An electron beam lithography tool, which employs the SCALPEL technique, requires an extremely uniform beam to illuminate the scattering Mask, with the cathode operating in the temperature limited mode. It has been previously shown that LaB6 cathodes are not stable in this mode of operation. We have explored the possibility of implementing refined Tantalum-based emitters in the SCALPEL source cathode, and have developed large-area flat cathodes featuring suitably high emission uniformity under temperature limited operation.

An investigation is presented of the possibility to improve electron-beam uniformity of the SCALPEL system by imaging the angular distribution. First, some calculations are carried out which suggest that this angular distribution image should be corrected to enlarge the area of the beam that is uniform within the specifications. Then an optical system is introduced with which this could be done using spherical aberration, and computer simulation results are presented to illustrate the possibilities of such a system.

Novel beam monitoring methods for electron beam lithography systems were studied. In order to achieve high patterning accuracy, precise control of the beam position and of the beam exposure time is important. In conventional electron beam writing system, the written patterns are measured in order to evaluate the accuracy of the writing system. In this paper, two in-situ beam monitoring methods are proposed. One is the beam position monitoring method using a magnification lens and a microchannel plate (MCP) with a CCD camera. The beam image data projected on the MCP were observed using the prototype electron optical system. The beam position could be calculated by an image processing method. Also the simulation result of the conceptual in-situ beam monitoring system was shown. The other one is the beam blanking response measurement method using a fast MCP which has good pulse resolution and a fast response. The MCP output of pulse waveforms correlated with the beam blanking signal were observed with a good time resolution.

This paper investigates the accuracy of direct ray tracing on finite element solved potential distributions in charged particle optics. The results show that while the conventional approach of first-order element solutions on region block meshes gives inaccurate results, reliable results are produced by the use of second-order elements and structured mesh refinement. Direct rays are plot on a test objective lens to calculate third and fifth-order spherical aberration coefficients can be kept below 1%. For the direct ray tracing of secondary electrons, a single pole objective test example is used to demonstrate that field interpolation may limit the final accuracy, and that in this case, structured mesh refinement is the most effective means for improving the accuracy.

In computing the optical properties of electron and ion beam columns, the actual beam blur needs to be obtained from the computed aberration coefficients of the column and the beam parameters. A traditional method, which has successfully been used for many years, computes aberration disks for each individual aberration and obtains overall beam blur by adding these disks in quadrature. However, this method gives no information of beam current densities to compare with experimental measurements. A study of a new simulation method for analyzing pattern edge sharpness is described in this paper. The method involves the simulation of the point spread function ('PSF'), which can be proven to be equivalent to the pattern edge sharpness, provided that the PSF is smaller than the pattern feature. This method provides the current density distribution of the PSF and a quantitative assessment of the aberration, defined in terms of the rise distance of the PSF, in a through-focal series of planes, thereby enabling the best focus plane to be determined. An illustrative example is presented for a typical SCALPEL^TM column.

Spatial resolution of an optical system can be evaluated accurately taking into account of signal-to-noise ratio in terms of the information-passing capacity (IPC) of an optical system. In order to determine resolution of an optical system including effects of aberrations and source size, the IPC is approximated in terms of various analytical functions determined by numerically computed results of the IPC. This approximation method (the IPC method) allows to estimate resolution of an optical system under geometrical condition (wavelength equals 0) and diffraction limited condition (wavelength does not equal 0). The calculated resolution well represents the behavior of the actual SEM images obtained at various beam convergence half-angles using a field emission type in-lens SEM.

The SCALPEL e-beam lithography tool requires an extremely uniform e-beam to illuminate the Mask. To meet this requirement, the SCALPEL POL tool source cathode operates in the temperature limited mode. In this mode, all cathode irregularities are imaged at the Mask plane due to the high DOF of the gun immersion objective. We have studied the possibility of Mask illumination with a laminar e-beam having its virtual source located beyond the immersion objective DOF. In this case, using a positively biased Wehnelt, one can obtain a laminar e-beam that provides high emittance and low brightness illumination, while also yielding an efficient in- gun correction of beam properties.

Simulation software has been written to calculate the properties of electron guns which have flat cathodes and a fully three-dimensional electrode structure. Volumetric space charge effects are significant in such guns and a three- dimensional solution of Poisson's equation is required. This, in turn, requires a simulation of the cathode and its emission properties, a three-dimensional electrostatic potential calculation and a direct ray trace of charged particles through the gun. The motivation for this work was to have software tools to enable the analysis and design of flat cathode guns, for example, guns for cathode ray tubes (CRTs) and a suitable source for the SCALPEL projection lithography column. CRT guns usually have three cathodes and non-circular apertures in the electrodes. A proposed design for the SCALPEL gun has a large-area flat cathode with a fine grid parallel to the cathode and just in front of it. The techniques used in the software are presented and described and the capabilities of the software are illustrated by the analysis of some flat cathode guns.

The SCALPEL E-beam lithography tool requires an extremely uniform, high emittance E-beam to illuminate the Mask. The existing SCALPEL source utilizes a pure metal cathode operating in the temperature limited mode, thus having limited total emission current available. The usable emitter size of this cathode is constrained by its direct heating scheme, which sets an upper limit for the beam emittance. Furthermore, to generate a uniform beam, a conventional source should be designed to have a high cut-off voltage, which precludes an efficient electronic beam current control. We have studied the possibility of implementing a large area flat cathode and fine control grid mesh combination, potentially capable of providing high emission uniformity, high beam current and low beam control voltage.

Under e-beam irradiation of insulators the introduced electron charge is accumulated in the material. As a result an electric field appears and increases with time causing parasitic deflection of the beam and decrease of the energy of incident electrons. This general problem creates seemingly insuperable obstacles to the e-beam processing and electron microscopy of insulators. However the presented extended study of the physical processes accompanying electron irradiation of insulators has allowed to find the ways around this problem, especially of the case of e-beam engraving studied with full details.

A software package has been developed for simulating and designing multipole systems containing electrostatic round lenses, electrostatic and magnetic quadrupole, hexapole and octopole lenses, and Wien filters. Using our SOFEM and 3D packages, the field functions and their derivatives of these optical elements can be computed very accurately. This new software, using those field functions as input, computes and plots paraxial rays, primary and secondary aberrations for the analyzed systems. Computing paraxial rays, primary geometrical aberrations, primary and secondary chromatic aberrations is based on the formulae presented by Smith; while a set of newly derived formulae is employed to evaluate the secondary geometrical aberrations. Three examples are presented to illustrate the functionality of this software package.

Variable axis lens (VAL) system for magnetic round lenses can be achieved by using electrostatic deflectors (ME-VAL) instead of magnetic deflectors (MM-VAL). The condition for the ME-VAL is obtained from the paraxial ray equation rather than from axial focusing field expansions. The study shows that the ME- VAL also reduces the off-axis aberrations significantly, though not as much as its MM-VAL counterpart. A ME-VAL has been proposed for a magnetic objective lens using octopole deflector electrodes, in which the VAL condition is slightly mismatched. The results shows that the ME-VAL is less sensitive to mismatches in the VAL fields than the MM-VAL counterpart in terms of off-axis aberrations, and comparable performance can be obtainable if the advantages of electrostatic deflection can be fully exploited.

This paper presents Hall probe measurements on the recently proposed high resolution portable Scanning Electron Microscope (SEM) concept. A test column using permanent magnet lenses was constructed and has a height of 120 mm. Experimental axial flux density measurements were found to correlate well with simulation predictions. A method of varying the axial field strength by using magnetic shorting plates was investigated and found to be successful. In this way, the beam energy can be varied, and the portable permanent magnet column will be able to operate in a similar way to conventional SEMs.

The evaluation of the thermionic emission characteristics of a variety of cathode technologies that may have application in the SCALPEL (Scattering with Angular Limitation Projection Electron-beam Lithography) instrument, has been conducted in a modified Scanning Electron Microscope. The thermionic emission image of the source, projected along the column axis by the electrostatic immersion lens of the gun, is analyzed by scanning this image across the entrance aperture of the column by driving the normal alignment coils with the scan drive electronics. The technique may be referred to as Scanning Thermionic Emission Electron Microscopy (STEEM). With this technique, the projected image of the cathode, the cross- over(s) and the cathode surface itself may be imaged by adjusting the focal length of the double condenser lens of the SEM. Images of 0.84 mm diameter cathodes in various forms, including polycrystalline Ta, coated polycrystalline cathodes and single crystal Ta have been examined at a range of magnifications. In addition to operation of the gun with a single large diameter Wehnelt aperture (2.5 mm), cathodes have been studied when located behind a fine mesh in the Wehnelt aperture. Multiple cross-overs with associated beams overlapping further along the axis of the instrument are observed. Single crystal Ta cathodes have been shown to provide the extremely uniform emission in the temperature limited mode, that is required for the effective operation of the SCALPEL technique.

High resolution inspection and metrology is an important part of current semiconductor technology and has an increasingly active role as miniaturization is pushed beyond 200 nm. Current and future semiconductor design rules require not only high resolution CD control and inspection but also the ability to image high aspect ratio structures patterned on complex layers. This goal is usually achieved by using e-beam based tools that exploit voltage contrast to form images of deep structures; although useful, such images are not obviously and uniquely determined by their topographical counterpart since other parameters may significantly affect image appearance. In this paper we present a simulation approach that explains the imaging properties of charged surfaces under different conditions. This approach shows that in order to get a physical description of an e-beam image formation process, the surface must be considered as an electrostatic optical element with its own properties.

A novel mass spectrometer comprising a Matrix Assisted Laser Desorption/Ionization (MALDI) source, a Quadrupole Ion Trap (QIT) and a Reflectron Time of Flight (reToF) Mass Spectrometer (MS) has been developed. Computer simulations have been carried out to model different methods for efficiently introducing MALDI ions into the QIT and for subsequently extracting ions from the QIT to a dual-stage gridless reToF. The parameters for the system were optimized to get near 100% trapping efficiency and the highest mass resolution. A prototype instrument was built to realize the performance predicted from the computer simulations. Methods for the near orthogonal laser irradiation of a sample, fast switching of large amplitude Radio Frequency (RF) voltages and a gridless dual-stage reflectron were developed. These new developments were combined with a number of other already known techniques to provide the facility to perform high efficiency ion trapping and MS/MS and higher (MSⁿ) analysis. High mass spectra for m/z up to 16,000 have been obtained, and MS³ experiments have been successfully carried out. A sensitivity of 0.1 fmol has been achieved at a mass resolution exceeding 3,000.

A novel IPL technique called Maskless Micro-ion-beam Reduction lithography (MMRL) is being studied for future DRAMs and microprocessors manufacturing. In addition extendible minimum feature sizes to 50 nm or less, required of next generation lithography (NLG) candidates, this MMRL system can completely eliminate the first stage of the conventional IPL system that contains the complicated beam optics design in front of the stencil mask and the mask itself. Its main components consist of a multicusp RF plasma generator, a multi-beamlet extraction system, and an accelerator column for beam reduction. The viability of this MMRL system hinges upon the successful development of these components, most importantly the proposed all-electrostatic accelerator column. This paper describes the different components of the MMRL system and its ion optics. Computational results of beam demagnification and optics optimization are also presented along with design progress of the prototype MMRL system.

Focused ion beam (FIB) tools are widely used for scanning ion microscope (SIM) image observation and for ion milling in semiconductor and other industries. The demands for a higher resolution in SIM and for a more intensive beam in ion milling are increasing. Limiting in 2 lenses FIB optical system, we studied the influence of the first lens's properties, particularly magnification M₁ and extraction voltage V_ext, on the attainable beam diameter through an optimizing calculation. From this point of view, we investigated the attainable smallest beam size in the low current region by varying the parameters of the first lens, and found out that the lower extraction voltage has an advantage for getting a smaller beam. It is of big concern, as far as emission is possible, how much the extraction voltage can be minimized. It is related to M₁, and the change of V_ext between 5 and 12 kV produces the beam size variation of about 1 to approximately 1.5 nm. It is not negligible compared with the beam size of approximately 5 nm, which is attainable today. Therefore, we have a possibility to reduce the beam size by reviewing the first lens properties including V_ext. Finally, a guide line is shown for the FIB column design from this point of view.

A focused ion beam system using a multicusp plasma ion source and an all-electrostatic accelerator column design is being investigated for maskless direct-write lithography processes. The all-electrostatic accelerator column is very compact with a total length of 3 cm. It consists of an extraction lens, a collimator aperture, a focusing lens and a deflector. Ion beam transport code IGUN and charged particle optics design software (Munro's code) are used to analyze and optimize the performance of the accelerator column. The column can accelerate an 0.1 (mu) A O₂⁺ ion beam to about 1 keV and focus it down to 0.2 micrometer spot size. Both axial and deflection aberration of the beam are investigated using the OPTICS and SOFEM packages of Munro's code.

The charge-tube method is an accurate and efficient way of assigning the space-charge of a beam in computational simulations of charged particle systems. The method makes use of the trajectory steps that result from the process of trajectory integration. The space-charge associated with each step of each trajectory is assigned to a narrow cylindrical tube that surrounds the step. The total space-charge of a beam is then the sum of the charges in all the resulting the tubes. In systems of 2-dimensional axial symmetry the charge tubes become conical sheets of charge, and for some purposes these need to be given a finite thickness. The charge-tube method is particularly useful for simulating the space-charge of beams that are very narrow compared with their length. The implementation of the method is described and results obtained with it are compared with those obtained by the traditional charge-cell method.

Recently global space charge effects were found to seriously limit the performance of high throughput projection electron beam lithography systems. A fundamental analytical theory describing the global space charge lens has been developed using the variational principle. A modified paraxial ray equation and a set of aberration integrals is derived. All the space charge effects, including the defocus, the magnification variation, and the third order aberrations, are found to be proportional to the perveance, the weighted integrals of the normalized current density distribution, and a combination of the system parameters, such as: the field size and the convergence angle. A simple scaling law for the space charge aberrations, where the aberrations at the image edge scale linearly with the radial dimension, has been found for the telecentric projection configuration. Both the theoretical calculations and the Monte Carlo simulations have been done for a SCALPEL configuration with 25 (mu) A beam current and two scaled systems, whose radial dimensions are scaled from SCALPEL by twice and 3 times, and current by 4 times and 9 times respectively at 10 kV. From both theoretical and simulation results, the space charge aberrations at the edge show approximately a 63 times increase in the twice-scaled system, and about 95 times increase in the three-time-scaled system. All these aberration scaling factors are very close to those predicted from the simple scaling law. An experiment based on the simple scaling law was designed to verify the theory and evaluate the performance of the high throughput projection system. In the scaled testing column which has a 1.6 mA beam current, 5 kV beam voltage, 40 cm column length, 8 mm field diameter, and 4 mrad convergence angle at the mask, the space-charge-aberration blur to be measured will be as large as 200 micrometer. Then the final image blur of the real high throughput system can be derived by using the scaling law.

A new method is presented for simulating discrete Coulomb interaction effects in electron and ion beam columns. The method is applicable to the latest high-throughput electron and ion beam projection systems currently under development as possible candidates for next generation lithography. Monte Carlo simulation is used to trace bunches of several thousand particles simultaneously down the column. Compared with previous simulations, two key improvements have been made: (1) Instead of using thin lens approximations, the real fields of the magnetic and electrostatic lenses are used, which enables the lens properties and aberrations to be accurately included in the computation; (2) The N-body inter-particle Coulomb forces are computed with a hierarchical tree-code algorithm, which is orders of magnitude faster that the direct pair-wise force evaluation method used previously. The real lens fields are accurately computed with second-order finite element method ('SOFEM'), and the lens fields are then fitted with Fourier-Bessel series that accurately represent the real lens fields while simultaneously being exact solutions of Laplace's equation. The discrete inter-particle Coulomb fields, evaluated with the new tree-code algorithm, are then added to the external fields of the lenses. Trajectories through these combined fields are then computed by direct ray-tracing, using a fifth-order Runge-Kutta formula, to an internal self- consistency of better than 1 picometer. This method enables, for the first time, the combined effects of the discrete Coulomb interactions and the lens aberrations to be predicted accurately in a completely unified and self-consistent way. The method is illustrated for the case of a magnet doublet projection system. The method can equally well be applied to multi-beam columns, electrostatic lenses, cathode lenses and electron mirrors.

An adaptively refinable Fast Multipole library called Pbody has been developed and used to rigorously analyze statistical electron-electron interactions at high density field free regions in crossovers in electron beam lithography systems. The parallel algorithm and associated interaction decision regimes, communication and processor load balancing are portable to multiple processor networks supporting C and MPI. Beam blur effects at beam currents up to 30 (mu) A can be analyzed in a few hours. A basic imaging system with a crossover and no initial angular or energy spread was analyzed. At a given time step, electrons which experience a transverse force sufficient to influence the beam blur were first recorded. This set of electrons was then analyzed for the number of close neighbors and their relative contributions to the transverse statistical force. The data indicates that interactions with multiple rather than nearest neighbors almost immediately becomes the norm rather than the exception once the current reaches a level at which the average spacing between the electrons is about 48 micrometer.

Software for simulating 3D electric and magnetic fields followed by the direct ray tracing in individual field and combined fields (EO3D, MO3D and CO3D) are well applied to the design of energy filters attached to electron microscopes. When we had designed a high resolution EELS instrument, we had no 3D software, and encountered problems in designing a retarding Wien filter used as the monochromator and analyzer. At that time, electric field homogeneity inside the gap of magnet and the deflection of beam at the fringing region due to the deviation of the Wien condition were unsolved problems. When we designed a low energy reflection electron microscope (LEEM), we had 3D software, and some of the above problems were solved. We used an arc shaped electrode for the beam separator and an eight-pole filter for the analyzer. The coincidence of the magnetic and electric fringing field distributions at the fringing regions (Wien condition) was not perfect but was improved. We have designed an omega filter for in-column energy filtered transmission electron microscope (EFTEM). The omega filter consists of four sector magnets. Optical behavior of the system is very complicated. First, we designed the filter by 2D approximation and then checked by electron trajectories by the 3D software. The designed omega filter works successfully.

A new type of electrostatic electron energy analyzer is described that can acquire an electron energy spectrum in 'one shot.' It uses a hyperbolic field to focus electrons emitted from a solid in the energy range 50 eV to 2500 eV into a dispersive plane of about 50 mm length. An expression for the energy resolution is given and the effect of side and base plates on the behavior of the device is discussed. The main intended area of application for this type of analyzer is parallel data acquisition in Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The potential to acquire a spectrum is just a few seconds is possible with this device.

This paper presents the results of numerical investigations on electron trajectories in different 3D fringing fields of spherical defectors. We start with a chosen set of geometrical values for the electrodes such as radius of curvature, electrode gap, angle between entrance and exit face. We do a first numerical calculation of the spatial potential distribution using a 3D electron optics program based on the finite difference method (FDM). Ray tracing through this potential distribution is then performed using another program, which also gives the potential and the electric field strength along the curved beam path. In the next step we estimate the position and the geometry of the field clamp using Herzog's formulae assuming the entrance of a parallel plate condenser to be a good approximation for the entrance of the spherical deflector in first order. For the consecutive numerical recalculations of the real potential distribution of the spherical deflector with clamps we alter the position of the field clamp in beam direction under the constraint that the curved trajectory in the main field of an electron with defined energy will be the same as without fringing field. In our case the edges of the clamps are curved in the same way as the deflector electrodes are curved in the plane perpendicular to the curved optical axis. To check if the constraint is fulfilled we do a ray tracing from outside the field of the deflector through the fringing field into the main field and compare the trajectories of different setups with each other. For a considered example it can be shown that the best position of the clamps is approximately 9% further away from the entrance plane of the spherical deflector than calculated with Herzog's method.