DE1798021A1 - Microanalysis device - Google Patents

Description

DR.-ING. DIPL-ING. G. RIEBLIHG My sign

A 333 - Gu / Sö

Repeat bine in answer

L J

899 Lindau (Bodensee) Your reference Your message from My Message from Rennerle 10 PO Box

August 6, 1968

Reference:

Applied Research Laboratories, Inc., Glendale / California / USA

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Microanalysis device (elimination from patent application A 53 728 VIIIc / 21 g, 21/01)

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The invention relates to a microanalysis device in which a Ion beam is directed onto a selected surface section of a material sample by accelerating the ions after their generation and focusing into a narrow bundle of rays, the cross-section of which is smaller at the material sample surface than at the Outlet aperture of the ion source, an analysis device are fed.

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The invention is based on the object of increasing the sensitivity of such a microanalysis device. These The object is achieved according to the invention in that in the beam path

and/
A sector lens and at least one electrical equipotential lens, which is arranged in series with the sector lens and between its object and image planes, is provided in front of / behind the material sample, the equipotential lens essentially reducing the distance along the axis of the particle beam between the object - and image planes compared with this distance in the presence of the sector lens alone.

This ensures that the ion beam hits a small surface area the material sample can be focused, specifically on an area that is smaller than the ion exit opening of the Ion source. The mass spectrometer, which then analyzes the ion beam, can therefore have a large aperture and a high transmission factor own. In this way, a relatively large proportion of the emitted ions is collected in the mass spectrometer and at used in an analysis. In addition to a high sensitivity, a high signal-to-noise ratio is also achieved.

Particularly good results can be achieved if the analysis device of one with respect to the angle and the energy of the ions

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1 7 9 "?? 1

there is a sharpening, stigmatic imaging mass spectrometer.

To focus the analyzer on the ions of a According to an advantageous embodiment of the subject matter of the invention, certain alasse can additionally have an electrical equipotential lens be arranged between the! mass spectrometer and the material sample.

To automate an analysis, it is advantageous if a deflection device is provided for deflecting the ion beam over the material sample, so that the ion beam is arranged one behind the other Scans areas of the surface of the material sample, as well as a transducer for generating electrical signals in response to ions, which are analyzed by the mass spectrometer and the OsziUoskop, is provided and by means for modulating the intensity of the electron beam of the oscilloscope in response to signals from the transducer and deflection means for deflecting the electron beam of the oscilloscope synchronously with the deflection of the ion beam over the material sample.

Because of the lens device used according to the invention, the mass spectrometer can use an exit slit of very small width, it is advantageous to connect the output of the mass spectiometer to a

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ORiGHNAl '>; *? ·: «; to

To increase the intensity of the impacting ions.

To deflect unwanted ions from the focusing device, it is advantageous to place between the outlet diaphragm of the ion source and a sector lens can be arranged on the focusing device.

The invention is based on an exemplary embodiment below explained in more detail: ■

It shows:

Figure 1 is a schematic cross-sectional view of one of the microanalyzer lens system used according to the invention ^;

FIG. 2 shows a detail in cross section of that shown schematically in FIG Lens;

FIG. 3 shows a schematic cross section of a lens system according to a modified form;

FIG. 4 in a schematic representation the view of a microanalysis device, in which a lens system according to Figure 1.-3 is used and

Figure 5 is a partial side view in a schematic embodiment of a Section, the analyzer shown in Figure 4

seen in the direction of arrow 5 according to FIG. 109835/0672

INSPECTED

179P021

In FIGS. 1-3, sector field lenses are shown which, in the type identified at the outset, increase the sensitivity of the Increase microanalyzer according to the invention.

Referring to Figure 1, there is the effect of the series connection an electric equipotential lens 10 with an electric sector field lens 12, the zrB, Jn form of a spherically curved annular capacitor can be formed. When the sector lens 12 is operated alone, it has one Angular aperture - ^ T and its object focal plane, which as in FIG. 1 can be seen on the right, would be relatively far away from the lens 12, as is indicated by the object point 16. The angular image deviation of the lens 12 is represented by the line 18, which is perpendicular to the Gauss * image point 22 on the Main axis is. The angular image deviation indicates the width of the image of the individual, theoretically dimensionless thing point 16.

When the equipotential lens 10 is connected in tandem and in front of the sector lens 12, the thing plane becomes closer to the sector lens 12 moved to a point indicated by the image point 24, and

tQ with a corresponding increase in the angular opening, which is now co

^ω becomes oC ' . However, the scatter is not significantly increased and the cn

ο The location of the image point 22 is not changed. σ>

An ion source 26 is shown schematically in FIG. The source can be of any suitable type, such as e.g. B. in the form of a

OWeWAl INSPECTED

179: "0 2 1

Gefäßee-μη dem a noble glass through a continuous spark discharge is excited. Ions leave the source 26 through an opening 28 and are with the accelerator electrode 30 against the distribution system the invention accelerated. They then pass through a set of baffles 32 which are controllably energized to rotate

and the position of the beam oinzu & te ¥ £ € n. They then enter the equipotential lens 10, consisting of a first, grounded electrode 34, a second grounded electrode 36 and a charged electrode 38, which is located between these two grounded electrodes and is stripped from it. The diaphragm 40 is seated between the equipotential lens 10 and the spherical capacitor 12.

The spherical capacitor 12 includes inner and outer spherical curved ones Plates 42 and 44, respectively, the opposing surfaces of which are curved about a common center point. The plates 42 and 44 are attached to suitable bearings such as those shown Fasteners 46 and through the insulating spacers 48 thereof isolated. The ions exit the spherical capacitor 12 along the axis 20 and those of selected energy are conventional Manner for the purpose of modulation by means of any suitable devices through an exit aperture (not shown).

Figure 3 shows the effect of using two equipotential lenses in conjunction with a single sector field lens 12 *. Both the object

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INSPECTED

179-121

and the image plane are brought closer to the sector field line 12 * than would be the case without the flipotential lenses is the case and in spite of everything there is still no notable increase in the angular, image deviation of the system in comparison to the angular image deviation of the sector field used alone

Another advantage of using the present invention is in that it allows focusing with electrical devices rather than physically moving the ion source on the sector field line. Optimal focus can easily be achieved by changing the refractive power of the Equipotential lens is adjusted by adjusting the potential on the center electrode until the object or image plane depending aligns with the actual position of the object or with that of the image-taking device, as the case may be.

In the case of systems according to the invention, the focus in only one Coordinates direction are arranged, as z. B. is the case with one arranged in series with an electrical equipotential slit lens uniform magnetic sector falls, the rough angle recording is greater than that of the sector field, in proportion to the ratio the object distance of the sector field solely for the object distance

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the series connection.

For systems that focus in two mutually perpendicular Coordinate directions are arranged, such as. B. in the system of Figures 1 and 2, consisting of an electric spherical capacitor and an equipotential, coaxial diaphragm lens, the solid angle recording is around the square of the ratio of the relevant object distance larger compared to the sector lens alone.

In all cases, however, the increase in deviation is one order of magnitude smaller than that of the sector field lenses alone than the deviations of the sector field lens and consequently for most Applications of no practical impact.

The size of the bombardment beam at its impact center on the material sample determines the resolving power of the analyzer

and this can be compared with the resolving power achieved so far be asked. The ions shot through the spectrometer are simply demodulated and not used to generate an enlarged one Ion image of the excited surface of the material sample used. There can therefore be relatively large spreads without any weight falling loss of resolution in the spectrometer can be tolerated, so that it is possible to use a spectrometer with a large aperture to use, with which a relatively large proportion of secondary ions can be directed into the spectrometer and analyzed by it,

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INSPECTED

- Figure 2 shows the design of a sector-shaped field lens. The same numbers denote the same parts. In the insight 26 there are devices 32 that generate serve the electrical equipotential lines. Mechanical adjustment options via lenses 34, 38 mounted in balls with the entrance 40 allow the propagation along the center line 20 and the inner boundary surfaces 42, 44 of the sector-shaped field lens 12, The housing 46 of this lens encloses the actual lens, the is held in brackets 48.

According to Figures 4 and 5, an analyzer comprises an ion source 110, which can be of any desired type. You can, for example, from consist of a vessel containing an atmosphere of a noble gas, such as. B. argon, under a pressure of a few microns of mercury contains. Electrodes (not shown) within the vessel are used to generate a low voltage arc discharge excited by the gas to produce ions, the positive ones escape through an opening 112 into a relatively highly evacuated portion of the analyzer. The ion source 110 is suitably used kept under a relatively high positive potential, about 20 KV with respect to ground, and the ions are grounded through a Accelerating electrode 114 away from opening 112 against a filter device 116 accelerated.

The ions emitted from aperture 112 do not contain any larger one

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Proportion of the ions of the noble gas, but at the same time also a small proportion of contaminated ions, which originate from gases which from the walls of the vessel surrounding the gas and from particles that are sprayed off by the electrodes that generate the arc will. The purpose of this filter device 116 is to deflect the foreign ions from the ions of the noble gas and the noble gas ions in essential φ licher pure form in one direction against the one to be analyzed

Concentrate material sample 124. As shown, the filter exists 116 from a wedge-shaped magnetic sector field, the plane of symmetry of which lies in the plane of the drawing and which is against the ion source 110 tapers. Such a field is sharply established both in the plane of symmetry and in the direction perpendicular to it, so that the desired ions emerge from these parallel paths at a selected moment.

After the noble gas ions have passed through the filter 116, strike out they an electric equipotential lens 118. This lens produces an ion image 119 of the opening 112 that is approximately ten diameters is reduced in size. The lens 118 can also be used as a condensate lens are designated. A part of the emerging from the condensate or lens 118 Ions are picked up by an objective lens 122 which, as shown, is also an equipotential lens and often on the surface the material sample 124 to be analyzed generates a further reduction. The ion beam is thus cleaned and applied to one point the surface of the material sample, which is approximately 1/100 des

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ORiQfN INSPECTED

Diameter of the ion aperture 112 is such that, for example, an area approximately only one micron diameter of the ion beam is fired when the opening 112 is approximately 0.1 mm in diameter.

A pair of deflector plates is located above the objective lens 122 126 for deflecting the ion beam in two coordinate directions. The ion beam can thus cover a selected area of the material sample scan.

Wherever the ion beam hits the material sample, there will be Spray particles of the material sample from the surface. These particles are predominantly neutral atoms that make up the composition represent the material sample. A small fraction of the particles sprayed off, however, consist of positive ions. The material sample is held below a positive potential, typically 2.5 kg / volt with respect to ground (earth) so that the emitted positive ions are accelerated via the grounded electrode 127 against the mass spectrometer, which in general is indicated by 130. Due to the small size of the ion-emitting There is no need for an entry slot for the mass spectrometer on the surface of the material sample.

The main details of the mass spectrometer according to the Invention are shown in FIGS.

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The spectrometer 130 has double focus, which means that the spectrometer has both an angle and a also generates an energy focus. It is about stigmatic image generation, i. E. that the Gaussian see pixel or the first order image point in the radial plane (the plane of curvature of the mean particle path 136, which is also the plane φ of the drawing) with the first-order pixel on the

axial plane (the plane through the mean particle path at the image point, which runs perpendicular to the radial plane) coincides. The spectrometer also has a relatively large recording angle * These features contribute to a relatively high ion transfer factor, making the analysis of a relatively high allows a large proportion of the ions emitted by the material sample 124 and thus a high sensitivity is created.

The first component of the mass spectrometer 130 is an electrical one Equipotential lens 132 extending from the accelerator electrode 128 Ions are directed onto a spherically curved, annular capacitor wherein the central particle path 136 is at an angle of approximately Is deflected by 45 °. The inlet opening of the condenser 134 is defined by a diaphragm 135, which is preferably adjustable, thus allowing the resolution and sensitivity of this spectrometer to be adjusted. The ring capacitor acts as a

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Energy filters to the ions according to their respective energies

to disperse. Ions with energies within a selected range then pass through an aperture 138, the energy selector, which is also preferably adjustable and only the ions in the selected one Energy range allows access to a wedge-shaped, magnetic sector field 140. The sector magnetic field 140 dissipates the ions according to their respective moments or masses and effects a focusing of ions of a selected mass on the exit opening 142, the width of which is also preferably adjustable. the The width of the outlet opening 142 determines the mass resolution of the spectrometer. This resolving power is also of the sizes of the entrance opening in the aperture 135 and that of the selector opening determined in the aperture 138. During operation, all of these Openings usually set together to a maximum Achieving resolving power with a desired sensitivity matches.

Ions that run through the outlet opening 142 hit the Receiver 144 of an electron amplifier 146 which, in response to the intensity of the ion flow arriving at the receiver 144 generates an electrical signal. This signal can be used on a measuring instru-

1 098 35 / Q6 7 2

ment or - as shown - is preferred amplified and used to modulate the intensity of the electron beam of an oscilloscope 148.

In the illustrated embodiment, the beam deflection of the oscilloscope 148 is with the deflection of the primary ion beam synchronized in both coordinate directions, so that when a selected area of the material sample is scanned by the bombarding Ion beam the screen of the oscilloscope will represent an enlarged image. This enlarged image shows the Distribution of a selected element or an isotope on the surface of the material sample, with differences in concentration can be shown from point to point by differences in brightness. The element or isotopes in question are determined by matching it of the mass spectrometer is chosen according to known principles.

A subordinate clause is preferably located between the second acceleration electrode 128 and the input to the mass spectrometer 130 baffles 150 to maximize the resolution of the microprobe by compensating for the effect which is created by scanning the surface of the material sample by means of the bombardment beam. In the absence of secondary

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Deflection plates 150 will become the bundle knot of the secondary Ion beam at the outlet opening 142 of the mass spectrometer move as the primary or bombardment beam scans the material sample surface and it would be necessary that the exit opening 142 is expanded enough to allow this movement. An enlargement of the outlet opening 142 would reduce the mass resolution of the spectrometer. The attachment of secondary baffle plates 150 'makes the outlet opening larger 142 obsolete because of the synchronous excitation of the secondary deflector plates 150 and the primary baffles 126 of the bundle knot can be kept quiet at the outlet opening 142.

According to a further feature of the invention is to increase the Ion emission of the material sample 124 provided an electron gun. Only a small fraction of that from the material sample in Response to ion bombardment leave hosed parts the material sample 124 in an ionized state, most of the Hosed particles are in the form of λ ^ οη neutral atoms and molecules. According to the invention, the electron gun 152 is against the side The ion beam is offset and arranged to form an electron beam Point at the surface of the material sample 124 under test. By appropriately choosing the size of the electron beam, the current and

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the energy, appropriately determined separately for each of the components subject to the analysis by trial and error can be, a substantial proportion of the neutral particles sprayed by the electron bombardment ß ionized, which the Amount of ions available for analysis is further increased.

Typical operating voltages (all relative to ground) of the various Elements of the microprobe are indicated in the drawing. These values are not limiting factors in practicing the invention but were found to be within optimal ranges for an ion microprobe in which the various elements relevant, approximate dimensions and distances have:

Distance from ion outlet port 112 to

Filter 116 5 "

mean radius of curvature of the mean ion path

through the filter 116 5.5 "

Distance between the relevant central electrodes of the equipotential lenses 118 and 126 10 "

Distance between the center electrodes of the second equipotential lens 126 and the material sample 124 J "

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ORIQINAL INSPECTEO

mean radius of curvature of spherical capacitor 134. 10 "

Inlet 135 and selector aperture 138: adjustable from about 1 mm to about 10 mm in diameter

Average radius of the mean ion path through

the magnetic sector field 140 5.5 "

Width of outlet opening 142:

adjustable between 1.2 mm and 10 microns

The embodiment shown deals mainly with the idea of microanalysis using secondary ion emission Producing good resolution by using only a very small surface area of a material sample under analysis and a large aperture mass spectrometer is used to measure the to analyze ions emitted from the excited surface. That at The resolving power achievable with the application of this invention can be equated with the best so far achieved in microanalysis, while the sensitivity, i.e. h, the ability to find constituents, which are only present in small concentrations, is improved by a substantial factor.

In the embodiment of Figures 4 and 5, the mass spectrometer covers the mass range up to mass 1000. Its mass resolution

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OHiOSNAL INSPECTED

power can be controllably varied from about 100 to about 10,000. The concentration sensitivity ranges from a few particles per million for most elements to a few particles per trillion for those Elements that are relatively easily ionized, such as the alkali metals,

Claims

"IIIIIIISSII" "

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INSPECTED

Claims (6)

- 19 P ate η t a η s ρ r ti c h e 1. Microanalysis device in which an ion beam is applied to a selected one Surface section of a material sample is directed by the ions after their generation, acceleration and focusing into a narrow bundle of rays, the cross-section of which is on the surface of the material sample is smaller than at the outlet diaphragm of the ion source, fed to an analysis device, because it is characterized in that it is in the beam path in front of and / or behind the material sample a sector lens and at least one electrical equipotential lens, which with the sector lens in series and between their object and Image planes is arranged, is provided, wherein the equipotential lens essentially a shortening of the distance along the axis of the Teilclienststrahls between the object and image planes compared effected with this distance in the presence of the sector lens alone. 2. Apparatus according to claim 1, characterized in that the analyzing device consists of one with respect to the angle and the energy there is a sharpening, stigmatic imaging mass spectrometer. 3, device according to claim 2, characterized in that in addition, an electrical equipotential lens between the mass spectrometer and the material sample is arranged, 1098 35/0672 173 ^ -321 4. Apparatus according to claim 2 or 3, characterized by a deflection device for deflecting the ion beam over the material sample, so that this successive, individual surfaces sweeps over the surface of the material sample, a transducer for generating electrical signals in response to ions emitted by the Mass spectrometer and the oscilloskbp are analyzed by means of modulating the intensity of the electron beam of the oscilloscope in response to signals from the transducer and deflection means for deflecting the electron beam of the oscilloscope in synchronism with the deflection of the ion beam over the material sample. 5. Apparatus according to claim 4, characterized in that that the mass spectrometer uses a very narrow exit slit and that the deflection of the ions to be analyzed by the Mass spectrometer of the type is that the selected output of the mass spectrometer is kept unchanged at one point. 6. Apparatus according to claim 1, characterized in that between the outlet aperture of the ion source and the focusing device, a sector lens for deflecting undesired ions from the focusing device is arranged. 1098 3 5/0672 BATH L e r s e i t e