JPH07296757A - Scanning electron microscope, and similar device thereto - Google Patents

Abstract

PURPOSE:To perform image observation and analysis in a precise position regardless of kind of sample or sample inclination. CONSTITUTION:When the distance between the surface of a sample 11 and an objective lens 7 is set, the current of an exciting coil 6 is set according to the signal of an optical system control part 13. At this time, whether the surface of the sample 11 is conformed to the position of a preset focusing point (focal point) or not is judged from the signal obtained by a secondary signal detector 9 by a focusing point detecting part 16. When it is not conformed, the signal is transmitted to a sample stage driving part 18 through a sample stage control part 17, and a sample stage 10 is vertically moved. According to this method, the sample stage 10 can be set in a position where the sample surface is conformed to the focusing point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope which obtains a scanning image based on a secondary signal obtained by irradiating a sample with a primary electron beam emitted from an electron gun, and a similar device.

[0002]

2. Description of the Related Art According to the method disclosed in Japanese Examined Patent Publication No. 3-66777, the position of the first stage is memorized in order to link the vertical movement of the sample stage and the exciting current of the objective lens. I need to keep it. Further, since the thickness of the sample varies, the focus adjustment is performed each time the observation position is moved without moving the stage position. That is, each time the observation position is changed, it is necessary to store the position and the exciting current value of the objective lens. This is not only due to the difference in height of the sample surface,
No consideration has been given to the horizontal movement of the stage. Further, according to the description, the procedure of first performing focus adjustment and then memorizing is required, so that operability is complicated.

In the conventional apparatus, the vertical position control is performed by the vertical position detection signal of the sample. However, in this conventional technique, it is difficult to accurately set the position of the sample surface (observation surface) because the variation in the sample thickness and the setting error of the sample height are not taken into consideration.

[0004]

In the above-mentioned prior art, the sample surface cannot be correctly set at a preset vertical position if there is variation in sample thickness or sample height setting error. For example, when performing X-ray analysis, since the distance between the sample and the objective lens has already been determined, the positional deviation of the sample surface (analysis point) in the vertical direction causes a decrease in analysis sensitivity.

An object of the present invention is to accurately align the sample surface with a preset position even if there are variations in sample thickness and sample height setting errors.

[0006]

In the present invention, as shown in FIG. 1, an electron gun 1 and a primary electron beam 2 emitted from the electron gun 1 are used.
Focusing coil 5, exciting coil 6 and objective lens 7 for irradiating the sample with a narrowed beam, deflectors 8a and 8b for two-dimensionally scanning the primary electron beam on the sample, and primary electron beam Secondary signal detector 9 for detecting the secondary signal generated from the sample by the irradiation of the sample, and the sample stage 1 capable of moving the sample in the horizontal and vertical directions with respect to the objective lens.
In an electron beam apparatus equipped with 0, means for electrically controlling the vertical position of the stage and focusing of the primary electron beam from secondary electron or backscattered electron signals obtained when the primary electron beam is scanned on the sample. A focus detection unit that detects whether or not the point (focus point) and the sample surface match is provided, and the preset focusing point (focus point) and the sample surface match by the signal obtained by the focus detection unit. The vertical position of the sample stage is controlled as described above.

[0007]

According to the above-described structure, when the distance between the sample surface and the objective lens is set, the vertical position of the sample stage is focused so that the preset focus point (focus point) and the sample surface coincide with each other. An accurate sample surface position is set by being electrically controlled by the signal from the detection means. This will set an accurate sample position regardless of the sample type and sample tilt angle.
This enables image observation and analysis at accurate positions.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. An example of the operation is shown below as a flowchart of FIG.

The primary electron beam 2 emitted from the electron gun 1 is narrowed down by the focusing coil 5 and the objective lens 7 to irradiate the sample, and two-dimensionally scanned on the sample by the deflectors 8a and 8b. The secondary signal generated from the sample by the irradiation of the primary electron beam is detected by the secondary signal detector 9. The sample can be moved horizontally and vertically with respect to the objective lens by the sample stage 10. Surface of sample 11 and objective lens 7
When the distance between and is set by the control unit 12, the exciting current control unit 14 sets the current value of the exciting coil 6 by a signal supplied from the optical system control unit 13. The signal detected by the secondary signal detector 9 is supplied to the focusing point detector 16 via the secondary signal detector 15. Here, the focus point detection unit 16 determines whether or not the surface of the sample 11 matches the focus point set by the optical system control unit 13 and the excitation current control unit 14 based on the signal obtained by the secondary signal detector 9. To detect. The detected signal is supplied from the focus point detection unit 16 to the sample stage drive unit 18 via the sample stage drive control unit 17, and the sample stage 10 is moved in the vertical direction. The movement signal at this time is supplied from the sample stage drive control section 17 and the sample stage drive section 18 to the focusing point detection section 16 via the sample stage position detection section 19. In this case, when it is detected that it coincides with the focus point, a detection signal is supplied to the sample stage drive unit 18 via the sample stage drive control unit 17, and the stage position is set.
Further, if it is not detected that it coincides with the focus point, an undetected signal is supplied to the sample stage drive unit 18 via the sample stage drive control unit 17, and the sample stage 10 is moved in the vertical direction. The movement signal at this time is supplied to the focus point detection unit 16 via the sample stage position detection unit 19.
While the sample stage 10 is moving, it is always detected by the above method whether or not the focusing point and the sample surface are coincident with each other. When the coincidence is detected, a detection signal is transmitted via the sample stage drive controller 17 to the sample. It is supplied to the stage drive unit 18 and the stage position is set.

The above-described series of operations may be performed by detecting the vertical position of the sample surface in advance by the focusing point detecting means before controlling the stage, and then controlling the stage by the amount of deviation between the sample surface position and the set value. The same effect can be obtained.

An example in which the sample stage 10 is tilted by the above method is shown in FIG.

When the tilt angle is set by the control unit 12,
The signal is transmitted to the tilt drive unit 21 via the tilt angle control unit 20.
And the sample stage 10 is tilted. This tilt signal is supplied to the sample stage position detector 19 via the tilt angle detector 22. This signal is supplied to the sample stage controller 17 via the controller 12 to control the vertical control range of the sample stage 10.

An example of a scanning transmission electron microscope to which the above method is applied is shown in FIG.

Similarly to the above, the surface position of the sample 11 is set,
The current value of the exciting coil 6 is set in the exciting current controller 14 by the signal supplied from the optical system controller 13.
The signal detected by the secondary signal detector 9 is supplied to the focusing point detector 16 via the secondary signal detector 15. Further, the signal detected by the elastic scattered electron detector 23 is supplied to the signal processing unit 25 via the elastic scattered electron detecting unit 24 to obtain a signal having a further improved S / N ratio, and transmitted electrons and inelastic scattering are obtained. The signal detected by the electron detector 26 is transmitted through the transmitted electron and inelastically scattered electron detector 27, and then the signal processor 25.
The signal, which is supplied to the signal processing unit 25 and processed by the signal processing unit 25, is supplied to the focus point detection unit 16. The elastic scattered electron detector 24
The signals of the transmitted electron and inelastically scattered electron detection unit 27 may be directly supplied to the excitation current control unit 14 and the focus point detection unit 16 without passing through the signal processing unit 25. Here, the focus point detection unit 16 detects whether or not the surface of the sample 11 coincides with the focus points set by the optical system control unit 13 and the excitation current control unit 14 based on the signal obtained by the means. The detected signal is transmitted from the focusing point detection unit 16 via the sample stage drive control unit 17 to the sample stage drive unit 1.
8 and the sample stage 10 is moved in the vertical direction. The movement signal at this time is supplied from the sample stage drive control unit 17 and the sample stage drive unit 18 to the focusing point detection unit 16 via the sample stage position detector 19. In this case, when it is detected that the focal point coincides with the focus point, a detection signal is supplied to the sample stage drive unit 18 via the sample stage drive control unit 17 to set the stage position. Further, if it is not detected that it coincides with the focus point, an undetected signal is supplied to the sample stage drive unit 18 via the sample stage drive control unit 17, and the sample stage 10 is moved in the vertical direction. The movement signal at this time is supplied to the focus point detection unit 16 via the sample stage position detection unit 19. Even during the movement of the sample stage 10, it is always detected by the above method whether or not the focusing point and the sample surface are coincident with each other. When the coincidence is detected, a detection signal is transmitted via the sample stage drive controller 17 It is supplied to the stage drive unit 18 and the stage position is set.

FIG. 5 shows an example of a vertical drive unit for the sample stage.

The sample stage 10 is set by moving the sample stage drive unit 18 by the method described above. A motor, hydraulic pressure, or magnetic one can be used as a drive source of the sample stage drive unit 18. It may also be driven by manual operation.

6 and 7 show an example of a drive mechanism in the vertical direction of the sample stage.

The drive unit is provided with means for performing two-stage adjustment of the sample stage drive unit 18 and the sample stage fine movement drive unit 32.
The sample stage 10 is set by the method described above. This is roughly set by the sample stage drive unit 18, and then the sample stage fine movement drive unit 32 adjusts the inside of the minute area.

FIG. 6 shows the sample stage drive unit 18 in which the sample stage fine movement drive unit 32 is provided. This is characterized in that fine adjustment can be easily performed by dividing it into two stages according to the above description.

FIG. 7 shows the sample stage drive unit 18 provided with the sample stage fine movement drive unit 32 above the sample stage drive unit 18. This is characterized by moving the sample holder 31, and requires less force than moving the sample stage 10.

[0021]

As described above, according to the present invention, while the control signal of the optical system is taken in real time, the exciting current is set in order to set the preset sample position, and the vertical direction of the sample stage is set. Along with the movement of the sample, it is judged from the obtained secondary signal whether or not the focus point and the sample surface match.If they match, the sample stage is set at that position, and if they do not match The stage is moved to, and the distance is set to a preset distance. As a result, the operator only needs to set the distance between the sample surface and the objective lens, and the focusing work that has been performed every time the sample stage is moved in the vertical direction becomes unnecessary. The sample surface can always be set at a preset vertical position regardless of the setting error of the sample thickness or sample height, and the distance between the sample and the objective lens such as X-ray analysis has already been determined. In this case, the sample surface (analysis point) is not displaced in the vertical direction, so that the analysis sensitivity is increased.

[Brief description of drawings]

FIG. 1 is a diagram showing an irradiation lens system, an objective lens system, a sample stage, and a control unit of a scanning electron microscope of the present invention.

FIG. 2 is a flowchart of an irradiation lens system, an objective lens system, a sample stage, and a control system of the scanning electron microscope of the present invention.

FIG. 3 is a diagram showing an irradiation lens system, an objective lens system, a sample stage, and a control unit of the scanning electron microscope of the present invention.

FIG. 4 is a diagram showing an irradiation lens system, an objective lens system, a sample stage, and a control unit of the scanning transmission electron microscope of the present invention.

FIG. 5 is a diagram showing a sample stage drive unit of the present invention.

FIG. 6 is a diagram showing a sample stage drive unit of the present invention.

FIG. 7 is a diagram showing a sample stage drive unit of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron beam, 3 ... Extraction electrode, 4 ... Accelerating electrode, 5 ... Focusing coil, 6 ... Excitation coil, 7 ... Objective lens, 8a, 8b ... Deflector, 9 ... Secondary signal detector, 10 ...
Sample stage, 11 ... Sample, 12 ... Control unit, 13 ... Optical system control unit, 14 ... Excitation current control unit, 15 ... Secondary signal detection unit, 16 ... Focus point detection unit, 17 ... Sample stage drive control unit, 18 ... Sample stage drive unit, 19 ... Sample stage position detection unit, 20 ... Inclination angle control unit, 21 ... Inclination drive unit,
22 ... Inclination angle detector, 23 ... Elastic scattered electron signal detector, 24 ... Elastic scattered electron signal detector, 25 ... Signal processing unit, 26 ... Transmission and inelastic scattered electron signal detector, 27 ...
Transmitted and inelastically scattered electron signal detectors, 28 ... Elastic electrons,
29 ... Transmission and inelastically scattered electrons, 30 ... Sample chamber, 31 ...
Sample holder, 32 ... Sample stage fine movement drive unit.

Claims (3)

[Claims] 1. An electron gun, an electron lens for narrowing a primary electron beam emitted from the electron gun and irradiating the primary electron beam onto a sample, and a two-dimensional scanning of the primary electron beam on the sample. An electron beam equipped with a deflector, a secondary signal detector for detecting a secondary signal generated from the sample by irradiation with the primary electron beam, and a sample stage capable of moving the sample horizontally and vertically with respect to the objective lens. In the device, means for electrically controlling the vertical position of the stage, and a focusing point (focus point) of the primary electron beam from secondary electron or backscattered electron signals obtained when the primary electron beam is scanned on the sample. A means for detecting whether or not the sample surface coincides is provided, and a means for controlling the vertical position of the stage so that the preset focusing point and the sample surface coincide and controlling them are provided. Featuring That the scanning electron microscope and the like apparatus. 2. The vertical control of the sample stage is performed by detecting the vertical position before control of the sample stage from the exciting current value of the objective lens obtained by the focus point (focus point) detecting means of the primary electron beam in advance. The scanning electron microscope according to claim 1, wherein the scanning stage is moved to move the sample stage by an amount corresponding to the deviation between the detected vertical position and the set position. 3. The scanning according to claim 1, wherein when the sample stage is tilted, a means for detecting the tilt angle as a signal is provided to control the control range of the vertical position of the stage based on the tilt angle. Electron microscopes and similar devices.