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We report a design methodology for creating high-performance photonic crystals with arbitrary geometric shapes. This design approach enables the inclusion of subwavelength shapes into the photonic crystal unit cell, synergistically combining metamaterials concepts with on-chip guided-wave photonics. Accordingly, we use the term “photonic metacrystal” to describe this class of photonic structures. Photonic metacrystals exploiting three different design freedoms are demonstrated experimentally. With these additional degrees of freedom in the design space, photonic metacrystals enable added control of light-matter interactions and hold the promise of significantly increasing temporal confinement in all-dielectric metamaterials.

Going beyond the limited design freedoms of traditional photonic crystals, we experimentally show how photonic metacrystals exploit the inclusion of subwavelength dielectric scatterers in the unit cell to deterministically modify k-space and real space profiles.

Dielectric cavities support record low mode volumes by incorporating subwavelength features into photonic crystal unit cells., The ability to highly localize light with strong electric field enhancement is critical for enabling higher-efficiency solar cells, light sources, and modulators. While deep-subwavelength modes can be realized with plasmonic resonators, large losses in these metal structures preclude most practical applications. We developed an alternative approach to achieving subwavelength localization of the electric and displacement fields that is not accompanied by inhibitive losses. We experimentally demonstrate a dielectric bowtie photonic crystal structure that supports mode volumes commensurate with plasmonic elements and quality factors that reveal ultralow losses. Our approach opens the door to the extremely strong light-matter interaction regime with, simultaneously incorporating both an ultralow mode volume and an ultrahigh quality factor, that had remained elusive in optical resonators.

We report the design and experimental characterization of deep subwavelength optical modes (V m ∼10−3 (λ/n si )3) in high quality factor dielectric photonic crystals (Q∼3 × 104). Our approach offers a low-loss alternative to metals for achieving extreme light concentration.

Magnetic recording areal densities using magnetoresistive (MR) head technology are increasing at annual rates in excess of 60% per year and in some applications as great as 100% per year. Today, the critical features of the thin-film head can be patterned with the same optical lithography techniques used by the semiconductor industry. However, with the assumption that areal density increases in magnetic recording are maintained, within the next rive years, thin-film head lithography requirements will exceed semiconductor roadmap projections. This paper describes the use of e-beam lithography as an alternative to optical lithography for the fabrication of critical features in the thin-film head. In particular, the unique geometry of the head structure, the low density of critical head features on the wafer, and the relatively low wafer volume requirements for thin-film heads allow e-beam lithography to become a viable manufacturing alternative for thin-film head fabrication. More important, e-beam lithography is ideally suited for producing thin-film head structures at a development level prior to the optimization of manufacturable optical processing.

The energy distributions of electron emission from a Schottky emitter have been studied at tip temperatures from 1450 to 1800 K and angular current densities from 0.1 to 240 μA/sr. We have observed broadening of the energy distribution, with increase of angular current density and decrease of tip temperature, from 0.4 to 1.32 eV resulting from electron tunneling and electron–electron interaction. Good agreement between the experimental results and predictions from Monte Carlo simulation of the emission process is observed.

We report sub-20 nm sacrificial nanochannels that enable stretching and translocating single DNA molecules. Sacrificial silicon nano-structures were etched with XeF2 to form nanochannels. Translocations of linearized DNA single molecules were imaged by fluorescence microscopy. Our method offers a manufacturable wafer-scale approach for CMOS-compatible bio-chip platform.

CMOS device patterning for aggressively scaled pitches (smaller than 80nm pitch) faces many challenges. Maybe one of the most crucial issues during device formation is the pattern transfer from a soft mask (carbon based) material into a hard mask material. A very characteristic phenomenon is that mechanical failure of the soft material may be observed. While this was observed first for patterning below 80nm pitch, it becomes increasingly important for even smaller pitches (≤ 40 nm). Further process optimization by various pre- and post-treatments has enabled robust pattern transfer down to 40nm pitch. A systematic study of the parameters impacting this phenomenon will be shown. Other challenges for patterning devices include profile control and material loss during gate stack patterning and spacer formation. Lastly, initial patterning experiments at an even more aggressive pitch show that the mechanical failure previously observed for larger pitches once again becomes an increasingly important issue to consider.

We present an aggressively scaled trigate device architecture with undoped channels, high-k gate dielectric, a single work function metal gate and novel BEOL processing yielding 6T SRAM bit cells as small as 0.06 µm2. This is the smallest SRAM cell demonstrated to date and represents the first time an SRAM based on a multi-gate FET (MUGFET) architecture has surpassed SRAM density scaling demonstrated with planar devices [1].

Highly scaled FinFET SRAM cells, of area down to 0.128 m2, were fabricated using high-kappa dielectric and a single metal gate to demonstrate cell size scalability and to investigate Vt variability for the 32 nm node and beyond. A single-sided ion implantation (I/I) scheme was proposed to reduce Vt variation of Fin-FETs in a SRAM cell, where resist shadowing is a great issue. In the 0.187 m2 cell, at Vd = 0.6 V, a static noise margin (SNM) of 95 mV was obtained and stable read/write operations were verified from N-curve measurements. sigmaVt of transistors in 0.187 m2 cells was measured with and without channel doping and the result was summarized in the Pelgrom plot. With the 22 nm node design rule, FinFET SRAM cell layouts were compared against planar-FET SRAM cell layouts. An un-doped FinFET SRAM cell was simulated to have significant advantage in read/write margin over a planar-FET SRAM cell, which would have higher sigmaVt mainly caused by heavy doping into the channel region.

Summary form only given. Highly miniaturized electron beam columns based on a field emission source and microfabricated electron optical components have been developed. A 1 keV microcolumn operating with a miniaturized Zr/O/W Schottky emitter has been successfully evaluated for the first time. This paper will present the results obtained with the new microcolumn and discuss present efforts to further improve column performance with respect to resolution, beam current, and deflection field size.

Research on continued complementary metal–oxide–semiconductor (CMOS) scaling has sparked an interest in fabricating silicon-based devices with features in the sub-30 nm pitch regime. Electron beam lithography using hydrogen silsesquioxane (HSQ) resist processed with developers that contain ionic salts, e.g., Na+, has demonstrated a way to cleanly pattern features in the 20–30 nm pitch regime. Contamination concerns, however, have prevented the application of salty developed HSQ to silicon CMOS device integration in laboratories with stringent contamination controls. This paper details the results of a study aimed at understanding and reducing the residual contamination of salty developer to a level suitable for continued processing in a CMOS device research line. Data from total reflection x-ray fluorescence measurements shows that significant levels of Na+ as well as other unexpected metal contaminants remain on substrates after the develop process. Capacitance versus voltage measurements of capacitor st...

This paper discusses the resolution capabilities of proximity x-ray lithography (PXRL) system. Exposure characteristics of features designed at 150 nm pitch size: 75 nm dense lines with 1:1 duty ratio, 2D features at 1:1 and 1:2 duty ratios and isolated lines have been studied. Aerial image simulations were compared to the experimental data. Verification of the aerial image model has been accomplished by measurements of exposure windows of 100 nm and 125 nm nested lines. The PXRL aerial image parameter, equivalent penumbra blur, has been determined from the experimental data. Contributions from the synchrotron radiation x-ray source, stepper and the chemically amplified resist to the degradation of the aerial image have been evaluated. Patterning capability of PXRL at 75 nm feature size is compared to projection optics using the optical k1 factor as a common figure of merit. To facilitate the comparison, optical imagin was at pattern sizes currently manufacturable by the mainstream optical tools while the PXRL imaging was at 75 nm pattern size. Requirements for a PXRL system of manufacturing VLSI at 70 nm minimum feature sizes with the critical dimension control better than 10 percent are also discussed.

Due to the serial pattern data transfer in electron beam lithography (EBL), there is a larger spectrum of dynamic overlay errors as compared to projection optical or extreme ultraviolet lithography. A good EBL overlay mark needs to be of high resolution, i.e., small enough size to capture the details of temporally and spatially distributed overlay error variations across a semiconductor chip. A small, one critical dimension unit or about 10–50 nm size, dot exposed in successive lithography layers is the smallest size overlay mark. This overlay mark size allows for multiple marks to be placed across the chip to measure and analyze spatial variation of the overlay errors. If the single dot is replicated into a small matrix of dots, additional overlay error information can be obtained from local variations within the matrix. Analysis of the time-dependent variations of the local overlay errors in these dot-matrix marks is useful in determining the frequency of sources of overlay errors affecting the different lithography layers.

A fully functional electron beam microcolumn, 3.5 mm in length, demonstrating a probe size of 10 nm and beam current >= 1 nA at 1 keV has been successfully developed. This paper presents its current status and future directions. Potential applications ranging from low cost scanning electron microscopy to arrays of such microcolumns for lithography, metrology, testing etc. will be discussed.

The authors report on a hybrid lithography process that integrates electron beam lithography (EBL) and optical photolithography. To maximize resolution and density, the EBL exposure is performed using a hydrogen silsesquioxane-based resist, while the photolithographic exposure is performed using standard positive or negative tone 248nm photoresists. Both exposures take place on a common underlayer consisting of an antireflective coating (ARC). During pattern transfer into the ARC layer, a composite image of the two lithographic exposures is formed creating a robust and versatile etch mask for further pattern transfer into the substrate. They demonstrate the utility of this technique by using it to pattern the active, gate, and wiring levels of complementary metal oxide semiconductor devices and circuits consisting of trigated Fin-based field effect transistors. These devices have a minimum active area pitch of 50nm, minimum gate pitch of 90nm, and achieve densities suitable for 15nm node static random acc...

Shape locate mark registration, a novel image processing technique to accurately locate even damaged registration marks, has been used to resolve alignment challenges in aggressively scaled lithography levels for sub-32 nm complementary metal oxide semiconductor devices. The achievable overlay using traditional registration hardware and software is ultimately limited by the quality of the registration marks and any changes in the registration mark signals caused by device process steps between overlay critical exposure levels. This article discusses the details in the shape locate mark registration and results achieved for the device program. The shape locate mark registration system has been implemented and tested on a Vistec VB6 electron beam lithography tool. Mark locate repeatabilities of better than 5 nm (3σ) across 200 mm wafers and better than 10 nm overlay for device lithography have been demonstrated. Highly scaled 22 nm node fin field effect transistor (FinFET) static random access memory cells ...

The electron-beam forward scattering parameter α characterizes the width of the incident beam plus an additional radius due to scattering of primary electrons in the resist. These “forward scattering” effects can be included in proximity-effect correction algorithms by using the point-spread energy function generated by a Monte Carlo simulation. Alternatively, correction algorithms may use a superposition of Gaussian functions to fit Monte Carlo simulations or to fit experimental data. Long-range (β>10μm) effects due to electrons backscattered from the substrate are well characterized by simulations; however, forward scattering effects are difficult to model or measure. Experimental methods of measuring α include the exposure of dot arrays, line arrays, or so-called “doughnut” patterns over a large range of doses. Proximity parameters are then inferred indirectly through fitting line and dot widths. We have instead used a simpler and faster technique based on the method of [Dubonos et al., Microelectron. ...

Magnetic head fabrication for >100 Gbit/in.2 areal density requires minimum lithographic feature size

Experimental measurements of emission stability and energy distributions from a Schottky emitter have been conducted at a tip temperature range from 1330 to 1800 K. The changes of emission properties have been observed at reduced tip temperatures. Noise fluctuations of the probe current increase with decrease of the tip temperature at a constant extraction voltage. The work function of the Schottky emitter increases with decrease of tip temperature. The energy distribution measurements show that the energy width at a given temperature increases with increasing angular emission current density. The energy width also increases with decreasing tip temperature at a given angular emission current density. The results indicate that the energy broadening is mainly contributed by electron tunneling. A comparison of the measured energy width with the theoretical predictions is discussed.

Lithography with an array of miniaturized scanning electron‐beam columns presents one of the most promising high‐throughput possibilities for fabrication of devices with feature sizes less than 100 nm. With scanning electron beams no mask is required and the necessary resolution and alignment of overlay structures are realizable. With arrays of microcolumns, the lithography throughput of a single column can be multiplied. The approach can also be used for a number of lithography related applications such as metrology, inspection, testing, etc. We review the status of the microcolumn program and discuss opportunities and challenges of this approach to high‐throughput nanolithography and related applications. Special emphasis is given to lithography in the 100 nm regime.

A miniaturized 1 kV electron beam column with a 20×20 mm square footprint for application in arrayed lithography was developed. The actual beam forming optics measured from the electron emitter to the last electrode in the beam focusing Einzel lens is only 3.5 mm in length. The electron source is a miniaturized, high brightness (120 μA/sr), low heating power (

A miniature Schottky electron source has been developed and evaluated for applications in a new generation of scanning tunneling microscope aligned field emission microcolumns. Both the physical dimensions and the heating power of this source have been significantly reduced from a conventional source of the same kind. Operating parameters for such a source in a microcolumn environment in terms of emission characteristics, suppressor operating range, etc., have been evaluated. Test results show that very good emission stability at ≥100 μA emission current over several hours, and axial angular current densities in excess of 100 μA/sr can be obtained. Energy distributions have been measured using a carefully calibrated analyzer, and the results show a full width at half‐maximum of 0.4 to 0.76 eV for a 0.3 μm radius Schottky source operating over an angular current density range of 1 to over 100 μA/sr. A significant change in the shape of the energy distribution was observed over this range of operation, indi...

We have built and tested a 1 keV electron‐beam microcolumn that focuses 1 nA of beam current into a 10 nm full width half‐maximum beam diameter at a working distance of 1 mm. The electron source is a miniaturized Zr/O/W Schottky field emitter with 150 μA/sr angular emission current density operating at about 1800 K at a distance of only 100 μm from a silicon membrane extractor electrode. The actual microcolumn is 3.5 mm long assembled mainly from silicon membrane electrodes. Improved einzel lens design and fabrication allowed the operation of this beam focusing element in the accelerating mode. Spherical and chromatic aberrations were reduced by factors of about 2–3, respectively, as compared to the retarding lens mode. Excellent beam current stability with less than 1% variation over several hours has been observed.

A small, 2×2×1.1 cm (height), three‐axis micropositioner has been developed. It combines sub‐nm positioning capability with a large range of travel of more than 1 mm in each direction. Its applications range from scanning proximal probe instruments to sample stages for electron or light microscopes. Two shear piezos are provided in each direction to facilitate motion. They are located at opposite sides of a moving frame which is guided by V grooves on sapphire balls (or rods). A critical point in designing this kind of positioners is how to generate the ‘‘attachment’’ force that holds the parts of the positioner together. Gravity cannot be used as the stage needs to work in all orientations. Springs, connecting the two parts moving relative to each other, generate a force in the direction of the desired motion that is changing with position, making the stage motion nonlinear. Magnets are not appropriate when low‐energy electrons are involved in the vicinity. This problem is solved by especially designed leaf springs coupled to V grooves and balls (or rods). This design allows the attachment force to remain constant and orthogonal to the direction of motion when the stage moves, thus making the motion very linear and independent of the orientation of the positioner. The positioner is exceptionally compact and can be operated in ultrahigh vacuum. These properties make the positioner attractive for atomic scale resolution scanning proximal probe microscopes and a wide range of other applications.

Schottky emission tips have been evaluated with microlenses for applications in scanning tunneling microscope aligned field emission microcolumns. Operation of Zr/O/W 〈100〉 Schottky emission tips at 1800 K with an axial separation of 50–100 μm between the tip and a microlens has been successfully tested. The microlens consists of an extraction electrode with a 5‐μm‐diam hole in a 1‐μm‐thick silicon membrane. The preliminary results of this study show that thermal field emission tips can be operated continuously in close proximity to a microlens over a long period of time, and that good emission stability of less than 1% noise fluctuation over 10 h is achieved with emission currents up to at least 100 μA.

Electron sensitive resists have been exposed on optical masks in a variably shaped spot electron beam lithography system, EL3, at 25 and 50 kV and beam current densities up to 50 A/cm2 to evaluate the effects of resist heating during electron exposure. Resist heating effects are primarily observed in dense patterns at high electron exposure dose. For the purpose of comparison resist heating effects are quantified in terms of the development rate change that is caused by the temperature rise in the resist during electron beam exposure. From an energy density point of view the maximum temperature rise in the resist during exposure is very similar for both 25 and 50 kV exposures. The area on the mask over which the temperature rise in the resist can change resist properties is significantly larger at 50 kV: up to 20 μm at 50 kV compared to ∼5 μm at 25 kV. Using sensitive electron beam resists requiring 1–5 μC/cm2 exposure dose no resist heating effects are observed at beam current densities up to 50 A/cm2.

A new method for high-resolution imaging, near-field scanning optical microscopy (NSOM), has been developed. The concepts governing this method are discussed, and the technical challenges encountered in constructing a working NSOM instrument are described. Two distinct methods are presented for the fabrication of well-characterized, highly reproducible, subwavelength apertures. A sample one-dimensional scan is provided and compared to the scanning electron micrograph of a test pattern. From this comparison, a resolution of > 1,500 A (i.e., approximately lambda/3.6) is determined, which represents a significant step towards our eventual goal of 500 A resolution. Fluorescence has been observed through apertures smaller than 600 A and signal-to-noise calculations show that fluorescent imaging should be feasible. The application of such imaging is then discussed in reference to specific biological problems. The NSOM method employs nonionizing visible radiation and can be used in air or aqueous environments for nondestructive visualization of functioning biological systems with a resolution comparable to that of scanning electron microscopy.

We review the program at Cornell University aimed at investigation of the size limits of patterning material using high energy electron beams. Structures at the 1–10 nanometer size scale have been fabricated using subnanometer diameter 100 keV electron beams. Using electron beam defined masks, we demonstrate ion beam replication of structures less than 30nm in width. Finally, in situ fabrication of metal structures with walls vertical to 0.8nm is shown using electron beam modification of AlF 3 .

A new method for computing proximity effect corrections for submicron electron‐beam lithography is introduced. It is based on a fast algorithm for shape partitioning to gain better control for resultant exposure intensity distribution across each shape in the pattern. By careful investigation of the intrashape and the intershape proximity effects the program supplies a means of controlling the submicron pattern delineation. Values for the parameters of the double Gaussian function used in the calculation of the dose variation factors are given for a variety of exposure conditions. Results of the application of the program to delineation of submicrometer patterns in PMMA and AZ 1350 resist on silicon substrate are presented.

The ability to fabricate structures with lateral dimensions in the sub-100-nm range has opened a new field of research. This paper first reviews recent advances in nanolithography techniques, with a brief discussion of their relative merits and fundamental limits. Special emphasis is given to the scanning electron-beam method, which is the most widely used nanolithography method at the present time. The two main areas of nanostructure research are device technology and basic science. Highlights of a number of exploratory programs in these two areas are presented.

Nanometer scale metal wires have been fabricated in a modified scanning transmission electron microscope for electrical measurements using samples with contact pads that were prefabricated in a conventional electron beam lithography machine. Using liftoff processing, electrically conductive metal wires made from Ag, Cu, Au, Al, Ni, and CuTa with lateral dimensions of 10nm–20nm have been successfully fabricated between the contact pads. The wires range in thickness from 20nm–40nm to achieve a resistivity as low as possible.

This paper describes the high resolution electron beam system and the lithography processes developed for the fabrication of ultra high speed, sub-0.1μm silicon FET circuits and other projects where complex multi-level structures with highly accurate overlay are required. Noise sources and short term instability in the lithography tool have been reduced to less than 4nm peak-to-peak, while still accepting 125mm wafers. Devices and circuits have been fabricated with 70nm polysilicon gates and level-to-level overlay of typically 30nm over a 250μm field. The devices have yielded record transconductance results of more than 910mS/mm at 77 K, and have shown clear evidence of velocity overshoot. Device switching speeds of 13 picoseconds have been observed in ring oscillator circuits.

100‐keV e‐beam lithography and electroplating of gold have been used to fabricate a device for the measurement of quantum changes in magnetic flux. The structure is defined in a 200‐nm‐thick layer of a copolymer of methyl methacrylate and methacrylic acid (PMMA/MAA) on top of a Si wafer covered by 150 nm of Si3N4. The device is a square frame of 2×2 μm2 and 100‐nm linewidth. Gold was electroplated to a thickness of 100 nm. This technique allows the fabrication of high resolution, high aspect ratio gold structures.

AlF3 evaporated thin films of 20–80 nm thickness have been used as self‐developing positive resists and also as negative resists forming metallic Al structures. The exposure mechanism of AlF3 resist has been investigated, and nanometer scale features have been fabricated in both cases at exposure doses of about 20 C/cm2 and 2 C/cm2 at 100 keV, respectively. Using reactive ion etching, AlF3 resist patterns have been transferred into Si3N4, resulting in feature sizes as small as 20 nm.

A piezo‐actuated locking stage is described, which minimizes stage mechanical vibrations relative to the column in a nanometer electron beam lithography system capable of using large 5‐in. diameter substrates. The performance of the piezo locking stage is compared to the performance of a laser position servo system with a resolution of about 5 nm. The measurements show that mechanically locking the stage with respect to the objective lens is far more effective than the servo loop in suppressing mechanical vibrations. With the stage locked, total beam position noise with respect to the substrate has been measured as 2.5‐nm peak‐to‐peak compared to 10‐nm peak‐to‐peak total noise for the servo loop within a bandwidth of 0.25 to 200 Hz. A more detailed analysis of the beam position noise shows that the piezo locking stage reduces the noise component which is caused by mechanical vibrations to 0.4‐nm rms.

Field emitters offer a particularly high potential in e‐beam lithography when writing in the nanometer range. Using a modified VG Microscopes Ltd., model HB 501 STEM, a current of 0.1 nA can be focused into a diameter of 2.5 nm at 100 kV with a final beam aperture of 1.6 mrad. In order to fulfill the demands of microlithography, an objective lens of 15 mm nominal focal length is used. Stage travel in the system is 5 mm in the X and Y directions and the maximum scan field is 250×250 μm2. The beam is deflected electromagnetically under computer control and vector scanning is used during lithography. The 14 bit digital pattern generator has been electrically isolated by optocouplers from the host computer and is connected via analog differential buffers to the deflection amplifiers. The cold tungsten field emitter exhibits a linear decrease in current of about 20% within 20 min of continuous writing. The decrease in current is corrected during lithography by a feedback to the clock frequency of the digital p...

Factors affecting the ultimate resolution of ion beam lithography are discussed. These factors are primary ion scattering, recoil atom scattering, range of secondary electrons, and resist properties (i.e., resist sensitivity and molecule size in the resist). From a consideration of these factors, it is estimated that minimum linewidths of ≲10 nm can be achieved in polymethyl methacrylate (PMMA) using light ions. For heavy ions such as gallium, the resolution limit is estimated to be ∼30 nm with the limitation being due to recoil atom scattering. Fabrication of high resolution silicon nitride stencil masks is described and replication of the masks with protons in PMMA is demonstrated with features as small as 20 nm.

Thin films of metal fluorides such as AlF3, FeF2, CrF2, CsF, LaF3, BaF2, and SrF2 have been used as electron beam sensitive resists. When exposed in an ultrahigh vacuum system by a high intensity electron beam at line doses of 0.5 to 400 μC/cm at 100 keV on a thin membrane substrate, the films act as positive resists. At line doses of typically an order of magnitude less than in the case of the positive resist mode, the films also act as negative resists requiring the use of an appropriate developer. The exposure properties for these metal fluoride resists are discussed along with their film properties, sensitivity, and etching characteristics.

A technique for the measurement of the beam diameter and the positional stability of an electron beam with respect to the substrate using an anisotropically etched silicon edge is described. Measurements are done either in a scanning beam mode to measure the beam diameter or in a stationary beam mode to measure beam positional noise. This technique has been used for a quantitative analysis of the resolution and stability in a 8‐nm spot size electron beam lithography system. The detection limit of the beam position stability measurements is