JP3965691B2 - Scanning electron microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for performing analysis, measurement, observation, and manufacturing using charged particles, and in particular, a signal obtained by irradiating a sample with charged particles with low acceleration (reflected electrons, secondary electrons, Auger electrons, light ( The present invention relates to a scanning electron microscope that performs analysis, measurement, and observation using cathodoluminescence) and X-rays (braking radiation, characteristic X-rays, etc.).
[0002]
[Prior art]
Secondary, reflected, and Auger electrons emitted from a sample by irradiating the object with a charged particle beam in an apparatus such as an electron microscope or an electron beam microanalyzer that analyzes, measures, or observes the object. Etc. are detected and analyzed. In addition, in a manufacturing apparatus that processes an object such as an electron beam drawing apparatus or an ion beam processing apparatus, by providing an electronic signal detector, signals such as secondary electrons, reflected electrons, and Auger electrons emitted from the sample are provided. Can be observed and analyzed.
[0003]
When analyzing and observing secondary electron signals and SEM images in this analysis and observation by irradiation of charged particles, the acceleration voltage of charged particles may be lowered.
[0004]
Conventionally, in analysis and observation using a low acceleration voltage, an electron gun that generates charged particles is used at low acceleration, and the energy of charged particles incident on a sample is low energy. When an electron gun is used at low acceleration, the energy of charged particles incident on the sample is determined by the potential difference between the anode and cathode of the electron generation source.
[0005]
FIG. 6 shows an outline of a general configuration of an electron optical system usually used in a scanning electron microscope. In this electron optical system, an electron gun 11 includes a condenser lens 4 and an objective lens 6 provided on the outer periphery of an electron source 2, an anode 3, a cylindrical body 5, and a cylindrical body 5. The sample S is irradiated with the discharged charged particles. Secondary electrons and backscattered electrons emitted from the sample S by irradiation with charged particles are detected by an electronic signal detector (not shown).
[0006]
A voltage is applied between the cathode 2 a and the anode 3 of the electron source 2 by the first power supply 21. When the electron gun is used at low acceleration, the energy of charged particles passing through the electron gun 11 is determined by the potential difference between the cathode 2 a and the anode 3.
[0007]
Therefore, when using at a low acceleration voltage, the energy of the charged particles passing through the electron gun is low, so that it is easily affected by external disturbances such as an external AC magnetic field while passing through the electron gun cylinder. There's a problem.
[0008]
Further, since the luminance of the scanning electron microscope is determined by the energy of the charged particles irradiated on the sample S, sufficient luminance cannot be obtained when used at a low acceleration voltage, and observation at high magnification is difficult. There is a problem.
[0009]
Therefore, in order to use the scanning electron microscope at a low acceleration voltage, there is a problem that it is easily affected by a decrease in luminance and disturbance.
[0010]
In order to increase the spatial resolution when using a scanning electron microscope at a low acceleration voltage, a cylindrical electrode is provided inside the objective lens and a high positive voltage is applied to reduce the energy of charged particles in the electron gun. A configuration is proposed.
[0011]
FIG. 7 is a schematic diagram of an electron optical system for explaining this configuration example. In the electron gun 11 shown in FIG. 7, the same voltage as that of the anode 3 is applied to the cylindrical electrode 15 a provided at the condenser lens 4 by the power source 23, and the cylindrical electrode 15 b provided at the objective lens 6 is applied to the cylindrical electrode 15 b. A high positive voltage is applied by the power source 24. High-energy charged particles are emitted from the electron source 2, the energy inside the electron gun is kept high, and the sample is irradiated with the sample after the energy is reduced by the cylindrical electrode 15b, thereby obtaining high spatial resolution. (For example, refer to Patent Document 1).
[0012]
[Patent Document 1]
US Pat. No. 5,146,090 specification
[Problems to be solved by the invention]
In order to use a conventional scanning electron microscope at a low acceleration voltage, there are a problem that luminance is lowered and observation at a high magnification is difficult, and a problem that it is easily affected by disturbance. In the scanning electron microscope with the proposed configuration, high brightness is expected by emitting high energy from the electron source, and it is difficult to be affected by disturbance by providing a cylindrical electrode in the electron gun. Although expected, there is a problem that the configuration of the electron gun becomes complicated because it requires a configuration in which cylindrical electrodes are provided inside the condenser lens and the objective lens, respectively, and different voltages are applied.
[0014]
Accordingly, an object of the present invention is to solve the above-described conventional problems, and to provide a scanning electron microscope which has a simple configuration and can obtain high luminance and is hardly affected by disturbance.
[0015]
[Means for Solving the Problems]
The first aspect of the scanning electron microscope of the present invention is a scanning electron microscope that irradiates a sample with charged particles of low energy and detects a signal generated from the sample. In order to obtain brightness, charged particles emitted from an electron source with high energy are decelerated on the sample side, and the potential on the sample side as viewed from the objective lens is floated with respect to the ground (predetermined voltage) The high-energy charged particles are decelerated between the objective lens and the sample to irradiate the sample, and analysis and observation are performed with a low acceleration voltage.
[0016]
As a result, since the charged particles are high energy until they are emitted from the electron source and emitted from the objective lens, it is difficult to be affected by disturbance and high brightness can be obtained. Further, by decelerating between the objective lens and the sample, the sample can be irradiated with charged particles of low energy.
[0017]
In the configuration in which the potential on the sample side as viewed from the objective lens is floated with respect to the ground, electrodes are provided inside the sample chamber, the outer side surface of the objective lens, and a part of the sample side end of the objective lens. It is formed by floating and applying a predetermined voltage.
[0018]
This electrode configuration is part of the inside of the sample chamber, the outer side surface of the objective lens, and the sample side end of the objective lens, and should be simpler than the configuration in which a cylindrical electrode is provided in the electron gun. Can do. Further, these parts may be formed integrally, and the formation of a scanning electron microscope is facilitated.
[0019]
A second aspect of the scanning electron microscope of the present invention is a scanning electron microscope that irradiates a sample with low-energy charged particles and detects a signal generated from the sample, and suppresses the influence of the electric field by the objective lens on the sample. In the sample chamber, the outer side surface of the objective lens, and a part of the sample side end portion of the objective lens are provided with an electrode that floats from the ground potential and applies a predetermined voltage. Suppresses the leakage of electric field. The tip position of the electrode is set between the objective lens center and the sample side end of the objective lens at the sample side end of the objective lens, and the signal is detected outside the objective lens.
[0020]
This electrode prevents the electric field of the objective lens from leaking to the sample side, so that secondary electrons and reflected electrons generated from the sample can be prevented from being drawn into the objective lens and emitted from the sample. The signal can be detected without being affected by the electric field of the objective lens.
[0021]
Since the electric field does not leak from the objective lens, a detector for detecting a signal can be provided at the sample side end of the objective lens. Thereby, signals (secondary electrons, reflected electrons, Auger electrons) and the like generated from the sample and emitted toward the objective lens side can be detected.
[0022]
Further, the scanning electron microscope of the present invention is applied to an apparatus for analyzing, measuring, or observing an object to be analyzed such as an electron microscope or an electron beam microanalyzer, and an object such as an electron beam drawing apparatus or an ion beam processing apparatus. The present invention can also be applied to a manufacturing apparatus for processing an object by providing an electronic signal detector.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram for explaining a scanning electron microscope of the present invention. FIG. 1 (a) shows an outline of an electron optical system, and FIG. 1 (b) shows a voltage state of the electron optical system. Yes.
[0024]
The electron gun 1 has an electron source 2, an anode 3, a condenser lens 4 and an objective lens 6 arranged in order in the charged particle irradiation direction, and a cylindrical body 5 is provided inside the condenser lens 4 and the objective lens 6. It is done. An acceleration voltage of voltage V1 is applied between the cathode 2a and the anode 3 of the electron source 2 by the first power source 21, and the charged particles extracted from the cathode 2a are accelerated and emitted toward the cylindrical body 5. The The charged particles passing through the cylindrical body 5 are focused by the condenser lens 4 and condensed on the sample S by the objective lens 6.
[0025]
At the tip of the electron gun 1 is provided a sample chamber 7 that holds the sample S in a vacuum state, and a secondary electron detector 30 and an electron energy analyzer 31 are provided. The sample S is emitted from the sample S by irradiation with charged particles. Secondary electrons, reflected electrons and Auger electrons detected.
[0026]
The scanning electron microscope of the present invention includes an electrode 10 that decelerates charged particles emitted from the electron gun outside the end of the electron gun 1 on the sample side. This electrode 10 is inside the sample chamber 7 (indicated by symbol A in FIG. 1), the outer side surface of the objective lens 6 (indicated by symbol B in FIG. 1), and a part of the sample side end of the objective lens 6 (Indicated by symbol C in FIG. 1) is provided in a state of floating from the ground potential. The electrode 10 is supported via the insulator 8 with respect to the sample chamber 7 so as to be in a state of floating from the ground potential. A predetermined voltage V <b> 2 is applied to the electrode 10 by the second power supply 22. In the sample side end of the objective lens 6, the tip position of the electrode 10 is between the center P of the objective lens 6 and the sample side tip of the objective lens 6.
[0027]
In the potential state shown in FIG. 1B, since the voltage V1 is applied between the cathode 2a and the anode 3 by the first power source 21 and the anode 3 is grounded by the earth 20, the cathode 2a to the anode 3 In the meantime, a potential gradient from −V1 to 0 is formed. Charged particles are accelerated by this potential gradient.
[0028]
Further, since the cylinder 5 is grounded by the earth 20 and there is no potential gradient in the cylinder 5, the accelerated charged particles pass through the cylinder 5 at a constant speed and reach the sample side end of the objective lens 6. It reaches. Since the voltage V2 is applied to the sample S from the second power source 22, a potential gradient from 0 to −V2 is formed between the sample side C of the objective lens 5 and the sample S. The charged particles are decelerated by this potential gradient.
[0029]
Therefore, the potential difference Ep between the electron source 2 and the sample S becomes (V1−V2) (V1> V2), and high energy charged particles are emitted from the electron source 2 by the high voltage V1, The sample S is irradiated with charged particles decelerated by the potential difference Ep (= (V1−V2)). Since the luminance is determined by the potential difference between the cathode and anode of the electron source, according to the present invention, the potential difference between the cathode and anode can be increased, thereby increasing the energy of charged particles emitted from the electron source 2. Energy can be obtained, and high luminance can be obtained. Further, since the charged particles pass through the cylindrical body 5 with high energy, it is possible to obtain an effect that the charged particles are hardly affected by disturbance such as an external magnetic field. Further, by decelerating outside the end of the electron gun on the sample side, analysis and observation with low acceleration can be performed.
[0030]
FIG. 2 is a diagram showing the electrode configuration and potential distribution at the sample side end of the electron gun. In FIG. 2, the objective lens 6 includes a magnetic pole 6 a and a magnetic pole 6 b, and the tip 5 a of the cylindrical body 5 extends to a partial position (position indicated by C in the drawing) inside the tip of the objective lens 6. A part 10a of the electrode 10 extends from the sample side to a part of the inside of the tip of the objective lens 6 (a position indicated by C in the drawing). The part 10a of the electrode can be formed integrally or electrically connected to the electrode provided inside the sample chamber and outside the side portion of the objective lens, and a negative voltage V2 is generated by the second power source 22. Applied. The electrode 10 can be composed of a plate or a mesh.
[0031]
In FIG. 2, the tip 5a of the cylinder 5 and a part 10a of the electrode 10 are arranged to face each other, the cylinder 5 is grounded by the earth 20, and the electrode 10 is applied with a negative voltage V2. From the sample side end of the objective lens, a potential distribution as shown by the equipotential surface 12 indicated by a broken line in the figure is formed toward the sample side. The equipotential surface 12 has a flat characteristic from the position indicated by C in the figure toward the sample S side, and is not formed on the sample S side from the end of the objective lens 6.
[0032]
Due to this potential distribution, leakage of the electric field of the objective lens to the sample S side is suppressed, and signals such as secondary electrons and reflected electrons emitted from the sample S due to irradiation of charged particles are drawn into the objective lens 6. In this way, the influence on the signal on the sample S side can be prevented.
[0033]
As a result, as shown in FIG. 3, the secondary electron detector 30 is arranged at the sample-side tip of the objective lens 6, and signals such as secondary electrons, reflected electrons, and Auger electrons are detected at positions outside the objective lens. be able to. Reflected electrons are best placed 180 degrees opposite to the incident electrons, and must be placed so as not to interfere with the incidence of the electron beam. By detecting at a position outside this objective lens, the sample Thus, a signal emitted in the direction of the electron source can be detected efficiently. For example, a photomultiplier tube (PMT) can be used as the secondary electron detector 30.
[0034]
The secondary electron detector 30 can be arranged at an arbitrary position of the electrode 10 so that the detection surface is on the sample S side. FIG. 4 is a schematic diagram for explaining an arrangement example of the secondary electron detector 30. In the arrangement example shown in FIG. 4A, the secondary electron detector 30 is supported with respect to the sample chamber 7 via the insulator 9, and the detection surface 30a is located on the sample S side through the opening 10b provided in the electrode 10. It is attached to become.
[0035]
In the arrangement example shown in FIG. 4B, similarly, the secondary electron detector 30 is supported with respect to the sample chamber 7 via the insulator 9, and the cross section provided in the electrode 10 is L-shaped. The detection surface 30a is attached to the sample S side through the opening 10c. In the example shown in FIG. 4B, the electrode 10 is provided at the tip of the secondary electron detector 30. With this electrode, a lens by an electric field is formed in front of the secondary electron detector 30. The efficiency of the lens can be improved by making the potential of the electrode 10 constituting the lens the same as the potential in the chamber.
[0036]
4 (a) and 4 (b), a negative predetermined voltage (for example, voltage V2 from the second power source 22) is applied to the electrode 10, so that a signal directed to the secondary electron detector 30 is drawn. There is no.
[0037]
FIG. 5 is a schematic diagram for explaining an arrangement example of the electronic energy analyzer 31. In the arrangement example shown in FIG. 5, the electron energy analyzer 31 is supported with respect to the sample chamber 7 via the insulator 9 and attached so that the detection surface 31 a is on the sample S side through the opening 10 d provided in the electrode 10. Yes. Since a predetermined negative voltage (for example, voltage V2 from the second power source 22) is applied to the electrode 10, a signal directed to the electronic energy analyzer 31 is not drawn.
[0038]
Since the electrode according to the present invention is provided outside the objective lens, it can be simplified.
[0039]
In order to detect the signal emitted from the sample toward the electron gun side, it is necessary to place an electronic signal detector at the sample side tip of the objective lens. Since it is drawn into the objective lens, sufficient detection intensity cannot be obtained. On the other hand, according to the present invention, since no signal is drawn into the objective lens, an electron signal detector is disposed at the tip end portion on the sample side, and the signal emitted from the sample toward the electron gun side is efficiently processed. Can be detected well.
[0040]
The scanning electron microscope of the present invention includes the above-described configurations such as an electron gun, a chamber, an electrode, an electronic signal detector, and an electronic energy analyzer.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a scanning electron microscope that can obtain high luminance with a simple configuration and is hardly affected by disturbance.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram for explaining a scanning electron microscope of the present invention.
FIG. 2 is a diagram showing the configuration of an electrode and a potential distribution at the sample side end of an electron gun.
FIG. 3 is a schematic diagram for explaining an arrangement example of the electronic signal detector of the present invention.
FIG. 4 is a schematic view for explaining an arrangement example of the electronic signal detector of the present invention.
FIG. 5 is a schematic view for explaining an arrangement example of the electronic energy analyzer of the present invention.
FIG. 6 shows an outline of a general configuration of an electron optical system normally used in a scanning electron microscope.
FIG. 7 is a schematic view of an electron optical system for explaining a configuration example of a conventional scanning electron microscope.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron source, 3 ... Anode, 4 ... Condenser lens, 5 ... Tube, 5a ... Tip, 6 ... Objective lens, 6a, 6b ... Magnetic pole, 7 ... Sample chamber, 8, 9 ... Insulator DESCRIPTION OF SYMBOLS 10,10a ... Electrode, 10b, 10c, 10d ... Opening part, 11 ... Electron gun, 12 ... Equipotential surface, 15a, 15b ... Cylindrical electrode, 20 ... Ground, 21 ... First power source, 22 ... Second Power source, 24, 23 ... power source, 30 ... secondary electron detector, 30a ... detection surface, 31 ... electron energy analyzer, 31a ... detection surface, S ... sample.

Claims (4)

In a scanning electron microscope that irradiates a sample with charged particles and detects a signal generated from the sample,
An objective lens in which a magnetic pole is arranged inside a casing that is axisymmetric with respect to the irradiation axis of the charged particles;
A sample chamber for holding the objective lens and holding the sample in a vacuum state by inserting a part of the objective lens into the opening and inserting the part of the objective lens;
A part of the end surface of the objective lens facing the sample, a side surface portion inserted into the sample chamber, and an electrode provided on the inner surface of the sample chamber,
Apply a predetermined voltage in a state of floating from the ground to the electrode,
A scanning electron microscope characterized in that charged particles emitted from an electron source are decelerated between an objective lens and a sample and irradiated on the sample. In a scanning electron microscope that irradiates a sample with charged particles of low energy and detects a signal generated from the sample,
An objective lens in which a magnetic pole is arranged inside a casing that is axisymmetric with respect to the irradiation axis of the charged particles;
A sample chamber for holding the objective lens and holding the sample in a vacuum state by inserting a part of the objective lens into the opening and inserting the part of the objective lens;
A part of the end surface of the objective lens facing the sample, a side surface portion inserted into the sample chamber, and an electrode provided on the inner surface of the sample chamber,
Apply a predetermined voltage in a state of floating from the ground to the electrode,
A scanning electron microscope characterized by suppressing leakage of an electric field from an objective lens to a sample side.   The tip position of an electrode provided on a part of the end surface of the objective lens facing the sample is located between the center position of the objective lens and the sample-side end of the objective lens. Or the scanning electron microscope of 2.   The scanning electron microscope according to claim 1, further comprising a detector that detects a signal on an end surface of the objective lens facing the sample.

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