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 PDFInfo
- 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
Links
- 238000001816 cooling Methods 0.000 title claims abstract description 16
- 238000000034 method Methods 0.000 title claims description 9
- 238000011109 contamination Methods 0.000 title abstract description 21
- 239000000523 sample Substances 0.000 title description 3
- 238000010438 heat treatment Methods 0.000 claims description 6
- 239000012530 fluid Substances 0.000 claims description 4
- 238000010894 electron beam technology Methods 0.000 abstract description 10
- 239000003575 carbonaceous material Substances 0.000 abstract description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 18
- 230000000694 effects Effects 0.000 description 13
- 229910052757 nitrogen Inorganic materials 0.000 description 9
- 239000007788 liquid Substances 0.000 description 7
- 238000005057 refrigeration Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 239000003507 refrigerant Substances 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 230000002411 adverse Effects 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000002452 interceptive effect Effects 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 241000237519 Bivalvia Species 0.000 description 1
- 235000020639 clam Nutrition 0.000 description 1
- 238000005202 decontamination Methods 0.000 description 1
- 230000003588 decontaminative effect Effects 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000002085 persistent effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
- 239000008399 tap water Substances 0.000 description 1
- 235000020679 tap water Nutrition 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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)
Abstract
Description
Claims (2)
- 2. Method according to claim 1 wherein the objective lens structure is electromagnetic and includes means for circulating a fluid in close thermAl contact with it, and the step of cooling is done by passing a cold fluid through the circulating means.
- 3. Method according to claim 1 including also the step of simultaneously heating the specimen to avoid excessive cooling of it by the lens structure.
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 (en) |
DE (1) | DE1935975A1 (en) |
FR (1) | FR2013091A1 (en) |
GB (1) | GB1225579A (en) |
Cited By (4)
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)
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 |
-
1968
- 1968-07-17 US US745427A patent/US3558878A/en not_active Expired - Lifetime
-
1969
- 1969-07-08 FR FR6923186A patent/FR2013091A1/fr not_active Withdrawn
- 1969-07-15 DE DE19691935975 patent/DE1935975A1/en active Pending
- 1969-07-17 GB GB1225579D patent/GB1225579A/en not_active Expired
Patent Citations (3)
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)
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 |
---|---|
FR2013091A1 (en) | 1970-03-27 |
GB1225579A (en) | 1971-03-17 |
DE1935975A1 (en) | 1970-01-22 |
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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 |