JP2011238400A - Scanning electron microscope and sample inspection method using scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning electron microscope or a sample inspection method using the scanning electron microscope which is high in reliability of an element spectrum of a sample or accuracy of quantification thereof by means of suppression of a system peak by regulating an amount of electrons scattering on an objective lens diaphragm to control electrons which deviate from a main electron beam trajectory and are irradiated beyond analysis points.SOLUTION: In the present invention, a beam diameter is defined so that a system peak intensity is suppressed which an electron optics system having an objective lens diaphragm, a condenser diaphragm and a condenser lens includes, when a sample is inspected by focusing a primary electron beam emitted from an electron beam using the condenser lens to irradiate onto the objective lens diaphragm, stopping the lens down to reduce the beam diameter of the irradiation using the condenser diaphragm to focus by passing through a hole center of an objective lens, and detecting secondary electrons or scattering electrons which arise from the sample by irradiation of the electron beam thereonto.

Description

  The present invention relates to an electron scanning microscope and a sample inspection method using a scanning electron microscope, and more particularly to a scanning electron microscope and a sample inspection method using a scanning electron microscope that suppress electrons deviating from the primary electron beam trajectory and suppress system peaks during X-ray analysis. .

  One of the high performance energy dispersive spectrometers (EDX) is the expansion of detector elements. As a result, the solid angle for capturing X-rays has increased, and analysis in a short time has become possible, but due to scattering of the primary electron beam and scattered electrons, other than the electron beam irradiation point (analysis point) on the sample. X-rays from the area are also easily captured. For this reason, as shown in FIG. 10, the peak of the element not included in the analysis point appears in the spectrum. This peak is called a system peak, and it is desirable that the peak does not appear in the spectrum because it leads to a decrease in the authenticity of the elemental spectrum of the sample and a decrease in quantitative accuracy. However, a system peak appears due to factors such as scattering in the primary electron beam path and re-irradiation of reflected electrons onto the sample due to the influence of the objective lens magnetic field.

  As a conventional technique, Patent Document 1 discloses that a scanning electron microscope including an EDX apparatus feeds back an EDX measurement result to measurement conditions such as acceleration voltage and magnification of the scanning electron microscope.

JP 2007-86011 A

The inventors noticed that one of the major causes of the system peak is scattering of primary electrons on the objective lens stop 6, and found that the system peak can be reduced from the mechanism. The mechanism of primary electron scattering on the objective lens stop 6 and system peak generation due to this will be described with reference to FIGS.
Among the electrons passing through the objective lens stop 6, there are electrons indicated by a two-dot chain line that deviates from the main electron beam trajectory that is scattered on the lens barrel wall after being scattered on the objective lens stop. These electrons are irradiated on the sample other than the irradiation point (analysis point) of the main electron beam. FIG. 3 shows an example of a trajectory up to the sample of electrons deviating from the trajectory. FIG. 3 shows a state in which electrons deviated from the main electron trajectory approximately and shown by a two-dot chain line are once converged at the position of the objective lens stop 6 and then converged again by the subsequent lens system. In this way, irradiation is performed at a point other than the analysis point on the sample, and X-rays are generated from other than the analysis point during EDX analysis, and a system peak appears in the spectrum.

  In Patent Document 1, there is no recognition that one of the factors that cause a large system peak is the scattering of primary electrons on the objective lens aperture 6, and on the basis of the recognition, the system is used from other than the analysis point by the EDX apparatus. There is no disclosure of reflecting the peak measurement result in the suppression of primary electron scattering in the scanning electron microscope.

  The purpose of the present invention is to limit the amount of electrons scattered on the objective lens aperture, control the electrons that are off the main electron beam trajectory, and irradiate other than the analysis point, thereby suppressing the system peak and the elemental spectrum of the sample. It is to provide a sample inspection method using a scanning electron microscope or a scanning electron microscope with high reliability and quantitative accuracy.

  In order to achieve the above-mentioned object, the present invention focuses a primary electron beam emitted from an electron beam by a focusing lens and irradiates the objective lens aperture. Electron optics including the objective lens aperture, the condenser aperture, and the focusing lens when inspecting the sample by detecting the secondary electrons or scattered electrons generated from the sample by passing through the center to be focused and irradiating the electron beam The first feature is that the beam diameter is determined so as to suppress the system peak intensity of the system.

In order to achieve the above object, according to the present invention, in addition to the first feature, the suppression of the system peak intensity includes determining the beam diameter based on a system peak intensity characteristic of the electron optical system. Two features.
Furthermore, in order to achieve the above object, the present invention has a third feature that, in addition to the second feature, the beam diameter is determined by determining the hole diameter of the condenser aperture.

In addition to the second feature, the fourth feature of the present invention is that, in addition to the second feature, the beam diameter is determined by determining a crossover position of the focusing lens.
In addition to the second feature, the fifth feature of the present invention is to evaluate the limit of system peak reduction based on the system peak intensity characteristic in addition to the second feature.

In order to achieve the above object, according to the sixth aspect of the present invention, in addition to the second feature, the suppression of the system peak intensity defines the beam diameter based on a desired system peak intensity. To do.
Furthermore, in order to achieve the above object, the present invention provides the first feature, wherein the suppression of the system peak intensity is performed by crossover positions of the electron beam source, the objective lens aperture, the condenser aperture, and the focusing lens. The seventh feature is that the beam diameter is determined in accordance with the positional relationship.

  According to the present invention, the amount of electrons scattered on the objective lens aperture is limited, the system peak is suppressed by controlling the electrons emitted from the main electron beam orbit and other than the analysis point, and the elemental spectrum of the sample. It is possible to provide a sample inspection method using a scanning electron microscope or a scanning electron microscope with high reliability and quantitative accuracy.

1 is a schematic view of an electron scanning microscope that is an embodiment of the present invention. It is explanatory drawing explaining the mechanism of scattering of the primary electron on an objective lens aperture stop, and system peak generation by it. It is explanatory drawing explaining the mechanism of scattering of the primary electron on an objective lens aperture stop, and system peak generation by it. It is explanatory drawing of the electron optical system for suppressing the system peak in embodiment of this invention. It is a figure which shows the dependence data (intensity characteristic) of the system peak when the condenser aperture diameter in embodiment of this invention is made into small, medium, and large. It is a figure which shows the flowchart which calculates | requires the hole diameter of the capacitor | condenser aperture in 1st embodiment of this invention. It is a figure which shows a reset notification in the flowchart of FIG. 6A in 1st embodiment of this invention. It is a figure which shows the flowchart in 2nd Embodiment which can evaluate a system peak. It is a figure which shows the example of a display of the evaluation result of FIG. 7A. It is a figure which shows the flowchart in 3rd Embodiment which sets the crossover position (optical condition) of a 1st focusing lens so that the hole diameter of a condenser aperture | diaphragm is given and a stem peak intensity may be in tolerance. It is a figure which shows the reset notification or optical condition selection screen in the flowchart shown in FIG. It is a figure which shows one example of a system peak.

Embodiment 1 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of an electron scanning microscope 50 according to an embodiment of the present invention. The primary electron beam 3 emitted from the cathode 1 by the voltage V1 applied to the cathode 1 and the first anode 2 is accelerated by the voltage Vacc applied to the second anode 4 and proceeds to the subsequent electromagnetic lens system. The acceleration voltages Vacc and V1 are controlled by the high voltage controller 20. The primary electron beam is focused by the first focusing lens 5 controlled by the first focusing lens control unit 22. Here, although the electron beam sample irradiation current of the primary electron beam 3 is limited by the objective lens aperture 6, an electron beam central axis adjusting aligner 18 is used to pass the center of the electron beam to the hole center of the objective lens aperture 6. Also, an aligner control unit 21 and an electron beam center adjusting deflector 19 for scanning the electron beam on the objective lens aperture 6 are provided. Further, the primary electron beam 3 is focused again by the second focusing lens 7 controlled by the second focusing lens control unit 23, narrowed down to the sample 15 by the objective lens 10 controlled by the objective lens control unit 25, and further deflected. The sample 15 is scanned two-dimensionally by the upper deflection coil 8 and the lower deflection coil 9 to which the control unit 24 is connected. The sample 15 is on the sample fine movement device 14 controlled by the sample fine movement control unit 27.

  In addition, the EDX detector 17 can be installed in the electron scanning microscope 50 at all times or when necessary to detect the system peak intensity. The output of the EDX detector 17 is taken into the EDX spectrometer and the analysis result is obtained. The data is stored in the storage means (internal memory) 23 via the control unit (computer) 40.

  An electron optical system for suppressing system peaks will be described with reference to FIG. The primary electron beam 3 emitted from the cathode 1 is accelerated by the second anode 4, then formed by the condenser aperture 38, and proceeds to the first focusing lens 5. The electrons focused by the first focusing lens 5 are limited by the hole of the objective lens aperture 6, and the electrons that have passed through the aperture of the objective lens aperture 6 travel to the subsequent lens system. The amount of electrons that have passed through the hole of the objective lens aperture 6 is the probe current that is applied to the sample.

  One of the causes of system peaks is due to electrons deviating from the main electron beam orbit (orbits are two-dot chain lines). The electrons are scattered by the objective lens stop 6 and travel in the opposite direction to the primary electron beam 3, but are scattered by the wall of the lens body and the like, pass through the hole of the objective lens stop 6, and are irradiated to other than the analysis point. Since the electrons irradiated to other than the analysis point are caused by the scattering of the primary electron beam 3 on the objective lens aperture 6, the system peak is reduced by reducing the number of electrons scattered on the objective lens aperture 6. Is possible.

In order to reduce the number of electrons scattered on the objective lens stop 6, the beam diameter on the objective lens stop 6 may be reduced.
There are two methods for reducing the beam diameter on the objective lens aperture 6, one is to bring the crossover of the first focusing lens 5 closer to the objective lens aperture 6 side, and the other is to reduce the hole diameter of the condenser aperture 38. It is a method to do. In the former case, since the crossover position of the first focusing lens 5 moves, the probe current changes accordingly. This method may not be able to set a desired probe current during elemental analysis, but is an effective means when a desired probe current can be set. On the other hand, in the latter method of reducing the hole diameter of the condenser diaphragm 38, the crossover position does not move, so that the beam diameter on the objective lens diaphragm 6 can be reduced without changing the probe current. Therefore, it is effective to limit the beam diameter on the objective lens stop 6 by using the condenser stop 38.

  Therefore, in the present embodiment, based on the analysis result of the analyzed system peak intensity, at least one of the condenser aperture diameter and the crossover position of the first focusing lens 5 is determined so as to suppress the system peak. Based on the control, the condenser aperture diameter control unit 28 or the first focusing lens control unit 22 is controlled. In the present embodiment, the condenser throttle hole diameter is automatically controlled by the condenser throttle hole diameter control unit via the condenser throttle driving means 29. However, the hole diameter is manually adjusted by the condenser throttle driving means based on the contents instructed by the display device. It may be manipulated and changed. The determination is performed by the system peak suppression calculation means 33 shown in FIG.

  FIG. 5 shows dependency data (intensity characteristics) of the system peak when the diameter of the condenser throttle 38 is small, medium and large. 5 is a graph in which the vertical axis represents system peak intensity (weight (wt)%) and the horizontal axis represents the crossover position (= b: see FIG. 4) of the first focusing lens. It can be seen that even when the crossover position is the same, the system peak is reduced when the hole diameter of the condenser aperture 38 is small. When the position b, which is the distance from the first focusing lens 5 to the crossover position, moves, the amount of electrons passing through the hole of the objective lens aperture 6 changes. In this case, as described above, a desired probe current is obtained during elemental analysis. May not be set.

Next, with reference to FIG. 4, the system peak intensity at the crossover position b of the arbitrary first focusing lens 5, a pore diameter d _c of the condenser aperture 38, the beam diameter d _b and irradiation area S or the like on the objective aperture 6 The objective lens aperture 6 forms the primary electron beam 3 and determines the opening angle on the sample. Therefore, the beam diameter on the objective lens aperture 6 is limited to the extent that the system peak is allowed. To do.

The beam diameter on the objective aperture 6 as d _b, a condenser aperture 38 the hole diameter d _c, the cathode 1 and the first focusing lens 5 between the distance a, between the first focusing lens 38 and the objective aperture 6 distance L, the first focusing lens 5 and the condenser aperture 38 between the distance l, when the crossover position b of the first condenser lens 5, the beam diameter d _b of the above objective aperture 6,

It is expressed. Cathode 1 and the first focusing lens 5, because the objective aperture 6 is fixed mechanically position, the beam diameter d _b on the stop 6 hole diameter d _c and the objective lens of the condenser aperture 38 at some crossover position b is

It is expressed.

Here, Ip is the amount of electrons in the main electron beam orbit, and I _stray is the amount of electrons scattered on the objective lens aperture 6 and deviating from the orbit. The pore size of the objective aperture 6 as d _a, the use of the beam diameter d _b of the above objective aperture 6, Ip and I _stray is the density of the primary electrons emitted from the cathode 1 P Tosureba each area It can be expressed as a function of Sp and S _stray .

Substituting Equation 2 into Equation 4, the ratio of Ip and _Istray is

It becomes.

Since X-rays generated from the analysis point and X-rays generated from other than the analysis point are X-rays excited by Ip and I _stray , respectively, it is only necessary to realize an optical condition that makes I _stray sufficiently small. Since I _stray is expressed by the area S _stray of the electron beam irradiated onto the objective lens 6 as shown in the equation 4, it can be set to be equal to or less than the desired area S _d .

Should be satisfied. The hole diameter d _c of the condenser aperture 38 for less desired area S _d Rearranging Equation 6 can be obtained by Equation 7.

Area S _stray on objective aperture 6 for hole diameter d _c of the condenser aperture 38, FIG. 4 and Equation 2, as can be seen from Equation 4, a, L, l is a cross of the first focusing lens 5 are the fixed values It is obtained as a function of the over position b. On the other hand, the relationship between the system peak intensity and the crossover position b of the single focusing lens 5 is related by the actual data shown in FIG. Therefore, the relationship between the system peak intensity and the area S _stray on the objective lens aperture 6 can be defined via the crossover position b.
As a result, the crossover position b of the arbitrary first focusing lens 5, created by the system peak suppression calculation means 33 shown in FIG. 1 data table having a pore diameter d _c of the system peak intensity and condenser aperture 38 defined in Figure 5, Register in the storage means 34. Thereby, the beam diameter and the irradiation area S _stray on the objective lens stop 6 corresponding to the system peak intensity are found.

6A is a diagram showing a flowchart for determining the pore size of d _c of the condenser aperture 38 in the first embodiment of the present invention. First, the crossover position of the first focusing lens 5 is determined so as to obtain a desired probe current (Step 1). Next, the system peak intensity (allowable value) is selected (Step 2), and the beam on the objective lens aperture 6 for realizing it is determined from the relationship between the system peak intensity and the irradiation area S _stray on the objective lens aperture 6. The diameter and the irradiation area S _stray are obtained (Step 3). Obtaining a condenser aperture 38d _c pore size is precalculated and registered by the formula 7 (Step4). Obtained condenser aperture 38 of the smallest that is mounted a pore size d _c in the apparatus condenser aperture 38 diameter of (= d _cmin) and comparing (Step5). If d _c is greater than d _cmin, setting the condenser diaphragm driving means a pore size of the condenser diaphragm 38 in automatic or pore sizes manually operated the calculated (Step6), and carrying out elemental analysis (Step7). If it is smaller, a notification of resetting the optical condition (crossover position of the first focusing lens) (FIG. 6B (a)) is displayed on the display device 30 and goes to Step 1 (Step 7), or a notification of resetting the system peak tolerance is reset. (FIG. 6B (b)) is displayed on the display device 30 and the process goes to Step 2 (Step 8).

  According to the first embodiment described above, the amount of electrons scattered on the objective lens aperture is limited by setting or controlling the hole diameter of the condenser aperture and the crossover position of the first focusing lens. It is possible to provide a scanning electron microscope or an elemental analysis method using a scanning electron microscope with high reliability and quantitative accuracy of the elemental spectrum of the sample by controlling the electrons emitted outside the analysis point.

In the above description, the relationship between the system peak intensity, the beam diameter on the objective lens aperture 6 and the irradiation area is obtained, but the absolute value of the system peak intensity is not known, but the smaller the irradiation area, the smaller the system peak intensity. In consideration, it is also possible to determine the hole diameter of the condenser aperture and the crossover position of the first focusing lens so that a desired probe current is obtained and the irradiation area is reduced. In this case, it is possible to provide a scanning electron microscope or an elemental analysis method using a scanning electron microscope in which the credibility or quantitative accuracy of the element spectrum of the sample cannot be determined but is relatively enhanced.
(Embodiment 2)
FIG. 7A is a diagram showing a flowchart in the second embodiment in which the limit of reduction of the system peak can be evaluated. First, the crossover position b of the first focusing lens 5 is determined (Step 1). The minimum beam diameter (= d _bmin ) that can be realized on the objective lens aperture 6 is calculated from the crossover position of the first focusing lens 5 and the minimum aperture diameter of the condenser aperture 38 mounted on the apparatus (Step 2). The minimum beam diameter b _bmin that can be realized on the objective lens stop 6 is obtained from Equation 1.

Calculate with Since the density of the primary electrons emitted from the cathode 1 is P, the amount of electrons I _stray scattered on the objective lens aperture 6 from the equation 8 and the hole diameter of the objective lens aperture 6 is

(Step 3).

  Since the amount of electrons scattered on the objective lens stop 6 can be obtained by Equation 9, if data as shown in FIG. 5 is acquired in advance, it is associated with the system peak intensity (Step 4), and the limit of the reduction of the system peak is set. Can be evaluated. The result is displayed on the display device 30 (Step 5). FIG. 7B shows a display example of this result.

According to the second embodiment, since the limit of system peak reduction can be evaluated, the credibility or quantitative accuracy of the elemental spectrum of the sample can be grasped.
(Embodiment 3)
A third embodiment will be described with reference to the flowchart of FIG. In the first and second embodiments, the crossover position b of the first focusing lens is given to determine the hole diameter of the condenser aperture. In contrast, the third embodiment is an example in which the crossover position b (optical condition) of the first focusing lens is set so that the hole diameter of the condenser aperture is given and the stem peak intensity is within an allowable value.

  For example, when the condenser aperture 38 having a different hole diameter is set (Step 2), the system peak is estimated by the same method shown in FIG. 7A (Step 5).

  If this method is used, the system peak intensity can be estimated for the condenser aperture 38 having an arbitrary hole diameter. Therefore, for example, when the user sets a desired system peak intensity, it is determined whether this can be realized (Step 6). If it cannot be realized, in order to go to Step 1, notification for prompting resetting of the optical conditions shown in FIG. 9A is performed (Step 9). Even if the desired system peak intensity can be realized, the optical condition (first focusing lens crossover position) generally has a range, so the optical condition list shown in FIG. 9C (in this example, H1 to H16, N1). ~ N16 (32 types)), only the realizable optical conditions are selected and displayed on the display device 30 as shown in FIG. 9D (Step 7). The optical conditions are selected and set from the list of FIG. 9D (Step 8), and then elemental analysis is performed (Step 9).

  According to the third embodiment described above, an optical condition (crossover position of the first focusing lens) that can realize a desired system peak intensity can be set for the condenser aperture 38 having an arbitrary hole diameter.

  As described above, in the first to third embodiments, the condenser diaphragm is provided on the cathode 1 side of the first focusing lens 5, but it means that the electrons scattered from the objective lens diaphragm and the lens body wall are throttled to suppress the system peak. Then, the first focusing lens 5 may be provided on the objective lens stop 6 side.

  In the first to third embodiments, the elemental analysis has been described. However, the present invention can be applied to inspections such as sample observation.

1: Cathode 2: First anode 3: Electron beam 4: Second anode 5: First converging lens 6: Objective lens diaphragm 7: Second converging lens 8: Upper deflection coil 9: Lower deflection coil 10: Objective lens 12: Secondary electron detector 13: Orthogonal electromagnetic field device 14: Fine movement device 15: Sample 16: Amplifier 17: EDX detector 18: Aligner for electron beam central axis adjustment 19: Deflector for electron beam central axis adjustment 20: High voltage control Unit 21: aligner control unit 22: first converging lens control unit 23: second converging lens control unit 24: deflection control unit 25: objective lens control unit 26: signal control unit 27: sample fine movement control unit 28: condenser aperture diameter control Unit 29: Capacitor aperture driving means 30: Display device 31: Image acquisition means 32: Image processing means 33: System peak suppression calculation means 34: Storage means 35 Input means 40: Computer 45: EDX analyzer 50: electron scanning microscope.

Claims (17)

An electron beam source, an objective lens diaphragm for narrowing the primary electron beam emitted from the electron beam source, a focusing lens provided on the electron beam side of the objective lens diaphragm, and the primary electron beam to the objective lens diaphragm A condenser aperture for reducing the beam diameter of the objective lens, an objective lens for focusing the primary electron beam that has passed through the hole center of the objective lens, and secondary electrons generated from the sample by irradiation of the primary electron beam or In a scanning electron microscope equipped with detection means for detecting scattered electrons,
A scanning electron microscope comprising system peak suppression means for determining the beam diameter so as to suppress a system peak intensity of an electron optical system including the objective lens aperture, the condenser aperture, and the focusing lens.   The scanning electron microscope according to claim 1, wherein the system peak suppression unit determines the beam diameter based on a system peak intensity characteristic of the electron optical system.   The scanning electron microscope according to claim 2, wherein the system peak suppression means is means for determining a hole diameter of the condenser aperture.   The scanning electron microscope according to claim 2, wherein the condenser aperture is provided between the objective lens aperture and the electron beam source.   3. The scanning electron microscope according to claim 2, wherein the system peak suppressing means is means for determining a crossover position of the focusing lens.   The scanning electron microscope according to claim 2, further comprising a system peak intensity measuring unit that measures the system peak intensity, or a connecting unit that enables measurement of the system peak.   The scanning electron microscope according to claim 2, wherein a limit of system peak reduction is evaluated based on the system peak intensity characteristic.   The scanning electron microscope according to claim 2, wherein the system peak suppressing unit determines the beam diameter based on a desired system peak intensity.   9. The scanning electron microscope according to claim 8, wherein the desired system peak intensity is set, and a crossover position of the first focusing lens that realizes the system peak intensity is displayed on a display screen.   2. The scanning electron according to claim 1, wherein the system peak suppression unit determines the beam diameter according to a positional relationship among crossover positions of the electron beam source, the objective lens diaphragm, the condenser diaphragm, and the focusing lens. microscope. The primary electron beam emitted from the electron beam source is focused by the focusing lens and irradiated to the objective lens aperture, the beam diameter of the irradiation is reduced by the condenser aperture, and the beam is focused through the center of the hole of the objective lens. In the sample inspection method by a scanning electron microscope that detects secondary electrons or scattered electrons generated from the sample by the above and inspects the sample,
A sample inspection method using a scanning electron microscope, wherein the beam diameter is determined so as to suppress a system peak intensity of an electron optical system including the objective lens aperture, the condenser aperture, and the focusing lens.   The sample inspection method using a scanning electron microscope according to claim 11, wherein the suppression of the system peak intensity determines the beam diameter based on a system peak intensity characteristic of the electron optical system.   13. The sample inspection method using a scanning electron microscope according to claim 12, wherein the beam diameter is determined by determining a hole diameter of the condenser aperture.   13. The sample inspection method using a scanning electron microscope according to claim 12, wherein the beam diameter is determined by determining a crossover position of the focusing lens.   13. The sample inspection method using a scanning electron microscope according to claim 12, wherein a limit of system peak reduction is evaluated based on the system peak intensity characteristic.   The sample inspection method using a scanning electron microscope according to claim 12, wherein the suppression of the system peak intensity determines the beam diameter based on a desired system peak intensity.   12. The system according to claim 11, wherein the suppression of the system peak intensity determines the beam diameter according to a positional relationship among crossover positions of the electron beam source, the objective lens diaphragm, the condenser diaphragm, and the focusing lens. Sample inspection method using a scanning electron microscope.

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