Electron Beam Column Research Articles

Miniaturized finger-size electron-beam column with ceramic-type lenses for scanning electron microscopy

A miniaturized electron-beam column has been developed for portable scanning electron microscope, which has greatly reduced size and weight compared with those of conventional electron-beam column, in order to satisfy the demands of new applications in surface analysis, inspection and metrology, electrical testing. For column miniaturization and high precision lens fabrication, we have constructed a ceramic lens integrated column system, in which all of the electro-optical elements are integrated in one ceramics body. In this trial production, we use a newly developed alumina-based high resistive conductive ceramics for the optimization of this electro-static lens operation. All the lens electrodes are metalized and patterned on the inner surface of the cylindrical high resistivity conductive ceramic whose volume resistivity is 1010Ωcm. As the ceramic lens integrated column used here integrates all the lens electrodes and manufactured in a consecutive process, the mechanical alignment error can be reduced, resulting in the concentricity of 0.7 μm, in whole column fabrication. The initial images demonstrate the basic operation of the ceramic lens integrated column system.

Low energy large scan field electron beam column for wafer inspection

A swing objective retarding immersion lens (SORIL) column for wafer inspection is designed and constructed based on SOIL concept. The column consists of a compound retarding electrostatic and magnetic immersion lens and five electrostatic deflectors. The retarding electrostatic and magnetic immersion lens has small spherical and chromatic aberration coefficients for low landing energy. All electrostatic deflectors have a cylindrical duodecapole structure. One deflector is accommodated between the polepiece of the magnetic lens and the specimen surface, and operated at high voltage to fulfill SOIL condition. An on-axis annular semiconductor detector with a small opening in the center is employed to collect signal electrons. The annular detector achieves high collection efficiency over a large scan field. Experimental results show that the SORIL column has accomplished a 600μm×600μm scan field with 0.1μm maximum spot size in a wide landing energy range (from 200to2000eV) without dynamic aberration correction or dynamic focusing. Resolution of 15nm is achieved in a 50μm×50μm scan field. The probe beam current delivered by the SORIL column is from a few nA to more than 100nA because of the specially designed bright electron gun. The SORIL column has been installed onto HMI’s electron beam wafer inspection tool, eScan™ 300. The SORIL’s optical performances enable eScan™ 300 to be a powerful electron beam wafer inspection and in-line process monitoring tool.

Writing strategy and electron-beam system with an arbitrarily shaped beam

The greatly increased complexity of modern masks has in turn led to increased write times and cost of the masks. Any opportunity to decrease write time while providing the required accuracy of the fabricated pattern is highly beneficial. A writing strategy using an arbitrarily shaped beam (ASB) results in a considerably smaller number of flashes to write a complex pattern compared to other strategies. The design of an ASB system is proposed. The ASB electron-beam column is similar to that of a variable-shaped beam system, except for a modified beam-shaping block. This suggests the relatively easy integration of an ASB column. The throughput of an ASB system is higher than the throughput of other systems, except for patterns with low coverage or simple geometries. In addition to the throughput advantages, an ASB system enables higher accuracy, including the feasibility of writing features according to “ideal” optical proximity correction.

A Miniaturized Electron Beam Column Simulation by the Fast Moving Least Square Reproducing Kernel Point Collocation Method

A miniaturized electron beam column, microcolumn, operated at a low electron energy of 1–2 keV has been simulated by the fast moving least square reproducing kernel point collocation method (FCM) which is a new concept of point collocation calculations. The salient feature of the method here is the use of the dilation function instead of constant dilation parameter. The simulation results of FCM for microcolumn configuration show good agreement with previous calculation and experimental results. Typically, the electron beam column design has been simulated by the finite difference method (FDM) with the grid and finite element method (FEM) based on mesh generation. However, The FCM method dilation function can readily calculate high-aspect-ratio structures employing only nodes instead of grid or mesh generation. The accuracy of this method will be proved through careful analysis of the error between numerical and analytic solutions. The full microcolumn structure consisting of electron emitter, source lens, and Einzel lens parts can be readily calculated by FCM. We will discuss the basic concept of FCM and its applications in this paper.

Prototype raster multibeam lithography tool

A prototype raster multibeam lithography tool was constructed and is being evaluated for use as a mask writer at the 50 nm node. The photocathode illumination module (PIM) focuses a linear brush of 32 individually modulated laser beams into 300 nm full width at half maximum spots on the surface of a photocathode. The PIM has been module tested with satisfactory results and integrated into the prototype tool. A new electron-beam photocathode gun and column have also been integrated into the tool. The tool has generated a linear array of 32 electron beams which have been magnified and focused onto a YAG screen as well as demagnified and scanned across a knife edge. Preliminary results have produced 86 nm spots at the writing plane.

High-Density Recording Using an Electron Beam Recorder

A high-density optical disk fabricated using electron beam mastering exhibited excellent performance. Read-only disks with the recording capacity of 25 to 30 GB were fabricated by electron beam mastering and their jitter values were evaluated by a blue laser read out system. As a result, very low jitter values of 5.4, 6.2 and 7.7% were obtained for the disks whose capacity was 25, 27.5 and 30 GB, respectively. Characteristics of the disks such as track pitch variation, track roundness and recording stability are also shown. The electron beam recorder used in the experiments is described. In particular, details of the electron beam column, properties of the beam, how to adjust and evaluate the beam and a beam blanker are presented. Finally, several problems are addressed.

PREVAIL Alpha system: Status and design considerations

An overview is given of the PREVAIL Alpha system program, a joint project of IBM and Nikon to develop a production-level electron project lithography system. The Alpha system program is based on the successful completion of an initial feasibility phase conducted by the IBM/Nikon alliance team and on the PREVAIL proof of concept results reported at EIPBN 1999. The electron beam column and associated electronics and software are under development at IBM’s Semiconductor R&D Center in East Fishkill, New York, while the high speed, high precision stages for both reticle and wafer as well as the overall systems architecture are being developed at Nikon’s facilities. A key architectural objective is the combination of leading edge stepper technology with state-of-the-art PREVAIL electron optics. The design of the electron optics is based on carefully balancing geometric aberrations and Coulomb interactions for optimum resolution at the required high beam current. Cornerstones of the design are the high emittance gun and the curvilinear variable axis lens concept developed for PREVAIL. Design considerations of the Alpha column are emphasized including a detailed treatment of space-charge lens aberrations.

Electron optical image correction subsystem in electron beam projection lithography

To obtain ultimate image fidelity in the PREVAIL electron beam projection lithography system (EB stepper) [Pfeiffer et al., J. Vac. Sci. Technol. B 17, 2840 (1999)], precise dynamic corrections [Zhu et al., Proc. SPIE 2522, 66 (1995)] of an exposed reticle subfield image on the wafer are required. The electron beam column for the EB stepper covers a large deflection area by a curvilinear variable axis lens (CVAL) [Stickel and Langner, J. Vac. Sci. Technol. B 17, 2847 (1999)] type deflection with high current, and very large 0.25 mm square beam. Because of these features together with tighter specifications for electron optics in below 70 nm node, aberrations which can be negligible in prior art electron beam lithography systems, can no longer be ignored. Therefore the electron optical image correction subsystem in the EB stepper is required to precisely correct the increased numbers of possible measurable aberrations caused by deflection as well as by space charge effects. In this article, a systematic overview of beam corrections is described.

Precision TEM Specimen Preparation for Integrated Circuits using Dual-Beam FIB Lift-Out Technique

Abstract Focused ion beam lift-out technique has become increasingly attractive to the TEM community due to its unique advantage of no mechanical grinding/polishing involved in the process [1-3]. The technique essentially consists of two parts: preparation of membrane using focused ion beam (FIB) and transfer of the membrane (lift-out) to a grid. Up to date, this technique has only been demonstrated on single beam FIB systems. From a practical standpoint, overall sample quality (thickness) and lack of end-point precision are two major issues associated with the conventional single beam FIB technique. These issues are primarily related to ion beam damage and endpoint control encountered during the final stages of specimen thinning. As a result, the widespread use of FIB lift-out technique for high precision TEM specimen preparation has been limited. Recent technological advances have made it possible to combine both an electron beam column and an ion beam column into an integrated dual beam-focused ion beam (DB-FIB) system.

Experimental evaluation of arrayed microcolumn lithography

Arrays of miniature electron-beam (e-beam) columns (microcolumns) show promise for high-performance e-beam lithography in the 70 nm and below generations for both maskmaking and direct-write applications. In addition to their demonstrated high resolution, high-throughput operation is obtainable with parallel operation of microcolumns (one or more per chip) and a continuously moving stage. Proof-of-concept arrayed microcolumn operation has been demonstrated. Preliminary 1 keV lithography experiments were conducted using new, first-generation microcolumns with micromachined blankers and a raster-scan multichannel pattern generator. Complex patterns have been generated and written in PMMA with resolution <75 nm.

A Study of Loading Effect during Electron-Beam Exposure and Etching Process in Photomask Fabrication

As the requirements of critical dimension (CD) uniformity on photomasks continue to tighten with advanced logic and memory devices, the dry etching process should be adopted to meet the needs of the optical proximity effect correction (OPC) and reduced bias process [W. T. Chen and M. Kamma: Proc. SPIE 3412 (1998) 149.]. There are severe CD variations in the dry etching process due to chrome (Cr) pattern density with various clear and dark fields. Through experiments, on the CD variation was investigated in the wet etching process, as well as in the dry etching process. This work focused on the tracing-determining the actual cause of the loading effect. It was revealed that what accounts for a major portion of the loading effect is not the Cr dry etching process, but the rescattering of electrons of the electron-beam exposure system. Rescattered electrons in this article refers to electrons that are reflected between the specimen and the lower parts of the electron-beam column and expose the unexposed area. In this paper, the existence of rescattered electrons was experimentally confirmed with a 10 kV acceleration-voltage system and the CD variation by reflected electrons was also investigated.

Electron microscopy and nanolithography with an integrated low-energy electron beam

We present nanolithographic lines written with a low-energy (300 eV) electron optical system integrated in a microfabricated planar lens. The system is a versatile tool to operate: the lens reaches a resolution of 30 nm in electron microscopy mode, and in lithography mode the written pattern demonstrates a linewidth of less than 100 nm. Successful writing into polymethyl methacrylate and into sensitive chemically amplified resist has been performed. The generalization and advantages of the integrated microlens for high-throughput multibeam lithography is also discussed in comparison with standard electron-beam columns.

Direct-write Electron Beam Lithography: History and State of the Art

AbstractDirect-write electron beam lithography is a patterning technique that has rapidly evolved over the last 40 years. For many years it has been possible to use electrons to pattern lines with widths as narrow as 10 rum. Recent advances in resist materials, electron sources, and system integration have further enhanced the capabilities. High-sensitivity resists provide substantial increases in the throughput without sacrificing resolution. Thermal field-emission sources improve the stability and reduce the minimum attainable spot size. Modem lithography systems integrate the electron beam column with advanced control electronics, making a system capable of nanometer-scale placement accuracy. In addition to these improvements, the technology is more accessible now than ever before, thanks to the proliferation of lithography systems consisting of modified scanning electron microscopes.

Distributed, multiple variable shaped electron beam column for high throughput maskless lithography

The ultimate resolution obtainable with focused electron beams is, for practical purposes in lithography, unlimited. Existing e-beam lithography systems are too slow to be practical for high volume manufacturing of semiconductor devices, however. The usable current in probe forming systems is limited by the stochastic Coulomb interaction in the beam path, which causes loss of resolution at high current. This is due to the need to pass all of the writing current through an aperture. Distributed systems, by contrast, do not suffer from this problem, as the current is spread over a large volume. The purpose of this article is to propose a distributed system, employing multiple, variable shaped beams for direct write (maskless) lithography. We call this system DiVa, to emphasize the key attributes of distributed writing current, and variable beam shaping. It utilizes a planar cathode, patterned with a rectilinear array of square emitters. Focusing is accomplished by a uniform, axial magnetic field, oriented along the optic axis. This transfers a one-to-one image of the emitters onto the writing surface. Deflection plates between adjacent rows of beamlets effect motion in one Cartesian axis, while mechanical translation of the stage effects motion in the orthogonal axis. Theoretical resolution is diffraction limited to 4.6 nm at 50 kV. Experimental results are presented which demonstrate the first order optics using a rudimentary apparatus.

Tolerancing of electron beam lithography columns

A new software package has been developed for the tolerancing of complete electron and ion beam columns. The software computes the asymmetry aberrations caused by small mechanical imperfections in the construction and alignment of the lenses and deflectors. The imperfections considered include misalignments, tilts and ellipticities of individual polepieces, electrodes, coil windings and deflection plates. The asymmetry fields due to these mechanical errors are computed by perturbation methods, and the resulting parasitic aberrations are evaluated with asymmetry aberration integrals. The effects of aberration correction elements, such as alignment coils and stigmators, are also handled by the software. The overall effects of the aberrations can be displayed graphically. Illustrative results are presented for nanolithography and high-throughput lithography systems.

Miniature electron beam column with a silicon micro field emitter

Silicon micro field emitters (Si-MFEs) are expected to be promising as electron sources for their high brightness and ease in making arrayed microcolumns due to small physical size. We have developed a Si-MFE electron gun assembly that produces an electron beam of 1 keV. All components including the Si acceleration electrode are mounted on an integrated circuit (IC) package stem (TO-8) by anodic and eutectic bonding. A high brightness (75 μA/sr) and a long lifetime (&amp;gt;1000 h) have been observed. To overcome the intrinsic emission instability of Si-MFEs, we developed a simple feedback circuit which controls an extraction voltage. The source position shift and the aberration coefficient change caused by stabilization were evaluated analytically and found to be negligible due to the scaling law as applied to micron size. We confirmed that the total emission fluctuation could be stabilized to less than 1% by detecting the absorption current but also found that this detection should be done in the electron beam column to stabilize the probe current due to the instability of the emission angle. Using the Si-MFE electron gun along with a miniature electron beam column 5 cm in length, we evaluated the electron optical properties and succeeded in demonstrating a scanning electron microscope operation with a resolution less than 0.5 μm.

Electron and ion optical design software for integrated circuit manufacturing equipment

This article describes methods for the computer aided design of electron and ion beam columns for the integrated circuit (IC) manufacturing industry. The techniques described include computation of field distributions in electron lenses and deflectors, electron trajectories and aberrations, dynamic corrections, effects of discrete Coulomb interactions, design of electron guns, treatment of diffraction effects, optimization, and tolerancing of complete columns. These techniques are illustrated with examples relevant to the IC manufacturing industry, including systems for high-throughput electron beam lithography, nanolithography systems, and electron beam systems for inspection, metrology, and voltage testing.

Compact electrostatic lithography column for nanoscale exposure

This article introduces an all-electrostatic electron-beam column which uses conventional electrode assemblies, resulting in a system which is very much smaller than a magnetic lens column. Computer modeling of the electron-optical performance of the column has shown that the concept has promise as a lithography tool. Beam broadening due to electron–electron interactions and aberrations of the final accelerating lens are both small enough to give a resolution which matches that of present-day magnetic columns.

Characterization of MQW heterostructures with acoustooptical cathodoluminescence spectrometer

We report a development and application to SEM studies of semiconductors of a cathodoluminescence spectrometer based on acoustooptical filters, that has several advantages in comparison with commonly used spectrometers and can be directly placed on a SEM electron-beam column. Digital control and high transmission of the unit permit to measure spectra of cathodoluminescence emission of a solid solution of A 3B 5 semiconductors and to study an image of the nonradiative defects in a multi quantum well active layer of laser heterostructures. The results are discussed on the point of view of initial stages of growth of an InP layer on the surface of InGaAs layer during the MOCVD epitaxial growth of heterostructures.

Experimental evaluation of a 20×20 mm footprint microcolumn

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 (&amp;lt;1.5 W) Zr/O/W Schottky field emitter that provides a stable beam current with &amp;lt;1%/h current fluctuations. A custom designed, ultralow profile (0.8 mm high) annular microchannel plate (MCP) detector is fitted into the working distance, which can be varied between 1 and 5 mm, between the Einzel lens and the sample. The MCP provides a high gain, up to 3×104, detector for secondary and backscattered electron detection from solid samples. The beam is scanned over the sample using a prelens double octupole deflector for large field size, ≥100 μm, at low distortions and low deflection aberrations. Using a computer controlled digital pattern generator, patterns with less than 100 nm linewidth were exposed in polymethylmethacrylate resist and reactively ion etched into an underlying tungsten layer.