US3558878A - Method of reducing specimen contamination in an electron probe by cooling the objective lens - Google Patents

Method of reducing specimen contamination in an electron probe by cooling the objective lens Download PDF

Info

Publication number
US3558878A
US3558878A US745427A US3558878DA US3558878A US 3558878 A US3558878 A US 3558878A US 745427 A US745427 A US 745427A US 3558878D A US3558878D A US 3558878DA US 3558878 A US3558878 A US 3558878A
Authority
US
United States
Prior art keywords
specimen
cooling
objective lens
contamination
lens
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US745427A
Other languages
English (en)
Inventor
Hermann Neuhaus
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Applied Research Laboratories Inc
EIDP Inc
Original Assignee
Applied Res Lab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Applied Res Lab filed Critical Applied Res Lab
Application granted granted Critical
Publication of US3558878A publication Critical patent/US3558878A/en
Assigned to E.I. DU PONT DE NEMOURS AND COMPANY reassignment E.I. DU PONT DE NEMOURS AND COMPANY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: BUCKFELDER, JOHN J., SCHLEINITZ, HENRY M.
Assigned to JAMES TALCOTT, INC., LLOYDS BANK INTERNATIONAL LIMITED reassignment JAMES TALCOTT, INC. SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: APPLIED RESEARCH LABORATORIES, INC., ARL APPLIED RESEARCH LABORATORIES, S.A.
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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
    • H01J37/252—Tubes for spot-analysing by electron or ion beams; Microanalysers
    • 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 or ion-optical arrangement
    • H01J37/10—Lenses
    • H01J37/14—Lenses magnetic
    • H01J37/141—Electromagnetic lenses

Definitions

  • This invention relates to a novel method of and apparatus for rapid chemical analysis by bombarding a specimen with electrons and spectrometrically analyzing x-rays emitted by the specimen in response to the bombardment. More particularly, the invention has special reference to instruments known as electron microprobes, in which the bombarding electron beams are usually focused to very small incremental surface areas of the specimens typically about I a to about a in diameter.
  • Microprobes are well-known. One that has found substantial commercial acceptance is described and claimed by D. B. Wittry in US. Pat. No. 3,l07,297, and that patent may be referred to to augment the description herein.
  • electron microprobes are similar to electron microscopes, but they are basically different in that in the microprobe, the conditions that are sensed are those that occur on the same surface of the specimen upon which the electron beam impinges, whereas in the electron microscope, the desired information is gathered from the surface opposite from the impinging beam.
  • the electrons are controlled and focused after they have passed through the specimen. It has long been known that in the electron microscope, certain deleterious effects thought to be due to contamination of the bombarded surface of the specimen can be reduced by mounting a cryogenic element close to the sur face where the electrons impinge.
  • the technique has also been used in the electron microprobe butwith limited success and acceptance because of the need to provide for observation of the bombarded surface. It is difficult to arrange a cryogenic element closely adjacent to the area of the specimen to be bombarded without at the same time interfering with the operation of the instrument such as, for example, by obscuring the x-ray radiation it is desired to detect.
  • FIG. I is a cross-sectional view of the objective lens and specimen holder of an electron microprobe in accordance with the invention.
  • FIG. 2 is a chart comparing the effects of contamination by carbonaceous materials in the practice of the invention with the effects noted in a previous practice;
  • FIG. 3 is a chart showing the contamination effects as a function of the temperature of the objective lens in the electron microprobe.
  • FIG. 4 is a schematic diagram of a refrigeration system for cooling the objective lens in accordance with a presently preferred embodiment of the invention.
  • the surface of the specimen being bombarded be pure, that is, representative only of the materials of which the bombarded region of the specimen is composed and free of contamination by materials deposited on the specimen from the atmosphere.
  • the surface of the specimen should remain in a static condition; none of its constituents should be removed, not should any other constituents be added.
  • the surface of the specimen is actually contaminated by the deposit thereon of material from the atmosphere in which it is supported.
  • the contaminating materials of primary concern that is, those that have the most important adverse effects on analysis, are carbonaceous. They may come from any part of the vessel in which the electron bombardment is carried out, and may often be inadvertently or unavoidably carried into the vessel by the specimen itself.
  • the rate of contamination has been found not to be the same for all specimens, but to vary depending on the composition of the specimen, the condition of its surface. the atmosphere in which it is maintained during the analysis, and the temperatures of other bodies near the specimen and of the specimen itself.
  • the rate of contamination may be reduced by improving the vacuum, by providing a relatively cold, heat-absorbing body near the specimen, or by heating the specimen.
  • Improvement of the vacuum appears to provide only limited reduction in contamination, and to be uneconomically expensive. It has been found empirically that for a 50 percent reduction in the rate of contamination. the vacuum must be improved by about a full magnitude. Microprobes operate typically in the 10- torr. range, and an improvement to l() torr. or l0 torr. would require the use of much more expensive pumping equipment than is generally used at present. Moreover, it is desirable to reduce the rate of contamination not by a factor of two or four, but by at least an order of magnitude. It was also found that back streaming of oil vapors from the diffusion vacuum pump contributes only to a negligible extent to the contamination of the specimen, and it was concluded that the major part of the contamination originates from objects and substances that are normally within the evacuated chamber.
  • cryogenic surfaces in proximity to the surface of the specimen, and also to heat the specimen.
  • elements of various different shapes and sizes were tried, each being mounted as closely as possible to the specimen, typically about one-eighth inch. They were cooled by liquid nitrogen to about l96 C. The best that could be achieved in the manner was a reduction in contamination effects to about onequarter of the effects noted in conventional operation. It was noted, however, that the size of the cryogenic element appeared to be an important factor in its effectiveness; the larger elements reduced the effects of contamination more than the smaller elements did.
  • the lens 12 includes an energizing coil 16 contained within a copper shell 18, which, in turn, is secured within an iron housing comprised of a cover plate 20 and a cup-shaped lower member 22.
  • An annular tube 24 surrounds the copper shell 18 in intimate thermal contact with it. Originally, ordinary tap water had been circulated through the tube 24 to remove heat generated in the coil 16 by the current used to energize it.
  • FIG. 2 shows the carbon Ka signal emitted from a specimen of supposedly pure nickel under bombardment by an electron beam at various different energies.
  • the upper curve 30 indicates the signal strength noted when the objective lens 12 was maintained, in accordance with prior practice, at about +22 C.
  • the lower curve 31 indicates the signal strength noted when the lens 12 was cooled to 35 C.
  • the signals were plotted as a fraction of the signal emitted by a control specimen of pure carbon.
  • the ordinate scale is logarithmic.
  • the carbon Ka signal from the nickel specimen was smaller by a factor of 20 or more when the objective lens 12 was operated at 35 C. than at ordinary room temperature.
  • the chart of FIG. 3 illustrates the effect of changes in the operating temperature of the objective lens 12 over the range of about +55 C. to about 70 C. ceteris paribus.
  • the specimen was of carbon-free iron
  • the bombarding electron beam was 0.1a. amp.
  • the accelerating voltage was l kilovolts
  • the beam was focused and scanned in a raster pattern to cover an area of about 8000 square microns.
  • the excitation chamber was evacuated to about torr.
  • the specimen 14 it is preferred in the practice of the invention also to heat the specimen 14 during the analysis. Otherwise, it may be cooled excessively by the objective lens I2, because it is so close to the lens, and detract from the contaminating effect of the lens 12. It is thought that the reduction of contamination is the surface nearest the face 10 of the objective lens. Heating may be controlled by securing a sensing device 28 to the specimen and controlling the energization of the heating element 27 in accordance with the output signal of the sensing device.
  • Refrigeration apparatus of the Carnot cycle type is generally capable of cooling the lens 12 to about C., and is fully adequate for most purposes. In some cases, however, it may be desired to use a simpler system, or to chill to temperatures lower than 40 C. In these cases, liquid nitrogen, or any other cryogenic source may be used.
  • FIG. 4 illustrates a refrigeration system arranged for the selective alternate use of either liquid nitrogen or a conventional refrigerant.
  • the economy of the conventional refrigerant is available for the usual run of work, and liquid nitrogen. is available when more intense cooling is desired.
  • the refrigeration system includes a compressor and condenser unit 40, which feeds refrigerant to the tube 24 I in the objective lens through an expansion valve 42.
  • an electrical control circuit 52 'of any desired type which is arranged to adjust the throttle valve 44 in rcsponsc'to changes in temperature sensed by a sensor 26.
  • the sensor 26 is secured in good thermal contact with the lens l2. preferably on the face I0 thereof adjacent to the specimen I4. Fairly good temperature regulation, within about 3.1).1" C., is important when maximum stability and accuracy of analysis are desired. Otherwise, the effects of thermal expansion may change the focus and location of the electron beam on the specimen. Temperature control within this range of accuracy is easily achievable with presently available commercial equipment.
  • the lens 12 typically dissipates about watts of energy in operation, and this is usually ample to warm it quickly to room temperature, or a bit above, once the refrigeration is stopped. Auxiliary heating means may be used if desired.
  • Method of operating an electron microprobe of the kind having an objective lens structure positioned closely adjacent to the region where the electron beam normally impinges on a specimen comprising the steps of focusing the electron beam on the specimen, and cooling the electron lens structure to a temperature between about 20 .C. and 70 C. thereby to reduce the adverse effects of contamination of the specimen.
  • the objective lens structure is electromagnetic and includes means for circulating a fluid in closethermal contact with it, and the step of cooling is done by passing a cold fluid through the circulating means.
  • Method according to claim 1 including also the step of simultaneously heating the specimen to avoid excessive cooling of it by the lens structure.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Sampling And Sample Adjustment (AREA)
US745427A 1968-07-17 1968-07-17 Method of reducing specimen contamination in an electron probe by cooling the objective lens Expired - Lifetime US3558878A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US74542768A 1968-07-17 1968-07-17

Publications (1)

Publication Number Publication Date
US3558878A true US3558878A (en) 1971-01-26

Family

ID=24996636

Family Applications (1)

Application Number Title Priority Date Filing Date
US745427A Expired - Lifetime US3558878A (en) 1968-07-17 1968-07-17 Method of reducing specimen contamination in an electron probe by cooling the objective lens

Country Status (4)

Country Link
US (1) US3558878A (enrdf_load_stackoverflow)
DE (1) DE1935975A1 (enrdf_load_stackoverflow)
FR (1) FR2013091A1 (enrdf_load_stackoverflow)
GB (1) GB1225579A (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4599869A (en) * 1984-03-12 1986-07-15 Ozin Geoffrey A Cryogenic deposition of catalysts
US6046457A (en) * 1998-01-09 2000-04-04 International Business Machines Corporation Charged particle beam apparatus having anticontamination means
US6188071B1 (en) * 1998-08-11 2001-02-13 Nikon Corporation Feedback method for increasing stability of electron beams
US20080304168A1 (en) * 2006-12-04 2008-12-11 Quality Vision International, Inc. System and method for focal length stabilization using active temperature control

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3008044A (en) * 1960-02-25 1961-11-07 Gen Electric Application of superconductivity in guiding charged particles
US3107297A (en) * 1960-08-29 1963-10-15 Applied Res Lab Inc Electron probe X-ray analyzer wherein the emitted X-radiation passes through the objective lens
US3387132A (en) * 1963-09-09 1968-06-04 Siemens Ag Particle beam apparatus with a cryogenically cooled specimen cartridge that is below the specimen holder temperature

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3008044A (en) * 1960-02-25 1961-11-07 Gen Electric Application of superconductivity in guiding charged particles
US3107297A (en) * 1960-08-29 1963-10-15 Applied Res Lab Inc Electron probe X-ray analyzer wherein the emitted X-radiation passes through the objective lens
US3387132A (en) * 1963-09-09 1968-06-04 Siemens Ag Particle beam apparatus with a cryogenically cooled specimen cartridge that is below the specimen holder temperature

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4599869A (en) * 1984-03-12 1986-07-15 Ozin Geoffrey A Cryogenic deposition of catalysts
US6046457A (en) * 1998-01-09 2000-04-04 International Business Machines Corporation Charged particle beam apparatus having anticontamination means
US6188071B1 (en) * 1998-08-11 2001-02-13 Nikon Corporation Feedback method for increasing stability of electron beams
US20080304168A1 (en) * 2006-12-04 2008-12-11 Quality Vision International, Inc. System and method for focal length stabilization using active temperature control
US7602563B2 (en) * 2006-12-04 2009-10-13 Quality Vision International, Inc. System and method for focal length stabilization using active temperature control

Also Published As

Publication number Publication date
DE1935975A1 (de) 1970-01-22
FR2013091A1 (enrdf_load_stackoverflow) 1970-03-27
GB1225579A (enrdf_load_stackoverflow) 1971-03-17

Similar Documents

Publication Publication Date Title
Hillier On the investigation of specimen contamination in the electron microscope
US4833330A (en) Anticontaminator for transmission electron microscopes
EP0302716B1 (en) X-ray detectors
Wlegmann The photo‐emission electron microscope: Its technique and applications
US3558878A (en) Method of reducing specimen contamination in an electron probe by cooling the objective lens
Bøttiger et al. A cryogenic system for low-temperature and clean-environment channeling measurements
Homo et al. Improved anticontaminator for cryo‐electron microscopy with a Philips EM 400
JP6608769B2 (ja) イオンビーム装置
Zemlin et al. A 200 kV electron microscope with Schottky field emitter and a helium-cooled superconducting objective lens
Valdrè et al. A liquid helium cooled goniometer stage for an electron microscope
US4179605A (en) Cold trap for electron microscope
Talmon Thermal and radiation damage to frozen hydrated specimens
WO2025011677A1 (zh) 无液氦消耗循环制冷系统及液氦温区电子显微镜
JPS62100936A (ja) 荷電粒子線を用いた分析装置の試料汚染防止方法
Stokes et al. Static and dynamic experiments in cryo‐electron microscopy: comparative observations using high‐vacuum, low‐voltage and low‐vacuum SEM
EP0126909B1 (en) Cryopump with rapid cooldown and increased pressure stability
US3171957A (en) Specimen holder for an electron microscope with means to support a specimen across a thermocouple junction
US9773639B2 (en) Electron microscope
Robards et al. Specimen heating during sputter‐coating
Salomé et al. A side-entry liquid He cooled stage for the Philips EM400 electron microscope (ion implantation application)
JPH06208841A (ja) 走査電子顕微鏡のクライオ装置
US3171956A (en) Variant temperature environment for specimen stage of scientific instrument
Ranzetta et al. Specimen contamination in electron-probe microanalysis and its prevention using a cold trap
JP2020013801A (ja) イオンビーム装置
Cosslett et al. A reflexion electron microscope

Legal Events

Date Code Title Description
AS Assignment

Owner name: JAMES TALCOTT, INC., NEW YORK

Free format text: SECURITY INTEREST;ASSIGNORS:APPLIED RESEARCH LABORATORIES, INC.;ARL APPLIED RESEARCH LABORATORIES, S.A.;REEL/FRAME:004326/0899

Effective date: 19840828

Owner name: LLOYDS BANK INTERNATIONAL LIMITED, NEW YORK

Free format text: SECURITY INTEREST;ASSIGNORS:APPLIED RESEARCH LABORATORIES, INC.;ARL APPLIED RESEARCH LABORATORIES, S.A.;REEL/FRAME:004326/0899

Effective date: 19840828

Owner name: E.I. DU PONT DE NEMOURS AND COMPANY, DELAWARE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BUCKFELDER, JOHN J.;SCHLEINITZ, HENRY M.;REEL/FRAME:004326/0513

Effective date: 19840925

Owner name: JAMES TALCOTT, INC., 1633 BROAWAY NEW YORK, NY 10

Free format text: SECURITY INTEREST;ASSIGNORS:APPLIED RESEARCH LABORATORIES, INC., A MA CORP.;ARL APPLIED RESEARCH LABORATORIES, S.A. A SWITZERLAND CORP.;REEL/FRAME:004326/0899

Effective date: 19840828

Owner name: LLOYDS BANK INTERNATIONAL LIMITED, ONE SEAPORT PLA

Free format text: SECURITY INTEREST;ASSIGNORS:APPLIED RESEARCH LABORATORIES, INC., A MA CORP.;ARL APPLIED RESEARCH LABORATORIES, S.A. A SWITZERLAND CORP.;REEL/FRAME:004326/0899

Effective date: 19840828

Owner name: E.I. DU PONT DE NEMOURS AND COMPANY, WILMINGTON, D

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:BUCKFELDER, JOHN J.;SCHLEINITZ, HENRY M.;REEL/FRAME:004326/0513

Effective date: 19840925