JP2004294275A - Method for measuring element distribution in depth direction and measuring instrument therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure an element distribution of the region extremely shallow from the surface of a sample while suppressing the mixing of the atom layer in the vicinity of the surface of the sample. <P>SOLUTION: The method for measuring the element distribution in a depth direction has a process for adding an alkali metal to the surface of the sample, a process for irradiating the measuring region of the surface of the sample with primary ions comprising alkali metal ions and a process for performing the mass separation of secondary ions discharged from the measuring region by irradiation with primary ions and measuring the discharged quantity of specific secondary ions to analyze the element distribution. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a depth direction element distribution measuring method and a depth direction element distribution measuring device for measuring a depth direction element distribution (concentration distribution) of a sample by secondary ion mass spectrometry.
[0002]
[Prior art]
In a CMOS transistor, controlling the concentration distribution of an impurity element in a process of forming a PN junction, a gate insulating film, and the like has a great influence on its electrical characteristics. Therefore, in the manufacture and development of CMOS transistors, it is necessary to grasp the concentration distribution of impurity elements in a region extremely shallow from the surface of a substrate or a thin film in the depth direction with high accuracy.
[0003]
A secondary ion mass spectrometry (hereinafter, SIMS) apparatus is used for measuring the concentration distribution of the elements in the depth direction of the sample.
[0004]
FIG. 1 is a perspective view showing a main part of the SIMS device.
[0005]
As shown in FIG. 1, the SIMS apparatus includes a sample operation table 11 on which a sample 10 is mounted, a cesium ion gun 12 for accelerating cesium ions (hereinafter, referred to as Cs ⁺ ) and irradiating the sample with oxygen ions ( The oxygen ion gun 13 for accelerating and irradiating the sample with O ₂ ⁺ ), a quadrupole mass analyzer 15 for measuring the amount of ions, a detector 16 for measuring the amount of ions, An electron gun 14 for correcting the charged state of the sample due to the irradiation.
[0006]
Cs ⁺ and O ₂ ⁺ are called primary ions, and irradiate the sample 10 with any of these. The sample operation table 11 can be moved, tilted, and rotated in X, Y, and Z directions orthogonal to each other, so that the irradiation angle and irradiation position of the primary ions on the sample 10 can be changed. . When the primary ions are irradiated on the sample 10, the surface of the sample 10 is sputter-etched, and ions (hereinafter, referred to as secondary ions) of elements constituting the sample 10, neutral particles, and electrons are emitted. Of these, secondary ions are physically mass-separated in the quadrupole mass analyzer 15 so that only specific secondary ions pass through. The detector 16 includes an electron multiplier and a Faraday cup, and converts the number of secondary ions that have passed through the quadrupole mass spectrometer 15 into ion intensity. The element distribution of the sample is analyzed from the ionic strength.
[0007]
As described above, in SIMS, the element distribution is analyzed based on the secondary ions emitted from the sample by the irradiation of the primary ions. However, some of them are emitted as neutral particles without being secondary ions. For this reason, primary ions with high reactivity are supplied to the sample surface, and the detection sensitivity is increased by increasing the generation rate of secondary ions by a chemical reaction. For these reasons, usually, oxygen ions (O ₂ ⁺ ) are irradiated to detect positive secondary ions, and alkali metal such as cesium ions (Cs ⁺ ) are detected to detect negative secondary ions. Irradiate ions.
[0008]
When the primary ions are continuously irradiated on the sample 10, sputter etching proceeds in the depth direction from the surface of the sample 10, and secondary ions are continuously emitted while the inside of the sample 10 appears on the surface one after another. Therefore, the secondary ion intensity reflects a change in the concentration of the sample 10 in the depth direction as the measurement time elapses. Thereby, information on the concentration distribution of the element in the depth direction of the sample 10 can be obtained. This method is called D-SIMS (Dynamic Secondary Ion Mass Spectrometry).
[0009]
[Non-patent document 1]
K. Wittmaack, Journal of Vacuum Science and Technology, B18, 1 (2000)
[Non-patent document 2]
B. Schueller and D.S. F. Reich, Journal of Vacuum Science and Technology, B18, 296 (2000).
[Non-Patent Document 3]
R. Kansavi, Y .; Sun, G .; See Mount, P.M. Pianetta, P .; B. Griggin, and J.M. D. Plummer, Electrochemical and Solid State Letter, 4, G1 (2001)
[0010]
[Problems to be solved by the invention]
Using the SIMS apparatus shown in FIG. 1, a single silicon substrate made of only silicon is used as a sample, and Cs ⁺ is continuously irradiated as primary ions from an angle of 45 ° with respect to a perpendicular direction of the surface, thereby obtaining ²⁹ Si ^- intensity, which is a secondary ion emitted from the silicon substrate, was measured. The measurement results are shown in the graph of FIG. 3 where the horizontal axis is the irradiation time of Cs ^{+ as} the primary ion and the vertical axis is ²⁹ Si ⁻ intensity.
[0011]
Since the silicon substrate has a constant silicon concentration at any depth, a constant ²⁹ Si ^- strength should be obtained in an ideal measurement. However, as is apparent from FIG. 3, the ²⁹ Si ⁻ intensity increases with time from the start of Cs ⁺ irradiation to about 0.6 minutes, and becomes almost constant after about 0.6 minutes. The period during which the ion intensity in the initial stage of the irradiation is not stable is called a transition region (Transient region), and the period during which the ion intensity is stable is called the steady region. As described above, since the intensity of the secondary ions is unstable in the transition region, the measurement cannot be performed accurately. However, since the sputter etching of the sample proceeds during this time, the concentration of the sputter-etched portion cannot be known until the intensity of the secondary ions is stabilized.
[0012]
In order to measure an extremely shallow region from the sample surface by SIMS, the transition region must be shortened as much as possible, and the secondary ion intensity must be stabilized from the beginning of the measurement. As shown in FIG. 2, this transition region occurs because the irradiation amount of the primary ions or the secondary ionization rate is unstable, and the supply amount of the primary ions and the emission amount of the secondary ions are not in an equilibrium state. In this case, the supply amount of the primary ions is an amount including the primary ions supplied by irradiation and the primary ions remaining on the sample surface. In addition, even when the acceleration energy of the primary ions is large, the irradiation of the primary ions causes the mixing layer 41 in which the atomic layers near the surface of the sample 10 intersect in multiple layers, and the secondary ions emitted from the mixing layer 41 are generated. Since the intensity is measured, the concentration distribution inherent in the sample is not measured.
[0013]
Therefore, in order to perform measurement in an extremely shallow region from the sample surface by SIMS, (1) the sample surface is gently sputter-etched to reduce the depth of the mixing layer, and (2) the sample layer remains on the sample surface by sputter etching. The primary ion concentration is kept constant from the beginning of the measurement, the supply amount of the primary ions and the emission amount of the secondary ions are in equilibrium, and the transition region is shortened. (3) In addition to the irradiation of the primary ions, It is necessary to shorten the transition region by supplying the same element to the sample surface so that the same amount of elements as the steady region is present on the sample surface from the beginning of the measurement.
[0014]
Conventionally, many attempts have been made to lower the irradiation of primary ions O ₂ ⁺ or Cs ⁺ mainly by using the above method (1). In recent years, there has been reported an example in which the acceleration energy of primary ions is reduced to 150 eV and measured. However, it is difficult to narrow the spot of the primary ion beam with such a low acceleration energy, that is, to secure the convergence of the primary ions, so that the current density of the primary ions is reduced. Therefore, sputter etching by primary ions is unlikely to occur, and secondary ions are not sufficiently emitted, making it difficult to measure the secondary ion intensity. For this reason, the primary ion energy of 500 eV or more is practically required, and it is difficult to measure in an extremely shallow region by the method (1).
[0015]
Therefore, from the viewpoints of (2) and (3) above, Non-Patent Documents 1 and 2 disclose methods of blowing oxygen gas onto a sample surface and performing a depth direction analysis while promoting oxidation of the sample surface. I have. Further, the incident angle of the primary ions O ₂ ^{+ on} the sample surface is made closer to the direction perpendicular to the sample surface, and oxygen is left on the sample surface to promote oxidation and measure the element concentration in the depth direction. The method is described in the literature. As described above, when irradiating O ₂ ⁺ as primary ions, the supply amount of oxygen to the sample surface is increased by the methods (2) and (3), and the transition region is formed by performing sputter etching using the primary ions. Shortening is being considered.
[0016]
Even when Cs ⁺ is irradiated as primary ions, it is considered that the transition region can be shortened by the methods (2) and (3). However, when irradiating Cs ⁺ as primary ions, it is difficult to supply cesium in gaseous form simultaneously with Cs ⁺ irradiation, as in the case of irradiating O ₂ ⁺ , because it is a metal element, so it is difficult. Further, if Cs ⁺ is irradiated such that sufficient secondary ions are emitted from the beginning of the measurement, the width of the mixing layer becomes large, so that the original element concentration of the sample cannot be measured. Therefore, when irradiating Cs ⁺ , it is difficult to perform the methods (2) and (3), and no attempt has been made other than the method (1) (for example, see Non-Patent Document 3).
[0017]
In view of the foregoing, the present invention provides a depth direction element distribution measuring method and a depth direction element distribution for measuring element distribution in an extremely shallow region from a sample surface while suppressing mixing of an atomic layer near the surface of the sample. It is an object to provide a measuring device.
[0018]
[Means for Solving the Problems]
The above-described problems include a step of allowing the surface of the sample to contain an alkali metal, a step of irradiating primary ions composed of the ions of the alkali metal to a measurement region on the surface of the sample, and the irradiation of the primary ions from the measurement region. Mass-separating the released secondary ions, analyzing the element distribution by measuring the amount of specific secondary ions released, and solving the elemental distribution in the depth direction.
[0019]
In the above-described method for measuring the element distribution in the depth direction, the step of allowing the surface of the sample to contain the alkali metal is performed by ion-implanting the alkali metal into the surface of the sample. Further, the ion implantation of the alkali metal is performed with an acceleration energy of 100 eV or less.
[0020]
In the above-described method for measuring the element distribution in the depth direction, the step of including the alkali metal on the surface of the sample is performed by vapor-depositing the alkali metal on the surface of the sample.
[0021]
Alternatively, the above-described problem may be solved by a vapor deposition unit that vapor-deposits an alkali metal on the surface of a sample, an ion source that irradiates the surface of the sample with primary ions composed of ions of the alkali metal, and an ion source that emits an alkali metal from the surface of the sample. The problem is solved by a depth direction element distribution measuring device, comprising: a mass spectrometer for mass-separating secondary ions; and a detector for detecting the specific secondary ion mass-separated by the mass spectrometer.
[0022]
According to the above-described depth direction element distribution measuring method and depth direction element distribution measuring apparatus, before irradiating the primary ion composed of an alkali metal, the alkali metal is previously contained on the surface of the sample, so that the irradiation of the alkali metal ion is performed. Insufficient supply of alkali metal in the initial stage can be compensated by the alkali metal contained in the sample. Thus, the transition region can be shortened, so that the concentration distribution of elements in an extremely shallow region from the sample surface can be analyzed.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0024]
(First embodiment)
In this embodiment mode, the concentration distribution of impurities in the depth direction of the silicon substrate is measured using the secondary ion mass spectrometer shown in FIG. This measuring method will be described with reference to FIGS.
[0025]
First, after attaching the silicon substrate 20 to the sample operation table 11 in the secondary ion mass spectrometer and evacuating the interior of the secondary ion mass spectrometer, as shown in FIG. Cs ⁺ is pre-irradiated in a defocused state with an acceleration energy of 100 eV from an angle of 0 ° with respect to the perpendicular direction. When irradiation is performed at an acceleration energy of 100 eV or less, Cs ⁺ is injected into the vicinity of the surface of the sample without sputter etching the surface of the silicon substrate. Thereby, as shown in FIG. 5B, the cesium injection layer 51 is formed near the surface of the silicon substrate 20.
[0026]
Next, after tilting the sample operation table 11, as shown in FIG. 5C, the same Cs ⁺ as in the pre-irradiation was applied at an acceleration energy of 500 eV from an angle of 45 ° with respect to the perpendicular direction of the surface of the silicon substrate 20. To perform main irradiation in a focus state. Thus, if the acceleration energy is 150 eV or more, the sample surface is sputter-etched to such an extent that the intensity of the secondary ions can be measured. When the acceleration energy is 250 eV or more, the intensity of the secondary ions can be measured more accurately. Secondary ions emitted from the surface of the silicon substrate 20 by this main irradiation are mass-separated by the quadrupole mass spectrometer 15, and only specific secondary ions pass through the quadrupole mass spectrometer 15, and 16 and output as ion intensity. Thus, by analyzing the element distribution in the depth direction of the silicon substrate 20, the concentration distribution of the impurity in the depth direction contained in the silicon substrate 20 can be measured.
[0027]
The inventor conducted the following experiment in order to confirm that the transition region was shortened by the above-described measurement method.
[0028]
In order to clarify the effect of shortening the transition region, a single silicon substrate made of only silicon having a uniform silicon concentration was used as a sample. The silicon substrate was pre-irradiated with Cs ^{+ in} a defocused state. The irradiation conditions were as follows: the irradiation angle was 0 ° with respect to the direction perpendicular to the sample surface, the beam diameter was about 500 μm, the acceleration energy was 100 eV, the current amount was 10 nA, and the scanning range was 1000 μm × 1000 μm. The irradiation was performed under five conditions of 5, 10, 20, 30, and 60 minutes. Under each of these conditions, the main irradiation with Cs ⁺ was performed in a focused state. The irradiation conditions were as follows: the irradiation angle was 45 ° with respect to the direction perpendicular to the sample surface, the beam diameter was about 5 μm, the acceleration energy was 500 eV, the current amount was 14 nA, and the scanning range was 350 μm × 350 μm. The intensity of ²⁹ Si ⁻ as secondary ions emitted from the silicon substrate by the main irradiation was measured. The measurement results of this experiment are shown in FIG. 4 as the main irradiation time of Cs ⁺ on the horizontal axis and the intensity of ²⁹ Si ⁻ on the vertical axis.
[0029]
According to FIG. 4, focusing on the ²⁹ Si ^— intensity of the irradiation time from 0 to 0.5 minute, it can be seen that the ²⁹ Si ^— intensity is increased by increasing the pre-irradiation time. Accordingly, when the pre-irradiation is not performed, the transition region is about 0.6 minutes. On the other hand, when the pre-irradiation is performed, the ²⁹ Si ^- intensity at the beginning of the main irradiation is stabilized, so that the transition region is reduced to half About 0.3 minutes.
As described above, according to the measuring method of the present embodiment, the supply of primary ions can be supplemented at the initial stage of the main irradiation by injecting Cs ⁺ , which will be primary ions later, into the vicinity of the sample surface in advance. The ionization rate of the next ion increases, and the transition region can be shortened. Therefore, the concentration distribution can be measured even in an impurity region of an element such as a CMOS formed in a very shallow region on the surface of the silicon substrate.
[0030]
(Second embodiment)
In the first embodiment, Cs ^+, which is to be primary ions later, is implanted into the sample surface, and the concentration distribution in the impurity region of the silicon substrate is measured. In this embodiment mode, measurement is performed by forming a cesium layer on a sample surface. This will be described below.
[0031]
FIG. 6 is a schematic diagram of the SIMS device according to the present embodiment.
[0032]
The SIMS device according to the present embodiment has the same structure as the SIMS device shown in FIG. 1, and further includes a cesium source 27, an electrode 26 that generates a high temperature by energization, and a wiring for depositing cesium on the surface of the silicon substrate 20. 28, a current introduction terminal 25, and a shielding plate 29.
[0033]
The current supplied from the current introduction terminal 26 flows to the electrode 26 via the wiring 28. This current raises the temperature of the electrode 26, evaporates cesium from the cesium source 27, and deposits cesium on the surface of the opposing silicon substrate 20 that is not shielded by the shielding plate 29.
A method for measuring the element distribution in the impurity region of the silicon substrate using the SIMS apparatus will be described with reference to FIG.
[0034]
First, after the inside of the chamber 31 is evacuated, cesium is evaporated by applying a current to the electrode 26, and cesium is vapor-deposited on the surface of the silicon substrate as shown in FIG. As a result, a cesium layer 52 having a thickness of several to several tens of degrees is formed on the surface of the silicon substrate 20 as shown in FIG.
[0035]
Next, the surface of the silicon substrate is fully irradiated with Cs ⁺ from the cesium ion gun 22. As a result, as shown in FIG. 7C, secondary ions are emitted from the surface of the silicon substrate 20. This irradiation condition is the same as in the first embodiment. Secondary ions released from the surface of the sample 20 by this irradiation are mass-separated by the quadrupole mass spectrometer 23, and only specific secondary ions pass through the quadrupole mass spectrometer 23 and are detected by the detector 24. Detected and output as ionic strength.
[0036]
According to this embodiment, as in the first embodiment, cesium to be subsequently irradiated as primary ions is previously deposited on the surface of the silicon substrate, thereby supplementing the supply of primary ions in the initial stage of main irradiation. The transition region can be shortened. Therefore, the concentration distribution can be measured even in an impurity region of an element such as a CMOS formed in a very shallow region on the surface of the silicon substrate.
[0037]
(Third embodiment)
In this embodiment, a SIMS device having a structure different from that of the second embodiment will be described.
[0038]
FIG. 8 is a schematic diagram of a SIMS device according to the present embodiment.
[0039]
The SIMS device according to the present embodiment is different from the SIMS device according to the second embodiment shown in FIG. 6 in that a deposition chamber 31b for depositing cesium on the surface of the sample 20 and a measurement of the concentration distribution of the sample. In that two chambers are provided, one for analysis chamber 31a and the other for analysis chamber 31a.
[0040]
The analysis chamber 31a and the deposition chamber 31b are connected by the transfer path 30, and after the cesium layer 52 is formed on the surface of the silicon substrate 20 in the deposition chamber 31b, the silicon substrate 20 is transferred to the analysis chamber 31a without releasing the vacuum state. Can be transported. Although not particularly shown, the transfer of the silicon substrate 20 is performed by, for example, a robot arm. In addition, it is preferable that the transfer path 30 be provided with an openable / closable shutter that spatially separates the chambers 31a and 31b so that the atmospheres in the analysis chamber 31a and the vapor deposition chamber 31b are not mixed with each other.
[0041]
The measuring method using this is the same as the method described in the second embodiment, and the description is omitted here.
[0042]
According to the SIMS apparatus of the present embodiment, since the chamber is divided into the deposition chamber and the analysis chamber, deposition elements are prevented from adhering to the inside of the analysis chamber, so that the analysis chamber can be kept clean. The element distribution can be measured with higher accuracy.
[0043]
(Other embodiments)
In the embodiment described above, Cs ⁺ after forming the injection layer or cesium layer was irradiated with Cs ⁺ as primary ion, the present invention is not limited thereto. For example, lithium may be used instead of cesium. In addition, other alkali metals (sodium, potassium, and rubidium) may be used. If the alkali metal ions are used as primary ions, a secondary ionization rate sufficient for measurement can be obtained.
[0044]
Further, in the above-described embodiment, the Cs ⁺ implanted layer or the cesium layer is formed on the surface of the silicon substrate in the same device, but these layers are formed using another device, and then transported to the SIM device and transferred to the SIM device. The concentration distribution in the depth direction of the substrate may be measured.
[0045]
Further, the element distribution can be measured using a measuring method and a measuring apparatus of the present invention for a semiconductor element in which an impurity is implanted into a very shallow region near the surface, similarly to a CMOS. In the present invention, the measurement target does not need to be a silicon substrate, but may be a compound semiconductor substrate such as SiGe, GaAs, and InP. Furthermore, the present invention can be widely applied to not only the semiconductor substrate as described above but also a substrate that requires measurement of element distribution in a region extremely thin from the surface.
[0046]
(Supplementary Note 1) A step of allowing the surface of the sample to contain an alkali metal, a step of irradiating a measurement region on the surface of the sample with primary ions composed of the ions of the alkali metal, and an emission from the measurement region by irradiation of the primary ion Mass-separating the obtained secondary ions, and analyzing the element distribution by measuring the emission amount of the specific secondary ions.
[0047]
(Supplementary Note 2) The method for measuring the element distribution in the depth direction according to Supplementary Note 1, wherein the step of including the alkali metal in the surface of the sample is performed by ion-implanting the alkali metal into the surface of the sample. .
[0048]
(Supplementary note 3) The method for measuring the element distribution in the depth direction according to supplementary note 2, wherein the ion implantation of the alkali metal is performed with an acceleration energy of 100 eV or less.
[0049]
(Supplementary Note 4) The method for measuring the element distribution in the depth direction according to Supplementary Note 1, wherein the step of including the alkali metal on the surface of the sample is performed by depositing the alkali metal on the surface of the sample.
[0050]
(Supplementary note 5) The method for measuring the element distribution in the depth direction according to Supplementary note 1, wherein the acceleration energy of the primary ion is 250 eV or more.
[0051]
(Supplementary note 6) The method for measuring the element distribution in the depth direction according to supplementary note 1, wherein the alkali metal is any one of cesium, lithium, sodium, potassium, and rubidium.
[0052]
(Supplementary Note 7) The method for measuring the element distribution in the depth direction according to Supplementary Note 1, wherein the sample is a semiconductor substrate.
[0053]
(Supplementary Note 8) A deposition unit that deposits an alkali metal on the surface of the sample, an ion source that irradiates the surface of the sample with primary ions composed of the alkali metal ions, and a secondary ion emitted from the surface of the sample. A depth direction element distribution measuring device comprising: a mass spectrometer for mass separation; and a detector for detecting the specific secondary ion mass-separated by the mass spectrometer.
[0054]
【The invention's effect】
As described above, according to the depth direction element distribution measuring method and the depth direction element distribution measuring apparatus of the present invention, by preliminarily including alkali metal ions to be primary ions in the vicinity of the sample surface, it is possible to perform the main irradiation. Since the supply of the primary ions can be supplemented in the initial stage, the ionization rate of the secondary ions can be increased and the transition region can be shortened. Therefore, the concentration distribution of the constituent elements can be measured even in a very shallow region of the sample surface.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a main part of a conventional SIMS device.
FIG. 2 is a cross-sectional view showing a problem with a conventional SIMS.
FIG. 3 is a graph showing an experimental result obtained by a conventional SIMS method for measuring the element distribution in the depth direction of a sample.
FIG. 4 is a graph showing experimental results obtained by a method for measuring the element distribution in the depth direction of a sample by SIMS according to the first embodiment of the present invention.
FIGS. 5A, 5B, and 5C are cross-sectional views illustrating a method for measuring the element distribution in the depth direction of a sample according to the first embodiment of the present invention.
FIG. 6 is a schematic diagram showing a SIMS device according to a second embodiment of the present invention.
FIGS. 7A, 7B, and 7C are cross-sectional views illustrating a method for measuring the element distribution in the depth direction of a sample according to the second and third embodiments of the present invention. .
FIG. 8 is a schematic diagram showing a SIMS device according to a third embodiment of the present invention.
[Explanation of symbols]
10 ... sample, 11 ... sample operation table, 12 ... cesium ion gun,
13 ... oxygen ion gun, 14 ... electron gun,
15: quadrupole mass spectrometer, 16: detector, 20: silicon substrate,
21 ... sample operation table, 22 ... cesium ion gun,
23 ... quadrupole mass spectrometer, 25 ... detector
25 ... current introduction terminal, 26 ... electrode, 27 ... cesium source,
28: wiring, 29: shielding plate, 30: transport path,
31 ... chamber, 31a ... analysis chamber,
31b: evaporation chamber, 41: mixing layer,
51 ... Cs ⁺ injection layer, 52..Cesium layer

Claims (5)

A step of containing an alkali metal on the surface of the sample,
Irradiating primary ions composed of the alkali metal ions to a measurement region on the surface of the sample,
Mass-separating secondary ions emitted from the measurement region by the irradiation of the primary ions, and measuring the amount of emission of specific secondary ions to analyze the element distribution. 2. The method according to claim 1, wherein the step of allowing the alkali metal to be contained in the surface of the sample is performed by ion-implanting the alkali metal into the surface of the sample. 3. The method according to claim 2, wherein the ion implantation of the alkali metal is performed with an acceleration energy of 100 eV or less. The method for measuring the distribution of elements in the depth direction according to claim 1, wherein the step of including the alkali metal on the surface of the sample is performed by depositing the alkali metal on the surface of the sample. A deposition unit for depositing an alkali metal on the surface of the sample,
An ion source that irradiates the surface of the sample with primary ions composed of the alkali metal ions,
A mass spectrometer for mass-separating secondary ions emitted from the surface of the sample,
A detector for detecting the specific secondary ion mass-separated by the mass analyzer.

Images