JP2018101557A - Ion microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion microscope suitable for observing a water-containing sample and the like.SOLUTION: An ion microscope 10 comprises: an inductively coupled plasma ion source 14 for generating an ion beam; a sample chamber 13 connected to the ion source via orifices (including a first orifice 1112 and a second orifice 1213) through which the ion beam travels, and having a sample-holding part (sample holder 17) for holding a sample at a position where the ion beam is applied thereto; a scan part (scan electrode 163) for relatively moving the ion beam and the sample-holding part so that a surface of a sample S held by the sample-holding part is scanned by the ion beam; an electron detector 18 for detecting secondary electrons generated in the sample S held by the sample-holding part; and a pressure regulator for retaining a pressure in the sample chamber at 10Pa or higher. In the ion microscope 10, the pressure in the sample chamber 13 can be made 10Pa or higher. Therefore, the ion microscope is suitable for observing a sample such as a water-containing sample which cannot be observed in a high vacuum condition, with stability in such a state that no sputtering or contamination is caused.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ion microscope that observes a sample surface using an ion beam.

  An ion microscope is an apparatus that observes a sample surface by scanning the sample surface with an ion beam and thereby detecting secondary electrons generated from the sample surface. The ion microscope corresponds to an electron beam in which the electron beam in the electron microscope is replaced with an ion beam, but has the following features that the electron microscope does not have. (i) Since ions have a larger mass than electrons, the de Broglie wavelength is small when compared at the same acceleration voltage, and the resolution is higher than that of an electron microscope. (ii) Ions can suppress the amount of current more than electrons, and thereby damage to the sample due to heat can be suppressed more than an electron microscope. (iii) In both cases of ions and electrons, there is a problem of charging of the sample (charge-up), but in an ion microscope, the charge can be neutralized by supplying electrons to the sample surface using an electron gun. . In addition, (iv) it is possible to sputter the sample surface by irradiating an ion beam composed of ions with a large mass, so there is no electron microscope that processes the sample surface while observing it with secondary electrons. It can also be used in applications.

  Conventionally, ion microscopes are (1) equipped with a liquid metal ion source (LMIS), (2) equipped with a gas field ion source (GFIS), and (3) inductive coupling. Those equipped with a plasma (ICP: Inductively Coupled Plasma) ion source have been used. Among these, an ion microscope equipped with LMIS mainly uses an ion beam of Ga (gallium), and the irradiated sample surface is easily sputtered by the ion beam, so that it is suitable for processing applications. An ion microscope equipped with GFIS mainly uses an ion beam of He (helium) or Ne (neon), and is suitable when it is desired to suppress damage to the sample by the ion beam (see Non-Patent Documents 1 and 2). . An ion microscope equipped with an ICP ion source mainly uses an Xe (xenon) ion beam, and the sample surface is easily sputtered by the ion beam, so that it is suitable for processing applications (Non-Patent Document 3).

Onishi Keiko, “Development and Sharing of Advanced Nanomaterial Evaluation Technology Using Scanning Helium Ion Microscope”, Microscope (Journal Name), Japan Society for Microscopy, Vol. 48, No. 3, pp. 154-158, 2013 Shinichi Ogawa, “Evaluation and Processing of Nanodevice Materials Using Helium Ion Microscope”, Microscope, Japan Society for Microscopy, Vol. 48, No. 3, pp. 149-153, 2013 "Vion Plasma FIB System", [online], FEI Company, [Search September 17, 2016], Internet <URL: http: //www.fei.co.jp/_documents/VionPlasmaFIBDatasheet.pdf>

The ion microscope equipped with GFIS uses a He or Ne ion beam mainly, so it is difficult to sputter the sample under observation and is suitable for observation. However, to prevent destabilization of the ion beam due to impurity gas, The source must be kept in a high vacuum (about ^10-7 Pa in absolute pressure). In order to maintain such a high vacuum in the ion source, even if differential evacuation is performed and the cross-sectional area of the ion beam passage (orifice) between the ion source and the sample chamber is made as small as possible, the pressure in the sample chamber is It is necessary to keep it lower than 10 ^-5 Pa (vacuum degree higher than 10 ^-5 Pa).

  On the other hand, in an ion microscope equipped with an LMIS, since a Ga ion beam is mainly used, the sample is easily sputtered and contaminated, and is not suitable for observation.

  In addition, since an ion microscope equipped with a conventional ICP ion source mainly uses an Xe ion beam, the sample is likely to be sputtered and is not suitable for observation.

  For this reason, the conventional ion microscope has a problem that a sample containing water (a water-containing sample) such as a biological sample cannot be observed in a state in which no spatter or contamination occurs. In an ion microscope equipped with a GFIS, moisture easily evaporates from the sample at such a sample chamber pressure (degree of vacuum), the sample dries in a short time, and the sample characteristics change. Further, the water (water vapor) volatilized in this way enters the ion source, and the ion beam in the ion source becomes unstable. On the other hand, in an ion microscope equipped with an LMIS or a conventional ICP ion source, the sample is sputtered.

  The problem to be solved by the present invention is to provide an ion microscope suitable for stably observing a water-containing sample or the like in a state in which no spatter or contamination occurs.

The ion microscope according to the present invention made to solve the above problems is
a) an inductively coupled plasma ion source for generating an ion beam;
b) a sample chamber connected to the inductively coupled plasma ion source through an orifice through which the ion beam passes and having a sample holding unit for holding a sample at a position irradiated with the ion beam;
c) a scanning unit that relatively moves the ion beam and the sample holding unit so as to scan the surface of the sample held in the sample holding unit by the ion beam;
d) an electron detector for detecting secondary electrons generated in the sample held in the sample holding unit;
e) a pressure adjusting unit that maintains the pressure in the sample chamber at 10 ⁻⁴ Pa or more.

Since the ion microscope according to the present invention uses an inductively coupled plasma ion source (ICP ion source) as an ion source, it is possible to generate ions even in a relatively low vacuum (about 10 ⁻⁵ Pa). For this reason, the pressure in the sample chamber can be made 10 ⁻⁴ Pa or more (the degree of vacuum is made 10 ⁻⁴ Pa or less). Thereby, the evaporation rate of moisture from the water-containing sample can be suppressed, and observation can be performed before the characteristics of the water-containing sample are changed.

  In the present specification, the pressure is expressed as an absolute pressure with an absolute vacuum as a reference (0). In the ion microscope according to the present invention, the sample to be observed is not limited to a water-containing sample, and it is also possible to observe a sample such as an adhesive containing a volatile component that is not suitable for observation under high vacuum.

In the ion microscope according to the present invention, the water-containing sample in the following state can be observed by adjusting the pressure in the sample chamber by the pressure adjusting unit.
By adjusting the pressure in the sample chamber to 2400 Pa or higher, which is higher than the vapor pressure (2300 Pa) of water at room temperature (20 ° C.), it is possible to observe a water-containing sample at room temperature.
By adjusting the pressure in the sample chamber to 10 Pa or more, it is possible to observe a water-containing sample cooled to about −30 ° C. using a Peltier element.
By adjusting the pressure in the sample chamber to 10 ⁻³ Pa or higher, it is possible to observe a water-containing sample cooled to about −110 ° C. using liquid nitrogen.

In addition, when the pressure in the sample chamber is 10 ⁻³ Pa or more, the positive charge can be neutralized by electrons generated by ionizing the gas remaining around the sample by the ion beam, Charge (charge-up) due to ions irradiated on the sample can be suppressed.

Note that the pressure in the sample chamber is preferably higher in terms of observing the water-containing sample, but is preferably 10 ⁴ Pa or less in consideration of ion beam scattering, secondary electron detection efficiency, and the like.

  The scanning unit may move the sample holder or move the ion beam.

  The sample chamber and the inductively coupled plasma ion source may be directly connected via an orifice. Alternatively, an intermediate chamber is provided between the inductively coupled plasma ion source and the orifice and / or between the sample chamber and the orifice so that the sample chamber and the inductively coupled plasma ion source are connected via the intermediate chamber and the orifice. It may be.

  The pressure adjusting unit may change the pressure in the sample chamber, or may set the pressure in the sample chamber to one specific value. A pressure adjusting unit that makes the pressure in the sample chamber variable can be used as a pressure adjusting unit by installing a valve in the sample chamber, for example.

  As the ion beam, for example, an ion beam of any one of H (hydrogen), He, N (nitrogen), O (oxygen), Ne, Ar (argon), and Xe can be used. Of these ions, it is preferable to use any one of H, He, N, O, and Ne ions in that damage to the sample is relatively small.

The luminance in the inductively coupled plasma ion source is preferably 6400 A / m ² / sr / V or more and the energy width is preferably 5.5 eV or less. Thereby, the spot diameter of the ion beam can be reduced to 30 nm or less, and the sample can be observed with high spatial resolution. The brightness is adjusted by the current, and the energy width is adjusted by the acceleration voltage.

In the ion microscope according to the present invention, since an inductively coupled plasma ion source (ICP ion source) is used as the ion source, the pressure in the sample chamber can be set to 10 ⁻⁴ Pa or more. In addition, any ion beam of H, He, N, O, Ne, and Xe can be used. Therefore, according to the present invention, an ion microscope suitable for stably observing a sample such as a water-containing sample that cannot be observed under a high vacuum in a situation where sputtering or contamination does not occur can be obtained.

1 is a schematic configuration diagram showing a first embodiment of an ion microscope according to the present invention. The schematic block diagram which shows the ion microscope of 2nd Embodiment provided with a cooling device. The schematic block diagram which shows 3rd Embodiment of the ion microscope which concerns on this invention.

  An embodiment of an ion microscope according to the present invention will be described with reference to FIGS.

  The ion microscope 10 according to the first embodiment includes an ion generation chamber 11, an intermediate chamber 12, and a sample chamber 13. The ion generation chamber 11, the intermediate chamber 12, and the sample chamber 13 are arranged in a line. The ion generation chamber 11 and the intermediate chamber 12 communicate with each other through a first orifice 1112, and the intermediate chamber 12 and the sample chamber 13 communicate with each other through a second orifice 1213. The first orifice 1112 and the second orifice 1213 are provided to face each other with the inside of the intermediate chamber 12 interposed therebetween.

  A gas supply nozzle 141 that supplies gas, which is a raw material for generating ions, into the ion generation chamber 11 is inserted into the ion generation chamber 11. A supply port 1411 at the tip of the gas supply nozzle 141 is disposed so as to face the first orifice 1112. A coil 142 is wound around the side of the supply port 1411 and outside the wall of the ion generation chamber 11 so as to surround the ion generation chamber 11. A high frequency power source (not shown) that supplies a high frequency current to the coil 142 is connected to the coil 142. The ion generation chamber 11, the gas supply nozzle 141, and the coil 142 constitute an inductively coupled plasma ion source 14.

An exhaust port 151 for exhausting the gas in the ion generation chamber 11 is provided on the wall of the ion generation chamber 11 at a position closer to the opposite side of the first orifice 1112 than the supply port 1411. A vacuum pump 15 is connected via a valve 152. This vacuum pump 15 has the capability of making the pressure of the ion generation chamber 11 10 ⁻⁵ Pa or less.

  In the intermediate chamber 12, an extraction electrode 161, a first ion lens electrode 1621, a scanning electrode 163, and a second ion lens electrode 1622 are provided in order from the first orifice 1112 side to the second orifice 1213 side. The extraction electrode 161 is an electrode that extracts positive ions from the ion generation chamber 11 by applying a negative potential difference to the ion generation chamber 11. The first ion lens electrode 1621 and the second ion lens electrode 1622 are ion lenses that form an ion beam by focusing ions extracted from the ion generation chamber 11. The scanning electrode 163 is an electrode that generates an electric field in an orthogonal plane orthogonal to the ion traveling direction, and controls the direction of the ion beam by changing the intensity of the electric field and the direction in the orthogonal plane. Electrode. The power supply connected to each electrode is not shown.

  In the sample chamber 13, a sample holder (sample holding unit) 17, an electron detector 18, and a neutralizing electron gun 19 are provided. The sample holder 17 is a holder that holds the sample S at a position where the ion beam is irradiated, specifically, a position facing the second orifice 1213, and is a stage on which the sample S is placed in the present embodiment. The electron detector 18 is a detector that detects secondary electrons generated when the sample S is irradiated with an ion beam. The neutralizing electron gun 19 is an electron gun that emits electrons toward the sample S in order to neutralize the charge of the sample S charged with positive ions when irradiated with an ion beam. In addition, the sample chamber 13 is provided with a lid for keeping hermeticity, and a sample loading / unloading port 131 for loading the sample S into and out of the sample chamber 13 is provided.

The intermediate chamber 12 is provided with an exhaust port 151M for exhausting gas, and a vacuum pump 15M is connected to the exhaust port 151M via a valve 152M. The sample chamber 13 is similarly provided with an exhaust port 151S, and a vacuum pump 15S is connected to the exhaust port 151S via a valve 152S. Note that the diameters of the first orifice 1112 and the second orifice 1213 are set to such a size that the pressure in the ion generation chamber 11 can be reduced to 10 ⁻⁵ Pa or less by a preliminary experiment.

The operation of the ion microscope 10 of this embodiment will be described.
First, the sample loading / unloading port 131 is opened, and the sample S is loaded into the sample chamber 13 and mounted on the sample holder 17. Thereafter, the sample loading / unloading port 131 is hermetically closed.

Next, the vacuum pump 15 is operated to open the valve 152, and the pressure in the ion generation chamber 11 is reduced to 10 ⁻⁵ Pa or less. Further, the vacuum pumps 15M and 15S are also operated to open the valves 152M and 152S. At that time, the opening of the valve 152S, adjusts the pressure in the sample chamber 13 in the range of from 2,400 to 10 ⁴ Pa. In the present embodiment, the sample S is not cooled.

Subsequently, gas is supplied from the gas supply nozzle 141 into the sample chamber 13. This gas includes hydrogen (H ₂ ) gas, helium (He) gas, nitrogen (N ₂ ) gas, oxygen (O ₂ ) gas, neon (Ne) gas, argon (Ar) gas, xenon (Xe) gas Etc. can be used. At the same time, a high frequency current is supplied to the coil 142 from a high frequency power source. As a result, plasma is generated in which the molecules of the supplied gas are ionized into ions and electrons. At this time, the magnitude of the high-frequency current is adjusted so that the luminance of the generated plasma is 6400 A / m ² / sr / V or more. The acceleration voltage is adjusted so that the energy width of the generated plasma is 5.5 eV or less.

  In this state, a voltage is applied between the extraction electrode 161 and the ion generation chamber 11 so as to give the extraction electrode 161 a negative potential difference with respect to the ion generation chamber 11. Thereby, ions generated in the sample chamber 13 pass through the first orifice 1112 and are extracted into the intermediate chamber 12. The extracted ions become an ion beam by focusing the spread in the direction perpendicular to the traveling direction at the first ion lens electrode 1621. Subsequently, the scanning electrode 163 applies an electric field in one direction within a plane orthogonal to the ion traveling direction, thereby controlling the direction of the ion beam according to the intensity of the electric field and the direction within the plane. . The ion beam that has passed through the scanning electrode 163 is further focused by the second ion lens electrode 1622.

  The ion beam that has passed through the second ion lens electrode 1622 passes through the second orifice 1213, is introduced into the sample chamber 13, and enters the sample S. Here, by controlling the direction of the ion beam at the scanning electrode 163, the irradiation position of the ion beam on the sample S changes, and the surface of the sample S can be scanned with the ion beam. Secondary electrons are emitted from the region in the sample S irradiated with the ion beam. The secondary electrons are detected by the electron detector 18. Thus, the surface image of the sample S can be obtained by sequentially obtaining the detection intensity of the secondary electrons by the electron detector 18 while scanning the surface of the sample S with the ion beam.

  Note that if the sample S is continuously irradiated with the ion beam during the observation of the surface of the sample S, the surface of the sample S is positively charged (charged up) with ions. It is desirable to alternately irradiate electrons emitted from the neutralizing electron gun 19.

  The present invention is not limited to the first embodiment described above, and can take other various configurations. Hereinafter, other embodiments will be described.

  As shown in FIG. 2, the ion microscope 10 </ b> A of the second embodiment includes a cooling device 21 that cools the sample S on the back surface of the sample holder 17. The cooling device 21 absorbs heat from the sample holder 17 by passing a direct current through the Peltier element. Other configurations are the same as those of the ion microscope 10 of the first embodiment.

  According to the ion microscope 10A of the second embodiment, the surface image of the sample S can be observed while the sample S is cooled to about −30 ° C. by the cooling device 21.

In addition, if a cooling device that cools the sample S to the liquid nitrogen temperature by bringing the liquid nitrogen into contact with the sample holder 17 is used, the pressure in the sample chamber 13 is adjusted to 10 ⁻³ Pa or more. The surface image of the sample S can be observed.

  As shown in FIG. 3, the ion microscope 10 </ b> B of the third embodiment includes an ion detector 23 that detects ions reflected in the sample chamber 13 around the second orifice 1213 so as to face the sample holder 17. Is provided. Other configurations are the same as those of the ion microscope 10 of the first embodiment. A similar ion detector 23 may also be provided in the ion microscope 10A of the second embodiment.

  In general, when a sample is irradiated with an ion beam, some of the irradiated ions are subjected to elastic scattering (Rutherford scattering) by atomic nuclei in the sample. In the ion microscope 10B of the third embodiment, a surface image of the sample S is obtained from secondary electrons as in the first and second embodiments, and the detection intensity of the cation detected by the ion detector 23 is also used. A surface image can be obtained.

DESCRIPTION OF SYMBOLS 10, 10A, 10B ... Ion microscope 11 ... Ion production chamber 1112 ... First orifice 12 ... Intermediate chamber 1213 ... Second orifice 13 ... Sample chamber 131 ... Sample loading / unloading port 14 ... Inductively coupled plasma ion source 141 ... Gas supply nozzle 1411 ... Supply port 142 ... Coils 15, 15M, 15S ... Vacuum pumps 151, 151M, 151S ... Exhaust ports 152, 152M, 152S ... Valve 161 ... Extraction electrode 1621 ... First ion lens electrode 1622 ... Second ion lens electrode 163 ... Scanning Electrode 17 ... Sample holder 18 ... Electron detector 19 ... Neutralizing electron gun 21 ... Cooling device 22 ... Aperture mechanism 23 ... Ion detector

Claims (7)

a) an inductively coupled plasma ion source for generating an ion beam;
b) a sample chamber connected to the inductively coupled plasma ion source through an orifice through which the ion beam passes and having a sample holding unit for holding a sample at a position irradiated with the ion beam;
c) a scanning unit that relatively moves the ion beam and the sample holding unit so as to scan the surface of the sample held in the sample holding unit by the ion beam;
d) an electron detector for detecting secondary electrons generated in the sample held in the sample holding unit;
e) An ion microscope comprising: a pressure adjusting unit that maintains the pressure in the sample chamber at 10 ⁻⁴ Pa or more. The ion microscope according to claim 1, wherein the pressure is 10 ⁻³ Pa or more.   The ion microscope according to claim 2, wherein the pressure is 10 Pa or more.   The ion microscope according to claim 3, wherein the pressure is 2400 Pa or more. 5. The ion microscope according to claim 1, wherein the inductively coupled plasma ion source has a luminance of 6400 A / m ² / sr / V or more and an energy width of 5.5 eV or less.   6. The ion microscope according to claim 1, wherein the ion beam is made of any one of ions of H, He, N, O, Ne, Ar, and Xe.   The ion microscope according to claim 6, wherein the ion beam is composed of any one of ions of H, He, N, O, and Ne.

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