Extreme Ultraviolet Lithography

Since the early 1980's, the resolution of optical projection lithography has improved dramatically primarily due to three factors: increases in projection lens numerical aperture, reduction of the imaging source wavelength, and continued reduction of the k1 factor. These three factors have been enabled by the concurrent improvements in lens making technology, DUV light sources, photoresist technology, and resolution enhancement techniques. The DUV light source, excimer KrF and ArF lasers, has entered main stream production and now images more than 50% of the critical layers in today's leading edge devices. Looking forward to both immersion lithography and beyond to EUV lithography, new light source technologies must be created to enable the continued progression of shrinking feature sizes embodied by Moore's law.

Shot noise is a significant issue in EUV lithography, especially in printing small area features like contact holes. This brings about LCDU (Local CD Uniformity) issue and LCDU-sensitivity tradeoff. This paper describes efforts to alleviate this issue through a novel EUV Underlayer (UL) chemistry design approach. The novel component "buffer" was introduced into EUV UL formulations to balance back exposure energy from UL to the resist at different incident positions. Measured back exposure dose from UL shows much lower variation (6σ/mean) compared with shot noise of resist absorbed dose. Thus summed energy variation will be suppressed when counting back exposure effect of UL, namely shot noise is reduced. Through reported shot noise model, our calculation suggests 30% sensitivity improvement and 13.4% shot noise suppression can be expected. Actual lithographic evaluations demonstrated simultaneous LCDU and sensitivity improvement. The feasibility of 30% sensitivity improvement by Metal hard mask (MHM) material was tested. The combination of buffer functionalized UL and MHM was modeled.

The cost of ownership (COO) of candidate technologies for 32 nm and 22 nm half-pitch lithography is calculated. To more accurately compare technologies with different numbers of process steps, a model that includes deposition, etching, metrology, and other costs is created. Results show lithography COO for leading edge layers will increase by roughly 50% from the 45 nm to the 32 nm half-pitch nodes. Double patterning and extreme ultraviolet lithography (EUVL) technologies have roughly the same COO under certain conditions. For 22 nm half-pitch nodes, EUVL has a significant cost advantage over other technologies under certain mask cost assumptions. Double patterning, however, may be competitive under worst case EUVL mask cost assumptions. Sensitivity studies of EUVL COO to throughput and uptime show EUVL may be cost-competitive at lower uptime and throughput conditions. In spite of these higher costs, total lithography costs for 32 nm and 22 nm half-pitches remain within reach of the Moore's Law trend. Finally, the COO of 450 mm lithography is calculated and shows the expected cost reduction is between 0% and 15%.

Extreme Ultraviolet Lithography (EUVL) masks have residual stress induced by several thin films on low thermal expansion material (LTEM) substrates. The stressed thin films finally result in convex out-of-plane displacement (OPD) of several 100s of nm on the pattern side of the mask. Since EUVL masks are chucked on EUVL scanners differently from on e-beam writer, the mask pattern placement errors (PPE) are necessary to be corrected for to reduce overlay errors. In this paper, experimental results of pattern placement error correction using standard chrome on glass (COG) plate will be discussed together with simulations. Excellent agreement with simple bending theory is obtained. Suitability of the model to compensate for other EUVL-related PPEs due to mask non-flatness will be discussed.

SP Vernon, PA Kearney, W. Tong, S. Prisbrey, C. Larson, CE Moore, F. Weber, G. Cardinale, PY. Yan, S. Hector ... This paper was prepared for submittal to the 18th Annual BACUS Symposium on Photomask Technology and Management Redwood City, CA September 16-18, 1998

Three different architectures were compared as candidates for EUV lithography masks. Binary masks were fabricated using two different stacks of absorber materials and using a selective etching process to directly pattern the multilayer of the mask blank. To compare the effects of mask architecture on resist patterning, all three masks were used to print features into photoresist on the EUV micro-exposure tool (MET) at Lawrence Berkeley National Laboratory. Process windows, depth of focus, mask contrast at EUV, and horizontal and vertical line width bias were use as metrics to compare mask architecture. From printing experiments, a mask architecture using a tantalum nitride absorber stack exhibited the greatest depth of focus and process window of the three masks. Experimental results obtained using prototype masks are discussed in relation to simulations. After accounting for CD biasing on the masks, similar performance was found for all three mask architectures.

The semiconductor industry faces a lithographic scaling limit as the industry completes the transition to 1.35 NA immersion lithography. Both high-index immersion lithography and EUV lithography are facing technical challenges and commercial timing issues. Consequently, the industry has focused on enabling double patterning technology (DPT) as a means to circumvent the limitations of Rayleigh scaling. Here, the IBM development alliance demonstrate a series of double patterning solutions that enable scaling of logic constructs by decoupling the pattern spatially through mask design or temporally through innovative processes. These techniques have been successfully employed for early 32nm node development using 45nm generation tooling. Four different double patterning techniques were implemented. The first process illustrates local RET optimization through the use of a split reticle design. In this approach, a layout is decomposed into a series of regions with similar imaging properties and the illumination conditions for each are independently optimized. These regions are then printed separately into the same resist film in a multiple exposure process. The result is a singly developed pattern that could not be printed with a single illumination-mask combination. The second approach addresses 2D imaging with particular focus on both line-end dimension and linewidth control . A double exposure-double etch (DE 2 ) approach is used in conjunction with a pitch-filling sacrificial feature strategy. The third double exposure process, optimized for via patterns also utilizes DE 2 . In this method, a design is split between two separate masks such that the minimum pitch between any two vias is larger than the minimum metal pitch. This allows for final structures with vias at pitches beyond the capability of a single exposure. In the fourth method,, dark field double dipole lithography (DDL) has been successfully applied to BEOL metal structures and has been shown to be overlay tolerant . Collectively, the double patterning solutions developed for early learning activities at 32nm can be extended to 22nm applications.

We are evaluating the readiness of extreme ultraviolet (EUV) lithography for insertion into production at the 15 nm technology node by integrating it into standard semiconductor process flows because we believe that device integration exercises provide the truest test of technology readiness and, at the same time, highlight the remaining critical issues. In this paper, we describe the use of EUV lithography with the 0.25 NA Alpha Demo Tool (ADT) to pattern the contact and first interconnect levels of a large (~24 mm x 32 mm) 22 nm node test chip using EUV masks with state-of-the-art defectivity (~0.3 defects/cm 2). We have found that: 1) the quality of EUVL printing at the 22 nm node is considerably higher than the printing produced with 193 nm immersion lithography; 2) printing at the 22 nm node with EUV lithography results in higher yield than double exposure double-etch 193i lithography; and 3) EUV lithography with the 0.25 NA ADT is capable of supporting some early device development work at the 15 nm technology node.

"EUV lithography at the 22nm technology node", Proc. SPIE 7636, Extreme Ultraviolet (EUV) Lithography, 76361M (March 22, 2010); doi:10.1117/12.847049; http://dx.doi.org/10.1117/12.847049

In this paper we present the latest results on developing and integrating extreme ultraviolet lithography (EUVL) at Intel. The world's first commercial EUV exposure tool was installed in Intel's development fab, linked to a resist track, and had successfully demonstrated key ...

Flare (stray light) is an important effect impacting extreme ultraviolet lithography (EUVL) imaging system performance. Four flare measurement methods including Kirk, modulation transfer function, double exposure, and zonal ring approximation method are reviewed and analyzed theoretically. The point spread function of an EUV NXE:3100 exposure tool is extracted from the measured Kirk flare (KF) and fitted with a double-fractal model. The KF for this NXE:3100 tool is determined to be 8.5% for a 2-μm diameter absorber pad placed in a 12-mm outer radius bright field, which is larger than the previous 5% KF data measured by ASML and IMEC in 2011. The observation of the increased flare level in the NXE:3100 tool suggests that contamination of EUV optics may be a potential problem for EUVL manufacturing.

Flare (stray light) is an important effect impacting extreme ultraviolet lithography (EUVL) imaging system performance. Four flare measurement methods including Kirk, modulation transfer function, double exposure, and zonal ring approximation method are reviewed and analyzed theoretically. The point spread function of an EUV NXE:3100 exposure tool is extracted from the measured Kirk flare (KF) and fitted with a double-fractal model. The KF for this NXE:3100 tool is determined to be 8.5% for a 2-μm diameter absorber pad placed in a 12-mm outer radius bright field, which is larger than the previous 5% KF data measured by ASML and IMEC in 2011. The observation of the increased flare level in the NXE:3100 tool suggests that contamination of EUV optics may be a potential problem for EUVL manufacturing.

For full commercialization, extreme ultraviolet lithography (EUVL) technology requires the availability of EUV mask blanks that are free of defects. This remains one of the main impediments to the implementation of EUV at the 22 nm node and beyond. Consensus is building that a few small defects can be mitigated during mask patterning, but defects over 100 nm (SiO 2 equivalent) in size are considered potential "killer" defects or defects large enough that the mask blank would not be usable. The current defect performance of the ion beam sputter deposition (IBD) tool will be discussed and the progress achieved to date in the reduction of large size defects will be summarized, including a description of the main sources of defects and their composition. This paper will discuss the main sources of >100 nm defects in the IBD tool and a path forward for eliminating ~70% of the large defects found during multilayer deposition (i.e., stainless steel and aluminum oxide particles). Extreme Ultraviolet (EUV) Lithography V, edited by Obert R. Wood, Eric M. Panning, Proc. of SPIE Vol. 9048, 90480H · © 2014 SPIE · CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2048541 Proc. of SPIE Vol. 9048 90480H-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/18/2014 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 9048 90480H-3 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/18/2014 Terms of Use: http://spiedl.org/terms

Approved for public release; further dissemination unlimited DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. This report has been reproduced directly from the best available copy.

ABSTRACT EUV lithography is considered one of the options for high volume manufacturing (HVM) of 16 nm MPU node devices [1]. The benefits of high k1 (~ 0.5) imaging enable EUVL to simplify the patterning process and ease design rule restrictions. However, EUVL with ...

Static microfield printing capabilities have recently been integrated into the extreme ultraviolet interferometer operating at the Advanced Light Source synchrotron radiation facility at Lawrence Berkeley National Laboratory. The static printing capabilities include a fully programmable scanning illumination system enabling the synthesis of arbitrary illumination coherence ͑pupil fill͒. This new exposure station has been used to lithographically characterize the static imaging performance of the Engineering Test Stand Set-2 optic. Excellent performance has been demonstrated down to the 70 nm equal line/space level with focus latitude exceeding 1 m and dose latitude of approximately 10%. Moreover, equal line/space printing down to a resolution of 50 nm has been demonstrated using resolution-enhancing pupil fills.

Spectra from xenon ions have been recorded at the NIST electron beam ion trap (EBIT) and the emission into a 2% bandwidth at 13.5 nm arising from 4d → 5p transitions compared with those from 4d → 4f and 4p → 4d transitions in Xe XI and also with that obtained from the unresolved transition array (UTA) observed to peak just below 11 nm. It was found that an improvement of a factor of 5 could be gained in photon yield using the UTA rather than the 4d → 5p emission. The results are compared with atomic structure calculations and imply that a significant gain in efficiency should be obtained using tin, in which the emission at 13.5 nm comes from a similar UTA, rather than xenon, as an EUVL source material.

The SEMATECH High Numerical Aperture Actinic Reticle Review Project (SHARP) is a synchrotron-based extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP has been operational and serving users since June, 2013, and in eight months, SHARP has recorded over 71,000 high-resolution images. Exposure times are 5 to 8 seconds, and 8 or more through-focus series can be collected per hour at positions spanning the entire mask surface. SHARP's lossless coherence-control illuminator and variable numerical aperture (NA) enable researchers to emulate the imaging properties of both current and future EUV lithography tools. SHARP's performance continues to improve over time due to tool learning and upgraded capabilities, described here. Within a centered, 3-μm square image region, we demonstrate an illumination power stability above 99%, and an average uniformity of 98.4%. Demonstrations of through-focus imaging with various illumination coherence settings highlight the capabilities of SHARP.

Critical dimension small angle X-ray scattering (CD-SAXS) is a metrology platform capable of measuring the average cross section and line width roughness (LWR) with a sub-nm precision in test patterns with line widths ranging from 10 to 500 nm. The X-ray diffraction intensities from a collimated X-ray beam of sub-Angstrom wavelength were collected and analyzed to determine line width, pitch, sidewall angle, LWR, and others structural parameters. The capabilities of lab-scale and synchrotron-based CD-SAXS tools for LWR characterization were tested by measuring a set of identical patterns with designed roughness amplitude and frequency. These test patterns were fabricated using EUV lithography with sub-50 nm linewidths. To compensate for the limited photon flux from the lab-based X-ray source, the incident beam of the lab system was collimated to a less extent than the synchrotron beam-based tool. Consequently, additional desmearing is needed to extract information from data obtained from lab-based equipment. We report the weighted nonlinear least-squares algorithm developed for this purpose, in addiiton to a comparison between the results obtained from our lab system and the synchrotron beam-based tool.

Extreme ultraviolet lithography (EUVL) has been recognized as the most promising candidate for the manufacture of semiconductor devices for the 7 nm node and beyond. A key point in the successful introduction of EUV lithography in high volume manufacture (HVM) is the effective EUV dose utilization while simultaneously realizing ultra-high resolution and low line edge roughness (LER). Here we show EUV resist sensitivity improvement with the use of a photosensitized chemically amplified resist PSCARTM system. The evaluation of this new chemically amplified resist (CAR) as performed using EUV interference lithography (EUV-IL) is described and the fundamentals are discussed.

At present, and for the last several decades, optical projection lithography has been the lithographic technique used in the high-volume manufacture of integrated circuits. The elementary line width of semiconductor device is now 90 nm, the extreme ultraviolet lithography (EUVL) with a wavelength in the range of 10 to 14 nm is vying to become the choice of the semiconductor industry for the so-called next generation of lithography that will enable future generations of integrated circuits to be printed with feature sizes of 45 nm and below around 2010. Plasma EUV source is regarded as the most promising source of EUV radiation, and a heated competition is underway over the world. The top priority issue for implementing EUVL is to upgrade the EUV power extensively. In the development of our Z-pinch plasma EUV source, xenon gas is used for the target. The Z-pinch plasma was driven by pulsed current with amplitude of 30 kA and pulse duration of 100 ns. Pinhole imaging, EUV spectrograph and in-band EUV energy monitor were used to characterize the EUV emission from the Z-pinch discharge plasma. In order to improve the convention efficiency (CE) from input electric energy to EUV radiation, also a solid tin rod was used as target material. The experimental analyses have demonstrated the CE was as high as 1.5%

We present a marking technology which uses extreme ultraviolet radiation to write invisible patterns on tags based on alkali fluoride thin films. The shape of the pattern is pre-determined by a mask (in the case of contact lithography) or by a suitable mirror (projection lithography). Tags marked using this method offer a much better protection against fakes than currently available anti-counterfeiting techniques. The complexity and cost of this technology can be tailored to the value of the good to be protected, leaving, on the other hand, the specific reading technique straightforward. So far, we have exploited our invisible marking to tag artworks, identity cards, electrical components, and containers of radioactive wastes. Advantages and limits of this technology are discussed in comparison with the anti-counterfeiting systems available in the market.

Imprint lithography has been proposed as a low cost method for next generation lithography for the manufacturing of semiconductors for the 45nm node and below, as costs for traditional optical lithography, and EUV lithography escalate to new levels that may ...

Various issues related to non-telecentric mask effects for EUV lithography will be discussed in this paper. First, a raytracing approach will provide a conceptual description as to the nature of non-telecentric thick mask effects, highlighting the behavior of various edge types and corners. Rigorous modeling of these effects are discussed along with a few consequences of improper modeling. A series of simulation and experimental studies are presented to probe both the one-and two-dimensional impact of thick mask effects. It will be shown that a simple constant edge bias appears sufficient for 1D features, but begins to break down when space-widths are less than about 45 nm. Investigation into the impact of corners and small 2D features indicates that a simple edge-based bias also breaks down for edge lengths less than about 60nm. A sample set of rules-based post-OPC HV corrections for 22nm node dimensions are proposed, although based on experimental results, it is concluded that more accurate resist modeling and scanner stability are required before being able to precisely predict and control HV effects. Finally, with some simplifying assumptions, simulation is used to predict the extent of potential HV effects of future EUV imaging systems.

As critical dimensions for leading-edge semiconductor devices shrink, the line-edge roughness (LER) requirements are pushing well into the single digit nanometer regime. At these scales many new sources of LER must be considered. In the case of extreme ultraviolet (EUV) lithography, modeling has shown the lithographic mask to be a source of significant concern. Here we present a correlation-based methodology for experimentally measuring the magnitude of mask contributors to printed LER. The method is applied to recent printing results from a 0.3 numerical aperture EUV microfield exposure tool. The measurements demonstrate that such effects are indeed present and of significant magnitude. The method is also used to explore the effects of illumination coherence and defocus and has been used to verify model-based predictions of mask-induced LER.

We present an approach to image-based EUV aberration metrology using binary mask targets and iterative model-based solutions to extract both the amplitude and phase components of the aberrated pupil function. The approach is enabled through previously developed modeling, fitting, and extraction algorithms. We examine the flexibility and criticality of the method using two experimental case studies. The first extracts the pupil phase behavior from an ASML NXE:3100 exposure system and shows primary aberration sensitivity below 0.2 mλ. The second experiment extracts both components of the pupil function from the SHARP EUV microscope. Extreme Ultraviolet (EUV) Lithography VI, edited by Obert R. Wood II, Eric M. Panning, Proc. of SPIE Vol. 9422, 942215 · © 2015 SPIE · CCC code: 0277-786X/15/$18 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/23/2015 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 9422 942215-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/23/2015 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 9422 942215-3 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/23/2015 Terms of Use: http://spiedl.org/terms

We compare the extreme ultraviolet emission characteristics of tin and galinstan (atomic %: Ga: 78.35, In: 14.93, Sn: 6.72) between 10 nm and 18 nm in a laser-triggered discharge between liquid metal-coated electrodes. Over this wavelength range, the energy conversion efficiency for galinstan is approximately half that of tin, but the spectrum is less strongly peaked in the 13–15 nm region. The extreme ultraviolet source dimensions were 110 ± 25 μm diameter and 500 ± 125 μm length. The flatter spectrum, and −19 °C melting point, makes this galinstan discharge a relatively simple high radiance extreme ultraviolet light source for metrology and scientific applications.

This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author.

Phase-shifting effect of thin-absorber EUV masks. [Proceedings of SPIE 8166, 816618 (2011)]. Hiroyoshi Tanabe, Tetsunori Murachi, Sang H. Lee, Manish Chandhok, Seh-Jin Park, Guojing Zhang, Tsukasa Abe, Taichi Ogase, Naoya Hayashi. Abstract. ...

While interferometry is routinely used for the characterization and alignment of lithographic optics, the ultimate measure of performance for these optical systems is the transfer of an image or pattern into photoresist. Simple yet flexible exposure systems play an important role in this task because they allow complex system-dependent effects to be isolated from the printing results. This enables the most direct lithographic evaluation of the optical system under investigation. To address these issues for commercial-class EUV optics, a synchrotron-based programmable illuminator exposure station has been implemented at Lawrence Berkeley National Laboratory (the Advanced Light Source). As previously presented, this static microfield exposure system has been used to lithographically characterize a 4-mirror optical system designed for the EUV Engineering Test Stand (ETS) prototype stepper. Based on the lithographic characterization, here we present a detailed performance analysis of the 0.1-NA ETS Set-2 optic. Operation of the static printing system with the Set-2 optic yielded approximately 330 exposed wafers, where each wafer contains one or more focusexposure matrices. A wide variety of parameters were studied including, among others, illumination conditions, resist thickness, and mask tone. Here we present a subset of this data in terms of process-window results. The results demonstrate a depth of focus (DOF) approximately 2 µm for isolated 70-nm line features, 1 µm for nested 70-nm line features, and 0.5 µm for 70-nm contacts on 270-nm pitch.

A new multilaser multichannel spectrometer system has been developed that allows a wide range of investigations of the interaction of extreme-ultraviolet (EUV) photons with matter in the form of free atoms or ions, eg, in gases or plasmas or bound as in solids. The EUV photons are ...

Results on micro- and nanoprocessing of organic polymers with extreme ultraviolet (EUV) radiation from a compact laser plasma EUV source based on a gas puff target are presented in the paper. Processing of polymers is connected with non-thermal ablation under the influence of energetic EUV photons. The process can be useful for practical applications as it makes possible to produce

In this paper some results of investigations concerning interaction of EUV radiation with inorganic and organic materials were presented. Samples of different materials were irradiated with a 10 Hz laser - plasma EUV source based on a gas puff target. The source was equipped with ...

In the paper a newly developed compact laser plasma EUV source is presented. The source is based on the double-stream gas puff target approach. The targets are formed by pulsed injection of high-Z gas (xenon) into a hollow stream of low-Z gas (helium) using the valve system composed of two electromagnetic valves and equipped with the double-nozzle setup. The outer stream of gas confines the inner stream improving the gas puff target characteristics (higher density of high-Z gas at longer distance from the nozzle output). It causes efficient absorption of laser energy in a plasma and strong EUV production. The source has been developed in the frame of the EUV sources development project under the MEDEA+ program.

The EUV excess emission from the clusters A2199 and A1795 remains an unexplained astrophysical phenomenon. There has been many unsuccessful attempts to ‘trivialize ’ the findings. In this Letter we present direct evidence to prove that the most recent of such attempts, which attributes the detected signals to a background non-uniformity effect, is likewise excluded. We address the issue by a re-observation of A2199 which features a new filter orientation, usage of a more sensitive part of the detector and, crucially, includes a background pointing at ∼ 2o offset- the first in situ measurement of its kind. We first demonstrate quantitatively two facts: (a) the offset pointing provides an accurate background template for the cluster observation, while (b) data from other blank fields do not. We then performed point-to-point subtraction of the in situ background from the cluster field, with appropriate propagation of errors. The resulting cluster radial profile is consistent with that ...

ABSTRACT Process variability in today's EUV lithography might be a showstopper for features below 27nm dimensions. At these feature sizes, electrical devices are influenced by quantum effects and thus have to face the discrete behavior of light and matter. More in general, lithography uncertainties arise from each lithographic element: the source, the photomask, the optical system, and the photoresist. In order to individually assess all the different contributions to the final resist roughness, a EUV mask with known absorber pattern variability was used to expose different resists at different process conditions. CD-SEM analyses were performed on both mask absorber and resist pattern and then used to build a stochastic resist model. In this first paper, we present a complete characterization of the root causes which are responsible of the CD nonuniformity for 27nm half-pitch dense contact-holes exposed with the ASML NXE:3100 scanner installed at imec. Using the same stochastic model, a simulated evaluation to quantify the possible impact of the different elements composing the lithographic process is performed at higher numerical aperture.

ABSTRACT One of the main challenges for developing extreme ultraviolet resists is to satisfy critical dimension uniformity (CDU) and sidewall roughness of contacts to the allowable limit. To this end, further understanding of the effects of resist ingredients on CDU and contact edge roughness (CER) is required. We investigate the effects of a photoacid generator (PAG), sensitizer and quencher concentrations on the CDU and CER. We find that the dependencies of CDU on sensitizer and quencher are dominated by photon shot noise (PSN) effects whereas a more complicated interplay between PSN and PAG distribution statistics should be considered in the dependence of CDU on PAG concentration. The estimated CER parameters [root mean square (RMS) value and correlation length.] exhibit a merging trend when plotted against the final critical dimension (CD). In addition, RMS value increases with exposure dose and PAG loading contrary to shot noise expectations. Power spectrum analysis reveals the dominant contribution of low-frequency undulations to CER, which is attributed to the enhanced interaction along specific directions between the aerial image and/or acid kinetics of nearby contacts. This inter-contact effect is further intensified with CD for fixed pitch and may explain the observed CER behavior. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)

Approved for public release; further dissemination unlimited DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. This report has been reproduced directly from the best available copy.