This PDF file contains the front matter associated with SPIE Proceedings Volume 6517, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

With the introduction of alpha tools, extreme ultraviolet lithography (EUVL) has reached a key milestone. Users of those tools must have access to critical EUV infrastructure capabilities to evaluate the technology in a pilot line operation. In cooperation with universities, national laboratories, suppliers, integrated device manufacturers, and other industry consortia, SEMATECH has been spearheading the worldwide effort to develop this EUV infrastructure in the source, mask, optics, and resist areas. In the process, SEMATECH's Mask Blank Development Center, its EUV Resist Test Center, and the EUV expertise built within the SEMATECH EUV program have become key enablers for the successful introduction of EUV technology. We will highlight the significant contributions that the SEMATECH EUV Program has made, and continues to make, to the worldwide EUV infrastructure development effort. Moving beyond the alpha tool phase, the industry must have a clear understanding of the challenges that need to be addressed before EUV beta tools can be successfully introduced as early as 2009. We will identify those areas that still need a substantial effort to overcome technical and business challenges to meet 32 nm half-pitch requirements in time. Although some of those areas are clearly EUV-specific, others are generic and impact other lithography technologies as well. One of the major attractions of EUVL is that it is an extendible technology that can likely support patterning for several technology generations. We will review the outlook for EUVL technology extendibility and discuss what the industry needs to start working on to enable EUVL's bright future and long lifetime.

ASML has built and shipped to The College of Nanoscale Science and Engineering of the University at Albany (CNSE) and IMEC two full field step-and-scan exposure tools for extreme ultraviolet lithography. These tools, known as Alpha Demo Tools (ADT), will be used for process development and to set the foundation for the commercialization of this technology. In this paper we will present results from the set-up and integration of both ADT systems, status of resist and reticles for EUV, and the plans for using these tools at the two research centers. We will also present the first resist images from one of the tools at the customer site, and demonstrate 32nm half-pitch dense lines/spaces printing as well as 32nm dense contact hole printing.

Extreme Ultra Violet Lithography (EUVL) has been widely regarded as the lithography technology to succeed optical lithography. It is now considered as one of the most promising technologies below hp45nm node [1], following ArF immersion lithography considering trend of achievable process K1 factors shown in Fig. 1. In this paper we would like to present significant progress on the development of EUV exposure tool. There are several key important areas which should be developed to realize EUVL to be feasible such as reflective mask, resist, and tool itself. The reflective mask features such characteristics as pellicle-less, ultra-smooth blank flatness and defect free. The resist should be of high sensitivity and small line edge roughness (LER) as well as fine resolution. EUV exposure tool itself consists of major modules such as EUV light source, projection optics, vacuum body, vacuum stages, and so on. As far as EUVL optics development is concerned, through the development of high-NA small-field EUV exposure system (HiNA) in conjunction with EUVA (Extreme Ultraviolet Lithography System Development Association) projects, we have developed new polishing technologies such as ion-beam figuring and elastic emission machining, and new ultra high-precision interferometers for aspheric surface metrology. Wave front sensor system has been also developed partly in EUVA project. A new wave front sensor system which can be used for evaluating the projection optics with EUV light has already been installed in New SUBARU synchrotron facility in University of Hyogo. Our multi-layer coating technology has been also improved. High reflective Mo/Si multi layer coating has been successfully achieved and irradiation tests using synchrotron radiation have been conducted [8]. Successful achievement of those developments enables us to produce full-field projection optics for EUVL process development tool called EUV1. Proto-type development of full-field projection optics has been successfully completed and evaluated to be of enough performance. Preparation of complete set of production and metrology tools necessary for projection optics production was completed and all tools are now in full operation. Nikon has studied reticle protection method and developed Dual Pod Concept in cooperation with Canon. Nikon also has developed its own reticle cover to be implemented in EUV1 tool. Nikon has completed almost all module fabrication such as full-field projection optics module, illumination optics module, vacuum body module, vacuum compatible reticle/wafer stage modules, reticle/wafer loader modules, and EUV light source module. Nikon has already got into module integration production process to meet EUV1 development schedule. Nikon announced to start EUV1 tool installation in 1st half of 2007 and has been proceeding it on schedule. Nikon also would like to announce that development of 1st generation production EUVL tool dubbed EUV2 is now considered and that system concept design is under way.

We have constructed a small field exposure tool (SFET) in collaboration with EUVA, and shipped out to the Selete (Semiconductor Leading Edge Technologies; Japanese Consortium). The SFET has a field size of 0.6*0.2mm2 and two-mirror type projection optics. This machine is developed not only to assist the resist and mask development, but also to demonstrate manufacturing technologies for the full field tool. In this paper we discuss the SFET performances with aberration and flare of the projection optics and exposure results based on the simulation and exposure results. To fabricate the SFET projection optics, we improved our key manufacturing tools such as the wavefront measurement tool and the ion beam etching equipment (IBF). These machines are proved to be effective on production of the SFET, and will be applicable for the full field machines. We introduce the outline of Canon's activities for full field tool development and the other key technology such as mask handling, contamination protection and it's removal technology studies.

IMEC has started an EUV lithography research program based on ASMLs EUV full field scanner, the Alpha Demo Tool (ADT). Currently, the ADT is in the final phase of installation. The program focuses on three main projects: EUV resists, EUV reticles and assessment of the ADT performance. The intent of this program is to help improve and establish the necessary mask and resist infrastructure. In this paper, the status and the progress of the program is reviewed. In preparation for a resist process for the ADT, interference lithography has been used to track the progress of resist performance. Steady progress in resist development is seen, especially in terms of resolution, as some materials are now able to resolve 25nm HP. In its initial phase, the reticle project has concentrated on working with the mask and blank suppliers to assure timely availability of reticles for the ADT. An overview is given of the other reticle related activities, as well as first results of a defect printability study by simulation. In the ADT assessment project, simulation studies are reported aimed at the development of optical correction for flare and reticle shadowing effects. The impact of flare and shadowing effects are well understood and strategies for flare mitigation and shadowing effect correction are proposed.

To simulate the interaction of buried defects and absorber features in EUV masks and their effects on projection printing, a prototype 2D, fast, integrated, simulator based on ray tracing and a thin mask model is presented. RADICAL (Rapid Absorber Defect Interaction Computation for Advanced Lithography), consists of three sequential steps: the propagation of the mask illumination down through the absorber pattern, the reflection off the defective multilayer, and the propagation back up through the absorber. A propagated thin mask model is used to model the down/up propagation through the absorber pattern and a ray tracing simulator is used for the multilayer reflection. These simulators are linked together using a Fourier transform to convert the near field output of one component into a set of plane wave inputs for the next. This new method gives a 100x-300x speed increase compared to FDTD, and agrees to a point to point average of less than 2% with FDTD for 22nm lines on the wafer for NA=0.5. The errors in RADICAL and FDTD are examined to determine the sources of error for each simulator.

Extreme ultraviolet (EUV) lithography technology has gradually developed, and the industry is now progressing toward beta EUV lithography processes. However, very little has been reported on the effects of phase defects on wafer critical dimension (CD) and on tolerable defect sizes. We have fabricated programmed defect masks with programmed substrate pits and absorbing iso line patterns. The substrate pit depth measured with AFM ranged from ~2-3 to ~6-10 nm and the full width half maximum (FWHM) varied from 45 to 150 nm. A line-pattern was etched into the reflective multilayer coating using focused ion beam (FIB) milling. The iso line pattern is 225nm wide, corresponding to 45nm on a wafer in 5x demagnification tool we used for the EUV exposure. In this paper, we will present an analysis of the measured relationship between phase defect size and CD change using data obtained with an EUV micro-exposure tool (MET) and with an actinic imaging microscope at Lawrence Berkeley National Laboratory. Printable distance between pit and line edge will also be discussed according to pit sizes. Comparison result between real test and aerial image simulation will be reported to confirm the simulation.

We report the actinic (EUV wavelength) and non-actinic inspection of a multilayer-coated mask blank containing an array of open-field defect repair sites created in different ways. The comparison of actinic brightfield and darkfield measurements shows the importance of having both local reflectivity and scattering measurements. Although effective mask blank repair capabilities have not been adequately demonstrated, the data acquired in this experiment have been very instructive. Correlation with non-actinic inspection methods shows the difficulty of establishing a successful predictive model of the EUV response without EUV cross-comparison. The defect repair sites were also evaluated with SEM, AFM, and 488-nm-wavelength confocal microscopy. The data raise important questions about mask quality specifications and the requirements of future commercial actinic inspection tools.

Extreme ultraviolet lithography (EUVL) mask blanks must be free of printable defects. The SEMATECH Mask Blank Development Center (MBDC) is focused on driving down the defect density of EUVL mask blanks by providing a collaborative environment for EUVL mask substrate and equipment suppliers and a state-of-the-art analytical toolset for them to improve their products. Multilayer (ML) coating, substrate cleaning, and substrate suppliers are on site improving their products with a toolset that includes defect inspection, multilayer deposition, and substrate cleaning capabilities. X-ray diffraction (XRD) and EUV reflectance measurement capability as well as focused ion beam scanning electron microscopy/energy-dispersive X-ray (FIBSEM/EDX) and atomic force microscopy (AFM) for defect characterization are on site. The SEMATECH MBDC has just installed a Lasertec M7360, an advanced EUV mask blank inspection tool. The M7360 operates at a much shorter wavelength than the previous generation of confocal scanning inspection tools (266nm vs. 488nm for the M1350). The M7360 represents a significant improvement in our defect detection sensitivity. This paper will center on the capabilities of this new tool and show initial inspection results on EUV multilayer at sensitivities well below those that have been previously reported.

Mask substrate defects continue to be one of the critical issues for EUV technology development. Current specifications call for allowable defects in the 25nm height range for production masks blanks. Simulations seem to indicate that defects as small as 3nm high will cause printable defects on the wafer. To study the effects of small aspect defects on the printed image we undertook a study to look at 10nm height (mask substrate size) defects. A mask was fabricated with 12nm height defects in arrays based on area. Defects of 110nm, 190nm, 300nm, and 1000nm were fabricated. Multi-layers were then deposited and the mask was patterned with line/space patterns with pitches (mask size) of 600nm, 800nm, and 1000nm. Wafers were then exposed using a well characterized resist and the results were analyzed. All sizes of defects printed at least once. The largest defect size (1000nm mask) caused multiple bridges to form while even the smallest defect size (110nm mask) could cause a bridge on the 600nm (mask size) pitch.

Atomic hydrogen cleaning has been developed to reduce the amount of surface oxide on Ru-capped Mo/Si multilayer mirrors for EUVL. Atomic hydrogen generated by a heated W wire catalyzer was supplied to a Ru cap layer that had been lightly oxidized by ECR O2 plasma or EUV irradiation. The effectiveness of atomic hydrogen in deoxidizing it was examined by ex situ AES, XPS, and EUV absolute reflectivity measurements; and it was found that the amount of surface oxide was reduced to the initial level and that the EUV reflectivity of a multilayer degraded by oxidation recovered. In addition, the transport of atomic hydrogen thorough a winding quartz tube was demonstrated to be a promising technique. The actual density of hydrogen radicals was directly measured under various conditions so that the conditions for generating atomic hydrogen could be optimized and the required treatment time shortened.

Endurance testing of Ru-capped multilayer mirrors (MLMs) at the NIST synchrotron facility has revealed that the damage resulting from EUV irradiation in a water-dominated environment is nonlinear and may be influenced by competing oxidation and carbon-deposition processes. Concurrent results from two different environmental chambers reveal non-intuitive relationships between reflectivity loss and the admitted water-vapor partial pressure, the ambient background-gas composition, the presence or absence of hot filaments in the chamber, the EUV intensity and the irradiation dose. We discuss possible mechanisms and propose further experiments to test them. Determining the MLM lifetime from accelerated tests is a very difficult task. It is crucial that any lifetime testing procedure involves duplicate exposures for consistency, and, if possible, testing in multiple facilities.

A new deposition technique that builds on the thermal particle characteristics typical for e-beam deposition is described. This technique applies magnetron sputtering in a special scheme where these characteristics of the e-beam deposition method are achieved. The method was used for interface engineering of Mo/Si multilayers, with different barrier layer materials being tested. Composition of the barrier layers formed was studied using XPS. Results are shown on the general example of a Mo/B₄C/Si/B₄C system. The ultra-thin reflectance enhancement B₄C barriers can be deposited with low added stress, resulting in a multilayer stress as low as about -150 MPa. The best interface engineered multilayers reflect 70.5% at 13.3 nm and 70.15% at 13.5 nm. These results were achieved with 50 period multilayers terminated with a standard Si layer.

Nikon is now conducting a development of the full-field EUV exposure tools for EUVL process development named EUV1, which will be delivered in 2007. Polishing and coating of six different kinds of mirrors for the projection optics of EUV1 were finished and adjustment of the projection optics has been started. Sophisticated polishing process for aspheric mirrors, which can reduce LSFR, MSFR and HSFR down to less than 0.1nmRMS simultaneously, were developed. Process conditions of Mo/Si multilayer coatings have been optimized to obtain high reflectivity, low internal stress and graded coating simultaneously. Wavefront error of the projection optics under adjustment process is now 3nmRMS. We will try to achieve a wavefront error of less than 1nmRMS by further precise adjustment. Fabrication process of fly's eye mirrors, which is a key device of illumination optics of EUV1, was developed. All the mirrors of the illumination optics for EUV1 were finished and evaluation of its performance using an illumination-optics test stand has been started. Development and fabrication of both the projection optics and the illumination optics for EUV1 are satisfactorily in progress.

Modern integrated circuit fabrication uses the dual damascene process to create the copper interconnects in the Back End of the Line (BEOL) processing. The number of wiring levels is increasing to eight or more in advanced microprocessors, and the complexity and cost of the BEOL processes is growing rapidly. An approach to dual damascene processing using Step and Flash Imprint Lithography (S-FIL®) in conjunction with Sacrificial Imprint Materials (SIM) offers the ability to pattern two levels of interconnect structures simultaneously. By using a multi-level imprint template built with both the via and trench structures, one imprint lithography step can produce the same structures as two photolithography steps, greatly reducing the number of patterning process steps in the BEOL layers. This paper presents progress in formulation of new sacrificial imprint materials and the development of S-FIL and etch processes to incorporate the SIM strategy. The SIM is formulated as a two-component system, with a tunable etch rate adjusted by the ratio of the monomer and cross-linker components. High quality imprints were produced with a multi-level template on wafers with blank films of black diamond® dielectric material. The quality of the multi-level pattern transfer from the SIM into black diamond was evaluated.

Researchers have demonstrated that imprint lithography techniques have remarkable replication resolution and can pattern sub-5nm structures. However, a fully capable lithography approach needs to address several challenges in order to be useful in manufacturing. For successful manufacturing insertion of Step and Flash Imprint Lithography (S-FILTM) into a broad set of applications such as photonics, magnetic storage, and integrated circuits (ICs), the following practical process related challenges need to be addressed: (i) Printing sub-50nm structures with non-uniform pattern densities: (ii) Precise alignment and overlay with the ability to mix-and-match with photolithography; (iii) Availability of 1X templates; (iv) Achieving appropriate throughput for acceptable cost of ownership; and (v) Minimizing template and imprint process-induced defects to allow acceptable process yields. The last challenge - the ability to achieve low defect densities - is desirable for all applications. However, it is one of the biggest challenges for S-FIL to be accepted in IC fabrication. This article specifically focuses on this last challenge and presents the current status of defect reduction in S-FIL technology. The article starts out by providing a brief background of S-FIL technology, and by including a discussion of the overall status of S-FIL technology in Section 1. Next, an overview of the experiments performed including the defect inspection approaches used is provided in Section 2. Section 3 introduces the classes of defects that are relevant to the S-FIL process. It also provides recent defect data for each of these classes. Section 4 presents defect data gathered over the last three years and provides defect reduction trends over this period. Section 5 discusses the topic of template lifetime. Finally Section 6 provides some concluding remarks. The defect data presented here is based on a large number of short-loop experiments based on optical inspection of templates and wafers; these data are complemented by a modest number of high resolution e-beam inspections to provide insight into S-FIL specific defects at leading edge line widths.

Nano-imprint lithography (NIL) has the capability to transfer very fine patterns. As NIL was described in ITRS Roadmap in 2003, there are plans to apply NIL to semiconductor volume production at 32nm half pitch devices. This study is describes the critical issues of nano-imprint tool for semiconductor volume production. For an exposure tool supplier such as CANON, overlay control is not a critical issue for nano-imprint lithography because CANON has experience from proximity X-ray lithography (PXL). CANON can build an overlay system for nano-imprint tool using the CANON PXL's alignment and chip magnification correction technologies easily. Using our background, we focus on the Cost of Ownership (CoO) considering mold durability and compare NIL to Extreme Ultra Violet (EUV) and double patterning (DP) by immersion ArF lithography, to clarify the required specification of NIL from the viewpoint of productivity.

Hot embossing throughput is a key issue, which has been addressed in this paper. We show how it is possible to remove the mold from the imprinted resist at the imprint temperature. We study reflow behavior of imprinted patterns, and make a cooling and quenching simulation. This work can lead to design of cooling tools adapted to a given application, and suits as well for the full wafer imprint, as well for the roll imprint.

We develop a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light source is based on a short pulse, high power, high repetition rate CO₂ master oscillator power amplifier (MOPA) laser system and a Tin droplet target. A maximum conversion efficiency of 4.5% was measured for a CO₂ laser driven Sn plasma having a narrow spectrum at 13.5 nm. In addition, low debris generation was observed. The CO₂ MOPA laser system is based on commercial high power cw CO₂ lasers. We achieve an average laser power of 3 kW at 100 kHz with a single laser beam that has very good beam quality. In a first step, a 50-W light source is developing. Based on a 10-kW CO₂ laser this light source is scalable to more than 100 W EUV in-band power.

Xenon-fueled gas discharge produced plasma (DPP) sources were integrated into Micro Exposure Tools already in 2004. Operation of these tools in a research environment gave early learning for the development of EUV sources for Alpha and Beta-Tools. Further experiments with these sources were performed for basic understanding on EUV source technology and limits, especially the achievable power and reliability. The intermediate focus power of Alpha-Tool sources under development is measured to values above 10 W. Debris mitigation schemes were successfully integrated into the sources leading to reasonable collector mirror lifetimes with target of 10 billion pulses due to the effective debris flux reduction. Source collector mirrors, which withstand the radiation and temperature load of Xenon-fueled sources, have been developed in cooperation with MediaLario Technologies to support intermediate focus power well above 10 W. To fulfill the requirements for High Volume chip Manufacturing (HVM) applications, a new concept for HVM EUV sources with higher efficiency has been developed at XTREME technologies. The discharge produced plasma (DPP) source concept combines the use of rotating disk electrodes (RDE) with laser exited droplet targets. The source concept is called laser assisted droplet RDE source. The fuel of these sources has been selected to be Tin. The conversion efficiency achieved with the laser assisted droplet RDE source is 2-3x higher compared to Xenon. Very high pulse energies well above 200 mJ / 2&pgr; sr have been measured with first prototypes of the laser assisted droplet RDE source. If it is possible to maintain these high pulse energies at higher repetition rates a 10 kHz EUV source could deliver 2000 W / 2&pgr; sr. According to the first experimental data the new concept is expected to be scalable to an intermediate focus power on the 300 W level.

This paper provides a detailed review of development progress for a laser-produced-plasma (LPP) extreme-ultra-violet (EUV) source with performance goals targeted to meet joint requirements from all leading scanner manufacturers. We present the latest results on drive laser power and efficiency, source fuel, conversion efficiency, debris mitigation techniques, multi-layer-mirror coatings, collector efficiency, mass-limited droplet generation, laser-to-droplet targeting control, and system use and experience. The results from full-scale prototype systems are presented. In addition, several smaller lab-scale experimental systems have also been constructed to test specific physical aspects of the light sources. This report reviews the latest experimental results obtained on these systems with a focus on the topics most critical for a source intended for use in high volume manufacturing (HVM). LPP systems have been developed for light-sources applications to enable EUV scanners for optical imaging of circuit features at nodes of 32 nm and below on the international technology roadmap for semiconductors (ITRS). LPP systems have inherent advantages over alternate source types, such as discharge produced plasmas (DPP), with respect to power scalability, source etendue, collector efficiency, and component lifetime. The capability to scale EUV power with laser repetition rate and pulse energy is shown, as well as the modular architecture for extendability. In addition, experimental results of debris mitigation techniques and witness sample lifetime testing of coated multi-layer-mirrors (MLM) are described and used to support the useful lifetime estimation of a normal incidence collector. A roadmap to meet requirements for production scanners planned well into the next decade is also presented.

Tin is one of the most efficient source materials for both gas discharge plasma sources and laser produced plasma sources for EUV lithography. Unlike Xenon which was the material commonly investigated for the EUVL source application, recycling of the target materials is not necessary for tin targets because of its low relative cost. However, in assessing the benefits of different source architectures, there are large differences in the size of the tin inventory used, and consequences that ensue. In this paper we make a first attempt to compare these differences, and assess their impact. Utilizing tin as the radiator at 13.5 nm reduces the total cost of the source system significantly.

The joint specification projected in-band EUV power requirements at the intermediate focus will rise beyond 185W 2%-bw to maintain the necessary 80-100WPH throughput for economic viability. New improvements in photon efficiency and mask illumination are needed to reduce reflections and power demand, as well as improving source spatial uniformity. In 2006, Starfire Industries presented a microdischarge plasma light source concept for consideration as a potential HVM solution for high-power spatial and temporal multiplexing. Using a distributed array architecture, thermal and particle loadings become manageable when spread over 100s to 1000s of discrete units allowing power scalability. In addition, a key tenant is the potential for novel collection and illumination geometries that could simulate Kohler and pupil fill effects found in conventional fly's-eye mirror systems; thus leading to a reduction in optical elements and a factor of >5x increase in total throughput. A top-level illuminator optical design based on the microsource array technology is presented, as well as thoughts on illumination efficiency, reticle uniformity, partial coherence and uniformity of the pupil fill for a realistic EUV source array. In addition, experimental data from xenonbased sources will be presented with a suite of plasma and optical diagnostic instruments, including conversion efficiency.

The International Venture for Nanolithography (INVENT) initiative announced in mid 2005, a unique industry-university consortium between the College of Nanoscale Science and Engineering at Albany and a group of leading edge integrated device manufacturers, has launched an extensive R&D program on EUV lithography (EUVL). The overall scope of the INVENT EUVL program, the status of our efforts to establish a baseline lithography process on a full-field EUVL scanner, and our progress in evaluating EUV resist materials, in designing a custom reticle for scanner characterization and in developing an actinic EUV mask imaging microscope, are discussed.

Operating as a SEMATECH resist test center, the Berkeley 0.3-NA EUV microfield exposure tool continues to play a crucial role in the advancement of EUV resists and masks. Here we present recent resist-characterization results from the tool as well as tool-characterization data. In particular we present lithographic-based aberration measurements demonstrating the long-term stability of the tool. We also describe a recent upgrade to the tool which involved redesign of the programmable coherence illuminator to provide improved field uniformity as well as a programmable field size.

The concept of Extreme Ultra-Violet Lithography (EUVL) mask dual pods is proposed for use in both mask shipping and handling in exposure tools. The inner pod was specially designed to protect masks from particle contamination during shipping from mask houses to wafer factories. It can be installed in a load-lock chamber of exposure tools and evacuated while holding the mask inside. The inner pod upper cover is removed just before the mask is installed to a mask stage. Prototypes were manufactured and tested for shipping and for vacuum cycling. We counted particle adders through these actions with a detectable level of 54 nm and up. The adder count was close to zero, or we can say that the obtained result is within the noise level of our present evaluation environment. This indicates that the present concept is highly feasible for EUVL mask shipping and handling in exposure tools.

In extreme ultraviolet (EUV) lithography, defocusing influences on a pattern position shift due to off-axis incident light on a reflective mask. The pattern position shift with defocusing generates a newly random error source of overlay. Analyzing an exposure and defocus window (ED-window) being merged with a distribution of the pattern position shift reveals that the new error source creates a small impact for the criterion within 10% of the overlay tolerance. Next, 3rd order coma aberration and two modified illumination sources, annular and dipole, are investigated with respect to a pattern position shift which is associated with the asymmetrical phase distribution of diffracted rays. The results show that coma aberrations create no significant impact, and also the modified illumination sources are of little concern whenever semi-dense pitches are forbidden.

Characterizing the effect of electrostatic chucking on the flatness of Extreme Ultraviolet Lithography (EUVL) reticles is necessary for the implementation of EUVL for the sub-32 nm node. In this research, finite element (FE) models have been developed to predict the flatness of reticles when clamped by a bipolar Coulombic pin chuck. Nonflatness measurements of the reticle and chuck surfaces were used to create the model geometry. Chucking was then simulated by applying forces consistent with the pin chuck under consideration. The effect of the nonuniformity of electrostatic forces due to the presence of gaps between the chuck and reticle backside surfaces was also included. The model predictions of the final pattern surface shape of the chucked reticle have been verified with chucking experiments and the results have established the validity of the models. Parametric studies with varying reticle shape, chuck shape, chuck geometry, and chucking pressure performed using FE modeling techniques are extremely useful in the development of SEMI standards for EUVL.

The character projection (CP) lithography is utilized for maskless lithography (ML2) and is a potential for the future photomask manufacture. The drawback of the electron beam (EB) lithography is its low throughput and leads to a rise in IC prices. The number of EB shots to project an IC chip determines the fabrication time and the amortization cost and must be reduced. A multi-column-cell (MCC) system is a lithographic one in which column-cells can independently project patterns onto a silicon wafer in parallel with the CP and variable shaped beam (VSB) lithographies. This paper presents a technology mapping technique for enhancing the throughput of MCC systems. Our technique enhances the throughput of MCC systems by reducing the number of EB shots to project an entire IC chip. The target MCC system for which our technology mapping optimizes a circuit is the one which has not uniform but multiform CP masks among column-cells. Such an MCC system can project more cell functions with the CP than a uniform CP masks-based system. Comparing with an conventional technique, our technique has achieved a 19.8% smaller number of EB shots without any performance degradation of ICs under a timing constraint. Moreover, our technique has achieved a 33.4% smaller number of EB shots under no performance constraints. Our technique is easy for both IC designers and equipment developers to adopt because it is a software approach with no additional modification on character projection equipment.

With an evident requirement for Gaussian electron beam direct write lithography for prototyping and development on 300mm substrates below the 32nm node Vistec Lithography began the development of a new tool. A key requirement of this tool development was the integration and use of an interferometry solution for stage position measurement. Existing products had shown limitations in their practical application and performance and a new solution sought by the design team. Vistec entered into a development programme with Renishaw to utilise their newly developed interferometry systems.

For Electron Beam Direct Write (EBDW) a systematic investigation of defect density using a Negevtech 3100 darkfield inspection system was performed. A special defect learning pattern for memory applications with coverage of 50% was designed and printed partially on 300mm wafers using chemically amplified positive and negative E-Beam resists. By optical defect measurements post litho it was possible to inspect 50nm dense lines to characterize the exposure system as well as the used resist process. Using this method a large exposed area in millimeter range can be inspected and an overview on exposure quality can be gained in a reasonable amount of time. Particle measurements were performed additionally to distinguish between particles and exposure issues. By using darkfield measurements, process related issues like development problems and resist residuals can be found, as well as writing issues like shot butting and write field stitching can be quickly determined and controlled with this method. In this paper, the measurement methodology is described as well as the effect of writer imperfections on the darkfield images. A pareto analysis is performed and shows the frequency of occurrence of different defects. Measures to reduce defects - especially on the tool side - are given. The method is feasible to use in a regular check to control tool and process performance.

Using Monte Carlo simulation, we studied voltage contrast (VC) image caused by negative charging. In order to simulate the VC image, we have developed an electron scattering program based on a consideration of the spatial charge conduction model. Also we have established a cluster computing system of 60 CPUs to shorten the processing time. Using a Monte Carlo simulator, we succeeded in obtaining the simulated VC image. Comparison between simulated images and experimental images reveals that the simulated images are in good agreement with some experimental images.

We have developed the EBIS (Electron Beam Integrated System), which is a character projection (CP) type low-energy electron-beam direct writing (LEBDW) system. In this system, the proximity effect due to backscattering electrons is very small under the condition that the energy of primary electron is 5 keV. However, there is a serious problem, in that the signal of the mark buried under a thick insulator couldn't be detected. To overcome this problem, we adopted a mark detection method using Voltage Contrast (VC) image with negative charge on the sample surface. So far, we have detected the signal of alignment mark buried under 600nm-thick (nmt) tri-layer resist using VC image on EBIS. Then we exposed overlay patterns with alignment using the mark detection with VC image. The mark image is very clear with a sufficiently high contrast. The asymmetry originating from VC is mitigated by means of FB scanning. Using this VC mark detection method, EB drawing was performed with alignment with 600nmt tri-layer resist on Si substrate. Moreover, VC mark detection with 600nmt tri-layer resist on the substrates of back-end-of-line (BEOL) of logic device was performed and the mark images with sufficient contrast were obtained. Although the characteristic distortion of VC image exists, mark detection is possible by using X/Y separate scanning, which consists of X-direction scanning to get an X position and Y-direction scanning to get a Y position in non-charged area.

For the first time, electrically testable snake and comb structures were used to quantitatively characterize the defectivity associated with imprint lithography, specifically with Step and Flash Imprint Lithography. Whereas the overall yield for quarter micron optically-patterned snakes was found to be approximately 95%, the corresponding value for imprinted snakes was about 84%. The yield of imprinted snakes was found to fall rapidly with decreasing feature size. For example, the yield of 1:5 50 nm short snakes was only about 55%. Complementary optical inspection suggested feature pullout (release agent failure and mechanical layer separation) was a prevailing occurrence. Qualitatively, defects were binned into four primary, broad categories: self-cleaning template defects; non self-cleaning template defects; imprint-impeding defects; and template damaging defects. Additionally, the template cleaning process employed was found to be fairly efficient at removing particles, particularly when considering defects at the larger feature sizes. There is no doubt that the control of defectivity will be the next large hurdle that will challenge imprint lithography as it strives to make inroads in manufacturing arenas. Finally, a future study is planned with improved etch barrier and transfer layers.

Directly patterning dielectric insulator materials for semiconductor devices via nanoimprint lithography has the potential to simplify fabrication processes and reduce manufacturing costs. However, the prospect of mechanically forming these materials, especially when they are highly porous, raises concerns about their physical integrity. We report the direct imprinting of 100 nm parallel line-space patterns into a high modulus poly(methylsilsesquioxane)-based organosilicate thin film that is capable, in its non-patterned form, of meeting the ultra-low dielectric constant requirement of k ≈ 2.3. Immediately after imprinting a (5 to 10) % shrinkage in the pattern height of the partially vitrified patterns relative to the mold is quantified using X-ray reflectivity. Nanoscopic pores with an average diameter of approximately 2.2 nm are then generated in the patterns at high temperatures, through the volatilization a second phase porogen, while the material simultaneously vitrifies into a glassy organosilicate network. Pattern shape changes upon vitrification are also quntified and indicating that a 12 % reduction in the pattern height of the porogen-loaded imprint is observed with very little change in the pattern width. For a imprint without the added porogen, the shrinkage is still anisotropic in the height direction, but reduced approximately by 4 %. Our results show that nanoporous low-k patterns can be replicated via nanoimprint lithography with very little loss in the pattern quality.

We propose a very large-area (> diagonal 20 inch) ultraviolet nanoimprint lithography (UV-NIL) process as a breakthrough strategy for the thin-film transistor liquid-crystal display (TFT-LCD) industry. The large-area UV-NIL process is a promising alternative to expensive conventional optical lithography for the production of TFT-LCD panels. In this study a UV-NIL process using a large area hard stamp in a low vacuum environment is presented. The hard stamp made from quartz is used for achieving a high overlay accuracy and the vacuum environment is employed to ensure that air bubble defects are not formed during imprinting. It is demonstrated that the quartz stamp can be used for imprinting diagonal 20-in. substrates via single-step UV-NIL in a low vacuum environment. Experimental results demonstrate the potential of the proposed approach as a low-cost lithographic process applicable to flat panel displays.

Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22 nm nodes. Step and Flash Imprint Lithography (S-FILTM) is a unique method that has been designed from the beginning to enable precise overlay for creating multilevel devices. A photocurable low viscosity monomer is dispensed dropwise to meet the pattern density requirements of the device, thus enabling imprint patterning with a uniform residual layer across a field and across entire wafers. Further, S-FIL provides sub-100 nm feature resolution without the significant expense of multi-element, high quality projection optics or advanced illumination sources. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates. This paper addresses steps required to achieve resolution at or below 32 nm. Gaussian beam writers are now installed in mask shops and are being used to fabricate S-FIL templates. Although the throughput of these systems is low, they can nevertheless be applied towards applications such as unit process development and device prototyping. Resolution improvements were achieved by optimizing the ZEP520A resolution and exposure latitude. Key to the fabrication process was the introduction of thinner resist films and data biasing of the critical features. By employing a resist thickness of 70 nm and by negatively biasing features as much as 18 nm, 28 nm half-pitch imprints were obtained. Further processing improvements, including a high resolution lift-off method, show promise for achieving 20 nm half pitch features on a template.

The International Technology Roadmap for Semiconductors (ITRS) lays out a quite challenging path for the further development of the patterning techniques needed to create the ever-smaller feature sizes. In recent years the standard lithography reached its limits due to the diffraction effects encountered and the necessary complexity of compatible masks and projection optics. The restrictions on wavelength, in combination with high process and equipment costs, make low cost, simple imprinting techniques competitive with next generation lithography methods. Nanoimprint Lithography (NIL) is predicted as one candidate for the 32 nm and 22 nm technological nodes according to the ITRS. There are several NIL techniques which can be categorized depending on the process parameters and the imprinting method - either step & repeat or full wafer imprinting. A variety of potential applications has been demonstrated by using Nanoimprint Lithography (e.g. SAW devices, vias and contact layers with dual damascene imprinting process, bragg structures, patterned media) [1,2]. In Soft UV-NIL processes the overlay alignment accuracy was not demonstrated to be prepared for nanoelectronic devices; however other applications are already in high volume manufacturing such as the production of optical components (e.g. micro lenses).

We have investigated a number of key resist factors using EUV lithography including activation energy of deprotection. Our standard high activation resist material, MET-2D (XP5271F), is capable of robust performance at CDs in 40 nm regime and thicknesses above 100 nm. Below 100 nm film thickness, controlling acid diffusion becomes a difficult challenge. We have also developed a low activation resist (XP6305A) which shows superior process window and exposure latitude at CDs in the 35 nm regime. This resist is optimal for 80 nm film thickness. Lastly, we have demonstrated 25 nm 1:1 resolution capability using a novel chemical amplification resist called XP6627. This is the first EUV resist capable of 25 nm resolution. The LER is also very low, 2.7 nm 3&sgr;, for the 25 nm features. Our first version, XP6627G, has a photospeed of 40 mJ/cm². Our second version, XP6627Q, has a photospeed of 27 mJ/cm². Our current focus is on improving the photospeed to less than 20 mJ/cm². The outstanding resolution and LER of this new resist system raises the possibility of extending chemically amplified resist to the 22 nm node.

Extreme ultraviolet (EUV) substrates have stringent defect requirements. For the 32 nm node, all particles larger than 26 nm must be removed from the substrate. However, real defects are irregularly shaped and there is no clear dimension for an irregular particle corresponding to 26 nm. Therefore, the sphere equivalent volume diameter (SEVD) for a native defect is used. Using this definition and defect detection measurements, all particles larger than 20 nm must be removed from the substrate. Atomic force microscopy (AFM) imaging and multiple cleaning cycles were used to examine the removal of particles smaller than 50 nm SEVD. Removal of all particles larger than 30 nm was demonstrated. Particles that required multiple cleaning processes for removal were found to be partially embedded. The best cleaning yield can be obtained if the cleaning history of the substrate is known and one can choose the proper cleaning processes that will remove the remaining particles without adding particles. Ag, Au, Al₂O₃, Fe₂O₃, and CuO particles from 30 nm to 200 nm were deposited on quartz surface. It was shown that these deposited defects are much easier to remove than native defects.

Extreme ultra-violet (EUV) lithography has become the technique of choice to print the ever-shrinking nanoscale features on the silicon wafer. For successful transfer of patterns on to the wafer, the EUV photomask cannot contain defects greater than 30 nm. Megasonic cleaning is a very successful cleaning technique for removal of particles on photomasks, but also causes a relatively high amount of damage to the fragile EUV photomasks thin film structures. Though it is believed that acoustic cavitation is the primary phenomenon responsible for cleaning as well as pattern damage, a fundamental picture of the acoustic cavitation mechanisms in play during megasonic cleaning has not yet clearly emerged. In this study, we characterize the role of acoustic cavitation in megasonic cleaning by examining the effects of acoustic power densities, cleaning solution properties, and dissolved gas content on cavitation via experiments and molecular dynamics (MD) simulations. MD is an atomistic computation technique capable of modeling atomic-level and nanoscale processes accurately making it well suited to study the effect of cavitation on nano-sized particles and patterns.

The authors introduce initial simulation work on Photonic Bandgap Enhanced or PBE reticles that tends to address the manufacturing problems associated with typical PSM reticles while improving potential resolution capabilities to 35 and 25 nm utilizing 193 nm immersion lithography. The proposed approach for manufacturing reduces the overall defect issues associated with PSM approaches.

We have fabricated extreme ultraviolet lithography (EUVL) blank masks consisting of a TaN absorber, Ru capping layer, and Mo/Si multilayers using ion-beam sputter deposition and investigated their dependence on capping layer and absorber stack structure. At EUV wavelengths, the reflectivities of the multilayers, including their dependency on the thickness of the capping and absorber layers, are in good agreement with simulation results obtained using Maxwell equations and the refractive indexes of each layer. Ru, one of the most promising capping materials on Mo/Si multilayers due to its resistance to oxidation and selectivity to etching, also shows better EUV reflectivity than Si as a capping layer if we choose a thickness that produces a constructive interference. To meet the reflectivity requirements (⩽ 0.5 %) in the SEMI EUVL mask standard specifications, a TaN absorber at least 70 nm thick should be applied. However, aerial image results simulated by using EM-Suite show that 40 nm is sufficient for the TaN absorber to display the maximum image contrast. In addition, horizontal-vertical (HV) biasing effects due to mask shadowing become negligible if the TaN is reduced to about 40 nm. As a result, we suggest using a thin TaN absorber 40 nm thick since it is able to minimize mask shadowing effects without a loss of image contrast.

Molecular-ruler nanolithography uses individual molecules as building blocks to create nanometer-scale features in a low-cost, high-throughput process. Self-assembled multilayers are used in combination with radiation-sensitive polymeric resists to interface nanometer-scale features with structures fabricated using conventional lithographic methods. This technique is advantageous for its high precision, parallel processing, and low capital investment. Here, we provide an overview of molecular-ruler nanolithography and describe how this technology is being applied to the creation of nanometer-scale devices, patterning of large-area sub-200-nm grating structures, and the fabrication of quartz templates for use as molds in imprint lithography.

Pixelated photoresists, i.e. resists that compartmentalize photochemistry into discrete imaging elements are an emerging design for improved resolution. A pixelated design seeks to overcome chaotic organization in complex resist formulations through application of small regular or symmetric imaging species, and/or through the application of preorganization of resist components. [1] Another approach, backbone scission, has also emerged as a powerful method to improve resist performance. [2] In this approach, the parts of the resist structure that have undergone radiation driven chemistry are disconnected from the unaffected material. This enhances contrast and also confers an additional mechanism: structural disruption. Bile acids have been used recently as building blocks to enable host-guest chemistry [3] and have been incorporated as additives in photoresists [4] and structural elements [5]. They as a class are fairly large (mw ~400) highly functionalized molecules possessing a hydrophobic face, alcohol groups and a carboxylic acid group. We describe here a scissionable pixelated resist architecture based on bile acids bound by acid-sensitive tertiary ester linkages into dendrimeric arrays. This design seeks to employ structural disintegration and catalyst pre-organization in addition to solubility switching as contrast mechanisms. Preliminary EUV and ebeam studies have shown G0 and G1 materials capable of sub-micron imaging.

We present a simple method for fabricating high aspect-ratio polymer nanostructures on a solid substrate by sequential application of molding and drawing of a thin polymer film. In this method, a thin polymer film is prepared by spin coating on a solid substrate and the temperature is raised above the polymer's glass transition while in conformal contact with a poly(urethane acrylate) (PUA) mold having nano-cavities. Consequently, capillary force induces deformation of the polymer melt into the void spaces of the mold and the filled nanostructure was further elongated upon removal of the mold due to tailored adhesive force at the mold/polymer interface. The optimum value of the work of adhesion at the mold/polymer interface ranged from 0.9 to 1.1 times that at the substrate/polymer interface. Below or above this range, a simple molding or detachment occurred, corresponding to earlier findings.

This paper reports a novel lithography method that utilizes local nanoscale thermal decomposition of polymer films using heated atomic force microscope cantilever probe tips. Cross-linkable polymers, for example based on poly(hydroxystyrene) (also referred to as PHOST), are used as the writing material in these methods. The experimental results show that the cross-linked polymer can prevent the thermal flowing induced by melting of the polymer, and very fine feature can be achieved. 100 nm lines have been successfully written using a heated cantilever probe in a cross-linked PHOST film. 60 &mgr;m/sec writing speeds have also been achieved using this technology. The amount of material decomposed by the heated tip can be very well controlled by modulating both the cantilever probe temperature and writing speed. This ability to modulate the removal rate of material from the film makes it possible to directly pattern 3-D structures into a polymer film using such heated AFM cantilever tips.

Photonic device structures often require nano scale lithography techniques for their device fabrication. The techniques are electron beam lithography and FIB(focused ion beam) pattering. Focused ion beam etching has been used as a nanolithography tool for the creation of these nanostructures without mask. We obtain nano scale mesa patterns on InGaN/GaN LED(light emitting diodes) wafer using focused ion beam and characterized. The InGaN/GaN LED wafer was grown by molecular organic vapor deposition (MOCVD). To reduce the surface damage during FIB patterning, we used a dielectric mask layer and wet etching to eliminate re-deposition of sputtering materials and Ga+ ion implantations and ion damage layer during FIB patterning, and finally, removed SiO₂ with wet etching. A metal thin layer was deposited by an ion beam sputter to avoid charging effects during FIB patterning. We obtain a 2-Dimensional patterning for the fabrication of the high brightness LEDs. This FIB pattering technique can be applied to nanofabrication optoelectronic devices.

The non-telecentricity of EUV lithography exposure systems translates into a very severe specification for EUV mask flatness that is typically 10 times tighter than the typical current specification for masks used in 193 nm wavelength exposure systems. The mask contribution to the error budget for pattern placement dictates these specifications. EUV mask blank suppliers must meet this specification while simultaneously meeting the even more challenging specification for defects density. This paper suggests a process flow and correction methodology that could conceivably relax the flatness specification. The proposal does require that the proposed method of clamping the mask using an electrostatic chuck be accurate and reproducible. However, this is also a requirement of the current approach. In addition, this proposal requires the incorporation of an electrostatic chuck into a mask-shop metrology tool that precisely replicates the behavior of the chuck found in the EUV exposure tool.

In extreme ultraviolet lithography (EUVL), the lack of a suitable material to build conventional pellicles calls for industry standardization of new techniques for protection and handling throughout the reticle's lifetime. This includes reticle shipping, robotic handling, in-fab transport, storage, and uses in atmospheric environments for metrology and vacuum environments for EUV exposure. In this paper, we review the status of the industry-wide progress in developing EUVL reticle-handling solutions. We show the industry's leading reticle carrier approaches for particle-free protection, such as improvements in conventional single carrier designs and new EUVL-specific carrier concepts, including variations on a removable pellicle. Our test indicates dual pod approach of the removable pellicle led to nearly particle-free use during a simulated life cycle, at ~50nm inspection sensitivity. We will provide an assessment of the remaining technical challenges facing EUVL reticle-handling technology. Finally, we will review the progress of the SEMI EUVL Reticle-handling Task Force in its efforts to standardize a final EUV reticle protection and handling solution.

The EUV lithography is the most promising candidate for the next generation semiconductor exposure technology to fabricate fine patterns of 32nm and below 32nm, now that ArF immersion technology is expected to cover the 45 nm node these days. This paper focuses on the optical performance of EUV projection optics that will be the lithography tool under 32nm node. EUV projection optics is consists only of the mirrors, and the number of mirrors varies depending on the numerical aperture (NA) of projection optics. As the NA becomes higher, more mirrors are required. For example, it is expected that 6-mirror projection optics (6M-PO) could have 0.25NA, and 8-mirror projection optics (8M-PO) could have over 0.35NA. Assuming a process factor K1 of 0.6, EUV projection optics with NA of 0.25 can achieve 32nm resolution, and projection optics with NA of 0.35 can achieve 22nm resolution. Therefore, 6M-PO and 8M-PO are suitable for 1st EUV generation and 2nd EUV generation, respectively. In EUV optics, each mirror has multi-layered Mo/Si coating to get high reflectivity. The reflectivity is extremely sensitive to the layer thickness of coating, the exposure wavelength, and the ray incidence angle, so the multilayer coating is designed to give a best performance at exposure wavelength of 13.5nm. This means that thickness and optical indices in the multilayer coating cause serious degradations on the imaging performance. Therefore, more mirrors might cause greater degradation on the image performance. This paper discusses the relationships between the multilayer coatings and the imaging performance in order to apply EUV lithography for below HP32nm technology node. We compare 6M-PO to 8M-PO from the point of view of the multilayer coatings numerically. 1. Imaging performance with error-less multilayer coating in consideration of chromatic aberration Even If the multilayer coating without any coating errors can be coated on all of the mirrors, the chromatic aberration cannot be avoided. We compare the imaging performance of 6M-PO to 8M-PO in consideration of chromatic aberration. 2. Influence of multilayer coating errors on transmittance of optical system and aberration There are some kinds of multilayer coating errors. In this paper, we discuss thickness errors that have a great influence on transmittance and aberration. 3. Influence of contamination on aberration We discuss the influence of carbon contamination films that deposit on the top surface of the multilayer coatings.