JP5070074B2 - Scanning electron microscope - Google Patents

Description

  The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope equipped with a three-dimensional shape measuring apparatus.

  One of the electron microscopes is a scanning electron microscope (hereinafter referred to as SEM) and an energy dispersive X-ray analyzer (hereinafter referred to as EDX) that processes a signal from a semiconductor X-ray detector attached to the SEM. There is a combination of. This EDX is a device that performs elemental analysis of a micro area of several μm, and performs qualitative analysis, quantitative analysis, element distribution analysis by X-ray image, etc. at the same time as image observation by SEM It is.

  The SEM can measure not only a two-dimensional shape but also a three-dimensional shape. As an example of a three-dimensional shape measurement method, as in Patent Document 1, a backscattered electron detector arranged in an annular shape facing a sample is equally divided radially, and directivity from detection elements provided in each is obtained. There is a three-dimensional shape measuring apparatus for measuring the surface shape of a sample using a difference between detected signals.

JP-A-6-236746

  In recent years, the size of a sample that can be observed and analyzed has been increasing with the spread of low vacuum type SEM, the increase in the size of a sample chamber, and the increase in the motor drive of a sample fine movement device. For this reason, only the portion of the sample that is to be observed and analyzed is cut and miniaturized, the sample is embedded in a resin embedding and the observation surface is flattened, or in the case of a non-conductive sample, such as coating with a metal film. It is becoming mainstream to carry out observation and analysis by mounting the sample itself on a sample fine movement apparatus without performing processing. Therefore, it is not uncommon to have a sample with large irregularities on the sample surface.

  However, when observing and analyzing a sample with large irregularities on the sample surface by SEM, for example, in quantitative analysis using EDX, the X-ray extraction angle with respect to the sample and the interaxial distance between the sample and the X-ray detector However, if the X-ray generated from the analysis position is completely or partially blocked by the unevenness of the sample, there is a problem that a correct quantitative analysis result cannot be obtained.

  Therefore, the present invention provides an SEM that solves the above-described problems and can obtain a highly accurate result in observation and analysis of a sample without specialized knowledge and ability.

  In order to solve the above problems, the SEM according to the present invention can operate a total of five axes in the horizontal direction, the rotational direction, the tilt direction, and the vertical direction with a motor drive or the like, and can grasp the position information of the sample. It has a fine movement device and a three-dimensional shape measuring device. Thus, by acquiring the three-dimensional shape of the sample and controlling the sample fine movement device according to the shape of the sample, it is possible to provide an optimum observation and analysis environment according to the purpose.

  According to the present invention, an SEM capable of reducing the complicated operation of observation and analysis depending on the form of the sample and obtaining a highly accurate result in the observation and analysis of the sample without specialized knowledge and ability is provided. Will be able to.

  The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described in detail below with reference to the drawings.

<First Embodiment>
A first embodiment according to the present invention will be described in detail with reference to FIG.

  FIG. 1 is a schematic diagram of an SEM according to the first embodiment.

  The SEM 1 of the first embodiment includes an electron source 2, a condenser lens 4 that converges the electron beam 3 emitted from the electron source, a deflection coil 5 that scans the electron beam 3, and an object that focuses the electron beam 3. An electron optical system 7 including a lens 6; a control device that adjusts each condition of the electron optical system; and a secondary electron detector 9 that detects electrons emitted from the sample 8 when the sample 8 is irradiated with the electron beam 3. A control device for processing signals from the detector, a reflected electron detector 10 for detecting backscattered electrons, a control device for processing signals from the detector to perform three-dimensional shape measurement processing, two horizontal axes, A total of five axes in the rotation direction, tilt direction, and vertical direction can be operated by a motor drive or the like, and a sample fine movement device 11 that can grasp the position information of the sample is provided. Is constituted by through a pipe 13 vacuum pump 14 is connected to the sample chamber 12, etc., X-rays detector 15 EDX is combined thereto.

  When performing analysis, particularly quantitative analysis, in the SEM 1 equipped with EDX, as shown in FIG. 2, the X-ray extraction angle 17 with respect to the sample 8 and the axial distance 18 between the sample 8 and the X-ray detector 15 are kept constant. If you ask, you can't do an accurate analysis. In general, since the X-ray detector 15 of EDX is fixed in advance in the sample chamber 12, the measurer can set the distance in the vertical direction of the sample surface at the analysis position to a certain distance (hereinafter referred to as analysis distance). Thus, it was necessary to adjust the vertical direction of the sample fine movement device 11.

  Therefore, the three-dimensional shape measurement of the sample 8 is performed using the three-dimensional shape measurement apparatus provided in the SEM 1 before performing the analysis. In the present embodiment, the backscattered electron detector 10 that faces the sample 8 and is arranged in an annular shape is radially divided into four, and the backscattered electrons generated from the sample 8 by the scanning of the electron beam 3 are detected from the detection elements provided in each. Three-dimensional shape measurement is performed by a method of measuring the surface shape of a sample using a difference between detection signals having directivity. From the sample height at the analysis position obtained from the height information at each pixel obtained by the three-dimensional shape measurement and the position information in the vertical direction of the sample fine movement device 11 capable of grasping the position information of the sample, the sample surface at the analysis position is vertical. The distance in the direction is calculated, and the vertical direction of the sample fine movement device 11 is automatically adjusted so that it matches the analysis distance.

  Accordingly, the measurer can automate the adjustment of the analysis distance in the analysis of the sample 8 having a large unevenness on the sample surface, can provide a constant analysis distance regardless of the analysis position, and the analysis is complicated. Operation can be reduced. Further, it is possible to prevent a failure in quantitative analysis due to an unadjusted analysis distance.

  Further, the SEM 1 equipped with the sample fine movement device 11 that can operate a total of five axes in the horizontal direction, the rotation direction, the inclination direction, and the vertical direction with a motor drive or the like and can grasp the position information of the sample is the sample fine movement device. As a control parameter of the movable range 11, the sample size (type) and the sample height of the sample 8 are input in advance, so that the sample 8, the objective lens 6, the secondary electron detector 9, the inner wall of the sample chamber 12, etc. The movable range of the sample fine movement device 11 is controlled so as not to come into contact, and the operation of the measurer is assisted. However, if the measurer forgets to input the sample size (type) and the sample height of the sample 8 or inputs an incorrect value, the sample 8 and the objective lens 6, the secondary electron detector 9, the inner wall of the sample chamber 12, etc. May come into contact with the product and damage it. Therefore, in the above-described example, the height information at each pixel is used for automatic adjustment of the analysis distance. By automatically inputting as a control parameter of the movable range of the apparatus 11, an input error by the measurer is eliminated, and there is no possibility of contact between the sample 8 and the objective lens 6, the secondary electron detector 9, the inner wall of the sample chamber 12, and the like. An SEM 1 that can be operated can be provided.

<Second Embodiment>
An example of reducing the complicated operation of observation and analysis according to the form of the sample by combining the height information in each pixel obtained by the three-dimensional shape measurement and the sample fine movement device 11 capable of grasping the position information of the sample is the first example. It is not limited to the embodiment. A second embodiment according to the present invention will be described in detail with reference to FIGS.

  FIG. 2 is a schematic diagram of the X-ray detection range.

  Of the X-rays 16 generated from the sample 8 by the irradiation of the electron beam 3, the range of X-rays taken into the X-ray detector 15 is the size (d) of the detection window of the X-ray detector 15 and the distance 18 between the axes. From (L), the X-ray take-out angle 17 is set as the center and the X-ray take-in angle 19 (2α) is within the range.

  When the surface of the sample 8 is flat, all the X-rays 16 generated within the range of the X-ray capturing angle 19 generated from the sample 8 are captured by the X-ray detector 15.

  However, in the case of the sample 8 having large irregularities on the sample surface, the sample 8 may overlap within the range of the X-ray capturing angle 19 as shown in FIG. In such a case, the X-ray 16 generated from the sample 8 is not sufficiently taken into the X-ray detector 15, so that it takes time for the analysis or a correct analysis result cannot be obtained.

  Therefore, an example of a method for determining whether a correct analysis result can be obtained will be described with reference to the flowchart of FIG.

  When the measurer designates an arbitrary analysis position (S41), the sample fine movement device 11 moves the sample 8 to the designated analysis position (S43). Next, as in the first embodiment, the three-dimensional shape measurement apparatus provided in the SEM 1 is used to perform the three-dimensional shape measurement of the sample 8 before the analysis, and each pixel obtained by the three-dimensional shape measurement is measured. The height information is stored (S43). Then, the sample height of the sample 8 at the ΔY position from the analysis position to the X-ray detector 15 is compared with the height ΔZ of the lower limit of the X-ray capturing angle (S44). The sample depth direction (X direction in FIG. 2) of the ΔY position for comparing the sample height of the sample 8 at the ΔY position with the height ΔZ of the lower limit of the X-ray capture angle is an X-ray detector centering on the analysis position. The range is ± 1/2 of the size (d) of 15 detection windows. The formula for calculating ΔZ is shown below.

試料８の試料高さ≦ΔＺの場合（Ｓ４４の“Ｙｅｓ”）、試料８により、Ｘ線取り込み可能角１９の範囲内にあるＸ線１６が遮断されることはないため、分析可能と判断する（Ｓ４５）。

When the sample height of the sample 8 ≦ ΔZ (“Yes” in S44), since the sample 8 does not block the X-ray 16 within the range of the X-ray capturing angle 19, it is determined that analysis is possible. (S45).

  When the sample height of the sample 8 is greater than ΔZ (“No” in S44), the X-ray 16 within the range of the X-ray capturing angle 19 is blocked by the sample 8, and therefore it is determined that analysis is impossible (S45). ).

このとき、θ_n≦９０°−ＴＯＡ−αであれば、試料８により、Ｘ線取り込み可能角１９の範囲内にあるＸ線１６が遮断されることはないため、分析可能と判断する。θ_n＞９０°−ＴＯＡ−αであれば、試料８により、Ｘ線取り込み可能角１９の範囲内にあるＸ線１６が遮断されるため、分析不可能と判断することも可能である。 Further, in the direction from the analysis position of the sample selected by the measurer to the X-ray detection unit (that is, the Ymax direction in FIG. 2), the position where the height of the sample reaches the maximum value and the Ymax direction distance to the analysis position are expressed as ΔY. _{Let n} . When the height of the maximum sample mentioned above is H _n ,

At this time, if θ _n ≦ 90 ° −TOA−α, the X-ray 16 within the range of the X-ray capturing angle 19 is not blocked by the sample 8, and therefore it is determined that analysis is possible. If θ _n > 90 ° −TOA−α, the X-ray 16 within the range of the X-ray capturing angle 19 is blocked by the sample 8, so that it can be determined that analysis is impossible.

  As a result, it is possible to determine whether or not a correct analysis result can be obtained at the designated analysis position, and the quantitative analysis failure due to the X-rays 16 generated from the sample 8 being blocked by the unevenness of the sample 8. Can be prevented.

In the above-described example, it is determined only whether the analysis is possible or not. However, the sample height of the sample 8 at the ΔY position and the height ΔZ that is the lower limit of the X-ray capturing angle in the range of 360 ° around the analysis position. Even if it is determined that the analysis is impossible in the above example, if the sample height of the sample 8 ≦ ΔZ exists in the range of 360 ° around the analysis position, the sample of the sample 8 Analysis can be performed by rotating the sample 8 in a range of height ≦ ΔZ. The sample 8 can be automatically rotated by using the sample fine movement device 11 that can grasp the position information of the sample. At this time, a function of rotating the scanning direction of the electron beam 3 and rotating the direction of the display image may be used in combination so that the direction of the observation field of view is not changed by automatic adjustment of the rotation direction of the sample fine movement device 11 or the like. This method can also be determined at the angle θ _n described above.

<Third Embodiment>
In the first and second embodiments, the sample height of the sample is obtained from the height information at each pixel obtained by the three-dimensional shape measurement, but the SEM automatic focus correction function (hereinafter referred to as autofocus) is used. In this way, the sample height of the sample can be obtained.

  An example of a method for acquiring height information in each pixel using autofocus will be described with reference to the flowchart of FIG.

  The sample 8 is set in the sample fine movement device 11, and the sample fine movement device 11 is set in the sample chamber 12 at a position where the sample 8 and the sample fine movement device 11 do not contact the sample chamber 12, the objective lens 6, the secondary electron detector 9 and the like. (S51). After evacuating the sample chamber 12, the electron beam is irradiated (S52), the electron beam 3 is scanned to scan the entire sample (S53), and information on the height direction of each pixel is acquired using autofocus. The position and height of the sample 8 are stored in the SEM control device (S56). At this time, when the entire sample cannot be scanned only by scanning with the electron beam 3 (“No” in S53), the sample 8 is moved by the sample fine movement device 11 to scan the whole (S54), and a plurality of scans are connected. Thus, information on the entire sample is stored (S55).

  The acquisition of the height information at each pixel using autofocus uses the electron beam 3 used when observing the SEM image, so the configuration of the existing SEM 1 is not changed, and the SEM of the present embodiment is provided. Is possible.

  Needless to say, the present invention can be applied not only to SEMs including SEMs and EDXs, but also to SEMs including wavelength dispersive X-ray analyzers and similar devices.

It is the schematic of SEM of 1st Embodiment. It is the schematic about the detection range of a X-ray. It is the schematic about the case where the sample has overlapped on the detection range of X-rays. It is the flowchart which illustrated the procedure of the method of determining whether the correct analysis result in 2nd Embodiment is obtained. 10 is a flowchart illustrating a procedure of a method for acquiring height information in each pixel using autofocus according to the third embodiment.

Explanation of symbols

1 Scanning electron microscope (SEM)
2 Electron source 3 Electron beam 4 Condenser lens 5 Deflection coil 6 Objective lens 7 Electron optical system 8 Sample 9 Secondary electron detector 10 Reflected electron detector 11 Sample fine movement device 12 Sample chamber 13 Vacuum pipe 14 Vacuum pump 15 X-ray detector (Detection window size: d)
16 X-rays generated from the sample 17 X-ray extraction angle (TOA)
18 Distance between axes (L)
19 X-ray capture angle (2α)

Claims (6)

An electron source,
A stage on which the sample is mounted;
An objective lens for focusing the electron beam emitted from the electron source on the sample;
A first detector for detecting electrons emitted from the electron beam irradiation position of the sample;
A second detector for detecting a signal other than electrons emitted from the electron beam irradiation position of the sample;
A calculation unit for processing a signal detected by the first detector to obtain a three-dimensional shape of the sample;
A control device that moves the sample stage according to the electron beam irradiation position of the sample so as to maintain the distance between the second detector and the electron beam irradiation position of the sample using the three-dimensional shape ,
The calculation unit determines whether the sample exists on a path from the electron beam irradiation position of the sample to the second detector based on the height information of the sample based on the three-dimensional shape of the sample. A scanning electron microscope characterized by judging .   2. The scanning electron microscope according to claim 1, wherein the first detector is a reflected electron detector that detects reflected electrons emitted from an electron beam irradiation position of the sample, and the reflected electron detector has a divided detection surface. A scanning electron microscope characterized by comprising:   3. The scanning electron microscope according to claim 1, wherein the second detector is an X-ray detector that detects X-rays generated from an electron beam irradiation position of the sample. The scanning electron microscope of claim 1 ,
When the sample exists on the path, the stage is moved so that the sample does not exist on the path. The scanning electron microscope according to any one of claims 1 to 4,
The scanning electron microscope according to claim 1, wherein the movable range of the stage can be set by calculating the size and maximum height of the sample from the height information. An electron source,
A stage on which the sample is mounted;
An objective lens for focusing the electron beam emitted from the electron source on the sample;
A first detector for detecting electrons emitted from the electron beam irradiation position of the sample;
A second detector for detecting a signal other than electrons emitted from the electron beam irradiation position of the sample;
A calculation unit for obtaining the height of the sample for each electron beam irradiation position of the sample by an automatic focus correction function;
A control device is provided that moves the sample stage according to the electron beam irradiation position of the sample so as to maintain the distance between the second detector and the electron beam irradiation position of the sample using the height of the sample. ,
The calculation unit determines whether the sample is present on a path from the electron beam irradiation position of the sample to the second detector based on the height information of the sample. Scanning electron microscope.

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