US3686499A

US3686499A - Ion micro-analyzer

Info

Publication number: US3686499A
Application number: US36755A
Authority: US
Inventors: Itiro Omura; Toshio Kondo; Hifumi Tamura
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1969-05-16
Filing date: 1970-05-13
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: DE2023688B2; DE2023688A1; JPS5034439B1

Abstract

An ion micro-analyzer, wherein a finely collimated ion beam is projected onto the surface of a sample to be analyzed, the projected ion beam repeatedly scans the sample surface while, one time in fixed scanning-frequency intervals, a fixed point on the sample surface is bombarded by the ion beam for a constant time, the image of the secondary electrons from the sample surface is projected on the screen of a Braun tube oscilloscope sweeped synchronously with the ion beam and observed by performing intensity modulation of the oscilloscope in correspondence with the amount of the secondary electrons emitted from the sample surface, the fixed position on the sample surface bombarded by the ion beam in the way described above is moved to a position for analysis while observing the brilliant point on the image of secondary electrons which corresponds to the fixed point on the sample bombarded by the ion beam, and then a mass-spectroscopic analysis of the secondary ions emitted from the fixed point on the sample surface is done while the fixed position on the sample desired for analysis is bombarded by the ion beam.

Description

United States Patent Omura et al.

1541 my MICRO-ANALYZER [72] Inventors: Itiro ()mura, l-lino; Toshio Kondo, Koltunbunji; Hifumi Tamura, l-lachioji, all of Japan [7 3] "Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: May13, 1970 [21] Appl. No.: 36,755

[30] Foreign Application Priority Data Primary ExaminerJames W. Lawrence Assistant Examiner-C. E. Church Attorney-Craig, Antonelli & Hill [151 3,686,499 i451 Aug. 22, 1972 [57 ABSTRACT An ion micro-analyzer, wherein a finely collimated ion beam is projected onto the surface of a sample to be analyzed, the projected ion beam repeatedly scans the sample surface while, one time in fixed scanningfrequency intervals, a fixed point on the sample sur-' face is bombarded by the ion beam for a constant time, the image of the secondary electrons from the sample surface is projected on the screen of a Braun tube oscilloscope sweeped synchronously with the ion beam and observed by performing intensity modula tion of the oscilloscope in correspondence with the amount of the secondary electrons emitted from the sample surface, the fixed position on the sample surface bombarded by the ion bearn in the way described above is moved to a position for analysis while observing the brilliant point on the image of secondary electrons which corresponds to the fixed point on the sample bombarded by the ion beam, andthen a massspectroscopic analysis of the secondary ions emitted from the fixed point on the sample surface is done while the fixed position on the sample desired for analysis is bombarded by the ion beam.

2 Claims, 7 Drawing Figures 3 Sheets-Sheet l Patented Aug. 22, 1972 $8 2&6 mwmw Qlq 4 $.33 m QM ITIRO OMURA TOSHIO KONDO, HIFUMI TAMURA roN MICRO-ANALYZER BACKGROUND OF- THE INVENTION 1. Field of the Invention This invention relates to an improvement of an ion micro-analyzer. 7

2. Description of the Prior Art The ion micro-analyzer to be described hereinbelow is a device, wherein .asmall surface portion (a small area whose diameter is usually about several microns and this portion will be referred to as the analysis point hereinbelow) of a solid-state sample to be analyzed is bombarded by a finely collimated primary ion beam and the composition analysis and the like on the analysis point is obtained by analyzing and/or measuring the secondary radiations (such as secondary ions, secondary electrons etc.) emitted from the bombarded point. In

conventional devices, the-secondary ions from the anal.- ysis point 'are'analyzed byuse of a mass spectrometer,

- The ion micro-analyzer comprising a mass spectrometer has the advantage that the composition of a small part of a'solid-state sample 'canbe analyzed quantitatively with high precision, but conventional devices. of this type suffer from the'disadvantages that the selection of the small part for analysis (analysis point) is troublesome and that it is difiicult to see the relationship between the data obtained by mas-analysis and the position of the analysis point on the sample.-

Namely, it is necessary for analysis to select an analysis point properly by considering which position on the sample is most appropriate for analysis and to project the ion beam spot accurately on the analysis point thus selected. In the subsequent process ofdata analysis, it is necessary to make an I accurate correspondence between the data and the analysis point, and thus great care'must be taken in making such correspondence.

' v In a conventional method, the irradiation spotlof a ion beamon the sample surface is observed with an optical microscope and the irradiation spot is v 2 however, the distribution of only such elements corresponding to the secondary ions having the specified moved to a desired analysis point bysuitably adjusting deflection voltages for .the ion This method is however, laborious due tothe need to move the irradiation spot to the analysis point and, moreover,

it is impossible to read the position of the analysis point on the optical image of the sample quantitatively so that the relationship between the data and the position of the analysis point becomes obscure. Particularly, when many analysis points on a sample surface are to be analyzed in series, it becomes difficult to distinguish which datum corresponds to aparticular analysis point.

Thus, not only is the data analysis laborious and timev consuming, but also errors in data analysis may easily occur.

In another conventional method, only such ions having a specific mass-to-charge ratio (m/e value) among the secondary ions emitted from the sample are analyzed and measured with a mass spectrometer by pl nely sc nning he primary ion be m, on the sample surface, the output signal is. add d to the terminal for intensity modulation of a Braun tube oscilloscope sweeped synchronously with the scanning of the primary ion beam to display the image of secondary ions (the distribution of the specified'seeondary ion beam described above) fromthe sample'surface on the screen of the Braun tube, and thus the state of the sample may be observed beforeanalysis. In this method,

surface region not including the above elements or the distributions of the other elements in the sample cannot be observed. Thus, it is impossible to obtain information sufficient for the selection of an analysis point. Further, it is impossible to perform an analysis while displaying the image of the secondary ions from the sample surface on the screen of a Braun tube. In other words, the irradiation spot of the primary ion beam must be fitted and fixed to a desired analysis point for analysis, but this process cannot be performed'when the image of the secondary ions is displayed (or when the primary ion beam is-scanned). Conversely, whena mass-spectroscopic analysis is done for a particular analysis point, the sample surface cannot be observed. Thus, it is difficult to obtain accurate information on the relationship between the data andthe position on thesample. v SUMMARY F INVENTION I This invention is intended to obvia'te the deficiencies described hereinabove, and a primary object of this invention is to provide an improved ion micro-analyzer, wherein an irradiation spot of a primary ion beam can be made to strike accurately on a desired arralysispoint and a mass-spectroscopic analysis of the analysis point can be achieved while observing the surface of a sample for analysis.

A second object of this invention is to provide an improved ion micro-analyaer, wherein the relationship between the analysis data and the analysis point can be accurately determined.

In order to achieve the primary object described above, the ion micro-analyzer according to .this invention is characterized in that the primary ion beam irradiating a sample surface is scanned at a plane angle, the secondary electrons emitted from the sample surface by ion bombardment are detected, and the detected signal is added to a terminal for intensity modulation .by' a Braun tube oscilloscope sweeped synchronously with the scanning of they primary ion beam to display the image of secondary electrons corresponding to the sample surface on the fluorescent screen of the oscilloscope; the brilliant point corresponding to the fixed position of the irradiation spot of the primary ion beam is displayed on the image of secondary electrons by fixing the irradiation spot of the primary ion beam at an arbitary point on the sample surface for a constant time interval during scanning; the irradiation spot is made to strike accurately on a desired analysis point by adjusting the deflection voltage of the primary ion beam while observing the posiing analysis point is recorded in the ion micro-analyzer described hereinabove.

Other objects, features and advantages of this invention will become more apparent from the following detailed description of the embodiments of this invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block circuit diagram showing the principle of an in micro-analyzer according to an embodiment of this invention;

FIG. 2 shows a train of waveforms for schematically illustrating the relationship between the ion beam scanning signal in the ion micro-analyzer shown in FIG. 1 and the output signal;

FIG. 3 is a schematic diagram showing the relationship between the image of secondary electrons from the sample surface displayed on a Braun tube oscilloscope and the deflection voltage for the ion beam;

FIG. 4 shows a train of waveforms for schematically illustrating the relationship between the deflection voltage for an ion beam in analysis, the mass scanning signal and the output signal from an ion collector;

FIG. 5 shows a table indicating an example of analysis data recorded by a printer;

FIG. 6 shows a train of waveforms for schematically illustrating the relationship between the ion beam scanning signal, the instruction signal for analysis, the mass-scanning signal and the ion collector output signal when the irradiation spot of an ion beam is made to lie at a desired analysis point and a mass-spectroscopic analysis of the analysis point is done; and

FIG. 7 shows a train of waveforms for schematically illustrating the relationship between various signals to be recorded as analysis data.

DESCRIPTION OF THE PREFERRED EMBODHVIENTS FIG. 1 illustrates the principle structure of an ion micro-analyzer according to an embodiment of this invention. The analyzer according to this invention consists, when loosely stated, of an ion beam generator system for producing a primary ion beam I, for irradiating a sample for analysis, an ion beam scanning system for planely scanning the sample surface with the primary ion beam I,,, an analysis point display system for displaying the image of secondary electrons emitted from the sample surface, a mass spectrometer system for performing a mass-spectroscopic analysis of the secondary ion beam I, emitted from the sample surface, a scanning signal generator system for synchronously controlling the ion beam scanning system and the analysis point display system, a mass-scanning system for mass-scanning the mass spectrometer system, an analysis instruction signal generator system for initiating the mass spectrometer system, a data-recording system for recording analysis data, and other accessories.

A more concrete structure of these fundamental components and the operations thereof will be described in detail hereinbelow.

In FIG. 1, the ion beam generator system consists of an ion source 1, a mass separator 2, a focusing lens 3 etc. The ions emitted from the ion source 1 (for example, a duoplasmatron) are separated according to their mass-to-charge ratio (m/e values) by the magnetic type mass separator 2, and only such ions having a specified m/e value are taken out of a slit. The ion beam taken out in this way is finely collimated by the focussing lens 3 and forms a primary ion beam l which hits a small surface portion of a sample 5.

The ion beam scanning system consists of a pair of horizontal deflection electrode plates 4X and a pair of vertical deflection electrode plates 4Y. These deflection plates receive scanning signals e and e, (see FIG. 2 (f) and (c)) from the scanning signal generator system described hereinbelow and scan the irradiation spot of the primary ion beam I, planely over the sample surface. Here, the primary ion beam 1,, is not continuously scanned, but the irradiation spot is made to fix at an arbitary point on the sample surface for a constant time during scanning. Namely, the plane scanning of the irradiation spot and the fixing of the irradiation spot at a point on the sample surface are done alternately.

The analysis point display system consists of a secondary-electron detector 9 and a Braun tube oscilloscope 11. The detector 9 detects secondary electrons e emitted from the sample surface and the output signal E (FIG. 2(g)) is applied to an intensity modulation terminal 12 of the oscilloscope 11 to thereby display an image of secondary electrons from the sample surface as shown in FIG. 3. The electron beam (3,, for display on the oscilloscope 11 is sweeped planely in synchronization with the scanning of the primary ion beam I,,. Thus, the same sweeping signals (or proportional signal voltages) as the scanning signals e,, e, (FIG. 2(f) and (0)) applied to the pairs of defection plates 4X and 4Y of the ion beam scanning system are applied to pairs of horizontal and vertical deflection electrode plates 13X and 13Y of the oscilloscope 11. Accordingly, an image of secondary electrons from the sample as shown in FIG. 3 appears on the screen of the oscilloscope 11. The position of the fixed irradiation spot when the primary ion beam is fixed at a point for some constant time during scanning is displayed in the form of a brilliant point on the secondary electron image.

The mass spectrometer system comprises an energy selector 6, a magnetic field 7 for mass spectrometry, an ion collector 8 etc. In this system, the secondary ion beam 1, emitted from the analysis point is energyanalyzed into a beam of a definite energy by the energy selector 6 and injected into the magnetic field 7. The incident ions are mass-separated according to their m/e values and ions of different m/e values are detected sequentially by the ion collector 8. For this purpose, a scanning-type magnetic field is used as the magnetic field 7. This magnet receives a mass scanning signal e, (FIG. 4(e)) from the mass scanning system and the excitation current for this analyzer magnet is changed in correspondence with the variation in the signal voltage, to facilitate mass scanning.

The scanning signal generator system consists of sawtooth voltage generators Ztl and 30 for scanning an ion beam, rectangular voltage generators 21 and 31 for setting an analysis point, variable-voltage DC voltage sources 22 and 32 for setting the rectangular voltages, and adders 23 and 33 for superposing signals. In this embodiment, a horizontal scanning signal e, (FIG. 2(f)) is obtained by adding the output signal E, (FIG. 2(d)) from the saw-tooth voltage generator 20 and the output voltage V (FIG. 2(e)) from the rectangular wave voltage generator 21 in a time relationship as shown in FIG. 2 using a circuit changing switch 23.

TI-Ie vertical scanning signal e, (FIG. 2(c)) is obtained by adding the output signal E, (FIG. 2(a)) from the saw-tooth voltage generator30 and the output signal V, (FIG. 2(b)) from the rectangular voltage generator 31 in a time relationship as shown in FIG. 2 by use of a circuit changing switch 33. The rectangular voltage generators 21 and 31 receive output voltages from the variable DC voltage sources 22 and 32 and produce rectangular voltages V, and V having the same voltage values. Thus, the magnitude of the rectangular voltage V, and V, may be changed arbitarily. The horizontal and vertical scanning signals e, and e, obtained in this way are applied not only to the pairs of horizontal and vertical deflection electrode plates 4X and 4Y of the ion beam scanning system, but also to the horizontal andvvertical deflection plates'13X and 13Y of the oscilloscope 11. Thus, theprimary ion bearnl, and the.-

image electron beam e, are scanned synchronously.

The mass scanning system consists "of a saw-"tooth voltage generator40 for slow scanning,a step voltage generator 41 for fast jump scanning, a variable DC voltage source 42 for setting the value of the step voltage and an adder 43 for adding signal voltages. The mass scanning signal e (FIG. 4(e)) is obtained by adding the output voltage E (FIG. 4(d)) from the step voltage generator 41 and the output voltage E, (FIG. 4(c)) from the saw-tooth voltage generator 40 with the adder 43. The excitation current flowing through the magnet for the analyzer magnetic field 7 is controlled in correspondence with the mass scanning signal e, and thus mass scanning is performed. In this case, mass scanning is done selectively only for a plurality of ion peaks having specific mass numbers. Therefore, each step voltage of the output voltage E, from the step voltage generator 41 is made to be freely adjustable by changing the setting voltage for each step of the variable DC voltage source 42.

The analysis-instruction-signal generator system consists of a pulse generator 50 and a button-switchSl. When the button switch 51 is pushed (switched on), the analysis initiating pulse P, (FIG. 6(a)) is sent out from the pulse generator 50. The pulse P, is sent to the saw-tooth voltage generator 40 and the step voltage generator 41 of the mass scanning system to initiate mass scanning. The signal is also sent to the other circuit elements to adjust the timing of each circuit in operation.

- The data-recording system consists of a multichannel digital printer l9 and desired data processing circuits connected to each recording channel. Namely, there is connected to a recording channel 18 for an ion peak display an ion collector output display circuit 15, a peak value read-out circuit 16 and an A D converter 17. Each peak P P P and P of the output signals I, (FIG. 4(f)) from the ion collector 8 is displayed in the form of a mass spectrum through thedisplay circuit 15, the peak value Rt (FIG. 4(g)) is read out by a read-out circuit 16, and the peak values R R R and R are converted into digital quantities by the A D converter 17 and displayed in a digital form in the recordingchannel 18. To a recording. channel. 47 for massnumber display are connected a step voltage read-out circuit 44, a mass number display circuit .45 and an A D converter 46. The voltage value at each step of the step voltage E (FIG. 4(d)) generated by the step voltage generator 41 is read out by the read-out circuit 44 and the mass number (m/e value) corresponding to the voltage at each step is displayed by the display circuit 45. The voltage value at each step is further converted into a digital quantity corresponding to its m/e value by the A D converter 46 and displayed in a digital form in the recording channel 47. Thus, an ion peak value R, and the corresponding mass number (m/e value) are simultaneously recorded in the printer 19. The printer 19 further comprises recording channels for 26 and 36 for displaying the position of the analysis point corresponding to the analysis data. The recording channel 26 records the rectangular voltage V, which displays the horizontal position of the analysis point and the recording channel 36 records the rectangular voltage V, which indicates the vertical position of the analysis point. Thus, the horizontal position recording channel 26 comprises a rectangular voltage read-out circuit 24 and an A D converter 25. The read-out circuit 24 reads out the rectangular voltage V, at the time of analysis and the read-out voltage is then converted into a digital quantity by the A D converter 25 and displayed by the recording channel 26 in a digital form. Similarly, the vertical position recording channel 36 comprises a rectangular voltage read-out circuit 34 and an A D converter 35. The circuit 34 reads out the rectangular voltage V, at the time of analysis, and the voltage is then converted into a digital quantity by the A D converter 35 and displayed in a digital form in the recording channel 36. In order to distinguish between analysis data for a plurality of analysis points, the printer 19 comprises a channel 53 which records a number n indicating the order of setting the analysis points. This channel 53 counts the number of analysis instruction signals P, with the counter 52 and displays the number n in a digital form. v

Thus, the printer records not only the analysis data R, for respective analysis points and m/e values, but also the number n of the analysis point and the voltage values V and V of the deflection voltages.

The analysis instruction signal P, is set to the

readout circuits

16, 24, 34 and 44 to adjust the timing of signal reading. Thus, these circuits read the voltage values of signals at the time of analysis (at the time of mass-scarming).

The ion beam generator system, the ion beam scanning system, the parts composing the mass spectrometer system, the sample, the secondary-electron detector and so forth are contained in an appropriate evacuation system 10 and maintained in a suitable reduced-pressure state.

The specific composition of the device according to this invention has been described hereinabove. Now, the procedures of analysis and the performances of the device when analyzing a sample with the device of this invention will be described.

Let the sample surface be composed of B(boron), Al(aluminum), Si(silicon) and Ge(germanium) and these four components be distributed in a solid-state sample as .shown in FIG. 3.-Assume further that the horizontally (in a direction of V, axis in FIG. 3) with a frequency t, by a horizontal frequency t by a horizontal scanning signal e, (FIG. 2(f)) in a time interval t shown in FIG. 2 and the ion beam I, is deflected slightly in a vertical direction (direction of V,, axis in FIG. 3) by a vertical scanning signal e, (FIG. 2(0)). Thus the beam scans a limited region of a sample planely within a time interval t,. The size of the scanned region depends on the peak values of the beam deflecting saw-tooth voltages E, and E,,. The relationship between the size of the scanned region and the magnitudes of the ion beam deflecting voltages E, and E, is shown in FIG. 3.

The amount of secondary electrons emitted from the sample surface by scanning changes with the change of the sample composition along the scanning line of the ion beam, and the output signal E, (FIG. 2(g)) from the secondary-electron detector 9 changes thereby, now, the output signal E, from the secondary-electron detector 9 is added to the intensity modulation terminal 12 of the oscilloscope 11 sweeped synchronously with the scanning of the ion beam I, by the scanning signals e, and e, so that a secondary-electron image of the sample surface as shown in FIG. 3 appears on the fluorescent screen 14 of the oscilloscope. This secondary-electron image naturally represents the component distributions in the sample surface.

After the first plane scanning ends after a time interval t the ion beam irradiation spot is fixed at a point on the sample surface for the subsequent time interval t the point on the sample being determined by the magnitudes of the rectangular voltages V, and V The relationship between the position of the fixed irradiation spot and the ion deflection voltages V, and V is shown in FIG. 3. In the time interval t the sweeping of an electron beam for image display s in the oscilloscope is stopped and the more brilliant point is displayed at the fixed irradiation position on the secondary electron image. This brilliant position on the secondary-electron image naturally corresponds to the position of a fixed irradiation spot on the sample surface.

Further, the plane scanning of the ion beam and the fixed position irradiation are repeated alternately with a time frequency of T as shown in FIG. 2, so that the secondary-electron image of the sample surface and the brilliant point corresponding to the fixed irradiation spot are displayed at all times on the fluorescent screen of the oscilloscope 1 1. Accordingly, the position of the fixed irradiation spot of the ion beam on the sample surface can be constantly monitured by observing the position of the brilliant point on the secondary electron image.

Now, if the'time interval t, for horizontal scanning of the ion beam is 0.001 second and the number of scanning lines is 100, then the time needed for one vertical scanning (the time needed for one plane scanning) is 0.1 second. Further, if the time t, for fixed point irradiation of the ion beam is 0.025 second which is one-fourth of the time 2 the time interval T for repetitive scanning becomes 0.125 second. If the afterglow time of the fluorescent screen of an oscilloscope is made equal to or longer than the time interval T the secondary-electron image of a sample surface is ceaselessly displayed. Since the secondary-electron image is static, no trouble occurs in observing the sample surface even if the afterglow time of the fluorescent screen is made sufficiently long. Thus, it is possible to make the time t, for fixed irradiation of the ion beam as long as desired. For example, when the afterglow time is 5 seconds, T is made to be 5 seconds. The plane scanning time t, and the fixed irradiation time t can be suitably chosen within this time interval. For example, when the relation t At, holds, 1' l/5 T, I second, and when t, 0.1 second constant, t 4.9 seconds. Thus, by making the afterglow time of the fluorescent screen of an oscilloscope sufficiently long, the time t, for fixed irradiation of an ion beam may be set relatively freely. It is to be noted that the time t is set by considering the relationship with the time t necessary for the mass-scanning described hereinbelow. Such a relationship in time is obtained by synchronously controlling the saw-

tooth voltage generators

20, 30 and the rectangular voltage generators 21, 31.

When a secondary-electron image of a sample surface is displayed, the analysis point is selected by observing the image. Namely, in doing an analysis, it is necessary to select such a position as requires minimum operations for analysis. In the device according to this invention, the selection of an analysis point for massspectroscopic analysis is easily done because the secondary-electron image represents in itselfa distribution of compositions in the sample surface as shown in FIG. 3. For example, when the composition distribution on the sample surface is as shown in FIG. 3, it will be easily understood that a plurality of analysis points need not be selected in a region consisting of a single component, and that it is appropriate to choose an analysis point near the boundary of the respective regions. Thus, the selection of an analysis point is facilitated by displaying a secondary-electron image on an oscilloscope. Here, it is assumed that the points n 1 8 in FIG. 3 are chosen as analysis points.

After the analysis points are selected in this way, a mass-spectroscopic analysis is done for each point sequentially. For this purpose, the fixed irradiation spot of an ion beam must be made to coincide with the position of a desired analysis point. In the device of this invention, this operation is the same as the operation of moving the brilliant point on the secondary-electron image to the position for analysis (the point corresponding to the analysis point on the sample). Accordingly, this operation is performed by manually adjusting the output voltages from the variable DC voltage sources 22, 32 so as to make the brilliant point coincide with the position of the desired analysis point while observing the secondary-electron image. Namely, by adjusting the output voltages from the variable DC voltage sources 22 and 32, the rectangular voltages V, and V,, are made to coincide with the deflection voltages for an ion beam corresponding to the desired positions of analysis. In this way, the setting of the ion beam irradiation spot to a desired analysis point can be done accurately and quickly. In this case, the setting is further facilitated if horizontal and vertical scales are provided on the fluorescent screen of an oscilloscope to make it possible to read the position of an arbitary point on the secondary-electron image and the output voltages from the variable DC voltage sources 22 and 32 are made readable with a voltmeter comprising corresponding scales. Namely the fixed irradiation spot of an ion beam may be fitted to the analysis point more 9 easily by measuring the position of theidesired analysis point on the secondary-electron image with a scale provided to the fluorescent screen and adjusting the output voltages from the voltage sources 22 and 32 so to make the indicater of each voltmeter coincide with the corresponding position on the scale.

After the fixed irradiation spot of an ion beam is made to coincide with the desired analysis point, a mass-spectroscopic analysis on this point is started. The start instruction is made by pushing a button-switch 51 after it is verified by observing the secondary-electron image that the fixed irradiation spot coincides with the analysis point. Namely, when the switch 51 is closed, an instruction pulse P, (FIG. 6(0)) is sent out from the pulse generator 50. The pulse P, is sent to the mass scanning system to start mass-scanning and simultaneously it is sent to the scanning signal generator system to increase the time for fixed irradiation of an ion beam.

I The saw-tooth voltage generator 40 and the step voltage generator 41 of the mass scanning system receive the instruction pulse P, for analysis, and operates in a way to generate a mass scanning signal e, (FIG. 6(d)) from the time when the fixed irradiation of an ion beam is started as shown in-FIG. 6. The rectangular voltage generators 21 and 31 of the scanning signal generator system receives the instruction pulse P for analysis and increases the time for the subsequent fixed irradiation with an ion beam. Namely, as shown in FIGS. 6(a) and 6(b), the time interval of the rectangular portions of the ion beam scanning signal voltages e, and e,, (time for the fixed irradiation with an ion beam) is-changed from t before analysis to a time interval T at the time of analysis.

The above description refers to a case where the time interval for the fixed irradiation with an ion beam is increased to T (T= t t only at the time of analysis. This case takes into account the fact that a desired mass-spectroscopic operation may not be performed within the time interval t for the fixed irradiation with an ion beam before analysis (for example, when t is 0.1 second and a mass-spectroscopic analysis requires a time t of several seconds). However, when required mass-spectroscopic operations can be performed satisfactorily within the time interval t i.e. t e t by making the time t for the fixed irradiation sufliciently long (for example, several seconds), it is not necessary to increase the time T for the fixed irradiation at the time of analysis (or it is sufficient to make T=. t

The required mass scanning is done within the time interval T during which a fixed analysis point (for example, point n 4 in FIG. 3) is irradiated with an ion beam. The scanning is done only for such peaks as have required mass numbers i.e. ion peaks of boron, aluminum, silicon and germanium having mass numbers (m/e) of 10, 27, 28 and 72 in the examples shown in FIGS. 3 and 4). For this purpose, slow scanning intervals S S S and S (interval width 1- 'T/4) for the scanning signal e, are set in advance so that only the desired ion peaks P P P and P may be observed with an ion collector. The mass number of the ion peak measured with the ion collector each slow scanning interval of the scanning signal is determined approximately by the potential E E E or E which is a voltage at each step of the step voltage E,,.

l Each step voltage is supplied from each setting terminal of the variable DC voltage source 42. Thus, an ion beam having an arbitary mass number can be selectively measured by adjusting each terminal voltage of the variable DC voltage source 42. It is preferable in this case to make the terminal voltages of the voltage source 42 readable in the form of a mass number. A case where only four ion peaks are observed has been described hereinabove, but it is needless to mention that an arbitrary number of ion peaks may be selectively measured by changing the step numbers of the step voltage E By the mass scanning described above, the ion peaks P P P and P. as shown in FIG. 40) are detected by the ion collector 8, these peaks are displayed in the form of a mass spectrum by the display circuit 15, and the peak values R R R and R (FIG. 4(g)) are read out by the read-out circuit 16 and displayed sequentially in a digital form by the channels 18 of the printer l9. v

In order to display the mass numbers (m/e values) corresponding ,to these peaks, voltages at respective steps E E E E (FIG. 4(d)) of the step voltage E, are read out by the read-out circuit 44, converted into their corresponding mass numbers (m/e values) and displayed sequentially in a digital form by the channels 47 of the printer 19.

Further, in order to display which analysis datum corresponds to a particular analysis point, the values of rectangular voltages V, and V (FIG. 4(a) and (b)) within the time T, during which the fixed analysis point is irradiated with an ion beam, are read out by the

readout circuits

24 and 34 and displayed in a digital form by the

channels

26 and 36 of the printer 19.

The channel 53 of the printer l9 digitally displays the number of pulses counted by the counter 52 as the number of the analysis points.

After an analysis is completed in this way for a particular analysis point, all the circuits are reset immediately and return to the state of non-analysis as shown in FIG. 6. By repeating these processes, a massspectroscopic analysis is done for a plurality of analysis points as required. FIG. 7 shows the time relationship between the instruction pulse P, for analysis at each analysis time, the corresponding rectangular voltages V and V,,, the step voltage E corresponding to the analysis point and the ion peak display signal R These signal voltages are read out and digitally displayed by the printer 19 at the time of analysis. FIG. 5 shows an example of analysis data printed out by the printer l9 and the number at each channel corresponds to each signal voltage shown in FIG. 7.

In the analysis data (FIG. 5) obtained in this way, the fourth analysis data (n 4) correspond to the analysis point of n 4 shown in FIG. 3 (ion beam deflection voltages V 300 V and V, 200 V). It is understood that the ion peak values are 35 mV for B of m/e l, 15 mV for A of m/

e

27, 50 mV for Si of m/e 28 and 0 mV for Ge" of m/e 72.

As has been fully described hereinabove, the analysis point can be selected by observing the secondary-electron image of a sample surface in the device of this invention so that the selection of unnecessary analysis points and thus unnecessary operations can be avoided.

, Further, since the position of the fixed irradiation spot of an ion beam can be determined accurately on the secondary-electron image of the sample surface, the operation of making the irradiation spot coincide with the analysis point is quite simple and accurate. Further, not only analysis data, but also the position of each corresponding analysis point is automatically recorded. Thus, the relationship between each analysis datum and each analysis point becomes apparent so that errornous treatments of analysis data may be avoided and the accuracy of analysis may be enhanced.

Accordingly, the device of this invention enables an accurate and fast analysis of a small region in a solidstate sample and has great practical advantages.

We claim:

1. In an ion micro-analyzer having means for projecting a primary ion beam on a surface of a sample to be analyzed, electric deflecting means for scanning the sample surface with the primary ion beam, means for detecting secondary electrons emitted from the sample surface in response to the irradiation with the primary ion beam, an oscilloscope for displaying the secondaryelectron image of said sample surface, which is sweeped synchronously with the scaiming of the primary ion beam and which is intensity-modulated by the output signal from said detecting means, and massspectroscopic analyzer means for analyzing secondary ions emitted from a fixed position on the sample surface by the irradiation with the primary ion beam, the improvement which comprises a saw-tooth voltage generator for generating a sawtooth voltage,

a rectangular voltage generator for generating a rectangular voltage, means for adding the rectangular voltage to the trailing edge of the saw-tooth voltage, thereby producing a scanning signal consisting of both voltages, means for applying the scanning signal to said electric deflecting means and said oscilloscope, and means for adjusting the rectangular voltage.

2. An ion micro-analyzer according to claim 1, which further comprises means for deriving the rectangular voltage from said rectangular voltage generator, means for determining the fixed position of the primary ion beam on the sample surface from the derived rectangular voltage and means for recording said position as well as the analysis data obtained by said mass-spectroscopic analyzer means.

Claims

1. In an ion micro-analyzer having means for projecting a primary ion beam on a surface of a sample to be analyzed, electric deflecting means for scanning the sample surface with the primary ion beam, means for detecting secondary electrons emitted from the sample surface in response to the irradiation with the primary ion beam, an oscilloscope for displaying the secondary-electron image of said sample surface, which is sweeped synchronously with the scanning of the primary ion beam and which is intensity-modulated by the output signal from said detecting means, and mass-spectroscopic analyzer means for analyzing secondary ions emitted from a fixed position on the sample surface by the irradiation with the primary ion beam, the improvement which comprises a saw-tooth voltage generator for generating a saw-tooth voltage, a rectangular voltage generator for generating a rectangular voltage, means for adding the rectangular voltage to the trailing edge of the saw-tooth voltage, thereby producing a scanning signal consisting of both voltages, means for applying the scanning signal to said electric deflecting means and said oscilloscope, and means for adjusting the rectangular voltage.