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Nov 2008

Volume 26, Issue 6, pp. L45-2635

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back to top Line Edge Roughness/Resists

Preface

Cynthia Hanson

J. Vac. Sci. Technol. B 26, 2024 (2008); http://dx.doi.org/10.1116/1.3043663 (1 page)

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Abstract Unavailable
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81.16.-c Methods of micro- and nanofabrication and processing
01.10.Fv Conferences, lectures, and institutes
back to top E-Beam Maskless Lithography

Electron beams in individual column cells of multicolumn cell system

Akio Yamada, Hiroshi Yasuda, and Masaki Yamabe

J. Vac. Sci. Technol. B 26, 2025 (2008); http://dx.doi.org/10.1116/1.2976603 (7 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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In the Mask D2I project at ASET, the authors designed a novel electron beam exposure system having the concepts of multicolumn cell (MCC), character projection, and variable shaped beam to improve the throughput of electron beam exposure systems. They presented the electron optical structure of an individual column cell in the MCC and have shown shaped beam performances in the column cell. They evaluated the impacts on beam position in one column cell caused by deflections of major and minor deflectors in other column cell, which were less than 2.5 nm for both averaged and transitional impacts between +full and −full deflections. They will improve the evaluation accuracy to analyze the origin of the impacts and decrease the impacts from other column cell.
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41.75.Fr Electron and positron beams

Process variation-aware three-dimensional proximity effect correction for electron beam direct writing at 45 nm node and beyond

Kozo Ogino, Hiromi Hoshino, and Yasuhide Machida

J. Vac. Sci. Technol. B 26, 2032 (2008); http://dx.doi.org/10.1116/1.3013861 (7 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The simplified electron energy flux (SEEF)model by which the backscattered energy distribution in the multilayered structure is calculated has been applied to the analysis of critical dimension (CD) variations caused by the thickness variations in copper interconnect. The SEEF model defines the reflection, downward transmission, and upward transmission of electron energy fluxes in each layer. Parameters of the SEEF model are expressed as functions of the depth from the substrate surface and are modified by the approximation in regard to the thickness variation. Using this approach, the process window for the dose and thickness variation has been analyzed quantitatively and the necessity of improving the process window has been confirmed especially at 45 nm node and beyond. Moreover, a variation-aware proximity effect correction method, in which CD variations caused by process variations are reduced and dose margins for various patterns with the same linewidth are equalized, is proposed. The correction method improves the process window for isolated line pattern and 1:1 line-and-space pattern when the sixth wiring layer is fabricated.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

Charging and error budgets in electron beam lithography tools

John G. Hartley and Adam Lyons

J. Vac. Sci. Technol. B 26, 2039 (2008); http://dx.doi.org/10.1116/1.3021373 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Given a set of end user requirements that establish the overall performance goals of a system, the error budget allows a system architect to seek an optimum balance between various subsystems to achieve the most efficient design. When factors that contribute to the overall error budget are poorly understood the result is likely a suboptimal design that relies on the designer’s knowledge of the “art” as opposed to the desired but absent scientific understanding. This typically leads to overengineering of other subsystems to compensate. One factor not strongly quantified is drift due to charging. In this article, the authors explicitly examine contributions due to particle contamination, voids in conductive coatings that expose insulating material, and contamination induced insulating films on conductors in the electron optic subsystem.
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85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

An innovative design of wafer height and tilt sensor for lithography systems

Junru Ruan and John Hartley

J. Vac. Sci. Technol. B 26, 2043 (2008); http://dx.doi.org/10.1116/1.3013318 (6 pages)

Online Publication Date: 1 December 2008

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Since lithography systems have limited depth of focus, precise and real-time measurement of wafer height is important for the image quality control. The traditional grazing incidence height sensor for lithography system consists of two basic components: a light source to illuminate the wafer surface and a detection surface to receive the reflected light beam from the wafer. Mathematical study of this type of height sensor shows that they will fail to differentiate the height difference of the wafer from the tilt of the wafer. In order to obtain the tilt information, height sensors with more complicated designs are used, and examples of these designs are briefly reviewed. A new design for a wafer height sensor is proposed here. By adding an independent detection surface, the new design is able to obtain wafer height and tilt information without using a complicated optical design, which results in easy alignment and calibration.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
81.16.Nd Micro- and nanolithography

Influence of hydrogen silsesquioxane resist exposure temperature on ultrahigh resolution electron beam lithography

Vadim Sidorkin, Emile van der Drift, and Huub Salemink

J. Vac. Sci. Technol. B 26, 2049 (2008); http://dx.doi.org/10.1116/1.2987965 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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Performance of hydrogen silsesquioxane (HSQ) resist material with respect to the temperature during electron beam exposure was investigated. Electron beam exposure at elevated temperatures up to 90 °C shows sensitivity rise and slight contrast (γ) degradation compared to lower temperature cases. Ultrahigh resolution structures formed at elevated temperatures manifest better uniformity together with aspect ratio improvement and less linewidth broadening with overdose. Potential mechanisms for observed phenomena are proposed.
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85.40.Hp Lithography, masks and pattern transfer

Dynamic stencil lithography on full wafer scale

Veronica Savu, Marc A. F. van den Boogaart, Juergen Brugger, Julien Arcamone, Marc Sansa, and Francesc Perez-Murano

J. Vac. Sci. Technol. B 26, 2054 (2008); http://dx.doi.org/10.1116/1.2987953 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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In this paper, the authors present a breakthrough extension of the stencil lithography tool and method. In the standard stencil lithography static mode, material is deposited through apertures in a membrane (stencil) on a substrate which is clamped to the stencil. In the novel dynamic mode, the stencil is repositioned with respect to the substrate inside the vacuum chamber and its motion is synchronized with the material deposition. This can be done either in a step-and-repeat or in a continuous mode. The authors present the first results proving the accurate x-y-z in situ positioning and movement of our stages during and in between patterning.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography

Projection maskless patterning for nanotechnology applications

Elmar Platzgummer, Hans Loeschner, and Gerhard Gross

J. Vac. Sci. Technol. B 26, 2059 (2008); http://dx.doi.org/10.1116/1.2993260 (5 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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Projection maskless patterning (PMLP) is based on a programmable aperture plate system and on charged particle projection optics with 200× reduction, providing thousands of electron or ion (H+, He+, Ar+, Xe+, C60−) beams working in parallel on the substrate. As part of the European CHARPAN project a PMLP proof-of-concept tool has been realized. Using resolution templates, with 10 keV H+ multibeams a resolution of 16 nm lines and spaces was achieved in HSQ resist across the proof-of-concept tool 25×25 μm2 exposure field at an exposure dose of 25 μC/cm2. Enhancing the dose by 10% there was <1 nm increase in linewidth. With 10 keV Ar+ multibeams resistless nanopatterning of various materials was accomplished. Inserting a wired programmable aperture plate system providing ∼ 4000 beams, first HSQ resist exposure and patterning results have been accomplished, implementing gray scale exposure techniques. The system is being upgraded to a PMLP engineering tool integrating an aperture plate system with complementary metal oxide semiconductor electronics providing ∼ 40 000 programmable beams, a precursor gas injection system for in situ ion multibeam induced etching and deposition, and a laser-interferometer controlled high-precision vacuum stage. Industrial PMLP nanotechnology applications are discussed.
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81.16.Rf Micro- and nanoscale pattern formation
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Cd Deposition by sputtering
42.82.Cr Fabrication techniques; lithography, pattern transfer
back to top Electron Beam Sources

Sub-50 nm resolution surface electron emission lithography using nano-Si ballistic electron emitter

A. Kojima, H. Ohyi, and N. Koshida

J. Vac. Sci. Technol. B 26, 2064 (2008); http://dx.doi.org/10.1116/1.2981068 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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It is demonstrated that parallel electron beam lithography using a nano-Si planar ballistic electron emitter (PBE) provided the resolution below 30 nm even in a low accelerating voltage. This high resolving power is explained by the nature of ballistic electron transport in nanocrystalline silicon. The parallel EB lithography was performed on a 1:1 electron imaging system. The system was composed of the PBE as a patterned surface electron source, a target wafer parallel to the surface electron source, and vertical electromagnetic fields. The PBE projected a patterned electron image on the target. A replica of the pattern was transferred into a resist on the target wafer within less than 1 s. The experimental exposure was performed over 10 mm2 area. The PBE was composed of a thin metal surface electrode, nanosilicon layer, and semiconductor substrate. The electrons injected from semiconductor substrate were accelerated via cascade tunneling through the nanosilicon layer and reached the outer surface as ballistic or quasiballistic electrons. As a result, the chromatic aberration limiting resolution is expected to be quite small. The 1:1 electron imaging system based on the PBE provides promising solution for high resolution and high throughput lithography with low cost system with the simple electron optics for the next generation device fabrication in the sub-30 nm scale.
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81.16.Nd Micro- and nanolithography
72.80.Cw Elemental semiconductors
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport

Multilevel visualization of local electric field at probe apex using scanning electron microscopy

Jun-ichi Fujita, Yuta Ikeda, and Ikumi Suzuki

J. Vac. Sci. Technol. B 26, 2069 (2008); http://dx.doi.org/10.1116/1.2991517 (4 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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The authors have found that the locally enhanced field at a probe apex can be visualized using conventional scanning electron microscopy (SEM) under a low accelerating voltage. The local electric field deflects the primary electrons in the vicinity of the apex. They placed a gold grid detector just beside the beam axis to detect these deflected primary electrons. The secondary electrons thus generated from the grid simultaneously created a concentric contour ring around the probe apex in the SEM image. Thus, a simple Rutherford scattering model could be adopted to analyze the local electric field distribution at the tip apex.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Effect of the electric field on the form stability of a Schottky electron emitter: A step model

M. S. Bronsgeest and P. Kruit

J. Vac. Sci. Technol. B 26, 2073 (2008); http://dx.doi.org/10.1116/1.3010732 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The stability of the physical shape of an electron emitter (co)determines the stability of the performance of electron-beam equipment. A typical short-term instability of the Schottky electron source is the instability of the (100) facet at the tip end known as “collapsing rings.” This instability causes probe instabilities, but it is known from experiments that this can be prevented by applying high enough extraction voltages. The phenomenon of collapsing rings can be explained with a step-flow model, which is based on variations in equilibrium concentrations of adatoms on the surface. The effect of the extraction voltage can be incorporated by acknowledging the redistribution of the surface charge associated with adatom formation. For operation at constant extraction voltages the adatom formation energy becomes a function of the local charge density. The charge-density distribution on the emitter surface as a function of the applied extraction voltage can be calculated with boundary-element methods. It is shown that, provided the relevant material properties are known, it can be predicted if, for a given tip shape, a collapse is to be expected.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Range of validity of field emission equations

A. S. Bahm, G. A. Schwind, and L. W. Swanson

J. Vac. Sci. Technol. B 26, 2080 (2008); http://dx.doi.org/10.1116/1.2978403 (5 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The analytical equations for field emission current density and total energy distribution are compared with a rigorous numerical solution of the fundamental emission equations over a wide range of electric field, work function, and temperature. In particular, the range of the latter parameters where agreement occurs between the analytical and numerical results is established. Some interesting periodic deviations with applied electric field are observed for the numerically calculated current density and total energy distributions.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions

Evaluation of electron energy spread in CsBr based photocathodes

Juan R. Maldonado, Yun Sun, Zhi Liu, Xuefeng Liu, Sayaka Tanimoto, Piero Pianetta, and Fabian Pease

J. Vac. Sci. Technol. B 26, 2085 (2008); http://dx.doi.org/10.1116/1.2976572 (6 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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Photocathodes with relatively low energy spread (<0.5 eV) are required for electron sources in several applications including single and multiple electron beam inspection and lithography tools and free electron lasers. CsBr based photocathodes have been shown to be very robust and capable of operation at high current density (>150 A/cm2) with very long lifetime (approximately hundreds of hours/spot). Experimental results of the photoelectron energy spread obtained in CsBr films deposited on both metal and InGaN substrates will be presented in this paper.
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85.60.Ha Photomultipliers; phototubes and photocathodes
back to top Ion Beam Technology

Brightness measurements of a gallium liquid metal ion source

C. W. Hagen, E. Fokkema, and P. Kruit

J. Vac. Sci. Technol. B 26, 2091 (2008); http://dx.doi.org/10.1116/1.2987958 (6 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The virtual source size of a liquid metal ion source is an order of magnitude larger than the size of the region from which the ions are emitted at the source. This source size has a direct effect on the reduced brightness and, hence, on the performance of these sources. The variation of the virtual source size of a gallium liquid metal ion source as a function of the angular current density at the source has been measured. This was done by measuring the source image size from images of a pencil lead sample taken with an FEI focused ion beam system. The measurements indicate that the virtual source size grows from about 50–80 nm when the emission current increases from 1 to 10 μA. The experimental data on the virtual source size are compared with the theory on stochastic Coulomb interactions in the source region. On the basis of these measurements the authors show that the reduced brightness deteriorates with an increasing angular current density. The maximum reduced brightness measured was 1×106 A/(m2 sr V).
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative

The use of ionic liquid ion sources in focused ion beam applications

Anthony N. Zorzos and Paulo C. Lozano

J. Vac. Sci. Technol. B 26, 2097 (2008); http://dx.doi.org/10.1116/1.2991619 (6 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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A new monoenergetic, high-brightness ion source can be constructed using an arrangement similar to liquid metal ion sources by substituting the liquid metal with an ionic liquid or room-temperature molten salt. Ion beams produced by these ionic liquid ion sources (ILISs) have energy deficits and distributions that closely resemble their metallic counterparts, with the exception that they can be stably operated at current levels as low as a few nanoamperes if needed. ILISs are here presented as having two further key advantages: (1) the ability to obtain both positive and negative ion beams and (2) the ability to produce very diverse molecular ions in terms of their masses, compositions, and properties due to the fact that the number of available ionic liquids is large. In this article an overview of ILISs is presented, as well as preliminary results of their performance in a focused ion beam column.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors

Elemental analysis with the helium ion microscope

Sybren Sijbrandij, Bill Thompson, John Notte, Bill W. Ward, and Nicholas P. Economou

J. Vac. Sci. Technol. B 26, 2103 (2008); http://dx.doi.org/10.1116/1.2993262 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The newly developed helium ion microscope is an instrument well suited to high resolution surface specific imaging with several unique contrast mechanisms. In addition to its imaging capabilities, the focused helium ion beam (subnanometer in size) has recently been used for elemental analysis. The scattering probability, angular distribution, and recoil energy combine to provide valuable information about the specimen being analyzed.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.-d Microscopy of surfaces, interfaces, and thin films
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Sputtering limits versus signal-to-noise limits in the observation of Sn balls in a Ga+ microscope

V. Castaldo, C. W. Hagen, B. Rieger, and P. Kruit

J. Vac. Sci. Technol. B 26, 2107 (2008); http://dx.doi.org/10.1116/1.3013306 (9 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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In principle, a scanning ion microscope can produce smaller probe sizes than a scanning electron microscope because the diffraction contribution is smaller. However, the imaging resolution is often severely limited by the sputtering damage. In this article, an experimental procedure to establish the limit of a focused ion beam system for imaging purposes is proposed. The procedure is based on the observation of the change in geometry (i.e., shrinking) of the features in a Sn-ball sample imaged with a Ga+ beam. Plots of the balls’ diameter versus the irradiation time give a straightforward visual evaluation of the time allowed for the observation of a single feature before the removal of material due to the ion bombardment becomes unacceptable. For each particle, the curve, together with the error band connected with the imaging process, gives the values of uncertainty/resolution due to the two competing processes, collecting of information (for example, from secondary electrons) and damaging of the target. A plot of the uncertainty that is derived from these two processes for different sampling times allows the determination of the limiting factor of the imaging mode in use, and, ultimately, the highest possible resolution obtainable with a given machine for the observation of a certain sample. Together with simulations and theoretical studies, the described procedure will be able to confirm the effectiveness of the new ion sources that are currently being developed.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
61.80.Jh Ion radiation effects
back to top Photon Beam Technology

Enhancement in hyper-numerical-aperture imaging through selective TM polarization

Bruce Smith, Jianming Zhou, and Peng Xie

J. Vac. Sci. Technol. B 26, 2116 (2008); http://dx.doi.org/10.1116/1.3002565 (5 pages)

Online Publication Date: 1 December 2008

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The degradation of projected images using TM polarization is not intrinsic because losses in image contrast can be recoverable. By controlling the photoresist/substrate interface reflectivity, high modulation for TM polarization can be maintained for angles approaching 90° in a photoresist. Although there is calculated loss of image contrast with increasing polarization angle using suppressed reflection (i.e., with an antireflection coating), the loss is not nearly as large when imaging over a reflective substrate. These results can potentially impact the design of illumination, possibly away from most recent TE-only schemes for oblique imaging angles and high numerical apertures (NA). Several cases of TM illumination are presented combined with tuned substrate reflectivity for 0.93 NA, 1.20 NA, and 1.35 NA and compared to results using TE illumination. Additionally, a scheme for frequency doubling with a single TM polarized exposure is presented. Using a single exposure and selective TM polarization, the reflective component produced at the photoresist/substrate interface is utilized for a four-beam imaging scenario. In doing so, patterns deposited into a photoresist film with double density are made possible.
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85.40.Hp Lithography, masks and pattern transfer

Image quality improvement in focused ion beam photomask repair system

Anto Yasaka, Fumio Aramaki, Masashi Muramatsu, Tomokazu Kozakai, Osamu Matsuda, Yasuhiko Sugiyama, Toshio Doi, Osamu Takaoka, Ryoji Hagiwara, and Koji Nakamae

J. Vac. Sci. Technol. B 26, 2121 (2008); http://dx.doi.org/10.1116/1.2981071 (3 pages)

Online Publication Date: 1 December 2008

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Focused ion beam (FIB) technology has widely been adopted as a defect repair tool on photomasks for semiconductor manufacturing. In the FIB mask repair process, scanning ion image (FIB image) is used for the defect area recognition. Quality of the FIB images is one of the most important factors in order to improve the repair accuracy. Precise imaging of the small features on the photomasks, however, is a challenging subject due to the surface charge buildup induced by FIB scanning, even though simultaneous electron beam irradiation is used for the charge compensation. The authors have developed new method of the FIB scanning for better image quality. This method utilizes software accumulation of multiple images with different scan directions and results in higher peak-to-background ratio and higher contrast images with isolated mask patterns on the quartz substrate, compared to the images acquired from conventional single scanning. The images also show better uniformity and symmetry of the secondary electron intensity.
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85.40.Hp Lithography, masks and pattern transfer
61.80.Fe Electron and positron radiation effects
85.30.-z Semiconductor devices

High-speed optical beam-steering based on phase-arrayed waveguides

Mona Jarrahi, R. Fabian, W. Pease, David A. B. Miller, and Thomas H. Lee

J. Vac. Sci. Technol. B 26, 2124 (2008); http://dx.doi.org/10.1116/1.2978945 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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The authors present a high-speed optical beam-steering system employing phase-arrayed waveguides. They demonstrate a 100 mrad deflection angle at the fastest ever reported instrument-limited deflection speed of 18 GHz and power consumption of 1.8 mW.
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42.82.Et Waveguides, couplers, and arrays
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Gn Optical waveguides and couplers
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Hp Optical processors, correlators, and modulators
85.60.-q Optoelectronic devices

Application of vector scanning in focused ion beam photomask repair system

Anto Yasaka, Fumio Aramaki, Masashi Muramatsu, Tomokazu Kozakai, Osamu Matsuda, Yasuhiko Sugiyama, Toshio Doi, Osamu Takaoka, Ryoji Hagiwara, and Koji Nakamae

J. Vac. Sci. Technol. B 26, 2127 (2008); http://dx.doi.org/10.1116/1.2976574 (4 pages)

Online Publication Date: 1 December 2008

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With continuous reduction in linewidth of the VLSI devices, the pattern integrity of photomasks becomes considerably more important than ever. Consequently, requirement for the defect repair technology on photomasks is more severe and strict. Focused ion beam (FIB) technology has been widely used for defect repairing in photomask industry. Therefore, the performance of the FIB mask repair tool has to be improved especially in repair accuracy and precision. The FIB repair processes are classified into two kinds; one is additive repair using FIB induced deposition for missing patterns, the other is subtractive repair using gas assisted FIB etching for extra patterns. In both processes, precursor gas is applied onto the processing area through a small nozzle. Thus, the repair processes are controlled by the FIB irradiation and the precursor gas supply. Important characteristics of the repairs, such as size, shape, and placement of the repair area, are defined by the FIB scanning control. As conventional FIB systems used raster type of beam scanning for the repair processes, the size, shape, and placement could be controlled with the unit of pixel size (typically about 6–12 nm). However, in order to satisfy the recent requirement, more precise beam control is needed. The authors have developed a vector scanning system to meet the requirement. The vector scanning system enables us to control ion beams more precisely and more arbitrarily. Furthermore, unicursal beam scanning can be applied to the repair processes, which minimizes beam blanking times. By adopting the vector scanning, repair precision is improved. Additionally, sidewall angle of the repair region is also improved because the repair shape is formed without beam blanking.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Linewidth uniformity in Lloyd’s mirror interference lithography systems

Thomas B. O’Reilly and Henry I. Smith

J. Vac. Sci. Technol. B 26, 2131 (2008); http://dx.doi.org/10.1116/1.3013391 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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Control of linewidth in patterns written with interference lithography (IL) is an important part of process control for many applications, requiring an understanding of how exposure parameters, such as dose and dose modulation, vary across the exposed area, and how a given photoresist will respond to changes in those parameters. This article presents a model of linewidth variation in a common IL system, Lloyd’s mirror, along with some results derived from that model that relate to optimizing the linewidth uniformity that can be achieved for a given application. An extension to a previously reported resist-characterization method that makes it possible to directly measure how changes in dose modulation affect linewidth is also discussed.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers
42.79.Bh Lenses, prisms and mirrors

Spatial-frequency multiplication with multilevel interference lithography

Chih-Hao Chang, Y. Zhao, R. K. Heilmann, and M. L. Schattenburg

J. Vac. Sci. Technol. B 26, 2135 (2008); http://dx.doi.org/10.1116/1.2976604 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The authors present a large-area spatial-frequency multiplication fabrication process for patterning one-dimensional periodic structures using multilevel interference lithography. In this process, multiple grating levels with different phase offsets are overlaid by aligning to a reference grating. Each grating level is pattern transfered into a single hard mask layer, effectively reducing the grating period. The linewidth of the grating lines is controlled with nanometer repeatability by plasma etching and an image-reversal process. The authors demonstrate overlay accuracy of 0.6±1.9 nm over 16×12 mm2 for two levels of 200 nm period gratings. Using this process, a subdiffraction-limited resolution grating with 100 nm period is fabricated using light with λ = 351.1 nm. This process can also be used to fabricate more complex periodic geometries.
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42.79.Dj Gratings
42.86.+b Optical workshop techniques

Light modulation with nanopatterned diffractive microelectromechanical system pixels

Jack L. Skinner, A. Alec Talin, and David A. Horsley

J. Vac. Sci. Technol. B 26, 2139 (2008); http://dx.doi.org/10.1116/1.2998725 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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The design, fabrication, and testing of a microelectromechanical system (MEMS) optical modulator is presented. Polarization effects of noncircular holes on reflectivity are examined. Thermal nanoimprint lithography is used to form an array of 150 nm diameter nanoholes in a 60 nm thick metal film on a silicon-on-insulator wafer. A quartz superstrate with an indium tin oxide electrode and a photoresist spacer is used to electrostatically actuate the MEMS pixel. The motion of the pixel in relation to the superstrate causes shifts in the wavelengths of optical interference from the periodic nanohole array. An optical modulation depth of over 67% is demonstrated with this modulation method. Dynamic modal analysis is also presented.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.79.Hp Optical processors, correlators, and modulators
85.40.Hp Lithography, masks and pattern transfer

Improving lithography pattern fidelity and line-edge roughness by reducing laser speckle

Oleg Kritsun, Ivan Lalovic, Slava Rokitski, Bill Partlo, Bruno La Fontaine, Nigel Farrar, and Harry Levinson

J. Vac. Sci. Technol. B 26, 2145 (2008); http://dx.doi.org/10.1116/1.2992027 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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In this article the authors discuss the impact of coherence, or laser speckle, of current generation 193 nm argon fluoride (ArF) excimer sources on lithographic patterning. They report a new metrology capability to characterize single-pulse speckle patterns at the exit of the laser aperture and quantify the speckle dependence on time integral square (TIS) pulse duration for different system configurations. The authors performed lithographic exposures on high-numerical-aperture immersion and dry ArF systems as a function of source pulse duration and have quantified the speckle impacts on measured photoresist line-edge roughness (LER) and linewidth roughness (LWR) using immersion and dry lithography processes. Measurements were obtained for multiple feature sizes, pitches, and illumination modes using both static and scanning exposures. They have compared the measured LWR due to laser speckle to results of a line-roughness image model, which accounts for the LER, LWR, and critical dimension uniformity due to the effective dose variation from laser speckle. Finally, the authors present measurements that demonstrate the proportionality between laser speckle contrast and the inverse root of the TIS pulse duration and find that the lithographic LWR exhibits a similar relationship with pulse duration.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
42.30.Ms Speckle and moiré patterns
back to top Nano-optical Devices

Fabrication of metallic nanoslit waveguides with sharp bends

M. Lu, L. E. Ocola, S. K. Gray, and G. P. Wiederrecht

J. Vac. Sci. Technol. B 26, 2151 (2008); http://dx.doi.org/10.1116/1.3013398 (5 pages)

Online Publication Date: 1 December 2008

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Metallic nanoslit waveguides are promising candidates for ultrahigh-density optical interconnections. A variety of devices based on metallic nanoslit waveguides have already been proposed that show a great superiority over conventional photonic devices for compactness. However very few two-dimensional devices have been experimentally demonstrated with in-plane geometries due to fabrication difficulties. In this article, a feasible process is presented using traditional semiconductor fabrication technologies such as mix-and-match lithography and electroplating, which is cable of fabricating complicated 100 nm wide, 800 nm deep gold slit waveguides with multiple sharp right-angle corners. The process can be extended to volume production manufacturing with minor modifications, thus enabling the fabrication of nanoslit photonic circuits and networks.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers

Optical antennas: A boost for infrared detection

Huifeng Li and Xing Cheng

J. Vac. Sci. Technol. B 26, 2156 (2008); http://dx.doi.org/10.1116/1.3013272 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Optical antennas that operate at infrared wavelengths are studied for their potential application in enhancing the sensitivity of infrared detectors. Huge enhancement of infrared intensity can be achieved at the gap region of dipole and bowtie aperture antennas. The intensity enhancement is found to increase monotonically with a narrower gap size. The infrared radiation is also found to be concentrated above and below the antenna plane at the gap region, which allows for easy integration of the optical antennas with infrared detectors. The advantages of the infrared antennas, such as strong field enhancement and easy fabrication, may present a viable solution toward achieving highly sensitive and highly compact uncooled infrared detectors to impact numerous infrared technologies.
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84.40.Ba Antennas: theory, components and accessories
85.60.Gz Photodetectors (including infrared and CCD detectors)

Fabrication of Fresnel zone plates by holography in the extreme ultraviolet region

Sankha S. Sarkar, Pratap K. Sahoo, Harun H. Solak, Christian David, and J. Friso Van der Veen

J. Vac. Sci. Technol. B 26, 2160 (2008); http://dx.doi.org/10.1116/1.2987960 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Fabrication of Fresnel zone plates (FZPs) with nanometer scale resolution is one of the major challenges in lithographic fabrication. The authors present a holographic approach to create FZPs where the interference pattern between a spherical beam and a plane wave is recorded to obtain the FZP structure. The spherical beam is obtained by diffraction from a circular aperture (pinhole) in a semiopaque membrane which is illuminated by a spatially coherent extreme ultraviolet beam. The beam transmitted by the membrane serves as the reference plane wave. The resulting pattern gives rise to a FZP with outermost zone width comparable to the dimension of the circular aperture. Fabrication and test results of a FZP obtained with this method are presented. The technique offers a solution to the pattern-placement problem encountered in serial ZP writing techniques as well as high resolution potential.
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42.79.Ci Filters, zone plates, and polarizers
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.86.+b Optical workshop techniques
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication strategies for filter banks based on microring resonators

C. W. Holzwarth, R. Amatya, M. Dahlem, A. Khilo, F. X. Kärtner, E. P. Ippen, R. J. Ram, and Henry I. Smith

J. Vac. Sci. Technol. B 26, 2164 (2008); http://dx.doi.org/10.1116/1.3021389 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Wavelength-division demultiplexers are a fundamental component needed for many proposed integrated photonic systems. By using filter banks based on microring resonators it is possible to create demultiplexers that are two orders of magnitude smaller and achieve better performance than the discrete component demultiplexers currently used. To create a filter bank out of microring resonators the resonant-frequency spacing must be controlled to within 1 GHz. This is achieved by controlling the electron-dose during scanning-electron-beam lithography in order to change the average ring waveguide width on the tens of picometer scale. Using this method a second-order twenty-channel dual filter bank (80 microrings) is fabricated with a average channel spacing of 83 GHz demonstrating the capability to make changes in the average ring waveguide width with an accuracy of 75 pm. It is shown that any frequency errors that remain after fabrication can be corrected using thermal tuning with integrated microheaters. The amount of power needed to correct for all frequency errors in the fabricated filter banks is 0.09 W, compared to the 2.4 W that is needed if no attempt is made to control the frequency spacing during fabrication. Also a temperature stabilization circuit is demonstrated that can stabilize the temperature of the filters to 80 mK (280 MHz).
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Ci Filters, zone plates, and polarizers

Focused ion beam fabrication of metallic nanostructures on end faces of optical fibers for chemical sensing applications

A. Dhawan, J. F. Muth, D. N. Leonard, M. D. Gerhold, J. Gleeson, T. Vo-Dinh, and P. E. Russell

J. Vac. Sci. Technol. B 26, 2168 (2008); http://dx.doi.org/10.1116/1.3013329 (6 pages) | Cited 9 times

Online Publication Date: 1 December 2008

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Focused ion beam (FIB) fabrication of fiber optic sensors, mainly chemical sensors, which are based on plasmonics-active nanostructures formed on the cleaved tips of optical fibers, is reported. The nanostructures fabricated included nanoholes in optically thick metallic films as well as metallic nanopillars and nanorods. The sensing mechanism is based on detecting shifts in surface plasmon resonances (SPRs) associated with nanoholes in metallic films and localized SPRs of metallic nanopillars and nanorods, when the refractive index of the medium surrounding the nanostructures is changed. These sensors can be employed for the detection of chemical agents in air as well as liquid media surrounding the sensors. FIB milling was employed to fabricate ordered arrays of nanoholes in optically thick (100–240 nm) metallic films deposited on cleaved end faces of multimode, four-mode, and single-mode optical fibers. Separately, metallic nanorods and nanopillars were formed by first depositing a metallic (gold or silver) film on tips of optical fibers, which was followed by FIB milling large area patterns to form freestanding nanorods and nanopillars. Utilizing FIB allows engineering nanostructure geometries, i.e., nanostructure shapes and sizes that are chosen based on the plasmon resonances associated with them. Formation of periodic arrays of nanoholes provides a means of tuning plasmon resonance peaks, associated with extraordinary transmission of light through the array of nanoholes in the metallic films, based on periodicity and shape of the nanoholes as well as on refractive index changes to form sensitive chemical sensors.
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42.81.Pa Sensors, gyros
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

NIL processes and material characterization on transparent substrates for optical applications

N. Chaix, C. Gourgon, C. Perret, S. Decossas, S. Landis, V. G. Lambertini, and N. Li Pira

J. Vac. Sci. Technol. B 26, 2174 (2008); http://dx.doi.org/10.1116/1.2998726 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Several nanoimprint lithography polymers have been investigated for optical applications. The objective was to establish which materials can be used as a permanent polymer coated on top of a glass substrate to provide nanostructures imprinted by nanoimprint lithography. 400 and 600 nm dots were realized in polystyrene, polymethylmethacrylate (PMMA), mr-I T85, and mr-I6000. The adhesion study shows that PMMA and mr-I6000 materials are the best candidates for demolding issues. Scanning electron microscopy characterization confirmed that PMMA structures are well defined, whereas dots printed in other polymers exhibit defects due to sticking issues which lead to local pattern deformation. Finally, optical characterization showed that the nonperfect profiles are a benefit in terms of light extraction. Polycarbonate sheets were also imprinted on one or two sides in order to study the influence of a double side patterning. It was also concluded that a double side imprinted device leads to an increase in the external efficiency.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
61.41.+e Polymers, elastomers, and plastics
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Fabrication of 200 nm period blazed transmission gratings on silicon-on-insulator wafers

Minseung Ahn, Ralf K. Heilmann, and Mark L. Schattenburg

J. Vac. Sci. Technol. B 26, 2179 (2008); http://dx.doi.org/10.1116/1.2968613 (4 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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The authors report on the fabrication of 200 nm period blazed transmission gratings on silicon-on-insulator (SOI) wafers. These critical angle transmission (CAT) gratings require 3–5 μm tall freestanding grating bars with a very high aspect ratio (>100) and smooth sidewalls. In order to meet the challenging geometrical requirements, they modified and improved our previously reported process for the fabrication of a CAT grating prototype with 574 nm period. They have used potassium hydroxide (KOH) solutions to fabricate high aspect ratio gratings on ⟨110⟩ SOI wafers. The KOH etching process was improved to minimize the lateral undercut through precise grating alignment to ⟨111⟩ planes within ±0.05° and a room temperature etch process with 50 wt % KOH. In addition, an image-reversal technique with a high silicon content spin-on polymer was applied to increase process latitude with a high duty cycle nitride mask. A surfactant was also added to the KOH solution to promote hydrogen bubble release. With the improved process, they achieved a high etch anisotropy of above 300 on a ⟨110⟩ silicon wafer. They successfully fabricated 200 nm period CAT gratings with support mesh periods of 25 and 40 μm in a 9 mm2 area of 4-μm-thick silicon membranes on ⟨110⟩ SOI wafers.
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42.79.Dj Gratings
42.86.+b Optical workshop techniques
81.65.Cf Surface cleaning, etching, patterning
back to top Metamaterials

Engineering surface plasmon grating couplers through computer simulation

Daniel P. Ceperley and Andrew R. Neureuther

J. Vac. Sci. Technol. B 26, 2183 (2008); http://dx.doi.org/10.1116/1.3021378 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Surface plasmon grating couplers are optimized by separately characterizing the collection efficiency, rescattering, and transmission effects of isolated grating elements with finite difference time domain methods and then using signal flow graph methods to assess the performance of arrays of N identical elements. Small bars, ridges, and trenches on silver at a wavelength of 700 nm are shown to have different coupling patterns and efficiencies from near zero to the physical width of the element. The overall efficiency requires a suitable trade-off of coupling and surface wave transmission and an example structure exhibiting an equivalent 100% capture length over ten wavelengths is shown.
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42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings

Light transmission through a metallic/dielectric nano-optic lens

Hyungduk Ko, Hyun Chul Kim, and Mosong Cheng

J. Vac. Sci. Technol. B 26, 2188 (2008); http://dx.doi.org/10.1116/1.2990791 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The authors analyze transmission of a normally incident plane wave through a Ag/dielectric layered concentric ring structure using finite-difference time-domain (FDTD) analysis. The authors study the dependency of the transmission efficiency on the refractive index in slit. The numerical analysis indicates that the focusing beyond diffraction limit is found even at the extended focal length comparable to the distance of 7λ from exit plane using a circularly polarized coherent plane wave, λ = 405 nm. Especially, compared to Ag-only structure, the Ag/LiNbO3 structure exhibits over 2.85 orders of larger transmission power. Therefore, this Ag/dielectric layered lens has the potential for significantly the high resolution imaging and optical data storage.
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42.79.Bh Lenses, prisms and mirrors

Photomask image enhancement using grating-generated surface waves

Neal V. Lafferty, Anatoly Bourov, Andrew Estroff, and Bruce W. Smith

J. Vac. Sci. Technol. B 26, 2192 (2008); http://dx.doi.org/10.1116/1.3002560 (5 pages)

Online Publication Date: 1 December 2008

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In recent years, the anomalous transmission of subwavelength apertures has become an emergent subject within the physical sciences. While the gain mechanism of these structures is still uncertain, the effect has been observed in several studies. Similar transmission enhancements may be realized for near-wavelength sized photomask structures by including buried grooves in a dual write mask design. Several configurations of one-dimensional transmitting apertures and buried grooves have been investigated under TM illumination using the finite element method. Periodic subwavelength apertures with identical sized nontransmitting assist grooves were used to validate the model against reference data in the near-IR. The method was also used to investigate similar structures featuring a larger than wavelength transmitting aperture. Although transmission through the slot was increased by 1.67×, the primary lithographic benefit was an increase in the magnitude of the primary imaging orders relative to the zeroth diffracted order. A similar approach was extended to structures scaled to 248 nm to show application as a potential lithographic assist feature. A 5.7× transmission increase was observed using aluminum on fused silica configuration using 30 nm slots on a 192 nm pitch.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.30.Va Image forming and processing

Optical focusing of plasmonic Fresnel zone plate-based metallic structure covered with a dielectric layer

Hyun Chul Kim, Hyungduk Ko, and Mosong Cheng

J. Vac. Sci. Technol. B 26, 2197 (2008); http://dx.doi.org/10.1116/1.3021380 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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By modulating the zone width of a plasmonic Fresnel zone plate, consisting of metallic nanostructures covered with a dielectric layer, the authors demonstrated numerically that a focused beam can be achieved with higher intensity and smaller spot size than the diffraction-limited conventional Fresnel zone plate. Rigorous electromagnetic simulation predicts a full width at half maximum of 162 nm (equivalent to an effective numerical aperture of 1.30) at 0.5 μm focal length, using 405 nm wavelength illumination. This sub-diffraction-limit focusing has potential in applications such as maskless nanolithography, high resolution scanning optical microscopy, optical data storage, and optical antenna. This focusing capability is related to extraordinary optical transmission, which is explained by the complex propagation constant in the zones afforded by higher refractive index dielectric layer and surface plasmons.
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78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
back to top EUV Lithography

Extreme ultraviolet lithography: Status and prospects

Jos Benschop, Vadim Banine, Sjoerd Lok, and Erik Loopstra

J. Vac. Sci. Technol. B 26, 2204 (2008); http://dx.doi.org/10.1116/1.3010737 (4 pages) | Cited 11 times

Online Publication Date: 1 December 2008

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Extreme ultraviolet lithography (EUVL) using 13.5 nm wavelength light is the leading candidate to succeed 193 nm immersion lithography, enabling semiconductor chips with features smaller than 22 nm. Several major programs worldwide have developed this technology in recent years [ D. A. Tichenor et al., OSA Proceedings on Soft X-Ray Projection Lithography, edited by A. M. Hawryluk and R. H. Stuten (1993), Vol. 18, p. 79; H. Kinachita, OSA Proceedings on Soft X-Ray Projection Lithography, edited by A. M. Hawryluk and R. H Stulen (1993), Vol. 18, p. 74; J. P. H. Benschop, W. M. Kaiser, and D. C. Ockwell, Proc. SPIE 3676, 246 (1999) ] and in 2006, ASML shipped the first EUV Alpha Demo tools (NA = 0.25 full-field scanners) to IMEC in Belgium [ A. M. Goethals et al., Proc. SPIE 6517, 651709 (2007) ] and CNSE in Albany [ O. Wood et al., Proc. SPIE 6517, 6517–041 (2007) ], USA. Currently the development of preproduction tools with targeted shipment of 2009 is well under way. This paper discusses the most critical items for EUVL development, namely, EUV imaging and EUV sources. Furthermore, it elaborates on the necessary development of masks and resists and, for example, quantifies how resist diffusion length can impact imaging capabilities. Results obtained and lessons learned with the Alpha Demo tools are discussed, as well as potential solutions to some of the remaining challenges. Additionally, this paper explains how EUV can realize high productivity (>100 wafers/h) and high resolutions (<22 nm) to continue the cost-effective shrink of semiconductors for several generations.
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85.40.Hp Lithography, masks and pattern transfer

Effects of mask absorber structures on the extreme ultraviolet lithography

Hwan-Seok Seo, Dong-Gun Lee, Hoon Kim, Sungmin Huh, Byung-Sup Ahn, Hakseung Han, Dongwan Kim, Seong-Sue Kim, Han-Ku Cho, and Eric M. Gullikson

J. Vac. Sci. Technol. B 26, 2208 (2008); http://dx.doi.org/10.1116/1.3002488 (7 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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In this paper, the authors present the results of an investigation of the dependence of mask absorber thickness on the extreme ultraviolet lithography (EUVL) and suggest a new mask structure to minimize shadowing effects. For this purpose, several patterned masks with various TaN absorber thicknesses are fabricated using in-house Ru-capped EUVL mask blanks. According to the simulation using practical refractive indices, which are obtained at EUV wavelengths, the absorber thickness can be reduced to that of out-of-phase (ΔΦ = 180°) ranges without loss of image contrast and normalized image log slope. Thickness to meet out-of-phase in real mask can be obtained by comparing field spectrum intensity ratio using the EUV coherent scattering microscopy (CSM). 52.4 nm in thickness is close to ΔΦ = 180° for TaN absorber since it shows the highest 1st/0th order intensity ratio as well as the best resolution in the microfield exposure tool (MET) test. When we apply 40-nm-thick TaN instead of 80-nm-thick TaN, the amounts of H-V bias reduction in wafer scale correspond to 80% (2.46–0.48 nm) by CSM and 70% (2.23–0.65 nm) by MET test results. Considering the fact that H-V bias in the MET is similar with that of simulation using the resist model, the degree of H-V bias in the alpha demo tool (ADT) is supposed to be much higher than that of MET due to its higher incident angle (θ = 6°). Our final goal is to develop a thin absorber EUVL mask which has a low H-V bias, high EUV printability and DUV contrast, and sufficient optical density at the border. To achieve this, blind layer treatment and integration with anti-reflective coating layer are in progress.
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85.40.Hp Lithography, masks and pattern transfer

Experimental validation of full-field extreme ultraviolet lithography flare and shadowing corrections

A. M. Myers, G. F. Lorusso, I. Kim, A. M. Goethals, R. Jonckheere, J. Hermans, B. Baudemprez, and K. Ronse

J. Vac. Sci. Technol. B 26, 2215 (2008); http://dx.doi.org/10.1116/1.3013297 (5 pages) | Cited 10 times

Online Publication Date: 1 December 2008

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Extreme ultraviolet lithography (EUVL) is the leading candidate for 22 nm half-pitch device manufacturing. IMEC has a fully integrated 300 mm EUVL process line incorporating an Alpha Demo Tool (ADT) from ASML, aimed to understand issues related to the introduction of EUV technology in high-volume manufacturing. This study experimentally investigates flare and shadowing correction strategies. Experimental characterization of the flare of the ADT is reported, as well as experimental rules for flare variation correction. With respect to shadowing, shadowing corrections are experimentally estimated. Comparisons of experimental data and rigorous simulation are also presented, and a computationally efficient methodology to generate a full-chip flare map is proposed.
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85.40.Hp Lithography, masks and pattern transfer

Actinic extreme ultraviolet mask inspection beyond 0.25 numerical aperture

K. A. Goldberg, P. Naulleau, I. Mochi, E. H. Anderson, S. B. Rekawa, C. D. Kemp, R. F. Gunion, H.-S. Han, and S. Huh

J. Vac. Sci. Technol. B 26, 2220 (2008); http://dx.doi.org/10.1116/1.3002490 (5 pages) | Cited 9 times

Online Publication Date: 1 December 2008

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The SEMATECH Berkeley actinic inspection tool (AIT) is an extreme ultraviolet (EUV)-wavelength mask inspection microscope designed for direct aerial image measurements and precommercial EUV mask research. Operating on a synchrotron bending magnet beamline, the AIT uses an off-axis Fresnel zoneplate lens to project a high-magnification EUV image directly onto a charge coupled device camera. The authors present the results of recent system upgrades that have improved the imaging resolution, illumination uniformity, and partial coherence. Benchmarking tests show image contrast above 75% for 100 nm mask features and significant improvements and across the full range of measured sizes. The zoneplate lens has been replaced by an array of user-selectable zoneplates with higher magnification and numerical aperture (NA) values up to 0.0875, emulating the spatial resolution of a 0.35 NA 4× EUV stepper. Illumination uniformity is above 90% for mask areas 2 μm wide and smaller. An angle-scanning mirror reduces the high coherence of the synchrotron beamline light source giving measured σ values of approximately 0.125 at 0.0875 NA.
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85.40.Hp Lithography, masks and pattern transfer

The effects of oxygen plasma on the chemical composition and morphology of the Ru capping layer of the extreme ultraviolet mask blanks

Leonid Belau, Jeong Y. Park, Ted Liang, and Gabor A. Somorjai

J. Vac. Sci. Technol. B 26, 2225 (2008); http://dx.doi.org/10.1116/1.3021368 (5 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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Contamination removal from extreme ultraviolet (EUV) mask surfaces is one of the most important aspects to improve reliability for the next generation of EUV lithography. The authors report chemical and morphological changes of the ruthenium (Ru) mask surface after oxygen plasma treatment using surface sensitive analytical methods: x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and transmission electron microscopy (TEM). Chemical analysis of the EUV masks shows an increase in the subsurface oxygen concentration, Ru oxidation, and surface roughness. XPS spectra at various photoelectron takeoff angles suggest that the EUV mask surface was covered with chemisorbed oxygen after oxygen plasma treatment. It is proposed that the Kirkendall effect is the most plausible mechanism that explains the Ru surface oxidation. The etching rate of the Ru capping layer by oxygen plasma was estimated to be 1.5±0.2 Å/min, based on TEM cross sectional analysis.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.Fx Diffusion; interface formation
81.65.Cf Surface cleaning, etching, patterning

Protection and reduction of surface oxidation of Mo/Si multilayers for extreme ultraviolet lithography projection optics by control of hydrocarbon gas atmosphere

Masahito Niibe, Keigo Koida, and Yukinobu Kakutani

J. Vac. Sci. Technol. B 26, 2230 (2008); http://dx.doi.org/10.1116/1.2998703 (6 pages) | Cited 6 times

Online Publication Date: 1 December 2008

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To protect the surface oxidation of Mo/Si multilayer films by extreme ultraviolet (EUV) irradiation under a vacuum atmosphere with residual water, two experiments were carried out. One consisted of examining the oxidation protection effect for isopropyl alcohol (IPA) and n-decane gases. The reflectivity change of the Ru-capped multilayer film by EUV irradiation was investigated under a vacuum atmosphere with residual water vapor at a pressure of 1.3×10−5 Pa, and, in addition, each hydrocarbon (HC) gas was introduced by changing its pressure. A protective effect against oxidation was observed in both gases when introduced at a pressure in the order of 10−6 Pa. For IPA, no remarkable decrease in the reflectivity was observed even when the introductory pressure was raised to the order of 10−4 Pa. However, for n-decane, the reflectivity decreased remarkably when pressure in the order of 10−5 Pa was introduced. The other experiment consisted of examining the reduction effect of the oxidized surface by EUV irradiation when introducing HC gas. Ru- and Si-capped multilayers were once oxidized by EUV irradiation under a water vapor atmosphere. However, for the Ru-capped multilayer, the reflectivity was recovered when EUV was irradiated in the presence of ethanol gas at a pressure of 3.8×10−5 Pa. The oxide layer of the Ru cap was reduced at this time.
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81.65.Mq Oxidation

Decomposition of catechol and carbonaceous residues on TiO2(110): A model system for cleaning of extreme ultraviolet lithography optics

Peter Jacobson, Shao-Chun Li, Chuandao Wang, and Ulrike Diebold

J. Vac. Sci. Technol. B 26, 2236 (2008); http://dx.doi.org/10.1116/1.3002566 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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High energy photons used to expose photoresists in extreme ultraviolet lithography (92 eV, 13.5 nm) photoexcite electrons from Mo/Si multilayer mirror surfaces. Photoemitted electrons participate in the formation of carbonaceous residues on the mirror surface significantly affecting the mirror reflectivity. We explore mitigation strategies utilizing TiO2(110) as a model for the capping layer. Two carbon containing surfaces are examined; an ordered catechol monolayer and a carbonaceous layer. Excimer laser sources (XeF and KrF) coupled with oxidizing gas backgrounds (NO and O2) are shown to be effective for the photocatalytic removal of carbon. Utilizing x-ray photoemission spectroscopy and scanning tunneling microscopy carbon removal is shown to proceed through oxidation of the overlayer.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Interaction of benzene with TiO2 surfaces: Relevance to contamination of extreme ultraviolet lithography mirror capping layers

Shimon Zalkind, Boris V. Yakshinskiy, and Theodore E. Madey

J. Vac. Sci. Technol. B 26, 2241 (2008); http://dx.doi.org/10.1116/1.2978392 (6 pages) | Cited 9 times

Online Publication Date: 1 December 2008

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The authors focus on thermal and nonthermal (radiation-induced) surface processes that affect the reflectivity of TiO2-capped multilayer mirrors used in extreme ultraviolet (EUV) lithography. Low energy electron beams mimic excitations initiated by EUV radiation. Where appropriate, comparison is made with electron bombardment in the vapor of methyl methacrylate (C5H8O2). Benzene adsorbs and desorbs reversibly on TiO2, and the steady state coverage Θ is found to be proportional to the logarithm of the benzene pressure p. This behavior is described by the Tempkin adsorption isotherm, which has the form Θ = const+log p. This isotherm is a consequence of a linear dependence of benzene adsorption energy on Θ. In addition, measurements of cross sections σ (cm2) for electron-stimulated dissociation of benzene on clean and C-covered TiO2 in the range of 10–100 eV reveal surprisingly large values (e.g., ∼ 3.5×10−17 cm2 at 10 eV primary energy). Thus, low energy secondary electrons excited by EUV lithography photons are expected to contribute substantially to carbon accumulation on clean TiO2 cap layers.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Nr Desorption kinetics
back to top Line Edge Roughness/Resists

Stability of HSQ nanolines defined by e-beam lithography for Si nanowire field effect transistors

Suresh Regonda, Mukti Aryal, and Wenchuang (Walter) Hu

J. Vac. Sci. Technol. B 26, 2247 (2008); http://dx.doi.org/10.1116/1.3002561 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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Multiple instability states, e.g., grouped collapse, single collapse, wavy, and grouped wavy states, have been observed in hydrogen silses quioxane (HSQ) nanolines defined by electron beam lithography (EBL). Experimental data show that the critical aspect ratio of the HSQ lines dramatically increase when the line pitch reduced to sub-100-nm, which is opposite to theoretical models for capillary forces and swelling strain. Such contradiction can be well explained only if Young’s modulus is considered as a significantly varying factor. Further, experimental data show a dramatic decrease in swelling strain and increase in oxygen contents in HSQ with increasing EBL dose, indicating that it is the change in Young’s modulus rather than the capillary force or swelling strain that dominates the instability behaviors at the nanoscale. Stable high aspect ratio HSQ nanolines over metal pads were used to make working Si nanowire transistors on Si on insulator substrates. 12–14 nm HSQ lines with aspect ratios of 11–14 have been obtained. Fabricated field effect transistors using back-gate configuration has shown expected performance towards biosensing applications.
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85.40.Hp Lithography, masks and pattern transfer
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography

Novel negative-tone molecular resist based on polyphenol derivative for extreme ultraviolet lithography

Hiroaki Oizumi, Takafumi Kumise, and Toshiro Itani

J. Vac. Sci. Technol. B 26, 2252 (2008); http://dx.doi.org/10.1116/1.2976599 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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This study investigated the extreme ultraviolet (EUV) lithographic performance of negative-tone molecular resists based on 2,7-bis[bis(2,3,5-trimethyl-4-hydroxyphenyl)methyl]naphthalene (MGR002) and their negative-tone imaging mechanism. EUV imaging experiments were performed using the high-numerical-aperture (NA = 0.3), small-field EUV exposure tool (HINA). Patterning results showed the resolution of one resist to be 29 nm at an EUV exposure dose of 18 mJ/cm2 and the obtainable aspect ratio to be as high as 2. Analyses by matrix-assisted laser desorption/ionization mass spectroscopy, Fourier transform infrared spectroscopy, and UV-visible absorption spectroscopy of EUV-exposed resists revealed that one reason for the good performance is that the negative-tone imaging mechanism involves both cross-linking and a change in polarity.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Latent image formation in chemically amplified extreme ultraviolet resists with low activation energy for deprotection reaction

Takahiro Kozawa, Seiichi Tagawa, Julius Joseph Santillan, and Toshiro Itani

J. Vac. Sci. Technol. B 26, 2257 (2008); http://dx.doi.org/10.1116/1.2990787 (4 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The trade-off relationships between resolution, sensitivity, and line edge roughness have become a serious problem in device manufacturing as the minimum feature size is reduced. To solve this problem, the improvement of pattern formation efficiency is necessary. The efficiency of pattern formation is mainly determined by the efficiencies of incident radiation absorption, acid generation, and deprotection. The deprotection efficiency is the number of times an acid can induce catalytic reactions during the diffusion of a unit distance. The highest expected deprotection efficiency is achieved by a diffusion-controlled reaction. In this study, the authors investigated the feasibility of low-Ea resists for 22 nm fabrication. It was found that their efficiency is inadequate for 22 nm fine patterning even when a diffusion-controlled rate is assumed. For 22 nm fabrication with 5–10 mJ cm−2 exposure dose, increases in acid generation efficiency and polymer absorption are essential.
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81.16.Nd Micro- and nanolithography
82.20.Pm Rate constants, reaction cross sections, and activation energies
81.16.Rf Micro- and nanoscale pattern formation
81.16.Be Chemical synthesis methods

Dissolution characteristics of chemically amplified extreme ultraviolet resist

Toshiro Itani, Koji Kaneyama, Takahiro Kozawa, and Seiichi Tagawa

J. Vac. Sci. Technol. B 26, 2261 (2008); http://dx.doi.org/10.1116/1.2987959 (4 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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The dissolution characteristics of the resist film into alkaline developer have been investigated in order to understand inherent extreme ultraviolet (EUV) resist characteristics and improve resist performance. The combined increase in dissolution “slope” and dissolution contrast (Rmax/Rmin) was confirmed to improve the resolution capability of an EUV resist. Also, a higher Rmin value, which means easy and smooth dissolution of the resist into the alkaline developer, will mean a lower line-width roughness (LWR). However, more evidence and further detailed investigation are necessary to prove this relationship between this dissolution characteristic and LWR. It was also found that the slope of dissolution rate curve for the poly(hydroxystyrene) resist increases as protecting ratios is increased. However, it was found that higher protection ratios increase the amount of released resist outgassing upon EUV exposure. The dissolution rate analysis of presently available high performance EUV resist Selete standard resist 2 (SSR2) was also performed. Based on these results, a high slope and dissolution contrast value of the SSR2 correlated with its improved resolution capability at the 26 nm hp L/S.
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64.75.Bc Solubility

Improvement in linewidth roughness by postprocessing

Manish Chandhok, Kent Frasure, E. Steve Putna, Todd R. Younkin, Willy Rachmady, Uday Shah, and Wang Yueh

J. Vac. Sci. Technol. B 26, 2265 (2008); http://dx.doi.org/10.1116/1.3013860 (6 pages) | Cited 11 times

Online Publication Date: 1 December 2008

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In order to meet the linewidth roughness (LWR) requirements for the 16 nm node, postprocessing methods need to be investigated to reduce the LWR after the lithography step. We present the results of five different techniques applied to a single extreme ultraviolet photoresist. The results show that rinse has the most promise in achieving the nearly two time LWR improvement needed. However, other techniques such as etch/trim, hardbake, vapor smoothing, and ozonation give at least 10%–20% LWR reduction and could be further optimized. Some of the physical based techniques which melt the photoresist reduce the midspatial frequency (50–10 nm period) roughness, whereas chemical based techniques reduce the low order spatial frequencies ( ∼ 500–50 nm period). Hence, a combination of techniques may be the ultimate solution.
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85.40.Hp Lithography, masks and pattern transfer

Epoxy silsesquioxane resists for UV nanoimprint lithography

J. De Girolamo, M. Chouiki, J.-H. Tortai, C. Sourd, S. Derrough, M. Zelsmann, and J. Boussey

J. Vac. Sci. Technol. B 26, 2271 (2008); http://dx.doi.org/10.1116/1.2998709 (5 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Photopolymerizable epoxy polyhedral oligomeric silsesquioxane monomers with variable aliphatic spacer have been prepared and cured under UV radiation. Due to their organic/inorganic composition, these materials are promising candidates for microelectronic applications which requires high thermal and mechanical stabilities as well as a low dielectric constant, for example, for the fabrication of electrical interconnects. The authors pointed out by ellipsometric measurements that the use of a sensitizer in addition to the photoinitiator enhances the kinetic of the cationic polymerization of epoxy groups. The polymerization performed either in an EVG770® nanoimprint lithography stepper or under normal atmospheric conditions has been investigated by infrared spectroscopy, delivering information concerning polymerization mechanisms and allowing the optimization of the resin composition. Thermogravimetric analyses have shown that an annealing step is necessary after the UV curing of the resin to eliminate inert residues of the photoinitiator dissociation and thus improving the thermal resistance of the polymer. Finally they have demonstrated that the obtained polymers form interpenetrated networks and that their mechanical properties are retained up to a temperature of 375 °C.
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81.16.Nd Micro- and nanolithography
82.35.Lr Physical properties of polymers
77.22.Ch Permittivity (dielectric function)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Understanding the effects of photoacid distribution homogeneity and diffusivity on critical dimension control and line edge roughness in chemically amplified resists

Cheng-Tsung Lee, Richard A. Lawson, and Clifford L. Henderson

J. Vac. Sci. Technol. B 26, 2276 (2008); http://dx.doi.org/10.1116/1.2976601 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Resist critical dimension (CD) control and line edge roughness (LER) reduction has been one of the most challenging issues for sub-100 nm feature patterning in integrated circuit manufacturing. Among those factors dominating CD and LER, photoacid distribution homogeneity and diffusivity are major elements which are correlated to resist material design and have a direct impact on the lithography performance. In this work, a mesoscale stochastic model has been applied to investigate the joint effect of photoacid distribution homogeneity and diffusivity on resist lithography performance. Simulation results suggest that the high photoacid generator (PAG) loading and low photoacid diffusivity provided by polymer bound-PAG resist systems can provide superior lithography performance as compared to traditional blended-PAG resists, which is in good agreement with our previous experimental characterization of polymer bound-PAG resists. The results also suggest that resist image blur is proportional to the square root of the product of photoacid concentration generated at the line edge and the photoacid diffusion coefficient. LER was observed to be proportional to the product of the standard deviation of the extent of deprotection along the nominal line edge and the reciprocal of the gradient of the deprotection profile along the resist line edge.
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85.40.Hp Lithography, masks and pattern transfer

Contributions of resist polymers to innate material roughness

Theodore H. Fedynyshyn, David K. Astolfi, Russell B. Goodman, Susan Cann, and Jeanette Roberts

J. Vac. Sci. Technol. B 26, 2281 (2008); http://dx.doi.org/10.1116/1.2993259 (9 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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The authors have extended the atomic force microscopy-based technique to measure intrinsic material roughness after base development to evaluate a number of different polymer types in resist formulations. These polymers include environmentally stable chemical amplified photoresist type copolymers and terpolymers, methacrylate polymers, and fluoropolymers. The surface roughness of resists containing these polymers was measured along with the clearing dose with both extreme ultraviolet (EUV) and deep ultraviolet (DUV) exposures. Selected resists containing a representative sampling of different lithographic polymers were imaged with both EUV and DUV exposures. It has been suggested by many that there is a fundamental inverse relationship between resist sensitivity and LER that leads to a fundamental limit to resist performance. It was found that no simple relationship exists between intrinsic material roughness (IMR) and sensitivity and instead some other, more complex relationship between the material properties of the polymer and resist process that is determining both the IMR and sensitivity. It was also found that no simple relationship existed between resist sensitivity and LER. This suggests that resist performance is not innately limited by any fundamental law but is instead open to further improvements through the use of new materials or material combinations.
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68.35.bm Polymers, organics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.16.Nd Micro- and nanolithography

Optical characterization of a hydrogen silsesquioxane lithography process

A. Samarelli, D. S. Macintyre, M. J. Strain, R. M. De La Rue, M. Sorel, and S. Thoms

J. Vac. Sci. Technol. B 26, 2290 (2008); http://dx.doi.org/10.1116/1.2998694 (5 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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In this article the authors report on a new optical linewidth metrology method which uses measured changes in the resonant wavelength of fabricated ring resonator structures to establish the linewidth of waveguides. The technique has a precision of better than 0.5 nm for 500 nm linewidths and can be used for process control although it cannot be used with arbitrary optical structures. To demonstrate the technique they fabricated ring resonator structures on silicon on insulator substrates several times over a period of 70 days, using electron beam lithography with hydrogen silsesquioxane (HSQ) negative tone resist followed by dry etching. They show that waveguide width variations of less than 0.5 nm can consistently be achieved when the HSQ is diluted immediately prior to use but highly irreproducible results are soon obtained if a single dilution is prepared and used for an extended period.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Influence of base and photoacid generator on deprotection blur in extreme ultraviolet photoresists and some thoughts on shot noise

Christopher N. Anderson, Patrick P. Naulleau, Dimitra Niakoula, Elsayed Hassanein, Robert Brainard, Gregg Gallatin, and Kim Dean

J. Vac. Sci. Technol. B 26, 2295 (2008); http://dx.doi.org/10.1116/1.2968615 (5 pages) | Cited 4 times

Online Publication Date: 1 December 2008

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A contact-hole deprotection blur metric has been used to monitor the deprotection blur of an experimental open platform resist (EH27) as the wt % of base and photoacid generator (PAG) were varied. A six times increase in base wt % is shown to reduce the size of successfully patterned 1:1 line-space features from 52 to 39 nm without changing deprotection blur. Corresponding isolated line edge roughness is reduced from 6.9 to 4.1 nm. A two times increase in PAG wt % is shown to improve 1:1 line-space patterning from 47 to 40 nm without changing deprotection blur or isolated line edge roughness. A discussion of improved patterning performance as related to shot noise and deprotection blur concludes with a speculation that the spatial distribution of PAG molecules has been playing some role, perhaps a dominant one, in determining the uniformity of photogenerated acids in the resists that have been studied.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

The effect of thin metal overlayers on the electron beam exposure of polymethyl methacrylate

C. B. Samantaray and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2300 (2008); http://dx.doi.org/10.1116/1.3021397 (6 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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Here, the authors consider the effect of thin metal coatings on the contrast, clearing dose, and resolution of polymethyl methacrylate (PMMA) electron beam resist. They present processes suitable for deposition, exposure through, and removal of 5-nm-thick Al, Cr, and Cu layers. Contrast and clearing dose were determined by exposing large features and resolution was assessed using single pixel lines at beam energies from 2 to 30 keV. In all cases the presence of the metal layer increases the clearing dose. They obtained a minimum linewidth of 40 nm from the single pixel patterns. Both the experimental results and Monte Carlo simulations of the point spread function (PSF) support the feasibility of direct writing of sub-40-nm patterns despite of additional forward electron scattering. Applying thin metal coatings on resist provides an alternative to conductive polymers for charge reduction and an excellent foundation for fiducial grids used in spatial-phase locked electron beam lithography.
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85.40.Hp Lithography, masks and pattern transfer

The effects of molecular weight on the exposure characteristics of poly(methylmethacrylate) developed at low temperatures

M. Yan, S. Choi, K. R. V. Subramanian, and I. Adesida

J. Vac. Sci. Technol. B 26, 2306 (2008); http://dx.doi.org/10.1116/1.3002562 (5 pages) | Cited 11 times

Online Publication Date: 1 December 2008

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Poly(methylmethacrylate) (PMMA) with various molecular weights exposed using 50 keV electron beam have been investigated at subzero developer temperatures. Contrast curves for Methyl Isobutyl Ketone (MIBK):Isopropyl Alcohol (IPA) = 1:3 and MIBK:IPA = 1:7 developers were determined. The contrast curves for different molecular weight PMMA resists converge into a single curve at lower temperatures. At low temperatures, the line edge roughness and resolution improved. However, minimum line pitch shows no significant improvement while dose latitudes for a particular line pitch increased. It is shown that at low temperatures, linewidth resolution and periodicity are invariant for the different PMMA molecular weights (50 K to 2.2M) used in this work.
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61.41.+e Polymers, elastomers, and plastics
61.80.Fe Electron and positron radiation effects

Effect of microstructure on deprotection kinetics in photoresist

David S. Fryer, Vivek Singh, Srinivas B. Bollepalli, and Alex A. Granovsky

J. Vac. Sci. Technol. B 26, 2311 (2008); http://dx.doi.org/10.1116/1.2998700 (5 pages)

Online Publication Date: 1 December 2008

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This article describes the result of predictions based on a novel continuum model for the effect of microstructure on deprotection reaction kinetics during postexposure bake (PEB). The effect of neighboring blocking groups is incorporated in a continuum PEB model. Provided blocking groups with neighbors react at a slower rate than isolated blocking groups, an up to 8% improvement in latent image contrast is predicted. In addition, a first principles calculation of the equilibrium structure for poly(methyl methacrylate-co-t-butyl methyl methacrylate) copolymer with acid present is reported. Hybrid quantum mechanics/molecular mechanics (QC/MM) results indicate that a strong hydrogen bond forms between blocked and unblocked neighbor sites in the presence of acid. The QC/MM prediction provides evidence confirming the rate constant for deprotection reaction with a neighboring blocked site is reduced relative to isolated blocking groups. The new PEB model form is shown to improve the fit to kinetic Fourier transform infrared data over conventional deprotection kinetics for those resists that contain carboxyl group deprotection chemistry. The new model also explains the difference in reaction rate between resists with otherwise identical deprotection chemistry by altering only neighboring blocked site content. Finally, a 50% greater lithographic advantage in development rate contrast is demonstrated for microstructure with increased neighboring blocked sites.
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85.40.Hp Lithography, masks and pattern transfer
back to top Metrology, Alignment, and Inspection

Field-programmable gate array implementation of real-time spatial-phase locking for electron-beam lithography

Yugu Yang and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2316 (2008); http://dx.doi.org/10.1116/1.2991976 (6 pages) | Cited 1 time

Online Publication Date: 1 December 2008

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Spatial-phase locked electron-beam lithography provides feedback control of electron-beam position by monitoring the signal from a fiducial grid on the substrate. Formerly, a real-time spatial-phase-locking algorithm has been implemented on general purpose microprocessor to provide control for raster-scan system. However, it would be advantageous to provide real-time spatial-phase locking for both vector- and raster-scan systems with accelerated sampling and computational rate demanded by many modern electron-beam lithography tools. In addition, it is desirable for the phase-locking system to be easily parallelizable for multibeam/multicolumn systems. Implementation of vector- and raster-scan spatial-phase locking algorithms on a field-programmable gate array (FPGA) addresses both of these issues. Initial experimental results demonstrate that the FPGA implementation can provide real-time spatial-phase locking effectively at accelerated speed even when the algorithm is performed in the noise limited regime.
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84.30.Sk Pulse and digital circuits
42.60.Fc Modulation, tuning, and mode locking
42.82.Cr Fabrication techniques; lithography, pattern transfer

Abbe singular-value decomposition: Compact Abbe’s kernel generation for microlithography aerial image simulation using singular-value decomposition method

Charlie Chung Ping Chen, Ahmet Gurhanli, Tse-Yu Chiang, Jen-Jer Hong, and Lawrence S. Melvin

J. Vac. Sci. Technol. B 26, 2322 (2008); http://dx.doi.org/10.1116/1.3013310 (9 pages)

Online Publication Date: 1 December 2008

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Abbe’s method and Hopkin’s method are among the most popular microlithography aerial image simulation methods. In particular, Hopkin’s method is generally more popular for the high speed aerial image simulation domain, and it is used in model-based optical proximity correction. This is due to a general perception that Hopkin’s method can generate more compact sets of kernels compared with Abbe’s method, due to the application of a singular-value decomposition (SVD) process to Hopkin’s large transmission cross coefficient matrix. On the other hand, the primitive Abbe’s method is very simple, since it only needs to decompose the source field into independent point sources with a two-dimensional partitioning criteria. Albeit its simplicity, compared with Hopkin’s method, in general, Abbe’s method, generates a larger set of kernels. In this article the authors propose applying SVD to the original Abbe’s kernels, the essential kernels according to their singular values. Experimental results show that the algorithm, the Abbe-SVD method, accomplishes over 68 times of both runtime and memory saving over the traditional Hopkin’s SVD method for kernel generation.
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85.40.Hp Lithography, masks and pattern transfer

Aberration correction for electron beam inspection, metrology, and lithography

Eric Munro, John Rouse, Haoning Liu, and Liping Wang

J. Vac. Sci. Technol. B 26, 2331 (2008); http://dx.doi.org/10.1116/1.2991515 (6 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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This article investigates, with computer simulations, whether electron optical aberration correctors could be used to improve the performance of electron beam equipment for the semiconductor manufacturing industry. The simulations are performed using the differential algebraic method. Three types of aberration corrector are investigated: (1) a quadrupole-octopole corrector for critical dimension scanning electron microscopy for metrology and inspection (it is shown that this type of corrector, which corrects spherical and chromatic aberrations, can provide a smaller probe diameter with a larger numerical aperture, thereby improving resolving power and throughput), (2) a hexapole planator for projection electron beam lithography (it is demonstrated that field curvature, astigmatism, and spherical aberration can be corrected, thereby permitting a larger field size), and (3) a mirror corrector for reflective electron beam lithography (it is shown how field curvature and chromatic aberration in such systems can be corrected by using an electron mirror).
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41.85.Gy Chromatic and geometrical aberrations
41.75.Fr Electron and positron beams
85.40.Hp Lithography, masks and pattern transfer
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Study of machine to machine overlay error for sub-60-nm memory devices

Jangho Shin, Sihyeung Lee, Jeongho Yeo, Hochul Kim, Junghyeon Lee, and Woosung Han

J. Vac. Sci. Technol. B 26, 2337 (2008); http://dx.doi.org/10.1116/1.2998727 (4 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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According to the 2007 international technology roadmap for semiconductors, the overlay budget of 60 nm memory devices is 11.3 nm. To meet such a tight requirement, each overlay error budget should be controlled carefully. It turns out that scanner contributions due to machine to machine overlay (MMO) error are nearly half of the total overlay error budget. In a conventional way, overlay errors are corrected by ten linear terms: offset x and y, wafer rotation x and y, wafer magnification x and y, shot rotation x and y, and shot magnification x and y. Especially for the shot correction, average correction values are applied commonly for all shots. MMO cannot be compensated by only linear correction to meet such a tight specification any longer. In this article, a grid matching strategy through per-shot-correction (PSC) is investigated so that scanner contributions are minimized. In PSC, shot correction is implemented for each shot with different correction parameter values. By matching wafer grids from machine to machine, overlay budget is feasible for sub-60-nm memory devices.
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84.30.Sk Pulse and digital circuits

Nanometer-level alignment to a substrate-embedded coordinate system

Euclid E. Moon and Henry I. Smith

J. Vac. Sci. Technol. B 26, 2341 (2008); http://dx.doi.org/10.1116/1.3010734 (4 pages)

Online Publication Date: 1 December 2008

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The authors describe a method that uses infrared (IR) radiation to detect alignment on the nanometer level between grating marks on the front side of a template and a checkerboard-type mark on the back side of an IR-transparent, double-side-polished substrate. The mark can cover the entire substrate back side. No alignment marks are required on the front of the substrate. A back-side-specific mark is utilized with λ = 1065 nm illumination to detect alignment within σ = 0.4 nm.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Resist charging effect in photomask: Its impact on pattern placement error and critical dimension

Jin Choi, Dong Seok Nam, Byung Gook Kim, Sang-Gyun Woo, and Han Ku Cho

J. Vac. Sci. Technol. B 26, 2345 (2008); http://dx.doi.org/10.1116/1.2978406 (6 pages)

Online Publication Date: 1 December 2008

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By the development of the double exposure technique or the double patterning technique, the pattern placement error of a photomask is interesting because of its impact on the size and position of wafer pattern. Among various sources to induce the pattern placement error, we have focused on the charging effect of the FEP-171 resist and have shown that the resist charging effect generates the pattern position error of a clear pattern and the critical dimension variation of a dark pattern. Based on experiment and simulation, we present quantitatively the dependence of position error on pattern density, pattern shape, and writing order. Furthermore, we have discussed the model to describe the charging effect and its agreement with experiment and the correction method to remove the resist charging effect.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.16.Rf Micro- and nanoscale pattern formation

Self-assembled monolayer fiducial grids for spatial-phase-locked electron-beam lithography

C. B. Samantaray and J. T. Hastings

J. Vac. Sci. Technol. B 26, 2351 (2008); http://dx.doi.org/10.1116/1.2993261 (5 pages) | Cited 2 times

Online Publication Date: 1 December 2008

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The authors characterize a new fiducial grid based on a self-assembled monolayer (SAM) that is well suited to low-energy ( ⩽ 10 keV) spatial-phase locked electron-beam lithography (SPLEBL). SAMs significantly alter the secondary electron yield of the metal films on which they are formed. In addition, SAMs are not expected to strongly scatter the primary beam, even at low energies, because they are less than 2-nm-thick and are composed of low atomic number elements. In this work the authors evaluate the signal-to-noise ratio (SNR) of SAM grids on gold and copper coated electron-beam resist. 400 nm period octadecanethiol fiducial grids were microcontact printed onto the gold and copper metal layers using polydimethylsiloxane stamps. Gold serves as a model system and provides excellent SNR; however, its strong forward scattering makes it impractical in many applications. Copper offers reduced forward scattering but exhibits inverted secondary electron contrast and greatly reduced SNRs. In all cases, SNR decreases with increasing beam energy as overall secondary electron yield decreases. These results suggest that SAM fiducial grids are promising for low-energy SPLEBL; however, further optimization of the interlayer and SAM composition is warranted.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.55.J- Morphology of films
back to top Imaging/Microscopy

Development of the compact low-energy soft x-ray CT instrument for the soft material structural analysis

Motosuke Miyoshi, Takao Hamakubo, Tatsuhiko Kodama, Masatoshi Tsuchiya, Atsushi Koishikawa, and Nobutada Aoki

J. Vac. Sci. Technol. B 26, 2356 (2008); http://dx.doi.org/10.1116/1.2978397 (6 pages)

Online Publication Date: 1 December 2008

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Microtomography using the combination of microfocus x-ray source and the cone-beam technique is now becoming widely used in material science and in industry. Recently, the structural analysis of soft materials, such as polymer fibers and biological materials, is strongly required. A compact low-energy soft x-ray computed tomography (CT) instrument capable of soft material observation was developed, and the proof-of-concept system was constructed and evaluated. In this article, the authors describe an instrument that they developed for the x-ray CT of soft materials. A newly developed x-ray tube for generating the low-energy continuum soft x ray is also described. Tomographic observation examples of both biomaterials and industrial polymers are demonstrated.
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81.70.Tx Computed tomography