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We report on the fabrication and characterization of planar superconductor‐normal‐superconductor (SNS) weak links in which the normal region is deposited n‐InAs. The InAs is part of a heterostructure consisting of 100 nm of n‐InAs grown on an undoped GaAs buffer layer on a semi‐insulating GaAs substrate. The superconductor is Nb, patterned by electron beam lithography with interelectrode spacings as small as 260 nm. Device behavior is well explained by SNS weak link theory, with coherence lengths calculated from measured material parameters. These heterostructure weak links can be the basis for superconducting field‐effect devices. They have the significant advantage of allowing simple device isolation compared with bulk InAs, which has been used in previous attempts to make such devices.

Transport properties are investigated in self-aligned NMOS devices with gate lengths down to 0.07 mu m. Velocity overshoot was observed in the form of the highest transconductances measured to date in Si FETs, as well as in the trend of the transconductance with gate length. The measured transconductance reached 910 mu S/ mu m at liquid-nitrogen temperature and 590 mu S/ mu m at room temperature. Velocity overshoot, by making such transconductances possible, should extend the value of miniaturization to dimensions that are smaller than what was commonly assumed to be worthwhile to pursue. >

Electron cyclotron resonance and radio frequency reactive ion etching have been used to fabricate narrow n+‐GaAs wires employing CCl2F2/He as the etch gas. A comparison of the induced sidewall damage is made using room‐temperature conductivity measurements of the etched structures and the effect of overetching is investigated. In addition, preliminary analysis of low‐temperature transport reveals that the amplitude of universal conductance fluctuations is extremely sensitive to sidewall damage.

We describe how the unique capabilities of molecular beam epitaxy together with the electron-beam lithography and reactive-ion etching can be utilized to realize novel quasi-one- and zero-dimensional electron systems. We also present the results of capacitive and tunneling studies on these quantum systems.

We have devised and demonstrated a novel technique for fabricating structures with nanometer scale features in semiconductor heterostructures. The technique is based on definition of nanometer scale patterns by submicron trenches in a GaAs‐AlGaAs heterostructure. The depletion of free carriers below the trenches gives rise to very strong electrostatic confinement. This technique avoids the complications associated with the use of negative resist materials and lift‐off techniques while minimizing the time required to expose densely packed patterns. Aharonov–Bohm rings fabricated using this technique exhibit interference oscillation larger than any reported previously.

A Fresnel zone plate lens, with a nominal outer zone width of 400 A, has been used to image nanostructures with soft x‐ray synchrotron radiation at 45 A wavelength with the Gottingen x‐ray microscope at BESSY in Berlin. The structures, consisting of gold lines in thin silicon nitride membranes, were selected for tests of spatial resolution and image forming capabilities. Several patterns associated with deep submicron electronic circuits were also imaged, showing clearly resolved features smaller than 0.1 μm. Images of periodic structures, including 600 A lines on 2000 A centers, suggest a spatial resolution approaching the theoretical limit of approximately 500 A.

Switching delay measurements are reported for self-aligned, almost fully scaled, liquid-nitrogen-temperature operation NMOS inverters with deep-submicrometer gate lengths. The shortest delay per stage of 13.1 ps was measured in 0.1- mu m gate-length circuits. Circuit simulations based on the measured device characteristics show that still shorter delay times can be reached with such a technology. >

It is very important to study variability of nanodevices because the inability to produce large amounts of identical nanostructures is eventually a bottleneck for any application. In fact variability is already a major concern for CMOS circuits. In this work we report on the variability of dozens of silicon single-electron transistors (SETs). At room temperature their variability is compared with the variability of the most advanced CMOS FET i.e. the ultra thin Silicon-on-Insulator Multiple gate FET (UT SOI MuGFET). We found that dopants diffused from Source –Drain into the edge of the undoped channel are the main source of variability. This emphasizes the role of extrinsic factors like the contact junctions for variability of any nanodevice.

The Stony Brook / NSLS scanning microscope started operation in 1983. It is based on the use of high resolution zone plates to create an x-ray microprobe; the specimen is then scanned through the spot by a piezoelectrically driven stage. Synchrotron radiation from the NSLS is used as the x-ray source, and the portion of the beam that is transmitted by the specimen and detected by a flow proportional counter has been used to form the image. The apparatus and results obtained with it during the first three years of operation have been published elsewhere [1,2,3,4]. Ref.4 also includes a historical review of other work in the field. Recent advances by other groups using scanning microscopes are presented elsewhere in this volume [5,6].

Electron Beam techniques, which have been applied for VLSI testing, are also useful for contactless testing of packaging modules. A test system has been developed to detect electrical opens and shorts in multilayer network wiring using specimens of 100 x 100 x 6mm in size. Various physical effects including charging, discharging, secondary electron emission and others allow a complete test to be performed. The contrast mechanism of the detected signal is based on the secondary electron yield vs. the beam potential and will be discussed in detail. Other signal mechanisms were also applied. By coordinating a pulsed electron beam in a vector mode to predetermined network terminals, computer controlled experiments were carried out. Results on the present status of this new testing approach will be presented.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have recently completed our first run [21.1] with the Stony Brook scanning microscope at the National Synchrotron Light Source (NSLS), using a Fresnel zone plate fabricated at IBM as the principal focusing element. The brightness of this synchrotron radiation source coupled with our high — resolution optics have made a substantial improvement in resolution and throughput compared with our earlier work [21.2,3] which lacked these features.

We report the ability of focused soft X-rays to visualize at spatial resolution well beyond that of the optical microscope (less than 100 nm) the interior of a small, whole biological object without fixation, staining, dehydration or sectioning. Quantitative estimation of its protein content with unique femtogram sensitivity is also reported. The present results represent a significant step towards the goals of natural imaging and chemical mapping of biological structures with soft X-rays.

Of the three main surface analysis techniques: SIMS (Secondary Ion Mass Spectrometry), XPS (X-ray Photoelectron Spectroscopy) and AES (electron induced Auger Electron Spectroscopy), both SIMS and AES have lateral resolution in the 50 nm range [1]. Yet only XPS makes use of the wealth of chemical shift information. Recent publications on radiation damage [2,3] estimated (considering only microscopic causes of the damage) that for the sanie lateral resolution and induced damage, XPS is one to two orders of magnitude more sensitive then AES. This is mainly due to the intrinsic difference in the signal/background ratio of the two techniques, which is 10 to 100 for XPS and 0.1 to 1 for AES. Taking into account macroscopic damage, such as local heating and charging, the advantages of XPS are even greater, particularly for polymers and other radiation sensitive materials. Experimental investigation is required, however, to fully assess the advantages of an XPS microscope over other techniques.

A high resolution Vector Scan electron beam lithography system for fabrication of structures with minimum dimensions below 100 nm is described. A selection was made from a variety of processes suitable for high resolution fabrication, in order to provide the desired properties of apodized Fresnel zone plates used in the Stony Brook X-ray scanning microscope. Experimental characterization of the zone plates with regard to resolution and efficiency in the microscope is described.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The biologist’s dream is to observe cellular structure and content by natural contrast mechanisms and, if possible, to observe variations as a natural consequence of cell function. While the x-ray microscope will not likely allow full satisfaction of this dream, it does offer new and exciting possibilities in this direction. In what follows we will consider the basis for this view both in general and by means of a specific example, the important and ubiquitous cellular process of secretion.

Nonlinear optical effects in plasmonic metal nanostructures are attracting widespread interest [1]. The plasmonic resonances of individual nanoparticles can be modified by constructing oligomers of several particles, allowing the collective (simultaneous) excitation of several particles or the modification of the resonances of the overall structure by the interaction between the individual particles [2, 3]. The collective effects can be accessed through near-or far-field methods by modifying the oligomeric configuration and by using illumination schemes that depart from traditional excitation geometries based, e.g., plane waves. Recently, linear optical response of oligomers has been tailored using beams that exhibit inhomogeneous polarization states, such as cylindrical vector beams (e.g., azimuthal and radial) [4, 5]. Here, we design plasmonic oligomers whose structure is matched to the distribution of local polarization of tightly-focused cylindrical vector beams and demonstrate their potential in tailoring second-harmonic generation (SHG) on the nanoscale.

A different approach in microcolumn design is presented, aiming at a large number of pixels at minimal probe size for the deflected beam. An optimization routine resulted in a seven times magnifying column featuring a more than 7×7 mm2 scan field at 40 mm working distance. Simulations for 1 keV electrons from a field emission source predict an increase in beam size from 85 nm on axis up to only about 200 nm for a beam deflected 3 mm off axis. Within a 1 mm scan field this microcolumn could address over 100 Mpixels of less than 100 nm in size. Tests of this design using the 130 nm electron probe of a scanning electron microscope as the electron source resulted in a beam size of ~930 nm on axis up to ~1000 nm for a beam deflected 3 mm off axis.

This paper describes techniques suitable for the fabrication of silicon field effect transistor (FET) circuits with gate lengths as small as 0.07 μm, intended for experiments to assess the feasibility of FET technology in the 0.1‐μm channel length regime. High‐resolution electron‐beam lithography using a vector scan system capable of an 8‐nm Gaussian spot size has been performed successfully for all levels, with various resist systems tailored to the specific processing requirements. Proximity correction has been found to be a critical issue and was performed using parameters derived from measured point exposure distributions. Metal liftoff using double‐layer poly(methyl methacrylate) resist has been performed successfully with complex patterns. Better than 0.1‐μm linewidth and 0.05‐μm alignment accuracy is achieved over a 250‐μm field, using tantalum silicide alignment marks.This paper describes techniques suitable for the fabrication of silicon field effect transistor (FET) circuits with gate lengths as small as 0.07 μm, intended for experiments to assess the feasibility of FET technology in the 0.1‐μm channel length regime. High‐resolution electron‐beam lithography using a vector scan system capable of an 8‐nm Gaussian spot size has been performed successfully for all levels, with various resist systems tailored to the specific processing requirements. Proximity correction has been found to be a critical issue and was performed using parameters derived from measured point exposure distributions. Metal liftoff using double‐layer poly(methyl methacrylate) resist has been performed successfully with complex patterns. Better than 0.1‐μm linewidth and 0.05‐μm alignment accuracy is achieved over a 250‐μm field, using tantalum silicide alignment marks.

Presently available electron‐beam lithography systems for submicron lithography have minimum beam sizes or edge resolution on the order of 0.1–0.2 μm. Satisfactory proximity correction, linewidth control, and profile quality are critically dependent on beam size. Moreover, variations in beam size about the expected size can result in severe degradation of linewidth control. In this paper, we will examine the relationships between linewidth control, beam size, and proximity correction and show that it is possible, but difficult, to successfully use electron‐beam lithography under these conditions. High resolution vector scan electron‐beam systems with known Gaussian beam sizes are used to produce features down to 0.25 μm in single and multilayer resist. It is shown that the beam size and forward scattering must be included in the proximity correction of submicron patterns. The effects of varying the beam size are also investigated and it is shown, for example, that an increase in beam size of only 0.02 μm can significantly reduce the developed resist linewidth of sub‐half‐micron features in 1.0 μm thick resist.

A finely focused electron beam is used as a source of energy to decompose molecules, e.g., organometallics or hydrocarbons, adsorbed on the surface of a substrate. Films deposited by these means can be used as etch mask for reactive ion etching, as an absorber for various types of radiation, or directly as part of a device structure. A vector scan electron beam system with a LaB6 cathode has been equipped with a temperature controlled reservoir to supply vapors into a differentially pumped sample chamber. The substrate is mounted on a stage which can be cooled or heated in the range of −40 to +110 °C. The ability to utilize backscattered electron micro‐ scopy is maintained. Area, line, and spot deposition rates have been measured for tungsten hexacarbonyl [W(CO)6] and dimethyl–gold–trifluoro–acetylacetonate [Me2Au(tfac)] at various fluxes, sample temperatures, and current densities. Three‐dimensional buildup of tips and free standing lines across holes in membranes and resolution better than 0.25 μm have ...

In this preliminary study we have used a modified scanning tunneling microscope (STM) to directly deposit metallic features as small as 10 nm by decomposing organometallic gases containing tungsten and gold. Dots as well as lines have been formed. Tungsen deposits analyzed by Auger electron spectroscopy contained 48% tungsten, 40% carbon, and 12% oxygen. A resistivity of 0.01 Ω/cm for the deposits was measured by aligning the STM to a metal contact pattern. This is the first reported combination of STM lithography with conventional lithography. A discussion of several interesting physical and chemical mechanisms involved in the deposition process is also presented.

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.

The fabrication of microstructures with minimum dimensions below 100 nm introduces several additional problems not normally associated with electron‐beam lithography at the 1/2 to 1 μm level. The quality of a 100 nm resist image, when defined by an electron beam pattern generator, depends strongly upon the exposure conditions such as beam energy and dose. Another important factor is the substrate, since it greatly influences the range and amount of backscattered electrons and, hence, the exposure contrast achievable in a given resist system. There is generally a big difference in energy deposited in the resist whether the exposure is performed on a thin membrane, on bulk silicon, or on a thick layer of a heavy metal, and also whether a single thin layer of resist or thick two or three‐layer systems are used. The characteristics of the resist and the development process itself are important aspects, too. In addition to controlling the resist image, one must also consider the properties and requirements of the subsequent transfer process to the working material such as lift‐off, plating, ion milling, and reactive ion etching. The specific process is often dictated by the materials and the geometry of the particular structure to be fabricated. So, as many of the conditions interact, it is impossible to define a single process that would be suitable for the wide range of applications that structures of this size are intended for. Using examples of x‐ray zone plates and FET gate definition, we discuss the merits of some of the processes used together with the techniques and problems associated with the evaluation of process performance at these dimensions.

Advances in nanolithography using electron‐beam techniques have allowed a great variety of quantum devices to be fabricated and tested. The critical dimensions governing the design of these devices will be discussed. Fabrication and experimental results of several such devices for studies will be reported. These include structures aiming at the observation of the electrostatic Aharonov–Bohm effect and nonlocal oscillations, superconducting weak links, and devices for the investigation of quantum scattering effects.

This paper demonstrates a submicron trenching technique for defining low‐dimensional electron systems in GaAs/GaAlAs heterostructures for transport measurements. A variety of electron systems can be defined between trenches as narrow as 200 nm etched into a suitable heterostructure. The use of narrow trenches gives the advantages of high resolution, simplicity, and flexibility, and also avoids the complications associated with negative resists and lift‐off techniques. Using the trenching technique, we have fabricated Aharonov–Bohm ring devices with a Schottky gate over the entire ring. At 0.4 K, these devices exhibit clear interference effects which are dependent on the gate bias.

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

The exposure distribution function in electron beam lithography, which is needed to perform proximity correction, is usually simulated by Monte Carlo techniques, assuming a Gaussian distribution of the primary beam. The resulting backscattered part of the exposure distribution is usually also fitted to a Gaussian term. In this paper we demonstrate a technique, using a very high contrast resist, whereby the normalized point exposure distribution can be measured experimentally, both on solid substrates which cause backscattering, and on thin substrates where backscattering is negligible. The data sets so obtained can be applied directly to proximity correction and represent the practical conditions met in pattern writing. Results are presented of the distributions obtained on silicon, gallium arsenide, and thin silicon nitride substrates at different beam energies. Significant deviations from the commonly assumed double Gaussian distributions are apparent. On GaAs substrates the backscatter distribution cannot adequately be described by a Gaussian function. Even on silicon a significant amount of exposure is found in the transition region between the two Gaussian terms. This deviation, which can be due to non‐Gaussian tails in the primary beam and to forward scattering in the resist, must be taken into account for accurate proximity correction in most submicron lithography, and certainly on the sub‐100 nm scale.

Specific issues related to achieving high device performance in extremely small channel length field effect transistor circuits are discussed. Ultrahigh resolution electron beam lithography is needed to obtain the ultrashort channels which are key for fast devices, and for the important gate area, double‐layer poly(methylmethacrylate) for lift‐off of a metal reactive ion etching mask has proven to be a suitable technique. Good level to level overlay and dimensional control in the contact process allow miniaturization of all device elements, in particular, reduction of the distance between source/drain contacts and optimization of the contact size and geometry. These are key factors in minimizing parasitic effects. The design considerations are discussed and the fabrication techniques are described which resulted in devices with a maximum measured transconductance of 910 mS/mm at 77 K for a 70‐nm gate device, exhibiting the clearest evidence so far for electron velocity overshoot, and unloaded ring oscilla...

The main contribution to the proximity effect in electron beam lithography on solid substrates results from electrons backscattered from the substrate. The range around the point of incidence of the primary beam over which these electrons affect the resist as well as their total number depends very much on the substrate material, in particular on the atomic number of the material. In the case of isolated lines it has been shown earlier that the resulting dose variation can be compensated for by modulating the incident dose in accordance with the backscattered electron signal detected during exposure. Shape‐to‐shape interaction in dense patterns is normally simulated numerically and corrected for on a pattern data level, and this simulation could, in principle, include variable substrate material compositions. The purpose of this paper is to show that a suitable combination of numerical dose compensation for constant substrate composition and real time feedback from the backscattered electron signal can yield significantly improved results compared to either correction alone.

Fresnel zone plates with minimum zone widths down to 50 nm were fabricated by electron‐beam lithography, tested, and used in the scanning x‐ray microscope at the Brookhaven National Synchrotron Light Source. The zone plates consist of gold rings on a silicon nitride window. Characterization of the zone plates included efficiency and resolution measurements in the first order focus. Spatial resolution down to 75 nm was measured. The best zone plates showed negligible astigmatism, and a first order efficiency in excess of 5% has been achieved. A new method for development monitoring during the fabrication procedure using an optical microscope with polarized light and crossed analyzer was introduced. For the inspection of the fabrication accuracy and, in particular, for ellipticity, a moire pattern technique was employed. Using these zone plates as objective lenses, x‐ray images of biological specimens were obtained with 70 nm resolution.