Ion Optical System Research Articles

New Methods for Making the Qubits of a Solid-State Quantum Computer by Implantation of Single Highly Charged 31 P Ions

A step-and-repeat and a simultaneous method are proposed and evaluated for the implantation of single highly charged 31P ions into a Si/SixGe1 – x heterostructure with the aim of creating the qubits of a solid-state quantum computer. The capabilities of existing axially symmetric compound electromagnetic objective lenses and ion sources are examined in this context. The advantages of such lenses over electrostatic ones are shown. An electromagnetic objective lens of exceptionally small axial aberrations is designed. An optical system using the lens is proposed for a step-and-repeat implanter. The parameters of the implanter are identified that determine its performance. They are lateral ion-positioning tolerance, the chromatic-aberration coefficient of the objective lens, source brightness, and ion multiplicity. An equation is derived that relates the parameters. Requirements are stated on the ion source. Possible ways are discussed of improving the performance of the ion source and the ion-optical system.

Evaluation of ion projection using heavy ions suitable for resistless patterning of thin magnetic films

The ion projector at the Fraunhofer Institute ISiT has been used for the development of patterned magnetic media for potential future use in magnetic hard disk drives. By 8.8 times demagnification of an open stencil mask, magnetic contrast is generated by ion intermixing of Co/Pt sandwich layers. In this application a resist process is not necessary and the surface roughness of magnetic media is not altered. Monte Carlo simulations of the intermixing process with the dynamic T-Dyn software for H, He, Ne, Ar and Au ions show that the exposure dose can be reduced by a factor of 100 by irradiation with Ar+ ions instead of He+. This has been confirmed by magnetic force microscopy of 200 nm magnetic dots irradiated at a dose of 6×1013 Ar+/cm2 at 73 keV energy. Sufficient stability of the ion optical system concerning resolution and drift has been demonstrated by exposures in developed and undeveloped (latent image) resist down to 60 nm dots.

RF discharge-based plasma emitter

An injector of hydrogen atoms for plasma diagnostics in modern tokamaks has been developed at the Budker Institute of Nuclear Physics (Novosibirsk). The ion source of the injector produces a proton (helium ion) beam with a current of up to 2 A (1 A), an ion energy of up to 55 keV, a beam divergence of ∼0.6\deg, and a pulse duration of up to 10 s. An RF discharge-based plasma emitter, which is one of the main parts of the ion source, is described. The emitter diameter is 72 mm, the ion current density is 120 mA/cm2, and the inhomogeneity of the current density is ±6%. The beam is formed by a four-electrode ionoptical system with 163 round apertures. At a current of 2 A, the ion beam consists of 67% protons, 18% H2+ ions, and 15% H3+ ions, the total content of heavier ions in the beam being no higher than 2–3%.

The study of the transmission efficiency of the DRIBs transport lines

Computer simulation of the beam loss caused by the charge exchange with a residual gas and a transmission efficiency investigation of the ion optic system have been carried out for the DRIBs transport lines. The DRIBs accelerator complex will include two main ion guide lines for transport of low-energy radioactive ion beams ( E I∼15 keV): the line from the RIB-separator of the U400M cyclotron to the U400 cyclotron (‘Phase 1’) and the line from the MT25 microtron to the ECR-source of the U400-cyclotron axial injection system (‘Phase 2’), of the lengths exceeding 120 and 70 m, respectively. The results of the beam-loss numerical simulation and the optimization of the basic parameters of the vacuum and magnet optic systems allow to determine the main requirements for these systems which can provide effective transport of low-energy beams.

Methods for Estimating Theoretically the Influence of Ion Scattering and Reflection on the Isotopic Sensitivity of Static Magnetic Mass-Spectrometers

For purposes of optimizing ion-optical systems, analyzer construction, and pump placement in static magnetic mass-spectrometers for isotopic analysis of uranium compounds, a comparative analysis is made and a review is given of methods described in the literature for theoretical estimates of the influence of scattering and reflection of ions on the isotopic sensitivity. Conclusions which make it possible to solve the problem are drawn.

Characterization of a process development tool for ion projection lithography

This article describes the performance of a process development tool for ion projection lithography (IPL), realized as part of the MEDEA program of the European Union. This system was designed for a 12.5×12.5 mm2 exposure field and 4:1 reduction ratio between the mask and the wafer. The design incorporates several novel concepts, including a negative electrostatic lens at the mask to reduce distortion and field-composable lenses to provide electronic fine alignment of the system. Continuous control of magnification, position offset, distortion, and telecentricity is provided by a real-time feedback system (pattern lock) that monitors the position of reference beamlets traveling in parallel with the integrated circuit image through the ion-optical system. After mechanically aligning the center and tilt of the lenses relative to the optical axis to within 10 μm and 50 μrad, respectively, we achieved 100 nm resolution over the full design field, with 75 nm resolution in local areas within the field. The reduction ratio was within 0.01% of design predictions. We also discuss the experimental plan for further demonstrating the efficacy of IPL for integrated circuit manufacturing far below 100 nm design rules.

Small-size systems for separation of primary ion beams in microprobe equipment

The ion-optical properties and other characteristics of various versions of a double-focusing mass separator are studied. In these designs, the ion transit path is shortened by appropriately selecting the geometry of the ion-optical system. The resolving power of the separating systems is determined with allowance for second-order aberrations.

Ion projection lithography: status of tool and mask developments

As part of the European MEDEA project on ion projection lithography (IPL), the ion optical system of a process development tool (PDT-IOS) has been designed and integrated at IMS Vienna. The ion optics system (PDT-IOS) includes in situ metrology systems. The different PDT-IOS subsystems, including in situ diagnostics and metrology, were switched on in the fourth quarter of 2000 so that detailed testing should start in the first quarter of 2001. In parallel to integration of the PDT ion optics, a test bench for a vertical vacuum wafer stage has been realized by Leica. Operation of magnetic bearing supported stage movement has already been demonstrated. An ASML vacuum-compatible optical wafer alignment system has been integrated to this stage test bench system recently. In air, an X/ Y alignment repeatability of less than 3 nm (3σ) has been shown. Parallel to the IPL tool activities, intensive development of IPL stencil masks is ongoing at Infineon Technologies Mask House and the Institute for Microelectronics Stuttgart with success in producing 150 and 200 mm stencil masks. An overview of the stencil mask development is provided.

Multipass time-of-flight mass spectrometers with high resolving powers

Low energy ions can be stored in “rings” of electrostatic sector fields or in systems of electrostatic mirrors between which the ions are reflected back and forth repeatedly. Because of the long flight path in such systems they very well can be used as precision time-of-flight mass spectrometers. This statement is trivial for monoenergetic ions but also holds for polyenergetic ions if the ion–optical system is designed such that it guides more energetic ions on appropriate detours that cause the overall ion-travel times to become energy independent. Since the number of reflections between the mirrors can be varied by changing the timing of the voltage pulses on the mirrors, either a long well resolved mass spectrum can be recorded or only a section of such a mass spectrum for which then the mass resolving power is increased proportional to the number of reflections.

A dual 6T persistent-mode SC solenoid ion-optical system for radioactive nuclear beam research

A unique ion-optical system for the production of high-intensity, short-lived radioactive nuclear beams has been designed, constructed and put into operation at the Nuclear Structure Laboratory at the University of Notre Dame as a joint project between the University of Michigan and NSL-UND. The system consists of a matched in-line pair of large-bore (30 cm) 6T superconductive solenoid magnets which act as high-acceptance collectors and magnetic filters of secondary radioactive nuclear beam (RNB) products. The latter are brought to a focus on a secondary target and nuclear reactions using the RNB studied. These are primarily reactions of interest in Big-Bang nucleosynthesis and stellar helium burning and involve the production of /sup 6/He, /sup 7/Be, /sup 8/B and similar beams. A number of unique features were incorporated in the magnet design to permit use as a precise ion-optical device in the RNB mode. To the authors' knowledge this is the only large-scale in-beam ion-optical system to operate primarily in persistent mode. A similar device will also be built at the University of Sao Paulo for RNB research.

A diagnostic neutral beam system for the MST reversed-field pinch

A diagnostic neutral beam system has been developed for the Madison symmetric torus (MST) reversed-field pinch. The system is primarily used: (1) for measurement of the majority ion equilibrium and fluctuating velocity and temperature by Rutherford scattering (RS); (2) for measurement of the impurity ion velocity and temperature, both equilibrium and fluctuating, by charge-exchange recombination spectroscopy (CHERS); and (3) for magnetic field measurement via motional Stark effect (MSE). The system consists of two neutral beam injectors, and two neutral particle analyzers. One injector creates a 20 keV, 4 A helium beam for RS. The energy spectra of the helium beam atoms scattered from the plasma ions is measured with two 12-channel, 45° electrostatic energy analyzers equipped with a hydrogen stripping cell. A second injector creates a 30 keV, 4 A hydrogen beam, which is used for the CHERS and MSE diagnostics. In each injector ions are extracted from a plasma created by an arc discharge source and, after acceleration and focusing, neutralized in a gaseous target. A low ion perpendicular temperature at the plasma emission surface, achieved via plasma expansion cooling, results in a low (0.016 rad) intrinsic beam divergence. A hallmark of the beam design is the focusing ion optical system that consists of four multiaperture spherically curved electrodes. The geometric focusing, together with a low intrinsic beam divergence, provides a small beam size—5 cm in diameter-on the MST axis and a high neutral current density (0.4 equivalent A/cm2). A beam injector is compact in size—30 cm in diameter and 70 cm in length—and weighs about 70 kg. In this article we present details of the beam and analyzer designs and first results of their tests on the MST.

Forming a beam of ions extracted from glow-discharge plasma

In plasma-emitting structures based on glow-discharge, the potential difference between the ion-emitting plasma and the screening electrode of an ion-optic system depends on particular features of the electrode system of glow discharge and can vary in a range 0–1 kV. Results are presented of an experimental study and computer simulation of the formation of ion beams with ion energy 0–1 keV and current density 1–10 mA/cm2 in ion sources based on such structures.

Construction of a new multi-turn time-of-flight mass spectrometer.

A new type of multi-turn time-of-flight mass spectrometer was constructed, consisting of four cylindrical electric sectors and 28 electric quadrupole lenses, the size of the vacuum chamber being 60 x 70 x 20 cm. It was demonstrated that the mass resolution can be increased according to the number of cycles of the ions through the ion optical system.

New developments for shallow depth profiling with the Cameca IMS 6f

A new ion optical system has been developed for the duoplasmatron source of the Cameca IMS 6f instrument. This system improves performance at low impact energies. It consists of a new primary ion extraction system operating in acceleration/deceleration mode and an additional lens. It provides better source emittance matching with the primary column acceptance and a minimization of the space charge effect in the source plasma. The primary beam density in the sub-kilo-electron-volt impact energy range (down to 500 eV) is therefore improved. This article describes the new extraction system, the performance improvements are discussed in terms of beam intensity and density as a function of impact energy, and application examples for B and P shallow profiles are provided. Results demonstrating the benefits of the sample rotation technique for B depth profiling in silicon with low impact energy O2+ beam and oxygen flooding are also presented.

渦巻型飛行時間質量分析計

A new design of TOF mass spectrometer with spiral orbit is proposed. By the suitable arrangement of electric sector fields and free spaces, ion optical systems with spiral orbit are found. The long orbit has no overlapping part in comparison with the multi-turn system. The ion path length of more than 3 m is possible to obtain in a very small geometrical space of only 20 cm diameter. The systems have excellent focusing nature in both time and space.

マルチターン飛行時間型質量分析計「ＭＵＬＴＵＭ Ｌｉｎｅａｒ ｐｌｕｓ」の開発

A new type of multi-turn time-of-flight (TOF) mass spectrometer was constructed, consisting of four cylindrical electric sectors and 28 electric quadrupole lenses, the size of the vacuum chamber being 60 cm×70 cm×20 cm. As the mass resolution of a TOF mass spectrometer is proportional to the path length, it will be necessary to use multi-turn optics in order to achieve the desired resolution within the physical limitations imposed by the spacecraft. It was demonstrated that the mass resolution can be increased according to the number of cycles of the ions through the ion optical system. The mass resolution was 68,000 (m/z= 28, FWHM) after 150.5 cycles.

Status of Ion Projection Lithography

AbstractAs part of the European MEDEA project on Ion Projection Lithography (IPL), headed by Infineon Techologies, a process development tool (PDT) has been assembled at IMS, Vienna, with the final target of 50 nm resolution in a 12.5 mm exposure field at 4× demagnification. The ion-optical system (PDT-IOS) has been integrated, including the LEICA mask changer and a sophisticated metrology stage with in-situ diagnostics. In parallel, the LEICA wafer stage and the vacuum compatible off-axis ASML wafer alignment system have been realized. At the moment (Nov00) the He+ ion beam is aligned until the mask level. Ion beam proximity wafer exposures directly behind the mask show a performance of the illumination optics as predicted. 150 mm stencil masks with 125mm diameter, 3μm Si membranes, 50mm × 50mm design field, have been produced by IMS-Chips, Stuttgart. There is expectation to start the PDT-IOS test phase in Q1/01. Using the experimental ion projector at the Fraunhofer-Institute ISiT in Berlin recent resolution tests have demonstrated 50 nm lines and spaces without proximity effect in standard Shipley DUV resist UVIIHS at an exposure dose of 0.5 μC/cm2 for 75 keV He+ions. This was accomplished by 8.5 × demagnification of a new generation of stencil test masks from IMSChips. One further promising application of IPL is the resistless structuring of thin magnetic films to produce magnetic nano dots for future ≥ 100 G bit/in2 storage devices. A consortium of IBM Germany - Speichersysteme Mainz, Fraunhofer-ISiT, LEICA Jena and IMS-Chips in cooperation with IMS-Vienna has been formed to evaluate this technology.

Formation of intense focused ion and atomic beams

Abstract Series of injectors of focused neutralized ion and atomic beams with beam energy ranging from 5 to 40 keV, equivalent beam current of 1–20 A, angular divergence of beam ∼10 −2 rad, equivalent current density in focus of beam more than 1 A/cm 2 , pulse duration of 0.1–100 ms is developed in Budker Institute of Nuclear Physics. A specific approach to the formation of high brightness ion beams is used in these injectors. The low transverse ion temperature of the plasma emitter is achieved by the use of plasma emitter formed by the collisionlessly expanding plasma jet. Ion beams are extracted from the plasma emitter by precise multi-aperture four-electrode ion optics systems. Two methods of beam focusing have been tested and successfully applied. In the first one the formed ion beam is focused by a magnetic lens and charge-exchanged into atoms in a pulse gas target. The second method is based on geometrical focusing of the beam by spherically bent electrodes of an ion optics system. To profit better use of the nonuniform plasma jet, the developed ion optics systems with geometrical beam focusing have gaps extending with radius which provides optimal beam formation from the enlarged surface.

A space time-of-flight mass spectrometer for exobiologically-oriented applications

A new type of multi-turn time-of-flight mass spectrometer was designed and constructed as a laboratory model of the ‘COSAC’ project of the ‘ROSETTA’ mission cometary study. This miniature time-of-flight mass spectrometer (TOF/MS) comprises of four electric sectors and eight electric quadrupole lenses, and it was demonstrated that mass resolution can increase according to the number of cycles of the ions through the ion optical system.

Ion projection lithography: Status of the MEDEA project and United States/European cooperation

Structure and targets of the European MEDEA project on ion projection lithography as well as related U.S./European cooperation are explained. By assuming 10 μm virtual source size and 1 eV (full width half maximum) energy spread calculations for a multielectrode electrostatic ion–optical system (1.25 m between ion source and stencil mask, ≈1.8 m between mask and wafer) we realize the possibility of 100 nm resolution (line and space) over an exposure field of 22×22 mm2 even when using the MONTEC model for calculating the stochastic blur and when running 3.3 μA He+ ion beam current through the ion–optical column, thus more than twice exceeding target specifications. Thus, for 100 nm resolution and 50% pattern density the raw throughput is ≈12 cm2/s corresponding to >75 WPH (pattern within 80% of 300 mm wafer area).