Ion radiation device and surface analyzer using said device

Abstract

Used as an ion beam guiding unit for introducing primary ions to the surface of the sample is an ion optical system of reflectron TOFMS for achieving time focusing including an orthogonal acceleration unit for accelerating the ions in the orthogonal direction, a flight space of a non-electric field, and an ion reflector for forming a reflecting electric field. A dual stage type is used as the ion reflector to superimpose the correction potential showing a predetermined non-linear potential distribution on the potential having a linear gradient of a uniform electric field at the side deeper than the second order focusing position that fulfills the Mamyrin solution, thereby correcting the temporal spread of ion packets emitted from the orthogonal acceleration unit until the deviation of third or higher order in energy, achieving high time focusing.

Claims

1. An ion radiation device for irradiating ions to a surface of a sample, comprising: a) a beam formation unit for forming an ion beam consisting of ions having the same mass-to-charge ratio, and b) an ion beam guiding unit for pulsing the ion beam formed by the aforementioned beam formation unit and guiding the beam to the surface of the sample; wherein the ion beam guiding unit includes b1) an orthogonal acceleration unit for accelerating the incident ion beam in pulses in the direction substantially orthogonal to its travelling direction, b2) a flight space in which the ions accelerated by the orthogonal acceleration unit fly, and b3) a voltage generator for applying a predetermined accelerating voltage to the orthogonal acceleration unit and/or applying a predetermined voltage to an ion reflector arranged in the flight space and in which ions are reflected by the action of the electric field, so as to allow the time focusing of ion packets accelerated by the aforementioned orthogonal acceleration unit, fly in the flight space, and arrived on the surface of the sample.

2. The ion radiation device according to claim 1, characterized in that the aforementioned ion beam guiding unit includes an ion reflector, and the aforementioned voltage generator applies a predetermined voltage to the aforementioned ion reflector so that the potential gradient on the ion optical axis in the reflecting electric field by the aforementioned ion reflector becomes non-linear at least in some portions.

3. The ion radiation device according to claim 2, characterized in that the aforementioned voltage generator applies a voltage to the ion reflector so that a predetermined potential distribution UA (X) with which an inverse function XA (U) is uniquely obtained is formed in the hollow region of the ion reflector, after the potential is monotonically changed over the entire ion reflector along the central axis of the ion reflector, when X is set as the coordinate along the central axis of the ion reflector, thereby, forming an Nth order focusing position at the position of coordinate X0 and potential E0 inside the ion reflector, and at the same time applies a voltage to the ion reflector so as to superimpose on the predetermined potential XA (U) a predetermined correction potential XC (U) that becomes a smooth function at the back side from the coordinate X0 and can be approximated by the equation in proportional to {U (X)E.sub.0} N+3/2 in the vicinity of the coordinate X0 in a space at the back side where an Nth order focusing position with coordinate X0 is set as the starting point.

4. The ion radiation device according to claim 1, characterized in that the aforementioned ion beam guiding unit includes a dual stage ion reflector that fulfills Mamyrin solution.

5. The ion radiation device according to claim 1, characterized in that the aforementioned orthogonal acceleration unit carries out acceleration according to a dual-stage acceleration technique that fulfills Wiley-McLaren condition.

6. The ion radiation device according to claim 1, characterized in that the aforementioned beam formation unit includes at least one of a liquid metal ion source, a cluster ion source, a gas field ion source, or an ion source using electric discharge.

7. The ion radiation device according to claim 1, characterized in that the aforementioned beam formation unit includes a selection unit for selecting ions having a specific mass-to-charge ratio.

8. The ion radiation device according to claim 1, characterized in that the ion beam guiding unit further has a centroid adjustment unit for adjusting the spatial centroid of the ion beam.

9. The ion radiation device according to claim 1, characterized in that the beam formation unit has an ion storage unit for storing ions, wherein the ions temporarily stored in the ion storage unit are emitted and introduced to the orthogonal acceleration unit.

10. The ion radiation device according to claim 1, characterized in that the beam formation unit irradiates ions having two-dimensional spread to a sample by allowing incident of an ion beam with a predetermined width on the orthogonal acceleration unit, the ion beam of which spreads in the direction substantially orthogonal to both the incident direction of ions to the orthogonal acceleration unit and the acceleration direction in the orthogonal acceleration unit, and by allowing the orthogonal acceleration unit to accelerate in pulses only at a predetermined length the incident ion beam with a predetermined width in its incident direction.

11. The ion radiation device according to claim 10, characterized in that a sample stage is provided to hold a sample, wherein the sample stage is made to be slidable and tiltable.

12. A surface analyzer using the ion radiation device according to claim 1, characterized in that the surface analyzer is used to observe ions, neutral particles, photons, or phonons emitted as secondary particles from a sample with respect to the ions that are made incident to the surface of the sample by the aforementioned ion radiation device.

13. The surface analyzer according to claim 12, characterized in that the surface analyzer is a time of flight-type secondary ion mass analyzer for measuring the secondary ions emitted from a sample by a time of flight-type mass analyzer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an overall configuration diagram of TOF-SIMS in an example of embodiment using the ion radiation device according to the present invention.

(2) FIG. 2 is a configuration diagram of a beam guiding unit of TOF-SIMS of the example of embodiment.

(3) FIG. 3 at (a) is a schematic diagram of a reflectron-type TOFMS used in the beam guiding unit of the TOF-SIMS of the example of embodiment, and at (b) is a drawing illustrating a schematic potential distribution on the ion optical axis.

(4) FIG. 4 is a configuration diagram of the beam guiding unit assumed during a simulation for confirming the time focusing of the ion beam in TOF-SIMS of the example of embodiment.

(5) FIG. 5 is a drawing illustrating the calculation results of the potential distribution on all ion flight path in the beam guiding unit shown in FIG. 4.

(6) FIG. 6 is a drawing illustrating the results of the detailed calculation of the potential distribution in the reflectron of the beam guiding unit shown in FIG. 4.

(7) FIG. 7 is a drawing illustrating the simulation results of the ion trajectory from the orthogonal acceleration unit until the sample surface.

(8) FIG. 8 is an enlarged view of the ion trajectory in the vicinity of the orthogonal acceleration unit.

(9) FIG. 9 is an enlarged view of the ion trajectory in the vicinity of the sample surface.

(10) FIG. 10 is a drawing illustrating the simulation results of the trajectory of secondary ions emitted from the sample surface with respect to the incident of the primary ions.

(11) FIG. 11 is an enlarged view of the secondary ion trajectory in the vicinity of the sample surface.

(12) FIG. 12 is a schematic diagram of the beam guiding unit of TOF-SIMS according to another example of embodiment using the ion radiation device of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(13) TOF-SIMS of one example of embodiment of the surface analyzer using the ion radiation device according to the present invention will be described below in details with reference to the accompanying drawings.

(14) FIG. 1 is an overall configuration diagram of TOF-SIMS in this example of embodiment, and FIG. 2 is a configuration diagram of a beam guiding unit.

(15) As shown in FIG. 1, TOF-SIMS of this example of embodiment is equipped with an ion source 1 for generating primary ions; a mass selection unit 2 for selecting only ions with a specific mass-to-charge ratio m/z among the ions generated by the ion source 1; an ion beam guiding unit 3 that includes an orthogonal acceleration unit 4, a flight space 5, and an ion reflector 6; a sample holder 7 for holding sample S, which is the subject of measurement; a time-of-flight mass spectrometer 8 for separating secondary ions emitted from the sample S depending on the irradiation of the primary ions according to the mass-to-charge ratio; a detector 9 having a detection surface that is two-dimensionally wide; and a data processor 10 for processing a detection data by the detector 9.

(16) A liquid metal ion source widely used in SIMS, a cluster ion source, a gas field ion source, and various plasma ion sources using a discharge phenomenon can be used as the ion source 1. In addition to a quadrupole mass filter capable of arbitrarily controlling the ratio of the mass-to-charge value or the range of the mass-to-charge ratio of ions to be selected by changing the voltage applied to an electrode, a technique of selecting, by a gate electrode, ions with a specific mass-to-charge ratio from among the ions that have been separated depending on the time of flight corresponding to the mass-to-charge ratio, a technique of selecting ions with a specific mass-to-charge ratio using a magnetic field, or a Wien filter that superimposes the electric field and the magnetic field can be used as the mass selection unit 2. When the mass-to-charge ratios of ions generated by the ion source 1 are uniform, it is not necessary to provide a mass selection unit 2.

(17) The configuration of the ion beam guiding unit 3 and the time-of-flight mass spectrometer 8 will be described in details with reference to FIG. 2.

(18) As shown in FIG. 2, the orthogonal acceleration unit 4 includes a flat push-out electrode 41, a grid-type extraction electrode 42, a plurality of accelerating electrodes 43, and an accelerating voltage generator 44 for applying each predetermined voltage to each electrode 41-43. The ion beam sent in from the mass selection unit 2 in the Z axial direction is introduced to a flat acceleration space 45 between the push-out electrode 41 and the extraction electrode 42 arranged in parallel. At this point, although the spatial spread of the ion beam in the X axial direction is small, it has the spread to a certain extent in the Y axial direction (By is the width of the ion beam in the Y axial direction).

(19) When the respective predetermine DC voltages are applied to the push-out electrode 41 and the extraction electrode 42 from the accelerating voltage generator 44 at a preset timing, an extraction electric field is formed in the acceleration space 45, and the ions that pass through the acceleration space 45 at this time receive an energy in the X axial direction and are extracted outside the extraction electrode 42. The ions are further accelerated in the X axial direction from the accelerating electric field formed by the applied voltage to the accelerating electrodes 43 to fly in the direction where the velocity component in the X axial direction and the velocity component in the Z axial direction merge (the direction inclined in the Z axial direction with respect to the X axial direction). The ion beam in the acceleration space described above is simultaneously accelerated with ions that have a width of By in Y axial direction and a length to a certain degree in the Z axial direction (this length here will be referred to as Bz). Therefore, ion packets in a very thin sheet form (the height in the X axial direction is very small), which is a rectangle of Bz x By, are emitted from the orthogonal acceleration unit 4.

(20) The flight space 5 is formed inside a housing 51 to maintain in a vacuum atmosphere and does not receive external influence of electric field or magnetic field. That is, the flight space 5 is a field free space in which ions fly without being affected by electric field or magnetic field. The ion packets emitted from the orthogonal acceleration unit 4 described above are charged into and fly inside the flight space 5. The ion reflector 6 that includes a plurality of guard-ring electrodes 61, a back plate 62, and a reflected voltage generator 63 is arranged at the back side of the flight space 5 toward the travelling direction of the charged ions, and the ion packets are reflected by a reflecting electric field formed by this ion reflector 6. The reflected ion packets then fly again inside the flight space 5 and finally arrive at the surface of the sample S. The sample holder 7 includes a sample stage 71 that is movable in five axial directions (X, Y, Z, , and ) and on which the sample S is placed on the surface, and a stage driving unit 72 including a driving mechanism of a motor, or the like, for moving the sample stage 71 in each five axial direction described above.

(21) The time-of-flight mass spectrometer 8 has a linear configuration including an accelerating electrode 81 arranged on top of the sample S and a flight space 82 formed inside the housing 51. That is, when the ion packets in a sheet form as described above are irradiated to the sample S as primary ions, secondary ions originating from various components existed on the surface of the sample S fly from the sample S. These secondary ions receive a certain initial energy by an accelerating electric field formed by the voltage applied to the accelerating electrode 81 from a voltage generator, not shown in the drawing, to be sent to the flight space 82, which is a non-electric and non-magnetic field. The secondary ions that fly in the flight space 82 are separated depending on the mass-to-charge ratio, and the secondary ions having different mass-to-charge ratios arrive at the detector 9 having a time lag.

(22) The secondary ions fly from the entire two-dimensional region on the sample S irradiated with the primary ions; however, these secondary ions fly while almost maintaining the positions in the Z axial direction and Y axial direction and arrive at the detector 9. The detector 9 detects the secondary ions that arrive in a state of being two-dimensionally spread for each of their positions and outputs the detection data depending on the amount of ions arrived. Therefore, the data processor 10 can acquire a spectrum data showing the relationship between the ion intensity and the time of flight for each position having different coordinates (Z, Y) on the sample S, and obtain the mass spectrum data by converting the time of flight to the mass-to-charge ratio. And a mass spectrometric imaging image at any mass-to-charge ratio is created based on this mass spectrum data.

(23) As such, the TOF-SIMS of the present example of embodiment is a TOF-SIMS capable of imaging mass spectrometry by means of a projection-type imaging technique.

(24) In such TOF-SIMS, the primary ions irradiated on the surface of the sample S preferably fulfill the following requirements.

(25) (1) The spreads of ion packets in the Z axial direction and the Y axial direction irradiated on the surface of the sample S are from about several mm to about several cm, and the ions inside the ion irradiation region are to have a uniform distribution as much as possible.
(2) All ions contained in the ion packets, which are in a sheet form, focused on a surface parallel with the surface of the sample S are to simultaneously arrive on the surface of the sample S. That is, the time focusing of ion is high at each different position inside the ion irradiation region, and the arrival time of ion at each position is to be as small as possible (provided that the surface of the sample S is flat).

(26) The requirements no. (2) above are especially important in achieving high mass resolution and high mass accuracy. In the TOF-SIMS of the present example of embodiment, using an ideal reflectron (refer to Patent Literature 2) for orthogonal acceleration-type mass analyzer developed by the present inventors for the ion beam guiding unit 3 realizes high time focusing of ions on the surface of the sample S.

(27) First, the key points of one example of the reflectron-type TOFMS using the ideal reflectron will be described with reference to FIG. 3. The ideal reflectron here is the one in which energy focusing is possible up to an infinite higher order of terms regarding the spread of time of flight at a certain energy E.sub.0 or greater with complete isochronous energy being the most important. The time of flight T(E) of ions, where E is an initial energy, in TOFMS can be represented by the following equation (1).
T(E)=T(E.sub.0)+(dT/dE)(EE.sub.0)+()(d.sup.2T/dE.sup.2).Math.(EE.sub.0).sup.2+()(d.sup.3T/dE.sup.3)(EE.sub.0).sup.3+ . . . (1)
Complete isochronous refers to the terms of first and all subsequent differential coefficients in equation (1) becoming 0.

(28) FIG. 3 at (a) is a schematic diagram of a reflectron-type TOFMS, having a configuration in which the top portion shows Z-X planes on which the ion trajectory rests and the bottom portion shows Y-X planes. The ions receive an initial energy at an accelerating region 100 to fly in a non-electric field flight space 101. And then the ions are reflected by an ion reflector 102, returned to the non-electric field accelerating region 101, and arrive at the detector 103. FIG. 3 at (b) shows a schematic potential distribution on the ion optical axis.

(29) This reflectron is based on the dual stage reflectron proposed by Mamyrin. The ion reflector in the dual stage reflectron is configured by a uniform electric field of two stages, where 1st denotes the first stage and 2nd denotes the second stage in FIG. 3. The potential distribution in the first stage of the non-electric field flight space 101 and the ion reflector 102 is as shown by the solid line in FIG. 3 at (b). The potential distributions in the second stage of the ion reflector 102 are as shown by straight solid and dashed lines in FIG. 3 at (b). That is, the electric fields in the first and second stages are both uniform electric fields, so the potential gradient is linear, and the inclination of the straight line is different in the first stage and the second stage. As has been well known, with this configuration, it is possible to correct the spread of time of flight at the time the ions arrive at the detector 103 until the second derivative of the energy the ions have, by appropriately determining the potential gradient of each stage, that is, the electric field. That is, the first and second order differential coefficients in equation (1) become 0. However, in this case, the third order and subsequent differential coefficients do not become 0. The potential distribution X.sub.A (U) of the optimized model in the uniform electric field of two stages as described above is called a base potential.

(30) On the contrary, with the ideal reflectron developed by the present inventors, the correction potential X.sub.C (U) properly calculated is superimposed on the base potential X.sub.A (U), and the sum of the potential X.sub.R (U)=X.sub.A (U)+X.sub.C (U) is made so as to fulfill complete isochronism. In order to prevent disturbance to the time focusing until the second order is achieved by Mamyrin solution, the second order focusing position in the Mamyrin solution determined in the second stage is made as the starting point of superimposing the correction potential X.sub.C (U), and the correction potential X.sub.C (U) is superimposed only on the back side from this position. The detailed invention is omitted, but the theoretical correction potential X.sub.C (U) is expressed by the following equation (2).

(31) $\begin{array}{cc}\left(\mathrm{Mathematical}\mathrm{formula}1\right)& \\ X_C\left(U\right)=\frac{1}{2\sqrt{2}}{}_1^U\frac{T_D\left(1\right)-T_D\left(E\right)}{\sqrt{U-E}}\mathrm{dE}& \left(2\right)\end{array}$

(32) Ideally, the correction potential X (U) in the vicinity of the point from which the superimposing of the correction potential X.sub.c(U) starts is approximated by the power of 3.5, which is a half-integer. That is,
X.sub.C(U)(U1).sup.3.5.

(33) It is possible to realize complete isochronism of ions reaching the detector 103 by determining the voltage applied to each guard-ring electrode that constitutes the ion reflector 102 so that the electric field having the potential distribution added with the correction X.sub.C (U) described above to the base potential X.sub.A (U) is formed inside the ion reflector 102.

(34) Similarly in a single stage reflectron that achieves first order focusing by a uniform electric field at a single stage that fulfills the requirements of Wiley-McLaren instead of a dual stage reflectron, by superimposing the correction potential on the base potential, it is possible to realize an ideal reflectron. However, the correction potential, which is non-linear, of the dual stage reflectron can be small, so the effect of time aberrations due to divergence and off-axis of undesired ions is easy to suppress.

(35) The ideal reflectron described above realizes a complete isochronism of ions when the ions emitted from the acceleration region 100 arrive at the detector 103; therefore, basically by replacing the detector 103 onto a sample S, it is possible to realize time focusing of ions at the surface of the sample S. However, in the case of TOFMS as shown in FIG. 3 at (a), as opposed to the path of ions coming out from the ion reflector 102 until reaching the detector 103 being a non-electric field, as shown in FIG. 2, in the TOF-SIMS of the present example of embodiment, an accelerating electric field for secondary ion extraction by the accelerating electrode 81 is formed in the upper space of the sample S, and the primary ions also pass through that accelerating electric field. For this reason, the potential distribution inside the ion reflector 6 for realizing the complete isochronism of ions is calculated also by taking the effect of the accelerating electric field into consideration.

(36) Even when the ion packets in a very thin sheet shape arrive at the sample S, if the surface of the spread of those ion packets is not parallel with the surface of the sample S, the times the ions arrive become vary according to their position within the surface, leading to the deterioration of the mass resolution of the secondary ions. Therefore, in TOF-SIMS of the present example of embodiment, by properly tilting the sample stage 71 by the stage driving unit 72, it is possible to secure the parallelism between the surface of the sample S and the surface of the spread of ion packets, which are the primary ions. Specifically, a user may simply perform a fine adjustment of the inclination of the sample stage 71 so as to make the width as small as possible, that is, to make the mass resolution as good as possible, while observing the width of a peak having a predetermined mass-to-charge ratio in the secondary ion spectrum.

(37) Next, the potential distribution on the entire ion flight path when using the configuration of the ideal reflectron described above in the ion beam guiding unit 3 and a simulation for proving its effect will be described.

(38) FIG. 4 is a drawing illustrating the geometric shape and arrangement of electrodes of the beam guiding unit 3 assumed during a simulation calculation of the ion trajectory, FIG. 5 is a drawing illustrating the potential distribution on all ion flight path in the structure shown in FIG. 4, and FIG. 6 is a drawing illustrating the detailed potential distribution in the ion reflector 6 shown in FIG. 5. In FIG. 4 and FIG. 5, the numerical values indicating the size (the unit is mm) for distinguishing it from the references indicating each part are denoted in brackets.

(39) As for regions in which ions are accelerated or decelerated other than the free flight space of a non-electric field, there are three regions, which are an acceleration region Pa for initially accelerating ions, a reflection region Pb for reflecting the ions after the ions discharged from the acceleration region Pa pass through the flight space 5, which is a non-electric field, and a sample holding region Pc for irradiating the ions to the surface of the sample S after the reflected ions pass through the flight space 5 again. The ions in the acceleration space 45 in the acceleration region Pa progress at an initial energy Ez=600 eV in the Z axial direction. The gap between the push-out electrode 41 and the extraction electrode 42 is 4 mm, and the ions are accelerated in the X axial direction by the voltages applied to the electrodes 41 and 42 and the voltage applied thereafter to the accelerating electrode 43 arranged in a region having 40 mm in length in the X axial direction.

(40) Suppose that the initial spread of ions in the X axial direction in the acceleration space 45 is 2 mm. The ions that fly inside the flight space 5 have a kinetic energy of 10.6-14.6 keV in width due to the difference in the initial positions of ions in the X axial direction. These ions fly in the flight space 5 again after being reflected by the ion reflector 6 in the reflection region Pb (however, the depth of penetration into the reflection region Pb differs depending on the energy the ions have). As described above, an electric field for accelerating the generated secondary ions having a low initial kinetic energy is always formed in the sample holding region Pc. For this reason, as shown in FIG. 5, when primary ions, which are of positive polarity, are made to incident to sample S, and secondary ions, which are of positive polarity, are emitted from the sample S, the primary ions towards the sample S receive a decelerating force as they advance in the sample holding region Pc.

(41) As described above, when calculating the potential distribution inside the ion reflector 6 for realizing the isochronism of ions on the surface of the sample S, the decelerating electric field in the sample holding region Pc is also taken into consideration. Specifically, a secondary focusing condition (a, p) that fulfills Mamyrin solution is obtained (where a represents the position of the second order focusing point, and p represents the ratio of ion energy lost at the first stage of the ion reflector), so that the time of flight with respect to the ions with energy exceeding 10 keV becomes equal, in accordance with the technique described in Patent Literature 2; a non-linear correction potential in a region deeper than the position of the second order focusing point (a={87+18(5)}/6) (where p=) is obtained, and this is added to the base potential having a linear potential gradient to calculate the ideal potential distribution. As can be seen from FIG. 6, simply by making the potential gradient after correction to be slightly curved, the deviation from the linear potential is minimal.

(42) The results of investigating whether the isochronism of ions is actually achieved using a simulation of ion trajectory are shown in FIG. 7 to FIG. 9. FIG. 7 is a drawing illustrating the ion trajectory from the orthogonal acceleration unit 4 until the surface of the sample S, FIG. 8 is an enlarged view of the ion trajectory in the vicinity of the orthogonal acceleration unit 4, and FIG. 9 is an enlarged view of the ion trajectory in the vicinity of the surface of the sample S.

(43) In the simulation calculation, suppose that the ions, wherein m/z=1000, fly in the acceleration space 45 in the Z axial direction at an initial kinetic energy of 600 eV, and the kinetic energy of ions at the time of incident to a free flight space varies at a width of 10.6-14.6 keV by the difference in the initial position in the X axial direction. The ions come out from the accelerating region Pa, are reflected in the reflection region Pb, and arrive at the sample holding region Pc, during which uniform motion continues in the Z axial direction. For this reason, when the time of flight becomes equal with respect to the ion packets having a kinetic energy in the flight space 5 of 10.6-14.6 keV in width, all ions with position deviation in FIG. 8 should arrive at the same Z coordinate position on the surface of the sample S. Actually, the fact that all ions emitted from different positions in the X axial direction arrived at one point, i.e., the same Z coordinate position, on the surface of the sample S can be confirmed from the results shown in FIG. 9. That is, this means that the ideal ion isochronism is realized. According to the results of such simulation, it can be confirmed that the time of flight is contained in the range of deviation within 1 nsec focusing on 21.858 sec with respect to the ion packets having a width (the width of kinetic energy) of the initial position in X axial direction. That is, it was confirmed that isochronism at high level can be realized.

(44) The simulation results of the trajectory of secondary ions occurred when the primary ions collided on the surface of the sample S as described above are shown in FIG. 10 and FIG. 11. FIG. 11 is an enlarged view of the secondary ion trajectory in the vicinity of the surface of the sample S shown in FIG. 10. Here, it is assumed that the secondary ions, wherein m/z=500, are separated from the surface of the sample S at an angle of spread of 10 at an initial energy of 2 eV. The state of the ions emitted from the surface of the sample S passing through the sample holding region Pc while almost maintaining the initial position distribution can be confirmed from FIG. 10 and FIG. 11. Therefore, it was found that it is possible to realize TOF-SIMS by means of the projection-type imaging technique by arranging a proper ion imaging lens immediately after the sample holding region Pc and then detecting the ions using a position-sensitive detector.

(45) In the example of embodiment described above, the ideal reflectron capable of realizing high ion isochronism with respect to the ion packets having a wide spread of energy was used as the ion beam guiding unit 3, as disclosed in Patent Literature 2. However, the ideal reflectron may not necessarily be used as long as the tolerance of the temporal spread of the ion packets that arrive on the surface of the sample S is widened.

(46) The easiest configuration to use as the ion beam guiding unit 3 is an ion optical system equivalent to the linear TOFMS using a dual stage acceleration-type ion source that fulfills Wiley-McLaren conditions. This configuration is shown in FIG. 12. The primary ions are accelerated by an orthogonal acceleration unit 4 and introduced into the flight space 5, and the primary ions that fly in the flight space 5 are made to arrive on the surface of the sample S, which is completely the same as that in the example of embodiment described above. As has been described before, in this case, since only the first order time focusing is achieved, the time focusing compared to the case of using the ideal reflectron considerably deteriorates.

(47) As another configuration, a dual stage reflectron by Mamyrin can also be used in the ion beam guiding unit 3. This is equivalent to the case where a correction potential is not added to a base potential in the example of embodiment described above, which in this case, it is possible to achieve second order time focusing. Therefore, the time focusing is excellent as compared to the case of using Wiley-McLaren-type accelerator, while the time focusing deteriorates as compared to the case of using the ideal reflectron.

(48) In such TOF-SIMS of the present example of embodiment, ion optical systems in various time-of-flight mass separators configured so as to improve the time focusing of ions arrived at the detector in TOFMS can be used as the ion beam guiding unit 3.

(49) In the TOF-SIMS of the example of embodiment described above, since the primary ion beam incident to the orthogonal acceleration unit 4 in the Z axial direction is cut-out only at a predetermined length in the Z axial direction to be accelerated, when the ion beam is supplied continuously to the orthogonal acceleration unit 4, the use efficiency of the ions decreases due to issues in the orthogonal acceleration unit 4, the so-called dual cycle. That is, there will be a large amount of ions discarded without being used for ion radiation. This is the same as in the case of TOFMS of orthogonal acceleration technique (refer to Non-Patent Literature 4). Therefore, in order to improve the use efficiency of ions at the orthogonal acceleration unit 4, the ions may be temporarily captured by the action of an electric field (or a magnetic field) in the mass selection unit 2, the accumulated ions may be send to the orthogonal acceleration unit 4 in a packet form, and an orthogonal acceleration may be performed by adjusting the timing with the feeding of ions. For example, a linear-type ion trap, or the like, may also be used to accumulate the ions.

(50) In order to adjust the position of the region irradiated by the primary ions on the surface of the sample S, as for the Z axial direction, the initial kinetic energy imparted to the ions at the time of introducing the ions to the orthogonal acceleration unit 4 (that is, the energy in the Z axial direction possessed by the ions introduced to the orthogonal acceleration unit 4) may be adjusted. As for the position in the Y axial direction, adjustment cannot be done even when the initial kinetic energy is changed, so the deflection electrode for deflecting the ions incident to the orthogonal acceleration unit 4 in the Y axial direction are disposed right before the orthogonal acceleration unit 4. By doing so, it is possible to adjust or change the position of the region irradiated by the primary ions on sample S without moving within the Y axis-Z axis surface the sample stage 71 on which the sample S is placed.

(51) In the example of embodiment described above, tilting the sample stage 71 secures the parallelism between the surface of the sample S and the spread surface of the ion packets incident to the surface; however, in place of mechanically tilting the sample stage 71, the spread surface of the ion packets at the time of emission in the orthogonal acceleration unit 4 may be tilted instead. For this reason, a beam deflector may be provided in front of the orthogonal acceleration unit 4 so as to slightly tilt the incident direction of the ions incident to the orthogonal acceleration unit 4 by the beam deflector with respect to the YZ surface. Or, it is possible to adjust the parallelism between the surface of the ion packets and the surface of the sample S also by adjusting the applied voltage to the push-out electrode 41 or the extraction electrode 42 at the time of introducing the ions to the orthogonal acceleration unit 4. Also in this case, similarly to the description above, a user may adjust the width of the peak having a specific mass-to-charge ratio in the secondary ion spectrum to be as small as possible while observing such width.

(52) In the example of embodiment described above, a mass selection unit 2 is provided in front of the orthogonal acceleration unit 4 to align the mass-to-charge ratios of the primary ions; however, in place of this mass selection unit 2, an opening and closing blind (refer to Non-Patent Literature 4) by an electric field may be provided inside the flight space 5 of a non-electric field, and ions with a predetermined mass-to-charge ratio may be selected by this blind.

(53) In the examples of embodiment described above, the ion radiation device of the present invention was applied to TOF-SIMS by means of projection-type binding technique, and the secondary particles subjected to measurement were the separated ions emitted from the surface of the sample S. However, the ion radiation device having the same configuration can be used in various types of surface analyzers in which primary ions in a very thin sheet shape are uniformly irradiated to a somewhat wide range on the surface of the sample S, and depending on this, various types of particles, electromagnetic waves, and so on, other than the ions emitted from the sample S are observed. For example, surface analyzers for observing light, x-rays, neutral particles, and the like, emitted from the sample S depending on the ion radiation can be typically used. To be more specific, it is possible to apply to surface analyzers for uniformly irradiating primary ions to a solid surface with a different spatial distribution and measuring the light or the separated particles at a time resolution of nanoseconds by a chemical reaction on the solid surface.

(54) A transmission-type analyzing technique of irradiating ions to a sample in a thin sheet form and observing the ions that are emitted after passing through the sample (secondary ions) can also be considered. In short, the present invention can be applied to all surface analyzers that use ions in a sheet form as the primary particles and observe ions such as molecules, atoms, photons as well as metastable particles as the secondary ions.

(55) The present invention is also useful not only for TOF-SIMS according to the projection-type imaging technique and other surface analyzers but also for TOF-SIMS according to the scanning-type imaging technique and other surface analyzers.

(56) The present invention is not limited to the examples of embodiment and various modification examples described above; it shall be readily understood that proper modifications, corrections, and additions are also included within the range of the Scope of Patent Claims.

EXPLANATION OF REFERENCES

(57) 1 . . . Ion source 2 . . . Mass selection unit 3 . . . Ion beam guiding unit 4 . . . Orthogonal acceleration unit 41 . . . Push-out electrode 42 . . . Extraction electrode 43 . . . Accelerating electrode 44 . . . Accelerating voltage generator 45 . . . Acceleration space 5 . . . Flight space 51 . . . Housing 6 and 102 . . . Ion reflector 61 . . . Guard ring electrode 62 . . . Back plate 63 . . . Reflection voltage generator 7 . . . Sample holding part 71 . . . Sample stage 72 . . . Stage driving unit 8 . . . Time-of-flight mass analyzer 81 . . . Accelerating electrode 82 . . . Flight space 9 and 103 . . . Detector 10 . . . Data processor S . . . Sample 100 and Pa . . . Accelerating region 101 . . . Non-electric field flight space Pb . . . Reflecting region Pc . . . Sample holding region