JP4874157B2 - Atom probe device - Google Patents

Description

  The present invention relates to an atom probe apparatus, which improves the function of an atom probe apparatus capable of examining the atomic structure of a very fine region by directly measuring each atom of a sample. This greatly contributes to the development of the materials used.

  As introduced in Non-Patent Document 1 (Text of the 53rd and 54th Shiraishi Memorial Lecture “Nanotechnology to Support the Advancement of Steel Materials” text), the atom probe device is the spatial position and elements of the constituent atoms of the sample. It is an apparatus that can measure a species with a high spatial resolution of nanometers or less, and is used for structural analysis at the atomic level of conductive materials. The principle is that a pulse voltage is applied to a high DC voltage on a sample processed into a needle shape, the sample surface atoms are sequentially evaporated by a high electric field formed on the needle surface, and the generated ions are captured and analyzed by a detector. To do. In addition to voltage, laser irradiation is also promoted to promote field evaporation. Since the flight time is determined by the mass of the ions, the element species can be determined from the measurement of the flight time. To date, several types of atom probe devices have been developed.

  The one-dimensional atom probe apparatus is this basic type, and is an apparatus that measures the arrangement of atoms in the depth direction from the order of ions that reach the detector. The three-dimensional atom probe apparatus is an apparatus that measures not only the arrangement in the depth direction but also the actual three-dimensional position by measuring the arrival coordinates of ions with an ion coordinate detector. Usually, the atomic data measured for 500,000 atoms or more is used to calculate the flight direction of ions based on the radius of curvature of the needle tip, thereby obtaining a three-dimensional element distribution in the sample. More recently, as disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 7-43373), instead of the needle-like sample electrode, the extraction electrode on the funnel having a hole formed at the tip is used and moved. A scanning atom probe has been developed, in which an atom on the surface of the analysis region is analyzed by field evaporation in the vicinity of the determined analysis region surface. In addition, irradiation with a pulse laser facilitates measurement of a non-conductive material, and an observation region is being expanded due to an increase in measurement speed and a high field of view.

  In general, an atom probe apparatus is provided with a field ion microscope (FIM) in most cases. FIM usually uses an inert gas such as Ne or Ar as an image gas, and by applying a high voltage to the sample, the inert gas atoms on the surface of the needle tip are ionized and imaged on the detection screen. It is a device that observes the atomic arrangement on the surface with atomic level spatial resolution. This includes not only observation of a field of view wider than the atom probe measurement region, but also information on crystal structures that are difficult to obtain by only atom probe measurement, such as information on crystal systems, crystal orientations, and phases. In normal atom probe measurement, the FIM image of the needle sample is always observed before the measurement, and electric field evaporation is performed as necessary to remove surface contamination, locate the desired measurement area, and determine the orientation. It was used. In particular, when performing atom probe measurement including grain boundaries and other phases, information on the presence / absence of crystal grain boundaries is obtained from the FIM image, and the phases are recognized from the difference in contrast, which is useful for measurement.

  However, in the conventional atom probe apparatus, even if there is a user's knowledge and experience, information (for example, exact crystal orientation, grain boundary type / angle, etc.) that is effective “in-situ” during FIM observation It was not easy to pull out. This is because the atom probe apparatus was not provided with a function of analyzing information such as crystal orientation from the FIM image.

JP 7-43373 A Japan Iron and Steel Institute 53rd and 54th Shiroishi Memorial Lecture “Nanotechnology to Support the Progress of Steel Materials” Text (2004)

  The point that the atom probe device lacks in the transmission electron microscope (TEM) is the function of examining the crystal system and crystal orientation. In TEM, this function is explained in detail from the electron diffraction pattern and the Kikuchi pattern. It is possible to obtain.

  The present invention improves the function of an atom probe apparatus by providing means for easily obtaining information on crystal orientation and crystal structure on the spot, which is lacking in conventional atom probe apparatuses. It is an object of the present invention to provide an atom probe apparatus having the following.

  The present inventor has intensively studied the improvement of the apparatus for extracting detailed information on the crystal structure in a short time. As a result, in the conventional atom probe apparatus, it has become possible to greatly improve the function of the atom probe apparatus itself by improving the capability of the FIM which has been devoted to auxiliary functions. This is because the FIM image that is always observed before the atom probe measurement is performed on the “in-situ” analyzer using the equipment attached to this device, so that the crystal structure, phase, and crystal of the sample can be obtained in a very short time. This makes it possible to obtain information that is the main target of the present analysis apparatus, such as defects and crystal grain boundaries, almost simultaneously with FIM observation. The present invention has been achieved based on this new knowledge, and the gist of the present invention is as follows.

(1) Field ion microscope apparatus, field ion microscope image capturing apparatus that captures a field ion microscope image captured by the field ion microscope apparatus, and field ion microscope image analysis apparatus that analyzes the captured field ion microscope image The field ion microscope image analyzer has a function of fitting at least one of a crystal orientation, a crystal rotation angle, or a crystal rotation axis to the field ion microscope image, The atom probe apparatus further has a function of determining the orientation of two crystals sandwiching a crystal grain boundary .
(2) The field ion microscope image analyzer specifies the structure and type of crystals existing in the field ion microscope image using crystal data including at least data relating to a crystal system and a lattice constant input in advance. The atom probe device according to (1), further having a function of:

  According to the present invention, it is possible to improve the function of an atom probe apparatus capable of examining a material from the structure of elements, and greatly contribute to material development using nanotechnology.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  One of the basic embodiments of the present invention is an FIM observation apparatus that can display the surface structure of a needle sample, an image capture apparatus that captures the FIM image as data, and crystal orientation information from the captured FIM image. The FIM analysis device can extract the sample and the atom probe device that can check the atomic configuration of the sample.

  The atom probe apparatus described here includes all of the one-dimensional atom probes, one-dimensional atom probes, three-dimensional atom probes, and scanning atom probes.

  Details of each component will be described below.

As described above, the FIM apparatus applies a high voltage to the needle sample in an atmosphere into which an image gas made of an inert gas is introduced, and gas atoms ionized on the sample surface are arranged to face the sample. It is a device that projects it. A sharp needle sample whose tip radius of curvature is processed to 100 nm or less is cooled to 100 K or less by a cryostat or the like and placed in a vacuum evacuated chamber. An inert gas of 1 × 10 ^{−3 to} 5 × 10 ⁻³ Pa is introduced into this, and a high voltage of 4 kV or higher is applied. The inert gas is ionized by the high electric field formed on the surface of the needle tip, accelerated by the electric field on the surface of the needle sample, and collides with a grounded double channel plate arranged in front. A voltage difference is provided between the channel plates, the electrons generated on the front channel plate are amplified, and an image is displayed on the fluorescent screen disposed behind. This image is usually observed from behind. Also, this function can be achieved by detecting and integrating the ionized gas with the coordinate position detector.

  An image capturing device that captures an FIM image as data is a device that captures an image projected on a screen for FIM, and can be realized by a CCD element or the like, a digital camera, a video camera, or the like disposed behind the screen. The image capture device can transfer the captured data to the FIM analysis device. A coordinate position detector may be provided with this image reading function.

  The FIM image analyzer can automatically or manually recognize the orientation (pole) of the low index plane from the ring structure appearing in the FIM image, and can accurately determine the orientation of the sample crystal. Even when two or more different crystal grains are included in one FIM image, the orientation relationship and rotation angle between the crystal grains can be individually examined by automatic or manual fitting. Furthermore, it is possible to calculate the rotation angle and rotation axis between these crystals. This analysis function can be realized, for example, by a computer capable of graphic display including a program for calculating the pole position of the FIM. ATOM PROBE TOMOGRAPY Analysis at the Atomic Level (Kluwer Academic / Plenum Publishers, New York, 2000) The surface of the FIM is a semi-sphere, as described in p49-52. Can be approximated. The FIM image captured by the image capturing device and the FIM figure obtained by calculation (pole position is displayed) are displayed on the computer display screen, and the orientation parameters are input so that the FIM image and the FIM figure overlap. Thus, the orientation of the crystal grains included in the FIM image can be determined accurately. Alternatively, by automatically recognizing the pole position of the FIM by a computer, the fitting can be automatically performed and the crystal grain orientation can be automatically determined. Even for crystals with different crystal structures, FIM simulation images can be drawn by inputting crystal parameters (crystal system, lattice constant, etc.).

  The atom probe device applies high voltage to the above-mentioned needle sample in vacuum, ionizes the surface atoms with a high electric field formed at the tip of the needle, and measures the ions accelerated by the surface electric field with a detector It has the function to do. The one-dimensional atom probe measures only the flight time, and the three-dimensional atom probe and the scanning atom probe measure the flight time and the ion arrival position as coordinates. Since the time of flight is determined by the mass-to-charge ratio of ions, the element species can be determined. The depth position can be determined in the order of arrival of many atoms, and the position of the needle sample surface can be determined from the arrival coordinates on the detector. By measuring a large number of ions of 10,000 atoms or more and processing them with a dedicated analysis computer, it is possible to obtain the desired three-dimensional element distribution result.

  Although the conventional atom probe apparatus usually has an FIM apparatus, it has no FIM image analysis function. In this case, the role of FIM is used to confirm the optimality of the needle sample before measurement, to determine the measurement position by field evaporation, to qualitatively recognize different phases (precipitates and grain boundaries), and to determine the measurement position of the atom probe. It had been. On the other hand, in the present invention, by using an atom probe apparatus having an FIM apparatus, an FIM image capturing apparatus, and an FIM image analysis apparatus, it is possible to greatly improve the function of the atom probe. Next, the functional improvement will be described.

(1) The FIM image analysis apparatus can determine the atom probe measurement direction precisely and in a short time. In the conventional atom probe experiment, the crystal orientation that can be read from the FIM image is limited to orientation recognition of the low index surface observed as a pole. Was also low. On the other hand, in the atom probe apparatus of the present invention, the crystal orientation on the FIM can be strictly recognized by the FIM image analysis apparatus immediately after the FIM observation. By rotating the sample in the direction indicated by the FIM image analyzer, measurement in a desired direction can be performed. Also, the time spent on it is very short, and atom probe measurement can be performed continuously from FIM observation.

(2) Furthermore, in the case of grain boundary and interface observation, this effect becomes enormous. It is difficult to examine elements segregated at grain boundaries and phase interfaces from the viewpoint of the lower limit of detection and spatial resolution by electron microscopes and surface analysis methods, and the method using an atom probe apparatus is an effective method. However, since the state of the grain boundary element depends on the nature of the grain boundary (for example, grain boundary angle, rotation axis, grain interface orientation, etc.), it is necessary to obtain this information at the same time. In the conventional atom probe apparatus, even though the grain boundary position can be recognized by FIM, information on the grain boundary angle cannot be obtained. 381 (2004) P26-30, this sample was taken out and calculated by Kikuchi pattern analysis using an electron microscope. Much time and expertise were required for Kikuchi pattern analysis using this electron microscope. On the other hand, in the atom probe apparatus of the present invention, after FIM observation, data is transferred by the FIM image capturing apparatus, and the orientation of two crystals sandwiching the crystal grain boundary can be easily determined by the FIM image analyzing apparatus. Therefore, the grain boundary angle and the rotation axis can be determined accurately and in a very short time. Based on this result, it is possible to quickly determine whether or not the target grain boundary is on the spot, eliminating the need for TEM analysis that requires a lot of time, and in particular, interrupting a series of experiments from FIM to atom probe measurement. It is a great advantage to be able to conduct experiments in situ (In-situ).

(3) Although FIM observation is usually effective for analysis of known crystals, the atom probe device of the present invention provides a sample or another phase in the sample by giving any crystal as data to the FIM analysis device. Even if the feature of is unknown, it is possible to determine the structure and type of the crystal from the FIM image. This is because, when a sample includes a plurality of different crystal phases, the type can be recognized in a short time and the measurement can be judged.

  Examples of the atom probe apparatus having the FIM image analysis function of the present invention are shown in FIG. 1, FIG. 2, and FIG. All of these apparatuses are composed of an atom probe apparatus having an FIM apparatus, an FIM image capturing apparatus 104, and an FIM analysis apparatus 105. FIG. 1 shows a three-dimensional atom probe in which a sample is rotated in a horizontal plane with respect to the FIM observation direction, the reflected flight ions are measured by a position coordinate detector 107 toward a reflectron 106 for energy compensation. . FIG. 2 shows a one-dimensional atom in which an FIM image is reflected by a mirror 114, and a flying ion passing through a probe hole in the FIM screen 113 by removing the mirror 114 is measured by an ion detector 115 through a reflectron. It is a probe. FIG. 3 shows a three-dimensional atom probe or scanning atom probe equipped with a position coordinate detector having an FIM image observation function and an image capture function by a coordinate detector 116 including an FIM function and an image capture function.

  Hereinafter, using these apparatuses, an actual usage example will be described.

(Example 1: Atom probe measurement in a specific direction)
A needle-like sample 101 made of ferritic iron whose tip radius of curvature was processed to 50 nm was cooled to 60 K in a evacuated container (chamber) 103 using a cryostat or the like. Ne gas is introduced into the gas introduction line 108 at 1.3 × 10 ⁻³ Pa, and a DC voltage of 8 kV is applied to the sample to project an FIM image on the FIM screen 102 composed of a channel plate and a fluorescent screen. I let you. Usually, by controlling the voltage of the needle sample, field evaporation is caused, and surface contamination and the like are removed, whereby an FIM image having atomic level resolution can be obtained. The FIM image reflected on the screen was captured by the FIM image analysis device 105 by the FIM image capture device 104 such as a CCD camera arranged behind the screen. In the FIM image analysis apparatus, the program included in this apparatus was used to automatically recognize the [110] and [002] poles of the ferrite crystal and uniquely determine the crystal orientation displayed in the FIM image.

  Next, the [132] direction of the measurement orientation of the atom probe, which is the object of this experiment, is shown on the image. Based on this result, the sample was rotated so that the center of the FIM image was in the [132] direction. Next, the gas in the chamber 103 was evacuated 109 with a pump, and the entire sample was rotated 92 ° in a horizontal plane. This is because the sample is directed toward the reflectron 106. In this apparatus, the center of the FIM image and the center of the reflectron coincide with each other by a rotation of 92 °. Thereby, the center of the reflectron, ie the center of the detector, coincides with the center of the FIM image, ie in this case the [132] direction of the sample. After this state, an atom probe measurement was performed by applying a DC voltage and a pulse voltage of 20% of this voltage. It took about 2 minutes from the FIM observation to the precise determination of the azimuth to the atom probe measurement. According to the present invention, even if the measurer does not have a high level of expertise, the position of a specific orientation can be accurately performed in a short time, and an atom probe measurement in a target crystal direction can be performed.

(Example 2: Atom probe measurement of specific grain boundary)
The atom probe measurement of the grain boundary position using this apparatus will be described. The needle-like sample processed to have a radius of curvature of the tip of 50 nm was cooled to 80 K using a cryostat or the like in a evacuated container. Ne gas was introduced from the gas introduction line 108 at 1.5 × 10 ⁻³ Pa, and field evaporation was performed by applying a DC voltage to the sample until the grain boundary was observed by FIM. In the FIM image of FIG. 4, the grain boundary positions appearing in this way are indicated by dotted lines. FIM image data was moved to the FIM image analyzer by the FIM image capturing device, and grain boundary analysis was performed by the FIM image analyzer. As shown in FIG. 4, the orientation of the two crystals is determined by manually fitting the [002] pole and the [110] pole position of the two grains at the boundary of the grain boundary, The rotation angle (grain boundary angle) was determined at the same time. The result was a large-angle grain boundary of 53.9 ° as shown in FIG. In this experiment, since the purpose was to measure a large-angle grain boundary with a large angle, the measurement position was determined, and the sample was rotated so that it was positioned at the center of the FIM. Thereafter, the same operation as described in Example 1 was performed, and the atom probe measurement was performed. FIG. 5 shows the measurement results. C segregation and a small amount of P segregation that could never be observed by other methods could be clearly and quantitatively observed. The grain boundary angle was determined from FIM observation, and the time to start the measurement was only 4 minutes.

(Comparative example 1: Grain boundary atom probe measurement by a conventional apparatus)
Using the same sample as in Example 2, while FIM observation, the grain boundary was observed until were field evaporation. When the grain boundary appeared, the sample was taken out from the atom probe apparatus and observed by TEM. The tip of the needle was observed at a magnification of 100,000 times, and a photograph of the Kikuchi pattern of two crystal grains including the grain boundary was taken. The photograph was developed and baked on photographic paper, from which the orientation analysis of the crystal grains was performed. From the calculation results, it was found that the grain boundary angle of this sample was 5.3 °, which was not the intended grain boundary. Therefore, the sample was again electropolished, and the grain boundary was positioned by electrolytic evaporation while observing the FIM image. The sample at the grain boundary position was again observed by TEM, a photograph of the Kikuchi pattern was taken, developed and baked, and the grain boundary angle was calculated. Since it was found to be a 46.5 ° large-angle grain boundary, an atom probe measurement was performed. It took 2 days to determine the grain boundary angle from the first FIM observation and to start the measurement, and 8 hours from the second FIM observation to the measurement.

(Example 3: Identification of crystal system from FIM image)
In order to measure the carbon content of a trace amount of retained austenite phase contained in martensite, FIM observation of a needle-like sample made of martensite iron was performed using the apparatus shown in FIG. Since retained austenite has a different crystal structure from martensite, it is usually identified by TEM electron diffraction or X-ray diffraction. The sample is cooled to 60K, Ne gas is introduced, a 10 kV DC voltage is applied to cause field evaporation, and the mirror 114 is placed behind the FIM screen 113 with the probe hole at an angle of 45 ° and reflected to obtain an FIM image. When a new phase appeared, the field evaporation was stopped and the FIM image was captured by the FIM image capturing device 104. A new phase observed in the martensite image was analyzed with a FIM image analyzer. The crystal system and lattice constant of retained austenite were input to this apparatus in advance. The pole seen in the new image could not be fitted with a BCC structure, but could only be fitted as an FCC structure. Based on this result, this phase was judged to be the desired retained austenite. The measurement position of the FIM image was aligned with the probe hole position, the mirror was removed, and the atom probe measurement was performed. It took only 3 minutes from the FIM observation to the atom probe measurement.

  In the measurement with a conventional atom probe not having an FIM analysis function, a new phase was observed in an FIM image, a sample was taken out, and a TEM diffraction pattern was examined for FCC. In this case, it took about 3 hours from FIM observation to measurement.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is a block diagram for demonstrating an example of the atom probe apparatus containing the FIM image analyzer which concerns on one Embodiment of this invention. It is a block diagram for demonstrating an example of the atom probe apparatus containing the FIM image analyzer which concerns on one Embodiment of this invention. It is a block diagram for demonstrating an example of the atom probe apparatus containing the FIM image analyzer which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the result of the grain boundary analysis by the FIM image analyzer which concerns on one Embodiment of this invention. 3D element maps of ferrite iron grain boundaries and C and P concentration profiles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Needle sample 102 FIM screen 103 Analysis chamber 104 FIM image capture device 105 FIM analysis device 106 Reflectron (energy compensator)
Reference Signs List 107 Position coordinate detector 108 Gas introduction line 109 Vacuum exhaust line 110 Gas ion trajectory 111 Cable 112 Ion flight trajectory 113 FIM screen with probe hole 114 Mirror 115 Ion detector 116 Position coordinate detector having FIM image measurement and capture function

Claims (2)

A field ion microscope device;
A field ion microscope image capturing device for capturing a field ion microscope image captured by the field ion microscope device;
A field ion microscope image analyzer for analyzing the captured field ion microscope image;
An atom probe device comprising:
The field ion microscope image analyzer has a function of fitting at least one of a crystal orientation, a crystal rotation angle, or a crystal rotation axis to the field ion microscope image, and further, two crystal crystals sandwiching a crystal grain boundary. An atom probe apparatus having a function of determining an azimuth . The field ion microscope image analyzer has a function of specifying the structure and type of a crystal existing in the field ion microscope image by using crystal data including at least data relating to a crystal system and a lattice constant input in advance. The atom probe apparatus according to claim 1, further comprising: