DE2041422A1 - Element analyzer - Google Patents

Description

M 2878 PATENTANWÄLTE Dr ₁ -In ₉ . HANS RUSCHKE

'Dlpi.-Ing. HEIMZ AßULAR

BEfit.IM 33

Auflu »t« -Vlktoria-Str »l · ff -

Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, 55101, .7.St.A.

Element analyzer

The science of determining the elemental composition of a solid surface for the purpose of elemental analysis, the Detection of impurities and the state of cleanliness determining a surface has created the need for a concept and an apparatus to identify such a surface to analyze non-destructively.

It is known to produce high-energy ions from a noble gas Shoot a target area and get away from that in a relative to allow a large angle to be scattered away in order to determine the state of charge and the scattering energy of the primary ion after the collision An apparatus and method for analyzing elemental composition a solid surface is known from US Pat. No. 3,480,774.

The present invention represents an advance in the art over US Pat. No. 3,480,774 and relates to a low energy element analyzer which provides higher resolution for a sufficiently large signal and which , being compact, sees in closer proximity to the components

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can order, lam to improve the resolution. It shows:

A compact ion generator for producing a beam of essentially single-energy ions, the energy variation of the primary ion beam being 0.5 $> or less at the full width half maximum, the ions being well collimated and focused before the bombardment of the sample and the Ion generator is arranged close to the sample in order to avoid collisions of the ions with the surrounding gas, as well as a compact energy analyzer, which is arranged in the immediate vicinity of the sample, in order to collect as many scattered ions as possible and thus the number of ions supplied to the detector to optimize, and used an entrance membrane with a narrow slit, which reduces the divergence of the ions passing through it as much as possible to improve the resolution.

It is therefore the main advantage of the apparatus of the present invention that the resolution of the system, which is definitely and clearly determined the atomic mass of the target element was improved.

Another advantage of the device according to the present invention is the higher ion beam stability, which with this relative compact and simplified device over the entire working range of the ion beam was achieved.

Another advantage of the present invention is that the ion generator works stably below 100 eV.

Another advantage of the present invention is that the Analyzer can be operated under static gas conditions to increase stability and ease of operation, and avoids the need for dynamic pumping of the noble gas during operation. The present invention anion creates an arrangement in which several · part · in one are arranged in a single chamber and are openly connected to each other

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and thus the need for multiple chambers, Bypasses connecting valves and pumps.

These and other advantages of the invention emerge from US Pat following description and accompanying drawings.

Pig. 1 is a side elevation of an apparatus in accordance with the present invention Invention.

Pig. 2 is a block diagram and partially pictorial and FIG Schematic representation of the electrical components of the device according to Pig. 1.

Pig. 3 is a diagram showing the analysis of a solid surface as well as by the pretensioning of the inlet and outlet membranes resulting in improved resolution and sharpness.

Pig. 4- is a graph showing the analysis of a copper sample and shows the scattering of the isotopes Gu and Ou

The drawings and the description - and in particular Pig. 1 - show a compact slement analyzer 10 with a puddle 12, which fits on a (not shown) commercially available vacuum chamber of normal size, with a support frame 16 attached to the puddle, a multi-directional sample carrier ₍ ^ Hler is attached to the frame, an Ioatner ic euger 26, an energy analyzer 45 * an ion detector 70 and a display device 80. With this device for relatively non-destructive surface analysis or the corresponding method, a beam of primary ions 30 of known hate and energy is generated on the directed surface to be analyzed and analyzing the energy of the solid surface forming elements scattered primary ions, one that is, the en energy loss follows due to the collision of the primary ions with the Elea "at" a "measures and bestiaat from the atomic mass of the elements" analysis of a solid surface is based on the theory and formulation of binärela elastic collision based on the following assumptions. First, it is believed that the target atoms are essentially not attached to their

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Neighboring atoms are bound. Behave during the impact the target atoms are as independent as if they were gas atoms acted. Second, it is assumed that the target atoms are essentially stationary before colliding with the primary ions, Third, the energy losses of the primary ions during collision with the target atoms are said to be entirely kinetic accepted. On the basis of these three assumptions and the principle of conservation of energy and momentum, those that are present after the collision can be determined Energies of the primary ions from the scattering angles, the mass ratio and the energy present before the collision determine. It is essential that this process does not require variable or empirical factors. The following relationship for the ratio of the kinetic energy of the primary ion after the collision to that before the collision in one for simplification assumed - scattering angle ö »90,

results, resolved after

1 +

^M 2 - ^M 1 1 - E

where M ₁ - mass of primary ions,
M ₂ ■ mass of the target atoms,

E ₀ ■ is the kinetic energy of the primary ion before the collision, M ₁ ■ is the kinetic energy of the primary ion β after the collision.

Some of the main components used to complete the surfaces mentioned Analysis by ion scattering are: a source of single-energy ions with good focusing properties at low Energy values, an energy analyzer that is able to precisely define scattering angles with good resolution, a & * Ion detector and a Voretell device, bits of the samples one after the other be brought into a predetermined position without losing the vacuum »baw. d ·· carry gas ·· su lead. Uu the resolution for a given electrical signal lamp

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to enlarge a "device operating at low energy, the following points are critical!

1. The ion energy spread within the ion beam must be minimized f

2. The collimation and focusing of the ion beam must be optimized before the bombing |

3. The resolution of the energy analyzer at a known scattering angle must be optimized .

In order to achieve a reasonable compromise between the desired high resolution of the device and an appropriate electrical signal level, it is advantageous to bring the ion generator I and the energy analyzer into the immediate vicinity of the sample to be analyzed.

The flange 12 is, a normal 200-mm ultrahigh vacuum consolidates with a number of openings along its circumference with which be the Plansch to the direction indicated in Fig. 1 Housing ρ together they represent the tjl tr Ahigh vacuum chamber is. After the flange attached to the housing, which also contains the frame, the sample carrier, the ion generator and other system parts shown in Fig. 1, the chamber is evacuated to 10 Torr by a vacuum pump (not shown). Ua the remaining active elements in the chamber to further purify λ is provided in the chamber also a (not shown) getter. The pumping process is ended by switching off the pump. A noble gas is then let into the chamber through suitable valves until the static pressure, measured with a Bayard-Alpert manometer, is 5 x 10 "Torr, and then official chamber openings are closed, ie no additional noble gas is allowed into the Chamber inside. The precious atmosphere in the chamber is used to analyze the elements that make up the solid surface of the sample. The gas used can be any noble gas, but helium (He) and argon (Ar) are generally used. Electrical feed-throughs or connections 14 »extend through the flange by the required

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Union electrical connections between the components in the chamber and the electrical system parts outside the Chamber manufacture.

The drag frame 16, which is attached to the flange 12, has a lower part 18, a lower part carrier 20 for the purpose of maintaining a spacing between the electrical connections 14 and the lower part, and a vertical column 22 which is fastened to the lower part and carries the sample carrier 60.

The multiply orientable sample carrier 60 has a rotatable octagonal sample wheel 61 and side arms 62 with which the wheel is fixed relative to the column 22 so as to be rotatable and insulated therefrom, and means for stepping the wheel with it a rate gear 63 »which the sample wheel step by step, i.e. per actuation of the electromagnet magnet by a sixteenth Turn, keep turning. On each of the peripheral surfaces 66 of the A sample to be analyzed can be attached to the octagonal wheel, which is held on it by suitable holding means - e.g. Screw or spring mounts - is held in place. It 1st It can be seen that the test wheel can also be provided with a different number of circumferential surfaces, i.e. it can also be made hexagonal, for example, and that the guessing gear has a different number of teeth, which numerically corresponds to the number of surfaces on the Froben wheel. The frost carrier also has a from the frame 16 insulated sliding contact arm, which snaps into notches, around the wheel 61 and the bombarded sample to be electrically connected to an ammeter 81 (see Fig. 2), which measures the ion beam current. The electromagnet 64, a normal vacuum electromagnet, is electrically connected to a power supply unit 82 for the sample selector, which is used for Continuation of successive samples in the predetermined division of goals (as shown in Pig. 1) can be freely activated is.

The ion generator includes a grounded tubular housing 25 the dimensions 50 χ 75 χ 100 mm, dme βο designed let, deJ

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it can carry the operational parts of the compact ion generator. The compact ion generator - essentially 25 × 25 × 75 mm in size - has a hot filament 27 for generating electrons, a highly permeable grid 28 which has an open area of more than 80 $ and defines an ionization region 29 within an extractor plate 31 the reflector 30 surrounding the filament 27, four anodes 33 _S 35, 37 or 39 and a stabilization loop 41 on »

A power supply unit 42 supplies the energy for a filament so that it can supply electrons, and a grid biasing part 83 biases the grid with respect to the filament. The electrons g supplied by the filament are accelerated by the relatively permeable grid 28 to a potential which is sufficient to ionize the noble gas atoms. For example, the electrons can have an energy of 100 - 125 eV! that's enough to ionize helium with an ionization potential of approx. 24 e7 »

The reflector 30 is at the filament potential and steers electrons approaching it in a long flight path that increases the likelihood that an electron is a gas atom meets and ionizes it.

If the static pressure of the noble gas in the evacuable chamber is increased, the ion beam flow also increases. By \ an electron current control with constant gas pressure so you can control the ion beam. With the plasma source of the prior art, a large number of settings for regulating the ion beam flow could be made, but none of these could be directly related to the ion beam flow. With such a plasma source, it is therefore extremely difficult to set up a jet flow control loop. The stabilization loop 41 of the present embodiment comprises the heating power supply and the grid adapter and maintains a stable electron grid current which regulates the ion beam flow in the event of pressure fluctuations in the vacuum.

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A voltage divider circuit 85 for the ion gun is charged the extractor plate 31 to a potential with which positive ions can be extracted from the ionization region 29. The circuit 85 contains nine resistors R1 of 470 kOhm each and three linear 500 ~ kOhm potentiometers R2 with 10 turns each, which are connected in parallel and in series that, with the exception of the fourth anode 39, which is grounded, the Have the extractor plate 31 and the anodes 33, 35 and 37 pretensioned as required.

The extractor plate 31 contains an extraction opening 32 of approx. 6 mm in the beam axis 42 in order to extract the positive ions, which are then bundled into a beam by the anodes. At each anode there is one supplied by circuit 85 Potential. The first anode 33 essentially serves to control, modulate and control the extracted ions preparing to focus a collided beam. The second anode 35, from the first anode 33 further than away from the rest of the anodes, serves as the main collimating and focusing anode. The third anode 37 is on one of the Voltage divider supplied, essentially constant potential. The fourth anode 39 is grounded or could also be connected to a terminal of a high-voltage source 86, biased towards ground. Each of the anodes is off made of thin conductive material and has a small opening to control the ion flow and a single-energetic Maintain beam. The anode plates are e.g. 2 mm thick, around the wall thickness at the openings to keep as small as possible and thus interactions between the ions passing through and the wall surface and thus keeping energy losses low.

The jet emerging from the tubular housing 25 is now through the noble gas atmosphere over a distance of less alβ 100 mm on a sample to be analyzed Flat · directed. The collisions of the particles in ray b -

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limit the mean free path of the ions in this pressure— area estimated at approx. 300 mm. With the help of deflection plates arranged at the end of the housing 25 on both sides of the beam 57 the beam can be deflected slightly in order to scan the sample. The plates 57 loads a hand »or program-controlled power supply unit 87 for the ion deflection arrangement. The deflection plates 57 also help to optimize the scattering angle or the beam onto the sample surface align so that the axis of the scattered ions is aligned with the input membrane of the energy analyzer, to get an optimal electrical signal.

The ion beam bombards the sample on the preselected sample area, causing the impinging primary ions from this be scattered. The current flowing through the sample as a result of the beam is detected by an ammeter 81 and is used to determine the current density on the surface of the sample.

The energy analyzer 45 has an inlet membrane 46 a long, narrow rectangular entry slot 47; an exit membrane 49 with a rectangular exit slot 50 and two curved electrostatic analyzing plates 48. The input and output diaphragms 46 and 49 are of a Membrane preload unit 88 charged They can be connected to ground separately or together, or to similar or different ^ & e ^ positive potentials are biased. The membrane slots preferably have a width of 0.1 mm, and the The inlet membrane is located approx. 10 mm from the surface of the sample to be analyzed.

The charge on the inlet and outlet membranes 46 and 49 prevents some ions from entering the energy analyzer, thereby effectively reducing the electrical signal background detected. 3 shows the effect of the positive bias on the inlet and outlet membranes. The diagram represents the energy ratio E ₁ ZE _{0 of} the captured

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positive stray electrons above the ion current, namely from 1500 eV He ions, which from an aluminum surface with a thin coating of alumina. The curve 92 shows the typical sample spectrum without biasing the Membranes (Hull potential), curve 93 the spectrum with a positive bias of the membranes. The maxima of curves 92 and indicate the presence of aluminum and oxide at energy ratios of approx. 0.55 and 0.7, respectively. The diagram proves in other words, the increased resolution and elimination of the signal background when the membranes are pretensioned to get this through to suppress stray ions generated background spectrum.

The analyzer plates 48 are charged by a deflector 90 which receives power from a dual power supply unit. The deflector 90 allows a suitable charge to be applied to the plates to direct ions of predetermined mass and energy onto the slot in the Auegang membrane. The Analysatorplatten have an average radius of 50 mm \ the analyzer 45 shown is a normal 127 ° analyzer.

The ions scattered by the sample are captured by the energy analyzer and those with a predetermined energy passed through him. The ion detector 70 detects the number of ions passed through. That generated by it electrical signal reaches a display device 80, where the result is available for analysis.

The ion detector 70 is a single channel (continuous channel) Electron multiplier 71 with an 8 mm cone input that supports the covers the entire exit slit of the exit membrane of the 127 energy analyzer. The electron multiplier can be a Commercially available Exemρla * of the type CEM-4028 from Bendix Corporation in Ann Arbor, Michigan.

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Claims (1)

-11- Claims A compact element analyzer which fits into an evacuable chamber containing a noble gas and is of particular use for determining the egg tar composition of a solid surface by measuring the energy and number of primary ions scattered by the elements forming that solid surface and from one to the other Surface arranged energy analyzer were collected so as to identify the elements selectively and to determine the amount of each of them, the device in combination "having a sample carrier to carry a sample to be analyzed for elemental composition in a predetermined position, an ion generator for Generation of a beam of primary ions with known mass and essentially the same known kinetic energy, which also aligns the primary ions along the beam axis on the sample, an energy analyzer for the continuation of the scattered primary ions, which has a second known energy value which is less than the original kinetic energy of the primary ions in order to measure the energy lost as a result of the collision with the surface and thereby identify the atomic masses of the element scattering the primary ions, Λ and an ion detector that receives the transferred primary ions and converts them into converts an electrical signal, characterized in that the device supplying the ions has an ion generator with a filament for supplying electrons and a largely permeable grid in the vicinity of the filament which forms an ionization zone with the latter, the grid being at an electrical potential In order to accelerate the electrons to a kinetic energy which is sufficient to ionize noble gas atoms within the ionization zone, a reflector surrounding the filament and the ionization zone, eLssseii potential for redirecting electrons back into the Iojaisisrmigs-- 'zone, an extractor plate with one of the eggs 109811/1802 2ÜAH22 extraction zone around the jet axis, wherein the extractor plate is electrically biased, to attract ions from the ionization zone and direct them to the sample, as well as a first anode with a first Opening located near the extractor opening around the Located around the beam axis, the first anode being electrically biased to bring the extracted primary ions into a collimated beam of primary ions collimates, modulates and focuses, which is directed at the sample. 2. Compact element analyzer according to claim 1, the energy analyzer thereof is characterized by an inlet membrane arranged on the sample carrier and having an inlet slot, wherein the entrance slot is arranged so that it passes through the sample at a predetermined angle to the Before the sample bombardment existing primary ion beam collects primary ions scattered by curved electrostatic Analyzer plates with applied electrical potential, to pass the scattered primary ions with a certain energy value through an output membrane, the is arranged in the vicinity of the analyzer plates and has a slot which is between the analyzer plates transferred ions, and by biasing means, which are applied to the inlet and outlet membrane, to the Input membrane to a first predetermined potential and the output membrane to a second predetermined potential to lay. 3. Compact element analyzer according to claim 2, its sample carrier is characterized by a rotatable device with mutually spaced surface parts in order to this to carry a plurality of individual samples, wherein the rotatable device is arranged so that a sample in a predetermined position can be brought to the Intercept ion beam, and by feed means operatively connected to the rotatable device, with which successive Samples are placed in the predetermined position 1 0!:! HM / 1 8 Ü 2 Compact element analyzer according to claim 2, its more compact Ion generators continue to be characterized by duraji a second Anode with a second opening, the second anode in the vicinity of the first anode and the second opening in the vicinity of the first opening are arranged about the beam axis, and wherein the second anode is electrically biased to the to further collimate and focus the sample directed primary ion beam. Compact element analyzer that fits in a noble gas-filled evacuable chamber and is particularly suitable for determining the elemental composition of a solid surface by measuring the energy and number of primary ions that are dispersed by the elements forming the solid surface and by an energy analyzer located at the surface so as to selectively identify the elements and determine the amount of each element, the analyzer having in combination a sample carrier that holds a sample to be analyzed by elemental composition in a predetermined position, an ion generator for supplying a beam of primary ions of known mass and essentially the same known kinetic energy that directs the primary ions onto the sample along a beam axis, an energy analyzer that determines the scattered primary ions with a second known kinetic energy value that is less than that original, continues to measure the energy lost as a result of the collision with the surface and thus to identify the atomic mass of the element * which scatters the primary ions, and an ion detector that picks up the continued primary ions and converts them into an electrical signal, the energy analyzer - is characterized by an entrance membrane, which is located near the sample carrier ¹ and has an entrance slot which is arranged in such a way that it scatters the ions from the sample at a predetermined angle to the direction of the samples before the sample is bombarded. * t «n catches ions, curved electrostatic analyzer plate 1098 1 1/1802 204U22 -H- ten with applied electrical potential to the scattered To transmit primary ions with a predetermined energy value, an outlet membrane on the analyzer plates, one Slit to collect the between the analyzer plates further ions is arranged, as well as operationally connected to the inlet and outlet membrane Biasing means for applying a first predetermined potential to the input membrane and to the output membrane to apply a second predetermined potential. Compact element analyzer, which fits into a noble gas filled evacuable chamber, and is particularly useful for d ⁴ * determining the elemental composition of a solid C .lache by measuring the energy and number of primary ions, scattered the forming of the solid surface elements and one arranged at the surface energy analyzer were collected, and thus selectively identifies the elements and their amount is determined, wherein the analyzer in combination having a sample carrier, which ΐ a ung on Elenentarzusammenset ^ to anal / egg sample at a predetermined Si ¹ transmits lung, a An ion generator that generates a beam of primary ions with a known mass and essentially the same known kinetic energy and directs these primary ions onto the sample along a beam axis, an energy analyzer for passing on the scattered primary ions with a second known value of the kinetic energy that is lower than the original k Inetic energy of the primary ions to measure the energy lost as a result of the collision with the surface and thus to identify the atomic mass of the element scattering the primary ions Element analyzer has a plan, which forms the end wall of an evacuable chamber, as well as a support frame attached to this plan, a tubular housing carried by the frame, which can accommodate a compact ion generator 109311/1802 on the lame "fastened several times from rieh" bar en samples. support, which is in the vicinity of the tubular housing ", in order to bring successive samples into a predetermined target position, whereby this sample carrier is a rotatable device with spaced apart ' Has surface parts that have a number of individual Carry samples, and the rotatable gate direction is arranged so, that they put the samples one after the other in the predetermined position, brings, as well as an energy analyzer, that of the railways carries and the one lying in the vicinity of the sample carrier Entrance and look along this tubular.housing. stretches to carry ions with a predetermined energy, and an ion detector that the frame supports and | the one near the * tubular housing and the energy analyzer is arranged and the continued ions in converts an electrical signal in which the primary ions from the compact ion generator are directed at a first sample and bombard this and the scattered ions collected and forwarded to the ion detector, in order to establish the elementary interconnection by means of the electrical signal to display the sample surface « Method for determining the elemental composition of a solid surface by measuring the energy and number of developed an ion generator and one to be analyzed Primary ions scattered on the surface, characterized in that an ion generator, arranges a sample to be analyzed, an energy analyzer and an ion detector, the active gases in the, Chamber up to a predetermined active gas pressure of evacuated less than 10 "Torr, the evacuation of the chamber is interrupted, the chamber again with an inert gas up to fills a partial pressure that is sufficient to generate a The ion beam determines the purity of the noble gas and by going to the analysis of the surface © by means of the ion generator an ion beam from the Eds? ^ gaF. generated. 109811/1802 8. The method according to claim 7, further characterized by that you get the interior of the chamber after evacuation to the aforementioned active gas pressure to substantially chemically absorb all active gas in the chamber. 9. The method of claim 8, wherein evacuating the chamber is further characterized in that the chamber cryogenically pumps. 10. The method of claim 9, wherein the inserted into the chamber energy analyzer with conductive input and output membranes Has slots and the method is further characterized in that the membranes are positively biased, in order to reduce the noise level caused by splashing and disruptive stray ions. M 2878
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