Joost Bekaert

imec Belgium, Louvain, Flanders, Belgium

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Publications (31)9.05 Total impact

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    ABSTRACT: For future VLSI technology nodes, directed self-assembly (DSA) using block-copolymer (BCP) is considered as patterning technique alternative or complimentary to Extreme ultra-violet (EUV) lithography. As a consequence, it is essential to develop a cost-effective DSA process using existing lithography infrastructure as guiding template, i.e. 193 immersion-based. Recent progress in DSA focused on the lithography and chemical formulation processes, however, DSA integration into CMOS process flows remains to be demonstrated. Arindam Mallik et al presented the process assumptions for the 10nm (N10) and 7nm (N7) nodes [1]. DSA lithography is perfectly fit into the desired pitch requirement for N7 technology node. Thus, our current research focuses on the CMOS process integration for fin and via contact holes with DSA technology, using relevant film stacks and state-of-the-art integration flow.
    Micro and Nano Engineering (MNE), Lausanne, Switzerland; 09/2014
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    ABSTRACT: With the implementation of multi-patterning ArF-immersion for sub 20nm integrated circuits (IC), advances in equipment monitoring and control are needed to support on-wafer yield performance. These in-situ equipment monitoring improvements, along with advanced litho-cell corrections based on on-wafer measurements, enable meeting stringent overlay and CD control requirements for advanced lithography patterning. The importance of light-source performance on lithography pattering (CD and overlay) has been discussed in previous publications.[1-3] Recent developments of Cymer ArF light-source metrology and on-board monitoring enable end-users to detect, for each exposed wafer, changes in the near-field and far-field spatial profiles and polarization performance, [4-6] in addition to the key `optical' scalar parameters, such as bandwidth, wavelength and energy. The major advantage of this capability is that the key performance metrics are sampled at rates matched to wafer performance, e.g. every exposure field across the wafer, which is critical for direct correlation with on-wafer performance for process control and excursion detection.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2014; DOI:10.1117/12.2047449 · 0.20 Impact Factor
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    ABSTRACT: Directed Self-Assembly (DSA) of Block Co-Polymers (BCP) has become an intense field of study as a potential patterning solution for future generation devices. The most critical challenges that need to be understood and controlled include pattern placement accuracy, achieving low defectivity in DSA patterns and how to make chip designs DSA-friendly. The DSA program at imec includes efforts on these three major topics. Specifically, in this paper the progress in setting up flows for templated DSA within the imec program will be discussed. A process has been implemented based on a hard mask as the template layer. In this paper primarily the impact of local pattern density and BCP film thickness on the templated DSA process are discussed. The open hole rate and the placement accuracy of BCP patterns within the template are the primary figures of merit.
    SPIE Advanced Lithography; 03/2014
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    ABSTRACT: The roughness present on the sidewalls of lithographically defined patterns imposes a very important challenge for advanced technology nodes. It can originate from the aerial image or the photoresist chemistry/processing [1]. The latter remains to be the dominant group in ArF and KrF lithography; however, the roughness originating from the mask transferred to the aerial image is gaining more attention [2-9], especially for the imaging conditions with large mask error enhancement factor (MEEF) values. The mask roughness contribution is usually in the low frequency range, which is particularly detrimental to the device performance by causing variations in electrical device parameters on the same chip [10-12]. This paper explains characteristic differences between pupil plane filtering in amplitude and in phase for the purpose of mitigating mask roughness transfer under interference-like lithography imaging conditions, where onedirectional periodic features are to be printed by partially coherent sources. A white noise edge roughness was used to perturbate the mask features for validating the mitigation.
    Proceedings of SPIE - The International Society for Optical Engineering 02/2014; DOI:10.1117/12.2045668 · 0.20 Impact Factor
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    ABSTRACT: Line edge roughness (LER) is a common problem to all lithography techniques and is seen as an increasingly important challenge for advanced technology nodes. Contributions to LER can come from the aerial image itself or the resist related processes. Mask roughness belongs to the former group, which can contribute to the low frequency roughness. This paper investigates the mitigating effect of pupil plane filtering on the mask roughness transfer. Experiments were performed using a mask with edge roughness programmed at different periods on 128 nm pitch vertical line/space patterns. A target phase filter was optimized for ArF illumination source and the roughness period of 200 nm. The filter introduces an orientation dependent defocus; hence, reducing the image fidelity in the direction of roughness features without significantly impacting the fidelity of vertical line and space features. Experimental results showed significant reduction in mask roughness transfer for the target roughness period.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 11/2013; 31(6):06F801-06F801-6. DOI:10.1116/1.4825102 · 1.36 Impact Factor
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    ABSTRACT: Reducing lithography pattern variability has become a critical enabler of ArF immersion scaling and is required to ensure consistent lithography process yield for sub-30nm device technologies. As DUV multi-patterning requirements continue to shrink, it is imperative that all sources of lithography variability are controlled throughout the product life-cycle, from technology development to high volume manufacturing. Recent developments of new ArF light-source metrology and monitoring capabilities have been introduced in order to improve lithography patterning control.[1] These technologies enable performance monitoring of new light-source properties, relating to illumination stability, and enable new reporting and analysis of in-line performance.
    SPIE Advanced Lithography; 04/2013
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    ABSTRACT: As semiconductor optical lithography is pushed to smaller dimensions, resolution enhancement techniques have been required to maintain process yields. For some time, the customization of illumination coherence at the source plane has allowed for the control of diffraction order distribution across the projection lens pupil. Phase shifting at the photomask plane has allowed for some phase control as well. Geometries smaller than the imaging wavelength introduce complex wavefront effects that cannot be corrected at source or mask planes. Three-dimensional photomask topography effects can cause a loss of both focal depth and exposure latitude across geometry of varying density. Wavefront manipulation at the lens pupil plane becomes necessary to provide the degrees of freedom needed to correct for such effects. The focus of this research is the compensation of the wavefront phase error introduced by the topographical photomask structures of high resolution phase shift masking combined with off-axis illumination. The compensation is realized through phase manipulation of the lens pupil plane, specifically in the form of spherical aberration. Subwavelength resolution optimization and imaging is presented showing how phase pupil filtering can measurably improve the depth of focus for several photomask structures and types.
    Applied Optics 01/2013; 52(3):314-22. DOI:10.1364/AO.52.000314 · 1.78 Impact Factor
  • Journal of Photopolymer Science and Technology 01/2013; 26(6):779-791. DOI:10.2494/photopolymer.26.779 · 0.91 Impact Factor
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    ABSTRACT: We studied the potential of optical scatterometry to measure the full 3D profile of features representative to real circuit design topology. The features were selected and printed under conditions to improve the measurability of the features by scatterometry without any loss of information content for litho monitoring and control applications. The impact of the scatterometry recipe and settings was evaluated and optimal settings were determined. We have applied this strategy on a variety of structures and gathered results using the YieldStar angular reflection based scatterometer. The reported results show that we obtained effective decoupling of the measurement of the 3 dimensions of the features. The results match with predictions by calibrated lithographic simulations. As a verification we have successfully performed a scanner matching experiment using computational Pattern Matcher (cPM) in combination with YieldStar as a metrology tool to characterize the difference between the scanners and verify the matching. The results thus obtained were better than using CD-SEM for matching and verification.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2012; DOI:10.1117/12.919050 · 0.20 Impact Factor
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    ABSTRACT: As semiconductor lithography is pushed to smaller dimensions, process yields tend to suffer due to subwavelength topographical imaging effects. Three dimensional or "thick mask" effects result in such things as a pitch dependent best focus and, for alternating phase shift masks (AltPSMs), an intensity imbalance between etched and un-etched features. Corrective mask structures such as the dual trench AltPSM have been introduced to compensate for such intensity imbalances. In this work, the compensation of thick mask effects is explored using the manipulation of the pupil wavefront through the addition of spherical aberration. The wavefront has been experimentally varied through the manipulation of the lens aberration in a state of the art full field scanner. Results reveal that the influence of spherical aberration on best focus is predictable, allowing focus deviation through pitch to be tuned. Simulations further predict that aberration manipulation can provide compensation for thick mask effects by increasing the useable depth of focus for a particular set of features on both AltPSM and thicker film attenuated PSM masks. Such pupil wavefront correction has the potential to compensate for mask topography by matching thick mask effects to those of thin masks.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2012; DOI:10.1117/12.917440 · 0.20 Impact Factor
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    ABSTRACT: Once a process is set-up in an integrated circuit (IC) manufacturer's fabrication environment, any drift in the proximity fingerprint of the cluster will negatively impact the yield. In complement to the dose, focus and overlay control of the cluster, it is therefore also of ever growing importance to monitor and maintain the proximity stability (or CD through pitch behavior) of each cluster. In this paper, we report on an experimental proximity stability study of an ASML XT:1900i cluster for a 32 nm poly process from four different angles. First, we demonstrate the proximity stability over time by weekly wafer exposure and CD through pitch measurements. Second, we investigate proximity stability from tool-to-tool. In a third approach, the stability over the exposure field (intra-field through-pitch CD uniformity) is investigated. Finally, we verify that proximity is maintained through the lot when applying lens heating correction. Monitoring and maintaining the scanner's optical proximity through time, through the lot, over the field, and from toolto- tool, involves extensive CD metrology through pitch. In this work, we demonstrate that fast and precise CD through pitch data acquisition can be obtained by scatterometry (ASML YieldStarTM S-100), which significantly reduces the metrology load. The results of this study not only demonstrate the excellent optical proximity stability on a XT:1900i exposure cluster for a 32 nm poly process, but also show how scatterometry enables thorough optical proximity control in a fabrication environment.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2011; DOI:10.1117/12.881606 · 0.20 Impact Factor
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    ABSTRACT: IC manufacturers have a strong demand for transferring a working process from one scanner to another. Recently, a programmable illuminator (FlexRayTM) became available on ASML ArF immersion scanners that, besides all the parameterized source shapes of the earlier AerialTM illuminator (based on diffractive optical elements) can also produce any desired freeform source shape. As a consequence, a fabrication environment may have scanners with each of the illuminator types so both FlexRay-to-Aerial and FlexRay-to-FlexRay matching is of interest. Moreover, the FlexRay illuminator itself is interesting from a matching point-of-view, as numerous degrees of freedom are added to the matching tuning space. This paper demonstrates how the upgrade of an exposure tool from Aerial to FlexRay illuminator shows identical proximity behavior without any need for scanner tuning. Also, an assessment of the imaging correspondence between exposure tools each equipped with a FlexRay illuminator is made. Finally, for a series of use-cases where proximity differences do exist, the application of FlexRay source tuning is demonstrated. It shows an enhancement of the scanner matching capabilities, because FlexRay source tuning enables matching where traditional NA and sigma tuning are shortcoming. Moreover, it enables tuning of freeform sources where sigma tuning is not relevant. Pattern MatcherTM software of ASML Brion is demonstrated for the calculation of the optimized FlexRay tuned sources.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2011; DOI:10.1117/12.881607 · 0.20 Impact Factor
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    ABSTRACT: The desire to reduce cost in volume manufacturing has driven up the throughput in the lithographic exposure machines. As a result the power transmitted in the projection optics increases. Although small, the absorption levels in the lens materials are not zero, which leads to localized heating of the lens and hence lens aberrations. To squeeze out the maximum process windows, the pupil shapes have transformed from simple annular shapes to shapes with very concentrated poles. As a result, the exposure energy transported through the lens is no longer equally distributed over the lenses of the projection options. Instead only a fraction of the lens gets to transport the total power. This concentration of power further aggravates the lens heating induced aberrations and enhances the importance of advanced lens heating control schemes which are available on ASML scanners. To analyze the effects of lens heating on the final imaging, a model was developed by the lens manufacturer Carl Zeiss SMT GmbH, and incorporated into a litho simulation environment by ASML BRION. This tool can be used to analyze the impact of dose/throughput, illumination shapes and reticle layout on aberrations. It provides a means to assess potential lens heating issues even before production masks are manufactured. Moreover, this computational tool opens the possibility to calculate parameters for lens heating correction, rather than measuring them, saving valuable machine time. In this paper, the performance of the novel computational lens heating control is demonstrated on wafer and compared with the traditional way of measuring the relevant parameters. In addition, a modeling study is performed to assess possible lens heating effects for freeform or non-traditional source shapes, thereby demonstrating the advanced correction potential of ASML latest aberration manipulator, called FlexWaveTM.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2011; DOI:10.1117/12.881609 · 0.20 Impact Factor
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    ABSTRACT: A negative tone development (NTD) process benefits from the superior imaging performance obtained with light field (LF) masks to print metal and contact layers, resulting in improved process window. In this paper, we introduce an inverse Mack development model to simulate the NTD process and validate its process advantage. Based on this model, a NTD resist model calibration has been carried out and the model results are presented. Various NTD application cases have been studied and the prediction capabilities of simulations are demonstrated: 1) LF+NTD process helps to achieve a broader pitch range and smaller feature size compared to the traditional dark field (DF) with positive tone development (PTD) process. NTD brings a significant improvement in exposure latitude (EL) and MEEF for both line-and-space (L/S) and contact hole (CH) patterns through pitch. 2) The NTD process has been explored for double exposure lithography with extreme off-axis illumination using L/S patterns with horizontal and vertical orientation, respectively, which creates dense contact hole arrays down to a 80 nm pitch. 3) Simulation can also be used to explore new NTD process variances. We have demonstrated the simulations of the NTD model in applications such as printing specific CH or Metal patterns, a dual-tone development process and a combination of source mask optimization (SMO) and NTD to print SRAM patterns at smaller sizes.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2011; DOI:10.1117/12.880949 · 0.20 Impact Factor
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    ABSTRACT: To ensure defect-free printing, pellicles are mounted on the masks used in optical lithography for IC manufacturing. The pellicle, a thin transparent polymer film, protects the reticle from dust. But, as the 193 nm light transmittance through the pellicle has an angular dependency, the pellicle also acts as an apodization filter. In the current work, we present both experimental and simulation results at 1.35 NA showing the influence of two types of pellicles on proximity and intra-die Critical Dimension Uniformity (CDU) on wafer. The considered structures are compatible with the 32 nm logic node for poly and metal. For the standard ArF pellicle (thickness 830 nm), we experimentally observe a distinct effect of several nm's of the pellicle presence on both the proximity and the intra-die CDU. For the more advanced pellicle (280 nm thin) no signature of the pellicle on proximity or CDU could be found. By modeling the pellicle's optical properties as a Jones Pupil, we are able to simulate the pellicle effects with good accuracy. These results indicate that for the 32 nm node, it is recommended to take the pellicle properties into account in the OPC calculation when using a standard pellicle. Simulations also indicate that, in addition to that, a local dose correction can compensate to a large extent for the intra-die pellicle effect. When using the more advanced thin pellicle (280 nm), no such corrections are needed.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2010; DOI:10.1117/12.848219 · 0.20 Impact Factor
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    ABSTRACT: The use of customized illumination modes is part of the pursuit to stretch the applicability of immersion ArF lithography. Indeed, a specific illumination source shape that is optimized for a particular design leads to enhanced imaging results. Recently, freeform illumination has become available through pixelated DOEs or through FlexRayTM, ASML's programmable illuminator system, allowing for virtually unconstrained intensity distribution within the source pupil. In this paper, the benefit of freeform over traditional illumination is evaluated, by applying source mask co-optimization (SMO) for an aggressive use case, and wafer-based verification. For a 22 nm node SRAM of 0.099 mum² and 0.078 mum2 bit cell area, the patterning of the full contact and metal layer into a hard mask is demonstrated with the application of SMO and freeform illumination. In this work, both pixelated DOEs and FlexRay are applied. Additionally, the match between the latter two is confirmed on wafer, in terms of CD and process window.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2010; DOI:10.1117/12.846918 · 0.20 Impact Factor
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    ABSTRACT: A strong demand exists for techniques that can further extend the application of ArF immersion lithography. Besides techniques like litho-friendly design, dual exposure or patterning schemes, customized illumination modes, also alternative processing schemes are viable candidates to reach this goal. One of the most promising alternative process flows uses image reversal by means of a negative tone development (NTD) step with a FUJIFILM solvent-based developer. Traditionally, the printing of contacts and trenches is done by using a dark field mask in combination with positive tone resist and positive tone development. With NTD, the same features can be printed in positive resist using a light field mask, and consequently with a much better image contrast. In this paper, we present an overview of applications for the NTD technique, both for trench and contact patterning, comparing the NTD performance to that of the traditional positive tone development (PTD). This experimental work was performed on an ASML Twinscan XT:1900i scanner at 1.35 NA, and targets the contact/metal layers of the 32 & 22 nm node. For contact hole printing, we consider both single and dual exposure schemes for regular arrays and 2D patterns. For trench printing, we compare the NTD and PTD performance for one-dimensional patterns, line ends and twodimensional structures. We also assess the etch capability and CDU performance of the NTD process. This experimental study proves the added value of the NTD scheme. For contacts and trenches, it allows achieving a broader pitch range and/or smaller litho targets, which makes this process flow attractive for the most advanced lithography applications, including double patterning.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2010; DOI:10.1117/12.848228 · 0.20 Impact Factor
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    ABSTRACT: Several options are being explored to extend device scaling towards and beyond the 32nm Half Pitch (HP) using the current immersion lithography tools and this in order to compete with the costly EUV technology that is still under development. These extension techniques all involve compromises between design and process. In this paper, several options for the extension beyond the 32nm HP node are investigated and illustrated with experimental results. In a first stage, a litho-friendly design is created, enabling the scalability by lithography. Secondly, aerial image contrast and pitch can be pushed to the ultimate limits by splitting the design into two masks. One mask contains horizontal features and the other one vertical features and both will be printed with extreme off-axis illumination. Double Patterning (DP) is the next step which enables pitch scaling beyond the limits of 1.35NA exposures. The most common double patterning technique used is litho-etch-litho-etch. A splitted design is recombined through two subsequent patterning steps. Self- Aligned Double Patterning is another pitch doubling technique, interesting for one-dimensional designs on narrow pitches. Next to it, alternative, more cost effective DP approaches are discussed. These techniques show the capability of immersion lithography and double patterning to scale beyond the 32nm HP node.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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    ABSTRACT: Several options are being explored to extend device scaling towards and beyond the 32nm Half Pitch (HP) using the current immersion lithography tools and this in order to compete with the costly EUV technology that is still under development. These extension techniques all involve compromises between design and process. In this paper, several options for the extension beyond the 32nm HP node are investigated and illustrated with experimental results. In a first stage, a litho-friendly design is created, enabling the scalability by lithography. Secondly, aerial image contrast and pitch can be pushed to the ultimate limits by splitting the design into two masks. One mask contains horizontal features and the other one vertical features and both will be printed with extreme off-axis illumination. Double Patterning (DP) is the next step which enables pitch scaling beyond the limits of 1.35NA exposures. The most common double patterning technique used is litho-etch-litho-etch. A splitted design is recombined through two subsequent patterning steps. Self- Aligned Double Patterning is another pitch doubling technique, interesting for one-dimensional designs on narrow pitches. Next to it, alternative, more cost effective DP approaches are discussed. These techniques show the capability of immersion lithography and double patterning to scale beyond the 32nm HP node.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2009; DOI:10.1117/12.854658 · 0.20 Impact Factor
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    ABSTRACT: Contact Hole (CH) resolution is limited by the low aerial image contrast using dark field masks. Moreover the 2- Dimensional character of CH is a limiting factor in the use of extreme Resolution Enhancement Techniques for reaching the smallest pitch. These limitations can be overcome if one deconvolves the 2D CH into two exposures of 1D structures (i.e. lines). These 1D structures can indeed be printed at the ultimate resolution limit of the scanner using dipole exposures. Recently, several materials have become available to pattern CH from such a double exposure of line patterns. It is shown in this paper how this concept of deconvolution can be used in different techniques: Two 1D aerial images can be recomposed in order to obtain 2D images which will subsequently be reversed into CH. We can distinguish, on the one hand, a reversal based on the positive development of line crossings into resist pillar patterns, on which are deposited or coated a gap-fill material layer. The pillars are then removed, leaving a masking material layer with holes. On the other hand, negative tone development can be used to reverse directly the recomposed 2D aerial image: while the classical positive development creates pillars, the negative tone development inverses immediately this image to create contact holes in the resist layer. In this paper, we demonstrate the potential of the double exposure method. We characterise three reversal techniques using a NA=1.35 immersion scanner for patterning 40nm or lower CH at pitch 80nm. We also show etch performance of these processes and address the complexity of each solution.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2009; DOI:10.1117/12.814867 · 0.20 Impact Factor