KR100460482B1 - Scanning electron microscope - Google Patents

Abstract

High-precision beam current is measured without mechanical or electrical adjustment while maintaining high resolution conditions.

In a scanning electron microscope in which an orthogonal electromagnetic field generating means is provided from an objective lens to an electron source side and detects secondary electrons generated from a sample through an orthogonal electron field, a deflection electrode or a deflection coil is disposed in the scanning coil portion, A beam current detecting means was provided in the generating portion.

Accurate beam current measurement without mechanical or electrical adjustment is possible while maintaining high resolution optics placement.

Description

Scanning electron microscope

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam apparatus, and more particularly, to a scanning electron microscope capable of easily measuring and setting a current irradiated onto a sample in a scanning electron microscope suitable for obtaining a high resolution image, and a similar apparatus thereof.

Conventionally, in order to obtain a high resolution secondary electron image, the focal length of an objective lens is shortened, and the secondary electron which generate | occur | produces from a sample is detected by the secondary electron detector arrange | positioned from the objective lens to the electron source side. At this time, in order to prevent the primary electron beam from being affected by the voltage applied to the secondary electron detector, means for generating an electric field and a magnetic field orthogonal to the electron source side in the objective lens, as in Japanese Patent Laid-Open No. 6-132002. And a method of inducing secondary electrons generated from a sample by the orthogonal electron system to a secondary electron detector has been devised.

By the way, in order to obtain a high resolution secondary electron image with a scanning electron microscope, it is necessary to select an appropriate beam current (sample irradiation current) according to the sample. In the case of performing X-ray analysis, it is important to grasp the beam current. Conventionally, for this purpose, as a means for measuring the beam current, a Faraday cup is provided on a part of the sample stage, and the Faraday cup of the sample stage is moved to the beam irradiation point at the time of beam current measurement, or mechanically moved to the objective lens side by the throttle plate. When the Faraday cup apparatus which can move to this is arrange | positioned and the beam current is measured, the method of mechanically moving a Faraday cup to an optical axis was taken.

However, such a prior art has a drawback of missing the part observed by measuring a beam current from a field of view, adjusting a Faraday cup mechanically, and increasing cost.

The object of the present invention is to eliminate the shortcomings of the prior art and to measure the beam current easily and at high speed when it is necessary without missing the observation part from the field of view or adjusting the mechanical position. It is to provide a scanning electron microscope which does not deteriorate.

In order to achieve the above object, the primary electron current detection means is disposed near the primary electron beam passage, and the primary electron current detection means is provided with deflection means for deflecting the primary electron beam.

Moreover, the throttle plate with respect to the primary electron beam was arrange | positioned by the electron source side by the primary electron current detection means or the deflection means.

Further, a focusing lens was disposed between the primary electron beam current detection means and the throttle.

Further, the primary electron current detecting means was formed in a groove shape.

The groove-shaped primary electron current detecting means is arranged along the inner wall of the body tube of the scanning electron microscope, and as a specific configuration, the primary electron current detecting means having a groove-shaped structure in the component of the orthogonal electromagnetic field generating means. Was added. And deflection means for positioning the primary electron beam in the primary electron current detection means at the same position as the scanning coil.

Also, a means for detecting the primary electron current while deflecting the beam and providing a means for detecting the maximum value from the output of the current detecting means obtained when the beam is deflected is provided.

Further, a beam current input means was provided, and a control means for controlling the beam current control convergence lens disposed from the throttle plate toward the electron source side was provided so that the current value input from the beam current input means coincided with the output of the maximum value detecting means. .

According to the configuration of the present invention described above, the following actions are obtained.

By positioning the primary electron beam in the primary electron current detection means by the deflection means, it is possible to detect the primary electron current, which is the primary electron that has passed through the throttle, and thus should be irradiated on the sample. The primary electron current to be detected can be detected accurately.

By arranging the deflection means of the primary electron beam at the same position as the scanning coil of the primary electron beam, and assembling the beam current detection means to a part of the orthogonal electromagnetic field generating means, the beam current without changing the electron optical system arrangement that is optimal for high-resolution observation Can be detected. That is, in such an optical system, when the distance between the scanning coil and the objective lens becomes longer, disturbance effects such as an external magnetic field are easily affected, and realization of low magnification becomes difficult. Therefore, by incorporating the beam current detecting means into a part of the quadrature field generating means which is indispensable for obtaining a high resolution image, the beam current can be detected without lengthening the distance between the scanning coil and the objective lens.

In addition, the longer the traveling distance of the beam from the electron source to the sample is, the easier the primary electron beam is to be affected by the external magnetic field, but according to the configuration of the present invention, it is not necessary to lengthen the barrel even when the primary electron current detector is disposed. Therefore, the fall of the resolution by an external magnetic field can be prevented.

Since the beam current detection means has a groove-like structure as shown in Fig. 2, the deflection means for detecting the beam current may be any one direction, and the deflection means may be formed by a simple electrode or a deflection coil in one direction. There is an effect that can be realized and the control can be simplified.

In order to prevent emission of secondary electrons or reflected electrons from the entrance (beam inlet) of the groove for beam current detection, and to accurately detect the beam current, the beam inlet should be as narrow as possible. However, if the beam entrance port is narrowed, accurate detection of the beam current is impossible unless the beam is deflected correctly at the entrance hole.

On the other hand, since the output of the beam current detection means becomes maximum when the beam is deflected exactly to its entrance, in the present invention, the primary electron beam is deflected while monitoring the output of the beam current detection means, so that the maximum output of the beam current detection means The maximum value detecting means for detecting the pressure is provided. By this maximum value detecting means and the beam deflection control means, it is possible to detect the correct beam current without special adjustment.

In addition, since the present invention includes a detector formed in the shape of a groove elongated substantially perpendicular to the deflection direction of the primary electron beam, the deflection direction and the detector even when the center trajectory of the primary electron beam deviates from the mechanical center of the deflector. It is possible to avoid the situation where the positions of the positions differ from each other, and to accurately position the primary electron beam on the detector even with a relatively simple deflection means.

Further, since a converging lens can be arranged between the throttle plate and the beam current detecting means, and the beam can belong to the vicinity of the entrance port of the beam current detecting means, a narrower beam current detecting groove can be provided. The detection accuracy of the current can be increased.

In addition, the beam current adjustment convergence lens can be controlled to have a beam current value input in advance by the control means of the beam current adjustment convergence lens disposed on the electron source side in the throttle plate while detecting the beam current, thereby realizing the specified beam current accurately. You can.

That is, the deflection position at which the primary electron beam indicates the maximum current value is specified by the above means, and the beam current to be irradiated to the specimen is precisely set by controlling the beam current adjusting convergence lens while deflecting the primary electron beam at the position. It becomes possible.

Example

1 is a schematic cross-sectional view of one embodiment of the present invention. A voltage is applied between the cathode 1 and the first anode 2 by a high voltage control power supply 20 controlled by a microprocessor (CPU) 30, and a predetermined emission current is drawn from the cathode. Since the accelerating voltage is applied between the cathode 1 and the second anode 3 by the high voltage control power supply 20 controlled by the CPU 30, the primary electron beam 4 emitted from the cathode 1. Is accelerated and proceeds to the rear lens system. The primary electron beam 4 is converged by the beam current control converging lens 5 controlled by the lens control power supply 21, and the unnecessary area of the beam is removed by the throttle plate 9. Thereafter, the microlens | fine-points to the sample 8 are controlled by the condensation lens 6 for reduction ratio adjustment controlled by the lens control power supply 22, and the objective lens 7 understood and controlled by the objective lens control electrode 23 ( The sample is converged as a spot, and the scanning coil 15 scans the sample image two-dimensionally. The scan signal of the scan coil 15 is controlled by the scan coil control power supply 24 in accordance with the observation magnification. The convergence angle (beam opening angle) of the primary electron beam is determined as an optimal value at the focal position of the objective lens throttle 9 and the condenser lens 6 for adjusting the reduction ratio. In the scanning coil 15, electrodes 10 and 11 are disposed on the objective lens side, and negative and positive voltages are applied to form an electric field E, respectively. Moreover, the coil which generate | occur | produces the magnetic field B is arrange | positioned in the position orthogonal to the electric field E, and forms the orthogonal electromagnetic field with the electric field E. As shown in FIG. The strengths of the electric field E and the magnetic field B forming the orthogonal electron field are set so that the deflection action of E and B with respect to the primary electron beam cancel each other out. On the other hand, the secondary electrons 19 generated from the sample are deflected toward the secondary electron detector by the action of the orthogonal electron field. Since the electrode 11 on the secondary electron detector side is composed of a mesh-like metal plate so that secondary electrons can pass, secondary electrons are transmitted to the electrode 11 and detected by the secondary electron detector 12. The output signal (phase signal) of the secondary electron detector is displayed as an SEM image by the trademark display device 13.

One electrode 18 is arranged inside the scanning coil 15, and its potential is controlled by the deflection control power supply 26. As shown in FIG. In normal correlation, the electrode 18 is at the earth potential, but when measuring the beam current, a negative voltage of the electrode 18 is applied to deflect the primary electron beam 4 to the position of the beam current detecting means 16. . The same function can be realized even if the electrode 18 is substituted with a deflection coil wound over the scanning coil portion. As shown in Fig. 2, the beam current detecting means 16 has a structure having a groove on the circumference, and when a beam is incident in the groove, it can function as a Faraday cup to detect the beam current. The inside of the groove of the current detecting means is coated with a substance such as carbon that is hard to generate secondary electrons or reflected electrons even when irradiated with an electron beam, so that the current of the electron beam incident in the groove can be accurately detected. This current detecting means is electrically insulated with the insulator 100, as shown in FIG. 3, and is disposed inside the electrodes 10 and 11, and is set to the earth potential at the time of normal correlation.

The condensing lens 6 for reduction ratio adjustment is controlled so that at least the primary electron beam is focused near the entrance port of the primary electron current detection means when measuring the beam current, and returns to the original condition after the beam current measurement. . However, when the convergence point 60 of the primary electron beam in the high resolution operating condition exists near the primary electron current detecting means, it is necessary to change the excitation condition of the convergence lens 6 for the reduction ratio adjustment at the time of beam current detection. none.

When measuring the primary electron current, the primary electron current detection means 16 is removed from the earth potential and connected to the beam current detection circuit 27. The control CPU 30 reads the output of the current detection circuit 27 while gradually increasing the voltage of the deflection control means 26. In the embodiment of the present invention, since the groove of the beam current detecting means is arranged on the circumference, the deflection direction of the beam may be arbitrary. For this reason, even if the center trajectory (solid axis) of the primary electron beam deviates from the mechanical center of the deflector, the primary electron beam can be accurately moved to the groove of the beam current detecting means. In addition, in the present embodiment, a cylindrical one is used for the primary electron detection means, but if the groove is disposed at a relative position of the deflection electrode and has a groove of any predetermined length or more, the same effect as that of the cylindrical one can be obtained. In addition, in the embodiment of the present invention, since an arc-shaped primary electron current detector is used, it can be arranged along the inner wall of the barrel of a scanning electron microscope which is generally cylindrical.

At this time, the output of the current detection circuit 27 changes as shown in Fig. 4 with respect to the deflection control voltage, and when the beam is the deflection control voltage which becomes the home position of the primary electron current detection means 16, the current detection is performed. The output of the circuit 27 is maximum. Therefore, the control CPU 30 determines whether the output of the beam current detection circuit 27 has been maximized, while raising the deflection control voltage to detect the maximum value of the output of the beam current detection circuit 27. The current can be measured. The above-mentioned procedure for measuring the beam current can be represented by the flowchart of FIG. 5.

When the beam current is set to a pre-input value, a voltage is applied to the electrode 18 to deflect the primary electron beam to the position of the beam current detection means 16, and the output signal of the current detection circuit 27 is previously The excitation of the converging lens 5 for beam current control is controlled so as to match the input beam current value.

6 shows another embodiment of realizing beam deflection when detecting a beam current. In addition to the scanning coil 15 which scans two-dimensionally on the beam sample, the deflection coil portion is provided with an axis adjustment coil 190 for adjusting the scanning center trajectory of the beam to the center of the objective lens 7. In normal observation, the current of the axis adjustment coil 190 is set by the axis adjustment coil control power supply 260 so that the trajectory of the beam passes through the center of the objective lens. At the time of beam current detection, while controlling the output of the beam detection means 27 by the control CPU, the current of the axis adjustment coil 190 is gradually increased, and the value at which the output of the beam detection means is maximized is detected as the beam current. In this way, the deflection means for primary electron current detection can be provided in a relatively simple manner without destroying the ideal optical arrangement.

According to the configuration of the present invention, since it is not necessary to change the positional relationship of the components of the electro-optical system that can observe high resolution, the beam current can be measured and set while maintaining the high resolution. In addition, since it is not necessary to lengthen the rigid body in order to measure the beam current, this does not make it easy to be affected by an external magnetic field. In addition, since there is no need to adjust mechanically or electrically, there is an effect that a simple and accurate measurement of the beam current is possible.

1 is a schematic cross-sectional view of one embodiment of the present invention;

2 shows the structure of the current detecting means;

3 is a view showing an arrangement of current detecting means;

4 is a diagram showing a relationship between an output of a current detection circuit and a deflection control voltage;

5 is a flowchart of beam current measurement,

6 is a schematic cross-sectional view showing another embodiment of the present invention.

※ Explanation of symbols for main parts of drawing

1: cathode 2: first anode

3: second anode 4: primary electron beam

5: convergence lens for beam current adjustment 6: convergence lens for reduction ratio adjustment

7: Objective lens 8: Sample

9: Throttle Plate 10: Electrode

11: mesh-like electrode 12: primary electron detection unit

13: Labeling device 15: Injection coil

16: beam current detection means 18: deflection electrode

19: secondary electronics 20: high voltage control power supply

21: convergence lens control power supply for beam current adjustment

22: convergence lens control power supply for reduction ratio adjustment

23: objective lens control power supply 24: scanning coil control power supply

27: beam current detection circuit 30: control CPU

100: Insulation

Claims (22)

In a scanning electron microscope for scanning a primary electron beam emitted from an electron source on a sample, and detecting a secondary electron generated from the sample to obtain a scanning image, A groove-shaped primary electron current detector for detecting a primary electron current disposed around a path of the primary electron beam And a deflection means for deflecting the primary electron beam on the detector. The method of claim 1, And the groove-shaped primary electron current detector is elongated in a direction perpendicular to the direction of deflection by the deflection means. The method of claim 1, And said primary electron current detecting means is located on the electron source side from the objective lens for focusing the primary electrons, and is disposed on the sample side from the throttle plate of the primary electron beam. The method of claim 3, wherein A focusing lens is disposed between the primary electron current detecting means and the throttle plate, and the focusing lens is used to focus the primary electron beam in the vicinity of the primary electron current detector. The method of claim 1, The deflection means detects the output of the primary electron current detector while deflecting the primary electron beam toward the primary electron current detector, and specifies the current value of the primary electron beam with the maximum value obtained by the detector. A scanning electron microscope comprising a current value specifying means. The method of claim 1, The deflection means is a scanning electron microscope, characterized in that the deflection coil disposed at the same position as the scan coil for scanning the primary electron beam on a sample. The method of claim 1, And the primary electron current detector is formed in a bow shape centering on the primary electron beam path. In a scanning electron microscope in which a primary electron beam emitted from an electron source is scanned on a sample and a secondary electron generated from the sample is detected to obtain a scanning image, A primary electron current detector for detecting a groove-shaped primary electron current disposed around the primary electron beam path; Deflection means for deflecting the primary electron beam toward the primary electron current detector and passing the detector image; And a current value specifying means for specifying a current value of said primary electron beam with the maximum current value obtained by said primary electron current detection means. The method of claim 8, And said groove-shaped primary electron current detector is elongated in the vertical direction with respect to the deflection direction by said deflection means. The method of claim 8, The primary electron current detector is located on the electron source side from the objective lens for focusing the primary electron beam, and is arranged on the sample side from the throttle plate of the primary electron beam. The method of claim 10, And a focusing lens disposed between the primary electron current detecting means and the throttle plate, and the focusing lens focuses the primary electron beam in the vicinity of the primary electron current detector. The method of claim 8, The deflection means is a scanning electron microscope, characterized in that the deflection coil disposed at the same position as the scan coil for scanning the primary electron beam on a sample. The method of claim 8, And the primary electron current detector is formed in a bow shape centering on the primary electron beam path. In a scanning electron microscope for scanning a primary electron beam emitted from an electron source on a sample, and detecting a secondary electron generated from the sample to obtain a scanning image, A primary electron current detector for detecting a primary electron beam current around a path of the primary electron beam; Deflection means for deflecting the primary electron beam to the detector; A throttle plate disposed on the electron source side as viewed from the deflection means with respect to the primary electron beam; It comprises a focusing lens for beam current control disposed on the electron source side, And the beam current control focusing lens is controlled to have a preset current value while the focusing point of the beam current control focusing lens is positioned at the detector. The method of claim 14, And the groove-shaped primary electron current detector is elongated in a direction perpendicular to the direction of deflection by the deflection means. The method of claim 14, A scanning electron microscope, characterized in that a focusing lens is disposed between the primary electron current detecting means and the throttle plate, and the focusing lens focuses the primary electron beam in the vicinity of the primary electron current detector. The method of claim 14, The deflection means detects the output of the primary electron current detector while deflecting the primary electron beam toward the primary electron current detector direction, and specifies the deflection position of the primary electron beam with the maximum value obtained by the detector. Scanning electron microscope, characterized in that provided with a deflection position specifying means. The method of claim 14, The deflection means is a scanning electron microscope, characterized in that the deflection coil disposed at the same position as the scan coil for scanning the primary electron beam on a sample. The method of claim 14, And the primary electron current detector is formed in a bow shape centering on the primary electron beam path. Primary electrons that scan a primary electron beam emitted from an electron source on a sample and detect primary electron currents around the primary electron beam path of a scanning electron microscope that detects secondary electrons generated from the sample and obtains a scanning image And a deflecting means for deflecting the primary electron beam in the detector while arranging a current detector, and a throttle plate with respect to the primary electron beam is disposed on the electron source side as viewed from the deflecting means, and on the electron source side In the detection method of primary electron beam current of a scanning electron microscope in which a current control focusing lens is disposed, A first step of deflecting the primary electron beam toward the primary electron current detector and specifying at which deflection position the primary electron current detector exhibits a maximum value; And a second step of controlling the beam current control focusing lens to have a preset current value in a state where the primary electron beam is positioned at the position. In a scanning electron microscope for scanning a primary electron beam emitted from an electron source on a sample, and detecting a secondary electron generated from the sample to obtain a scanning image, A primary electron current detector for detecting a groove-shaped primary electron current disposed around a path of the primary electron beam; It comprises a deflection means for deflecting the primary electron beam to the detector, And the primary electron current detector is arranged along an inner wall of the barrel of the scanning electron microscope. In a scanning electron microscope in which a primary electron beam emitted from an electron source is scanned on a sample and a secondary electron generated from the sample is detected to obtain a scanning image, Deflection means for deflecting the primary electron beam; And a primary electron current detector elongated in a direction perpendicular to the deflection direction of said deflection means arranged around said primary electron beam path.