Patent Description:
The present disclosure relates to a scanning electron microscope, in particular, to a technique for visualizing two dimensional spatial distribution of an absorption edge structure of a sample.

Methods have been known for analyzing elements of a sample by directing electrons, X-ray radiation, or the like to the sample and detecting electromagnetic waves generated from the sample.

One example of such a method is a method of applying an electron beam or an electrically-charged particle beam to a sample in an electron microscope to cause discharge of a characteristic X-ray from the sample. This method is used for analyzing elements, utilizing the fact that a characteristic X-ray has an energy unique to an element constituting a sample. The intensity spectrum of a characteristic X-ray indicates the number of times at which an X-ray is detected for each energy. An element in the sample can be identified based on the energy of a peak in the intensity spectrum, and the amount of that element contained in the sample can be determined based on the area of the peak in the intensity spectrum. With wavelength dispersive X-ray spectroscopy, a characteristic X-ray is dispersed through a diffraction grating, to thereby generate an intensity spectrum, and there is available a technique for collectively detecting spatially spreading characteristic X-rays outputted from the diffraction grating using a CCD camera.

<CIT> discloses a device for calculating a ratio of intensity spectra respectively obtained using two different acceleration voltages, and then comparing the ratio with information registered in a database, to thereby identify an element in a scanning electron microscope.

<CIT> discloses a device for determining the state of distribution of elements in the depth direction of a sample, based on an X-ray map obtained using two different acceleration voltages, in a scanning electron microscope. <NPL>, discloses the features of the preamble of claim <NUM>.

Here, there has been known a method for analyzing the state of chemical bonding of a sample, using TEM-EELS, or a combination of a Transmission Electron Microscope (TEM) and Electron Energy Loss Spectroscopy (EELS). For example, by observing a Near Edge X-ray Absorption Fine Structure (ELNES), which appears in a TEM-EELS spectrum, the state of chemical bonding is analyzed. According to such a method using a TEM, however, a sample must be made thin, and thus cannot be used to conduct a wide-range observation of bulk samples.

Another method available is a method for observing a Near Edge X-ray Absorption Fine Structure based on an X-ray absorption spectrum (XAFS), which is measured using synchrotron radiation. This method, however, requires a large device, and cannot readily conduct a wide-range observation of a sample.

An object of the present disclosure is to conduct a wide-range observation of a two-dimensional spatial distribution of an absorption edge structure of a sample using a scanning electron microscope.

According to one aspect of the present disclosure, there is provided a scanning electron microscope including an obtaining unit configured to apply individual electron beams to an area on a sample which uses two different acceleration voltages to obtain an electron beam excitation characteristic X-ray spectrum (hereinafter referred to as an emission spectrum) in the same soft X-ray area on the sample for each of the acceleration voltages; a calculation unit configured to calculate a spectral ratio between the emission spectra obtained through application of the electron beams with the two different acceleration voltages; and a display processing unit configured to extract a ratio in an energy region of interest corresponding to energy at an absorption edge of each element from the calculated spectral ratio, and display the extracted ratio as a spectral map on a display unit.

In one embodiment, the above-described scanning electron microscope may further include a storage unit configured to store an energy value at an X-ray absorption edge of an element, and, when the energy band of the calculated spectral ratio contains an energy value stored in the storage unit, the display processor may determine the energy value as the energy region of interest, then extract a ratio at the energy value as a ratio in the energy region of interest, and display the extracted ratio as the spectral map on the display unit.

In another embodiment, the calculation unit may calculate a spectral ratio between the emission spectra, while changing the energy band, depending on the element.

In another embodiment, the display processing unit may further display a graph generated by plotting the calculated spectral ratio for each energy on the display unit.

According to another aspect of the present disclosure, there is provided a map display method for displaying a map of an absorption edge structure, including the steps of applying individual electron beams to an area on a sample using two different acceleration voltages, to obtain an emission spectrum of a soft X-ray in the area on the sample for each of the acceleration voltages; calculating a spectral ratio between the emission spectra obtained through application of the electron beams with the two different acceleration voltages; extracting a ratio in an energy region of interest corresponding to energy at an absorption edge of each element from the calculated spectral ratio; and displaying the extracted ratio as a spectral map.

According to the present disclosure, it is possible to conduct wide-range observation of a two dimensional spatial distribution of an absorption edge structure of a sample, using a scanning electron microscope.

Embodiments of the present disclosure will be described based on the following figures, wherein:.

A scanning electron microscope <NUM> according to an embodiment of the present disclosure will be described referring to <FIG> illustrates a scanning electron microscope <NUM> according to an embodiment.

The scanning electron microscope <NUM> includes a wavelength dispersive X-ray spectrometer <NUM>, an electron-optical system <NUM>, a sample stage <NUM>, and an information processing device <NUM>. The wavelength dispersive X-ray spectrometer <NUM> includes an X-ray condensing mirror, not illustrated, a diffraction grating <NUM> having slits with inconsistent intervals, and a detection device <NUM>.

The electron-optical system <NUM> is a system for generating an electron probe. Specifically, the electron-optical system <NUM> includes an electron beam source <NUM>, such as an electron gun, for generating an electron beam <NUM>. The electron beam source <NUM> generates electrons having energy having been set, while changing an acceleration voltage for accelerating electrons. The electron-optical system <NUM> further includes a slit, a condenser lens, a scanning coil, and an object lens, or the like, not illustrated. The electron-optical system <NUM> condenses and scans the electron beam <NUM>.

The sample stage <NUM> is a component upon which a sample <NUM> is placed. With an electron beam <NUM> is directed at the sample <NUM>, the sample <NUM> generates a characteristic X-ray <NUM>. The characteristic X-ray <NUM> is an X-ray that is generated when an electron on an outer shell orbit (a shallower orbit) falls into an inner shell orbit (a deeper orbit) of an atom constituting the sample <NUM> when an electron on the inner orbit is bombard with an electron beam <NUM> and ejected from the inner shell orbit. In particular, a soft X-ray is a signal that is useful in analysis of a composition, bonding state, crystalline structure, or the like, of a sample. The characteristic X-ray <NUM> discharged from the sample <NUM> is condensed through an X-ray condensing mirror, not illustrated, before proceeding toward the diffraction grating <NUM>. In this embodiment, a soft X-ray is detected as a characteristic X-ray <NUM>. A soft X-ray is an X-ray having an energy of, for example, <NUM> keV or less, <NUM> eV or less, or <NUM> eV or less.

The diffraction grating <NUM> is an optical device (or a dispersive device) for dispersing a characteristic X-ray <NUM> for specific wavelengths. That is, an emission angle β relative to an incident angle α has a wavelength-dependency because of a diffraction phenomenon, and each characteristic X-ray component thus ejects at an angle in accordance with the wavelength. In this manner, the incident characteristic X-ray <NUM> is split into components for each wavelength, that is, components for each energy.

The detection device <NUM> includes a CCD detector <NUM> and a CCD controller <NUM>. The CCD detector <NUM> has a two dimensional photo detector array for receiving an X-ray and converting the received X-ray into an electrical signal. Using the two dimensionally disposed photo detectors, the CCD detector <NUM> can simultaneously or collectively detect characteristic X-rays in a predetermined wavelength range (that is, a predetermined energy range). For example, the CCD detector <NUM> has a first axis corresponding to a wavelength dispersion direction and a second axis orthogonal to the wavelength dispersion direction. For every wavelength, a plurality of detection signals are accumulated parallel to the second axis. The CCD controller <NUM> controls the operation of the CCD detector <NUM>, and counts an electric signal outputted from the CCD detector <NUM> for each photo detector. The number of electric signals counted during a set period of time (for example, one second, five seconds, ten seconds, or the like) is obtained for each wavelength. In this manner, an emission spectrum of a characteristic X-ray <NUM> is obtained.

The information processing device <NUM> comprises hardware or software. The hardware may include a Central Processing Unit (CPU), a memory, or the like, while the software may include an operating system (OS), an application program, or the like. The information processing device <NUM> may include a personal computer (PC). The information processing device <NUM> may include a single device or a plurality of devices.

The information processing device <NUM> includes a control device <NUM> and an analyzing device <NUM>. The control device <NUM> controls the electron-optical system <NUM> and the detection device <NUM>. The analyzing device <NUM> processes and analyzes a plurality of emission spectra (precisely, a plurality of emission spectral data) time-serially outputted from the CCD controller <NUM>.

In a measurement process, a characteristic X-ray <NUM> output from the sample <NUM> is continuously detected while an electron beam <NUM> is continuously applied to the sample <NUM> to thereby generate an emission spectrum.

The scanning electron microscope <NUM> can measure emission spectra of a plurality of different characteristic X-rays <NUM> having extremely low energy. For example, for a sample <NUM> made of transition metal compounds, it is possible to simultaneously measure the emission spectra of an Lα line and of an Lβ line, which reflects the distribution of outer shell electrons, and the emission spectra of an L1 line and of an Lnx line, which reflects the distribution of slightly inner shell electrons. It is also possible to measure an energy position. With the above, it is possible to accurately measure chemical bonding information.

Referring to <FIG>, the analyzing device <NUM> will now be described. <FIG> is a block diagram illustrating the analyzing device <NUM>.

The analyzing device <NUM> comprises an obtaining unit <NUM>, a calculation unit <NUM>, a display processor <NUM>, a display <NUM>, an operating device <NUM>, and a storage unit <NUM>.

The obtaining unit <NUM> obtains an emission spectrum output from the CCD controller <NUM>, and then generates a waveform (for example, a line graph) representing each emission spectrum. The waveform is a waveform representing an intensity array constituting the emission spectrum. In a waveform representing an emission spectrum, the abscissa represents the energy, and the ordinate represents the intensity.

The obtaining unit <NUM> applies electron beams <NUM> to the same area on the sample <NUM>, using two respectively different acceleration voltages, to obtain emission spectra of soft X-rays in the same area on the sample <NUM>.

Specifically, under control by the control device <NUM> the electron beam source <NUM> accelerates electrons at a first acceleration voltage, , to thereby generate an electron beam <NUM>. The electron beam <NUM> accelerated using the first acceleration voltage is directed to the sample <NUM>. The sample <NUM> generates a characteristic X-ray <NUM>, which is detected by the detection device <NUM>. With the above, an emission spectrum of electrons accelerated using the first acceleration voltage is obtained by the obtaining unit <NUM>. An emission spectrum obtained with electrons accelerated using the first acceleration voltage will hereinafter be referred to as a "spectrum A".

Under control by the control device <NUM>, the electron beam source <NUM> further accelerates electrons, using a second acceleration voltage different from the first acceleration voltage, to thereby generate an electron beam <NUM>. The electron beam <NUM> accelerated using the second acceleration voltage is directed to the sample <NUM>. The sample <NUM> generates a characteristic X-ray <NUM>, which is detected by the detection device <NUM>. With the above, an emission spectrum with electrons accelerated using the second acceleration voltage is obtained by the obtaining unit <NUM>. An emission spectrum obtained with electrons accelerated using the second acceleration voltage will hereinafter be referred to as a "spectrum B".

The control device <NUM> executes control such that the respective electron beams <NUM> accelerated using the first acceleration voltage and using the second acceleration voltage are separately directed from the electron beam source <NUM> to the same position on the sample <NUM>. With the above, a spectrum A and a spectrum B are separately obtained from the same position, so that the obtaining unit <NUM> obtains the spectrum A and the spectrum B at the same position.

Thereafter, while changing a position on the sample <NUM> to which the electron beam <NUM> is applied, the control device <NUM> executes control such that the respective electron beams <NUM> accelerated using the first acceleration voltage and using the second acceleration voltage are separately applied to the sample <NUM> from the electron beam source <NUM> at each used position. With the above, a spectrum A and a spectrum B are separately obtained for each position, so that the obtaining unit <NUM> obtains the spectra A and the spectra B in the respective positions.

Thereafter, the calculation unit <NUM> calculates a ratio of two emission spectra obtained using two respectively different acceleration voltages, the ratio of the intensities of two emission spectra. Such a ratio of two emission spectra will be hereinafter referred to as a "spectral ratio". To describe the processing of the calculation unit <NUM> in detail, the calculation unit <NUM> calculates a ratio of the spectrum A and the spectrum B obtained from the same position on the sample <NUM>. The calculation unit <NUM> calculates a ratio of the spectrum A and the spectrum B at each of the positions to thereby obtain spectral ratios at the respective positions.

The calculation unit <NUM> generates a waveform (or a ratio spectrum) representing the spectral ratio (hereinafter referred to as a spectral ratio waveform) of a ratio calculated between the respective waveforms representing the spectrum A and the spectrum B. In this spectral ratio waveform, the abscissa represents the energy, while the ordinate represents the spectral ratio.

Thereafter, the display processor <NUM> generates a spectral map with spectral ratios mapped thereon, and displays the spectral map on the display <NUM>. To describe this processing of the display processing <NUM> in detail, the display processor <NUM> extracts a spectral ratio in an energy region of interest (ROI) from a spectral ratio waveform at each of the positions on the sample <NUM>, and maps the extracted spectral ratios onto points corresponding to the respective positions on the sample <NUM>, whereby a spectral map showing spectral ratios at respective positions is generated. With the above, a spectral map in the energy ROI is generated. An energy ROI is an energy band corresponding to an absorption edge or near an absorption edge. The position and width of an energy ROI in the range of energy are determined in advance, for example, and may be changed, depending on an element constituting the sample <NUM> or by a user. The display processor <NUM> extracts a spectral ratio while changing the position of the energy ROI, and generates a spectral map for each energy ROI.

The storage unit <NUM> is a storage unit such as a hard disk drive, a memory, or the like. Energy values corresponding to the X-ray absorption edges of respective elements (that is, the position of an absorption edge in an energy band) are measured or calculated in advance and stored as a database in the storage unit <NUM>. For example, as to metals, oxides, sulfides, compounds, semiconductors, and the like, the values of energy corresponding to the respective X-ray absorption edges are stored in the storage unit <NUM>.

The operating device <NUM> includes a keyboard or a pointing device (for example, a mouse, a touch panel, a touch pad, or the like). A user operates the operating device <NUM> to input information to the information processing device <NUM>.

Referring to <FIG>, the operation of the scanning electron microscope <NUM> will now be described. <FIG> is a flowchart of the operation.

Initially, the control device <NUM> applies an electron beam <NUM> accelerated using the first acceleration voltage from the electron beam source <NUM> to each of the positions on the sample <NUM>, and the obtaining unit <NUM> obtains a spectrum A at the position, the spectrum A being obtained through application of the electron beam <NUM> (S01). For example, in the case of a sample <NUM> made of transition metals, the first acceleration voltage is <NUM> to <NUM> kV, and a spectrum A of an L line is obtained. In the case of a sample <NUM> made of rare-earth elements, the first acceleration voltage is <NUM> to <NUM> kV, and a spectrum A of an M line is obtained.

Thereafter, the control device <NUM> applies the electron beam <NUM> accelerated using the second acceleration voltage from the electron beam source <NUM> to each of the positions on the sample <NUM>, and the obtaining unit <NUM> obtains a spectrum B at the position, the spectrum B being obtained through application of the electron beam <NUM> (S02). The electron beam <NUM> accelerated using the second acceleration voltage is directed to the same position as where the electron beam <NUM> accelerated using the first acceleration voltage has been applied. For example, in the case of a sample <NUM> made of transition metals, the second acceleration voltage is <NUM> to <NUM> kV, and a spectrum B of an L line is obtained. In the case of a sample <NUM> made of rare-earth elements, the second acceleration voltage is <NUM> to <NUM> kV, and a spectrum B of an M line is obtained.

Thereafter, the calculation unit <NUM> calculates a ratio of the spectrum A and the spectrum B at each of the positions (S03). For example, the calculation unit <NUM> divides the intensity of the spectrum A at each of the positions by the intensity of the spectrum B, to thereby obtain a spectral ratio A/B at the position. With the above, waveforms representing the respective spectral ratios A/B (hereinafter referred to as a spectral ratio A/B waveform) at the respective positions are generated.

Thereafter, the display processor <NUM> extracts the value of a spectral ratio A/B in an energy ROI from the spectral ratio A/B waveform at each of the positions (S04). The display processor <NUM> then maps the extracted values of the respective spectral ratios A/B onto points corresponding to the respective positions on the sample <NUM>, to thereby generate a spectral map showing the spectral ratios A/B at respective positions (S05). In this manner, the spectral map of the energy ROI is generated.

Further, having changed the position of the energy ROI, the display processor <NUM> extracts the value of a spectral ratio A/B in the energy ROI from the spectral ratio A/B waveform at each of the positions, and maps the extracted values of the respective spectral ratios A/B, whereby a spectral map in the energy ROI is generated. While changing the position of the energy ROI, the display processor <NUM> generates spectral maps of the respective energy ROIs.

The display processor <NUM> displays the spectral maps in the respective energy ROIs on the display <NUM> (S06).

In a case wherein the energy band of a spectral ratio A/B waveform contains any value of an energy corresponding to an absorption edge contained in the database stored in the storage unit <NUM>, the display processor <NUM> may define that energy value as an energy ROI. In such a case, the display processor <NUM> may extract the value of the spectral ratio A/B at that energy value from the spectral ratio A/B waveform, and map the extracted value of the spectral ratio A/B, to thereby generate a spectral map.

An embodiment will now be described in detail by way of a specific example.

It is known that a higher acceleration voltage causes a larger change in waveform of an emission spectrum due to self-absorption of the sample <NUM>. That is, a low acceleration voltage leads to little influence of absorption, while a high acceleration voltage leads to a large influence of absorption. Calculation of a ratio of an emission spectrum obtained with an electron beam <NUM> accelerated using a low acceleration voltage and applied to the sample <NUM> and an emission spectrum obtained with an electron beam <NUM> accelerated using a high acceleration voltage and applied to the sample <NUM> makes it possible to observe an absorption edge unique to a compound.

For example, as to an Fe simple substance, a larger acceleration voltage increases the value of Lα/Lβ. As to Fe2SiO4 (fayalite), on the other hand, a larger acceleration voltage decreases the value of Lα/Lβ.

<FIG> illustrates the intensity of an emission spectrum of an Fe simple substance, in which the abscissa represents the energy, and the ordinate represents the intensity.

Specifically, <FIG> illustrates respective emission spectra with respect to the acceleration voltages of <NUM>, <NUM>, <NUM>, <NUM> kV. Although the intensity of the Lα line is the same or substantially the same with respect to different acceleration voltages, the intensity of the Lβ line becomes lower as the acceleration voltage becomes higher. This means that the ratio Lα/Lβ in intensity between the Lα line and the Lβ line increases as the acceleration voltage increases.

<FIG> illustrates the intensity of an emission spectrum of Fe2SiO4, in which the abscissa represents the energy and the ordinate represents the intensity.

<FIG> illustrates respective emission spectra with respect to the acceleration voltage of <NUM>, <NUM>, <NUM>, <NUM> kV. Although the intensity of the Lα line is the same or substantially the same with respect to different acceleration voltages, the intensity of the Lβ line becomes higher as the acceleration voltage becomes higher. This means that the ratio Lα/Lβ in intensity between the Lα line and the Lβ line decreases as the acceleration voltage increases. This phenomenon is mainly attributed to an absorption effect and the fact that absorption edges L3, L2 are different depending on compounds.

<FIG> illustrates a spectral ratio waveform of an Fe simple substance, in which the abscissa represents the energy and the ordinate represents the spectral ratio. In one example here, the first acceleration voltage, or a low acceleration voltage, is <NUM> kV, and the second acceleration voltage, or a high acceleration voltage, is <NUM> kV. A spectrum A is obtained using the first acceleration voltage of <NUM> kV, and a spectrum B is obtained using the second acceleration voltage of <NUM> kV. A spectral ratio A/B, or a ratio in intensity between the spectrum A and the spectrum B, is calculated to generate a spectral ratio A/B waveform. The spectral ratio assigned to the ordinate corresponds to this spectral ratio A/B. <FIG> illustrates a spectral ratio A/B waveform in an energy band (from <NUM> to 740eV) that contains the energy of the Lα line.

A ratio spectrum reflecting the absorption edge L3 and being substantially equivalent to an absorption spectrum that will be obtained with synchrotron radiation is obtained. The energy corresponding to a peak of the spectral ratio A/B waveform is an energy reflecting the absorption edge L3, which is <NUM> eV, for example.

<FIG> illustrates the spectral ratio waveform of Fe2SiO4 (fayalite), similar to that of an Fe simple substance. The energy value corresponding to a peak of the spectral ratio A/B waveform is <NUM> eV. That is, an energy reflecting the absorption edge L3 is <NUM> eV.

In an embodiment, spectral ratios are mapped, based on the above-described relationship, to thereby generate a spectral map. Generation of a spectral map will now be described.

<FIG> illustrates a sample <NUM>, viewed from the side of the electron-optical system <NUM>, in which the X axis and the Y axis are orthogonal to each other, and together define a two dimensional (2D) plane. Each position on the surface of the sample <NUM> is defined with the X axis and the Y axis.

The control device <NUM> executes control such that an electron beam <NUM> accelerated using the first acceleration voltage is applied from the electron beam source <NUM> to respective positions (positions P1, P2, P3,. , Pn (Xm, Xn),. ) on the sample <NUM>, so that the obtaining unit <NUM> obtains spectra A at those positions. That is, while changing a position to which the electron beam <NUM> is applied, the control device <NUM> applies the electron beam <NUM> to the surface of the sample <NUM>, so that the obtaining unit <NUM> obtains spectra A at the respective positions.

Similarly, the control device <NUM> executes control such that an electron beam <NUM> accelerated using the second acceleration voltage is applied from the electron beam source <NUM> to respective positions (positions P1, P2, P3,. Pn (Xm, Xn),. ) on the sample <NUM>, so that the obtaining unit <NUM> obtains spectra B at those positions. That is, while changing a position to which the electron beam <NUM> is applied, the control device <NUM> applies the electron beam <NUM> to the surface of the sample <NUM>, so that the obtaining unit <NUM> obtains spectra B at the respective positions.

With the spectra A, B obtained at the respective positions, the calculation unit <NUM> calculates a spectral ratio A/B, or a ratio in intensity between the spectral A and the spectral B, at each of the positions.

Referring to <FIG> and <FIG>, generation of a spectral map showing spectral ratios A/B will be described. <FIG> and <FIG> illustrate spectral ratios and spectral maps.

<FIG> and <FIG> illustrate spectral ratios A/B at a position Pn (Xm, Yn).

The display processor <NUM> extracts the value of a spectral ratio A/B in an energy ROI from the spectral ratio A/B waveform at the position Pn (Xm, Yn). In the example illustrated in <FIG>, the energy ROI ranges from <NUM> to <NUM> eV, and the display processor <NUM> extracts the value of a spectral ratio A/B in the energy band from <NUM> to <NUM> eV from the spectral ratio A/B waveform. For example, the display processor <NUM> extracts the value of a spectral ratio A/B at the middle position of the energy band from <NUM> to <NUM> eV or the average of the spectral ratios A/B in the energy band from <NUM> to <NUM> eV as the value of a spectral ratio A/B in the energy band from <NUM> to <NUM> eV. The display processor <NUM> similarly extracts the value of a spectral ratio A/B in the energy ROI in the following processing. The display processor <NUM> then maps the extracted value Sn (Xm, Yn) of the spectral ratio A/B onto a point corresponding to the position Pn (Xm, Yn).

The display processor <NUM> extracts the values S1, S2, S3,. , Sn (Xm, Yn). of the spectral ratios A/B in the energy band, or a ROI, ranging from <NUM> to <NUM> eV from the spectral ratio A/B waveforms at respective positions P1, P2, P3,. , Pn (Xm, Yn). , and then maps the extracted values onto points corresponding to the respective positions on the sample <NUM>. With the above, a spectral map showing the spectral ratios A/B in the energy band from <NUM> to <NUM> eV at the respective positions is generated.

The spectral map <NUM> illustrated in <FIG> is a spectral map in the ROI ranging from <NUM> to <NUM> eV.

The display processor <NUM> generates a spectral map while changing the position of the energy ROI. For example, the ROI in <FIG> ranges from <NUM> to <NUM> eV, and the spectral map <NUM> in <FIG> is a spectral map in the ROI ranging from <NUM> to <NUM> eV. That is, the display processor <NUM> extracts values S1, S2, S3,. , Sn (Xm, Yn). of the spectral ratios A/B in the energy band ranging from <NUM> to <NUM> eV at respective positions, and map the extracted values onto points corresponding to the respective positions on the sample <NUM>. With the above, the spectral map <NUM> is generated.

As described above, while changing the position of the energy ROI, the display processor <NUM> generates spectral maps in the respective energy ROIs.

It should be noted that, although the width of the energy ROI in the example illustrated in <FIG> and <FIG> is <NUM> eV, the display processor <NUM> may change the width of the energy ROI, depending on an element contained in the sample <NUM>.

A specific example will now be described. A compound containing a Fe·Si metal, Fe2SiO4, Fe3O4, and Fe2O3 is used as a sample <NUM>. The first acceleration voltage is <NUM> kV, and the second acceleration voltage is <NUM> kV. That is, a spectrum A is obtained using the first acceleration voltage of <NUM> kV, a spectrum B is obtained using the second acceleration voltage of <NUM> kV, and a spectral ratio A/B is then calculated. The range of energy is from <NUM> to <NUM> eV, and the width of an energy ROI is <NUM> eV. Under these conditions, a spectral map is generated. <FIG> illustrates spectral maps relevant to Fe·Si metal and Fe2SiO4, that are generated under these conditions.

The respective spectral maps illustrated in <FIG> are generated based on the ratio spectrum of Fe. Specifically, the calculation unit <NUM> calculates a spectral ratio A/B, that is, a ratio of the spectrum A of Fe, obtained using the first acceleration voltage of <NUM> kV, and a spectrum B of Fe, obtained using the second acceleration voltage of <NUM> kV. The display processor <NUM> extracts the value of a spectral ratio A/B for every energy ROI (<NUM> eV) from a spectral ratio A/B waveform within the range from <NUM> to <NUM> eV, or an energy band of the Lα line and Lβ line of Fe, and maps the extracted values onto points corresponding to the respective positions on the sample <NUM>, to thereby generate spectral maps.

<FIG> illustrates spectral maps at respective positions in areas 300A, 300B of the sample <NUM>.

Specifically, the spectral map 302A shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300A.

The spectral map 302B shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300B.

The spectral map 304A shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300A.

The spectral map 304B shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300B.

The spectral map 306A shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300A.

The spectral map 306B shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300B.

The spectral map 308A shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300A.

The spectral map 308B shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300B.

The spectral map 310A shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300A.

The spectral map 310B shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300B.

The spectral map 312A shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300A.

The spectral map 312B shows spectral ratios A/B in the energy ROI from <NUM> to <NUM> eV at respective positions in the area 300B.

The display processor <NUM> adds a color in accordance with the magnitude of the value of a spectral ratio A/B to a spectral map. For example, colors in the range from red to blue (for example, red, yellow, green, blue, and the like) in accordance with the magnitude of the respective values are added to a spectral map. Specifically, red corresponds to a large value, and blue corresponds to a small value. More specifically, a color in the range from red to blue in accordance with the magnitude of the value is added. That is, the larger the value of the spectral ratio A/B is, a color closer to red is added.

The display processor <NUM> displays the spectral maps 302A to 312A, 302B to 312B on the display <NUM>.

An energy band in which a peak of the spectral ratio A/B is measured is an energy band that contains the value of an energy corresponding to an absorption edge. By referring to a spectral map with spectral ratios A/B mapped thereon, a user can recognize an energy band in which a spectral ratio A/B having a large value or a peak of the spectral ratio A/B is measured. According to this embodiment, it is possible to display an absorption edge, such as is obtained with synchrotron radiation, in the form of a spectral map.

When an energy band (for example, an energy band from <NUM> to <NUM> eV) in which a spectral ratio A/B is measured contains any energy value stored in the storage unit <NUM> (that is, an energy value registered in the database containing energy values corresponding to the absorption edges of respective elements), the display processor <NUM> may define the energy value as an energy ROI, and extract the value of a spectral ratio A/B at the energy value as the value of a spectral ratio A/B in the energy ROI. Then, the display processor <NUM> may map the extracted value of the spectral ratio A/B to thereby generate a spectral map, and display the spectral map on the display <NUM>.

Referring to the database containing the values of energy corresponding to the absorption edges of respective elements, the display processor <NUM> may identify the components of the respective areas in the respective spectral maps 302A to 312A, 302B to 312B.

For example, there is a peak (<NUM>) of the spectral ratio A/B in the energy band from <NUM> to <NUM> eV. This energy band (<NUM> to 709eV) with this peak measured is an energy band that contains the value of energy corresponding to an Fe L absorption edge of an Fe·Si metal. A component having a peak of a spectral ratio A/B in the energy band from <NUM> to 709eV is an Fe·Si metal. The database contains the energy band from <NUM> to 709eV registered therein in advance as an energy band containing the value of energy corresponding to an Fe L absorption edge of Fe·Si. Referring to the database, the display processor <NUM> determines that an area with a peak of a spectral ratio A/B in the energy band from <NUM> to 709e is an area composed of Fe·Si.

Further, there is a peak (<NUM>) of the spectral ratio A/B waveform in the energy band from <NUM> to <NUM> eV. This energy band (<NUM> to <NUM> eV) with this peak measured is an energy band that contains the value of energy corresponding to an Fe L absorption edge of Fe2SiO4. A component having a peak of a spectral ratio A/B in the energy band from <NUM> to <NUM> eV is Fe2SiO4. The database contains the energy band from <NUM> to <NUM> eV registered therein in advance as an energy band containing the value of energy corresponding to an Fe L absorption edge of Fe2SiO4. Referring to the database, the display processor <NUM> determines that an area with a peak of a spectral ratio A/B in the energy band from <NUM> to <NUM> eV is an area composed of Fe2SiO4.

Although Fe·Si and Fe2SiO4 have been described above as an example, this process is similarly applied to Fe203 and Fe304, and an area composed of Fe203 and an area composed of Fe304 are similarly identified. In the above-described manner, an area composed of Fe·Si metal components, an area composed of Fe2SiO4 components, an area composed of Fe2O3, and an area composed of Fe3O4 in the sample <NUM> are identified.

The display processor <NUM> may add colors which differ for each component to areas corresponding to respective components in a spectral map. The, the display processor <NUM> colors respective areas corresponding to Fe·Si metal components, Fe2SiO4 components, Fe2O3 components, and Fe3O4 components in a spectral map with a different color for each component. For example, the display processor <NUM> displays an area corresponding to Fe·Si metal components in red, an area corresponding to Fe2SiO4 components in blue, an area corresponding to Fe2O3 components in yellow, an area corresponding to Fe3O4 in green. Such displaying in a different color for each component allows a user to recognize respective components, based on the difference in color. In another example, that of a spectral map displayed in a gray scale, areas corresponding to respective components may be displayed in gray with different shades corresponding to the respective components.

<FIG> illustrates a spectral ratio A/B for each component of the sample <NUM>. Specifically, <FIG> is a graph showing the values of the spectral ratios A/B of respective components, in which the abscissa represents the energy, and the ordinate represents the spectral ratio.

Specifically, the display processor <NUM> extracts the value of a spectral ratio A/B for each energy at a position in an area made of Fe·Si metal components (for example, any position in the area) of the sample <NUM>, from the spectral ratio A/B calculated by the calculation unit <NUM>, and then plots the extracted value of the spectral ratio A/B for each energy. For example, the display processor <NUM> extracts the value of a spectral ratio A/B for each energy ROI, and plots the extracted values. In an example here, the range of energy is from <NUM> to <NUM> eV, and the width of an energy ROI is <NUM> eV. The display processor <NUM> extracts the value of a spectral ratio A/B for every <NUM> eV within the range from <NUM> to <NUM> eV, and plots the extracted values of the spectral ratios A/B. The waveform <NUM> is obtained with the plotting, and shows change in spectral ratio A/B relative to the energy, with respect to Fe·Si metal.

With respect to each of Fe2SiO4, Fe2O3, and Fe3O4 as well, the value of a spectral ratio A/B for every <NUM> eV is plotted, similar to a Fe·Si metal, to generate a waveform.

The waveform <NUM> shows change in a spectral ratio A/B relative to energy with respect to Fe2O3. The waveform <NUM> shows change in a spectral ratio A/B relative to energy with respect to Fe304. The waveform <NUM> shows change in a spectral ratio A/B relative to energy with respect to Fe2SiO4.

Specifically, the waveform <NUM> is formed by extracting the value of a spectral ratio A/B for every <NUM> eV within the range from <NUM> to <NUM> eV at a position in an area composed of Fe2O3 (for example, any position in the area) and plotting the extracted values. This is similarly applied to the waveforms <NUM>, <NUM>.

Referring to the waveforms <NUM> to <NUM>, it is known that the spectral ratios A/B of metals (for example, Fe·Si metal) are higher than those of oxides (for example, Fe2O3, Fe3O4, Fe2SiO4). That is, the spectral ratio A/B of metals tends to be relatively high, while the spectral ratio A/B of oxides tends to be relatively low.

With respect to Fe·Si metal, Fe2O3, and Fe3O4, the energy at which a peak of the spectral ratio A/B is measured (that is, energy corresponding to an absorption edge) is around <NUM> eV. With respect to Fe2SiO4, the energy at which a peak of the spectral ratio A/B is measured (that is, energy corresponding to an absorption edge) is around <NUM> eV. As described above, by displaying the spectral ratios A/B in a graph, it is possible to distinctly show the difference in energy corresponding to an absorption edge.

Comparison between the waveform <NUM> of Fe2O3 and the waveform <NUM> of Fe3O4 shows that the gradient of the waveform <NUM> of Fe2O3approaching the peak is sharper than that of the waveform <NUM> of Fe3O4. This means that Fe2O3 is affected by absorption to a greater extent than Fe3O4.

As described above, a spectral map according to the embodiment enables observation of a fine absorption structure.

Although 2D spectral map is generated in the above-described embodiment, a spectral ratio A/B at one or more positions may be measured and displayed. Alternatively, a spectral ratio A/B at each position on a straight line or a curved line may be measured and displayed. Use of a point analysis or a line analysis can shorten a time necessary for analysis.

Although a sample <NUM> containing Fe is described in the above embodiment, a sample <NUM> containing an element other than Fe, such as Ni, Mn, Co, or the like, may be used for measurement. For example, valence modification of Ni, Mn, or Co due to charging and discharging may be observed, Ni, Mn, and Co being used for a positive electrode of a battery. An oxidation state of steels or non-ferrous materials may be observed.

Referring to <FIG>, a result of measurement of a sample <NUM> containing manganese (Mn) will be described. <FIG> illustrate waveforms representing the spectral ratio A/B of Mn, in which the abscissa indicates the energy, and the ordinate indicates the spectral ratio.

In an example here, the first acceleration voltage, or a low acceleration voltage, is <NUM> kV, and the second acceleration voltage, or a high acceleration voltage, is <NUM> kV. A spectrum A is obtained using the first acceleration voltage of <NUM> kV, and a spectrum B is obtained using the second acceleration voltage of <NUM> kV. A spectral ratio A/B, that is, a ratio in intensity between the spectrum A and the spectrum B, is calculated, and a waveform representing the spectral ratio A/B is generated. The spectral ratio assigned to the ordinate corresponds to the spectral ratio A/B. A spectral ratio A/B in the energy band from <NUM> to <NUM> eV is generated here. It should be noted that the combination of a low acceleration voltage and a high acceleration voltage is not limited to <NUM> kV/<NUM> kV, and may be arbitrarily changed depending on the kind of a sample to use or a depth in a sample (a depth from the surface of the sample) at which information (X-ray) is detected.

<FIG> illustrates a spectral ratio waveform of an Mn simple substance. The energy corresponding to a peak of the spectral ratio A/B waveform is an energy reflecting an absorption edge, and the value of the energy is <NUM> eV or <NUM> eV, for example.

<FIG> illustrates a spectral ratio waveform of MnO2. The value of energy corresponding to a peak of the waveform is <NUM> eV.

<FIG> illustrates a spectral ratio waveform of Mn2SiO4. The value of energy corresponding to a peak of the waveform is <NUM> eV or <NUM> eV.

<FIG> illustrates a spectral ratio waveform of MnCO3. The value of energy value corresponding to a peak of the waveform is <NUM> eV.

<FIG> illustrates a spectral ratio waveform of (MnCa)3SiO9. The value of energy corresponding to a peak of the waveform is <NUM> eV.

<FIG> illustrates a spectral ratio waveform of (MnFe)2O3. The value of energy corresponding to a peak of the waveform is <NUM> eV or <NUM> eV.

An electron beam <NUM> accelerated using an acceleration voltage of <NUM> kV and an electron beam <NUM> accelerated using an acceleration voltage of <NUM> kV are separately applied to each of the positions on the sample <NUM>, and a spectral ratio A/B in each of the positions on the sample <NUM> is calculated. Thereafter, as described referring to <FIG> and <FIG>, the value of a spectral ratio A/B is extracted for each energy ROI from each of the spectral ratio waveforms. The extracted values of the spectral ratios A/B are mapped onto points corresponding to the respective positions on the sample <NUM>. With the above, spectral maps showing spectral ratios A/B, similar to the spectral maps illustrated in <FIG>, are generated.

The energy band that contains the value of energy corresponding to a peak of the spectral ratio A/B will differ according to the composition of the sample <NUM>. For example, for a sample <NUM> containing Fe, an energy band containing the value of energy corresponding to a peak of the spectral ratio A/B is within the range from <NUM> to 740eV, as illustrated in <FIG> and <FIG>. For a sample <NUM> containing Mn, an energy band containing the value of energy corresponding to a peak of the spectral ratio A/B is in the range of <NUM> to 680eV is, as illustrated in <FIG>. Because the energy band containing the value of energy corresponding to a peak of the spectral ratio A/B differs between Fe and Mn as described above, the calculation unit <NUM> may calculate a spectral ratio A/B, while changing the energy band, depending on an element. Specifically, the calculation unit <NUM> calculates a spectral ratio A/B in the range from <NUM> to <NUM> eV with respect to a sample <NUM> containing Fe components, and the range from <NUM> to <NUM> eV with respect to a sample <NUM> containing Mn components.

In the above-described embodiment, it is possible to conduct wide-range observation of a 2D spatial distribution of an absorption edge structure of a sample using the scanning electron microscope <NUM>, and without using a device employing a transmission electron microscope (TEM) or synchrotron radiation.

Because a TEM is not used, it is possible, for example, to conduct a wide-range observation of an absorption edge structure of a bulk sample. For example, it is possible to observe a 2D spatial distribution of an absorption edge structure of a bulk sample having a face size of up to <NUM> x <NUM>. Further, as it is not necessary to employ a thing sample, an operator need not labor to thin out a sample. Further, unlike a device using synchrotron radiation, it is possible to conduct a wide-range observation of a 2D spatial distribution of an absorption edge structure of a sample without using a large device.

Claim 1:
A scanning electron microscope (<NUM>), comprising:
an obtaining unit (<NUM>) configured to apply individual electron beams to an area on a sample (<NUM>) using two different acceleration voltages, to obtain a spectrum of a soft X-ray in the area on the sample (<NUM>) for each of the acceleration voltages;
a calculation unit (<NUM>) configured to calculate a spectral ratio of the spectra obtained through application of the electron beams of the two different acceleration voltages; and
a display processor (<NUM>) configured to extract a ratio in an energy region of interest corresponding to energy at an absorption edge of each element from the spectral ratio calculated, characterized in that the display processor is further configured to display the ratio extracted as a spectral map on a display unit (<NUM>).