Alfred A. Mondelli

The MICHELLE three-dimensional electron gun and collector modeling tool: theory and design

The development of a new three-dimensional electron gun and collector design tool is reported. This new simulation code has been designed to address the shortcomings of current beam optics simulation and modeling tools used for vacuum electron devices, ion sources, and charged-particle transport. The design tool specifically targets problem classes including gridded-guns, sheet-beam guns, multibeam devices, and anisotropic collectors, with a focus on improved physics models. The code includes both structured and unstructured grid systems for meshing flexibility. A new method for accurate particle tracking through the mesh is discussed. In the area of particle emission, new models for thermionic beam representation are included that support primary emission and secondary emission. Also discussed are new methods for temperature-limited and space-charge-limited (Childs law) emission, including the Longo-Vaughn formulation. A new secondary emission model is presented that captures true secondaries and the full range rediffused electrons. A description of the MICHELLE code is presented.

A review of ion projection lithography

Although optical lithography has been extended to far smaller dimensions than was predicted 15 years ago, there are definite physical barriers to extending it to the minimum dimensions of 70 nm that are projected to be required 15 years from now. Both focused, point electron beams and ion beams have been used to write dimensions in resist well below 20 nm, albeit at speeds far too slow for production lithography. Projection systems, which employ a mask and, in effect, produce a large array of beams, can provide both small minimum dimensions and high throughput. Ions are particularly well suited for this because they suffer little or no scattering in the resist, the linewidth is not a strong function of dose (good process latitude), and the resist sensitivity is relatively independent to resist thickness or ion energy. IMS in Vienna, Austria has built two generations of ion projection lithography systems which have demonstrated many of the features needed for high throughput lithography. In these systems a...

Advances in modeling and simulation of vacuum electronic devices

Recent advances in the modeling and simulation of vacuum electronic devices are reviewed. Design of these devices makes use of a variety of physical models and numerical code types. Progress in the development of these models and codes is outlined and illustrated with specific examples. The state of the art in device simulation is evolving to the point such that devices can be designed on the computer, thereby eliminating many trial and error fabrication and test steps. The role of numerical simulation in the design places can be expected to grow further in the future.

Programmable aperture plate for maskless high-throughput nanolithography

One of the most serious challenges to extending lithography (by whatever radiation) into the sub-100 nm regime is mask manufacturing technology. We propose and analyze a pattern writing concept somewhat like a dot matrix printer that can expose resist with 25 nm pixels at rates needed for production lithography. It consists of a programmable aperture plate which defines an array of 3000×3000, 5 μm×5 μm apertures on 20 μm centers which is illuminated by a collimated beam of either ions or electrons. Each aperture can be blanked off by suitable electrodes and is individually addressed. The image of the array is demagnified on the wafer by 200×. The pattern is entered into the array from one edge only and is toggled across the array by shift registers. The wafer is moved in synchronism. Each pixel on the wafer is exposed 750 times by 750 different pixels to accumulate the total dose. If ions are used (e.g., H+) and a total maximum current of 3 μA is passed down the ion optical column, consistent with space c...

Ion Projection Lithography

In spite of the comparatively modest level of effort devoted to ion projection lithography, the results obtained so far indicate that the technology is highly promising. Accordingly, a

Novel electrostatic column for ion projection lithography

36M program has been launched in Europe to develop a full field, IPL process tool.

A finite integration method for conformal, structured-grid, electromagnetic simulation

Ion projection lithography (IPL) is being considered for high volume sub‐0.25‐μm lithography. A novel ion‐optical column has been designed for exposing 20×20 mm2 fields at 3× reduction from stencil mask to wafer substrates. A diverging lens is realized by using the stencil mask as the first electrode of the ion‐optical column. The second and third electrode form an accelerating field lens. The aberrations of the first two lenses (diverging lens and field lens) are compensated by an asymmetric Einzel lens projecting an ion image of the stencil mask openings onto the wafer substrate with better than 2 mrad telecentricity. Less than 30 nm intrafield distortion was calculated within 20×20 mm2 exposure fields. The calculation uncertainty is estimated to be about 10 nm. The calculation holds for helium ions with ≊10 keV ion energy at the stencil mask and 150 keV ion energy at the wafer plane. A virtual ion source size of 10 μm has been assumed. The calculated chromatic aberrations are less than 60 nm, assuming ...

Applications of the ARGUS code in accelerator physics

We describe a numerical scheme for solving Maxwells equations in the frequency domain on a conformal, structured, non-orthogonal, multi-block mesh. By considering Maxwells equations in a volume parameterized by dimensionless curvilinear coordinates, we obtain a set of tensor equations that are a continuum analogue of common circuit equations, and that separate the metrical and metric-free parts of Maxwells equations and the material constitutive relations. We discretize these equations using a new formulation that treats the electric field and magnetic induction using simple basis-function representations to obtain a discrete form of Faradays law of induction, but that uses finite integral representations for the displacement current and magnetic field to obtain a discrete form of Amperes law, as in the finite integration technique [T. Weiland, A discretization method for the solution of Maxwells equations for six-component fields, Electron. Commun. (AE U) 31 (1977) 116; T. Weiland, Time domain electromagnetic field computation with finite difference methods, Int. J. Numer. Model: Electron. Netw. Dev. Field 9 (1996) 295-319]. We thereby derive new projection operators for the discrete tensor material equations and obtain a compact numerical scheme for the discrete differential operators. This scheme is shown to exhibit significantly reduced numerical dispersion when compared to the standard linear finite element method. We take advantage of the mesh structure on a block-by-block basis to implement these numerical operators efficiently, and achieve computational speed with modest memory requirements when compared to explicit sparse matrix storage. Using the Jacobi-Davidson [G.L.G. Sleijpen, H.A. van der Vorst, A Jacobi-Davidson iteration method for linear eigenvalue problems, SIAM J. Matrix Anal. Appl. 17 (2) (1996) 401-425; S.J. Cooke, B. Levush, Eigenmode solution of 2-D and 3-D electromagnetic cavities containing absorbing materials using the Jacobi-Davidson algorithm, J. Comput. Phys. 157 (1) (2000) 350-370] and quasi-minimal residual [R.W. Freund, N.M. Nachtigal, QMR: a quasi-minimal residual method for non-Hermitian linear systems, Numer. Math. 60 (1991) 315-339] iterative matrix solution algorithms, we solve the resulting discrete matrix eigenvalue equations and demonstrate the convergence characteristics of the algorithm. We validate the model for three-dimensional electromagnetic problems, both cavity eigenvalue solutions and a waveguide scattering matrix calculation.

Axial energy spread measurements of an accelerated positive ion beam

ARGUS is a three-dimensional, electromagnetic, particle-in-cell (PIC) simulation code that is being distributed to U.S. accelerator laboratories in collaboration between SAIC and the Los Alamos Accelerator Code Group. It uses a modular architecture that allows multiple physics modules to share common utilities for grid and structure input., memory management, disk I/O, and diagnostics, Physics modules are in place for electrostatic and electromagnetic field solutions., frequency-domain (eigenvalue) solutions, time- dependent PIC, and steady-state PIC simulations. All of the modules are implemented with a domain-decomposition architecture that allows large problems to be broken up into pieces that fit in core and that facilitates the adaptation of ARGUS for parallel processing ARGUS operates on either Cray or workstation platforms, and MOTIF-based user interface is available for X-windows terminals. Applications of ARGUS in accelerator physics and design are described in this paper.

Global and stochastic space‐charge effects in ion beam lithography

Abstract A multicusp ion source has been designed for use in ion projection lithography. Longitudinal energy spreads of the extracted positive hydrogen ion beam have been studied using a retarding field energy analyzer. It has been found that the filament-discharge multicusp ion source can deliver a beam with an energy spread less than 3 eV which is required for the ALG-1000 machine. The multicusp ion source can also deliver the current required for the application.