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Nano-imprint lithography is attracting attention as a low cost method for printing nanometer-scale geometries and has obtained placement on the International Technology Roadmap for Semiconductors as a potential lithography solution at the 32 and 22nm fabrication nodes [International Technology Roadmap for Semiconductors, 2003 ed.]. As a result, nano-imprint technology and infrastructure development related to template infrastructure, imprinting capabilities, and wafer-level pattern transfer processes are essential to successfully make the transition from research and development to a viable manufacturing processing technique suitable for multiple applications. Motorola Labs has been focusing on developing the template and wafer-level processes while optimizing the imprinting process and collaborating with external partners to optimize both the inspection and repair of imprint templates. This paper reviews recent results of the above-mentioned focus areas.

Recent advancements made in step and flash imprint lithography (S-FIL) have enhanced the attractiveness of nanoimprint technology for sub-100nm resolution. Improvements in the area of material dispensing and refinement of the etch barrier itself have resulted in more uniform printing while producing a much thinner residual layer. These improvements, coupled with changes to the etch processes have facilitated direct pattern transfer of sub-45nm line/space (1:3) features. This leading-edge research could define the pathway for nanoimprint to become a competitive solution for advanced high resolution pattern transfer.

High-resolution overlay is considered to be an important challenge for imprint lithography processes. A key advantage of Step and Flash(TM) Imprint Lithography (S-FIL(TM)) is that it uses low-pressures (

If imprint lithography is to be considered as a viable method for fabricating high density silicon-based circuits, an infrastructure must be established that is capable of supplying users with 1X templates. It is critical, therefore, that tools are available that can expose, inspect, and repair these templates. The purpose of this work is to present initial step and flash imprint lithography template results using a shaped-beam system. A Leica SB350 MW was used to expose ZEP 7000 resist. The SB350 is a variable shaped-beam tool with 50 kV electron optics. A Motorola template pattern transfer process was used to obtain final images in the template. Trenches as small as 33 nm were resolved, as were 44 nm holes. Further improvements may be possible by increasing the operating voltage to 100 kV, and further increasing the e-beam system line edge acuity.

Several Monte Carlo approaches for modeling electron-solid interaction have been investigated as to their impact on simulation accuracy and performance. An optimum set of models, including the Mott elastic scatter cross-section, the Moller inelastic scatter cross-section, and the continuous slow down approximation with the relativistic Bethe stopping power, have been identified as giving a good agreement with published experimental data while providing better simulation performance than more sophisticated approaches. It has been validated that the Mott cross-section should be used instead of Rutherford's for correct prediction of both electron transmission and backscatter coefficients in the cases of thin films for incident beam energy in the range of 10-100 keV. The use of the Gryzinski cross-section for modeling inelastic scatter did not provide any accuracy improvement because the predicted beam widening in resist was of the same order as given by a more simplistic Moller model. It is also necessary to use the relativistic Bethe stopping power for incident beam energies >30 keV.

Step and flash imprint lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes, SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Several different methods for fabricating templates are presented in this study. One scheme addresses some of the weaknesses associated with a solid glass substrate by incorporating a conductive and transparent layer of indium tin oxide (ITO) on the surface of the substrate. Features are defined on the templates by patterning a thin layer of PECVD oxide that is deposited on the ITO layer. A second method bypasses the oxide etch process by imaging a thin layer of hydrogen silsesquioxane (HSQ). By using a combination of these two methods, it is also possible to form multi-tiered structures on a template. Templates with features as small as 20 nm have been fabricated using the methods described above. The templates were then used to imprint patterns on 200 mm silicon wafers. It appears that any feature defined in the template is faithfully replicated on the wafer.

Step and flash imprint lithography (SFIL) replicates patterns by using a transparent template with relief images etched into its surface. Recent work has examined alternative methods for template fabrication. One scheme incorporates a conductive and transparent layer of indium tin oxide (ITO) on the surface of the substrate. Features are defined on the templates by patterning a thin layer of PECVD oxide that is deposited on the ITO layer. A second method bypasses the oxide etch process by imaging a thin layer of hydrogen silsesquioxane (HSQ). By combining or iterating the two methods, it is possible to form multi-tiere, structures on a template. Two and three tier structures were fabricated on silicon wafers and templates. A two layer structure was fabricated on a quartz photoplate by patterning PECVD oxide and subsequently patterning a second tier using HSQ. The resulting relief structures were successfully replicated on wafers using SFIL.

Step and flash imprint lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes, SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. The purpose of this work is to investigate alternative processes for defining features on an SFIL template. The first method considered using a much thinner (

One promising technology for next generation lithography is the electron projection technique called SCALPEL. Relatively thin membrane and scattering materials are required for high contrast imaging during SCALPEL wafer exposures. The thin SCALPEL membranes allow a majority of the electrons to pass when exposing the masks at high accelerating voltages (>50 keV). Critical dimension (CD) control and uniformity is complicated by the contribution from large area electron scattering characteristics (‘fogging’ effect) of the material below the membrane mask. Depending on the material type, morphology and distance of the backing material from the membrane, the electron scattering contribution can be significant and cover a wide radius from the exposure pixel. The energy contribution associated with various materials, morphology and positions underneath a 200-mm SCALPEL membrane mask were investigated. The energy contribution was determined via Monte Carlo simulations and added to a resist exposure/process simulation model to determine the impact on CD results. The simulated and actual CD results are compared for various materials at two different distances from the membrane for verification of the model accuracy. Simulation and experimentation also revealed the electron trapping effect with various aspect ratio via holes did not significantly reduce the electron backscatter contribution to the resist features.

NEB-22, a chemically amplified negative tone resist has been formulated by Sumitomo for e-beam lithography direct write and mask making applications. The resist has exhibited excellent characteristics which would also make it applicable for use in a SCALPEL exposure tool.^1^,^2 The initial processing results for Sumitomo NEB-22A5 material demonstrated extremely high resolution capabilities with excellent exposure latitude. Although the process worked well for many direct write and mask applications, improvements were needed to address SCALPEL concerns. The process was modified to maintain sensitivity and optimize resolution, exposure latitude and PEB latitude. Excellent results were obtained in a 200 nm film of NEB-22 with new process parameters.

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.

Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22 nm nodes. Step and Flash Imprint Lithography (S-FIL TM ) is a unique method for printing sub-100 nm geometries. Relative to other imprinting processes S-FIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. 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. With respect to inspection, although defects as small as 70 nm have been detected using optical techniques, it is clear that it will be necessary to take advantage of the resolution capabilities of electron beam inspection techniques. The challenge is in inspecting templates composed purely of fused silica. This paper reports the inspection of both fused silica wafers and plates. The die-to-database inspection of the wafers was performed on an NGR2100 inspection system. Fused silica plates were inspected using an NGR4000 system. Three different experiments were performed. In the first study, Metal 1 and Logic patterns as small as 40 nm were patterned on a 200 mm fused silica wafer. The patterns were inspected using an NGR2100 die-to-database inspection system. In the second experiment, a 6025 fused silica plate was employed. Patterns with a limited field of view (FOV) were inspected using an NGR4000 reticle-based system. To test the tool's capability for larger FOVs, 16 × 16 μm areas on a MoSi half tone plate were scanned and stitched together to evaluate the tool's ability to reliably do die-to-database comparisons across larger inspection areas.

Nano-imprint technology has demonstrated the potential for a low-cost, high-throughput Next Generation Lithography (NGL) method extendable to ultra-fine geometry requirements. Although the development of nano-imprinting lithography has been focused on semiconductor applications, the technology could provide a pathway for non-semiconductor-related applications as well. Examples of technologies that may benefit from this nano-imprint are high-density drives and other stand-alone memories, organic and flexible electronics, photonics, nanoelectronics, biotechnology, etc. With the rapid advances in these industries, the need for sub-nanometer features to drive performance and innovation, while maintaining cost, is to be expected. Step and Flash Imprint Lithography (S-FIL TM ) is one of several cost-effective imprinting technologies being pursued for sub-100 nm resolution. In demonstrating successful final pattern transfer of features less than 45 nm, S-FIL has sparked some interest as a viable alternative to other NGL methods. Unlike optical-based lithography, imprint utilizes the basic concept of contact printing, and therefore, does not require expensive optics and complex resist material to create images. Thus, the cost of ownership for nano-imprint lithography compared with other optical-based NLGs could provide solutions for many applications. Improvements made in S-FIL in the areas of material dispensing and refinement of the etch barrier (EB) have resulted in more uniform printing while producing a thinner residual layer. These improvements, coupled with changes to the etch processes have enabled pattern transfer with minimal critical dimension (CD) loss. This paper will describe both the new imprinting results and pattern transfer to demonstrate sub-45nm features. CD bias at each of the process steps will also be discussed. Examples of sub-45 nm (1:3) line/space features post imprint and final pattern transfer into oxide will be shown.

In order for Step and Flash Imprint Lithography S-FIL or any other imprint lithography to become truly viable for manufacturing, certain elements of the infrastructure must be present. In particular, these elements include; fast and precise Electron Beam (E-beam) pattern writing, ability to inspect, and a methodology to repair. The focus of this paper will be to investigate repair of clear and opaque defects on S-FIL templates using Focused Ion Beam (FIB) and Electron beam technologies. During this study, FEI's Accura XT FIB mask repair system was used to selectively mill opaque line edge defects as small as 45 nm in the Cr-based and 30 nm in the quartz-based patterns. Repairs to the Cr pattern achieved a placement offset of 8.8 nm with a one sigma value of 11.4 nm. Additionally, a series of trench cuts were made perpendicular through line segments to determine the minimum cut resolution. In an effort to repair clear defects within chrome patterns, studies were performed to deposit carbon or a proprietary metallization using either FEI's FIB platform or E-beam mask repair research tool. This paper will discuss the repair strategy used and include characterization of repairs through Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM) imaging. Furthermore, repair efficiency was determined by assessing the ability of the repair to hold up through the remainder of the template fabrication process and ultimately pattern transfer of imprinted features.

Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22 nm nodes. Step and Flash Imprint Lithography (S-FIL ) is a unique method for printing sub-100 nm geometries. Relative to other imprinting processes S-FIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. Further, S-FIL provides sub-100 nm feature resolution without the significant expense of multielement, 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. With respect to inspection, although defects as small as 70 nm have been detected using optical techniques, it is clear that it will be necessary to take advantage of the resolution capabilities of electron beam inspection techniques. This paper reports the first systematic study of die-to-database electron beam inspection of patterns that were imprinted using an Imprio 250 system. The die-to-database inspection of the wafers was performed on an NGR2100 inspection system. Ultimately, the most desirable solution is to directly inspect the fused silica template. This paper also reports the results on the first initial experiments of direct inspection fused silica substrates at data rates of 200 MHz. Three different experiments were performed. In the first study, large (350 -400 nm) Metal 1 and contact features were imprinted and inspected as described above. Using a 12 nm pixel address grid, 24 nm defects were readily detected. The second experiment examined imprinted Metal 1 and Logic patterns with dimensions as small as 70 nm. Using a pixel address of 3 nm, and a defect threshold of 20 nm, a systematic study of the patterned arrays identified problem areas in the design of the pattern layout. Finally, initial inspection of 200 mm fused silica patterned substrates has established proof of concept for direct inspection of imprint templates.

Submicron magnetoresistive sandwich cells of various sizes are fabricated and their magnetic properties are studied. A novel coupling mechanism of magnetostatic origin has been found to be mainly responsible for unique switching characteristics in cells with small length to width ratio.

Step and Flash Imprint Lithography (S-FIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes S-FIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. Previous work on S-FIL templates has focused on a chromium and quartz pattern transfer process that is compatible with processes that are currently used in mask shops. It is likely that 1X templates will require electron beam inspection, however, and templates that include buried charge conduction layers may be required. The purpose of this work was to investigate the issues associated with fabricating and inspecting these types of templates. The patterning stack examined included a layer of ZEP520A positive electron beam resist, followed by thin layers of chromium, silicon oxynitride, and indium tin oxide. The chromium layer was needed to avoid laser height sensor problems encountered prior to electron beam exposure. The pattern transfer process was characterized, and CD uniformity was characterized in four quadrants of the photoplate. A prototype electron beam inspection system was then used to inspect an array of programmed defect patterns. Two methods for fabricating templates were considered.

Memory elements 0.2 microns wide made from multilayer GMR material have been studied experimentally and analytically. When etched into narrow elements, the 12 to 15% material exhibits a memory mode with large outputs of /spl plusmn/8%. Analysis shows that the mode is suitable for multi-megabit die with high performance if yield can be achieved.

the Leica SB350MW 50keV shaped-beam e-beam lithography tool was used to write large-area 1X templates applicable in Step and Flash Imprint Lithography (S-FIL). This paper describes how information from the pattern analysis can be used to define the ZEP7000 resist exposure optimization technique for the SB350 MW tool together with the Motorola template pattern transfer process to obtain final template images in the transparent template. As a result of the complete process, well-resolved trenches measuring 33 nm and contacts as small as 44nm were obtained. Further improvements in the resist patterning will be possible by an adaptation of our standard proximity corrector (currently used in the 90 nm node maskmaking) with a high resolution upgrade.

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

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

We report in this work experimental and theoretical results showing the effects of absorber reflectivity on standard flare measurements, image formation and how this may contribute to various image metrics used in lithography. Our study shows that under typical conditions the reflectance from the absorber film has only a small effect on the image produced by the exposure system.

Step and FLash Imprint Lithography (S-FIL) is one of several new methods of imprint lithography being actively developed. Since S-FIL is a 1X printing technique, fabrication of templates is especially critical. The requirement to produce defect-free pillars (needed for imprinting contacts on wafers) in a reliable and manufacturable manner only serves to compound this challenge. In this study, the feasibilty and methodology of fabricating templates having arrays of sub-80 nm pillars is demonstrated. This process involves the use of a Leica VB6 100 keV e-beam system to pattern ZEP 520A resist, followed by a series of chrome and quartz etches to arrive at the final all-quartz template. Wafer printing was done on 200 mm wafers using Molecular Imprints Inc., Imprio-100 system. Critical dimension of template contacts and pillars is shown as a function of e-beam dose. Results of the study have demonstrated that S-FIL templates made with sub-80 nm pillars can be used to reliably replicate 1:1 pitch contact hole arrays on wafers. Sidewall profiles of both template pillars and printed contacts were sloped somewhat, and resulted in an approximately a 20-30 nm bias between contact bottom (smaller) and top opening. Critical dimension uniformity of printed contact arrays within-field and from field-to-field was also explored. Within-field CD uniformity of contacts was found to be less than field-to-field CD uniformity, which was excellent. The feasibility of printing pillar array using S-FIL was also demonstrated. Arrays of pillars measuring 54 nm with a pitch of 1:3 were reliably printed.

In this work, we analyzed resist CD uniformity on 6025 substrates in terms of resist PEB sensitivity, PEB time, temperature variation during ramp up, hotplate vacuum and the application of a chill plate. We found that the resist PEB sensitivity, PEB time and the final temperature were the most important factors. By selecting low PEB sensitive resist and optimizing the bake conditions, the CD uniformity was greatly improved. The temperature profile of the hotplate configuration used for this study will be discussed along with the CD uniformity obtained using this hotplate under various conditions.

Despite very intense work since its re-discovery in the early 1990’s, phase-shift lithography is only in limited use today. The reason for its lack of wide spread use is not performance, for the benefits of phase-shift lithography are very well documented in the literature. The problem has been the greater complexity involved in making phase shirt masks, the inspection and repair of defects, and in dealing with phase-shift conflicts and other layout problems. The phase shift approach most commonly used is attenuated phase-shift. This is not very surprising in view of the fact that this phase-shift approach requires only one write-pass; and the inspection, repair and OPC are less difficult than the other phase-shift options. Despite these shortcomings, work on phase shift continues as we push resolution and extend the life of optical microlithography. The reason is that the alternatives, 157 nm and next-generation lithography, have its own set of issues. As we come to grips with the complexities of working in the vacuum region of the spectrum, we realize that 157 nm is likely to be delayed, and more expensive than originally thought. All next generation lithography options require a great deal of new infrastructure, with it associated coast. In this paper we report on a self-aligned rim phase shift approach. There have been reports of self-aligned rim phase shift approaches before, however our approach is unique in that it only requires one write-pass. This significantly simplifies the mask-making process.

Step and Flash Imprint Lithography (SFIL) is one of several new nano-imprint techniques being actively developed. While SFIL has been shown to be capable of sub-30 nm resolution, critical dimension (CD) control of imprinted features must be demonstrated if SFIL Is to become a viable and production worthy lithography technique. In the current study, a Molecular Imprints Imprio-100 system was used to imprint resolution patterns on 200 mm wafers. A characterization of critical dimension uniformity over the all-quartz template was done and compared to the same features printed on wafers. This analysis was performed for 100, 80, 50, and 30 nm features in three ways: over a single die using 64 sites arrayed across a 21 mm field, from field-to-field for 37 die across a single wafer, and from wafter-to-wafer for six wafers. Results show that CD's transfer from template to wafer with a slight positive bias which is greatest for 50 and 30 nm line sizes. Feature profiles studies. Despite this, the maximum calculated component of process variation from the SFIL process itself was calculated to be only 6 nm.

In this paper, we report on evaluation of a high e-beam sensitive CA resist, FEP171 for EUVL mask fabrication. This resist exhibits a PEB temperature sensitivity of ~1nm/°C and 8.3 nm (3 σ) CD uniformity across an EUVL mask patterned with 200 nm dense features using a 100 keV e-beam exposure system. This resist also showed a very high resolution and excellent exposure latitude. Dense line/space features down to 60 nm have been delineated in this resist. This paper will discuss the lithographic performance of this resist and compare it with that of UV-III CA resist and ZEP 520 non-CA resist.

The escalating cost for Next Generation Lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990s, several resarech groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1999, Willson and Sreenivasan discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as Step and Flash Imprint Lithography. The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of teh wafer and template. This paper traces the development of nanoimprint lithography and addresses the issues that must be solved if this type of technology is to be applied to high-density silicon integrated circuitry.

Step and Flash Imprint Lithography (SFIL) is an alternative lithography technique that enables patterning of sub-100 nm features at a cost that has the potential to be substantially lower than either conventional projection lithography or proposed next generation lithography techniques. SFIL is a molding process that transfers the topography of a rigid transparent template using a low-viscosity, UV-curable organosilicon solution at room temperature and with minimal applied pressure. Employing SFIL technology we have successfully patterned areas of high and low density, semi-dense and isolated lines down to 20 nm, and demonstrated the capability of layer-to-layer alignment. We have also confirmed the use of SFIL to produce functional optical devices including a micropolarizer array consisting of orthogonal 100 nm titanium lines and spaces fabricated using a metal lift-off process. This paper presents a demonstration of the SFIL technique for the patterning of the gate level in a functional MOSFET device.

Step and Flash Imprint Lithography (SFIL) is an attractive low-cost method for printing sub-100 nm geometries. Relative to other imprinting processes, SFIL has the advantage that the template is transparent thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Since SFIL is a 1X lithography technique, the template masks will require very good layer-to-layer overlay accuracy for multiple level device fabrication. To fabricate a transparent SFIL template, processing techniques familiar to existing binary phase shift mask fabrication are utilized. However, in order to fabricate the sub-100 nm features necessary for SFIL templates, thinner resist and chromium are necessary. Initial resolution tests have resulted in features sizes down to ~20 nm with the non-chemically amplified resist, ZEP520. Template to template overlay of

As semiconductor device requirements approach the 70 nm lithography node the development and implementation of a next-generation lithography (NGL) technology and the associated masks becomes of paramount importance. We have been developing Extreme Ultraviolet Lithography (EUVL) mask materials and processes. Fabrication of these masks includes the deposition and patterning of an EUV absorber stack. An understanding of the effect of pattern transfer on image placement is required due to the stringent image placement requirements for NGL masks. This article reports the measurement results of image placement caused by the pattern transfer of resist through final image for a candidate EUVL absorber stack using both bright field and dark field patterned 6025 (6” × 6” × 0.25”) masks. To determine stress related image distortion for EUV masks, an EUV stack consisting of SiON, TaSiN, and Cr was deposited onto Mo/Si coated mask blanks (6025 format) provided by Lawrence Livermore National Laboratory (LLNL). Both dark field and bright field masks were built and the pattern image placement was measured after e-beam lithography and after every etch process. Analysis of the data sets provided the resultant pattern transfer induced image displacement.

Electron projection lithography (EPL) is one possible successor to conventional optical lithography. One type of EPL mask, a SCALPEL mask, consists of an array of rectangular membranes on a 200 mm silicon support wafer. An image of a die is formed by scanning and stitching the patterns resident on the membrane array. Key areas of concern for controlling the mask critical dimension (CD) include temperature uniformity during the resist post exposure bake (PEB) process, heating issues during resist exposure, fogging effects caused by electron scattering from the mask chuck and variations resulting from the pattern transfer of the mask scattering layer. A finite element model was used to evaluate heating issues during the mask writing step and PEB process. Masks were then written to verify the models. A Monte Carlo model was used to evaluate CD variations caused by electrons scattering from the chuck during the mask writing process.

Sub 100 nm T-gate structures have been produced using a tri- level resist stack modified from previously published results utilizing ZEP7000A, PMGI and ZEP520A positive e-beam resists. The new resist stack replaces the top resist with the more sensitive ZEP7000A from Zeon Chemical. The does sensitivity of the ZEP1000A is an order of magnitude higher than the ZEP520A. This difference provides the flexibility to create T-gate structures with larger top cross-sectional dimensions, which increase the transconductance. The technique can also be used to create other novel structures such as gamma-gates and small air bridges, by varying the dose on the different parts of a feature design to achieve the desired three-dimensional resist structure.

Step and Flash Imprint Lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, minimizing magnification and distortion errors. The purpose of this work was to investigate alternative methods for defining high resolution SFIL templates and study the limits of the SFIL process. Two methods for fabricating templates were considered. The first method used a very thin layer of Cr as a hard mask. The second fabrication scheme attempts to address some of the weaknesses associated with a solid glass substrate. Because there is no conductive layer on the final template, SEM and defect inspection are compromised. By incorporating a conductive and transparent layer of indium tin oxide (ITO) on the glass substrate, charging is suppressed during SEM inspection, and the transparent nature of the final template is not affected. Using ZEP-520 as the electron beam imaging resist, features as small as 20 nm were resolved on the templates. Features were also successfully imprinted using both types of templates.

The Semiconductor Industry Association (SIA) has placed stringent requirements on Next GenerationLithography mask critical dimension (CD) control. A new chemically amplified (CA) positive resist,Shipley XP2040D was evaluated for mask making application. This resist exhibited an extraordinary postexposure bake (PEB) sensitivity, less than 0.6 nm/ C, along with a sub-50 nm resolution. The PEB stabilityin ambient was larger than 4.5 hours and the line-edge-roughness (LER) was less than 2.9 nm. 1. INTRODUCTION Critical dimension (CD) control and uniformity for a SCALPEL mask must be kept within 7 nm (3 ) inorder to meet the SIA Roadmap requirement for 70 nm NGL mask fabrication [1]. Chemically amplified(CA) resists have been considered for NGL mask patterning because of their high resolution, high electronexposure sensitivity and etch selectivity. However, CD variation due to the PEB sensitivity of CA resistcomplicates the mask making process and needs to be minimized.Previous Finite Element Analysis modeling indicates there are PEB temperature gradients across a 200 mmSCALPEL mask and within each membrane of the mask. The thermal variations are due to the combinedcomplex three-dimensional mask structure coupled with the thermal gradients associated with the bakechamber environment. These gradients were experimentally confirmed through the measurement of criticalfeatures across various membranes on the mask array. A CD uniformity of 8-10 nm for inter-membrane and4-7 nm for intra-membrane was observed using a CA negative-tone resist, NEB22[2]. This CD variationwas mainly attributed to the large PEB sensitivity of the resist ( ~8 nm/ C).In order to meet the 7 nm SIA mask budget, CD non-uniformity due to thermal variations must be reduced.One way to minimize the influence of this thermal effect is to use low PEB sensitivity resists. This paperreports on the performance of Shipley XP2040D positive CA resist for 200 mm SCALPEL maskfabrication using the Leica VB6HR 100 KeV e-beam exposure system.

A negative tone, chemically amplified deep ultraviolet resist, ShipleyR UVN30, has been evaluated for use in NGL mask fabrication and direct write applications. This resist displayed excellent exposure latitude and resolution for both dense and isolated features. At optimum conditions 50 nm isolated lines and 60 nm dense lines resolved in a 300 nm thick film. Exposure dose latitude was 32%. Resist coat shelf life tests produced CD variations of 5 nm after 1 week and 10 nm after 3 months. A 66 hour post exposure bake delay in vacuum produced a 9 nm CD variation. PEB temperature sensitivity was 3 nm per degree Celsius. By selecting appropriate process conditions exposure latitude and resolution were optimized while decreasing linearity and line edge roughness performance. This paper reviews the test conditions for performing the optimization experiments and discuses the potential of using this resist for both advanced mask fabrication and direct write application.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Two new positive tone, chemically amplified, DUV resists from Shipley, XP-9525 and XP- 9549Q (UV III) have been investigated for use as direct write e-beam resists. Both of these materials have shown extremely high resolution capabilities while maintaining excellent sensitivity to e-beam exposure. Sub-0.20 micrometers line and space gratings were resolved in UV III, and 0.10 micrometers gratings were resolved in XP-9525. A formal design of experiment was created and used as a framework to develop a process for UV III which would optimize several resultant responses including: exposure latitude, edge roughness, and sensitivity. This paper will discuss the process development of these resists, and detail their performance characteristics. Effects relating to post-exposure bake delay will also be considered due to the susceptibility of many chemically amplified resists to airborne contaminants. UV III exhibited much greater stability than XP-9525, and was able to maintain precise linewidth control after 4 hours of delay, making it acceptable for use in a normal process environment. In contrast, XP-9525 exhibited severe T-topping after post-exposure bake delays of only 15 minutes, a condition which can only be solved using additional processing steps and/or environmental controls.

Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22nm nodes. Step and flash imprint lithography (S-FIL™) is a unique method for printing sub-100-nm geometries. Relative to other imprinting processes S-FIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. Further, S-FIL provides sub-100-nm feature resolution without the significant expense of multielement, 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. With respect to inspection, although defects as small as 70nm have been detected using optical techniques, it is clear that it will be necessary to take advantage of the resolution capabilities of electron beam inspection techniques. This article reports the first systematic study of die-to-database electron beam inspection of patterns that were imprinted using an Imprio 250 ...

An approach to variable frequency characterization of high impedance devices such as a carbon nanotube field-effect transistor is presented. A top-gated nanotube transistor is configured as a common source amplifier, and frequency response function of the device is measured. Evidence of signal amplification is observed in time domain as well as frequency domain up to a unity gain frequency of approximately 600kHz. The observed roll-off in frequency is solely due to the measurement setup.

Previous work with the mechanical properties of step and flash imprint lithography etch barrier materials has shown bulk volumetric shrinkage trends that could impact imprinted feature dimensions and profile. This article uses mesoscopic and finite element modeling techniques to model the behavior of the etch barrier during polymerization. Model results are then compared to cross section images of template and etch barrier. Volumetric shrinkage is seen to impact imprinted feature profiles largely as a change in feature height.

Step and flash imprint lithography (S-FIL) is an attractive method for printing sub-100-nm geometries. Relative to other imprinting processes, S-FIL has the advantage of the template being transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, minimizing magnification and distortion errors. As a result, it may be possible to use S-FIL to build integrated circuits. The purpose of this work is to investigate the fabrication methods needed to form templates capable of printing sub-100-nm contact holes. A positive resist process is used to image both holes and pillars on the template. After fabrication, the templates are used to print both contacts and pillars. The dense 80-nm imprinted contacts measure 65 nm, a consequence of undersizing on the template. For relaxed pitches, contacts smaller than 30 nm are observed. Pillars as small as 50 nm are also cleanly printed. At 40 nm, pillar size is inconsistent, and missing pillars are evident. Modifications to the template fabrication process will be necessary to study the feasibility of printing even smaller contacts and pillars.

In order for step and flash imprint lithography (S-FIL) to become a truly viable manufacturing technology, infrastructure including template repair must be commercially available. Extensive template repair studies were undertaken using RAVE’s nm 650 tool which is predicated on an AFM platform and relies upon a nanomachining technique for opaque defect removal. On S-FIL templates, the standard deviation for depth repairs in quartz from the target depth was found to be 3.1nm (1σ). At 21.5nm (1σ), the analogous spread in edge placement data for opaque line protrusions was somewhat higher. Trench cuts through lines were successfully created with a minimum size of about 55nm. The effectiveness of the repairs on the template was verified by imprinting experiments. The range of depth offsets studied (−15to+15nm) had no bearing on the imprinting process. The edge placement on wafers virtually mirrored the edge placement of the repaired templates. Connections between features which were created by trench cuts on t...

Step and flash imprint lithography (SFIL) is an attractive, low-cost method for printing sub-100 nm geometries. The imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Since SFIL is a 1× lithography technology, the template will require precise image placement in order to meet overlay specifications for multiple level device fabrication. In order to simplify the template fabrication process and facilitate post fabrication scanning-electron-microscope-based inspection, an integrated charge dissipation layer, such as indium tin oxide (ITO), is desired that is transparent to the SFIL exposure wavelength. The use of low-stress dielectric films such as SiON for the image relief layer minimizes the pattern distortions (

Masks of any next generation lithography (NGL), such as imprint lithography, must eventually achieve and maintain the very low defect counts of current production masks. This requires typically fewer than 10 or even no defects over the entire field. We describe an inspection methodology and how it can be applied to the imprint template. Special test patterns etched onto the template enable both a die to die comparison, to find nuisance defects, and also calibration of sensitivity to different types of preprogrammed defects. A state of the art deep ultraviolet photomask inspection system (KLA-Tencor model 526) can detect these rare events with about 70nm threshold for imprint masks with reflection mode contrast. Initial scans are made at various stages of the imprint process: the newly processed mask, after dicing, and after several imprints. The scans show mostly isolated point defects at a density of ∼10–100permm2. This is an encouraging start for a new NGL, and reductions are expected from better proces...

We report the surface acoustic wave (SAW) correlator devices fabricated using nanoimprint lithography. Using step-and-flash imprint lithography (S-FIL), we produced SAW correlator devices on 100mm diameter z-cut LiNbO3 devices and an aluminum metal etch process. On the same chip layout, we fabricated SAW filters and compared both the filters and correlators to similar devices fabricated using electron-beam lithography (EBL). Both S-FIL- and EBL-patterned correlators and SAW filters were analyzed using a bit-error rate tester to generate the signal and a parametric signal analyzer to evaluate the output. The NIL filters had an average center frequency of 2.38GHz with a standard deviation of 10MHz. The measured insertion loss averaged −31dB. In comparison, SAW filters fabricated using EBL exhibited a center frequency of 2.39GHz and a standard deviation of 100kHz. Based on our preliminary results, we believe that S-FIL is an efficient and entirely viable fabrication method to produce quality SAW filters and ...

The escalating cost for next generation lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990’s, several research groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1999, Colburn et al. [Proc. SPIE 379 (1999)] discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as step and flash imprint lithography. The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of the wafer and template. ...

As a means of studying process windows with short turnaround time while avoiding substrate-to-substrate repeatability issues, Step and Flash Imprint Lithography templates were fabricated with physical masking of quadrants during dry etching used to introduce process perturbations. For every 20 s of descum (Ar/O2 etch) time, critical dimensions (CD) were observed to change approximately 2.6 nm on sub-100 nm features. Similarly, increasing Cr overetch time by 20% resulted in a positive CD change of 3.8 nm. Line edge roughness decreased with increasing descum and Cr overetch times. Best overall performance was observed for a 20 s descum used in conjunction with a 110% Cr overetch. Of four tip types studied, sharpened silicon atomic force microscopy tips were able to accurately measure etch depth of 80 nm trenches, but geometrical considerations limited sidewall angle determination to greater than 100°. Cross-sectioning of features on 6×6×0.25 in. quartz plates was successfully accomplished using a focused io...

Step and flash imprint lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, minimizing magnification and distortion errors. The purpose of this work was to investigate alternative methods for defining high resolution SFIL templates and study the limits of the SFIL process. Two methods for fabricating templates were considered. The first method used a very thin (

The feasibility of using hydrogen silsesquioxane (HSQ) to directly pattern the relief layer of step and flash imprint lithography (SFIL) templates has been successfully demonstrated. HSQ is a spin-coatable oxide, which is capable of high resolution electron-beam lithography. Negative acting and nonchemically amplified, HSQ has moderate electron-beam sensitivity and excellent processing latitude. In this novel approach, 6 ×6 × 0.25 in.3 quartz photomask substrates are coated with a 60 nm indium tin oxide (ITO) charge dissipation layer and directly electron-beam written using a 100 nm film of HSQ. Direct patterning of an oxide relief layer eliminates the problems of critical dimension control associated with both chromium and oxide etches, both required processes of previous template fabrication schemes. Resolution of isolated and semidense lines of 30 nm has been demonstrated on imprinted wafers using this type of template. During this evaluation, a failure of the release layer to provide a durable nonstic...

As compared to quartz relief structures currently employed, indium tin oxide-based (ITO-based) step and flash imprint lithography templates offer advantages in terms of electron-beam writing, scanning electron microscope inspection, and pattern transfer. The material properties of the ITO have been completely characterized, and data is presented for resistivity, crystal structure, transmission, stress, surface roughness, adhesion, composition, and etch characteristics. For a 600 A annealed ITO film, the resistivity is approximately 3.5×102 Ω/sq and the optical transmission 77% at 365 nm. The atomic film composition was found to be 31.5% In, 4.3% Sn, and 64.2% O by x-ray photoelectron spectroscopy. When contrasted with SiO2 films, temperature programmed desorption data suggests that hydroxyl groups on the ITO surface bind H2O less strongly but are more abundant. Ultimate verification of compatibility was obtained by imprinting features into an etch barrier layer using an ITO-based template. The fidelity of...