JPH11144656A - Scanning electron microscope and its similar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the information signal electrons emitted from a sample with high efficiency even when a sample stage is inclined and reduce the aberration of a primary electron beam by providing a means correcting the axial asymmetry, caused by the inclination of the sample, of the electric field acting on the electron beam radiated to the sample. SOLUTION: A deflection electrode device 17 is formed with two electrodes arranged symmetrically with the optical axis of an electron beam, and they are applied with different voltages respectively. The voltages applied to two electrodes of the deflection electrode device 17 are controlled by a controller 18 interlockingly with the inclination angle of a sample stage 10 arranged with a sample respectively. If the voltages are properly selected, the electric field component negating the incorrect electric field component generated in the direction perpendicular to the electron beam axis by the inclination of the sample can be generated. The axial asymmetry of the electric field applied to the electron beam based on the inclination of the sample is corrected, thereby the occurrence of astigmatism causing resolution deterioration can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a scanning electron microscope for obtaining a scanned image of a sample based on information signals unique to the sample obtained by irradiating the sample with an electron beam, and a similar device.

[0002]

2. Description of the Related Art In a scanning electron microscope, as a means for observing a sample with high resolution, a lens electric field is generated under an objective lens as described in Japanese Patent Application Laid-Open No. Sho 57-172643 to generate a sample from a sample. The secondary electrons to be accelerated by a positive voltage applied to the electrodes arranged in the objective lens are detected at the top of the objective lens, or a negative voltage is applied to the sample, as is known as the retarding method. There is a method in which the primary electrons are decelerated just before the sample. Also in this case, since the secondary electrons generated from the sample are accelerated by the voltage applied to the sample and proceed to the upper part of the objective lens, it is necessary to detect the secondary electrons at the upper part of the objective lens. In either method, an electric field is generated between the sample and the objective lens.

[0003]

In the above prior art, when the sample is tilted, the axial symmetry of the electric field between the sample and the objective lens is broken, and a horizontal electric field component is generated on the electron beam axis. Astigmatism increases and it is difficult to obtain high resolution. In addition, if the axial symmetry of such an electric field is broken, the trajectory of the information signal electrons generated from the sample is also disturbed, so that the information signal cannot reach the detector arranged above the objective lens, and therefore the information signal cannot be detected. .

An object of the present invention is to suppress the occurrence of astigmatism even when the sample stage is tilted, thereby preventing a reduction in resolution, and suitable for detecting information signals from the sample with high efficiency. It is to provide a scanning electron microscope and similar devices.

[0005]

A scanning electron microscope according to the present invention comprises an electron gun for generating an electron beam, an objective lens for irradiating the sample with the electron beam, and an objective lens for converging the electron beam on the sample. Means for deflecting the electron beam so as to scan the sample, a detector for detecting an information signal generated from the sample by the irradiation and characterizing the sample, and tilting the sample with respect to the electron beam. Means for generating an electric field having an action of accelerating or decelerating the electron beam between a sample and an objective lens, and applying the electron beam to irradiate the sample with the electron beam. Means for correcting non-axial symmetry of the electric field acting on the electric field due to the tilt of the sample.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention. The primary electron beam 2 emitted from the cathode 1 by the voltage V1 applied between the cathode 1 and the extraction electrode 3 of the electron gun is
It is accelerated by Vacc applied between the cathode 1 and the accelerating electrode 4. The primary electron beam 2 is focused on the sample 8 by the focusing lens 5 and the objective lens 6 controlled by the lens control power supply 14 and irradiates the sample 8. Deflectors 7a and 7b
Deflects the primary electron beam 2 two-dimensionally, thereby scanning the primary electron beam 2 two-dimensionally on the sample. The scanning signals of the deflectors 7a and 7b are controlled by the deflection control circuit 12 according to the observation magnification.

The information signal electrons 15 generated from the sample 8 by the irradiation of the primary electron beam 2 are accelerated by an electric field in the optical axis direction formed by the positive voltage Vse applied to the pull-up electrode 16, and passed through the objective lens 6. Detector 9b
Is displayed on the image display device 13 via the amplifier 21 as an enlarged image of the sample. The lifting electrode 1
Due to the positive voltage applied to 6, the primary electron beam 2 is accelerated by the amount of the applied positive voltage while passing through the objective lens. As a result, the primary electron beam 2 has a high accelerating voltage while passing through the objective lens 6, so that the aberration of the primary electron beam can be reduced.
Further, after passing through the objective lens 6, the voltage returns to the original accelerating voltage, so that damage to the sample due to the highly accelerated primary electron beam can be suppressed.

As shown in FIG. 2, the deflection electrode 17 has two electrodes 19 symmetrically arranged with respect to the optical axis of the electron beam.
And 20, and different voltages are applied to each. The voltage applied to the electrodes 19 and 20 of the deflection electrode device 17 is controlled by the control unit 18 in conjunction with the tilt angle of the sample stage 10 on which the sample 8 is disposed. If the voltage is appropriately selected, an electric field component that cancels an illegal electric field component generated in a direction orthogonal to the electron beam axis due to the tilt of the sample can be generated. This corrects the non-axial symmetry based on the sample tilt of the electric field acting on the electron beam, and therefore suppresses the generation of astigmatism that causes a reduction in resolution.

Further, by correcting the irregular electric field, the disturbance of the trajectory of the information signal electrons generated from the sample 8 can be suppressed, so that the information signal electrons can be efficiently transported to the upper part (electron source side) of the objective lens. Can be. In this embodiment, the control unit 18 is a supply source of the applied voltage to the deflection electrode device 17, but the control unit and the power supply unit may be separated. A quadrature electromagnetic field generator (L) 24 is located above the objective lens.
Are arranged, and the strength of each electric field and magnetic field cancels the deflecting action for primary electrons, and the information signal detector 9b side for information signal electrons transported to the upper part of the objective lens. Is controlled to generate a deflection action. Therefore, the information signal electrons generated from the sample are efficiently detected by the information signal detector 9b without affecting the trajectory of the primary electrons by the orthogonal electromagnetic field generator (L) 24.

The controller 18 adjusts the voltage applied to the deflection electrode 17 so as to satisfy a relationship determined in advance by experiments so that the voltage applied to the deflection electrode 17 becomes a value suitable for correcting an irregular electric field generated according to the tilt angle of the sample. Is controlled by The deflection electrode 1
The applied voltage of 7 can be manually set so that the discrepancy with the experiment caused by the shape of the sample can be further corrected.

FIG. 3 shows an example in which a deflection electrode 17 is arranged around the optical axis of the electron beam between the lower surface of the magnetic pole of the objective lens 6 and the sample. The deflection electrode 17 can be composed of two, four or eight electrodes as shown in FIG. 2, FIG. 4 or FIG. 5, and it is possible to increase the number of electrodes and apply different voltages to each of them. Thereby, the irregular electric field generated between the objective lens and the sample can be corrected with higher accuracy.

FIG. 6 shows an example in which the deflection electrode 17 is arranged so as to face the sample 8 tilted with respect to the optical axis of the electron beam, that is, the sample stage 10. The voltage applied to the deflection electrode device 17 is controlled by the control unit 18 in conjunction with the inclination of the sample stage 10. By applying a voltage to the deflection electrode device 17, an electric field having a component in a direction orthogonal to the optical axis of the electron beam is generated, and the sample stage 10
Since the horizontal electric field component generated on the optical axis when the light is tilted is corrected, the generation of astigmatism is suppressed, and the information signal electrons 15 generated from the sample 8 travel to the upper part of the objective lens. Can be done.

FIG. 7 shows an example in which the deflecting electrode 17 is made of a material having a function of generating a light or an electric signal by collision of electrons as a means for detecting the information signal electrons 15. Among the information signal electrons 15 generated from the sample 8 by irradiating the sample 8 with the primary electron beam 2, the signal with low energy travels to the upper part of the objective lens due to the effect of the pull-up voltage Vse, but the signal with high energy Some of the electrons (especially reflected electrons) do not sufficiently suppress their divergence, and some of them collide with the deflection electrode 17. The deflecting electrode 17 is connected to the information signal electron 1.
Since the light or electric signal corresponding to the amount of the colliding signal electrons is generated by the collision of 5, the light or electric signal can be extracted as an image signal. The image signal obtained from the deflection electrode 17 is
An enlarged image of the sample can be displayed on the image display device 13 via the amplifier 22.

The high-energy signal electrons detected by the deflection electrode 17 and the low-energy signal electrons detected by the information signal detector 9b disposed above the objective lens 6 are individually signaled by the information signal switching means 50. Or the display of the image display device 1 by selecting one of
3 can be displayed. By switching the information signal, only appropriate information of the information signal generated from the sample can be displayed, so that it is possible to prevent the S / N ratio of the image from being reduced due to the unnecessary information signal.

FIG. 8 shows an example of a configuration in which a negative voltage is applied to the sample 8 by the voltage control unit 23 so that primary electrons passing through the objective lens magnetic field are decelerated between the objective lens magnetic pole and the sample. Between the objective lens 6 and the deflectors 7a and 7b, an orthogonal electromagnetic field generator (L) 24 for generating an electric field and a magnetic field orthogonal to each other, and an electrode made of a material capable of generating secondary electrons by collision of electrons ( L) 25 and the information signal detector 9b. The information signal electrons 15 generated from the sample 8 and traveling to the upper part of the objective lens 6
Is accelerated by the decelerating electric field between
In the orthogonal electromagnetic field generator (L) 24, a sufficient deflection action cannot be obtained, and the secondary electron 15a is emitted from the electrode (L) 25 by colliding with the electrode (L) 25.

The secondary electron 15a is a quadrature electromagnetic field generator (L)
Since the light is deflected by the information signal detector 9b at 24, it is detected by the information signal detector 9b and displayed on the image display device 13 via the amplifier 21 as an enlarged image of the sample. According to the configuration of FIG. 8, even when a negative voltage is applied to the sample 8, an information signal generated from the sample 8 can be detected efficiently.

The negative voltage applied to the sample 8 is set so as to satisfy the relationship determined in advance by experiments, taking into account that the signal electrons travel in an appropriate trajectory with respect to the initial acceleration voltage of the primary electron beam 2. , And is controlled by the voltage control unit 23.
The negative voltage applied to the sample 8 is supplied to the voltage switching means 51.
To 0V. At this time, of the information signal electrons 15 generated from the sample 8, the signal electrons having small energy are directly deflected to the information signal detector 9b side by the orthogonal electromagnetic field generator (L) 24 and detected. Since large signal electrons are not sufficiently deflected by the orthogonal electromagnetic field generator (L) 24, they collide with the electrode (L) 25. High-energy information signal electrons that have collided with the electrode (L) 25 are converted into secondary electrons by the electrode (L) 25 and deflected by the orthogonal electromagnetic field generator (L) 24 to the information signal detector 9 b side, thereby obtaining information. The signal is detected by the signal detector 9b.

When the sample stage 10 is tilted while a negative voltage is applied to the sample 8 as described above, disturbance of equipotential lines as shown in FIG. 12 occurs between the sample stage 10 and the objective lens 6 which is a ground voltage. I do. The example of FIG. 12 shows a case where a negative voltage of -5 kV is applied. Since the objective lens 6 is at the ground potential (0 V), a potential difference occurs between the two, and the information signal electrons 15 are further bent in the inclined direction due to the disturbance of the equipotential lines. In order to solve this problem, in this embodiment, the application of the voltage to the deflection electrode 17 is controlled so as to cancel the disturbance of the equipotential lines. The disturbance of the equipotential lines also affects the primary electron beam and causes aberration. However, by controlling the voltage to the deflecting electrode 17, the adverse effect can be improved.

When a negative voltage is applied to the sample 8, as described above, the information signal electrons 15 are accelerated and have a correspondingly high energy, so that it is desirable that the deflection electrode has a stronger deflection action. For example, when a negative voltage is applied to the sample, control may be performed so that a larger voltage is applied to the deflection electrode than when no negative voltage is applied. However, the voltage actually applied to the deflection electrode depends on various requirements such as the magnitude of the tilt angle of the sample stage, the initial velocity of the primary electron beam, the type of information signal electrons to be detected, and the distance (working distance) between the objective lens and the sample. Should be determined in consideration of

Further, in this embodiment, as described above, the pull-up electrode 16 is used to pull up the information signal electrons and accelerate the primary electron beam. The voltage applied to the lifting electrode 16 is a positive voltage for the purpose. That is, it is conceivable that the same adverse effect as when a negative voltage is applied to the sample occurs. That is, since a positive voltage is applied to the objective lens 6 side, when the sample stage is tilted, FIG.
This is because the same disturbance of the isoelectronic beam as in the example 2 occurs.

When a positive voltage is applied to the lifting electrode and a negative voltage is further applied to the sample, the potential difference between the objective lens and the sample becomes larger, and the disturbance of equipotential lines when the sample is tilted becomes larger. It will be.

In order to solve this problem, the technique of the embodiment of the present invention in which the disturbance of the equipotential lines is controlled by the deflection electrode is particularly effective.

FIG. 9 shows an embodiment in which the electrode (L) 25 in FIG. 8 is replaced by a detector (L) 26 having a function of generating a light or an electric signal by collision of electrons. When a negative voltage is applied to the sample 8, the detector (L) 26
The signal generated in the step reflects the amount of information signal electrons generated from the sample 8 and accelerated between the sample 8 and the objective lens 6,
When the voltage applied to the sample 8 is 0 V, the signal reflects only the amount of the high-energy signal among the information signal electrons. At this time, information signal electrons having low energy in the information signal are directly deflected by the orthogonal electromagnetic field generator (L) 24 and detected by the detector 9b. These detectors 26, 9b
Are individually output by the switching means 50,
Alternatively, it is possible to select a combined signal of the two, and the selected information signal can be displayed on the image display device 13 via the amplifier 31 as an enlarged image of the sample.

Since the electrode (L) 25 and the detector (L) 26 are located around or near the optical axis, the deflectors 7a,
There is a problem that the deflection range of 7b is limited, and as a result, the observation visual field is limited. Therefore, by making the electrode (L) 25 and the detector (L) 26 movable,
If it is necessary to increase the observation field of view, it is possible to keep the primary electron beam at a distance that does not limit the deflection range.

FIG. 10 shows an embodiment in which the information signal electrons from the sample can be detected with high efficiency without limiting the deflection range of the primary electron beam. In FIG. 10, the electrode of FIG.
An electrode (U) 29 corresponding to (L) 25 is arranged closer to the electron source than the deflectors 7a and 7b. For this reason, it is possible to make the electrode (U) 29 a small transmission hole in a range that does not block the primary electron beam that has passed through the aperture plate 11. Since the orthogonal electromagnetic field generator (U) 28 is disposed between the electrode (U) 29 and the deflector 7a, of the information signal electrons generated from the sample, electrons that collide with the electrode (U) 29 Are converted into secondary electrons by the electrode (U) 29 and deflected by the orthogonal electromagnetic field generator (U) 28 toward the information signal detector 9a to be detected.

FIG. 11 shows another embodiment in which the electrode (U) 29 of FIG. 10 is replaced by a detector 30 capable of generating light or an electric signal by collision of electrons. Since the detector 30 can directly detect a signal colliding with the detector 30, it is not necessary to arrange the orthogonal electromagnetic field generator (U) 28 and the detector 9a arranged in FIG.

[0028]

As described above, in a scanning electron microscope and similar devices in which primary electrons passing through the objective lens magnetic field can be made higher in energy than when the sample is irradiated to improve the resolution, even if the sample is inclined at an arbitrary angle. Also, information signal electrons generated from the sample can be detected with high efficiency, and the aberration of the primary electron beam can be reduced.

Further, the detection signals can be separated by the energy of the information signal electrons generated from the sample, and these signals can be selected or synthesized, so that an optimum contrast according to the sample can be obtained.

Further, since it is possible to correct the disturbance of the equipotential lines when the sample is tilted when a negative voltage is applied to the sample or a positive voltage is applied to the pull-up voltage, the aberration of the primary electron beam is reduced as a result. Thus, it is possible to improve the detection efficiency of information signal electrons.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a scanning electron microscope according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a deflection electrode in FIG. 1;

FIG. 3 is a side sectional view showing positions of an objective lens, a sample stage, and a deflection electrode in FIG. 1;

FIG. 4 is a sectional view showing a configuration of a deflection electrode according to an embodiment of the present invention.

FIG. 5 is a sectional view showing a configuration of a deflection electrode according to an embodiment of the present invention.

FIG. 6 is a side view showing positions of an objective lens, a sample stage, and a deflection electrode according to an embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a scanning electron microscope according to an embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating the operation of a scanning electron microscope according to an embodiment of the present invention.

FIG. 9 is a schematic configuration diagram illustrating the operation of FIG.

FIG. 10 is a schematic configuration diagram of a scanning electron microscope according to an embodiment of the present invention.

FIG. 11 is a schematic configuration diagram of a scanning electron microscope according to an embodiment of the present invention.

FIG. 12 is a view showing equipotential lines between a sample and an objective lens, which are caused by the tilt of the sample to which a negative voltage is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cathode, 2 ... Primary electron beam, 3 ... Extraction electrode, 4 ... Acceleration electrode, 5 ... Focusing lens, 6 ... Objective lens, 7a, 7b
... deflector, 8 ... sample, 9a, 9b ... information signal detector, 1
0: sample stage, 11: aperture plate, 12: deflection control circuit, 13: image display device, 14: lens control power supply, 15:
Information signal electrons, 16: lifting electrode, 17: deflection electrode device, 18: control unit, 19, 20: electrode, 21, 22, amplifier, 23: voltage control unit, 24: orthogonal electromagnetic field generator (L), 25 ... electrodes (L), 26 ... detectors (L), 27
... image control unit, 28 ... orthogonal electromagnetic field generator (U), 29 ...
Electrodes (U), 30: Detector (U), 31: Amplifier, 50:
Information signal switching means, 51 ... Negative voltage switching means.

Claims (18)

[Claims] 1. An electron gun for generating an electron beam, an objective lens for irradiating a sample with the electron beam and converging the electron beam on the sample, and an electron beam for scanning the sample with the electron beam. A scanning electron microscope and similar devices having a means for deflecting, a detector for detecting an information signal characterizing the sample generated from the sample by the irradiation, and a means for tilting the sample with respect to the electron beam. Means for generating an electric field having an accelerating or decelerating action on the electron beam between the sample and the objective lens; and a tilt of the sample of the electric field acting on the electron beam irradiating the sample. And means for correcting non-axial symmetry of the electric field caused by the scanning electron microscope. 2. An electron gun for generating an electron beam, an objective lens for irradiating the sample with the electron beam and converging the electron beam on the sample, and an electron beam for scanning the sample with the electron beam. Means for deflecting, means for generating an electric field for extracting an information signal generated from the sample by the irradiation, which characterizes the sample through the objective lens, a detector for detecting the extracted information signal, and A scanning electron microscope having means for tilting with respect to the electron beam, and a similar device, wherein means for correcting non-axial symmetry of the electric field acting on the electron beam irradiating the sample due to the tilt of the sample; A scanning electron microscope and a device similar to the scanning electron microscope, comprising: 3. The scanning electron microscope according to claim 1, wherein the means for correcting the non-axial symmetry of the electric field includes a component in a direction orthogonal to the optical axis of the electron beam. A scanning electron microscope and a device similar to the scanning electron microscope, wherein the deflection electrode is a deflection electrode to which a voltage is applied so as to generate an electric field. 4. A scanning electron microscope according to claim 3, further comprising means for detecting a tilt angle of said sample and controlling a voltage of said deflection electrode in response to the detection. A scanning electron microscope and similar devices characterized by the above. 5. The scanning electron microscope according to claim 3, wherein the deflection electrode comprises at least two electrodes, which are provided between the objective lens and the sample. A scanning electron microscope and a device similar to the scanning electron microscope, wherein the scanning electron microscope is arranged around the optical axis. 6. The scanning electron microscope according to claim 3, wherein the deflection electrode is arranged so as to face the inclined sample with respect to the optical axis of the electron beam. Scanning electron microscope and similar devices. 7. The scanning electron microscope according to claim 1, wherein said tilting means includes means for applying a negative voltage to said sample. Scanning electron microscope and similar devices. 8. The scanning electron microscope according to claim 7, wherein the condition for correcting the non-axial symmetry of the electric field is determined depending on whether a negative voltage is applied to the sample or not. A scanning electron microscope and a similar device comprising a variable control means. 9. The scanning electron microscope according to claim 1, further comprising an electrode surrounding the optical axis of said electron beam in said objective lens, wherein said electrode has a positive voltage. Scanning electron microscope and a device similar thereto. 10. The scanning electron microscope according to claim 9, wherein the condition for correcting the non-axial symmetry of the electric field is determined depending on whether a positive voltage is applied to the electrode or not. A scanning electron microscope and a similar device comprising a variable control means. 11. The scanning electron microscope according to claim 3, wherein the deflection electrode is formed of a member that generates a light or an electric signal by collision of electrons, and converts the light or the electric signal into an image signal. A scanning electron microscope and a device similar to the scanning electron microscope, characterized by comprising a means for converting the scanning electron microscope. 12. The scanning electron microscope according to claim 1 or 2, wherein an electrode formed of a substance that generates secondary electrons by collision of electrons is provided near the optical axis of the electron beam. The secondary electron detector is provided at a position near the electrode formed of a substance from which the secondary electrons are generated and in which secondary electrons generated from the electrode can be detected with high efficiency. Scanning electron microscope and similar devices. 13. A scanning electron microscope according to claim 12, wherein an electrode formed of a material from which said secondary electrons are generated is arranged below a scanning electrode for scanning said electron beam. And a moving mechanism for moving the electron beam in a direction perpendicular to the optical axis of the electron beam. 14. A scanning electron microscope according to claim 1 or 2, wherein a light or an electric signal is generated by collision of an electron near the optical axis of said electron beam and on said objective lens. A scanning electron microscope and an apparatus similar to the scanning electron microscope, wherein the scanning electron microscope is provided with an electrode to be made. 15. The scanning electron microscope according to claim 14, wherein an electrode for generating a light or an electric signal by collision of the electrons is arranged below a scanning electrode for scanning the electron beam. A scanning electron microscope comprising a moving mechanism for moving the electron beam in a direction perpendicular to the optical axis of the electron beam, and a device similar to the scanning electron microscope. 16. A scanning electron microscope according to claim 1 or 2, and a device similar to the scanning electron microscope, wherein an electron beam impinges on a scanning electrode near an optical axis of the electron beam and scans the electron beam. A scanning electron microscope and an apparatus similar to the above, wherein an electrode for generating an electric signal is arranged, and means for converting the light or the electric signal into an image signal is provided. 17. A scanning electron microscope according to claim 1 or 2, further comprising a quadrature electromagnetic field generator for generating an electric field and a magnetic field orthogonal to each other with respect to said electron beam. A scanning electron microscope and a similar device, wherein the electron beam has a deflecting action that cancels out, and the information signal has a deflecting action both acting on the detector side. 18. The scanning electron microscope according to claim 17, wherein an electrode formed of a substance that generates secondary electrons by collision of electrons is arranged near the optical axis of said electron beam. The orthogonal electromagnetic field generator is provided at a position near an electrode formed of a substance from which the secondary electrons are generated and at a position where the secondary electrons generated from the electrode can be deflected to the secondary electron detector side. Scanning electron microscope and similar devices.