JPH11144666A - Electron beam detecting device and sample detecting method using electron beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure that energy distribution of irradiation beams on a sample surface is substantially uniform and to reduce an energy loss in the irradiation beams from an electron gun. SOLUTION: A crossover of electron beams is formed by an electron gun 21 having a cathode face, a crossover image is formed at an aperture diaphragm (AS) disposed inside of electron beam irradiating means for introducing the electron beam to a sample 11, an image of the cathode face is formed at a visual field diaphragm disposed inside the electron beam irradiation means, the electron beams are irradiated to the sample 11, a generated electron including at least one of a secondary electron and a reflected electron generated based on the electron beams irradiated to the sample 11 is guided onto a detector 42 via an aperture diaphragm, and an image of the sample 11 formed on the detector 42 is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a sample with an electron beam and generating electrons such as secondary electrons and reflected electrons generated in accordance with changes in the surface shape of the sample, the material of the sample, and the potential. TECHNICAL FIELD The present invention relates to an electron beam detection device and a detection method for detecting an image. More specifically, the present invention relates to an observation apparatus and method for observing an image of a sample obtained by detected generated electrons, and an inspection apparatus and method for inspecting the sample based on an image of the sample obtained by detected generated electrons.

[0002]

2. Description of the Related Art Conventional scanning electron microscope (SEM)
Unlike the electron beam, the beam cross section of the electron beam is made linear or rectangular by the primary optical system and irradiated to the sample, and the generated electrons such as reflected electrons and secondary electrons generated from the sample are transmitted through the secondary optical system. There is a system for detecting a surface image of a sample by detecting with a detector.

[0003]

In such a system, in order to obtain a clear and uniform surface image of the sample, the energy distribution of the irradiation beam on the sample surface is made substantially uniform, and the irradiation beam from the electron gun is emitted. Energy loss is required to be extremely reduced.

[0004]

In order to satisfy the above-mentioned requirements, an electron beam detecting apparatus according to the present invention comprises an electron gun (21) as shown in FIGS. 1 and 4, for example, and an electron beam (50). Electron beam irradiation means (21, 22, AS, CL) for irradiating the sample (11) with at least one of secondary electrons and reflected electrons generated from the sample by the electron beam from the electron beam irradiation means. An electron beam detecting means (42) for detecting position information of generated electrons (60), including: an aperture stop (AS), and detecting an image of the generated electrons in a detecting section (4) in the electron beam detecting means.
2) Mapping projection optical means (CL, A
S, 32); based on an output signal from the detection unit,
Image display means (48) for displaying an image of the sample
And; Then, based on this configuration, the electron beam irradiation means substantially forms an image of the crossover (51) formed by the electron gun on an aperture stop in the mapping projection optical means, and the cathode surface of the electron gun. (2
12a) is formed substantially on the sample surface.

In order to satisfy the above-mentioned requirements, a detection method according to the present invention uses an electron gun (21) having a cathode surface (212a) as shown in FIGS. An electron beam irradiation means (2) for forming a crossover (51) and guiding the electron beam to a sample.
1,22, AS, CL), an image of the crossover is formed on an aperture stop (AS) disposed inside, and a field stop (F) disposed inside the electron beam irradiation means.
Forming an image of the cathode surface in S1), irradiating the sample with the electron beam, and generating electrons (at least one of secondary electrons and reflected electrons generated based on the electron beam irradiated on the sample); 60) is guided to a detector (42) via the aperture stop (AS), and an image of the sample formed on the detector is detected.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing an example in which the present invention is applied to an electron beam inspection device. Also, FIG.
FIG. 3 is a diagram illustrating a beam trajectory near the electron gun 21. FIG.
FIG. 4 is a diagram illustrating a trajectory of a primary beam, and FIG. 4 is a diagram illustrating an operation of an electromagnetic prism for separating a primary beam and a secondary beam.

In FIG. 1, the inspection device is a primary column 2
0, a secondary column 30 and a chamber 40. An electron gun 21 is provided inside the primary column 20, and a primary optical system 22 having a plurality of electron lenses is arranged along a path of an electron beam (primary beam 50) emitted from the electron gun 21. You. A stage 41 that can move in the X and Y directions is installed inside the chamber 40, and the sample 11 is mounted on the stage 41.

On the other hand, the sample 1
1 along the path of the secondary beam 60 generated from the cathode lens CL, the aperture stop AS, and the E as an electromagnetic prism.
× B (E-cross B) 31, a plurality of lenses 32,
The field stop FS2 and the detector 42 are arranged. At this time, elements disposed between the cathode lens CL and the detector 42 constitute the secondary optical system 33.

On the other hand, the output of the detector 42 is input to a control unit 43, and the output of the control unit 43 is input to a CPU 45. The control signal of the CPU 37 controls the primary column control unit 46 for controlling the lens voltage of the primary optical system 22, the lens voltage of each lens in the secondary optical system 33, and the electromagnetic field applied to ExB. It is input to the secondary column control unit 39 and the stage drive mechanism 40.

The stage driving mechanism 44 transmits the position information of the stage to the CPU 45. Further, the primary column 20, the secondary column 30, and the chamber 40 are connected to a vacuum exhaust system (not shown). Thus, the interiors of the primary column 20, the secondary column 30, and the chamber 40 are evacuated by the vacuum pump of the vacuum exhaust system, and the vacuum state is maintained.

As shown in FIG. 2, the electron gun 21 includes a cathode 211, a Wehnelt 212, and an anode (anode) 2.
13. Electron beam 50 from cathode 211
Is converged by Wehnelt 212 and crossover 51
To form Then, this beam 50 is
3 to a plurality of electron lenses of the primary optical system 22.

As shown in FIG. 3, the primary optical system 22 has a plurality of electron lenses and a field stop FS1. In the following description, the field stop FS1 in the primary optical system 22
The electron lens disposed closer to the electron gun 21 than the front group 22
F, and an electron lens disposed on the sample 11 side of the field stop FS1 in the primary optical system 22 is a rear group 22R. These electron lenses may be circular electron lenses, quadrupoles, or octupoles.

The electron beam (primary beam 50) from the electron gun 21 is converged by the lens action of the front lens group 22F in the primary optical system 22, and is converged by the field stop FS in the primary optical system 22.
An image of the cathode surface 211a is formed on the first surface. Thereafter, the lens group E is subjected to a lens action by the rear lens group 22R in the primary optical system 22 and E
X Head to B31. The trajectory of the primary beam 50 that has passed through the primary optical system 22 is bent by the deflection effect of ExB31. E × B31 is such that when the magnetic field and the electric field are orthogonal to each other and the electric field is E, the magnetic field is B, and the velocity of the charged particles is v,
Only charged particles moving in a direction satisfying the Wien condition of vB are made to go straight, and the trajectory of the charged particles moving in the opposite direction is bent. As shown in FIG. 4, a force FB due to a magnetic field and a force FE due to an electric field are generated for the primary beam,
The beam trajectory is bent. On the other hand, the force FB and the force FE act on the secondary beam in opposite directions, and thus cancel each other, so that the secondary beam proceeds straight. Although this configuration itself is the same as a Wien filter that deflects an electron beam by its acceleration voltage, in the present embodiment, it functions as an electromagnetic prism (beam splitter). In addition,
In FIG. 3 described above, the trajectory of the primary beam is drawn ignoring the deflection effect of the E × B 31.

Returning to FIG. 3, the primary beam that has passed through the E × B 31 reaches the aperture stop AS, and forms an image of the crossover 51 at the position of the aperture stop AS. Aperture stop AS
The primary beam having passed through reaches the sample 11 under the lens action of the cathode lens CL. At this time, the sample 11 is conjugate with the cathode surface 211a of the electron gun 21. As described above, in the present embodiment, since the image of the crossover 51 formed by the electron gun is formed on the aperture stop AS, Koehler illumination is used in the illumination optical system, and the image of the cathode surface 211a of the electron gun is formed. This is a critical illumination referred to by the illumination optical system from the point where an image is formed on the sample 11.

In the present embodiment, when the image of the crossover 51 is formed on the opening of the aperture stop AS using the primary optical system 22, the image of the crossover 51 is used as the aperture stop AS.
The magnification of the primary optical system 22 is appropriately set so as to be smaller than the aperture of the first optical system. Further, in order to cut off the irradiation of the electron beam from the inclined surface 211b of the cathode 211 of the electron gun 21, a cathode surface 211a formed at the opening of the field stop FS1 is formed.
Is set to a size that can block the electron beam from the inclined surface 211b (a size that allows only the electron beam from the cathode surface 211a to pass). As a result, the primary beam is irradiated on the surface of the sample 11 under a distribution corresponding to the energy distribution of the cathode surface 211a. Since the energy distribution on the cathode surface 211a can be regarded as substantially uniform, the primary beam is irradiated on the surface of the sample 11 on which the image of the cathode surface 211a is formed under a substantially uniform energy distribution. Will be At this time, since it is unnecessary to irradiate the electron beam from the inclined surface 211b of the cathode 211, the energy loss of the electron beam required at the field stop FS1 is extremely small.

Here, it is sufficient that the cathode 21 has a planar portion, and the surface shape of the cathode surface may be a circle, a square, a rectangle, or a line. As described above, since the electron lens in the primary optical system 22 may be a circular electron lens or a quadrupole or an octupole, the cross-sectional shape of the electron beam applied to the surface of the sample 11 is circular, square, rectangular, It can take any shape, such as linear or elliptical.

With this configuration, the energy distribution of the primary beam applied to the surface of the sample 11 can be made substantially uniform, and the energy loss of the electron beam from the electron gun 11 can be extremely reduced. Now, in the above configuration, the image of the cathode surface 211a of the electron gun 21 is displayed on the field stop FS.
If it is not formed at the position 1, the energy distribution of the electron beam at the position of the field stop FS1 widens, and this tail is shaken by the field stop FS1, which is not preferable because energy loss is caused. In addition, electron gun 2
If the image of the crossover 51 formed by 1 is not formed at the position of the aperture stop AS, the primary beam irradiated onto the sample 11 is undesirably blurred by the aperture stop AS.

Next, returning to FIG. 1, the secondary optical system 33 will be described. In FIG. 1, secondary electrons and reflected electrons having a distribution corresponding to the surface shape of the sample 11, the material distribution of the sample 11, a change in potential, and the like are generated as a secondary beam 60 from the sample 11 irradiated with the primary beam. I do. The secondary beam receives the lens action of the cathode lens CL, passes through the aperture stop AS arranged at the focal position of the cathode lens, and reaches ExB31. As described above, ExB3
The magnetic field B and the electric field E orthogonal to each other formed by 1 are set so that the secondary beam from the sample 11 satisfies the Wien condition. As a result, the secondary beam that has passed through the aperture stop AS goes to the plurality of electron lenses 32 without being deflected by the E × B 31. In the present embodiment,
Although the one that bends the trajectory of the primary beam and makes the secondary beam go straight is used, the present invention is not limited to this, and an electromagnetic prism that makes the trajectory of the primary beam go straight and bends the trajectory of the secondary beam may be used.

The secondary optical system 33 includes a field stop FS2.
The field stop FS2 is conjugated to the sample 11 with respect to the cathode lens CL and a part of the electron lens 32. The secondary beam 60 that has passed through the field stop FS2 further reaches the detector 42 via the plurality of electron lenses 32. At this time, on the detection surface of the detector 42,
An image of the sample 11 enlarged by the secondary optical system is formed. As the electron lens in the secondary optical system, various types such as a circular electron lens, a quadrupole and an octupole can be used.

The detector 42 includes an MCP for amplifying electrons,
It is composed of a fluorescent plate for converting electrons into light, a lens and other optical elements for relaying a vacuum system to the outside and transmitting an optical image, and an image pickup device (CCD or the like). The secondary beam forms an image on the MCP detection surface, is amplified, the electrons are converted into optical signals by the fluorescent plate, and the photoelectric signals are converted by the imaging device.

The control unit 43 includes a detector 42
The image signal of the sample is read from the CPU and transmitted to the CPU 45. The CPU 45 performs pattern defect inspection on the image signal by template matching or the like. The position of the stage 41 that can be moved in the X and Y directions by the stage driving mechanism 44 is read by the CPU 45. Then, the CPU 45 outputs a drive control signal to the stage drive mechanism 44, drives the stage 41, and sequentially performs image detection and inspection.

If the image signal of the sample 11 read by the control unit 43 is displayed on the display 48 as it is, an observation device for observing the sample based on the electron beam is obtained.

[0023]

As described above, according to the present invention, the energy distribution of the irradiation beam on the sample surface can be made substantially uniform.
In addition, since the energy loss of the irradiation beam from the electron gun can be extremely reduced, a clear and uniform surface image of the sample can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment according to the present invention.

FIG. 2 is a diagram showing a configuration of an electron gun.

FIG. 3 is a diagram illustrating a trajectory of an electron beam in a primary optical system.

FIG. 4 is a diagram for explaining the operation of an electromagnetic prism (E × B).

[Explanation of symbols]

 11: Sample 21: Electron gun 22: Primary optical system FS1: Field stop in primary optical system 31: E × B (electromagnetic prism) CL: Cathode lens AS: Aperture stop 33: Secondary optical system 42: Detector 48: display

Claims (5)

[Claims] An electron beam irradiation means for irradiating a sample with an electron beam; and at least one of secondary electrons and reflected electrons generated from the sample by the electron beam from the electron beam irradiation means. An electron beam detecting means for detecting positional information of generated electrons including: an aperture stop, and a projection optical means for forming an image of the generated electrons on a detecting section in the electron beam detecting means; An image display unit for displaying an image of the sample based on an output signal from the detection unit; wherein the electron beam irradiation unit performs a crossover formed by the electron gun with the projection optical unit. An electron beam detection apparatus, wherein an image is formed substantially on a middle aperture stop, and a cathode surface of the electron gun is formed substantially on the surface of the sample. 2. The electron beam detecting device according to claim 1, wherein a cross-sectional shape of the electron beam reaching the surface of the sample is one of a circle, a square, a rectangle, and an ellipse. 3. A crossover of an electron beam is formed by an electron gun having a cathode surface, and an image of the crossover is formed on an aperture stop arranged inside an electron beam irradiation means for guiding the electron beam to a sample. And forming an image of the cathode surface on a field stop arranged inside the electron beam irradiation means, irradiating the sample with the electron beam, and generating the electron beam based on the electron beam irradiated on the sample. A detection method comprising: guiding generated electrons including at least one of secondary electrons and reflected electrons to a detector via the aperture stop, and detecting an image of the sample formed on the detector. 4. The detection method according to claim 3, wherein an image of the sample is displayed on a display for observation. 5. The detection method according to claim 3, wherein a defect of the sample is inspected based on the image of the sample.