JP2005166361A - Incident position detector of charged particle, and energy analysis device thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an incident position detector of charged particles and an energy analysis device thereof effective for the energy analysis of charged particles of a wide range including low-energy charged particles and having excellent detection accuracy. <P>SOLUTION: In this incident position detector of charged particles for detecting the incident position of the charged particles changing according to the energy of the charged particles, detection sensitivity at the incident position is set in inverse proportion to the energy of the charged particles assumed to enter into the incident position, or a moderating material having deceleration capability at the incident position in inverse proportion to the energy of the charged particles assumed to enter the incident position is disposed in front of a body of the incident position detector. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to a charged particle incident position detector and a charged particle energy analyzer used for energy analysis of charged particles such as electrons and ions.

  Some analyzers using charged particles such as electrons and ions use energy analysis of charged particles. Rutherford Backscattering Spectroscopy (RBS) is one of them, irradiating the target with accelerated hydrogen ions and helium ions, measuring the energy distribution of ions scattered backward, and non-destructive elemental analysis in the depth direction. Is possible.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 7-190963), scattered ions back-scattered by a sample on which an ion beam having a high and medium energy is incident are converged on a beam axis using a magnetic field parallel to the ion beam. A parallel field Rutherford backscattering analyzer is described. FIG. 7 shows a schematic configuration of the Rutherford backscattering analyzer described in the publication.

  The helium ion beam 2 emitted from the ion source 1 fed with a high voltage of about 400 kV is accelerated by the voltage applied to the acceleration tube 3 while passing through the acceleration tube 3, and travels toward the sample 4. On the surface of the sample 4, the scattered ions 5 elastically scattered are bent in a trajectory by a magnetic field parallel to the beam axis of the ion beam 2 generated by the electromagnet 6 including the solenoid coil 61 and the magnet yoke 62, thereby performing a spiral motion. Draw a trajectory that repeatedly touches (converges) the beam axis.

  An iris-type slit 7 (aperture) is arranged so that the scattered ion 5 having a specific energy and scattering angle passes through the ion beam 2 at a position where it converges on the beam axis. Only the scattered ions 5 having the following energy are discriminated, and the scattered ions 5 that diverge again are detected by a two-dimensional scattered ion detector 8 to obtain an energy spectrum. Based on the energy spectrum thus obtained, identification of the component elements of the sample 4 and composition analysis in the depth direction (ion channeling analysis) can be performed.

  Hereinafter, although energy analysis by the ion position detector used also in this example will be described, a case of a one-dimensional position detector will be described as an example for simplicity.

  In the energy analysis of charged particles, there is one that applies a magnetic field or an electric field to charged particles and analyzes the fact that the amount of deflection differs depending on the energy. In that case, energy analysis becomes possible by detecting the position where the charged particles have arrived.

  FIG. 2 shows a schematic diagram of energy analysis using a magnetic field. Here, scattering ion energy analysis by Rutherford backscattering analysis is shown as an example. The energy of helium ions (or hydrogen ions) incident and scattered on the sample varies depending on the elements of the sample. When the light is incident on the deflection magnet in order to analyze this, the amount of deflection changes according to the energy, so that the incident position on the position detector separated from the deflection magnet by a certain distance changes. That is, the lower the energy charged particles, the larger the trajectory deflection due to the force from the magnetic field.

  As shown in FIG. 3, there is a method for detecting the arrival position by deflecting the charged particle trajectory with an electric field as shown in FIG.

  In any energy analysis method, it is necessary to detect the incident position of charged particles. A charged particle position detector uses a position sensitive detector (PSD) or a fluorescent screen to convert it into light and detect it as an image.

  FIG. 4 shows a principle diagram of the position sensitive detector. Charged particles enter the semiconductor detector, generate electron-hole pairs at that position, and flow out to the left and right electrodes as charges. Since the charge amounts Q1 and Q2 flowing out to the left and right electrodes are distributed according to the distances L1 and L2 between the incident position of the charged particles and the electrodes, the arithmetic expression Q1 / (Q1 + Q2) obtained therefrom indicates the incident position. This corresponds to L2 / (L1 + L2). An equivalent circuit of the position sensitive detector is shown in FIG.

  Another principle of the position detector uses a fluorescent plate. As shown in FIG. 6, a fluorescent plate that emits light when charged particles are incident is arranged, and the emitted image is captured by a lens and a camera, converted into an electrical signal, and the position is detected.

  Patent Document 2 (Japanese Patent Laid-Open No. 4-26045, etc.) describes a position detector that deflects ions that have passed through plasma into an electric field and causes ions that have reached different positions depending on energy to enter a fluorescent plate. An apparatus for detecting is disclosed. When ions are incident on the fluorescent plate, light is emitted at that position. Therefore, the optical image is converted into an electrical signal, the position is detected, and energy analysis is performed.

  In these conventional position detectors, charged particles having different energies are incident and emit light or generate electron / hole pairs and detect them as signals. If the energy of the charged particles is different, the amount of light emission and the amount of generated electron / hole pairs are different, and the level of the signal converted into an electric signal is different. A / D (analog / digital) conversion is performed after passing through an amplifier with a constant amplification factor, so that the position of charged particles with high energy can be detected with good S / N, but the position of charged particles with low energy can be detected. It is a disadvantage that accuracy is inferior. That is, there is a possibility of being buried as a quantization error within the finite resolution of the A / D converter or having an adverse effect on electrical noise.

  In order to prevent this, a method of amplifying a low-range signal corresponding to low energy with a high-precision amplifier can be considered, but this method is disadvantageous because the signal corresponding to high-energy charged particles is saturated.

That is, when a wide dynamic range exists in the charged particles incident on the incident position detector, there is a problem that the signal processing / conversion unit in the subsequent stage cannot cope with it and deteriorates the S / N.
JP-A-7-190963 JP-A-4-26045

  It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a charged particle incident position detector excellent in detection accuracy effective for energy analysis of a wide range of charged particles including low energy charged particles. It is a thing.

In order to achieve the above object, the features of the invention proposed by the present inventors are as follows.
(1) In a charged particle incident position detector that detects the incident position of a charged particle that changes according to the energy of the charged particle, the detection sensitivity at the incident position is set to the energy of the charged particle that is assumed to be incident on the incident position. An incident position detector for charged particles, which is set in inverse proportion (Claim 1).
(2) The incident position detector for charged particles according to the above (1), wherein the detection sensitivity changes in an inclined manner or stepwise. (Claim 2).
(3) In a charged particle incident position detector that detects an incident position of a charged particle that changes in accordance with the energy of the charged particle, a deceleration capability at the incident position is provided before the main body of the incident position detector. An incident position detector for charged particles, wherein a moderator that is inversely proportional to the energy of the charged particles expected to be incident is disposed.
(4) The incident position detector for charged particles according to (3) above, wherein the thickness of the moderator is changed in an inclined manner or stepwise.
(5) The ion beam emitted from the ion source is accelerated to collide with the surface of the measurement sample, and the scattered charged particles generated thereby are discriminated through the slit, and then the trajectory is deflected by a magnetic field or an electric field to In a charged particle energy analyzing apparatus that enters an incident position detector and analyzes the energy of the charged particle according to the incident position, the incident position detector of the charged particle determines the detection sensitivity at the incident position to the incident position. A charged particle energy analyzer that is set in inverse proportion to the energy of the charged particles.
(6) The ion beam emitted from the ion source is accelerated to collide with the surface of the measurement sample, and after scattering charged particles generated thereby are discriminated through the slit, the trajectory is deflected by a magnetic field or an electric field, and In an energy analyzer for charged particles that enters an incident position detector and analyzes the energy of the charged particles according to the incident position, the charged particle incident position detector is disposed at the incident position before the main body of the detector. An energy analyzer for charged particles in which a moderator whose speed reducing ability is inversely proportional to the energy of charged particles assumed to be incident on the incident position is arranged (Claim 6).

  According to the present invention, the signal level obtained from the position detector can be made substantially constant regardless of the incident energy of the charged particles, and the S / N can be improved in the signal processing unit such as the A / D converter in the subsequent stage. In the end, the accuracy of the entire charged particle energy analyzer can be expected to improve.

  Hereinafter, the operation and the embodiment of the present invention will be mainly described.

  Even in a position detector that is deflected by an electric field or a magnetic field and receives different energy, when the energy is determined as described above, the incident position of the position detector is uniquely determined. Therefore, if the detection sensitivity of the position detector is changed according to the energy of the charged particle assumed according to the incident position, and the high energy charged particle is incident at the incident position of the charged particle, the incident position is detected. When the sensitivity is lowered and low energy charged particles are incident, the detection sensitivity at the incident position is set high.

  That is, the present invention proposes a position detector in which the detection sensitivity at each incident position is set to be inversely proportional (inversely proportional) to the energy (energy magnitude) of the charged particle assumed to be incident. Although it is described as inversely proportional here, it does not mean a mathematically inversely proportional meaning. If the incident charged particle is high energy, the detection sensitivity of the incident position is detected as the incident position of the low energy charged particle. If the incident charged particles are lower than the sensitivity, and the incident charged particles have low energy, the detection sensitivity at the incident position is increased, and the detection sensitivity at the incident position of the high energy charged particles is increased. Since the relation of is relatively opposite, it is only used as inverse proportionality for convenience.

  In such an incident position detector having a tilted sensitivity that is inversely proportional to the magnitude of the incident energy of the charged particles, the signal obtained from the position detector is almost constant regardless of the incident charged particles of any energy. Can be a level. If the signal level obtained from the position detector can be made substantially constant regardless of the incident energy in this way, it is possible to advantageously improve the S / N in the signal processing unit such as the A / D converter in the subsequent stage. . As a result, the accuracy of the energy analysis of the charged particles can be finally improved.

  As a method of changing the sensitivity of the position detector, for example, in a light emitting type position detector, the density of the fluorescent material (ZnS or the like) applied to the fluorescent plate is inclined so as to be inversely proportional to the energy of charged particles expected to be incident. The sensitivity can be changed by changing the luminous efficiency in a stepwise manner or by changing the coating thickness of the luminescent material in a tilted or stepwise manner. That is, the light emission efficiency can be controlled by applying a thin coating on the high energy side and applying a thick or thick coating on the low energy side. In the application of the fluorescent material, it is common to apply a solvent in which the fluorescent material is dispersed to the flat plate, but in order to change the thickness and concentration in an inclined manner, the concentration was reduced to about 1/10 of the normal concentration. Pour the solvent into the flat plate, hold the flat plate itself at an angle and hold it until the solvent dries, or increase the number of times of thickening and thickening by applying the diluted solvent several times. It is desirable. As a result, a substantially constant amount of light emission can be obtained regardless of the incident energy of the charged particles. When a light emission image at a later stage is captured by a lens or camera and converted into an electric signal, the dynamic range of the signal is small, and S / N good processing becomes possible.

  Also, even in a normal position detector with uniform detection sensitivity, the deceleration capability at each incident position is in inverse proportion to the energy of the charged particles expected to be incident before the position detector body (incident side). By devising the arrangement of the moderator, the same action / function as when the detection sensitivity is changed can be provided, and the same effect can be achieved.

  That is, in this position detector, the moderator's moderation ability is set high at the incident position where high-energy charged particles pass, and the moderator's moderation ability is set low at the incident position where low-energy charged particles pass. This makes the moderator's deceleration capacity that is passed in inverse proportion to the energy level of the current. By attaching such a moderator to the detector body, all charged particles with different energies incident on the detector body can be controlled to substantially the same energy, resulting in a signal level obtained from the position detector. Can be made almost constant. In this way, the signal level obtained from the detector can be made substantially constant regardless of the incident energy, so that it is possible to advantageously improve the S / N in the signal processing unit such as the A / D converter in the subsequent stage. Finally, the accuracy of energy analysis of charged particles can be improved.

  According to the present invention, in addition to the effect of the invention for changing the detection sensitivity, there is an advantage that it can be implemented relatively easily using an existing detector having a uniform detection sensitivity.

  In addition, as the moderator disposed in the detector main body, a polymer membrane (Mylar, polyimide, etc.) or a permeable membrane whose light reduction capability is made of a light element such as a carbon membrane changes in a certain direction. good.

  In particular, it is preferable that the thickness is changed in an inclined manner or stepwise. In this case, when using a moderator having a uniform moderator, the moderator at a position where charged particles pass is adjusted by its thickness. In other words, by placing a moderator whose thickness changes in a stepwise or stepwise manner according to the energy of the charged particles that pass through, the high-energy charged particles pass through the thicker part of the moderator, and the low-energy charge The particles can be passed through a thin part of the moderator. In this way, the charged particles incident on the detector can have substantially the same energy, and as a result, the signal level obtained from the position detector can be made substantially constant.

  And according to this invention, there exists an advantage which can implement still more easily using the existing detector which has uniform sensitivity.

  It is also possible to use a detector with the sensitivity of the main body changed as described above and to arrange the moderator with the above-described reduction capability changed. By using both, it is possible to cope with a case where the height of the energy of the detected charged particles is wide than when only one is used.

  Next, the present invention will be described more specifically based on the embodiment shown in FIG.

  Here, in Rutherford backscattering analysis (RBS analysis), hydrogen ions accelerated to about 400 keV are made incident on the sample, and the energy of the hydrogen ions repelled by the nuclei in the sample is measured. If there is a heavy element in the sample, the energy of the scattered ions is large, and conversely if the light element is present, the energy of the scattered ions is small. Therefore, by performing an energy analysis, the component composition of the sample can be analyzed.

  In order to analyze the energy of the scattered ions, it passes through the slit and enters the deflecting magnet from one place. The amount of deflection changes according to the ion energy. That is, low energy ions are largely deflected by receiving a force from a magnetic field, whereas high energy ions are difficult to deflect. A position detector is arranged at a certain distance from the deflecting magnet to detect the incident position. In the figure, higher energy ions are incident on the upper part.

  In general, the sensitivity of the position detector to charged particles is higher for higher energy particles and lower for low energy particles. Therefore, in this embodiment, a mylar film is installed in front of the position detector, that is, on the incident-side front surface, with an inclined moderator arranged so as to become thicker toward the upper part of the figure where high energy particles are incident. This mylar film is formed on the surface of the position detector by changing the thickness in an inclined manner so that the high energy side is 0.7 μm thick and the low energy side is 0 μm. Since it is difficult to hold such a thin film alone, it is desirable to form the film on the front surface of the position detector by the CVD method or the like. The film thickness can be controlled by changing the film formation time in an inclined manner by masking or the like.

In this case, it is assumed that 400 keV ions on the high energy side are decelerated to about 200 keV. As a result, the higher energy particles are decelerated greatly, and when entering the position detector, the energy becomes substantially the same, and the signal level at the position detector becomes constant.
The electric charge obtained from the electrodes at both ends of the position detector is passed through an amplifier, position-calculated, and A / D converted. Therefore, according to this position detector, the detection accuracy of the entire charged particle energy analyzer is improved.

  In this embodiment, for the sake of simplicity, a one-dimensional position detector is taken as an example. However, the present invention is applied to a two-dimensional position detector as used in Patent Document 1 (Japanese Patent Laid-Open No. 7-190963). It is possible to do as well. In this case, the detection sensitivity or deceleration capability may be set in inverse proportion to the magnitude of charged particle energy that is assumed to be incident from the center to the circumferential direction.

It is a figure which shows the outline of the Example of this invention. It is a figure which shows the principle of the conventional energy analysis by a magnetic field. It is a figure which shows the principle of the conventional energy analysis by an electric field. It is the figure which showed the principle of the position sensitive type incident position detector. It is the figure which showed the equivalent circuit of the position sensitive type incident position detector. It is the figure which showed the principle of the light emission type incident position detector. The figure which shows the schematic structural example of the conventional parallel magnetic field type | mold Rutherford backscattering analyzer.

1 ... ion source,
2 ... Ion beam 3 ... Accelerating tube 4 ... Sample 5 ... Scattered ions 6 ... Electromagnet, solenoid coil 61, magnet yoke 62
7 ... Iris type slit (aperture)
8 ... Ion detector

Claims (6)

In a charged particle incident position detector that detects the incident position of a charged particle that changes according to the energy of the charged particle, the detection sensitivity at the incident position is made inversely proportional to the energy of the charged particle that is expected to enter the incident position. Charged particle incident position detector characterized by the above. The charged particle incident position detector according to claim 1, wherein the detection sensitivity changes in an inclined manner or stepwise. In a charged particle incident position detector that detects an incident position of a charged particle that changes in accordance with the energy of the charged particle, a deceleration capability at the incident position is assumed to be incident on the incident position before the main body of the incident position detector. An incident position detector for charged particles, wherein a moderator that is inversely proportional to the energy of the charged particles is disposed. The charged particle incident position detector according to claim 3, wherein the thickness of the moderator is changed in an inclined manner or stepwise. The ion beam emitted from the ion source is accelerated to collide with the surface of the measurement sample, the scattered charged particles generated thereby are discriminated through the slit, and the trajectory is deflected by a magnetic field or electric field to detect the incident position of the charged particles. In a charged particle energy analyzer that analyzes the energy of the charged particle according to the incident position, the charged particle incident position detector is assumed to have a detection sensitivity at the incident position. Charged particle energy analyzer that is set in inverse proportion to the charged particle energy. The ion beam emitted from the ion source is accelerated to collide with the surface of the measurement sample, the scattered charged particles generated thereby are discriminated through the slit, and the trajectory is deflected by a magnetic field or electric field to detect the incident position of the charged particles. In a charged particle energy analyzer that analyzes the energy of the charged particle according to the incident position, the charged particle incident position detector has a deceleration capability at the incident position before the main body of the detector. A charged particle energy analysis apparatus in which a moderator that is inversely proportional to the energy of a charged particle assumed to be incident on the incident position is arranged.