US3840743A

US3840743A - Ion microanalyzer

Info

Publication number: US3840743A
Application number: US00327683A
Authority: US
Inventors: H Tamura; T Kondo
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1972-01-28
Filing date: 1973-01-29
Publication date: 1974-10-08
Anticipated expiration: 1991-10-08
Also published as: JPS5246514B2; JPS4879693A; DE2304159A1

Abstract

An ion microanalyzer wherein the intensity of a condenser lens for focusing an ion beam is periodically varied, to vary the spot diameter of the ion beam which is to impinge on a specimen, whereby the precision of analysis in the direction of the depth of the specimen can be enhanced.

Description

United States Patent 11 1 1111 3,840,743 Tamura et al. [4 Oct. 8, 1974 1 ION MICROANALYZER 3,535,516 10/1970 Munakata 250/310 3,628,012 12/1971 Plows et a1 250/310 175] Inventors 2:32; fig a 33 g 3,702,398 11/1972 Van Essen et al. 250/310 m a o apa I FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee m Tokyo Japan 1,183,310 3/1970 Great Britain 250/309 1 1 pp 327,683 New Developments in the Ion Microprobe Mass Analyzer, Liebl et a1. Hasler Research Center, 1968 30 Fori A I t' P' t Dt 1 J n 28 253 ca Ion "on y a a 47 9866 Primary Examiner-Archie R. Borchelt a apan Assistant Examiner B' C. Anderson 52 us. (:1 250/307, 250/396, 250/309 Attorney Firm-Crag Antonen [51] Int. Cl. H01j 37/26 58 Field of Search 250/309, 310, 311, 307, 1 W

' 5 3 An 101'] microanalyzer wherein the intensity of a con- 2 96 denser lens for focusing an ion beam is periodically 5 References Cited varied, to yary the spot diameter of the ion beam UNITED STATES PATENTS WhlCh 1s to lmpmge on a specimen, whereby the precl- 2 422 807 6/1947 Smith 250,310 sion of analysis in the direction of the depth of the 3:221:133 11/1965 14311311011211.2131 :1, 250/311 Speclmen can be enhanced 3,256,432 6/l966 Watanabe et a1 250/311 30' Claims, 8 Drawing Figures 24 V t M ERECODER 2'3 PULSIVE SIGNAL SOURCE PATEMEU 81W 3.840.743

sum

1 or 3 Pmmwm 8w 3,840,743 NEH 20$ 3 FIG. 3b

FIG. 4

PULSIVE 1 SIGNAL SOURCE RECODER AMPLIFIER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in an ion microanalyzer for the mass analysis of secondary ions which are created by irradiating a specimen with an ion beam.

2. Description of the Prior Art As compared with the other like devices, an ion microanalyzer has such features of being (a) capable of analysis of the thin surface layer of a specimen and (b) capable of measurement of a concentration distribution in the direction of the depth of a specimen. Among such features, (b) is an especially important one, and

provides the following fields of uses:

Analysis of 1) iron and steel materials, (2) semiconductor materials, (3) surface treating materials, (4) insulator materials, (5) surface pollution, (6) organic materials, and so forth.

The feature (b) is a merit not possessed by prior art analysis means, and is profitably put into practical use at present. As problems, however, the following points are mentioned:

i. Measurement of a concentration distribution in the direction of the depth of a specimen in a range from'a surface portion of the specimen to a comparatively deep layer, as for example several p. to several hundreds u.

ii. The case where, regarding the measurement of a concentration distribution in the direction of the depth FIG. 5 is a diagram showing measured results of the concentration distribution of boron (B) within a specimen of silicon (Si) as taken in the direction of the depth of the specimen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS which, as shown in FIG. la, the density is high at the central part and low at the peripheral part. When the 1 ion beam having such distribution is radiated on the of a specimen, a precision especially being smaller than several tens A is requested.

The problems (i) and (ii) are important for future studies on the surface or the thin surface layer of a specimen. If they are solved by the analyzing procedure of the ion microanalyzer, the ion microanalyzer will play an important role in the above-mentioned fields conjointly with its high sensitivity.

SUMMARY OF THE INVENTION An object of the present invention is to provide an ion microanalyzer which has a remarkably enhanced precision of analysis in the direction of the depth of a specimen.

In order to accomplish this object, the present invention is constructed such that the intensity of at least one electron lens for focusing an ion beam is varied, thereby to vary the spot diameter of the ion beam by which a specimen is irradiated.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la and lb are diagrams for explaining the relation between the density distribution of a primary ion beam and the etching profile of a specimen irradiated by the ion beam;

FIGS. 2a and 2b are diagrams illustratingthe principle of the present invention;

FIG. 3a is a schematic view for explaining a method of forming ion beams as in FIG. 20, while FIG. 3b is a diagram showing voltages V, and V which are applied to a condenser lens in order to obtain the ion beams having intensities and beam diameters as in FIG. 2a;

FIG. 4 is a schematic view showing an embodiment of the present invention; and

specimen, the specimen comes to have an etching profile which, as shown in FIG. lb, corresponds to the beam densities. When, under such state, secondary ions emitted from the specimenare analyzed by a mass analyzing device, the secondary ions ejected from parts of different depths as a point C at the central portion and parts d and d at the peripheral portions shown in FIG. 1b are simultaneously detected. As a result, the measuring precision of a concentration distribution in the direction of the depth, namely, the resolution in the direction of the depth is inferior. Even when the specimen is irradiated by a comparatively uniform ion beam the precision is not high on account of influences of the peripheral part of the beam. The problem is serious in the analyses of a thin film and a thin layer in the surface portion of a specimen.

The present'invention has been developed to eliminate the disadvantage of the prior art as stated above, and the principle of the invention is as'will be described hereunder. The spot diameter of an ion beam is varied on a specimen with time. First, the surface of the specimen is irradiated by the ion'beam of large current and large spot, to carry out ion etching of wide area. Subsequently, the beam is made fine, the'central part of the etched area isirradiated by the fined beam, and secondary ions emitted from the irradiated part are analyzed. These operationsare repeated, whereby the concentration distribution in the direction of the depth can be measured with high precision. FIGS. 2a and 2b illustrate these results.

Reference numerals l and 2 in FIG. 2a designate the intensity distributions of beams in the case where the intensity of an electrostatic lens 5 (FIG. 3a) is changed as shown in FIG. 3b, respectively. FIG. 3a shows a lens system which focuses an ion beam, emitted from an ion source 3, on a specimen 8 by means of the condenser lens 5 and an objective lens 7. FIG. 3b shows lens voltages to be applied to the condenser lens 5. When the voltages V, and v having the square waveform are applied to the condenser lens 5, the ion beam is focused as illustrated by solid lines and broken lines in FIG. 3a

in correspondence with the respective applied voltages. With the ion beams thus focused, the specimen is etched. In this case, the intensity distributions of the beams on the specimen correspond to the

curves

1 and 2 shown in FIG. 2a. When the voltages in the form of the square waves are applied to the condenser lens, the

, etching profile as illustrated in FIG. 2b is formed in the ing the time ratio of t /t of the square wave voltages illustrated in FIG. 3b.

In this manner, the analyzed outputs of secondary ions ejected from the etching profiles of the specimen in correspondence with the voltages V and V are pro vided from the mass analyzing device. If, in this case, the outputs of the mass analyzing device are taken out in synchronism with the intensity changes of the condenser lens or with the square wave voltages, then only the outputs in the cases of the lens voltage V or V can be derived. It is accordingly made possible to analyze only the parts of l, l" and 2', 2" in FIG. 212. Thus, according to the present invention, the precision of analysis in the direction of the depth can be arbitrarily selected by varying the ratio t /t in FIG. 3b.

Description will now be made of an embodiment of the present invention, reference being had to FIG. 4. First, the whole construction of the apparatus will be explained. When broadly classified in function, the apparatus is composed of a primary ion-radiating system and a mass analyzing device of the double focusing type. The primary ion-emitting system consists mainly of an ion gun 26, a condenser lens 5, a diaphragm or aperture 6, an objective lens 7, a deflecting electrode 9 and a shield electrode 25. An ion beam emitted from the ion gun 26 is focused on a specimen 8 by a condenser lens 5 and the objective lens 7. The focused state is adjusted by changing the electric potential of an

intermediate electrode

5 or 7 of the

electrostatic lens

5 or 7. Especially, the intensity of the beam is changed by the condenser lens 5. The determination of a place on the specimen to be analyzed, is done either by moving the specimen or by moving the beam with the deflecting electrode 9.

The spot diameter of the ion beam on the specimen can be varied to any desired value of from I u to several hundreds p. by the combination between the condenser lens and the objective lens.

The mass analyzing device consists of a secondary ion-drawing out electrode 10, an electrostatic lens 11 for correcting the trajectory of a secondary ion beam, a slit 13, an electric field device 14, a slit 15, a magnetic field device 16 having an exciting coil (not shown), a slit 17, a slit 19, an electron multiplier 20, an amplifier 22, a recorder 23 and a switch 24,.and deflecting electrodes 12 and 18 which are attached anew for the purpose of performing the present invention.

Secondary ions emitted from the specimen are subjected to energy selection by the electric field device 14. Then, they are introduced into the magnetic field device 16, and are analyzed therein. The analyzed output is detected by the electron multiplier 20. Thereafter, the detected signal is amplified by the amplifier 22, and is recorded by the recorder 23.

A power source 3] is composed of a power source section for supplying a lens voltage 8,, and a power source section for supplying a square wave voltage S which is synchronized with the lens voltage or is a function of the same.

In the performance of the present invention, the following methods have been adopted:

1. The intensity of the primary ions and the diameter of the beam spot are varied in the form of step waves. In synchronism with the step waves, the potential of the deflecting electrode 12 disposed between the specimen 8 and the electric field device 14 is varied in the form of square waves. Thus, the secondary ions are detected at specified times and at specified time intervals. More concretely, the square wave voltage S having V and V as its amplitudes is applied to the condenser lens 5. The deflecting electrode 12 or 18 is applied with the square wave voltage S of an amplitude V in synchronism with the voltage S, only for a period of time from t to t to turn on and off the input or output of the mass analyzing device. That is, only when the voltage V, is applied as the lens voltage (t t t t the secondary ions are introduced into the mass analyzing device, or the analyzed output is derived therefrom. During the periods t t t t during which the voltage V is applied, the secondary ions are not introduced, or the analyzed output is not derived.

2. Similarly to the method (I the stepped voltage S, is applied to the condenser lens 5. The signal S is applied to the specimen 8 and the shield electrode 25. Thus, the analyzed output is provided from the mass analyzing device only during the periods t t t t 3. As in the method (I), the sensitivity of the detection system may be turned on and off in synchronism with the signal 5,, the detection system consisting of the electron multiplier 20, amplifier 22 and recorder 23. For example, the amplification degree of the amplifier 22 may be changed.

4. As in the method (I), the electric field 14 or the magnetic field 16 are varied. In this case, ions of any mass are inhibited from passing through the slit 19.

In the foregoing embodiments, the mass analyzing device may have only the magnetic field device without the electric field device. The electrostatic lenses may be replaced with a single lens, and a magnetic lens or lenses may also be employed. Further, the square wave voltage S may also be applied to the objective lens 7, or to both the condenser lens 5 and the objective lens 7. The square wave voltage S need not be always varied periodically, but it is only required to be changed with time.

An example of results obtained by the above methods (1) to (4) is illustrated in FIG. 5. The specimen used as shown at Si is a silicon wafer epitaxially grown, and has a distribution of two orders of concentrations of boron (B) in a surface layer of 0.5 ,lL. In the figure, a curve (i) represents the concentration distribution of B as theoretically evaluated. A curve (ii) shows the measured results obtained by the prior art method. A curve (iii) shows the measured results in the case of applying the present invention. As apparent from the figure, the data obtained by the prior art method are considerably different from the theoretical values, to considerably expand the concentration distribution in the direction of the depth. This means that the ion current density distribution of the primary ion beam is not uniform, resulting in an inferior resolution along the depth. In contrast, in the case of (iii) with the present invention applied, the data conform to the theoretical values well, and represent the concentration distribution of B along the depth precisely.

As for the method of taking out the outputs of the mass analyzing device in synchronism with the intensity variation of the condenser lens, it may also be made to establish electric and magnetic fields in the passage of the secondary ion beam anew and to change the intensities thereof.

What is claimed is:

1. In an ion microanalyzer comprising ion beam generating means including an ion source device for emitting an ion beam; at least one ion lens disposed along the path of said ion beam for focusing said ion beam on a specimen, first deflecting means for deflectingsaid ion beam; mass analyzing means for analyzing secondary ions emitted from said specimen by ion impingement; and detecting means for detecting the output of said mass analyzing device, the improvement which comprises first control means for periodically varying the focus of said ion lens, said first control means including first signal source means for supplying a first periodic signal to said ion lens, and second control means for periodically inhibiting the output of said detecting means in synchronism with the intensity variation of said ion lens.

2. An ion microanalyzer according to claim 1, wherein said second control means includes means for periodically varying the analyzing operation of said mass analyzing device in synchronism with theintensity variation of the ion lens.

3. An ion microanalyzer according to claim 1, wherein said second control means'includes means for varying the output of said mass analyzing device in synchronism with the intensity variation of the ion lens.

4. An ion microanalyzer according to claim 1, wherein said second control means includes means for varying the sensitivity of said detecting device in synchronism with the intensity variation of the ion lens.

5. An ion microanalyzer according to claim 1 wherein said ion lens includes three electrodes disposed in parallel with one another, the intermediate one of said electrodes being connected to said first con trol means.

6. An ion microanalyzer according to claim 1 wherein said second control means comprises second deflecting means disposed between said specimen and said mass analyzing device for deflecting said secondary ions and second signal source means for supplying a second periodic signal to said second deflecting means in synchronism with the first periodic signal.

7. An ion microanalyzer according to claim 2 wherein said mass analyzing device includes an electric field device and a magnetic field device, and said second control means comprises second signal source means for supplying a second periodic signal to said electric field device in synchronism with the first periodic signal.

8. An ion microanalyzer according to claim 2 wherein said mass analyzing device includes an electric field device and a magnetic field device, and said second control means comprises second signal source means for supplying a second periodic signal to said magnetic field in synchronism with the first periodic signal.

9. An ion microanalyzer according to claim 3 wherein said second control means includes third deflecting means and second signal source means for supplying a second periodic signal to said third deflecting means in synchronism with the first periodic signal.

' l0. Method of measurement of the concentration distribution in the direction of the depth of a specimen, comprising the steps of generating an ion beam, focusing said ion beam on a portion of a specimen, mass analyzing the secondary ions generated by impingement of said ion beam on said specimen, detecting the mass analyzed secondary ions in synchronism with variation of the focusing of said ion beam to vary the diameter of the ion beam impinging on said specimen so as to vary the penetration pattern of said ion beam in said specimen.

11. Method as defined in claim 10 wherein .said focusing is varied periodically between first and second values and said detecting is performed in synchronism with one of said first and second values of focusing.

12. Method as defined in claim 10 wherein said focusing is varied periodically between first and second values and said mass analyzing is performed in synchronism with one of said first and second values of focusmg.

13. Method as defined in claim 10 wherein said focusing is varied periodically between first and second values and the sensitivity of said detecting is varied in synchronism with one of said first and second values of focusing.

14. Method as defined in claim 10 wherein said focusing is varied periodically between first and second values and the generation of secondary ions at said specimen is inhibited in synchronism with one of said first and second, values of focusing.

15. An ion microanalyzer comprising:

means for emitting a primary ion beam;

means for irradiating a specimen with said primary ion beam, said means including at least one electrostatic lens disposed along the path of said ionbeam;

means for varying alternately the spot diameter of the ion beam which is irradiated on a specimen by varying alternately a potential applied to said electrostatic lens; i

means for deflecting said ion beam;

means for analyzing secondary ions emitted from said specimen, said means consisting of a mass analyzer;

means for detecting and recording the output of said means for analyzing secondary ions in synchronism with said varying means; whereby a precision analysis of the concentration distribution in the direction toward the depth of said specimen can be enhanced. 16. An ionmicroanalyzer according to claim 15, in which said means for varying alternately the spot diameter of the ion beam comprises means for varying periodically the spot diameter of the ion beam.

17. An ion microanalyzer according to claim 15, which further comprises means for shielding the specimen and means for controlling the ability of said secondary ions emitted from said specimen to enter said means for analyzing secondary ions in synchronism with said means for varying alternately the spot diameter of the ion beam.

18. An ion microanalyzer according to claim 16, which further comprises means for controlling the output of secondary ions of said means for analyzing sec-' ondary ions, and said means for detecting and recording the output of said means for analyzing secondary ions.

19. An ion microanalyzer according to claim 18, in which said means for controlling the output of secondary ions comprises means for controlling the transmission of said secondary ions through said mass analyzer in synchronism with said means for varying alternately the spot diameter of the ion beam.

20. An ion microanalyzer according to claim 19, in which said mass analyzer comprises at least one of an electric field device and a magnetic field device.

21. An ion microanalyzer according to claim 20, in which said means for controlling the output of secondary ions comprises a deflecting electrode provided between said sample and said mass analyzer.

22. An ion microanalyzer according to claim 20, in which said means for controlling the output of secondary ions is a deflecting electrode provided between said mass analyzer and said means for detecting the output of said means for analyzing secondary ions.

23. An ion microanalyzer according to claim 20, in which said means for controlling the output of secondary ions comprises means for controlling the intensity of said electric field device.

24. An ion microanalyzer according to claim 20, in which said means for controlling the output of secondary ions comprises means for controlling the intensity of said magnetic field device.

25. An ion microanalyzer according to claim 15, in which said means for controlling the output of secondary ions comprises means for controlling the sensitivity of said means for detecting and recording the output of said means for analyzing secondary ions.

26. An ion microanalyzer according to claim 25, in which said means for detecting the output of said means for analyzing secondary ions comprises a photomultiplier, and said means for controlling the output of secondary ions comprises means for controlling the sensitivity to secondary ions of said photomultiplier.

27. An ion microanalyzer according to claim 25, in

which said means for detecting the output of said means for analyzing secondary ions comprises a photomultiplier and an amplifier connected to said photomultiplier, and said means for controlling the output of secondary ions comprises means for controlling the amplification factor of said amplifier.

28. An ion microanalyzer according to claim 15, in which said electrostatic lens consists of a group of three electrodes disposed in parallel with one another, and said means for varying alternately the spot diameter of the ion beam is connected to an intermediate electrode of said three electrode group.

29. Method of measurement of the concentration distribution in the direction of the depth of a specimen, comprising the steps of emitting a primary ion beam;

irradiating on a specimen with said ion beam having large spot diameter to etch said specimen;

irradiating a specimen with said ion beam having a small spot diameter;

mass analyzing secondary ions emitted with irradiation of said primary ion beam;

repeating the irradiation of said specimen with said ion beam having large and small spot diameters; detecting and recording an output of said secondary ions being mass analyzed; and controlling the output of secondary ions in synchronism with irradiation of said specimen with said primary ion beam having large and small diameters. 30. Method as defined in claim 29, in which said irradiation of the specimen is repeated periodically.

Claims

1. In an ion microanalyzer comprising ion beam generating means including an ion source device for emitting an ion beam; at least one ion lens disposed along the path of said ion beam for focusing said ion beam on a specimen, first deflecting means for deflecting said ion beam; mass analyzing means for analyzing secondary ions emitted from said specimen by ion impingement; and detecting means for detecting the output of said mass analyzing device, the improvement which comprises first control means for periodically varying the focus of said ion lens, said first control means including first signal source means for supplying a first periodic signal to said ion lens, and second control means for periodically inhibiting the output of said detecting means in synchronism with the intensity variation of said ion lens.

2. An ion microanalyzer according to claim 1, wherein said second coNtrol means includes means for periodically varying the analyzing operation of said mass analyzing device in synchronism with the intensity variation of the ion lens.

3. An ion microanalyzer according to claim 1, wherein said second control means includes means for varying the output of said mass analyzing device in synchronism with the intensity variation of the ion lens.

5. An ion microanalyzer according to claim 1 wherein said ion lens includes three electrodes disposed in parallel with one another, the intermediate one of said electrodes being connected to said first control means.

10. Method of measurement of the concentration distribution in the direction of the depth of a specimen, comprising the steps of generating an ion beam, focusing said ion beam on a portion of a specimen, mass analyzing the secondary ions generated by impingement of said ion beam on said specimen, detecting the mass analyzed secondary ions in synchronism with variation of the focusing of said ion beam to vary the diameter of the ion beam impinging on said specimen so as to vary the penetration pattern of said ion beam in said specimen.

11. Method as defined in claim 10 wherein said focusing is varied periodically between first and second values and said detecting is performed in synchronism with one of said first and second values of focusing.

12. Method as defined in claim 10 wherein said focusing is varied periodically between first and second values and said mass analyzing is performed in synchronism with one of said first and second values of focusing.

14. Method as defined in claim 10 wherein said focusing is varied periodically between first and second values and the generation of secondary ions at said specimen is inhibited in synchronism with one of said first and second values of focusing.

15. An ion microanalyzer comprising: means for emitting a primary ion beam; means for irradiating a specimen with said primary ion beam, said means including at least one electrostatic lens disposed along the path of said ion beam; means for varying alternately the spot diameter of the ion beam which is irradiated on a specimen by varying alternately a potential applied to said electrostatic lens; means for deflecting said ion beam; means for analyzing secoNdary ions emitted from said specimen, said means consisting of a mass analyzer; means for detecting and recording the output of said means for analyzing secondary ions in synchronism with said varying means; whereby a precision analysis of the concentration distribution in the direction toward the depth of said specimen can be enhanced.

16. An ion microanalyzer according to claim 15, in which said means for varying alternately the spot diameter of the ion beam comprises means for varying periodically the spot diameter of the ion beam.

18. An ion microanalyzer according to claim 16, which further comprises means for controlling the output of secondary ions of said means for analyzing secondary ions, and said means for detecting and recording the output of said means for analyzing secondary ions.

27. An ion microanalyzer according to claim 25, in which said means for detecting the output of said means for analyzing secondary ions comprises a photomultiplier and an amplifier connected to said photomultiplier, and said means for controlling the output of secondary ions comprises means for controlling the amplification factor of said amplifier.

29. Method of measurement of the concentration distribution in the direction of the depth of a specimen, comprising the steps of emitting a primary ion beam; irradiating on a specimen with said ion beam having large spot diameter to etch said specimen; irradiating a specimen with said ion beam having a small spot Diameter; mass analyzing secondary ions emitted with irradiation of said primary ion beam; repeating the irradiation of said specimen with said ion beam having large and small spot diameters; detecting and recording an output of said secondary ions being mass analyzed; and controlling the output of secondary ions in synchronism with irradiation of said specimen with said primary ion beam having large and small diameters.

30. Method as defined in claim 29, in which said irradiation of the specimen is repeated periodically.