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Author(s): Naulleau, P; Anderson, C; Chao, W; Goldberg, K; Wojdyla, A; Bhattarai, S; Neureuther, A; Goodwin, F; Neisser, M | Abstract: With the slipping of the insertion node for extreme ultraviolet lithography, demands on resist resolution have increased further stressing sensitivity requirements. A variety of resists, both chemically amplified and not, have been developed meeting resolution needs, but falling short on sensitivity and line-width roughness (LWR). Note that resolution is an absolute mandatory requirement, the true tradeoff that must be considered is between sensitivity and contact hole printing is a crucial application for extreme ultraviolet lithography and is particularly challenged by resist sensitivity due to inherent inefficiencies in darkfield contact printing. Checkerboard strong phase shift masks have the potential to alleviate this problem through a 4× increase in optical efficiency. The feasibility of this method is demonstrated using the SEMATECH-Berkeley Microfield Exposure Tool pseudo phase shift mask configuration and preliminary results are provided on the fabrication of an etched multilayer checkerboard phase shift mask.

Carbon contamination is a significant issue with extreme ultraviolet (EUV) masks because it lowers throughput and has potential effects on imaging performance. Current carbon contamination research is primarily focused on the lifetime of the multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However, contamination on patterned EUV masks can cause additional effects on absorbing features and can affect the printed images. In this work, various carbon contamination experiments were performed to study the impact between contamination topography and observed imaging performance. Lithographic simulation using calculated aerial images and experimentally determined resist parameters was performed and compared to the printing results to estimate the allowed carbon thickness with critical dimension compensation applied to the mask.

Availability of defect-free reflective mask has been one of the most critical challenges to extreme ultraviolet lithography (EUVL). To mitigate the risk, significant progress has been made on defect detection, pattern shifting, and defect repair. Clearly such mitigation strategies are based on the assumption that defect counts and sizes from incoming mask blanks must be below practical levels depending on mask specifics. The leading industry consensus for early mask product development is that there should be no defects greater than 80 nm in the quality area, 132 mm x 132 mm. In addition less than 10 defects smaller than 80 nm may be mitigable. SEMATECH has been focused on EUV mask blank defect reduction using Veeco Nexus TM IBD platform, the industry standard for mask blank production, and assessing if IBD technology can be evolved to a manufacturing solution. SEMATECH has recently announced a breakthrough reduction of defects in the mask blank deposition process resulting in the production of two defect-free EUV mask blanks at 54 nm inspection sensitivity (SiO 2 equivalent). This paper will discuss the dramatic reduction of baseline EUV mask blank defects, review the current deposition process run and compare results with previous process runs. Likely causes of remaining defects will be discussed based on analyses as characterized by their compositions and whether defects are embedded in the multilayer stack or non-embedded.

Ion Beam Deposition (IBD) has been the primary technique used to deposit EUV mask blanks since 1995 when it was discovered it could produce multilayers with few defects. Since that time the IBD technique has been extensively studied and improved and is finally approaching usable defectivities. But in the intervening years, the defectivity of magnetron sputtering has been greatly improved. This paper evaluates the suitability of a modern magnetron tool to produce EUV mask blanks and the ability to support HVM production. In particular we show that the reflectivity and uniformity of these tools are superior to current generation IBD tools, and that the magnetron tools can produce EUV films with defect densities comparable to recent best IBD tool performance. Magnetron tools also offer many advantages in manufacturability and tool throughput; however, challenges remain, including transitioning the magnetron tools from the wafer to mask formats. While work continues on quantifying the capability of magnetron sputtering to meet the mask blank demands of the industry, for the most part the remaining challenges do not require any fundamental improvements to existing technology. Based on the recent results and the data presented in this paper there is a clear indication that magnetron deposition should be considered for the future of EUV mask blank production.

We demonstrate numerically that oblique off-axis illumination could enhance the contrast and extend the depth of focus of EUV phase defects detection. In addition to quantitative observation, it also allows us to extract the resolution-limited defect phase profiles quantitatively. This scheme can be easily implemented in both full field and scanning mask inspection tools.

It is now well established that extremely ultraviolet (EUV) mask multilayer roughness can lead to wafer-plane line-edge roughness (LER) in lithography tools. It is also evident that this same effect leads to sensor plane variability in inspection tools. This is true for both patterned mask and mask blank inspection. Here we evaluate mask roughness specifications explicitly from the actinic inspection perspective. The mask roughness requirement resulting from this analysis are consistent with previously described requirements based on lithographic LER. In addition to model-based analysis, we also consider the characterization of multilayer mask roughness and evaluate the validity of using atomic force microscopy (AFM) based measurements by direct comparison to EUV scatterometry measurements as well as aerial image measurements on a series of high quality EUV masks. The results demonstrate a significant discrepancy between AFM results and true EUV roughness as measured by actinic scattering.

High numerical aperture (high-NA) extreme ultraviolet (EUV) is one option to enable a higher resolution than EUV can achieve with single patterning. An industry effort to achieve consensus on the key parameters of high-NA EUV is described. At high-NA, three-dimensional (3D) mask effects cause a loss of contrast in the image that is recovered by increasing the scanner de-magnification. This leads to a tradeoff between wafer field and mask size that has considerable impact on mask cost and scanner cost of ownership.

In our previous work, various techniques were used to confirm the contamination deposits on the sidewall of extreme ultraviolet (EUV) mask absorbers [1-2]. In order to further understand the effects of contamination topography on mask absorbing features, direct measurements of contaminated features is needed. In this work, we investigated the contamination topography using cross-section transmission electron microscope (TEM) image analysis on four different masks. TEM specimens of contaminated features from silicon and ruthenium capped EUV masks were prepared using a focused ion beam (FIB). We conducted the contamination experiment with three different exposure sources including EUV, out-of-band, and electron induced processes. Thickness measurements from each contamination experiment were provided. Shadowing effect and geometric analysis on the contamination topography is also discussed.

AFM-based roughness measurement reveals the topography of EUV masks, but is only sensitive to the top surface [1]. Scatterometry provides a more accurate approach to characterize the effective phase roughness of the multilayer, and it becomes important to determine the valid metrology for roughness characterization. In this work, the power spectral density calculated from scatterometry is compared to that from AFM for measurements before and after coating of substrates with a range of roughness levels. Results show noticeable discrepancies between AFM- and scatterometrymeasured roughness, and indicates that when the physical surface roughness increases with deposition the EUV penetration into the multilayer tends to mitigate this effect. In this paper, we describe an EUV scatterometry-based measurement method for the determination of phase roughness with the goal of minimizing the amount of physical scattering data to be collected and rendering the method compatible with potential future standalone EUV reflectometer tools.

With the insertion of extreme ultraviolet lithography (EUVL) for high volume manufacturing (HVM) expected in the next few years, it is necessary to examine the performance of low thermal expansion materials (LTEMs) and assess industry readiness of EUV substrates. Owing to the high cost of LTEM, most of the development work so far has been done on fused silica substrates. Especially in developing cleaning technology prior to multilayer deposition, fused silica substrates have been used extensively, and defect trends and champion blank data have been reported using multilayer deposition data on fused silica substrates. In this paper, the response of LTEMs to cleaning processes prior to multilayer deposition is discussed. Cleaning processes discussed in this paper are developed using fused silica substrates and applied on LTEM substrates. The defectivity and properties of LTEM to fused silica are compared. Using the dense scan feature of the substrate inspection tool capable of detecting defects down to 35 nm SiO 2 equivalent size and appropriate defect decoration techniques to decorate small defects on substrates to make them detectable, cleaning technologies that have the potential to meet high demands on LTEM for EUVL are developed and optimized.

We describe the printability of native phase defects categorized by type and dimension using NXE3100 EUV scanner and DPS (Defect Printability Simulator) software developed by Luminescent Technologies. The critical dimension (CD) error on wafers simulated by the DPS is strongly affected by the geometry of the multilayer (ML) used as an input parameter for simulation. This finding is supported by cross section images of the ML acquired from transmission electron microscopy (TEM) showing that the diameter of the defect and geometry of the ML are closely related. Accordingly, the selection of the type of ML geometry seems to be important in the accuracy of defect printability simulation. The CD error simulated from the DPS using reconstructed ML geometry shows better correspondence with that measured on a wafer than conformal or smoothed ML geometry. The DPS software shows good simulation performance in predicting defect printability at 27nm HP node. This is verified by wafer printing and RCWA simulation.

Although the quality of extreme ultraviolet (EUV) mask substrates has improved by continuous refinement of the polishing processes, the yield of defect-free blanks is still very low. Dressed-photon nanopolishing (DPNP) is a novel vapor phase, photo-chemical, non-contact etching process that has been shown to locally smooth bumps and pits to below 1 nm in height/depth while not affecting the surface roughness. DPNP is based on the concept of a dressed photon, which is a quasi-particle in the optical near field of a surface that can couple with lattice phonons in nanometric regions (< 100 nm). When illuminated with light of a suitable wavelength, such coupled states are generated on a nanometrically rough material surface and impart sufficient energy to an etchant gas to enable its dissociation and etching in the rough regions only. DPNP can be the last polishing step on EUV substrates to eliminate any remnant pits and/or embedded particles on the surface to yield potentially defect-free substrates.

EUVL requires a high yield of low-defect density reflective mask blanks, one of the top two critical technology gaps for the commercialization of this technology. One of the major sources of mask blank defects is the top of the substrate due to substrate quality, cleaning residue, and handling- or storage-induced defects. SEMATECH’s current inspection tool, the Lasertec 7360, can detect defects down to 37 nm on quartz substrates in dense scan mode. Defects below 40 nm on these substrate are difficult to detect, which challenges the quantification and characterization, and hence the determination of defect sources. SEMATECH developed a thin film decoration technique to quantify sub-40 nm defects and analyze composition to pinpoint defect sources. The technique involves oblique angle deposition in an ion beam deposition system, which decorates the particle. The decoration of particles is optimized by depositing enough thin film so that defects can be detected by the Lasertec7360 and yet keeping the film thin enough to employ several metrology techniques to efficiently analyze defect composition. The challenges involved with the metrology of such embedded defects and the impact of oblique angle deposition will be discussed. A theoretical model of defect decoration that can successfully simulate the thin film deposition on top of the defects will be provided. The effect of angle, deposition rate, and deposition time to quantify the decoration effect will also be presented.

EUVL requires high-yield, low defect density reflective mask blanks, a requirement which is considered one of the top two critical technology gaps for commercialization of the technology. At the SEMATECH Mask Blank Development Center (MBDC), research on defect reduction and yield improvement for EUV mask blanks is being pursued using the Veeco Nexus deposition tool. The defect performance of this tool is one of the factors limiting the availability of defect-free EUVL mask blanks. SEMATECH identified the key components in the ion beam deposition system that are currently impeding the reduction of defect density and the yield of EUV mask blanks. SEMATECH improved the defect performance of the champion blank with 12 defects above 45 nm which is a 36% improvement from the data reported last year for the champion blank (19 defects above 45 nm). The yield analysis on high quality mask blanks from ion beam deposition system is also presented. Substrate quality is currently the biggest source of mask blank defects, while high yield also requires complete elimination of large size defects from deposition. A roadmap to meet the required defectivity specification for EUV mask blanks is presented.

Photo-induced defects (or haze defects) on 193nm optic masks (haze defects) have been a serious problem not only to reticle engineers working for mask manufacturing and handling but also to photo-lithography engineers. The most widely accepted explanation of the root causes of haze defects is the cleaning chemical residues remaining on the mask surface and unavoidable outgassed molecules that outgas from pellicle materials when exposed to 193nm radiation. These have been significant challenges for reticle cleaning engineers who need to use cleaning chemicals whose residues do not lead to progressive defect formation on the mask and to find improved materials to minimize pellicle outgassing. It is assumed that contamination generation on EUV masks would have a higher probability than on optic masks, primarily since EUV masks are not protected by a pellicle and amorphous carbon films can accumulate during exposure to EUV light. While there is potential to mitigate the generation of carbon contamination by improving the exposure tool environment and removing carbon films using in-situ atomic hydrogen cleaning, it is not yet clear whether the reaction of mask cleaning chemicals to EUV radiation will lead to creation of progressive defects on EUV mask surfaces. With the work to being done it has been observed that carbon contamination on EUV masks dominates any effects of solvent chemicals under normal environmental or exposure conditions (from atmospheric pressure up to a vacuum level of 10 -6 Torr) during EUV exposure. However, it is still unknown whether residual cleaning chemicals will provide a nucleus for progressive defect formation during exposure. This lack of understanding needs to be addressed by the industry as EUV masks are expected to undergo more frequent cleaning cycles. In this work, we will report on an investigation of the molecular behavior of cleaning chemicals on EUV mask surfaces during EUV exposure. Movement (e.g., migration or aggregation) of cleaning chemical molecules near EUV exposure spots on the top surface and beneath the mask will be examined under high vacuum (~10 -8 Torr). We will also investigate whether EUV exposure can trigger the evaporation of cleaning chemical residues from the EUV mask surface, possibly contaminating the exposure environment. Better understanding of the influences of the mask cleaning chemicals during exposure, coupled with knowledge about mask tolerance and patterning performance affected by the cleaning chemicals, should enable the proper selection of mask cleaning processes and chemicals to meet EUV requirements.

Extreme ultraviolet lithography (EUVL) is the leading next-generation lithography (NGL) technology to succeed optical lithography at the 22 nm node and beyond. EUVL requires a low defect density reflective mask blank, which is considered to be one of the top two critical technology gaps for commercialization of the technology. At the SEMATECH Mask Blank Development Center (MBDC), research on defect reduction in EUV mask blanks is being pursued using the Veeco Nexus deposition tool. The defect performance of this tool is one of the factors limiting the availability of defect-free EUVL mask blanks. SEMATECH identified the key components in the ion beam deposition system that is currently impeding the reduction of defect density and the yield of EUV mask blanks. SEMATECH's current research is focused on in-house tool components to reduce their contributions to mask blank defects. SEMATECH is also working closely with the supplier to incorporate this learning into a next-generation deposition tool. This paper will describe requirements for the next-generation tool that are essential to realize low defect density EUV mask blanks. The goal of our work is to enable model-based predictions of defect performance and defect improvement for targeted process improvement and component learning to feed into the new deposition tool design. This paper will also highlight the defect reduction resulting from process improvements and the restrictions inherent in the current tool geometry and components that are an impediment to meeting HVM quality EUV mask blanks will be outlined.

EUV lithography is considered the most promising lithography solution for the 16 nm node and beyond. As EUV light is strongly absorbed by all known materials, reflective optics are used instead of conventional transmittance optics applied to ArF and KrF lithography. The EUV mask must also need be reflective. It typically consists of a Ta-based absorber layer, Ru capping layer, Si/Mo multilayer on a low thermal expansion material (LTEM) substrate with a backside Cr-based metal coating. Because of the strong absorbance of the EUV light, a pellicle is not practical. Therefore, EUV masks must be cleaned more frequently to maintain the necessary cleanliness. This poses numerous unique challenges in cleaning processes. For example, the EUV mask integrity, including critical dimension (CD), EUV reflectivity, and absorber thickness must be kept intact during multiple cleanings throughout the mask's lifetime. Requirements of defect size for the cleaning, furthermore, are becoming tighter as semiconductor circuit design rules get smaller. According to the International Technology Roadmap For Semiconductors (ITRS), the smallest defect size that must be removed is 23 nm for the 18 nm NAND Flash node in 2013. In addition to defects on the frontside, defects on a backside also need to be minimized since they might lead overlay error due to local distortions of EUV masks on an electrostatic chuck. This paper focuses on evaluations of cleaning performances using the Lasertec M1350 and M7360 blank inspection system, which has a 71 nm and 43 nm sensitivity. The 43nm is the current best sensitivity while keeping a >90% defect capture rate. First, the cleaning performance using the standard process has been investigated. We found a mitigation of adders was a key challenge for the EUV mask cleaning. The primary source of the adders was also identified as pits. Secondly, the megasonic cleaning process has been optimized to mitigate the adders. We could successfully reduce the adders by 30%. Thirdly, to confirm the entire cleaning process, a backside cleaning process combined with frontside cleaning was investigated, demonstrating that the backsides of the EUV mask blanks could be cleaned without additional impact on frontside defectivity.

One of the major technical hurdles to be overcome before EUV lithography can enter high volume manufacturing is the amount of defects in EUV mask blanks, many of which occur during the EUV reflector deposition process. The technology currently used to deposit this reflector is ion beam sputter deposition. Understanding the properties of the ion beam and the nature of the plasma in the deposition chamber is therefore critical to understanding defect production mechanisms and subsequently eliminating them. In this work, we have studied how the source parameters influence ion beam divergence, its footprint on the target, and the amount of beam that misses the target and hits the shielding. By optimizing the source parameters, we can modulate certain target- and shield-specific defect types. We have compared our data with models of source performance and found general agreement, enabling the theory to be fine-tuned based on the results of the measurements. Models are being developed to better describe actual source performance. We have also investigated the plasma conditions the ion beam creates in the tool, which is crucial to understanding the transport of defects from their source to the mask. A well characterized ion beam and plasma will lead to process and tool changes that will ultimately reduce defect levels in EUV mask blanks.

It is widely recognized in the semiconductor industry that getting to defect-free extreme ultraviolet (EUV) mask blanks is critical in achieving high volume chip manufacturing yield beyond the 22 nm half-pitch node. Total defectivity of an EUV mask blank depends on the defectivity of substrate and finished mask blank. Finished mask blanks are normally subjected to a cleaning process to get rid of the loosely adhered particles on the top. This is normally done in a spin-spray mask cleaning tool using traditional mask cleaning processes. It is important that this cleaning process does not degrade the properties of the multilayer blank or introduce additional particles or pits during the process. However, standard cleaning processes used to clean multilayer blanks result in EUV reflectivity loss, loss of uniformity in reflectivity, increased roughness and adds pits and particles on mask blanks. The standard cleaning process used consists of multiple steps, each of which may cause the oxidation of Ru capping layer as well as other underlying bilayers, etching of the multilayer stack and increased roughness of the bilayers thus leading to a loss in EUV reflectivity. It is a challenging task to experimentally correlate the processing steps to the resulting damage and to quantify the reflectivity loss. Furthermore, due to the high cost of materials we have not been able to do extensive experiments to determine the root cause of problems. In this work, we have combined mask blank cleaning using standard processes, TEM cross section studies and simulations to quantify the impact of the multilayer oxidation, etching and roughness on the EUV reflectivity loss and mask blank degradation.

EUV masks include many different layers of various materials rarely used in optical masks, and each layer of material has a particular role in enhancing the performance of EUV lithography. Therefore, it is crucial to understand how the mask quality and patterning performance can change during mask fabrication, EUV exposure, maintenance cleaning, shipping, or storage. The fact that a pellicle is not used to protect the mask surface in EUV lithography suggests that EUV masks may have to undergo more cleaning cycles during their lifetime. More frequent cleaning, combined with the adoption of new materials for EUV masks, necessitates that mask manufacturers closely examine the performance change of EUV masks during cleaning process. We have investigated EUV mask quality and patterning performance during 30 cycles of Samsung's EUV mask SPM-based cleaning and 20 cycles of SEMATECH ADT exposure. We have observed that the quality and patterning performance of EUV masks does not significantly change during these processes except mask pattern CD change. To resolve this issue, we have developed an acid-free cleaning POR and substantially improved EUV mask film loss compared to the SPM-based cleaning POR.

Next generation high volume manufacturing lithography tools will likely use CO 2 laser produced plasma sources to generate extreme ultraviolet (EUV) radiation needed for resist exposures. Existing mitigation techniques for out-of-band radiation from these sources result in reduced EUV (13.5 nm) transmission to the resist plane which decreases desired throughput. New methods to suppress the 10.6 μm radiation, which dominates the out-of-band spectrum at the intermediate focus (IF), need to be examined. A spectral filter design that uses an infrared absorbing gas to target the mitigation of 10.6 μm in these EUV tools may provide another alternative to suppress the unwanted radiation. This work explores infrared absorption of gases at 10.6 μm while focusing on gaseous sulfur hexafluoride (SF 6 ) whose υ 3 infrared active mode is vibrationally excited by 10.6 μm photons. A compact tunable CO 2 laser is used to measure the room temperature, low fluence absorption of SF 6 in the range of 10.53-10.65 μm. In addition, the EUV transmission of SF 6 as a function of pressure is estimated based on the absorption cross section measured for wavelengths between 11-17 nm. Design considerations such as the EUV transmission vs. infrared absorption tradeoff are discussed.

Extreme ultraviolet (EUV) lithography is the successor to optical lithography and will enable advanced patterning in semiconductor manufacturing processes down to the 8 nm half pitch technology node and beyond. However, before EUV can successfully be inserted into high volume manufacturing a few challenges must be overcome. Central among these remaining challenges is the requirement to produce “defect free” EUV masks. Mask blank defects have been one of the top challenges in the commercialization of extreme ultraviolet (EUV) lithography. To determine defect sources and devise mitigation solutions, detailed characterization of defects is critical. However, small defects pose challenges in metrology scale‐up. SEMATECH has a comprehensive metrology strategy to address any defect larger than a 20 nm core size to obtain solutions for defect‐free EUV mask blanks. SEMATECH's Mask Blank Development Center has been working since 2003 to develop the technology to support defect free EUV mask blanks. Since 2003, EUV mask blank defects have been reduced from 10000 of size greater than 100 nm to about a few tens at size 70 nm. Unfortunately, today's state of the art defect levels are still about 10 to 100 times higher than needed. Closing this gap requires progress in the various processes associated with glass substrate creation and multilayer deposition. That process development improvement in turn relies upon the availability of metrology equipment that can resolve and chemically characterize defects as small as 30 nm. The current defect reduction efforts at SEMATECH have intensively included a focus on inspection and characterization. The facility boasts nearly $100M of metrology hardware, including an FEI Titan TEM, Lasertec M1350 and M7360 tools, an actinic inspection tool, AFM, SPM, and scanning auger capabilities. The newly established Auger tool at SEMATECH can run a standard 6‐inch mask blank and is already providing important information on sub‐100 nm defects on EUV blanks. Complementary to Auger analysis, TEM provides ultimate resolution in the defect imaging of sub‐nanometer structures. Crystalline and phase information generated by this metrology technique also indicates the sources of defects. SEMATECH's TEM capability is further equipped with energy dispersive X‐ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), which provide higher analytical power than similar techniques in traditional secondary electron microscopy (SEM). This paper will describe SEMATECH's comprehensive effort to develop robust inspection of EUV mask defects. We will discuss the development of hardware and procedures for inspecting particles 70 nm and smaller. This paper will also outline challenges in the metrology of current defects on EUV mask blanks and metrology issues that arise with increasingly smaller defects.

The impact of carbon contamination on extreme ultraviolet (EUV) masks is significant due to throughput loss and potential effects on imaging performance. Current carbon contamination research primarily focuses on the lifetime of the multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However, contamination on patterned EUV masks can cause additional effects on absorbing features and the printed images, as well as impacting the efficiency of cleaning process. In this work, several different techniques were used to determine possible contamination topography. Lithographic simulations were also performed and the results compared with the experimental data.

With the projected rollout of pre-production extreme ultraviolet lithography (EUVL) scanners in 2010, EUVL pilot line production will become a reality in wafer fabrication companies. Among EUVL infrastructure items that must be ready, EUV mask carriers remain critical. To keep non-pellicle EUV masks free from particle contamination, an EUV pod concept has been extensively studied. Early prototypes demonstrated nearly particle-free results at a 53 nm PSL equivalent inspection sensitivity during EUVL mask robotic handling, shipment, vacuum pump-purge, and storage. After the passage of SEMI E152, which specifies the EUV pod mechanical interfaces, standards-compliant EUV pod prototypes, including a production version inner pod and prototype outer pod, were built and tested. Their particle protection capability results are reported in this paper. A state-of-the-art blank defect inspection tool was used to quantify their defect protection capability during mask robotic handling, shipment, and storage tests. To ensure the availability of an EUV pod for 2010 pilot production, the progress and preliminary test results of pre-production EUV outer pods are reported as well.

Extreme ultraviolet lithography (EUVL) is the most effective way to print sub-30 nm features. We characterized EUVL readiness of the three major resist platforms for sub-30 nm half-pitch (HP) manufacturability using a full-field ASML alpha demo tool (ADT) scanner and studied the extendibility of EUV chemically amplified resist (CAR). Based on an "M-factor" analysis, which shows the maturity of EUV resist for 28 nm HP manufacturability, a polymer-bound photoacid generator (PAG) resist was 78% ready, a PHS hybrid resist was 81%, and a molecular glass EUV resist was 58%. The polymer-bound resist showed good resolution for 25 nm HP using the ASML ADT. It also demonstrated fair linewidth roughness (LWR) and a good lithographic process margin of 18% exposure latitude (EL) and 160 nm depth of field (DOF) for 28 nm HP patterning compared with the other resist platforms, but its resist collapse and etch resistance need to be improved for manufacturability. PHS hybrid resist showed a fair etch resistance and resist collapse performance compared to the other resist platforms, but LWR needs to be improved. The molecular resist needs to mature further, especially in resist collapse and iso-dense (ID) bias. When considering its many strong points and control of lower acid diffusion, the polymer-bound PAG resist appears to be the most suitable platform for manufacturability and EUV CAR extension. We therefore would like to encourage the development of next generation polymer-bound PAG resist with a higher etch resistance. A process window of 80 nm DOF was demonstrated for 26 nm HP patterning and a measurable DOF for 25 nm HP was achieved with the polymer-bound PAG resist. Resist collapse and LWR are major issues for 22 nm HP patterning in manufacturing. LWR improvements were achieved with various techniques, and resist collapse was greatly improved with a novel approach that uses a residual resist layer. 16 nm HP line/space (L/S) image modulation and 18 nm HP resolution were demonstrated with an EUV CAR, indicating that EUV CAR could be extended to sub-20 nm HP patterning.

For extreme ultraviolet light lithography to be a viable process for the future development of computer chips, it is necessary that clean photons are produced at the intermediate focus (IF). To measure the flux at the IF, the Center for Plasma-Material Interactiosn (CPMI) at the University of Illinois at Urbana-Champaign has developed a Sn IF flux emission detector (SNIFFED) apparatus that is capable of measuring charged and neutral particle flux at the IF. Results will be presented that diagnose debris produced at the IF, as well as methods by which this debris can be mitigated. Advanced Materials Research Center, AMRC, International SEMATECH Manufacturing Initiative, and ISMI are servicemarks of SEMATECH, Inc. SEMATECH, and the SEMATECH logo are registered servicemarks of SEMATECH, Inc. All other servicemarks and trademarks are the property of their respective owners.

Carbon contamination of extreme ultraviolet (EUV) masks and its effect on imaging is a significant issue due to lowered throughput and potential effects on imaging performance. In this work, a series of carbon contamination experiments were performed on a patterned EUV mask. Contaminated features were then inspected with a reticle scanning electron microscope (SEM) and printed with the SEMATECH Berkeley Microfield-Exposure tool (MET) [1]. In addition, the mask was analyzed using the SEMATECH Berkeley Actinic-Inspection tool (AIT) [2] to determine the effect of carbon contamination on the absorbing features and printing performance. To understand the contamination topography, simulations were performed based on calculated aerial images and resist parameters. With the knowledge of the topography, simulations were then used to predict the effect of other thicknesses of the contamination layer, as well as the imaging performance on printed features.

The availability of defect-free masks remains one of the key challenges for inserting extreme ultraviolet lithography (EUVL) into high volume manufacturing. The successful production of defect-free masks will depend on the timely development of defect inspection tools, including both mask blank inspection tools and absorber pattern inspection tools to meet the 22 nm half-pitch node. EUV mask blanks with embedded phase defects were inspected with a reticle actinic inspection tool (AIT) and the Lasertec M7360. The Lasertec M7360 is operated at SEMA TECH's Mask blank Development Center (MBDC) in Albany, with sensitivity to multilayer defects down to 40-45 nm, which is not likely sufficient for mask blank development below the 32 nm half-pitch node. Phase defect printability was simulated to calculate the required defect sensitivity for the next generation blank inspection tool to support reticle development for the sub-32 nm half-pitch technology node. This paper will also discuss the kind of infrastructure that will be required in the development and mass production stages.

Extreme ultraviolet lithography (EUVL) is the most effective way to print sub-32 nm features. We have assessed EUVL resist readiness for 32 nm half-pitch (HP) manufacturing, presenting process feasibility data such as resolution, depth of focus (DOF), line edge roughness/line width roughness (LER/LWR), mask error enhancement factor (MEEF), resist collapse, critical dimension (CD) uniformity, post-exposure delay (PED) stability, and post-exposure bake (PEB) sensitivity. Using the alpha demo tool (ADT), a full field ASML EUV scanner, we demonstrate the feasibility of a k1 ~0.593 resist process for 32 nm HP line/space (L/S) patterning. Exposure latitude (EL) was 13% at best focus, and DOF was 160 nm at best dose using a 60 nm thick resist. By incorporating a spin-on underlayer, the process margin could be improved to 18.5% EL and 200 nm DOF. We also demonstrate ADT extendibility using a state-of-the-art EUV platform. A k1 ~0.556 resist process was demonstrated for 30 nm HP L/S patterns, providing a 13% EL, 160 nm DOF, and a common process window with isolated lines. 28 nm HP patterning for a k1 ~0.528 resist process could be feasible using a more advanced resist with improved DOF and resist collapse margin.

Extreme ultraviolet (EUV) mask blanks with embedded phase defects were inspected with a reticle actinic inspection tool (AIT) and the Lasertec M7360. The Lasertec M7360, operated at SEMA TECH's Mask Blank Development Center (MBDC) in Albany, NY, has a sensitivity to multilayer defects down to 40-45 nm, which is not likely sufficient for mask blank development below the 32 nm half-pitch node. Phase defect printability was simulated to calculate the required defect sensitivity for a next generation blank inspection tool to support reticle development for the sub-32 nm half-pitch technology node. Defect mitigation technology is proposed to take advantage of mask blanks with some defects. This technology will reduce the cost of ownership of EUV mask blanks. This paper will also discuss the kind of infrastructure that will be required for the development and mass production stages.

Extreme ultraviolet (EUV) photoresists are known to outgas during exposure to EUV radiation in the vacuum environment. This is of particular concern since some of the outgassed species may contaminate the nearby EUV optics and cause a loss of reflectivity and therefore throughput of the EUV exposure tools. Due to this issue, work has been performed to measure the species and quantities that outgas from EUV resists. Additionally, since the goal of these measurements is to determine the relative safety of various resists near EUV optics, work has been performed to measure the deposition rate of the outgassed molecules on Mo/Si-coated witness plate samples. The results for various species and tests show little measurable effect from resist components on optics contamination with modest EUV exposure doses.

It is widely recognized in the semiconductor industry that getting to defect-free extreme ultraviolet (EUV) mask blanks is critical in achieving high volume chip manufacturing yield beyond the 22 nm half-pitch node. Finished mask blanks are normally subjected to a cleaning process to get rid of the loosely adhered particles on the top. It is important that this cleaning process does not degrade the properties of the multilayer blank or introduce additional particles or pits during the process. However, standard cleaning processes used to clean multilayer blanks can result in EUV reflectivity loss, loss of uniformity in reflectivity, increased roughness, and add pits and particles on mask blanks. The standard cleaning process consists of multiple steps, each of which may cause the oxidation of the ruthenium capping layer, as well as the underlying bilayers, etching of the multilayer stack, and increased roughness of the bilayers, thus leading to a loss in EUV reflectivity. It is a challenging task to exper...

Out-of-band radiation in extreme ultraviolet (EUV) exposure tools remains one of the critical issues that must be addressed before the implementation of this lithography technique for high-volume manufacturing. The out-of-band spectrum at the intermediate focus of EUV sources that use a CO2 laser-produced plasma is dominated by scattered radiation from the drive laser, which operates near 10.6-μm wavelength. To reduce the unwanted heating of optical components in the exposure tool caused by the infrared wavelength, a 10.6-μm wavelength-absorbing gas can be used to reduce the number of photons at this wavelength reaching the intermediate focus. Gaseous sulfur hexafluoride (SF6), whose υ3 infrared active mode is vibrationally excited by radiation around 10.6-μm wavelength, can be used to function as a molecular absorber and thus, mitigate part of the infrared radiation. In this work, the optical absorption of gaseous SF6 is experimentally investigated at the CO2 laser wavelengths close to 10.6 μm as well as the EUV wavelength. Various considerations affecting the use of a gas-based spectral filter are also discussed in this paper.