JP2993873B2 - Charged particle beam application equipment and electron beam application equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning charged particle microscope and similar devices, and more particularly, to a charged particle optical system having high resolution in a low acceleration range and suitable for high secondary electron detection efficiency.

[0002]

2. Description of the Related Art In order to improve the resolution of a scanning electron microscope, an optical system as described in JP-A-61-294746 is used. That is, a field emission (FE) electron gun having a high brightness and a small energy width;
This is a combination of an in-lens type objective lens in which a sample is arranged inside a lens and aberration is minimized. Even in such an optical system, the resolution is reduced in the low acceleration region.

On the other hand, in order to reduce chromatic aberration, Japanese Patent Publication No.
An optical system as described in 3-34588 has been proposed.

This optical system has a high accelerating voltage until just before an electron beam irradiates a sample, and decelerates to a low accelerating voltage when irradiating the sample. In this case, since the energy of the electron beam when passing through the lens is high, lens aberration can be reduced. That is, high resolution can be achieved.

From the above viewpoints, it is possible to obtain higher resolution than before in the low acceleration region by combining the above two optical systems. That is, the sample may be placed inside the lens, and a negative voltage may be applied to the sample to reduce the speed.

However, the problem in this case is the detection of secondary electrons. In the conventional case where the sample is outside the lens, as shown in JP-B-63-34588, the electric field of the secondary electron detector is used until the secondary electrons are accelerated by the deceleration electric field of the primary electron beam. It should have been configured to detect secondary electrons. However, in the in-lens type where the sample is placed inside the lens, the magnetic field of the lens is so strong that not only the two-time electrons are strongly bound by this magnetic field but also the secondary electron detector cannot be placed inside the lens. Problems arise.

[0007] Japanese Patent Application Laid-Open No. Sho 62-31933 discloses that a primary electron beam and a secondary electron are separated only by a magnetic field.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electron optical system capable of obtaining high secondary electron detection sensitivity.

A charged particle source; and a second source from the charged particle source.
An objective lens for focusing the charged particle beam and irradiating the sample with the charged particle beam;
The first charged particles between the objective lens and the sample;
A deceleration means for decelerating the beam and the first charged particle beam.
And irradiates the sample with the second charged particles generated from the sample.
A first deflector for separating from the first charged particle beam;
To the first charged particle beam generated by the first deflector
A second electric field and a second magnetic field for generating a second magnetic field for compensating the influence;
Charged particle beam, comprising: two deflectors;
Applied equipment.

An electron source and a primary electron beam emitted from the electron source
Means for applying a negative voltage to the sample to decelerate
Irradiating the sample with the primary electron beam
A secondary electric field generated from the electron beam and the primary electron beam into a first electric field.
A first deflector separating the first deflector and a first magnetic field;
The influence on the first charged particle beam generated by the deflector
A second polarization generating a second electric field and a second magnetic field to be corrected;
An electron beam application device comprising:
is there.

Also, an electron source and a primary light emitted from the electron source.
2 generated from the sample by irradiating the sample with an electron beam
Means for applying a negative voltage to the sample to accelerate secondary electrons,
The accelerated secondary electrons and the primary electron beam
A first deflector separating the field and a first magnetic field;
Of the first deflector on the first charged particle beam
To generate a second electric field and a second magnetic field for correcting
An electron beam application device comprising: a deflector.
It is in.

Still further, an electron source and an electron source
An objective lens for focusing the primary electron beam and irradiating the sample with the primary electron beam;
Hand that generates an electric field that accelerates secondary electrons generated from the sample
A step, the primary electron beam passing through the objective lens, and the
A first deflector for separating the accelerated secondary electrons;
Shadow on the first charged particle beam generated by the first deflector
A second electric field generating a second electric field and a second magnetic field for
Electron beam application device, comprising:
It is in the place.

However, the problem in this case is the detection of secondary electrons. In the conventional case where the sample is outside the lens, as shown in JP-B-63-34588, the electric field of the secondary electron detector is used until the secondary electrons are accelerated by the deceleration electric field of the primary electron beam. It should have been configured to detect secondary electrons. However, in the in-lens type in which the sample is placed inside the lens, the secondary electron is not only strongly bound by the magnetic field of the lens, but also the secondary electron detector cannot be placed inside the lens. Problems arise.

On the other hand, regarding the secondary electron detection, since an E × B type filter is used between the sample and the detector, if the primary electron beam is made to go straight, the secondary electrons having different energies can be obtained. You will be naturally deflected. That is,
As shown in FIG. 5, with respect to the acceleration voltage V ₀ of the electron beam 2,
If E and B are applied so as to satisfy the following expression, the trajectory of the electron beam 2 is not affected.

[0015]

(Equation 1)

At this time, since the energy of the secondary electrons 8 to be detected is the deceleration voltage VR and the direction is opposite to that of the electron beam 2, the deflection angle θ of the secondary electrons 8 is

[0017]

(Equation 2)

## EQU1 ##

If this deflection direction is made to coincide with the direction of the detector, the secondary electrons travel toward the detector, so that the detection efficiency can be improved.

[0020]

FIG. 1 shows an embodiment of the present invention.

The electron beam 2 emitted from the electron gun 1 is narrowed down by a number of lenses (in this embodiment, an acceleration lens 3, a condenser lens 4, and an objective lens 5), and irradiates the sample 6 onto the sample. The electron beam 2 is two-dimensionally scanned on the sample 6 by the deflector 7. Also, secondary electrons 8 coming out of sample 6
Is detected by the secondary electron detector 9 and becomes a video signal.

Here, a negative voltage VR is applied to the sample 6 to decelerate the electron beam 2.

At this time, the emitted secondary electrons are accelerated in reverse by the deceleration voltage VR, and cannot be sufficiently deflected toward the detector 9 only by the electric field of the detector 9.

Therefore, a deflector may be arranged to deflect the emitted secondary electrons 8 toward the detector 9. However, the electric field E and the magnetic field B are changed so as not to affect the trajectory of the electron beam 2. An orthogonal so-called E × B filter 10 is arranged between the objective lens 5 and the detector 9. At this time, if E and B are applied as in the expression (1), only the secondary electrons 8 can be deflected to the detector without affecting the trajectory of the electron beam 2, and the detection efficiency can be improved. .

However, in this case, chromatic aberration caused by the filter 10 becomes a problem. The deflection angle β due to this chromatic aberration is

[0026]

(Equation 3)

## EQU2 ## Here, ΔV is the energy width of the electron beam 2.

That is, as shown in FIG. 2, this chromatic aberration causes the spread of Sβ at the object point 12, and when the magnification of the objective lens is M, the spread of MSβ occurs on the sample. As a typical example of specific numerical values, θ = 30
Assuming that °, Δ V = 0.3 eV and V ₀ = 1 kV, β for VR is as shown in FIG. From this figure, β is largely estimated to be 5 × 10 ⁻⁵ , S = 200 mm, M = 1/5
If it is set to 0, the spread will be 0.2 μm. This value is much larger than the desired value (〜 nm) of the electron beam 2.

Therefore, in the present invention, as shown in FIG. 4 and FIG. 1, an E × B type filter 11 is arranged so that this chromatic aberration can be self-erased. That is, as can be seen from FIG. 4, the filter 11 is operated so that the electron beam 2 having the energy of ΔV spreads as if it came out of one point of the object point 12. The deflection angle β ′ of this filter 11 is

[0030]

(Equation 4)

It is sufficient to set

As described above, it is possible to deflect only the secondary electrons 8 toward the detector 9 without increasing the diameter of the electron beam 2. That is, high resolution and high detection efficiency of secondary electrons can be obtained even in a low acceleration region.

One example of the result of implementing the present invention shown in FIG. 1 is shown below. Filter 11 is the object point 12 and filter 1
It was arranged almost at the center of 0, and the action length of the electric field E and the magnetic field B was set to about 20 mm. V0 was fixed at 1 kV and VR was changed to 0 to 900 V. At this time, the strengths of E and B of the filters 10 and 11 are set to E = 0 to 2
5 V / mm, 0 to 50 V / mm, B = 0 to 14 Gauss, 0 to 28 Gauss, and a high resolution of 4 to 6 nm were realized by changing the values in conjunction with VR.

According to the present invention, at a low acceleration voltage of 1 kV or less, nm
Although the filter is provided in two stages for the purpose of obtaining the resolution of the order, it is described in the present embodiment that the efficiency of secondary electron detection can be increased even if the filter is formed in one stage depending on the purpose. As expected.

In this embodiment, the sample is arranged inside the lens. However, the present invention can be applied to an optical system having a structure arranged outside the lens. In this case, it goes without saying that the secondary electron detector may be located between the sample and the objective lens, or may be located above the objective lens as shown in FIG. In short, it can be realized if there is an E × B type filter between the sample and the secondary electron detector.

Furthermore, the present invention has been described with respect to a scanning electron microscope. However, the present invention is not limited to this, but can be applied to similar electron beam application devices in general and further to general charged particle beam application devices such as ion beams. Needless to say. However, in the case of a charged particle beam having a positive charge, the deceleration voltage needs to be a positive value.

[0037]

According to the present invention, the secondary charged particles can be deflected toward the detector without increasing the charged particle diameter even in the low acceleration region, so that the secondary charged particles can be highly resolved and the secondary charged particles can be deflected. There is an effect that a high particle detection efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a charged particle optical system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating chromatic aberration of an E × B filter.

FIG. 3 is a graph showing a relationship between a deflection angle caused by chromatic aberration of an E × B filter and a deceleration voltage applied to a sample.

FIG. 4 is a longitudinal sectional view of a basic optical system for self-cancelling chromatic aberration of a filter.

FIG. 5 is an explanatory diagram showing trajectories of primary electron beams and secondary electrons by an E × B filter.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 electron gun 2 electron beam 3 acceleration lens 4 condenser lens 5 objective lens 6 sample 7 deflector
8 secondary electron, 9 secondary electron detector, 10, 11 Ex
B-type filter, 12 ... object point.

Claims (11)

(57) [Claims] 1. A charged particle source, and an objective lens for squeezing a first charged particle beam emitted from the charged particle source and irradiating the sample with the first charged particle beam;
Deceleration means for decelerating the first charged particle beam between the objective lens and the sample, irradiating the sample with the first charged particle beam, and causing the second charged particles generated from the sample to pass through the second charged particle. A first deflector for separating from the first charged particle beam, and a second electric field and a second magnetic field for correcting an influence on the first charged particle beam generated by the first deflector. A charged particle beam application apparatus, comprising: a second deflector. 2. The charged particle beam application device according to claim 1, wherein said first deflector and said second deflector are arranged so that an electric field and a magnetic field cross each other. 3. The charged particle beam application apparatus according to claim 2, wherein said first and second deflectors are E × B filters. Wherein said first energy to the charged particle beam is incident on the sample charged particle beam apparatus according to any one of claims 1, wherein 3 to or less than 1 KeV. 5. and the electron source, said sample by irradiation of a negative voltage for decelerating the primary electron beam emitted from said electron source means for applying to the sample, to the sample of decelerated the primary electron beam Deflector that separates secondary electrons generated from the primary electron beam from the primary electron beam by a first electric field and a first magnetic field, and the first charged particle beam generated by the first deflector An electron beam application device comprising: a second deflector for generating a second electric field and a second magnetic field for correcting the influence on the electron beam. 6. An electron source, and means for applying a negative voltage to the sample to accelerate secondary electrons generated from the sample by irradiating the sample with a primary electron beam emitted from the electron source; A first deflector that separates the secondary electrons and the primary electron beam by a first electric field and a first magnetic field; and a first charged particle beam generated by the first deflector. An electron beam application device comprising: a second deflector for generating a second electric field and a second magnetic field for correcting the influence of the above. 7. An electron source, and means for applying a negative voltage to the sample for accelerating secondary electrons generated from the sample by irradiating the sample with a primary electron beam emitted from the electron source; A first deflector that separates the secondary electrons and the primary electron beam by a first electric field and a first magnetic field; and a first deflector between the electron source and the first deflector. An electron beam application apparatus, comprising: a second deflector for generating a second electric field and a second magnetic field so as to remove aberration of the electron beam. 8. A electron source, an objective lens for irradiating the sample concentrates the primary electron beam emitted from said electron source, means for generating an electric field for accelerating secondary electrons generated from said specimen, said objective The primary electron beam passing through the lens and the accelerated 2
A first deflector for separating secondary electrons from a second electron; and a second deflector for generating a second electric field and a second magnetic field for correcting an influence on the first charged particle beam generated by the first deflector. An electron beam application apparatus, comprising: 9. An electron beam application apparatus according to claim 5, wherein said first deflector and said second deflector are arranged so that an electric field and a magnetic field cross each other. Wherein said first and second deflector charged particle beam apparatus according to claim 9, characterized in that the E × B filter. 11. The charged particle beam application apparatus according to claim 5, wherein an energy of the primary electron beam incident on the sample is 1 KeV or less.