer of advanced microfocus x-ray tube technology into the EUV spectral range. This concept allows the realization of a compact, debris-free, and long-term stable EUV source. In the EUV tube, silicon targets are used to generate radiation at 13.5 nm. Detailed characteristics of the source performance are reported and different applications of the source in the field of at-wavelength metrology are presented.

Lithography results using spatially-filtered coherent EUV radiation are presented. These experiments were done using a new 10× Schwarzschild optic and other significant upgrades for high stability and throughput of the system. Included are both single- and multiple-pitch images. A chemically-amplified EUV resist is shown performing at dense 50-nm linewidths and loose 25-nm features. High resolution polymers (HSQ and PMMA) were also tested and demonstrate dense 40-nm linewidths, which are the smallest 1:1 multi-pitch features attempted at this time.

The development of Electron Projection Lithography (EPL) has proceeded for more than 10 years since its first description. EPL is regarded as a practical technology for 65 nm technology node and below. Nikon has been developing an EPL tool, named as the EB stepper. NSR-EB1A is the first EPL tool that has full functions for practical R&D use such as dynamic exposure by combination of electron beam deflection and stage scanning, wafer alignment, and so on. Some features of the EB stepper, which uses a 100 kV electron beam, are high resolution, and a large process margin associated with large depth of focus (DOF). Large DOF is a major feature of electron beam lithography. In the previous paper, we reported data of dynamic resolution and subfield stitching accuracy as preliminary performances that were obtained by NSR-EB1A. Recently the development of EPL reticle is significantly progressed. Today, high quality 200 mm diameter EPL reticle is available from plural mask suppliers. Using 200mm EPL reticle, we achieved subfield stitching accuracy about 20nm (3s). And we also evaluated total performance such as CD uniformity, overlay accuracy. This paper reports the latest performance of NSR-EB1A.

Electron projection lithography (EPL) is a promising candidate for next-generation lithography (NGL) at the 65 nm technology node and beyond. Nikon has developed the world's first full-field EPL exposure tool, Nikon's NSR-EB1A. This tool was shipped to Selete in June 2003. Final installation is still in progress, but we have begun evaluating its applicability to the 65 nm technology node through trial fabrication of a test element group (TEG). A TEG of via-hole chains consisting of 1st metal, 1st via, and 2nd metal layers was fabricated using optical/EPL mix-and-match lithography. We applied EPL to the via layer. The purpose of the first fabrication is to clarify practical hole resolution of the EPL tool because EPL is expected to define finer hole patterns and enable denser integration than optical lithography. To prevent defects in metal layers from adversely affecting evaluation, we used moderate pattern layouts in metal layers. Metal layers were defined by an ArF scanner to obtain good pattern fidelity and sufficient pattern yield. We used a single damascene process with a low-k insulator and Cu interconnection. Practical hole resolution was evaluated by electrical measurement and SEM and TEM observation. SEM confirmed that via holes of 70 nm were resolved. TEM confirmed that via-hole chains of 80 nm were fabricated. Electrical measurement confirmed electrical conduction through via-hole chains of 75 nm. These results suggest that applying EPL to hole layers could realize denser integration than optical lithography. EPL application to TEG trial fabrication demonstrates its high-resolution capability in practical use.

The world’s first electron projection lithography (EPL) R&D exposure tool was installed at our laboratory in June 2003, and we have evaluated its basic performance. The most feasible introduction of EPL into ultra-large-scale integration (ULSI) is mix-and-match use with an optical tool for critical layers at the 65 nm technology node (TN) and beyond. Overlay is the most crucial issue in mix-and-match lithography, so we focused on overlay in this evaluation. We found that the overlay performance of the EPL tool in mix-and-match use is 48.0 nm in the X direction and 45.7nm in the Y direction. To clarify details of deteriorated overlay accuracy, we divided it into 7 factors, finding underlayer distortion to be about 15 nm, residual reticle distortion 5 nm, subfield (SF) distortion 15 nm, main-field (MF) distortion 20 nm, reticle alignment accuracy 15 nm, repeatability 25 nm, and exposure field distortion 25 nm. We also demonstrated that overlay accuracy was 30 nm using previous overlay data.

Electron projection lithography (EPL) is a potential candidate for next-generation lithography (NGL) at the 65 nm technology node and beyond. EPL presents two key issues influencing design, because EPL uses EB and a stencil mask: beam blur and mask image placement (IP). Beam-blur deterioration depends on the Coulomb effect and is proportional to the beam current on the wafer, which depends on pattern density and the beam current on the mask. Pattern density in each subfield (SF) must be limited if the beam current on the mask is decided from throughput. IP accuracy of the stencil mask depends on the pattern layout. Intrinsic stress vanishes at openings, and distorted stress distribution causes IP error. To determine the influence of pattern layout on mask IP accuracy, simulation is checked in two steps. In the first step, simulation calculates the correlation between maximum displacement and pattern density in the entire SF. In the second step, simulation calculates the correlation between the side length of local area L and maximum additional displacement. The result of the first simulation shows that pattern deformation depends on the difference between half of the SF’s patterns density difference. To estimate the influence of pattern density imbalance in an area smaller than half of the SF, additional deformation of local area (L x L) is calculated in the second simulation step. Maximum additional displacement increases with L and pattern density. Based on the correlation between beam blur and pattern density and simulations results, the design rule (DR) for EPL is defined as the maximum pattern density in each entire SF and local area (L x L).

Low Energy Beam Proximity Projection Lithography (LEEPL) has emerged as a lithographic production tool, named as LEEPL-3000, for a 60nm-node DRAM and MPU. The characteristics of this system are wide exposure field, highly-accurate overlay, deep depth of focus (DOF) and little proximity effect. A scanner or a stepper mono-field is able to be exposed by this system and maximum exposure filed size is 46mm x 46mm exclusively for two-or four-divided complementary masks. The acceleration voltage is 2kV and the exposed current varies up to 20μA. The critical dimension (CD) uniformity, including a mask-pattern deviation, is about 8nm as 3σ at 100-nm line and space patterns in 46mm x 46mm filed. A CD-dose margin for 60-nm isolated lines is over 12% and the focus margin is greater than 20μm. The accuracy (3σ) of machine-itself is less than 14nm and that of machine-to-machine is 20-25nm.

Masks for low energy electron proximity projection lithography (LEEPL) require thin membranes, which in turn make the development of low-distortion masks a critical issue for this technology. By using an evaporated resist, a flip side fabrication process is presented here in which mask patterning is carried out with the mask in the same orientation that it will have in the stepper. This new process reduces distortions of a typical LEEPL mask which usually requires patterning on the opposite side of the membrane causing a gravitational sag effects. In addition, an evaporated resist has significant advantages for mask fabrication as membrane distortion is reduced due to the absence of centrifugal force during the resist deposition process. Uniform heat distribution across the membrane during the etching process is also expected since the membrane can now be placed in direct contact with a cooled metal electrode, thereby improving the etch rate uniformity. Also, for large scale production, several mask replicates from the original mask must be made because they have limited lifetime when used in a stepper. Image placement distortion can be minimized and the yield can be improved in mask replication by using an evaporated resist.

The image placement (IP) error correction is one of the advantages for E-beam lithography tool. LEEPL (Low Energy Electron beam Proximity-projection Lithography) 1,2) which is using stencil mask is able to shift the mask patter image by e-beam angle control. To use this unique technique week point of the stencil mask distortion is compensated. The flexibility of LEEPL E-beam IP correction for over lay is evaluated. The LEEPL E-beam IP correction is done by Sub-Deflector beam control. The feature to improve the over lay accuracy is introduced. It is not only for Mask IP error correction but also for Mask distortion by holding, under layer shot distortion and wafer chucking distortion.

Low-energy electron-beam proximity-projection lithography (LEEPL) is considered the best candidate for the next-generation lithography (NGL) tool because a production tool will be available for 65nm-node mass production. Resolution capability has already exceeded the 65nm-node requirement and possibly also the 45nm-node requirement. Although LEEPL requires a resist less than 100nm thick to obtain the resolution, our tri-layer resist process provides the critical-dimension (CD) uniformity and dry-etching resistance necessary for fabricating 90nm-node via holes. As regards an overlay, a LEEPL tool aligned to an under layer printed by an ArF scanner attained 21.3nm (three sigma) overlay error, which exceeds the requirement for the 65nm node. Another concern with LEEPL application is mask contamination growth during exposure, however the contamination growth rate is gradual that the CD shift due to the contamination is under control. We applied LEEPL to 90nm-node via hole fabrication to examine whether it provides a higher resolution than an ArF scanner. We determined that the electrical-resistance limit for LEEPL is approximately 100nm diameter for a via hole and the limit for an ArF scanner is approximately 125nm diameter. Even without process optimization, LEEPL showed its advantages for via-hole fabrication over an ArF scanner.

It is time to revisit X-ray. By enhancing, in the Near Field, Proximity X-ray Lithography (PXL), the technique is demonstrated that extends to 15nm printed feature size with 2:1 ratio of pitch to line w