JPH08138611A - Charged particle beam equipment - Google Patents

Abstract

(57) [Summary] [Objective] In a charged particle beam device using an in-lens type deceleration electric field type objective lens, the axial chromatic aberration of the primary charged particle beam is suppressed small, and secondary electrons are efficiently collected in a detector. . [Structure] An electrode 4 forming an electrostatic lens for converting a primary electron from an electron gun 1 into a parallel beam together with an anode 3, and an objective lens 8 having a sample 15 mounted between an upper pole 5a and a lower pole 5b. A secondary electron detector 5 for detecting secondary electrons from the sample 15 is provided between the two, and a voltage of -100 V is applied to the electrode 4 and the sample 15 is set to the ground potential. The primary electrons to the sample 15 are decelerated by the liner tube 6 to which a voltage of 10 kV is applied. Secondary electrons from the sample 15 are emitted to the upper part of the liner tube 6 by the magnetic field of the objective lens 8 and then captured by the secondary electron detector 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam apparatus, and particularly to observing a sample with a low energy electron beam probe.
It is suitable for application to a scanning electron microscope, a line width measuring device, a microanalyzer, or the like that performs measurement and the like.

[0002]

2. Description of the Related Art A charged particle beam apparatus for focusing a charged particle beam on a sample by an electromagnetic lens as an objective lens and observing the sample is used today for inspection of a semiconductor integrated circuit having an ultrafine structure, DNA or protein, etc. It is useful for elucidating the ultrafine structure. Scanning electron microscopes, line width measuring machines, and the like are known as charged particle beam devices of this type. Below,
A scanning electron microscope will be described as an example of the charged particle beam device.

Generally, in a scanning electron microscope, an electron beam emitted from an electron gun is converged by a condenser lens or the like and then enters an electromagnetic lens as an objective lens. The electromagnetic lens has two magnetic poles, and the focus position of the electron beam is adjusted by the magnetic field generated between these two magnetic poles to irradiate the sample. The secondary electrons generated from the sample are 2
It is detected by the secondary electron detector.

In the above-mentioned structure, if the deceleration electric field type electromagnetic lens as the objective lens and the in-lens type electromagnetic lens for observing by placing the target sample between the two magnetic poles are used, It is known that the axial chromatic aberration coefficient of the electron beam (primary electron) radiated on the image is significantly reduced. Therefore, an in-lens type charged particle beam device having such a configuration has been conventionally put into practical use.

[0005]

However, when the conventional deceleration electric field type and in-lens type electromagnetic lens is used, there is a problem in the method of detecting secondary electrons, and the device has been put to practical use to date. Can't be seen. That is, in the conventional charged particle beam device, the secondary electrons emitted from the sample are accelerated and enter the liner tube or the like to which a potential for decelerating the primary electrons is applied, so that the secondary electron detector is detected. Since it does not enter, there is a disadvantage that an observation image of the sample cannot be obtained.

In view of the above point, the present invention reduces the axial chromatic aberration coefficient of the charged particle beam on which primary electrons or the like are incident, and
It is another object of the present invention to provide a charged particle beam device that can efficiently guide secondary electrons to a secondary electron detector.

[0007]

In a charged particle beam apparatus according to the present invention, a sample (15) is arranged between two facing magnetic poles (9a, 9b) of an objective lens (8) for focusing a charged particle beam. Then, the upper pole (9
In the charged particle beam device that forms an electric field between the electrode (6) arranged on the side a) and the sample (15) thereof and focuses the charged particle beam on the sample (15), the objective lens ( 8) A secondary electron detector (5) for detecting secondary electrons generated from the sample (15) by irradiation of the charged particle beam is provided above the upper electrode (9a).

In this case, the deflection for scanning for scanning the charged particle beam on the sample (15) between the upper pole (9a) of the objective lens (8) and the secondary electron detector (5). It is preferable to provide a coil (7). Further, it is preferable that at least a part of the periphery of the secondary electron entrance of the secondary electron detector (5) is covered with the auxiliary electrode (4) to which a potential lower than that of the sample (15) is applied.

Further, it is preferable that the charged particle beam does not form a light source image (crossover) by the converging action of the electrostatic lens formed including the auxiliary electrode (4).

[0010]

According to such a charged particle beam apparatus of the present invention, the in-lens type objective lens (8) is used, and the charged particle beam is irradiated onto the upper pole (9a) of the objective lens (8). A secondary electron detector (5) for detecting secondary electrons generated from the sample (15) is provided. Therefore, even if the electrode (6) is present on the side of the upper pole (9a), the secondary electrons generated from the sample (15) in almost all directions are once brought close to the optical axis by the strong magnetic field of the objective lens (8). After it converges and becomes almost parallel to the optical axis, it is trapped by the secondary electron detector (5) which is normally kept at a positive potential. Therefore, the axial chromatic aberration of the charged particle beam incident by the electrode (6) is reduced, and the secondary electron capturing efficiency is good, and a detection image with a good SN ratio can be obtained.

A charged particle beam is applied between the upper pole (9a) of the objective lens (8) and the secondary electron detector (5) to the sample (1).
5) When a scanning deflection coil (7) for scanning is provided, the scanning deflection coil (7) is a secondary electron detector (5).
Since it is below, even if a strong deflection electric field is generated in a space where the secondary electron detector (5) is present, the electron beam passes through the same place regardless of the visual field scanning, so that no visual field distortion occurs. , It is not necessary to dynamically perform astigmatism correction corresponding to scanning.

When at least part of the periphery of the secondary electron entrance of the secondary electron detector (5) is covered with the electrode (4) to which a potential lower than that of the sample (15) is applied, Since the secondary electrons are pushed back by the electrode (4), the secondary electrons from the sample (15) are efficiently incident on the secondary electron detector (5). Further, in the case where the charged particle beam does not form a light source image due to the converging action of the electrostatic lens formed including the electrode (4), the axial chromatic aberration coefficient of the primary electron can be suppressed to a smaller value.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the charged particle beam device according to the present invention will be described below with reference to the drawings. In this example, the present invention is applied to a scanning electron microscope. FIG. 1 shows a sectional view of the main part of the scanning electron microscope of this example. In FIG. 1, an electron beam (primary electron) 1 emitted from an electron gun 1 is shown.
Reference numeral 3 denotes a cylindrical anode electrode 3 arranged below the electron gun 1 and surrounding the optical axis AX and having a widened outlet, and is accelerated to about 10.5 kV. The accelerated electron beam makes a crossover (light source image) 19 by the condenser lens 2 arranged outside the anode electrode 3, and the electron beam from this crossover 19 is at a potential of about 10 kV and the anode electrode 3 and the anode. An electrostatic lens made by an electrode 4 having a potential of about −100 V arranged under the electrode 3 makes a substantially parallel beam. The electrode 4 has a through hole at its center for passing an electron beam, and is formed in a downward lid shape having an opening surrounding an introduction opening of a secondary electron beam detector described later. The electron beam that became a parallel beam
The deceleration electric field type objective lens 8 of the in-lens type in which the sample is arranged between the two magnetic poles is focused on the upper surface of the sample 15 placed on the sample table 11 substantially in the center thereof.

The objective lens 8 has a cylindrical space 16, the upper part of which is the upper pole 9a around a circular through hole through which the primary and secondary electrons pass, and the lower part of which is a columnar shape protruding toward the space 16 side. Is an electromagnetic lens composed of a cylindrical core 9 serving as the lower pole 9b and a coil 10 mounted around the lower pole 9b, and the primary electrons are the two magnetic poles 9a and 9b.
Is focused on the sample 15 by the magnetic field generated by. A sample table 11 is horizontally arranged directly above the lower pole 9b of the objective lens 8, and the sample table 11 can be moved by a driving device 17 fixed to the bottom of the sample table 11. The sample table 11 is grounded, and the potential of the sample 15 is the ground potential (0V).

Further, inside the upper pole 9a of the objective lens 8 through which the primary and secondary electrons pass, a liner tube 6 having a cylindrical shape and a sample side expanding like a brim through an insulator 12 is provided.
Has been fixed. A voltage of about 10 kV is applied to the liner tube 6 to reduce the speed of the primary electrons. Furthermore, on the upper surface of the end of the upper electrode 9a, the sample 1
A scanning deflector 7 for scanning the surface of the optical disc 5 is provided.

Secondary electrons generated from the sample 15 by the irradiation of the electron beam are bent by the magnetic field of the objective lens 8 while being accelerated by the electric field generated by the voltage applied to the liner tube 6, and do not enter the liner tube 6. , Above the virtual plane 14. The height of the imaginary surface 14 is approximately the middle position of the liner tube 6. Upper pole 9a of objective lens 8
The secondary electron detector 5 is arranged at a predetermined distance from the optical axis AX at a high position above the virtual surface 14 and at a predetermined distance L (see FIG. 2) from the virtual surface 14. Furthermore, 2
The front side surface of the secondary electron detector 5 is inserted through the opening on the side surface of the electrode 4.

The secondary electron detector 5 is composed of two meshes 5a and 5b in the front and rear, which are provided in the secondary electron introduction opening, and a photomultiplier 5c. To capture the secondary electron beam, voltages of about 20 kV and 10 kV are applied to the two meshes 5a and 5b, respectively.
2 captured by two high-potential meshes 5a and 5b
Secondary electrons enter the light-receiving surface of the photomultiplier 5c. The meshes 5a and 5b need not be provided on the entire surface of the secondary electron entrance, but may be provided only on a part thereof.

Next, the operation of the charged particle beam device of this example will be described. As described above, the primary electron emitted from the electron gun 1 is accelerated by the anode electrode 3 to which a high voltage of about 10 kV is applied after the crossover 19 is formed by the condenser lens 2 and the anode electrode 3 And -100
An electrostatic lens formed by the electrode 4 to which a voltage of V is applied forms a parallel beam, which passes through the front of the secondary electron detector 5 and enters the objective lens 8. In this case, a high voltage of about 20 kV is applied to the mesh 5a of the secondary electron detector 5 to capture the secondary electrons, but the primary electrons are accelerated at a high speed, so the secondary electron detector The optical path of the objective lens 8 is almost straightened by 5 and goes straight.
Incident on.

Further, the crossover 19 and the anode electrode 3
Since the distance between the main surface of the electrostatic lens formed by the electrode 4 and the electrode 4 is equal to or shorter than the focal length of this electrostatic lens,
Primary electrons do not create a crossover between this electrostatic lens and the objective lens 8. Therefore, the axial chromatic aberration coefficient of primary electrons does not increase, and in this example, a high-resolution primary beam with a chromatic aberration coefficient of 0.7 mm could be produced. Next, a strong magnetic field due to the two magnetic poles 9a and 9b of the objective lens 8 exists on the surface of the sample 15, and the secondary electrons emitted from the sample in all directions are converged by this magnetic field to cause the optical axis AX. After being converged in the vicinity and traveling on the virtual surface 14 and the direction of the beam is aligned at an angle close to parallel to the optical axis AX,
It emerges into the space above the upper pole 9a of the objective lens 8. In this space, the upper and side surfaces are kept at a potential of about −100 V by the electrode 4, and the mesh 5 a of the secondary electron detector 5 is about +2.
The potential is kept at 0 kV. Therefore, the secondary electrons from the virtual surface 14 efficiently enter the secondary electron detector 5. In this case, since the potential of the electrode 4 (−100 V) is lower than the potential of the sample 15 (ground potential), the secondary electrons are efficiently converted to 2
It is captured by the secondary electron detector 5.

FIG. 2 shows the secondary electron detector 5 from the virtual surface 14.
Shows an example of the orbit of the secondary electrons leading to, the horizontal axis represents the distance R (mm) from the optical axis AX, and the vertical axis represents the height H from the virtual surface 14. This FIG. 2 shows the orbits of secondary electrons diverging from the position deviated from the optical axis AX by 1 mm in the direction of an angle of ± 8 ° with respect to the optical axis AX, but all the secondary electrons are As shown in the orbit 18, the electrode 4 to which a voltage of −100 V is applied does not advance to the upper surface and the left side surface, and the central portion of the virtual surface 14 is L (in this example, L is 2 to 5 c
It is incident on the secondary electron detector 5 arranged at a position higher by m).

As described above, according to the charged particle beam apparatus of this example, almost 100% of the secondary electrons generated from the sample 15 are generated.
Since it enters the secondary electron detector 5 at a ratio of, the observation image of the sample 15 having a good SN ratio can be obtained. Further, the deflector 7 for scanning
Is arranged below the secondary electron detector 5, it is not necessary to dynamically perform astigmatism correction according to scanning.
In addition, a strong deflection electric field is generated in the space where the secondary electron detector 5 is arranged, but since it passes through the same place regardless of the visual field scanning, it is necessary to generate visual field distortion or change the astigmatism correction depending on the visual field. There is no.

In this example, the liner tube 6 has 10 k
The voltage of V was applied to bring the sample 15 to the ground potential.
The liner tube 6 may be grounded (grounded) to maintain the ground potential, and the sample 15 may have a negative potential. In that case, the potential of the electrode 4 is preferably lower than that of the sample 15. Furthermore, the present invention is not limited to the above-mentioned embodiment, and various configurations can be taken by applying it to, for example, a line width measuring machine, a micro analyzer or the like.

[0023]

According to the charged particle beam device of the present invention, the secondary electrons diverging from the sample travel to the upper part of the electrode by the magnetic field of the objective lens and then are captured by the secondary electron detector. Therefore, after improving the axial chromatic aberration of the primary charged particles at the electrode,
There are advantages that the secondary electron capturing efficiency is good and a detection image with a good S / N ratio can be obtained.

When a scanning deflection coil for scanning the charged particle beam on the sample is provided between the upper pole of the objective lens and the secondary electron detector, the electron beam is the same regardless of the field scanning. Since it passes through a place, no visual field distortion occurs and it is not necessary to dynamically perform astigmatism correction according to scanning. Also,
When at least a part of the periphery of the secondary electron entrance of the secondary electron detector is covered with an electrode to which a potential equal to or lower than the potential of the sample is applied, the secondary electrons from the sample are efficiently transferred to the secondary electron detector. Upon incidence, the SN ratio of the detection signal is improved.

Further, when the charged particle beam is prevented from forming a light source image by the converging action of the electrostatic lens formed including the electrodes, the axial chromatic aberration coefficient of the primary charged particles can be suppressed to a small value, and the high value can be obtained. It can converge with resolution.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a scanning electron microscope as an embodiment of a charged particle beam device according to the present invention.

FIG. 2 is a diagram showing an example of trajectories of secondary electrons from a virtual plane 14 in FIG. 1 to a secondary electron detector 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron gun 2 Condenser lens 3 Anode electrode 4 Electrode 5 Secondary electron detector 6 Liner tube 7 Deflector for scanning 8 Objective lens 9 Core 9a Upper pole of objective lens 8 9b Lower pole of objective lens 8 Of objective lens 8 Coil 11 Sample table 13 Primary electron 14 Virtual plane 15 Sample

Claims (4)

[Claims] 1. A sample is arranged between two opposing magnetic poles of an objective lens for converging a charged particle beam, and an electric field is formed between an electrode arranged on the upper pole side of the objective lens and the sample. In a charged particle beam device for forming and converging the charged particle beam on the sample, a secondary electron for detecting a secondary electron generated from the sample by irradiation of the charged particle beam on an upper pole of the objective lens. A charged particle beam device comprising an electron detector. 2. A scanning deflection coil for scanning the charged particle beam on the sample is provided between the upper pole of the objective lens and the secondary electron detector. Charged particle beam device. 3. The secondary electrode detector according to claim 1, wherein at least part of the periphery of the secondary electron entrance of the secondary electron detector is covered with an auxiliary electrode to which a potential lower than the potential of the sample is applied. Charged particle beam device. 4. The charged particle beam device according to claim 3, wherein the charged particle beam does not form a light source image due to a converging action of an electrostatic lens formed including the auxiliary electrode.