JP4372339B2 - Irregular image forming apparatus and electron beam analyzer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam analyzer that creates a quantitative concavo-convex image of a minute region, and performs line analysis and mapping analysis.
[0002]
[Prior art]
Electron beam analyzers such as electron microanalyzer (EPMA) and scanning electron microscope (SEM) using EDX (energy dispersive X-ray spectroscopy) and WDX (wavelength dispersive X-ray spectroscopy) irradiate a sample with an electron beam. Then, the surface analysis of the sample is performed by detecting the secondary electron beam, the reflected electron beam, the X-ray and the like emitted thereby. In such an electron beam analyzer, the shape and composition distribution are obtained by scanning the electron beam with which the sample is irradiated to obtain a secondary electron beam image, reflected electron beam image, X-ray image line analysis image and mapping image. be able to.
[0003]
When performing line analysis or mapping analysis with an electron beam analyzer, it is necessary to control the height of the sample surface at each analysis position in order to accurately perform point analysis, line analysis, and mapping analysis on an uneven sample surface. is there. For example, WDX is known that applies automatic height correction that always corrects the height of the sample stage so that the height of the sample surface satisfies the light collection conditions of the spectrometer.
[0004]
Conventionally, the height of the sample surface is obtained in advance using a height detector, the sample surface is approximated based on this height information, and the height position of the sample stage is adjusted based on the approximated data. From this, the height of the analysis point is obtained, and thereby the height of the sample stage is corrected. In a scanning electron microscope (SEM), a device that also serves as a secondary electron detector for measurement is known as a device for obtaining a three-dimensional image of a sample surface.
[0005]
[Problems to be solved by the invention]
Since the device using the secondary electron detector provided in the scanning electron microscope is not originally intended to determine the quantitative height of the sample surface, it also serves as a secondary electron detector for measurement. It is composed. The apparatus for obtaining the height of the sample using the secondary electron signal has a problem that the directivity of the secondary electron signal is low, so that the surface direction of the sample surface is not suitable for quantitative calculation. In addition, the secondary electron signal includes a large amount of edge effect, and the amount of the edge effect greatly depends on the composition of the sample, so that there is a problem that accurate height information is difficult to obtain.
[0006]
Further, the conventionally known height detector has a problem that it is difficult to accurately and easily obtain a complicated uneven surface.
Further, in the method of correcting the height control using an optical image, it is difficult to obtain a focal position with high accuracy when the brightness of the sample surface is low, and thus it is not possible to perform a good correction. There is.
Therefore, the concavo-convex image obtained with the conventional apparatus is qualitative, and there is a problem that it is difficult to obtain good height information. Such height adjustment using such a qualitative concavo-convex image makes accurate height correction. There is a problem that it is difficult to obtain.
[0007]
Therefore, the present invention aims to solve the above-described conventional problems and to provide a concavo-convex image creating apparatus for obtaining a quantitative concavo-convex image, and to perform accurate height correction by a quantitative concavo-convex image. An object is to provide an apparatus.
[0008]
[Means for Solving the Problems]
The present invention obtains a local normal vector on the sample surface by using highly directional reflected electrons, and generates a quantitative uneven image on the sample surface based on the normal vector and the height data of the reference position. The height correction is performed accurately using the quantitative uneven image created and obtained. By using reflected electrons with high directivity, a highly accurate quantitative uneven image can be obtained.
[0009]
FIG. 1 is a diagram for explaining the creation of a concavo-convex image according to the present invention. In FIG. 1A, when a point P on the sample S is irradiated with an electron beam e, electrons reflected at the point P are detected as a reflected electron beam. The reflected electron beam vector β indicates the traveling direction of the reflected electrons, and the reflected electron beam β is reflected in a direction symmetric with the electron beam e with the normal vector α as the symmetry position axis. Since the normal vector α represents the inclination of the sample surface, if the incident direction is known to the electron beam e, the normal vector α is obtained from the reflected electron beam vector β, and the normal vector α at the point P is obtained. The inclination of the sample surface can be obtained.
[0010]
As shown in FIG. 1B, the surface roughness of the sample S can be obtained by obtaining the normal vector α at each point on the sample surface. In addition, by obtaining the three-dimensional coordinates of the reference point on the sample surface, the inclination of the entire sample can be corrected and the height from the reference position can be obtained to obtain an uneven image on the sample surface.
[0011]
As a concavo-convex image apparatus using the reflected electron beam of the present invention, a plurality of reflected electron detectors, means for obtaining a normal vector on the sample surface from the intensity distribution of the reflected electron signal obtained from the reflected electron detector, and the sample surface The apparatus includes a means for obtaining the height at the upper reference point and a means for obtaining a quantitative uneven image on the sample surface.
[0012]
The concavo-convex image creating apparatus of the present invention creates a concavo-convex image of the sample surface according to the flowchart of FIG. A reflected electron beam is detected by a plurality of reflected electron detectors, a normal vector of each point on the sample surface is obtained from the intensity distribution of the reflected electron beam (step S1), and an optical function having a focusing function such as an optical microscope is provided. The height at the reference point on the sample surface is obtained by the focal position detection device (step S2).
[0013]
The height of the neighboring point is obtained by using the inclination information at the point obtained from the normal vector at the point. The heights of other neighboring points are obtained using the heights at the obtained neighboring points and the normal vectors at the neighboring points. By repeating this operation sequentially, the uneven shape of the sample surface is obtained (step S3). From the height at the reference point on the sample surface, the height from the reference position on the sample surface and the inclination of the entire sample are obtained, and a quantitative uneven image on the sample surface is obtained in combination with the uneven shape obtained in step S3 (step S4).
[0014]
In addition, the electron beam analyzer of the present invention obtains the height data of the sample surface from the quantitative uneven image obtained by the uneven image creating apparatus of the present invention, and controls the height direction of the sample stage using the height data. Then, accurate height correction is performed by aligning the sample surface with the analysis position. According to the electron beam analyzer of the present invention, for a sample having an uneven surface, mapping distribution is performed while controlling the sample stage in a WDX (wavelength dispersive X-ray spectrometer) or the like and automatically correcting the distribution position. Can do.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 is a diagram for explaining the concavo-convex image creating apparatus of the present invention. FIG. 3 shows a case where X-rays are detected in the electron beam analyzer.
In the electron beam analyzer 1, an electron beam e generated from an electron gun 8 such as a filament passes through a condenser lens, an objective lens (not shown) and a backscattered electron detector 2 a and is disposed on the sample stage 9. The sample is irradiated. The reflected electrons reflected from the sample surface are detected by the reflected electron detector 2a, and the X-rays emitted from the sample are detected by the X-ray spectrometer 7. The backscattered electrons are used to determine the uneven shape of the sample surface, and the X-rays are used for sample analysis. Note that the sample analysis is not limited to X-rays, and other signals may be detected and performed.
[0016]
The sample stage 9 is driven in the Z-axis direction and the X and Y-axis directions by the sample stage drive control means 6. The sample stage drive control means 6 can perform height adjustment in the Z axis direction and positioning in the X and Y axis directions by a control command from a computer (not shown).
The electron beam analyzer 1 includes a normal vector forming unit 2, a reference height forming unit 3, and a concavo-convex image forming unit 4 as a configuration for creating the concavo-convex image.
[0017]
The normal vector forming unit 2 includes a backscattered electron detector 2a having a plurality of detection surfaces and a normal vector calculating unit 2b. The reflected electron detector 2a calculates the intensity distribution of the reflected electrons, and the normal vector calculation means 2b calculates a reflected electron beam vector β indicating the traveling direction of the reflected electrons from the intensity distribution of the reflected electrons, and from the reflected electron beam vector β. A normal vector α is calculated.
The reference height forming means 3 obtains the height at the reference point of the sample surface, images the sample surface with an optical observation means 3a such as an optical microscope equipped with an imaging device such as a CCD camera, and calculates the height. In 3b, the height of the sample surface is obtained. The height calculation means 3b has a focusing signal detection forming function for detecting an optical focus position by an autofocus function, and a Z-axis feedback control signal forming function. The focus signal detection forming function forms a focus signal used for focusing from the optical image signal picked up by the optical observation means 3a, and the Z-axis feedback control signal forming function uses the focus signal to generate a Z-axis feedback control signal. Is fed back to the sample stage drive control means 6, and the sample stage 9 is controlled in the Z-axis direction to focus the image and acquire the height data of the sample.
[0018]
Usually, the height calculation means 3b having an optical focus position detection function sets the focus position on the sample and the analysis position satisfying the light collection condition on the sample of the X-ray spectrometer to match the optical image. The focusing condition of the X-ray spectrometer is adjusted by focusing.
The height data acquired by the Z-axis feedback control signal forming function is converted into Z-axis coordinates and stored in the reference position data storage unit 3c together with the X-axis coordinate values and the Y-axis coordinate values.
[0019]
The uneven image forming means 4 includes an uneven shape calculating means 4a and an uneven image creating means 4b. The concavo-convex shape calculating means 4a calculates the concavo-convex shape of the sample surface based on the normal vector α obtained by the normal vector calculating means 2b. In the calculation of the concavo-convex shape, at a certain point, inclination information at the point is obtained from the normal vector, and the height of the neighboring point is obtained using the inclination. Further heights of other neighboring points are obtained using the obtained heights of neighboring points and normal vectors at the neighboring points. By repeating this operation sequentially, the uneven shape of the sample surface is obtained.
[0020]
The concavo-convex image creating unit 4b creates a concavo-convex image from the concavo-convex shape calculated by the concavo-convex shape calculating unit 4a and the reference position data stored in the reference position data storage unit 3c. The concavo-convex image creating means 4b obtains the height of the sample surface from the reference position and the inclination of the entire sample from the reference position data, and obtains a quantitative concavo-convex image of the sample surface in combination with the concavo-convex shape.
The formed concavo-convex image is fed back to the sample stage drive control means 6 and used for correction of the height control of the sample stage. Further, the concavo-convex image is sent to the image data storage / display means 5 and stored in the concavo-convex image or displayed by an arbitrary display means.
[0021]
FIG. 4 is a flowchart for explaining a procedure for creating a concavo-convex image according to the present invention, and FIG. 5 is a schematic diagram for explaining detection of reflected electrons.
First, the sample stage is moved in the x and y directions by the sample stage drive control means 6 to determine the position where the electron beam e is irradiated on the sample surface. A point P in FIG. 5A indicates an irradiation position of the electron beam e (step S11). The irradiated electron beam e is reflected at the point P, and proceeds in the direction of the reflected electron beam vector β according to the surface inclination of the point P. The reflected electron beam vector β is determined by the incident direction of the electron beam e at the point P and the normal vector α. In general, reflected electrons have strong directivity. The shaded area in FIG. 5A shows the directivity characteristic of the reflected electrons, and the reflected electron beam vector β comprehensively shows the directivity characteristics.
[0022]
The backscattered electron detector 2a includes a plurality of detection surfaces. FIG. 5B is a configuration example of the backscattered electron detector 2a, and shows an example provided with four detection surfaces A1 to A4. The detection surfaces A1 to A4 are respectively arranged in the x-axis or y-axis direction, pass the electron beam e through the opening formed in the center, receive the reflected electrons reflected from the sample surface, and detect corresponding to the light receiving area. The intensity is output (step S12).
[0023]
A reflected electron beam vector β is obtained from the detected intensity detected by the reflected electron detector 2a. FIG. 6 is a diagram for explaining a detection state of reflected electrons by the reflected electron detector. FIG. 6A shows the received light distribution R of the reflected electrons on the detection surface of the reflected electron detector 2a. As shown in the perspective view of FIG. 6B and the plan view of FIG. 6C, the position of the received light distribution R of the reflected electrons on the detection surface corresponds to the reflected electron beam vector β. The x component and y component of the reflected electron beam vector β can be obtained from the center position of the light reception distribution R. The center position of the received light distribution R of the reflected electrons can be obtained from the area of the reflected electrons irradiated on the detectors A1 to A4. The irradiation area of the reflected electrons is determined by the divided detectors A1 to A4. It can be calculated from the detected intensity. In the configuration of the detection surface shown in FIG. 5B, it can be assumed that the irradiation area and the detection intensity are in a substantially proportional relationship.
[0024]
Therefore, the x component Ix and the y component Iy of the reflected electron beam vector β can be obtained from the detection intensities of the detectors A1 to A4. If the reflected electron beam vector β is a unit vector, the z component Iz can be obtained from the x component Ix and the y component Iy.
[0025]
The backscattered electron detector is not limited to the configuration shown in FIG. FIG. 7 shows another configuration example of the backscattered electron detector. The second configuration example shown in FIG. 7A is a configuration example in which the second configuration example is radially divided into four similarly to the first configuration example shown in FIG. 5B, but the detection positions B1 to B4 are made different in arrangement position. Are arranged in the first quadrant to the fourth quadrant, respectively. The second and third configuration examples shown in FIGS. 7B and 7C are examples of detection surfaces C1 to C3 radially divided into three and examples of detection surfaces D1 to D8 radially divided into eight. Moreover, the 4th structural example shown in FIG.7 (d) is an example of the detection surfaces E1-E12 divided | segmented radially and concentrically.
The calculation of the reflected electron beam vector β when using each reflected electron detector is performed corresponding to the configuration of each detection surface (step S13).
[0026]
While shifting the irradiation position of the electron beam e on the sample surface, Steps S11 to S12 are repeated for all the measurement points in the measurement region of the sample to obtain the reflected electron beam vector β at all the measurement points (Step S14).
A normal vector α at each measurement point on the sample surface is obtained from the obtained reflected electron beam vector β. Since the reflected electron beam vector β is geometrically symmetric with the incident direction of the electron beam e with respect to the normal vector α, the normal vector α is the incident direction of the reflected electron beam vector β and the electron beam e (usually a sample). (The direction is perpendicular to the coordinate system on the stage) and can be calculated geometrically (step S15).
[0027]
Next, the concavo-convex shape of the sample surface is obtained using the normal vector α. The calculation of the concavo-convex shape can be performed by repeating an operation for calculating the height of a nearby point from the normal vector α of a certain point while shifting the point as in the following calculation example. FIG. 8 is a diagram for explaining the calculation of the concavo-convex shape and the concavo-convex image.
[0028]
In FIG. 8A, a normal vector at a certain point P1 is α1, a normal vector at a nearby point P2 is α2, and a lateral distance between the points P1 and P2 is ΔL. At this time, since the inclined surface at the point P1 (broken line in the cross section of FIG. 8A) and the normal vector α1 are perpendicular to each other, the height difference Δh between the point P1 and the neighboring point P2 is the normal line. It can be calculated using the vector α and the distance ΔL. FIG. 8B shows a case where a normal vector α on one line (indicated by a broken line in the figure) of the sample surface is used, and the height on the line can be obtained by the above calculation. The uneven shape of the cross section can be obtained. By repeating the same calculation two-dimensionally on the sample surface, a three-dimensional uneven shape on the sample surface can be obtained (step S16).
[0029]
The concavo-convex shape obtained in step S16 uses the height of an arbitrary point as a reference in the z-axis direction, and the relationship with the coordinate system on the sample stage is not defined. Further, the entire sample may be inclined with respect to the sample stage. For this reason, in order to obtain a concavo-convex image on the sample surface, it is necessary to relate it to the coordinate system on the sample stage.
Accordingly, the height at the reference point on the sample surface is obtained by the reference height detection means 3 (step S17), the inclination of the entire sample is obtained from the height data, and the height at the reference point is determined, thereby providing the unevenness. A quantitative uneven image can be obtained by adding height data to the shape. FIG. 8C is an example of the concavo-convex image obtained for one cross section in FIG. 8B. Using the heights WD1 and WD2 of the reference points at both ends, the inclination is obtained and height data is added to each point. Thus, an uneven image is obtained (step S18).
[0030]
According to the embodiment of the present invention, since a quantitative unevenness image can be obtained, the height of the sample stage can be continuously controlled, and WDX analysis can be automatically performed on a sample with unevenness. it can.
[0031]
【The invention's effect】
As described above, according to the concavo-convex image creating apparatus of the present invention, a quantitative concavo-convex image can be obtained, and according to the electron beam analyzer equipped with the concavo-convex image creating apparatus of the present invention, a quantitative concavo-convex image is obtained. Accurate height correction can be performed.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram for explaining creation of a concavo-convex image according to the present invention.
FIG. 2 is a flowchart for explaining a procedure for creating an uneven image on a sample surface.
FIG. 3 is a diagram for explaining a concavo-convex image creating apparatus according to the present invention.
FIG. 4 is a flowchart for explaining a procedure for creating a concavo-convex image according to the present invention.
FIG. 5 is a schematic view for explaining detection of reflected electrons.
FIG. 6 is a diagram illustrating a detection state of reflected electrons by a reflected electron detector.
FIG. 7 is another configuration example of the backscattered electron detector.
FIG. 8 is a diagram for explaining calculation of an uneven shape and an uneven image.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electron beam analyzer, 2 ... Normal vector formation means, 2a ... Backscattered electron detector, 2b ... Normal vector calculation means, 3 ... Reference height detection means, 3a ... Optical observation system, 3b ... Height calculation means 3c, reference position data storage means, 4 ... concavo-convex image formation means, 4a ... concavo-convex shape calculation means, 4b ... concavo-convex image creation means, 5 ... analysis data storage means, 6 ... sample stage drive control means, 7 ... X-ray spectroscopy 8: electron gun, α: normal vector, β: reflected electron vector, e: electron beam.

Claims (2)

One backscattered electron detector with a detection surface divided into a plurality ;
Means for obtaining a normal vector on the sample surface from the detection intensity of the reflected electron signal obtained from the plurality of detection surfaces ;
A means for determining a height at the reference point , using a point determined arbitrarily on the sample surface as a reference point ;
A means for obtaining a quantitative uneven image of the sample surface,
The means for obtaining the normal vector obtains the irradiation area where the reflected electron beam irradiates each detection surface from the detection intensity of each detection surface, and receives the reflected electrons received by the reflected electron detector from the irradiation area of each detection surface. Obtain the center position of the distribution, obtain the reflected electron beam vector from the center position, obtain the normal vector on the sample surface from the reflected electron beam vector and the incident direction of the electron beam,
The means for obtaining the quantitative unevenness image is to obtain a quantitative unevenness image of the sample surface based on the unevenness shape of the sample surface sequentially obtained by the normal vector at each point on the sample surface and the height at the reference point. A concavo-convex image forming apparatus. Obtaining the height data of the sample surface from the quantitative uneven image obtained by the uneven image forming apparatus, and controlling the height direction of the sample stage using the height data to align the sample surface with the analysis position. The electron beam analyzer according to claim 1, wherein:

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