JPH02259408A - Charged particle beam apparatus - Google Patents

Abstract

PURPOSE:To facilitate automation and to enable efficient detection of secondary electrons by a method wherein the secondary electrons generated by irradiation are restricted in the vicinity of the optical axis of a lens-barrel and, after passing through an objective lens of the lens-barrel, they are detected by a secondary-electron detector. CONSTITUTION:A secondary electron beam 9 emitted from a sample 13 by the irradiation with a primary electron beam 4 is restricted by a magnetic field and taken out in front of the sample, and after converged again by an electrostatic objective lens 3b, it is detected by a secondary-electron detector 11 provided above the lens 3b. When the position of this detector 11 is apart from the lens 3b, secondary electrons diffuse after converged by the electric field of the objective lens and this sometimes causes lowering of a detection efficiency. In this case, a coil 6 is provided in front of the lens 3b, and thereby the secondary electrons are restricted in the vicinity of the optical axis and then can be led efficiently to the detector 11. A magnetomotive force of the structure of a unipolar magnetic field type lens 5 may not be so large a value as to converge the electron beam 4 on the sample, but needs only to be a value necessary for restricting the electron beam 9 of about 10V in the vicinity of the optical axis and making it proceed into an objective lens hole 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrostatic lens-controlled charged particle beam device that can efficiently detect secondary electrons from above an objective lens.

[Conventional technology]

Electron beam equipment such as electron beam measuring machines and electron beam testers are used in testing during the development and manufacturing of VLSIs.
These electrons! A magnetic field type lens is generally used in the lens barrel of the a-device. Magnetic field type lenses have the advantage of being able to reduce aberration coefficients and are widely used, but they inherently have the characteristic of hysteresis image rotation.

However, in recent years, in the above-mentioned electron beam apparatus, it has been desired to improve measurement accuracy and operability by computer-controlling and automating the electron optical parameters. For this purpose, it is important that there is no image shift, defocus, or image rotation when changing the accelerating voltage and probe current, but magnetic field type lens barrels have the above-mentioned characteristics, such as high speed, There is a problem with accuracy. Therefore, electrostatic lens barrels that essentially do not have the above-mentioned characteristics such as hysteresis are attracting attention.

[Problem to be solved by the invention]

Although electrostatic lens barrels do not have the above-mentioned disadvantages of magnetic lenses, they do have other problems. One problem is that
It is not easy to capture secondary electrons using the through-the-lens (TTL) method, and the secondary electron detector must be installed on the side of the sample.
This is inconvenient for high-precision length measurement, etc. (Autumn 1987, Japan Society of Applied Physics, 20a-G-9, NTT, Ken Saito et al.).

In addition, attempts have been made to attach a focused ion beam column to these electron beam devices and process the device, but the secondary and fi-son detectors installed on the side of the sample are not suitable for the sample size and the oblique angle of around 1. There are inconveniences such as restricting the amount of data being used or not being able to attach other detectors, etc.

The main object of the present invention is to provide a charged particle beam apparatus which employs an electrostatic lens barrel in place of the conventional magnetic field type lens barrel and which enables automation by computer.

Furthermore, when adopting an electrostatic lens barrel, we made it easier to capture secondary electrons using the TTL method, which was difficult with this lens barrel, and developed a charged particle beam device that made high-precision length measurement and automation possible. It is about providing.

Another object of the present invention is to provide a charged particle beam device having a plurality of lens barrels that can effectively detect secondary electrons with one detector.

[Means to solve the problem]

The means employed in the present invention to achieve the above object are as follows.

fi+ A charged particle source, an electrostatic focusing lens 2, an electrostatic objective lens, and a secondary electron detector provided in front of the objective lens, and the lens barrel portion facing the sample has an i-pole magnetic field type lens structure. A charged particle beam device whose presence is vFlfi.

(2) In a charged particle VA device having multiple lens barrels, at least one lens barrel is equipped with a secondary electron detector in front of its objective lens, and the portion of the lens barrel facing the sample is exposed to a monopolar magnetic field. A charged lens having a molded lens structure, wherein the secondary electron detector detects secondary electrons generated by charged particle irradiation onto the sample from a lens barrel other than the lens barrel. Particle beam device.

(Operation) The particle beam emitted from the charged particle source passes through an electrostatic focusing lens (and scanning system), is focused by an electrostatic objective lens, and is irradiated onto the sample.Secondary electrons generated by this irradiation are
The electron beam is restrained near the optical axis of a lens barrel having a monopolar magnetic field type lens structure, and after passing through the objective lens of the lens barrel, it is detected by a secondary electron detector provided in front of the objective lens.

〔Example〕

FIG. 1 shows an embodiment of the present invention. The electron beam 4 generated by the electron gun 2 and passed through the electrostatic focusing lens 3a is focused by the electrostatic objective lens 3b, and is sent to the sample 13 by the scanning system 7.
scanned over the surface. The outer tube (hunting and crosshatching portions) of the lens barrel 1 and the sample chamber wall 15 are made of a magnetic material, and shield the atomizer beam from a disturbance magnetic field. Further, a ground portion of the electrostatic objective lens 3b facing the sample and an outer cylinder portion connected thereto are made of a magnetic material, and a coil 6 is wound around the ground portion. Furthermore, an outer cylinder 8 made of a magnetic material surrounds the coil 6. These parts (cross-hunting parts) form a single-pole 61 field lens structure.The sample chamber wall 15 made of a magnetic material and the lens barrel l are
They are connected via a non-magnetic material 17, and the monopolar magnetic field type lens structure is configured so that the magnetic field formed near the sample is symmetrical about the optical axis 4.

The secondary electron beam 9 emitted from the sample 13 by the irradiation with the primary electron beam 4 is restrained by the upper ii2 magnetic field, taken out in front of the sample, focused again by the electrostatic objective lens 3b, and then directed above the objective lens. It is detected by a secondary electron detector 11 provided.

When the secondary electron detector is located away from the objective lens 3b, after the secondary electrons are focused by the objective lens electric field,
It may spread and the detection efficiency may decrease. In this case, an air-core solenoid coil is installed in front of the electrostatic objective lens, and after the secondary electrons are restrained near the axis, they can be efficiently guided to the secondary electron detector.

The magnetomotive force J of this monopole magnetic field type lens structure is not large enough to focus the atomizer beam 4 on the sample, but rather it confines the secondary electron beam 9 of about 10V near the optical axis 4, and the electrostatic objective lens Any value necessary for entering the hole 10 may be used.

Approximate conditions for the magnetomotive force of the monopolar magnetic field type lens structure 5 for allowing secondary electrons to enter the lens hole 10 are as follows.

An electron with a speed υ entering a uniform magnetic field B at an angle θ has a radius of moυsinθ γ　± e make a spiral movement.

Therefore, in the embodiment shown in FIG.
In order to enter the lens hole 10, (1) 2T≦D at the sample 14 position (i.e., the distance WD from the top surface 10).

It is necessary to satisfy the following conditions. Here, Do is the diameter of the top surface 10 of the electrostatic objective lens 3b facing the sample. Furthermore, at the position of the top surface 10, it is necessary to satisfy the condition 2 γ≦DI. Here DI is top surface 10
This is the diameter of the hole provided in the hole.

Among the above two conditions, the condition (1+ means that the secondary electrons 9 are
Condition (2) is a condition for restricting the secondary electrons 9 to the vicinity, and condition (2) is a condition for the secondary electrons 9 to enter the lens hole 10.

When each of the above conditions is determined using the formula for the distribution of magnetic flux density B, O holds true as condition (1), and DI holds true as condition (2).

Furthermore, if the focus excitation force of only the unipolar magnetic field type lens structure 5 at the sample position (i.e., the WD) is Jo, the primary electron beam is focused on the sample and focused mainly by the action of the electrostatic objective lens 3b. In order to control, the magnetomotive force J to be applied to the unipolar magnetic field type lens structure 5 needs to satisfy J<JO-- (3).

Secondary electron constraint condition when D o -1211φ, D, = 6x1φ +11. The lower limit J value of +21 is shown in FIG. 2 for WD. The solid line I indicates J obtained from conditional expression (1), and the broken line ■ indicates J obtained from conditional expression (2).

Furthermore, only the single-pole magnetic field type lens structure 5 allows the atomizer beam 4 to
The value of the n force J0 that occurs when it is assumed that can be focused on the sample is shown in I[IA for an accelerating voltage of 1 kv and as TI[B for an accelerating voltage of 5 kv. According to conditions (11 to (3)), region A (cross hatching) indicates the region that the magnetomotive force J of the single FiA magnetic field type lens structure 5 should satisfy.

As is clear from the explanation so far, the purpose of the monopole magnetic field type lens structure is not to focus the primary electron beam on the sample, but to efficiently guide the secondary electrons to the detector. It is sufficient to choose the minimum J for the WD that is A. For example, when WD=51■, J=40AT (point a in Figure 2). Although this value is small, at a low accelerating voltage of about lkv, it has a lens effect of about J150~1, so when J is kept constant and the accelerating voltage is changed, the focusing effect and rotation effect will change. Since J is a fixed value, there is no specific hysteresis, and high-accuracy and high-speed correction is easy.

In addition, in the present embodiment shown in FIG. 1, even if there is a hysteresis characteristic, when it is desired to obtain a high-resolution image, it is sufficient to increase the magnetomotive force J of the unipolar magnetic field type lens structure 5 (see the point shown in FIG. 2). ).

Furthermore, the same secondary electron detection method as described above can also be applied to a charged particle beam device equipped with a plurality of lens barrels.

An example is shown in FIG.

1 is an electron beam column similar to that shown in FIG. 1, and has a monopolar magnetic field type lens structure 5. 31 is a focused ion beam column, which includes a liquid metal ion a32, a two-stage electrostatic focusing lens 33a, a scanning system 37, and an electrostatic objective lens 33b.
have. A high-speed ion beam is affected by a disturbance magnetic field.
The outer tube of the lens barrel 31 can be made of a non-magnetic material such as stainless steel, which is much less affected by the electron beam. In this case, the disturbance from the axisymmetric magnetic field formed by the monopolar magnetic field type lens structure 5 There are fewer advantages.

Next, a method of using the embodiment shown in FIG. 3 will be described.

This embodiment is the same as the embodiment shown in FIG. 1 in that normal SEM image observation is performed by detecting the secondary electron beam generated by the primary electron beam irradiation onto the sample from the lens barrel 1 with the detector II. When processing devices with a focused ion beam,
After stopping the electron beam irradiation, the ion beam 34 and the sample 13
focus, scan, and process the device. The secondary electrons 9 generated by the focused ion beam irradiation are restrained by the axis-4 symmetrical magnetic field formed by the monopolar magnetic field type lens structure 5 and proceed in the direction of the apex va10, and after passing through the objective lens 3b, are detected by the detector 11. 31M image (scanning ion image) of the processed part
can be obtained. Furthermore, when performing normal SEM image observation, ion beam irradiation is stopped and electron beam irradiation is performed again.

In the embodiment shown in FIG. 1, an electron beam column has been described, but the present invention can be similarly applied to an apparatus in which the column 1 is a focused ion beam column. That is, the ion beam 4 is focused and scanned on the sample, and the resulting secondary electrons 9 can be efficiently detected using the unipolar magnetic field type lens structure 5 at <TTL.

Further, in the embodiment of the electron beam apparatus shown in FIG. 1, the scanning system is constructed of an electrostatic system, but it may be constructed of an electromagnetic system. This is because the hysteresis of an electromagnetic scanning system can be significantly smaller than that of a magnetic field type lens.

〔Effect of the invention〕

Since it is a charged particle beam device that uses an electrostatic lens system without hysteresis characteristics, it is easy to automate.
By cleverly using a single-pole magnetic field type lens structure, secondary electrons, which were considered difficult to use with electrostatic lens systems, can be efficiently captured in TTL.
It can be detected depending on the method. For this reason, measurement speed, measurement accuracy,
Operability can be improved.

In addition, in a charged particle beam device having multiple lens barrels,
Since it is not necessary to separately provide a secondary detector near the sample, the degree of freedom in the space around the sample increases, and secondary electrons can be detected efficiently using one detector.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the charged particle beam device of the present invention, Fig. 2 is a diagram showing the magnitude of the magnetomotive force that must be satisfied in a monopolar magnetic field type lens structure, and Fig. 3 is a diagram showing a plurality of lens barrels. This figure shows a practical example of the present invention in a 5I electron beam device. 1, 31... 2...Electron gun 3a, 33a... 3b, 33b... 4.34... 5... 6... 7.37... 8...9... ・Element barrel Electrostatic focusing lens Electrostatic objective lens Electron beam (optical axis) Unipolar magnetic field type lens coil Scanning system Outer cylinder secondary electron gun 10.40・・ 11. . . Sample irradiation position Sample chamber wall Non-magnetic material Liquid metal ion source Above Applicant Seiko Electronic Industries Co., Ltd. Agent Patent attorney Keisuke Hayashi Figure 1

Claims (2)

[Claims] (1) Equipped with an electrostatic focusing lens, an electrostatic objective lens, and a secondary electron detector provided in front of the objective lens, and the lens barrel portion facing the sample has a monopolar magnetic field type lens structure. A charged particle beam device featuring: (2) In a charged particle beam device having a plurality of lens barrels, at least one lens barrel is equipped with a secondary electron detector in front of the objective lens, and the portion of the lens barrel facing the sample is
It has a monopolar magnetic field type lens structure, and is characterized in that the secondary electron detector detects secondary electrons generated by charged particle irradiation to the sample from a lens barrel other than the lens barrel. A charged particle beam device.