JP3779581B2 - Electron beam equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam apparatus that obtains an image of a sample by a signal generated when the sample is scanned with an electron beam, and more particularly to an electron beam apparatus suitable for a scanning electron microscope.
[0002]
[Prior art]
For example, in an electron beam apparatus such as a scanning electron microscope, an electron beam (electron beam) is deflected by a deflector arranged in two stages along an optical axis (electron beam axis) between an electron gun and an objective lens, and the sample is irradiated. Electron beam (primary electron beam) scans the observation area of the sample.
[0003]
Since the deflection electric field (in the case of electric field type) or deflection magnetic field (in the case of magnetic field type) by the deflector, the uniformity of the electric field or magnetic field cannot be maintained as the distance from the central axis (optical axis) of the deflector is increased. If the deflection angle of the primary electron beam is increased to obtain a low magnification, the primary electron beam is affected by a non-uniform electric field or magnetic field in the deflector, resulting in distortion and blurring at the periphery of the obtained image. Will occur.
This effect depends on the structure of the deflector, in particular the inner diameter of the deflector, which limits the minimum magnification.
[0004]
Therefore, in conventional scanning electron microscopes, particularly in scanning electron microscopes that employ an in-lens or snorkel lens with a short focal length for the objective lens, the excitation of the objective lens is disabled or the objective lens is used when used at a low magnification. The primary electron beam was deflected by using only one stage of the deflector while setting the excitation of the beam to be weak.
[0005]
[Problems to be solved by the invention]
The above prior art cannot be said that sufficient consideration is given to the low magnification operation, and there is a problem in that it enables a wide field of view under extremely low magnification.
That is, as described above, in the prior art, when using at a low magnification, the excitation of the objective lens is disabled, or the excitation of the objective lens is set weak and the primary electron is used by using only one stage of the deflector. However, in this case, the minimum magnification (maximum observation field of view) is limited to the shape of the objective lens that is the last stage lens, particularly the hole diameter (hole diameter).
[0006]
In order to increase the resolution of the objective lens, it is known that reducing the hole diameter of the objective lens is effective, but this means that the field of view is narrowed. When the resolution is increased, an image with a low magnification suitable for searching the visual field cannot be obtained.
[0007]
In any case, it is extremely difficult to form an image with a low magnification of 10 times or less with the above-described conventional technology.
When the primary electron beam is converged on the sample by the objective lens, the convergence angle on the sample is only about several mrad at the minimum, and the depth of focus at this time is limited to about 0.5 mm at the deepest.
[0008]
The present invention has been made in view of the above-described problems of the prior art, and its purpose is to provide an electronic device that can easily cope with extremely low magnification due to a deep focal depth without distortion even when the deflection angle is increased. It is to provide a wire device.
[0009]
[Means for Solving the Problems]
In the electron beam apparatus of the type which observes the image of the sample by scanning the sample surface with an electron beam converged by at least two stages of electron lenses and detecting secondary electrons generated from the sample surface. An electron gun side deflection means positioned on the electron gun side of the electron lens forming the objective lens among the at least two stages of electron lenses, and a sample side deflection positioned on the sample side of the electron lens forming the objective lens And a moving means that enables the sample-side deflection means to be taken in and out of the electron beam path passing through the objective lens, and when observing a high-resolution image, the sample-side deflection means is taken out from the electron beam path, the electron gun side scanning the electron beam using a deflecting means, at the time of low-magnification image observation, put the sample side deflecting means in the path of the electron beam, so as to scan the electron beam with the sample-side deflecting means It is achieved.
[0010]
At this time, a means for substantially invalidating the function of the objective lens is provided, and at the time of observing the low-magnification image, the electron beam is converged by an electron lens located closer to the electron gun than the objective lens. May be.
[0011]
Similarly, at this time, a means for switching between the deflection means on the electron gun side and the deflection means on the sample side may be provided, and the electron beam is scanned by the deflection means on the electron gun side, and the sample side The deflection means may be provided with a control means for moving the scanning center.
[0012]
At this time, means for detecting the vertical position of the sample stage holding the sample is provided, and the deflection means on the sample side can be moved only when the sample stage is within a predetermined position range. Alternatively, the acceleration voltage of the electron beam may be controlled to 5 kV or less during low-magnification image observation.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electron beam apparatus according to the present invention will be described in detail with reference to embodiments shown in the drawings.
FIG. 1 shows an embodiment in which the electron beam apparatus according to the present invention is embodied as a scanning electron microscope, in which a lens barrel of the electron microscope is omitted.
In the configuration of FIG. 1, a cathode 1 and an extraction electrode 2 are provided on the top of a lens barrel, and a voltage V ₁ is applied between them, whereby electrons emitted from the cathode 1 are emitted from the cathode. 1 is accelerated by a voltage V _acc applied between the accelerating electrode 3 and the primary electron beam E, an unnecessary region is removed by the diaphragm 5, and the converging lenses 4 and 6 controlled by the lens control power source 12. Then, it is narrowed down by the objective lens 8 to become an electron beam Eb, which is irradiated onto the sample 9. Note that the letter E is normally fixed as a symbol representing an electric field, but is used here as a symbol representing a primary electron beam.
[0014]
The electron beam Eb is either a two-stage deflector 7a, 7b disposed on the cathode 1 side before the objective lens 8 or a deflector 17 disposed on the sample 9 side after the objective lens 8. The surface of the sample 9 which is deflected by the above and held on the sample stage 10 is scanned two-dimensionally.
[0015]
As shown in FIG. 2, the deflector 17 on the lower side in the figure is formed in a structure that can be taken in and out of the path of the electron beam Eb by the deflector driving unit 18, and the position is controlled from the outside of the sample chamber 21. The position of the deflector 17 can be detected by the deflector position detector 19.
[0016]
When the sample 9 is irradiated with the electron beam Eb, secondary electrons S _a and S _b are generated from the sample 9 and detected by signal detectors 14a and 14b made of, for example, a photomultiplier equipped with a scintillator.
Therefore, signals corresponding to the intensities of the secondary electrons S _a and S _b are obtained from these signal detectors 14a and 14b.
[0017]
Therefore, by supplying the signals of the signal detectors 14a and 14b as luminance modulation signals to the image display device 15, an enlarged image of the sample 9 is displayed on the image display surface of the image display device 15.
In this embodiment, a snorkel type lens is used as the objective lens 8 as shown in the figure, but any type of lens other than the snorkel type may be used.
[0018]
Which of the deflectors 7a and 7b and the deflector 17 is used to deflect the electron beam Eb is switched by a switch of the deflection control unit 16, which is determined by the user according to the observation purpose and observation conditions. Arbitrarily selected.
[0019]
For example, when high-resolution observation is intended, the deflector 17 is pulled out from the path of the electron beam Eb, the position of the sample 9 is brought close to the very vicinity of the objective lens 8, and the working distance for high-resolution observation (working distance: WD). ), The deflector 7a, 7b deflects the electron beam Eb so that the sample 9 is scanned by the electron beam Eb.
[0020]
Therefore, at this time, as in the prior art, the minimum magnification is limited to a range of several tens of times or more, but on the other hand, observation with a high resolution by a high-magnification image is obtained.
[0021]
On the other hand, when the objective is to observe a low-magnification image, the deflector 17 is inserted into the path of the electron beam Eb during this period so that the distance from the objective lens 8 to the sample 9 is increased to a required value. After setting the working distance for low magnification, the deflector 17 is operated so that the electron beam Eb is deflected and the sample 9 is scanned.
[0022]
Accordingly, at this time, the deflector 17 confirms the position of the sample stage 10 and can be inserted only when the distance from the objective lens 8 to the sample 9 is a predetermined value or more. A wide field of view can be secured at a low magnification of about 10 times.
[0023]
As shown in FIG. 3, the position of the sample stage 10 is controlled by the sample stage drive unit 22. At this time, the vertical position and the tilt angle of the sample stage 10 are detected by the stage position detection unit 23, and the objective lens 8. The position control unit 20 controls so that the deflector 17 can be inserted only when the distance from the sample 9 to the sample 9 is equal to or greater than a predetermined value.
[0024]
Similarly, the deflector 17 is pulled out from the path of the electron beam Eb, and either or both of the vertical position and the tilt angle of the sample stage 10 inserted are within a predetermined range. It is controlled by the position control unit 20 so that it can be pulled out only when it is present.
[0025]
Next, the operation of the scanning electron microscope according to the embodiment will be described with reference to the flowchart of FIG.
First, the user selects an observation condition (S1). When high-resolution observation is intended, the process proceeds to S10 and subsequent steps. When low-magnification image observation is intended, the process proceeds to S20 and subsequent steps.
[0026]
If high-resolution observation is selected (S10), first, the deflector 17 is first pulled out from the path of the electron beam Eb (S11), and then the position of the sample 9 is brought close to the objective lens 8 to achieve high resolution. The working distance for observation is set (S12).
[0027]
Thereafter, the controller 16 switches to the deflectors 7a and 7b (S13), thereby deflecting the electron beam Eb so that the sample 9 is scanned by the electron beam Eb (S14).
As a result, as in the prior art, at this time, the minimum magnification is limited to a range of several tens of times or more, but high-resolution observation with a high-magnification image can be obtained.
[0028]
On the other hand, when observation of a low-magnification image is selected (S20), first, the vertical position and tilt angle of the sample stage 10 are confirmed (S21).
If the result is NG, that is, if the distance from the objective lens 8 to the sample 9 has not increased to a required value, the distance from the objective lens 8 to the sample 9 is changed to a required value by moving the sample stage 10. Then, the deflector 17 is inserted into the path of the electron beam Eb (S23).
[0029]
On the other hand, if the result in S21 is OK, that is, if the distance from the objective lens 8 to the sample 9 is a required value, the process proceeds to S23 as it is, and the deflector 17 is inserted into the path of the electron beam Eb. .
After that, the control unit 16 switches to the deflector 17 (S24), thereby deflecting the electron beam Eb so that the sample 9 is scanned (S25), so that a wide field of view is obtained even at a low magnification of about 10 times. It can be secured.
[0030]
In this embodiment, when observing a low-magnification image, it is desirable that the voltage applied between the cathode 1 and the acceleration electrode 3, that is, the acceleration voltage _Vacc be 5 kV or less. This is because the lower the acceleration voltage, the smaller the magnetic field and electric field required for deflecting the primary electron beam Eb. Therefore, the magnetic field and electric field to be generated by the deflectors 7a and 7b and the deflector 17 are smaller. This is because a wider range of scanning can be obtained with the same intensity.
[0031]
Next, in this embodiment, a deflector 17 is provided, which is disposed closer to the sample 9 than the objective lens 8, so that the field of view to be observed can be electrically moved over a wide range. it can.
In this case, the operation of converging the primary electron beam Eb on the sample 9 is performed by the objective lens 8, and the primary electron beam Eb on the sample 9 is scanned by the deflectors 7a and 7b. In this state, a control signal necessary for visual field movement is supplied from the deflection control unit 16 to the deflector 17.
[0032]
As a result, the primary electron beam Eb is scanned two-dimensionally on the sample 9 by the deflectors 7a and 7b. At this time, the deflector 17 moves the center of scanning by the primary electron beam Eb. .
For example, as shown in FIG. 5, when the scanable range by the deflectors 7a and 7b is a × b, when the scan center is moved by the deflector 17, the entire scanable range a × b is obtained. Will be moved.
[0033]
As a result, as shown in the figure, the scanning range is wide as k1a × k2b (k1, k2: constant).
At this time, the sample stage 10 is controlled by the position controller 20 as described above.
[0034]
In this embodiment, an extremely low magnification image having a deep focal depth can be easily obtained.
In this case, first, the deflector 17 is selected by the deflection controller 16, and the primary electron beam Eb is scanned two-dimensionally on the sample 9 by the deflector 17.
[0035]
In this state, excitation of the objective lens 8 is invalidated by the lens control power source 12 or is set to weak excitation, and the primary electron beam Eb is obtained by the converging lenses 4 and 6 located on the cathode 1 side of the objective lens 8. To converge on the sample 9.
As a result, it is possible to easily obtain an extremely low magnification image with a deep focal depth and a small defocus.
[0036]
Next, the deflector 17 in this embodiment will be described. The deflector 17 may be composed of either a magnetic field type or an electrostatic type deflector as long as it can deflect in the two-dimensional direction of the X direction and the Y direction.
First, FIG. 6 shows an embodiment of a deflector 17 configured as a magnetic field type, in which X direction deflection is obtained by a pair of upper and lower electromagnetic coils 17a and 17b, and a pair of left and right electromagnetic coils 17c, 17d is configured to obtain a deflection in the Y direction. A current controlled by the control unit 16 is supplied to each coil, and the primary electron beam Eb is deflected in a two-dimensional direction by a magnetic field.
[0037]
Next, FIGS. 7 and 8 show an embodiment of the deflector 17 constituted by an electrostatic type. First, FIG. 7 shows four deflecting plates (electrode plates) 17e, 17f, 17g which are paired vertically and horizontally. FIG. 8 shows an embodiment of eight deflecting plates 17i, 17j, 17k, 17l, 17m, 17n, 17o sequentially arranged at an angle of 45 degrees. It is one Embodiment of the deflector 17 comprised by 17p.
[0038]
7 and 8, the voltage controlled by the control unit 16 is applied to each deflection plate, and the primary electron beam Eb is deflected by an electric field.
Further, in the above embodiment, the deflector 17 is operated at a relatively low acceleration voltage of 5 kV, so that the shape of the deflector 17 necessary for realizing extremely low magnification can be reduced. .
[0039]
【The invention's effect】
According to the present invention, an image having no distortion or blur can be obtained even when the deflection angle of the deflector is increased. Therefore, for example, it is possible to easily cope with image observation at an extremely low magnification of 10 times or less. According to the present invention, it is possible to easily search for a visual field.
In addition, according to the present invention, a deep depth of focus can be easily obtained even when a low-magnification image is obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment when an electron beam apparatus according to the present invention is embodied as a scanning electron microscope.
FIG. 2 is a configuration diagram for explaining a positional relationship between a deflector and a sample in an embodiment of the present invention.
FIG. 3 is a block diagram for explaining control of a deflector and a sample stage in an embodiment of the present invention.
FIG. 4 is a flowchart for explaining the operation of the embodiment of the present invention.
FIG. 5 is an explanatory diagram of a scannable range in an embodiment of the present invention.
FIG. 6 is an explanatory diagram showing an example of a magnetic field deflector according to an embodiment of the present invention.
FIG. 7 is an explanatory diagram showing an example of an electric field deflector according to an embodiment of the present invention.
FIG. 8 is an explanatory diagram showing another example of the electric field deflector according to the embodiment of the present invention.
[Explanation of symbols]
E electron beam (primary electron beam)
Eb Electron beam (Primary electron beam)
Sa, Sb Secondary electrons 1 Cathode 2 Extraction electrode 3 Acceleration electrode 4 Converging lens 5 Aperture 6 Converging lenses 7 a and 7 b Deflector 8 Objective lens 9 Sample 10 Sample stage 12 Lens control power supply 14 a and 14 b Signal detector 15 Image display device 16 Deflection control unit 17 Deflector 18 Deflector drive unit 19 Deflector position detection unit 20 Position control unit 21 Sample chamber 22 Sample stage drive unit 23 Sample stage position detection unit

Claims (6)

In an electron beam apparatus for observing an image of the sample by scanning the sample surface with an electron beam converged by at least two stages of electron lenses and detecting secondary electrons generated from the sample surface,
An electron gun side deflecting means located on the electron gun side of an electron lens forming an objective lens among the at least two stages of electron lenses ;
Sample-side deflecting means located on the sample side of the electron lens forming the objective lens;
Moving means for enabling the sample side deflection means to be taken in and out of the path of the electron beam passing through the objective lens ;
At the time of high-resolution image observation, the sample side deflection means is taken out from the electron beam path, and the electron gun side deflection means is used to scan the electron beam,
An electron beam apparatus characterized in that, when observing a low-magnification image, the sample-side deflection means is placed in an electron beam path and the electron beam is scanned using the sample-side deflection means. In the invention of claim 1,
Means for substantially disabling the function of the objective lens;
An electron beam apparatus characterized in that an electron beam is converged by an electron lens positioned closer to the electron gun than the objective lens during the low-magnification image observation . In the invention of claim 1,
An electron beam apparatus comprising means for switching between the electron gun side deflection means and the sample side deflection means . In the invention of claim 1,
An electron beam apparatus characterized in that a control means for moving the scanning center is provided in the sample side deflection means . In the invention of claim 1,
Provided means for detecting the vertical position of the sample stage holding the sample,
An electron beam apparatus configured to allow movement of the sample-side deflection unit only when the sample stage is within a predetermined position range . In the invention of claim 1,
An electron beam apparatus configured to control an acceleration voltage of an electron beam to 5 kV or less during the low-magnification image observation .

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