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1. WO2015094382 - APPAREIL D'ANALYSEUR DE MASSE DE BOBINE DE CULASSE EN FORME DE C PERMETTANT DE SÉPARER DES ESPÈCES IONIQUES SOUHAITÉES DES ESPÈCES IONIQUES NON SOUHAITÉES DANS DES FAISCEAUX IONIQUES EN RUBAN AYANT UNE LARGEUR ARBITRAIRE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

C-Shaped Yoke Coil Mass Analyzer Apparatus For Separating Desired Ion Species From Unwanted Ion Species In Ribbon Ion

Beams Of Arbitrary Breadth

PRIORITY CLAIM

The instant invention was first filed as U .S . Provisional Patent Application Serial No. 61/963,986 on December 20th, 2013. The legal benefits of this first filing are expressly claimed herein .

CROSS-REFERENCE

The instant invention is a Continuation-In-Part of U .S . Non-Provisional Patent Application Serial No. 13/385,618 filed February 27th, 2012 entitled "Mass Analyzer Apparatus And Systems Operative For Focusing Ribbon Ion Beams And For Separating Desired Ion Species From Unwanted Ion Species In Ribbon Ion Beams". All legal advantages and benefits of this earlier-filed patent application are expressly claimed herein .

FIELD OF THE INVENTION

The present invention concerns magnetic mass analyzers which are applied to streaming high-current ribbon-shaped ion beams in various systems and applications. Ribbon beams present unique problems to analyzing magnet designers, compared with those used with cylindrical beams in pure mass spectrometric analysis systems. All such mass analyzer devices are commonly used to separate wanted ion species from undesired ion species then present within the ribbon-shaped ion beam, and will deflect and alter the trajectory pathways of the traveling ion beam and provide a focusing of ions within the traveling ion beam, the deflection and focusing being in all cases dependent on the mass, energy, and charge of the ions.

BACKGROUND OF THE INVENTION

RECOGNIZED USES DVER TIME

The first analysis of ribbon beams was in the Calutron systems for uranium isotope separation in the Manhattan project. The ion source was immersed in a uniform magnetic field which deflected the extracted ribbon beam through 180 degrees, bending it in the plane of its narrow (width) dimension, the magnetic field being aligned with its broad dimension. Subsequent systems with ion sources removed at some distance from the analyzing magnets have utilized a variety of design approaches.

The use of magnetic mass analyzer devices to modify the attributes and traits of ribbon-shaped ion beams (also termed 'sheet beams' or 'belt-shaped beams') has become common and routine in ion implantation systems and methods, and is thus especially well-known. In evidence of the conventional practices in the relevant art, among the better known magnetic devices employed for this purpose are those individual constructs disclosed and described by: U.S. Patent Nos. 4,578,589 (Aitken); 5,126,575 (White); 5,350,926 (White et al.); 5,834,786 (White et al.); 6,162,262 (Aoki); 6,498,348 (Aitken); 7,112,789 (White); 8,263,941 (Benveniste); 8,723,135 (Glavish); U.S. Patent Publication No. 20120235053 (White) - the individual texts of which are expressly incorporated by reference herein.

TECHNICAL CONSIDERATIONS

§ It is very desirable to purify broad ribbon-shaped ion beams by mass selection for purposes of implanting ions into large substrates, such as flat-panel displays and solar cells. Under these system application circumstances, a most desirable feature for the chosen mass analyzer device is the capacity to be increased in dimensional size; and in particular, to become linearly extended in beam breadth dimension to any arbitrarily chosen measurable dimension . Another very desirable feature for the device is to be capable of performing its high resolution mass separation function without the need for any magnetic component aligned with the major transverse dimension of the beam, the breadth dimension .

§ Offered here merely as points of informational reference and comparative distinction are the following :

A low strength magnetic field is traditionally in the range of about 0 to 0.05 T ; a moderate strength magnetic field is typically in the range of about 0.05 T to 0.5 T; and a high strength magnetic field is conventionally in the range of about 0.5 T to 1.2 T; and higher strength fields are beyond consideration in the present context because the available ferromagnetic materials saturate at around 1.8T, which provides a limit above which the complexity and cost rise prohibitively.

It is typical to perform mass analysis on ion bea ms with

energies between about 5 keV and 100 keV, even when the final desired ion energy is higher or lower than this range. The magnetic field required to perform this task is inversely proportional to the charge and to the radius, and is proportional to the square root of the mass and the energy of the ion , The nu mber of ampere-turns in the electromagnet winding is proportional to the distance, measured normal to the motion and the plane of deflection of the ions, over which the field is established . This distance must exceed the

dimensions of the beam. The use of a well-designed ferromagnetic yoke is typical to minimize this ampere-turn requirement, to control the shape of the field, and thereby the precise focusing qualities of the field, and to minimize stray magnetic field .

Using such a ferromagnetic yoke, at least 80,000 ampere-turns are required to generate a field of 1 Tesla over a distance of 100 mm between the magnetic poles. This field is sufficient to deflect ion species and energies of commercial interest in a path whose radius is about 300mm. Consequently, the creation of high strength magnetic fields across larger gaps and spatial distances such as 1 to 2 meters requires significant electrical power and cooling - probably more than 1 million ampere turns.

Thus, as is well documented by the published technical literature: as the mass analyzer device is increased in size to accommodate ever-larger arbitrary beam breadth dimensions, and the direction of the magnetic field remains aligned with the beam's breadth direction (which favors high resolving power and the preservation of the high aspect ratio of the ribbon beam) - the number of ampere-turns in the electrical coil in the device which are needed to generate the desired magnetic field strength markedly increases, the device grows in three dimensions, and there is a tendency for magnetic to leak further from the device; and both the overall size and weight of the device grow greatly and become inconveniently very large, to the point where transportation is not merely difficult; transportation of the complete assembly becomes impossible. See for example: Alexeff, IEEE

Transactions on Plasma Science 07, 1983; Banford, Transport of Charged Particles, Spon, 1966; Livingood, Optics of Dipole Magnets, AP, 1969; Septier and Septier, ed. Focusing of Charged particles, AP,1967; and Stanley Humphries Jr., Charged Particle Beams, Wiley, 1990.

The occurrence of any of these events is highly undesirable and to be avoided whenever possible. Nevertheless, most if not all of these multiple disadvantageous incidents and unfavorable events continue to appear regularly and repeatedly with many mass analyzer devices, and yet there remains a need for mass separation of different ion species in a traveling ribbon-shaped beams of still larger sizes.

There has been successful commercialization of systems where the magnetic field is aligned with the narrow ribbon-beam dimension (see for example U.S. Patent Nos. 5,350,926 and 5,834,786), which reduces the ampere-turn requirement and can be extended to respectively 300 and 800 mm beam breadths. In the first of these cases, two magnets are required in order to produce a 300mm wide beam with a resolving power of about 80, and in the second case, an 800mm wide beam is generated with a single magnet, but the resolving power is only 5.

§ One other technical point of information should also be noted here as well: A focusing of ion trajectory pathways will generally occur when magnetic field gradients are applied to charged ion particles. One important prior art example of this result is the well-known case of the focusing which occurs between the inclined entrance and the exit poles of a dipole magnet, whereby the focusing arises in the fringe field. This focusing effect is well described in the technical literature by Enge in several publications, [see for example, Septier and Septier eds., Focusing of Charged Particles, Chapter 4.2, Vol 2 p. 203, A. P. (1967)]; and also by A, P. Banford, [see for example, Transport of Charged Particle Beams (Spon, 1966)].

A BRIEF HISTORICAL OVERVIEW Ur RELEVANT

PRIOR ART DEVICES

In magnetic field beam bending or focusing devices, deflections of the charged ions are proportional to the ion's charge value, and inversely proportional to the ion momentum.

Prior Art Fig . 1 (reproduced from US Patent No. 5, 126,575) shows how a ribbon beam may be focused (by a particular ion source geometry) so that its major dimension (which we refer to herein as its breadth) is focused to have a minimum size in the middle of the gap of a bending and analyzing magnet; then subsequently diverge again to provide an analyzed ribbon beam of large dimensions high aspect ratio. Unfortunately, it has been learned that the very high current density at the center of the analyzing magnet is the source of major beam instabilities, as further discussed in the following example.

Prior Art Fig . 2 (reproduced from US Patent No. 5,350,926) shows how a ribbon beam may be transmitted so that its breadth dimension lies parallel with the width of the magnet pole; thus the gap between the magnet poles can be one quarter or less the breadth of the beam . However, the large aspect ratio of the beam required is only recovered by subsequently passing this beam through a second large magnet whose primary function is to focus the expanding ribbon beam to be parallel . This '926 patent discusses why it is desirable to have low current density in the strong magnetic field to avoid plasma instabilities, which can limit the maximu m current density to an approximate maximum value. It is notable that the current density may be 200 to 1000 times greater at the focus between the magnets than it is at the center of the magnets - yet the worst bea m

degradation can occur within the magnets. This system has been commercially produced in large numbers, in part because of its success in avoiding this current limit; but even for a 300mm beam the weight of the magnets is 10 tons, and the system does not readily scale up for larger beams,

Prior Art Fig . 3 (reproduced from US Patent No. 7,112,789) shows how a ribbon beam may be deflected in the direction of its narrow dimension, while still expanding in the broad dimension ; and achieve high resolving power. In this case, very large coils are required (because of the large pole gap) with complex three-dimensional shapes, in order to wrap around the tall ion beam at the entrance and exit of the magnet. This approach has so far been successful up to about 1.2m in beam breadth, but it becomes very heavy and expensive to scale further. Furthermore, U.S. Patent No. 6,162,262 describes a 'window-frame' magnet used in a similar manner; but suffers from greater problems of stray magnetic field, which requires significantly more weight of ferromagnetic material in the yoke.

Prior Art Fig. 4 (reproduced from U.S. Patent No. 8,723,135) has a similar use of coils bent up and over the ends of the beam; has a large bending radius about three to four times the beam height; and has been used at larger sizes. But its weight, exceeding 100 tons for the larger commercial sizes, created considerable difficulty; while the resolving power is substantially less than 10.

In U.S. patent application serial no. 13/385,618 (U.S.

Publication No. 20120235053), a number of alternative approaches are reviewed, which generally use the chromatic aberration of magnetic lenses, in which the beam is transmitted off-center, to separate different ion species. These achieve low resolving power; but do have the merit of smaller size.

Many of these prior art devices have been used successfully up to a certain size. But, as the beam dimensions have grown, it is demonstrably true that the required power has increased faster than linear proportion to the beam size; the aberrations have grown with the square of the beam size; and the weight has grown faster than the square of the beam size, in some instances with the cube of the beam size, while the achieved resolving power has in most instances dropped.

TO DAY' S P E R S P E CT I VE S AN D N E E D S

Consequently in today's technology, it remains highly desirable to employ an operative magnetic analyzer device which is capable of separating out and removing unwanted ion species from a traveling ribbon-shaped ion beam when the measurable breadth size of the ion beam (its major transverse dimension) is arbitrarily extended to any desired useful magnitude - i.e. , a dimensional size varying today from about 150 mm to 3000 mm or more.

Consequently, in today's technology, there remains an unfulfilled need for a device which can separate unwanted ion species from beams of desired dopants or other processing ion species in ribbon ion beams of breadth greater than about 1 meter with sufficient resolving power to separate for example P+ from BF+ and without using more than about 100,000 A-t - with a footprint for the beam system of 1 to 2 sq . m instead of 10 to 20, and with a total weight of less than about 10 tonnes, so that transport and installation using conventional rigging tools is straightforward .

In addition, there is a continuing need for a magnetic field generating device where there is no variation in field profile along the breadth size-extended dimension - i. e., there are no systematic variations along the beam's major transverse dimension during beam focusing or deflection; and few, if any, inconsistencies or errors are introduced as an artifact created by the operative equipment.

Nevertheless, in so far as is presently known, neither of these significant goals and desirable outcomes have yet been successfully achieved by today's mass analyzer devices.

SUMMARY OF TH E INVENTION

The present invention has multiple aspects.

A first aspect is a mass analyzer apparatus suitable for

separating a ribbon-shaped beam of desired ions which have an energy val ue within the limited range from about 5 to 80 keV from unwanted ions of differing magnetic rigidity (that is, ions having a meaningfully different mass and/or energy and/or charge state), wherein the travel ing ribbon bea m passes adjacent to the a pparatus, said mass a na lyzer a ppa ratus comprising :

a substa ntia lly C-shaped yoke-coil assembly which is to be located adjacent to the travel pathway of the ribbon-shaped ion beam and thereby spans the breadth dimension of the adjacent ion bea m, said substantia l ly C-shaped yoke-coil assembly comprising

a tun nel-shaped yoke of set configuration and di mensions which (a ) has a C-shaped cross section encompassing more tha n 180 degrees and typically 190 to 210 degrees, and which surrounds on three sides a tunnel-shaped cavity, and which extends uniformly in a straight line to each of its two discrete ends,

(β) has two discernible solid wal l arm members as tunnel sides a nd a solid central bridging seg ment,

(y) provides two discrete arm member face surfaces with an included angle ranging from about 150 to 175 degrees, and

(δ) is fabricated of at least one magnetic metal material ;

a nd

at least one wound coil disposed upon said tu n nel -shaped yoke, wherein each such disposed wound coil

( i ) is a racetrack-shaped obround loop wound from multiple turns of an electrical conductor, comprisi ng two paral lel straight length sections of conductor winding as well as two discrete cu rved ends, wherein each straight length section is greater in length than the breadth dimension of the traveling ribbon bea m, and each curved end

bends through 180 degrees and is joined with said straight length sections,

(ii) extends around and encircles said yoke,

(iii) is located so that one of the two straight length sections lies within the tunnel space of the yoke, and the other straight length lies outside the yoke,

(iv) can generate a magnetic field on-demand, emanating orthogonally from the surfaces of the yoke, whereby multiple spatial zones of oriented magnetic field are created and lie disposed in sequential series, said multiple spatial zones of oriented magnetic field collectively being sufficient in volume, magnetic field strength, and directional effect to achieve a substantive modification of the adjacent traveling ion beam .

A second aspect of the present invention provides an operating system suitable for modifying the direction and convergence of an adjacent traveling ribbon-shaped ion beam of arbitrarily chosen breadth, said operating system comprising :

a traveling ribbon shaped beam containing at least one desired ion specie and at least one unwanted ion specie, wherein the ion beam's breadth dimension is preselected and fixed to be from less than 100 mm to more than 3000 mm in size, the ion beam's thickness dimension is preselected and fixed to be from about 1 mm to 10 mm in size, and the ion beam diverges in thickness by about +/- 2° or more;

a mass analyzer apparatus constituted as a substantially C-shaped yoke-coil assembly which is in adjacent position to the travel pathway of the ribbon-shaped ion beam and thereby spans the breadth dimension of the adjacent traveling ion beam, said

substantially C-shaped yoke-coil assembly comprising

a tunnel-shaped yoke of set configuration and dimensions which (a) has a C-shaped cross section encompassing more than 180 degrees and typically 190 to 210 degrees, and which surrounds on three sides a tunnel-shaped cavity, and which extends uniformly in a straight line to each of its two discrete ends,

(β) has two discernible solid wall arm members as tunnel sides and a solid central bridging segment,

(γ) provides two discrete arm member face surfaces with an included angle ranging from about 150 to 175 degrees, and

(δ) is fabricated of at least one magnetic metal material ;

and

at least one wound coil disposed upon said tunnel-shaped yoke, wherein each such disposed wound coil

(i) is a racetrack-shaped obround loop wound from multiple turns of an electrical conductor, comprising two parallel straight length sections of conductor winding as well as two discrete curved ends, wherein each straight length section is greater in length than the breadth dimension of the traveling ribbon beam, and each curved end bends through 180 degrees and is joined with said straight length sections,

(ii) extends around and encircles said yoke,

(iii) is located so that one of the two straight length sections lies within the tunnel space of the yoke, and the other straight length lies outside the yoke,

(iv) can generate a magnetic field on-demand, emanating orthogonally from the surfaces of the yoke, whereby multiple spatial zones of oriented magnetic field are created and lie disposed in sequential series, said multiple spatial zones of oriented magnetic field collectively being sufficient in volume, magnetic field strength, and directional effect to achieve a substantive modification of the adjacent traveling ion beam,

and

a source of electric current in on-demand electrical

communication with said obround coil or coils.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more easily understood and better appreciated when taken in conjunction with the accompanying Drawings, in which:

Prior Art Fig. 1 shows a proposed and abandoned system using a converging ribbon beam with a minimum breadth in the center of the field region of an analyzing magnet, expanding to produce a high aspect ratio broad ribbon beam;

Prior Art Fig. 2 illustrates conventionally known apparatus using two magnets, the first of which analyzes a ribbon beam by deflecting it in the plane of its breadth, and the second of which allows it to expand before focusing it to become a parallel ribbon beam of high aspect ratio;

Prior Art Fig. 3 shows the conventionally known White and

Chen magnetic analyzer which uses 'bedstead' coils and an optional expanding profile to analyze a high aspect-ratio high current ribbon beam;

Prior Art Fig.4 shows the conventionally known Glavish magnetic analyzer for a very tall ribbon-shaped ion beam

Fig 5a shows a side view and 5b shows a perspective view of the substantially C-shaped yoke-coil assembly in the present invention;

Fig. 6a and b show a side view of the tunnel-shaped yoke with an adjacent traveling ion beam;

Fig. 6c shows a cross section of the substantially C-shaped yoke-coil assembly with a adjacent traveling ion beam, illustrating the capability of the yoke-coil assembly to deflect and refocus the travel trajectories of a adjacent ion beam.;

Fig. 7 shows a number of perspective views of the modeled shape of a ribbon-shaped traveling ion beam as modified, deflected, and focused by the present invention.

Fig. 8 shows a detailed perspective view of the transversely mounted electrical coils in the substantially C-shaped yoke-coil assembly with auxiliary magnetic field-shaping bars, with an ion beam passing between the yoke and auxiliary bars;

Fig.9a shows the substantially C-shaped yoke-coil assembly in section, with magnetic flux lines shown, and with different zones of overall field orientation shown.

Fig. 9b shows a preferred embodiment of the substantially

C-shaped yoke-coil assembly in combination with three auxiliary magnetic field-shaping bars, showing the concentration of the magnetic field in three consecutive zones which the beam can traverse

Fig. 10 is a graph which shows a line plot of the Y-oriented component and the Z-oriented component of magnetic field along the projected path of an ion in a Y-Z plane, with the field zones from Fig 9a and 9b identified; and

Fig. 11 shows an embodiment of the C-shaped yoke coil analyzer in which the coil is external to the vacuum.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a substantially C-shaped yoke-coil assembly able to achieve at least one desired modification - such as an effective separation of charged ion masses - in an adjacent traveling ribbon-shaped beam of any arbitrarily chosen fixed breadth dimension. The substantially C-shaped yoke-coil assembly is a mass analyzer apparatus which is markedly lighter than predecessor devices of comparable capability; is far easier and less expensive to make and scales up to handle very broad but thin ribbon beams by extending only in the beam breadth direction; and is quickly installed, aligned, and operated in comparison to conventionally known devices.

The Value OfJL Mass ZnaCyzer Assembly it ig <Rf solving (Power

1. Conventionally, it is well recognized in the technical field that in many operational instances and for commercial applications in particular, it is necessary to separate P+ ions from P++ ions and from P2+ ions, as well as from certain other positively charged contaminants; and it is often necessary also to separate B+ ions from B++ ions and from F+ ions. A more stringent examples is the separation of 27AI+ from 31P+, while the separation of 19FnB+ (30 amu) from 31P+ is perhaps the most important routine example, where trace gas from a prior boron implant may contaminate a phosphorus implant

subsequently run on the same ion implanter. A high resolving power greater than 31 is necessary in this exemplary case.

The resolving power of a system for transmitting a beam

through a resolving aperture which can just transmit the desired ion species, is defined as reciprocal of the fractional change in ion mass (or energy) needed to physically displace the ion beam from a first misaligned position where transmission through an aperture is 50% one side of the maximum to a second misaligned position where transmission is 50% on the other side of the maximum. This is abbreviated to Μ/ΔΜ FWHM, where FWHM stands for Full Width at Half Maximum. It is usually measured by making very precise changes in either the beam acceleration voltage to control the energy, or the

current exciting the magnetic analyzer, and measuring the transmitted beam current.

A relatively high resolution is thus particularly important for achieving an effective separation of complex mixtures of charged particles, since such mixtures of different ion species will invariably contain a significant number of charged background ions. In such instances, a device with a higher resolving power can make the substantive difference between separating and blocking an unwanted ion species with a small difference in mass from the desired species, and neither detecting nor separating that unwanted ion species at all .

For example, in order to detect and separate B+ ions from B+ + ions and from F+ ions, a mass analyzer device will require a minimum resolving power of about 2. But, to achieve a high-quality separation of wanted charged particles with a reliable removal of undesired ion contaminants, a markedly increased resolving power of at least 20 is typically needed . Similarly, in order to detect, separate, and isolate BF+ ions from P+ ions effectively frequently requires that the mass analyzer device have a resolving power significantly greater than 31 ; and a device having a resolving power of 40 or more in these

operational instances is most welcome and highly desirable.

Consequently, the higher the resolving power of the mass analyzer device, the better the quality of the separation of ion species.

In addition, efficient coupling of such a high resolving power mass separation device to a high-current linear ion source would have great benefits and advantages for ion implantation of large substrates, such as flat-panel displays and solar cells.

2. Accordingly, one specific innovative feature offered by the present invention is its operational capability to obtain an effective detection and separation of similar, but identifiably different, ion species traveling together in an adjacent ribbon-shaped beam of almost any prechosen dimensional breadth, by simply extending the apparatus in that single dimension . Also, given the foregoing, it will be appreciated that this particular capacity is neither a small achievement nor a trivial feature.

The real-world resolving power of commercial high current implantation equipment for silicon wafers is in the range from 20 to 60, depending partly on beam energy and current. The present invention can routinely deliver a resolving power of approximately 40 while at the same time being capable of extension to 10 times the beam breadth and 10 times to beam current of those conventional

implanters. Precision mass spectrometers operating at lower currents can have much higher resolving powers, up to perhaps 500 and more, but conventional implanters for flat panel displays often achieve resolving powers of little more than 3.

Existing implanters for very large flat panel displays use multi-cusp ion sources with multi-aperture extraction systems of substantial width ( Dohi et al . IIT2006 (2006) 417-420, Matsumoto et al . , IIT2012 (2012), 324-327) . They use unusual but essentially conventional dipole bending magnets for mass resolution, bending through angles between 60 and 90 degrees, as is conventional . The ion beams have breadths (major dimension) in the range from l m to 2.2 meters, which are 10 to 20 times the beam thickness (around 100mm) and their bending radius has been increased to several meters to keep their dimensions in proportion to conventional devices on a smaller scale. They achieve resolving powers of around 5. This is not

adequate, for example, to separate phosphorus ions from PH+ ions, to separate boron from carbon ions, or to separate BF+ ions from P+ ions.

Accordingly, all embodiments of the present invention will routinely and reliably provide a high resolving power capacity ranging from about 15 to about 30; and via this most desirable feature and unique capability, be able to provide a far better quality of detection and a markedly improved separation for one or more individual ion species present in the mixture of charged particles traveling together in an adjacent ribbon-shaped beam of arbitrarily chosen dimensional breadth, and thus better purity of the dopant species implanted into the polysilicon film.

II. Capabilities And Characteristics Provided By The Substantially

C-Shaped Yoke-Coil Assembly As A Whole

§ The open three-sided yoke-coil assembly constituting the present invention can be employed in many alternative applications and can be used to achieve a variety of different resulting outcomes. In preferred embodiments, the yoke-coil assembly appears

predominately C-shaped, wherein the "C" configuration is an open loop bent about 200 degrees. The assembly may alternatively appear in a range of differently shaped formats which are more or less rounded in form; but in all cases the yoke encircles three sides of a central tunnel cavity which is occupied by straight lengths conductor of the obround electromagnetic coil or coils.

§ The diverse range of capabilities and traits for the invention as a whole therefore includes all of the following:

(i) The open yoke-coil assembly is demonstrably capable of deflecting a traveling ion beam from its incoming or initial trajectory through a net angle of change typically greater than about 8 degrees and not more than about 25 degrees.

(ii) The open yoke-coil assembly is demonstrably capable of separating at least one (and sometimes several) desired ion species from one or more unwanted ion specie impurities.

(iii) The open yoke-coil assembly is demonstrably capable of focusing the charged ion particles of the traveling ion beam in the Y-Z plane.

(iv) The open yoke-coil assembly is demonstrably capable of separating B ions from C ions, and of separating P ions from PH ions.

(v) The open yoke-coil assembly is demonstrably capable of performing the previous actions for ion beams of from 1 to 2.5 meters in breadth, and even more, without fundamental limit.

(vi) The open yoke-coil assembly is demonstrably capable of accomplishing this mass separation in a beam travel distance of the order of 1 meter for ion beams with a mass-energy product of 2.5 amu.MeV, that is to say up to 80 keV Phosphorus.

(vii) The open yoke-coil assembly is demonstrably capable of achieving all the above identified actions as a single piece of equipment weighing less than about 10 metric tons.

§ Also, not less than four unique traits of the invention as a whole must be properly recognized and truly appreciated, which are:

• First, the substantially C-shaped yoke-coil assembly

constituting the present invention is a single integrated mass analyzer assembly which stands alone and is fully functional and sufficient for the purpose of modifying a traveling charged particle beam which will spatially pass adjacently to it - i.e., there is no operational necessity for using pairs or greater multiples of the recited apparatus before a high strength magnetic field can be generated which is sufficient to achieve its stated purpose.

• Second, the volumetric zone nature and varying strengths of the entire magnetic field generated by the substantially C-shaped yoke-coil mass analyzer assembly is quantitatively sufficient for a ribbon shaped ion beam of any arbitrarily chosen fixed breadth dimension to pass adjacently across it - i. e. , the spatial zones of magnetic field generated and orthogonally extended by the yoke-coil assembly is adequate in both overall dimensional size and magnetic strength value to achieve an effective separation of different ion species and to achieve a focusing of charged ion particles (of a prechosen mass) then traveling in a beam

• Third, the total magnetic field generated by the substantially C-shaped yoke-coil mass analyzer assembly will always present certain minimal characteristics, which include :

(i) An orthogonally extending magnetic field of sufficient size to cover and uniformly overlay at least the entire breadth dimension of the traveling beam;

(ii) A magnetic field of predetermined strength whose flux lines lie always in Y-Z planes, and this magnetic field profile extends uniformly along the X-axis direction ; and

(iii) An effectively zero value of the magnetic field component along the X-axis (breadth, transverse) direction of the traveling ion beam.

• Fourth, the substantially C-shaped yoke-coil assembly as a whole never structurally is and never operationally functions as a solenoid lens - i. e., a charged ion particle beam will not at any time enter the spatial volume of a disposed coil in the assembly, nor ever pass through the material substance of a disposed coil of the apparatus. Instead, the yoke-coil assembly as a whole is juxtaposed to and located adjacently beside the traveling ion beam . Field-enhancing bars optionally placed on the opposite side of the beam from the yoke-coil are essentially passive components which raise the strength of the magnetic field for a given coil current, but which play no other crucial role .

III . The Substantially C-Shaped Yoke-Coil Assembly Structure The present invention can be best understood by considering an operating system in which a ribbon-shaped ion beam constituted of multiple ion species is moving over a set distance in a forward direction of travel . In such an operating system, the traveling ion beam can be identified and characterized using a Cartesian coordinate system .

It is common practice in ion beam systems to use a curvilinear Z-axis based on a reference ion trajectory. However, since the beam is bent through a relatively small angle, say 16 degrees, for simplicity this method is not used here; and the z-axis represents the mean of the directions of travel of ions entering and leaving the device.

Thus the Z-axis is the direction of approximate mean intended travel for the ion beam ; and the Y-axis is the mean direction of the narrow thickness dimension for the beam; and the X-axis is the direction of the breadth dimension for the beam. Thus, the Cartesian coordinate system is fixed in space and orientation .

The Cartesian Coordinate Orientation Of The Operating System The ion source launches the ion beam at a small angle of about 5 to 15 degrees to the Z-axis, with a component of motion in the positive Y-axis direction . However, the intent is that after traversing the apparatus, the beam will have an opposite component of motion in the Y-axis direction ; thus the Z-axis direction is the mean of the directions of the ions entering and leaving the vicinity of the C-shaped yoke-coil assembly structure.

The beam's major linear transverse dimension is its fixed breadth dimension, which arbitrarily can be chosen in magnitude from less than 100 mm to more than 3000 mm in size; and this breadth dimension is always parallel with the X-axis.

Comparably, the beam's minor transverse dimension is its thickness dimension - which typically varies in magnitude from about 3 mm to 30 mm or more in size as the beam ions diverge, and will approximately align with the Y-axis. However, given that the ion beam is deflected through about 16° in the negative Y-axis direction while traversing the mass analyzer apparatus, the Y-axis is selected arbitrarily (as shown in the figures). Thus the Y-axis extent of the beam is actually its thickness divided by the cosine of the angle between the direction of travel of the beam and the Z-axis.

In each instance, it is intended and expected that the traveling ribbon shaped beam will contain at least one (and sometimes several) desired ion species, as well as one or more unwanted ion specie impurities. The ribbon-shaped beam has a thickness dimension when extracted from its ion source of typically from 2 to 5 mm, but diverges in this minor dimension by typically +/- 2° (although this value depends on many factors relating to both ion physics and thermal expansion related problems of alignment and construction). The major breadth dimension for the beam can range from about 80 mm to more than 3000 mm in size. The Cartesian coordinates are more particularly described below, as required.

<The Construction Of The Vb^e-CoiiissemSCy

£ Within this exemplary Cartesian coordinate system, the present mass analyzer apparatus is purposefully employed. In this circumstance, the present invention appears as a discrete yoke-coil assembly which comprises two essential components: A tunnel-shaped yoke; and at least one transversely mounted electromagnetic coil disposed thereon. A perspective view of the invention as a whole is illustrated by Fig . 5b .

£ The tunnel-shaped yoke typically appears as a three-part sym metrical supporting structure, as shown by Fig . 5. As seen therein, the tunnel-shaped yoke

(a) has a C-sha ped cross section, encompassing more than 180 degrees a nd typical ly 190 to 210 degrees, and which surrounds on three sides a tunnel-shaped cavity, and which extends uniformly in a straight line to each of its two discrete ends,

(β) has two discernible solid wall arm members as tunnel sides and a solid central bridging seg ment,

(y) provides oppositely-situated face surfaces with a n i ncluded angle ra nging between about 150 and 175 degrees; and

(δ) is fabricated of at least one magnetic metal or meta llic al loy material,

£ Typically, the tun nel-shaped yoke is machined or cast from iron or low-carbon steel , or of another ( more expensive) magnetic material . It can be fabricated in one-piece ; or else assembled from two arms members 7a a nd 7b and a central linking bridge seg ment 1 . The individual arm member 7a ends in face surface 13 ; and discrete arm member 7b ends in face surface 15.

£ In comparison, the electromagnetic coil 2 is a racetrack-shaped loop winding made from an electrical conductor; a nd becomes part of the tunnel-shaped yoke structure, one part of the coil occu pying the tunnel cavity as shown in Figs . 5a and 5b . The coi l 2 typical ly presents two parallel straight length sections 52a and 52b of wound electrical conductor, each straight length section being greater in linear length than the breadth dimension of the travel ing ribbon beam, one section ( 52b) occupying at least part of the tunnel cavity of the yoke; and also concurrently presents two curved ends, each curved end bending through 180 degrees and joining seamlessly with the straight length sections 52a and 52b, a shape referred to as

Obround1.

While one discernible coil is functionally sufficient, two discrete electromagnetic coils 2a and 2b of smaller cross section may be substituted, as shown in Fig . 8, each of the two coils individually encircling one of the two side arms of the tunnel-shaped yoke, and one straight length section of each coil being located within the yoke tunnel cavity. This two coil arrangement has been found to reduce the magnetic field produced in non-productive areas; it does not, however, affect the basic functional principles of the yoke-coil assembly.

£ Electric current is passed on-demand by any conventional and controllable source through the electromagnetic coil or coils - whereby an orthogonally extending magnetic field is generated which not only encircles the current-carrying conductor material; but also is shaped by the ferromagnetic material of the arch yoke structure to become concentrated near the discrete ends of the two exposed arm face surfaces 13 and 15 -whereby one arm end face becomes the ' North' pole and the other arm end face serves as a 'South' pole, depending on the current flow direction . Between these individual two arm end face surfaces 13 and 15, a high strength magnetic field is generated by the electromagnetic coil which deflects the beam in a complex three-dimensional path described below.

The (Portioning Of The J%.ssem6Cy Over lnd Jlcross The Entire (Breadth

(Dimension Of an Adjacent Traveling Ion (Beam

H In each instance of use, the C-shaped yoke-coil assembly is to be transversely positioned as a magnetic analyzer unit which spatially passes over and completely spans the entire breadth dimension of an adjacently located traveling ion beam.

11 As shown in Fig.6a and 6b, the adjacent beam is initially deflected in the negative X-axis direction; and then is deflected back in the opposite direction in an S-curve, so the net velocity in the x-direction returns to zero. However, as a result, the beam's travel pathway becomes significantly offset in the X-axis direction - in this instance about 200mm.

Thus, the overall X-axis extent of the C-shaped yoke-coil assembly must be the entire fixed breadth dimension of the beam; plus about 200mm for the offset; plus a generous extra amount to ensure that the magnetic field is uniform up to the beam edges and is not distorted by the presence of magnet field edges.

To achieve this purpose, the C-shaped yoke-coil assembly 10 will lie disposed transversely across the travel pathway of the adjacent ion beam, then moving in the Z-axis direction with a small y-component of motion; and via this transverse disposition, the proper prechosen dimensions of the yoke-coil assembly will completely bridge and span the entire breadth dimension of the adjacent traveling ion beam, including the offset distance caused by the effect of the S-shaped deflection.

This intended spanning disposition and spatially adjacent transverse placement is well illustrated by Figs. 6a, 6b, 6c and 8 respectively. Specifically, Fig.6a and 6b show the yoke-coil assembly of the present invention when transversely positioned over and across the entire beam breadth dimension as the adjacent ion beam moves in the Z-axis travel direction; and Figs.6c and 8 illustrate the operational capability of the C-shaped yoke-coil assembly disposed in this bridging position to deflect the trajectory of the adjacent traveling ion beam.

Fig. 7 is a set of different perspective views of a very broad ribbon beam showing its shape as it is deflected and focused by the C-shaped yoke assembly. These views serve to show the complex 3-dimensional shape and path of the beam. These views were generated based on calculations using the computer code TOSCA sold by

Cobham Ltd.

H It is important to appreciate that the single wound coil of Fig. 6, or the multiple wound coils shown clearly in Fig. 8, encircle the ferromagnetic material of the tunnel-shaped yoke; and almost flll(s) the enclosed central space within its arch structure. The single or multiple electromagnetic coils do not under any operational

circumstances ever encircle or encompass the traveling ion beam.

It will be recognized also that the tunnel-shaped yoke and electromagnetic coil(s) can be located in an ambient air atmosphere. Thus, only the two arm member face surfaces presenting the 'North' and 'South' poles need be exposed to the vacuum environment in the embodiment shown by Figs.6 and 11; and it would be perfectly possible keep the tunnel-shaped yoke entirely outside the vacuum environment by interposing thin vacuum walls.

Note also that the electromagnetic coil(s) are located on only one side of the adjacent traveling ion beam (see Figs. 6 and 11). No magnetic field component is applied along the major breadth dimension of the ion beam. This is completely unique and distinct from all other conventionally known apparatus in this field.

(Defection Of an djacent Traveiing Ion (Beam

The practitioner working in this technical field must properly understand and recognize what is the detailed shape of the magnetic field generated by a C-shaped yoke-coil assembly in the adjacent spatial zone through which a juxtaposed ion beam will pass.

Φ Referring initially to the illustration of Fig. 5a, the adjacent traveling ion beam will first pass close to arm member face surface 13 of the tunnel-shaped yoke; then pass through a central intermediate spatial zone; and then will pass close to arm member face surface 15; and then continue away from the device. It will be recalled here that a magnetic field can deflect an ion in a direction orthogonal to both the field and the direction of travel of the ion, but such an imposed static magnetic field can neither accelerate nor decelerate the ion.

Φ Referring now to the illustrations of Figs 6c and 9a, the spatial zone in front of arm member face surface 13 is indicated by a rectangular box labeled 113. This spatial zone 113 approximately outlines where the direction of the magnetic field lies transverse to the direction of the beam trajectory; is directed orthogonal to the arm member pole surface; and extends in the negative Y-axis direction (though inclined at about 8°). The magnetic field lines are curved; so this event and result, while approximate, nevertheless remains substantially accurate.

Next, the trajectory pathway of the adjacent traveling beam moves into the central intermediate spatial zone, outlined in Fig. 9a by a rectangle 112. In this central intermediate spatial zone 112, the magnetic field is substantially (and on average) aligned with the Z-axis.

Finally, in the third spatial zone 115 existing next to the arm member pole surface 15, the magnetic field is substantially directed in the positive Y-axis direction, normal to the pole surface; and is tilted about 8° in the opposite direction to spatial zone 113.

Φ Given the series of deflections and changes in pathway direction described above for the adjacent traveling beam, the

practitioner must now consider the effect on the individual ion

trajectories.

An ion traveling within the adjacent beam is generally moving in the Z-axis direction, but has a travel pathway which is inclined at an angle βι = 8 degrees in the Y-axis direction. Thus, as seen in Figs 5a and 6 which show different views (and sometimes show a full ribbon beam), the ion then enters spatial field zone 113.

Within this spatial zone 113, the ion is traveling orthogonally to the magnetic field on average; and, as a consequence, the ion is deflected away - into the page, away from the viewer in Fig . 5a ; but this manner and direction of ion deflection cannot be seen in the view of Fig . 5a . However, this direction of ion deflection is clearly visible in Fig . 6b where spatial zone 113 is outlined ; and the magnetic field strength is adjusted - such that within spatial zone 113, the ion is deflected through an angle between approximately 25 and 45 degrees in the negative X-axis direction ; and in this illustrated instance about 30 degrees.

The ions quickly leave this spatial zone 113; and then enter central intermediate spatial zone 112, where the magnetic field is aligned in the Z-axis direction . If the ions were traveling evenly and in planar pathways in the Z-axis direction, they would be undetected within this spatial zone 113. But, the ions are in fact then traveling at an inclined angle within this spatial zone 113 ; and the X-axis directed component of velocity is thus the original ion velocity multiplied by -sin30°. In other words, half the initial velocity is now directed in the negative X-axis direction within spatial zone 113.

This component of velocity is orthogonal to the Z-axis directed magnetic field, and causes a deflection in the negative Y-axis direction .

Again, this deflection within spatial zone 113 is not seen in Fig. 6b because the act of ion deflection is directed away from the viewer; but such deflection is very clear in Fig. 6c. The magnitude of deflection depends upon many factors including the exact shape of the yoke and the current in the coils.

The moving ions then proceed into spatial zone 115, where the B field is orthogonal to its motion; and is directed toward face 15; and extends generally in the positive Y-axis direction. It will be noted and appreciated that this spatial zone 115 is the operational inverse of spatial zone 113. Here within spatial zone 115, the ions are deflected in the opposite direction through 30 degrees until they have no component of X-axis motion; and the ions are traveling in the Z-axis direction with an inclination of 8 degrees in the negative Y-axis direction.

Φ Such ion S-deflection motion is three-dimensional in effect and thus is often difficult to illustrate and visualize. Fig. 7 accordingly shows many projected perspective views of a sample ion beam, modeled in detail, for a case where the breadth exceeds 2200mm. The "S" shaped deflection transitions between the three respective spatial zones are not abrupt, but vary smoothly and seamlessly into each other. Accordingly, the above-given description gives an accurate and proper account of the average ion deflections, as well as a precise explanation of where and why they occur.

Φ In sum therefore, the overall deflection effects and

consequences upon the ion trajectories are:

(1). The ion trajectory is initially offset by a distance in the negative X-axis direction, which in this specific instance is about 200mm;

(2) . The ion trajectory is subsequently deflected through an angle in the negative Y-axis direction, in this instance 1.6 degrees;

(3) . If the mechanical symmetry is well preserved in practice, and the field strength adjusted so that the y-direction deflection is also symmetric in the mid-plane, i.e. angle βι = angle β2, then there will be zero net deflection (though there will be an offset) in the X-axis direction, and this is the intended operating condition;

(4) . If the initial angle of the trajectory in the Y-Z plane is increased from 8 to 10 degrees, the Y-axis deflection experienced is greater in magnitude, because the magnetic field is stronger when the ion passes closer to the yoke (particularly in spatial zone 112).

Conversely, if the angle is decreased from 8 to 6 degrees, the deflection in the Y-axis direction is smaller in magnitude. This effect causes the beam to be focused in the Y-axis direction; and an initially diverging beam exits zone 115 converging in the Y-axis direction - as is clearly visible in Fig. 6c.

(5) . Also, the X-axis direction offset which the ion undergoes is slightly different when this angle is varied (visible in Figs. 6b and 6c which present different views of the same exact calculation of a large array of ion trajectories). Thus, if the ion beam is a long ribbon beam, this effect is not a major concern in practice - because a 10mm growth in width of a 2000mm long beam is a minor proportional increase.

(6) . In addition, as with all magnetic devices used for focusing ion beams, the deflection effect is proportional to the magnetic field and the ion charge; and is inversely proportional to the square root of the product of the mass and energy.

(7) But note also that the three-dimensional deflection now leads to a markedly unexpected virtue, which is as follows:

The initial deflection within spatial zone 113 obeys the

aforementioned rule, which means that an unwanted ion which is 10% heavier than the desired ion will be deflected through about 5% less than 30 degrees, or 28.5 degrees. However, this ion now has a smaller component of velocity in the X-axis direction as it traverses central intermediate spatial zone 112.

As a result, the ion is deflected through a smaller angle as it traverses central intermediate spatial zone 112; but the reduction is about 5% less because of the increased mass, PLUS 5% because of the decreased velocity in the x-direction, for a net 10% reduction in angle, meaning it is deflected through 16 - 1.6 = 14.4 degrees in the negative Y-axis direction. The distance from the center symmetry plane of the C-shaped yoke-coil assembly to the focus in the beam is in this instance 500mm; and this 1.6 degree angle change means that the unwanted ion is displaced 14mm. In the jargon of mass analyzers, one says that the mass dispersion of the system is 14/10% = 140mm.

Furthermore, the width of the beam focus is in practice about 4mm, due to a combination of the finite size of the beam from a real ion source and imperfections in the focusing.

One can estimate the resolving power of this device using the specific working example to be 140/4 = 35 Μ/ΔΜ FWHM, as defined previously. This means that the pair of blocking plates 6a and 6b in Fig. 5c, if placed just tangent to the desired beam, will deliver a resolving power approaching 35. This value is unexpectedly high for a device only lm in overall length, deflecting through only 16 degrees, and handling an ion beam of such large dimensions.

The Tower Consumption Of The TransverseCy Mounted ' Cectrotna netic Coif The power consumed by the coils of a magnet for analyzing an ion beam (while depending on design details), can broadly be

generalized to be : Proportional to the product of the magnetic rigidity of the ions; multipl ied by the square of the pole gap (the effective distance between the two arm member face surfaces) of the coil magnet; multiplied by the width of the magnet; a nd then multiplied by the path length th rough the magnet. It is inversely proportiona l to the squa re of the cross section of the coils. There is also a trade-off between the size and weight of the electromagnetic winding coil(s) transversely mounted upon the yoke arch and the a mount of power and cooling required .

In the present invention , the effective pole ga p distance is proportional to two to three ti mes the thickness of the ri bbon ion beam . This calculated nu merical value is much less tha n the fixed breadth dimension of the beam ; and thus the practitioner ca n estimate a power saving benefit of the current design, as follows, If the term 'aspect ratio', denoted by A, is used to describe the ratio of breadth to thickness of the ion bea m, then the reduction i n power required of a magnet according to the present invention compa red with a conventional dipole magnet is of the order of a factor 3/A2.

For this purpose, the practitioner must use the aspect ratio at the approxi mate center of the device where the thickness di mension of the bea m is greatest; a nd where the beam divergence wil l have raised the bea m's measurable thickness to about a 35 to 40 m m size, a significant safety margin is needed . Accordingly, for a bea m 2m in breadth x 50m m i n thickness, the aspect ratio is 40. Furthermore, the present invention requires a smaller path length, typically a bout 1/3, compared with a conventional magnet ca pable of a nalyzing such a broad ion bea m .

Th us, for a ribbon-shaped bea m with an aspect ratio of 40, the present invention requires 1/500 the power of a conventional magnet, assuming that both magnets used coils with the sa me cross sectional area. In practice, a much smaller coil could be used, and a tradeoff found between manufacturing cost and power consumption.

The iJse Of J&uxjCiary Iron (Bars ToM ' odify Performance, § In Fig 9b (which should be compared with Fig. 9a), three additional iron or low-carbon steel bars 3a, 3b, and 4 are located where they modify the magnetic field - but concomitantly do not obstruct the passage of the ion beam. These discrete bars 3a, 3b, and 4 have a uniform prismatic cross section; and have the same X-axis extent as the C-shaped yoke-coil assembly. They are also oriented to and aligned with the X-axis.

It will be noted that bar 3a presents a face on the opposite side of the beam to face 13 of the C-yoke; while bar 3b presents a face on the opposite side of the beam to face 15 of the C-yoke. Bar 4 is positioned between the two discrete bars 3a and 3b; and the shape of the bars is such as to present parallel or near-parallel faces to each other. The gaps between the three bars 3a, 3b, and 4 is preferably uniform and will generally have the precise same value at opposite ends of the C-shaped yoke-coil assembly.

§ The role of these discrete bars is threefold:

0 Their first important role is that the magnetic field in the end spatial zones 113 and 115 is increased relative to that in central intermediate spatial zone 112 - because the air gap between arm member face surfaces 13 and 15 (which the magnetic flux bridges) is greatly reduced, being replaced by a magnetizable iron mass. This result increases the amount of X-axis directed beam offset occurring for a given deflection in the Y-axis direction. It also reduces the requirement for magnetic field in central intermediate spatial zone 112 for a given deflection in the Y-axis direction - because the bar's presence increases the amount of X-axis motion imparted to the beam in end spatial zone 113 (and corrected in the opposing direction within end spatial zone 115) .

0 Their second important role follows from the first stated above For a given Y-axis direction deflection, a smaller number of ampere turns is required, saving power and reducing the coil size requirement.

0 Their third role is that the shape of the auxiliary bars can be fine-tuned to modify the focusing properties - because the precise manner in which the Z-axis directed magnetic field in central intermediate spatial zone 112 varies with the Y-axis coordinate is critical to the strength and aberrations of this focus. This fine tuning of focusing properties can be accomplished, for example, by using 3D finite-element nonlinear computer codes such as Cobha m's

OPERA/TOSCA.

Jin ^[tentative Structural 'Tormat Tor The fl.ssem6[y As an alternative to the use of an electromagnetic wound coil in the assembly, a permanent magnet or multiple magnets may be introduced into the C-shaped yoke-coil assembly, by replacing part of the metal structure. One simple version of this alternative model is to eliminate the electromagnetic winding coil and replace the central arch section of the yoke structure with permanent magnet material, magnetized along the linear length dimension of the tunnel-shaped yoke.

As with the previously described electromagnetic winding coil format, there are two different polarity orientations possible for the permanent magnet material - either a 'North' pole followed by a 'South' pole, or a 'South' pole followed by a 'North' pole. There is no meaningful difference in operation or performance between these two alternatives; instead, the only relevant difference is that one

arrangement offsets the beam in the downward direction, while the other polarity arrangement offsets in the upward direction (see Figs, 6a and 6b). Both polarity arrangements will cause a roughly 16 degree deflection away from the magnet poles when set for the best focusing and resolution.

The use of permanent magnets is possible because the

integrated magnetic field along the z-axis of the beam defined in the figures is intended to be zero, which allows the requirement


to be met, By Busch's theorem this should mean that no angular momentum is imparted to the ion beam,

IV. A Representative And Exemplary Series

Of Alternative Embodiments

The present invention may be prepared in a range of different assemblies and structured in a variety of different formats, It will be expressly understood, however, that the range of these embodiments is wide; that the variety of these embodiments is diverse; and that the particulars of such embodiments are merely represented by Apparatus Versions 1-3 respectively, as described below.

APPARATUS VERSIDN 1 :

While either kind of polarity may be used, the description of Apparatus Version 1 relies upon and uses only a single alternating polarity consistently.

£ In the Apparatus Version 1 format of the invention illustrated by Fig. 5, 6, and 9a, a C-shaped yoke-coil assembly 10 is disposed adjacent to the ion beam traveling in the Z-axis direction. The yoke coil assembly completely spans the breadth dimension of the adjacent ion beam; and when an electric current is passed through the

transversely mounted electromagnetic winding coil, three different and distinct volumetric zones of magnetic field are individually created, through each of which the adjacent ion beam passes in serial sequence,

These three different and distinct volumetric zones of magnetic field extend in sequential series from the 'North' and 'South' poles existing at the end tips of the two discrete arm members in the tunnel-shaped yoke; and the three individual volumetric zones of magnetic field are contiguous with each other, merging by a smooth transition from discrete spatial zone to zone.

In addition, each discrete volumetric zone of magnetic field extending in sequential series from the assembly has individual characteristics, as shown in Fig. 8a. Thus, the end volumetric magnetic zone 113 is characterized by a magnetic field which spatially extends in a direction orthogonal to pole face surface 13.

In comparison, the second intermediate volumetric magnetic zone 112 occupies the medially located space between pole face surface 13 and pole face surface 15; lies adjacent to an exposed face of the transversely mounted coil 50; and presents a magnetic field which lies substantially normal to the plane of symmetry for the assembly, aligned with the Z-direction, as shown in Fig. 7.

Lastly, the third end volumetric zone 115 is a magnetic field which lies substantially normal to pole face 15, but spatially extends in the opposite direction to that magnetic field appearing at pole face 13. The lines of magnetic field in the third volumetric zone 115 are continuous; and the lines spatially flow from pole face 13 to pole face 15, and also from the edges of the two pole faces.

£ Fig . 9a shows the magnetic field components in these three different and distinct volumetric zones. In the second and medially positioned intermediate volumetric zone 112, the Z-axis component of magnetic field, "Bz", is large, and is greater in value than the

magnitude of the Y-axis field - which in this zone 112 passes through zero and is everywhere relatively small. In comparison, note that in the outer two volumetric zones 113 and 1 15, the opposite

circumstance is true- i. e., the Z-axis component of magnetic field is near zero in value, and in fact the component of magnetic field in the initial travel direction of the beam is substantially smaller still . Within the volumetric zone 113, the y-axis component "By" is negatively directed and large in value; while in volumetric zone 1 15, the Y-axis component "By" is positively directed and large in value.

Given the foregoing and on this basis, by placing stops adjacent to the desired beam pathway, the unwa nted ion species

(contaminants) in the traveling beam can be effectively separated from the needed or desired ion species. It is particularly important in this Apparatus Version 1 format instance to block the paths of ions passing at too great a distance from the transversely mounted coil and supporting arch yoke frame.

A P PAR ATU S VE R S I O N 2 :

A second format model version of the assembly is shown by Figs. 7 and 8b respectively; and comprises the structure of the Apparatus Version 1 format in combination with at least two shaped

ferromagnetic bars 3a and 3b, and preferably also with a third bar 4.

The magnetic field is effectively terminated on these

ferromagnetic bars at right angles to the exposed face surface. These ferromagnetic bars control the field shape; and by occupying a part of the magnetic circuit where they locally lower the value of the magnetic induction H, they raise the magnetic field in the gaps and alter its shape. In this manner, the ferromagnetic bars 3a, 3b, and 4 save further power and allow the precise focusing to be tailored for a particular use or application.

As shown by Fig.9b, in the end volumetric zones 113 and 115 bounded by the ferromagnetic bars 3a, 3b and the C-shaped core 1, the X-axis deflection of the ions is strong and fairly uniform, In the intermediate volumetric zone 112, the Y-axis deflection of ions will be greater as a result of an increase in the X- axis component of velocity from the higher magnetic field in end spatial zone 113b; but the gap distance between the two ferromagnetic bars 3a, 3b has the effect of modifying the spatial variation of the Z-axis component of magnetic field as a function of Y values. Thus, by varying the shape and/or spacing of ferromagnetic bars 3a and 3b, the spatial variation of field in intermediate volumetric zone 112b may be varied; and this variation in turn modifies the amount of Y-axis focusing that is provided.

Adjustment of the gap distances between the two ferromagnetic bars 3a, 3b and bar 4, (while also adjusting the coil current if required,) changes the amount of focusing even though the median Y-axis deflection angle hardly changes. The median Y-axis deflection angle may be adjusted by changing the current in the coil of the assembly; and this change in coil current will also modify the X-axis offset of the whole beam.

APPARATUS VERSION 3:

A third format model version of the apparatus omits the electromagnetic coils and replaces part of the steel structure in the yoke arch bridge by substitution of the electromagnetic winding with a permanent magnet material. This alteration and substitution means that the magnetic rigidity of the device can no longer be quickly adjusted .

However, some adjustment by changing the spacing of the permanent magnet material components is possible over a narrow range.

Nevertheless, for large sized ion beams, the cost of electricity to power a transversely mounted electromagnetic coil may be significant; so, if an application requiring a single beam ion species exists, the permanent magnet format version may be very advantageous.

V. A Summary Comparison Of The Three

Exemplary Apparatus Versions

A summary review is presented below of relevant and material information concerning the present invention as a whole. A

substantial quality and quantity of detail is summarily provided here in order that the true merits of the invention may be properly recognized ; and that the genuine advantages and benefits offered by the invention be appreciated for what they meaningfully offer the practitioner working in this technical field .

1. As concerns the present invention, the Y-axis deflection capability and the Y-focusing attributes are generated in the following manner: Because at all points other than near the curved ends of the electromagnetic winding coils (or permanent magnets), the generated magnetic fields lie entirely parallel to a Y-Z plane, it is impossible for these magnetic fields to impart any Y-axis directed deflection to charged ion particles then moving in a Y-Z plane in the Z-axis

direction of travel . However, even though the input or upstream beam content may only comprise charged particles traveling parallel or almost parallel to the Y-Z plane - as these ions begin to traverse the magnetic field generated by the C-shaped yoke-coil assembly, the Y-axis component of the magnetic field deflects the charged particles substantially in the ( positive or negative) X-axis direction .

Note that an X-axis directed component of ion motion i n a region with a Z-axis directed component of mag netic field will generate a Y-axis di rected deflection . Thus, if for example, the moving ions are deflected 30° i n the X-axis direction, the ion's velocity component in this X-axis direction is half their tota l velocity .

The a mount of X-axis deflection is al most independent of the Y-axis coordi nate of the ions, but a slight dependence is observable . In all cases, the a mou nt of Z-axis component of magnetic field depends on the Y-axis coordinate, but this variation can to some extent be modified by changing the spacing of bars; and the sha pe of one bar is such that it can be moved to adjust the spacing, while leaving the remaining ba rs unmoved in their optimu m position .

2. The net deflection in the X-axis di rection is zero; but the physical offset in the X-axis direction is the twice the offset from the first pole, and will depend on the coil current d i rection . The net deflection i n the Y-axis direction is proportiona l to the square of the current i n the coils; and thus is independent of the polarity of the current in the coils.

As the figure illustrations show, the net deflection in the Y-axis direction is proportional to the a mount of X-axis directed motion acquired in end spatia l zone 1 13, multiplied by the Z-axis component of field i n intermediate spatial zone 1 12. Since each of these is proportional to the cu rrent in the magnet, the total deflection effect i n the Y-axis direction is proportional to the square of the current in the coi ls . The effect of end spatial zone 1 15 is to accurately reverse the deflection effects of the other end spatial zone 113.

The square of any real number value is always positive, Thus, if the Y-axis directed deflection is proportional to the square of the current, it is always in the same direction whether the current is in the positive or negative direction in the coils.

To recapitulate: The X-axis deflection and the X-axis offset effect are both proportional to the current in the electromagnetic winding coil(s). If the practitioner reverses the current, that act and event also concomitantly reverses the offset. But the Y-axis directed deflection is always away from the magnetic poles of the assembly, and is always proportional to the square of the current.

If the practitioner continues to increase the current, the consequence is that the ions are turned around and then come back out of the entrance to the yoke-coil assembly.

3. The amount of Y-axis deflection will vary approximately linearly with the Y-axis coordinate of the ion. A linear variation generates well-behaved focusing with little to no aberration; and some optimization is possible with careful modeling, by adjusting the shapes and locations of the gap distances between the individual bars.

This Y-axis deflection parameter is of crucial importance in obtaining high resolving power - because the resolving power is calculated as the ratio of the dispersion (see above) to the beam breadth at its minimum, where it passes between slits 6a and 6b (see Figs. 6b or 10).

4. The greatest resolving power attainable is determined by the following considerations:

(a) The dispersion available from the device was calculated for a specific case earlier. To generalize, the dispersion of this device D is given by

D = 2pL

where 2β is the tota l deflection in radians in the negative y-d irection , and L is the distance of the point where this is to be determined from the center of the device .

( b) Also, the best resolving power of a ny device is

R= D/t

so in this case : R = 2βΙ_/ί

where t is the thickness dimension of the bea m at the point where the resolving aperture is located, in the direction of the mass dispersion .

(c) It is therefore apparent that : The resolving power is greatest where the bea m is focused to a minimu m thickness; and, if the focus can be moved further away from the center of the device the

dispersion wil l be greater. Unfortunately it is inva riably the case that the focus gets larger as you move further from the device .

Thus, in order to maximize resolving power, one must adjust the foca l properties of the ana lyzer device to place the focus at a

convenient distance - i. e., a chosen site which should be effectively beyond the magnetic boundaries of the device . Also, the focus q uality of the bea m focus should be as free of aberrations as possible .

5. It is a distinctive property and feature of the present invention that it is very strongly focusing . Thus, in the C-shaped yoke-coil assembly, as the total bend angle increases beyond about 16 degrees, the focal length correspondingly decreases. At present, however, there is no derived a nalytic expression for this relationship -but at a bend a ngle of 20 degrees, the conjugate focal poi nts l ie so close to the magnet that the coil windings would interfere with the mounting of the ion source and other related components, and at

larger bend angles, the conjugate focal points lie entirely within magnetic field zones 113 and 115.

It follows therefore, that with some care, resolving powers higher than 35 may be obtained for many embodiments of the C-shaped yoke-coil assembly; but at present, a resolving power of about 35 is considered to be a safe practical maximum for this invention.

The present invention is not restricted in form nor limited in scope except by the claims appended hereto.