SE542904C2 - Method and arrangement for distance control between a sample and an aperture - Google Patents

Method and arrangement for distance control between a sample and an aperture

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Publication number
SE542904C2
SE542904C2 SE1851528A SE1851528A SE542904C2 SE 542904 C2 SE542904 C2 SE 542904C2 SE 1851528 A SE1851528 A SE 1851528A SE 1851528 A SE1851528 A SE 1851528A SE 542904 C2 SE542904 C2 SE 542904C2
Authority
SE
Sweden
Prior art keywords
sample
aperture
pressure
low
distance
Prior art date
Application number
SE1851528A
Other languages
Swedish (sv)
Other versions
SE1851528A1 (en
Inventor
Anders Nilsson
Peter Amann
Original Assignee
Scienta Omicron Ab
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Filing date
Publication date
Application filed by Scienta Omicron Ab filed Critical Scienta Omicron Ab
Priority to SE1851528A priority Critical patent/SE542904C2/en
Priority to EP19821307.6A priority patent/EP3891774A1/en
Priority to PCT/SE2019/051242 priority patent/WO2020117124A1/en
Priority to JP2021531777A priority patent/JP7280359B2/en
Publication of SE1851528A1 publication Critical patent/SE1851528A1/en
Publication of SE542904C2 publication Critical patent/SE542904C2/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/227—Measuring photoelectric effect, e.g. photoelectron emission microscopy [PEEM]
    • G01N23/2273—Measuring photoelectron spectrum, e.g. electron spectroscopy for chemical analysis [ESCA] or X-ray photoelectron spectroscopy [XPS]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/227—Measuring photoelectric effect, e.g. photoelectron emission microscopy [PEEM]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/05—Electron or ion-optical arrangements for separating electrons or ions according to their energy or mass
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/285—Emission microscopes, e.g. field-emission microscopes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/07—Investigating materials by wave or particle radiation secondary emission
    • G01N2223/085—Investigating materials by wave or particle radiation secondary emission photo-electron spectrum [ESCA, XPS]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/30—Accessories, mechanical or electrical features
    • G01N2223/34—Accessories, mechanical or electrical features sensing means for gap between source and detector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/18—Vacuum control means
    • H01J2237/182—Obtaining or maintaining desired pressure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/18—Vacuum control means
    • H01J2237/188—Differential pressure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/20—Positioning, supporting, modifying or maintaining the physical state of objects being observed or treated
    • H01J2237/202—Movement
    • H01J2237/20221—Translation
    • H01J2237/20235—Z movement or adjustment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/26—Electron or ion microscopes
    • H01J2237/2602—Details
    • H01J2237/2605—Details operating at elevated pressures, e.g. atmosphere
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/26—Electron or ion microscopes
    • H01J2237/285—Emission microscopes
    • H01J2237/2855—Photo-emission

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Abstract

A method is provided for controlling a distance (d) between an aperture (3), in a wall (6) separating a sample region (2) from a low-pressure chamber (4) which is vacuum pumped, and a sample surface (Ss), facing the aperture (3), of a sample (1) placed in the sample region (2) at the distance (d) from the aperture (3). The distance (d) between the sample surface (Ss) and the aperture (3) may be controlled with a positioning system (Ps). The method comprises the steps of providing at least one gas outlet (5) arranged to direct gas into a volume between the wall (6) and the sample surface (Ss), providing a sample pressure by supplying a constant flow of gas from said at least one gas outlet (5), measuring at predetermined time intervals the pressure inside the low-pressure chamber (4), and controlling in a closed loop the positioning system (Ps) to keep the pressure inside the low-pressure chamber (4) constant, thereby keeping the distance (d) between the aperture (3) and the sample surface (Ss) constant.

Description

1METHOD AND ARRANGEMENT FOR DISTANCE CONTROL BETWEEN A SAMPLE AND AN APERTURE TECHNICAL FIELD The present invention relates to a method and an arrangement for controlling a distance between asample and an aperture. More specifically, the present invention relates to a method for controlling adistance between an aperture, in a wall separating a sample region from a low-pressure chamber which is vacuum pumped, and a sample surface, facing the aperture.
BACKGROUND ART ln the prior art systems for Ambient Pressure Photoemission Spectroscopy (APXPS) and AmbientPressure Photo Emission Spectroscopy (APPES) a high pressure is provided at a sample while radiatingthe sample to provide, e.g., photoelectrons or electrons originating from Auger processes. Thephotoelectrons are collected in an electrostatic lens system which is differentially pumped. Theelectrostatic lens system focuses the photoelectrons onto an entrance to a measurement region. Toenable a high vacuum in the electrostatic lens system, the aperture into the electrostatic lens system has to be small. ln prior art APPES is performed in three ways; 1) a sample is put in a chamber and the whole chamberis raised to ambient pressures in the mbar range, this is known as the backfill approach; 2) is a variantof the backfill approach where different chambers are sued for different set of experiments and thechambers are exchanged, hence this method is called the exchangeable chamber approach; and 3) anin situ gas cell encapsulate the sample with the front aperture of the analyser. All these three wayscould be operated in flow mode, where the gas is let in and simultaneously pumped out via an outletor the gas is only pumped out via the front cone and the pumping arrangement of the analyser.Electrons have a very small mean free path in gas at ambient pressure. Thus, to enable the electrons totravel from a sample and pass the gas and enter the lens system, the distance between the aperture and the sample must be kept small.
The general prior art of pressure estimation originates from Ogletree et al. ", Rev. Sci. lnstrum. (2002)73, 3872", where the pressure profile between the sample chamber and electrostatic lens chamberthrough an aperture is estimated using a simple analytical function. The pressure profile is alsodiscussed in H. Bluhm, "J. Electron. Spectrosc. Relat. Phenom., 177 (2010), 71-84, and in J. Kahk et al."J. Electron. Spectrosc. Relat. Phenom., 205 (2015) 57-65”. ln said articles it is estimated that the pressure at the sample surface is 95 % of the pressure measured in the sample chamber with a 2 distance of 1 aperture diameter between the sample surface and the aperture and 98 % of thepressure measured in the sample chamber with a distance of 2 aperture diameters between thesample surface and the aperture. Kahk et al. have also calculated that the pressure at the samplesurface is varying with pressure. The higher the pressure the more accurate the pressure reading for 1diameter distance, but for low pressures 2 diameters will be more accurate. The distance from the sample to the cone is related to the pressure of the sample surface as described said articles. lt is, thus, of great importance to keep the correct distance between the sample surface and theaperture, especially in APPES. ln the prior art the distance between the sample surface and theaperture has been controlled by manually observing the gap between the sample and the aperture by eye, using the scale of the manipulator, or with a camera microscope.
SUMMARY OF THE INVENTION An object of the present invention is to provide a method and a computer program for controlling adistance between an aperture, in a wall separating a sample region from a low-pressure chamberwhich is vacuum pumped, and a sample surface, facing the aperture, which method and computer program are alternatives to the methods and computer programs of the prior art.
Another object of the present invention is to provide an arrangement in which a distance between anaperture, in a wall separating a sample region from a low-pressure chamber which is vacuum pumped,and a sample surface, facing the aperture, may be controlled, which method and computer program are alternatives to the methods and computer programs of the prior art.
Favourable solutions to these objects are presented in the independent claims.
Further advantages are provided with the features of the dependent claims.
The method and computer program according to the invention are primarily intended to be used for ananalyser arrangement for determining at least one parameter related to charged particles emitted from a particle emitting sample. Primarily, the analyser arrangement is an electron spectrometer.
According to a first aspect of the present invention a method is provided for controlling a distance dbetween an aperture, in a wall separating a sample region from a low-pressure chamber which isvacuum pumped, and a sample surface, facing the aperture, of a sample placed in the sample region atthe distance from the aperture. The distance d between the sample surface and the aperture may becontrolled with a positioning system. The method is characterized in that the method comprises thesteps of a) providing at least one gas outlet, connected to a gas supply device, arranged to direct gas into a volume between the wall and the sample surface, b) providing a sample pressure by supplying, with the gas supply device, a constant flow of gas fromsaid at least one gas outlet, c) measuring at predetermined time intervals the pressure inside the low-pressure chamber, and d) controlling in a closed loop the positioning system to keep the pressure inside the low-pressurechamber constant, thereby keeping the distance between the aperture and the sample surface COnStant.
The method according to the first aspect provides a very precise distance control. Especially at smalldistances the method according to the first aspect is extremely precise and is better than the methodsof the prior art where an optical microscope is used to control the distance. At distances of below 50um, the contrast in optical microscopes is often very poor and a reliable distance measurement is difficult.
The method according to the first aspect of the invention may be used to compensate for movement of the sample surface in relation to the aperture due to, e.g., thermal expansion of the sample.
The method requires the flow of gas to be kept constant.
The term wall should be interpreted broadly. The wall in which the aperture is formed may have any shape.
With the method according to the first aspect of the invention, a constant distance may be maintainedbetween the sample and the aperture. The method is based on the discovery that the pressurebetween the sample surface and the aperture for a constant flow of gas increases with a decreasingdistance between the sample surface and the aperture, and that the pressure inside the low-pressurechamber, located behind/inside the aperture, increases with an increasing pressure on the outside ofthe aperture. The correct distance may be set initially by an absolute measurement. Such an absolutemeasurement may be performed in many different ways. lt may be possible to calibrate the pressureto different distances. Thus, it might be possible to move the sample surface to a position where thepressure in the low pressure chamber corresponds to an earlier determined pressure for the wanted distance.
One example of a situation in which the distance between the sample and the aperture has to becontrolled is when the sample is heated. Due to expansion of the sample when it is heated, the samplesurface will move towards the aperture, resulting in a decreasing distance. The method according tothe present invention is very precise for small distances between the sample and the aperture but loses its precision for larger distances. 4The pressure in the low-pressure chamber may be in the interval between 104 to 102 mbar, preferablylower than 2x10'3 mbar. A low pressure is necessary for many applications such as when the low-pressure chamber is an electrostatic lens arranged to focus electrons into an electron beam.
The sample pressure may be provided to be higher than 1 mbar, preferably higher than 10 mbar. Thesample pressure may be as high as several bars. A substantial pressure difference should be maintainedbetween the interior of the low-pressure chamber and the pressure at the sample, i.e., the samplepressure. A substantial pressure difference is necessary to be able to detect a pressure difference inside the low-pressure chamber for small apertures.
The aperture may have a largest dimension in the plane of the end surface being smaller than 1 mm. Thelargest dimension of the aperture in the plane of the end surface is preferably smaller than 300 um andmay be smaller than 100 um. For circular apertures the largest dimension is equal to the diameter of theaperture. A small aperture is necessary to be able to have a small distance between the aperture andthe sample, which is particularly desirable for a photoelectron spectrometer at high sample pressures.The diameter of the aperture determines the minimum achievable distance between the aperture andthe sample surface if a high pressure is to be maintained at the sample surface. According to establishedtheories a distance between the sample surface and the aperture being twice the diameter of theaperture enables a pressure at the sample surface of 99 % of the pressure at a very large distance fromthe aperture, when a vacuum is present on the opposite side of the aperture. At a distance being equalto the diameter of the aperture the pressure is 95 % of the pressure at a large distance from the aperture.Thus, the possible distance between the aperture and the sample surface is approximately equal to thediameter of the aperture to maintain a reasonable pressure at the sample surface. For a very smalldistance between the sample surface and the aperture, a very small diameter of the aperture is HGCGSSEFV.
The distance between the sample and the aperture should preferably be kept at no more than 3 times the diameter of the aperture for the method to function with very high precision.The low-pressure chamber may be an electrostatic lens for focusing electrons.
For the method to function properly the pressure should decrease in the direction outwards from thevolume between the sample and the aperture. For sample pressures above 1 bar the sample may beplaced in ambient pressure. However, for lower sample pressures the sample and the wall should bearranged in a chamber, which is vacuum pumped to provide a pressure gradient outwards from the volume between the aperture and the sample surface.
According to a second aspect of the present invention a computer program is provided for controlling adistance between an aperture in a wall, separating a sample region from a low-pressure chamber,which is vacuum pumped, and a sample surface, facing the aperture, of a sample placed in the sampleregion at the distance from the aperture. The distance between the sample surface and the aperturemay be controlled with a positioning system. At least one gas outlet, connected to a gas supply device,is arranged to direct gas into a volume between the wall and the sample surface. Said computerprogram comprises instructions which, when executed by at least one processor cause the at least oneprocessor to carry out the steps of a) controlling the gas supply device (20) to supply a constant flow of gas to said at least one gas outlet(5), b) receiving at predetermined time intervals the pressure values for the pressure inside the low-pressure chamber (4), and c) controlling, in a closed loop, the positioning system to keep the pressure values constant, thereby keeping the distance (d) between the aperture (3) and the sample surface (Ss) constant.
The computer program gives the advantages as were described in relation to the method according to the first aspect of the present invention.
The term wall should be interpreted broadly. The wall in which the aperture is formed may have any shape.
According to a third aspect of the present invention a computer-readable storage medium carrying acomputer program according to the second aspect for controlling a distance between an aperture and a sample surface is provided.
According to a fourth aspect of the present invention an arrangement is provided, for collecting chargedparticles from a sample surface of a sample. The arrangement comprises a sample holder, for holdingthe sample in a sample region, a low-pressure chamber, comprising an aperture, in a wall separating thesample region from the low-pressure chamber, wherein the aperture is arranged to face the samplesurface of the sample, when it is placed in the sample holder, in order to collect charged particles fromthe sample surface into the low-pressure chamber. The arrangement also comprise a positioning systemfor controlling the position of the sample holder and, thus, the distance between the sample surface andthe aperture, and means for vacuum pumping of the low-pressure chamber. The arrangement ischaracterized in that it comprises at least one gas outlet arranged to direct gas into a volume betweenthe wall and the sample surface, gas supply device for providing a constant flow of gas from said at leastone gas outlet, to supply a sample pressure, means for measuring the pressure inside the low-pressure chamber, a control unit connected to the means for measuring the pressure and to the positioning 6means and arranged to measure the pressure, with the means for measuring the pressure, atpredetermined time intervals and to control the positioning system in a closed loop control to keep thepressure inside the low-pressure chamber constant, thereby keeping the distance between the apertureand the sample surface constant. The advantages with the arrangement are the same as has been discussed above for the first aspect of the present invention.
The low-pressure chamber may be an electrostatic lens system comprising a first end, at which theaperture is arranged, and a second end, wherein the lens system is arranged to form a particle beam ofcharged particles, emitted from the sample surface and entering through the aperture at the first end, and to transport the charged particles to the second end.
The low-pressure chamber may be other types of chambers but the arrangement is especially suitable to be implemented with an electrostatic lens.
The pressure in the low-pressure chamber may be in the interval between 10'4 to 10* mbar, preferablylower than 2x10'3 mbar. A low pressure is necessary for many applications such as when the low-pressure chamber is an electrostatic lens arranged to focus electrons into an electron beam.
The means for providing a constant flow of gas is arranged to provide a sample pressure higher thanlmbar, preferably higher than 10 mbar. A substantial pressure difference should be maintainedbetween the interior of the low-pressure chamber and the pressure at the sample, i.e., the samplepressure. A substantial pressure difference is necessary to be able to detect a pressure difference insidethe low-pressure chamber for small apertures. The pressure in the low pressure chamber is typicallymeasured with a pressure gauge having a logarithmic sensitivity. The lower the pressure on the vacuum side, the better is the sensitivity of such a pressure gauge The aperture size and sample to aperture distance that was discussed above for the first aspect of the invention are valid also for the arrangement.
The arrangement may comprise a measurement region for determining at least one parameter relatedto charged particles emitted from a sample surface of a particle emitting sample, said measurementregion comprising an entrance allowing at least a part of said particles to enter the measurement region,wherein the second end is arranged at the entrance of the measurement region. This is a particularly suitable technical field for implementation of the invention.
For the arrangement to function properly the pressure should decrease in the direction outwards fromthe volume between the sample and the aperture. For sample pressures above 1 bar the sample may be placed in ambient pressure. However, for lower sample pressures the sample and the wall should be 7arranged in a chamber, which is vacuum-pumped to provide a pressure gradient outwards from thevolume between the aperture and the sample surface. To this end the arrangement may comprise avacuum chamber, wherein the sample and the wall are arranged in the chamber, and wherein thevacuum chamber is vacuum pumped to provide a pressure gradient outwards from the volume between the aperture and the sample surface. ln the following preferred embodiments of the invention will be described with reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows partly in cross section an arrangement for determining at least one parameter related to charged particles emitted from a sample surface of a particle emitting sample.
Fig. 2 shows in larger detail the sample and an aperture between which the distance to be controlled is present.
Fig. 3 shows a flow diagram illustrating the method and the computer program according to the invention.
DETAILED DESCRIPTION Fig. 1 shows partly in cross section an arrangement 100 for collecting charged particles from a samplesurface Ss of a particle emitting sample 1 and for determining at least one parameter related to thecharged particles. The arrangement 100 comprises a sample holder 10, for holding the sample 1 in asample region 2. The arrangement also comprises a low-pressure chamber 4, comprising an aperture 3,in a wall 6 separating the sample region 2 from the low-pressure chamber 4, wherein the aperture 3 isarranged facing the sample surface Ss of the sample 1 placed in the sample holder 10, in order tocollect charged particles from the sample surface Ss into the low-pressure chamber 4. A heater 18 isalso arranged on the sample holder 10 and is arranged to heat the sample 1. The arrangement alsocomprises a positioning system Ps for controlling the position of the sample holder 10 and, thus, thedistance d between the sample surface Ss and the aperture 3. The arrangement also comprises avacuum chamber 11 which encloses the aperture 3, the sample holder 10 and the positioning systemPs. The arrangement also comprises first pump means 12 for vacuum pumping of the low-pressurechamber 4. Furthermore, the arrangement 100 comprises at least one gas outlet 5 arranged to directgas into a volume between the wall 6 and the sample surface Ss, and gas supply device 20 for providinga flow of gas from said at least one gas outlet 5, to provide a sample pressure. The arrangement 100 also comprises means Gl for measuring the pressure inside the low-pressure chamber 4, and a control 8 unit CU. The control unit CU is connected to the first pressure measuring means G1 for measuring thepressure and to the positioning means and arranged to measure the pressure, with the first pressuremeasuring means G1 for measuring the pressure, at predetermined time intervals and to control thepositioning system Ps in a closed loop control to keep the pressure inside the low-pressure chamber 4constant, thereby keeping the distance d between the aperture 3 and the sample surface Ss constant.The control unit comprises an input 19 for an input signal, which may be used to control thepositioning system Ps. The arrangement 100 also comprises a second pump means 22 for vacuumpumping of the vacuum chamber 11 and a second pressure measuring means G2 for measuring thepressure in the vacuum chamber 11. The second pump means and the second pressure measuring means G2 are both connected to the control unit CU.
The low-pressure chamber 4 is an electrostatic lens system comprising a first end 16, at which theaperture 3 is arranged, and a second end 37 at which an aperture 8 is arranged. The lens system 13 isarranged to form a particle beam from charged particles, emitted from the sample surface Ss andentering through the aperture 3 at the first end 16, and to transport the charged particles to the secondend 17. The arrangement 100 a measurement region 3 for determining at least one parameter relatedto the charged particles emitted from the sample surface Ss of the particle emitting sample 1. Themeasurement region 3 comprising an entrance 8 allowing at least a part of said particles to enter themeasurement region 3. The second end 37 is arranged at the entrance of the measurement region 3.The electrons enter the measurement region 3 through an entrance 8 and electrons entering the regionbetween the hemispheres 25 with a direction close to perpendicular to the base plate 7 are deflected byan electrostatic field applied between the hemispheres 25, and those electrons having a kinetic energywithin a certain range defined by the electrostatic field will reach a detector arrangement 9 after having travelled through a half circle.
The first pump means 12 for vacuum pumping in the low-pressure chamber 4, is arranged to maintain apressure of less than 1 mbar, preferably less than 102 bar, in the low-pressure chamber 4. A typicalpressure in the electrostatic lens system 4 is 103 mbar. The means 20 for providing a constant flow of gas is typically arranged to provide a sample pressure of 1-100 mbar.
The vacuum chamber is vacuum pumped by a separate vacuum pump (not shown). The backgroundpressure in the vacuum chamber 11 is typically maintained at 101 to 10 mbar, but should be considerablylower than the sample pressure. The sample pressure is thus a local pressure in the volume between the sample surface Ss and the aperture 3.
Fig. 2 shows in larger detail the sample and an aperture between which the distance d to be controlled is present. ln Fig. 2 six gas outlets 5 are arranged symmetrically around the aperture 3, of which only 9two are shown in the cross section in Fig. 2. The length axis L is shown to extend through the aperture 3 essentially perpendicular to the end surface S of the wall 6.
A method for controlling a distance d between an aperture 3 and a sample surface Ss will be describedwith reference to Fig. 3. During the method the vacuum chamber 11 is vacuum pumped with the secondpump means 22. The pressure in the vacuum chamber 11 is monitored with the second pressuremeasuring means G2 connected to the control unit CU. The pressure in the vacuum chamber is keptsubstantially lower than the sample pressure. The low pressure chamber is vacuum pumped with thefirst pump means 12. The pressure in the low pressure chamber 4 is monitored with the first pressuremeasuring means G1 and is preferably kept between 104 to 102 mbar, preferably lower than 2x10'3mbar. ln a first step 101 at least one gas outlet 5 is provided and arranged to direct gas into a volumebetween the wall 6 and the sample surface Ss. ln a second step 102, a constant sample pressure isprovided by supplying a constant flow of gas from said at least one gas outlet 5. The constant flow of gasis provided by the gas supply device 20, which is controlled by the control unit CU. The control unit CUcontrols the positioning system to position the sample at a position determined by, e.g., an input signalon the input 19. Such positioning may be performed in real-time by a user observing the sample 1 andthe first end 16 from the side using a microscope. ln this way a desired gap may be set. An alternative isto first calibrate pressure readings with different distances determined with the microscope. Suchcalibration may be done for one or many different gas flows. After having performed such calibrationone never needs to use the microscope again but can set the correct distance d based on pressure in the low pressure chamber 4, and the gas flow.
After having set the desired distance d the control unit CU may control the distance d between thesample 1 and the aperture 3 automatically. To this end, in a third step 103 the pressure in the low-pressure chamber 4 is measured at predetermined time intervals by the means G; for measuring thepressure. The pressure is registered in the control unit CU. lf the sample 1 is heated using the heater 10the sample will increase in volume. This will lead to a decreasing distance d between the sample 1 andthe aperture 3. The decreased distance d will lead to a higher pressure in the low-pressure chamber 4.To compensate for the decreased distance d between the sample 1 and the aperture 3 the control unitCU controls in a forth step 104 the positioning system Ps to move the sample away from aperture 3. Thecontrol of the positioning system Ps and the measurement of the pressure in the low pressure chamber4 with the first pressure measuring means G1 is performed using a closed loop control such as PID- control.
The method described above is preferably implemented in a computer program. The computer program may be run on a central processing unit CPU in the control unit CU. When the computer program is run on the central processing unit CPU it will control the control unit CU to perform the method described above.
The above described embodiments may be amended in many ways without departing from the scope of the invention, which is limited only by the appended claims.
The low-pressure chamber must not be an electrostatic lens for focusing electrons. lt is possible that the low-pressure chamber is a different kind of chamber.

Claims (13)

1. A method for controlling a distance (d) between an aperture (3), in a wall (6) separating a sampleregion (2) from a low-pressure chamber (4) which is vacuum pumped, and a sample surface (Ss), facingthe aperture (3), of a sample (1) placed in the sample region (2) at the distance (d) from the aperture (3),- wherein the distance (d) between the sample surface (Ss) and the aperture (3) may be controlled witha positioning system (Ps), characterized in that the method comprises the steps of a) providing (101) at least one gas outlet (5), connected to a gas supply device (20), arranged to directgas into a volume between the wall (6) and the sample surface (Ss), b) providing a sample pressure (102) by supplying, with the gas supply device (20), a constant flow of gasfrom said at least one gas outlet (5), c) measuring (103) at predetermined time intervals the pressure inside the low-pressure chamber (4),and d) controlling (104) in a closed loop the positioning system (Ps) to keep the pressure inside the low-pressure chamber (4) constant, thereby keeping the distance (d) between the aperture (3) and the sample surface (Ss) constant.
2. The method according to claim 1, wherein a pressure of between 104 to 102 bar, preferably lower than 2x10'3 bar, is maintained in the low-pressure chamber (4).
3. The method according to claim 1, wherein the sample pressure is provided to be higher than lmbar, preferably higher than 10 mbar.
4. The method according to any one of the preceding claims, wherein the low-pressure chamber (4) is an electrostatic lens for focusing of electrons.
5. The method according to any one of the preceding claims, wherein the sample (1) and the wall (6) arearranged in a chamber (11), which is vacuum pumped to provide a pressure gradient outwards from the volume between the aperture (3) and the sample surface (Ss).
6. A computer program for controlling a distance (d) between an aperture (3) in a wall (6), separating asample region (2) from a low-pressure chamber (4) which is vacuum pumped, and a sample surface(Ss), facing the aperture (3), of a sample (1) placed in the sample region (2) at the distance (d) from theaperture (3), - wherein the distance (d) between the sample surface (Ss) and the aperture (3) may be controlled with a positioning system (Ps), 2 - wherein at least one gas outlet (5), connected to a gas supply device (20), is arranged to direct gasinto a volume between the wall (6) and the sample surface (Ss), said computer program comprising instructions which, when executed by at least one processor causethe at least one processor to carry out the steps of a) controlling the gas supply device (20) to supply a constant flow of gas to said at least one gas outlet(5), b) receiving at predetermined time intervals the pressure values for the pressure inside the low-pressure chamber (4), and c) controlling, in a closed loop, the positioning system to keep the pressure values constant, thereby keeping the distance (d) between the aperture (3) and the sample surface (Ss) constant.
7. Computer-readable storage medium carrying a computer program for controlling a distance (d) between an aperture (3) and a sample surface (Ss), according to claim 6.
8. An arrangement (100) for collecting charged particles from a sample surface (Ss) of a sample (1),comprising- a sample holder (10), for holding the sample (1) in a sample region (2), a low-pressure chamber (4), comprising an aperture (3), in a wall (6) separating the sample region (2)from the low-pressure chamber (4), wherein the aperture (3) is arranged to face the sample surface (Ss)of the sample (1), when it is placed in the sample holder, in order to collect charged particles from thesample surface (Ss) into the low-pressure chamber (4), - a positioning system (Ps) for controlling the position of the sample holder (10) and, thus, the distance(d) between the sample surface (Ss) and the aperture (3), and - means for vacuum pumping of the low-pressure chamber (4), characterized in that the arrangement (100) comprises - at least one gas outlet (5) arranged to direct gas into a volume between the wall (6) and the samplesurface (Ss), - gas supply device (20) for providing a constant flow of gas from said at least one gas outlet (5), to supplya sample pressure, - means (Gl) for measuring the pressure inside the low-pressure chamber (4), and - a control unit (CU) connected to the means (G1) for measuring the pressure and to the positioningmeans and arranged to measure the pressure, with the means (Gl) for measuring the pressure, atpredetermined time intervals and to control the positioning system (Ps) in a closed loop control to keepthe pressure inside the low-pressure chamber (4) constant, thereby keeping the distance (d) between the aperture (3) and the sample surface (Ss) constant.
9. 39. The arrangement (100) according to claim 8, wherein the low-pressure chamber (4) is an electrostaticlens system comprising a first end (16), at which the aperture (3) is arranged, and a second end (37),wherein the lens system (13) is arranged to form a particle beam from charged particles, emitted fromthe sample surface (Ss) and entering through the aperture (3) at the first end (16), and to transport the charged particles to the second end (37).
10. The arrangement (100) according to claim 8, wherein the means for vacuum pumping in the low-pressure chamber (4), is arranged to maintain a pressure of between 104 to 102 bar, preferably between 5x10'4 to 2x10-3 bar, in the low-pressure chamber (4).
11. The arrangement (100) according to claim 8, 9 or 10, wherein the means for providing a constant flow of gas is arranged to provide a sample pressure, higher than 1 mbar, preferably higher than 10 mbar.
12. The arrangement (100) according to any one of claims 8-11, comprising: - a measurement region (3) for determining at least one parameter related to charged particles emittedfrom a sample surface (Ss) of a particle emitting sample (1), said measurement region (3) comprising anentrance (8) allowing at least a part of said particles to enter the measurement region (3), wherein the second end (37) is arranged at the entrance of the measurement region (3).
13. The arrangement according to any one of claims 8-12, comprising a chamber (11) wherein the sample(1) and the wall (6) are arranged in the chamber (11), and wherein the chamber (11) is vacuum pumpedto provide a pressure gradient outwards from the volume between the aperture (3) and the sample surface (Ss).
SE1851528A 2018-12-07 2018-12-07 Method and arrangement for distance control between a sample and an aperture SE542904C2 (en)

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SE1851528A SE542904C2 (en) 2018-12-07 2018-12-07 Method and arrangement for distance control between a sample and an aperture
EP19821307.6A EP3891774A1 (en) 2018-12-07 2019-12-06 Method and arrangement for distance control between a sample and an aperture
PCT/SE2019/051242 WO2020117124A1 (en) 2018-12-07 2019-12-06 Method and arrangement for distance control between a sample and an aperture
JP2021531777A JP7280359B2 (en) 2018-12-07 2019-12-06 Method and apparatus for distance control between sample and aperture

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US4528451A (en) * 1982-10-19 1985-07-09 Varian Associates, Inc. Gap control system for localized vacuum processing
US4560880A (en) * 1983-09-19 1985-12-24 Varian Associates, Inc. Apparatus for positioning a workpiece in a localized vacuum processing system
US5103102A (en) * 1989-02-24 1992-04-07 Micrion Corporation Localized vacuum apparatus and method
JP3148353B2 (en) 1991-05-30 2001-03-19 ケーエルエー・インストルメンツ・コーポレーション Electron beam inspection method and system
US6300630B1 (en) * 1999-12-09 2001-10-09 Etec Systems, Inc. Annular differential seal for electron beam apparatus using isolation valve and additional differential pumping
JP3360115B2 (en) 2000-03-17 2002-12-24 東京大学長 Angle-resolved electron spectrometer with diffraction plane aperture transmission energy control system and analysis method using this spectrometer
GB201317026D0 (en) 2013-09-25 2013-11-06 Oxford Instr Nanotechnology Tools Ltd X-ray analysis in air
JP6097863B2 (en) 2016-05-16 2017-03-15 株式会社日立ハイテクノロジーズ Charged particle beam apparatus, sample image acquisition method, and program recording medium

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