JP3031378B2 - Charged particle 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 region 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, in which the sample is placed inside the lens, the magnetic field of the lens is so strong that not only the secondary electrons are strongly bound by this magnetic field, but also that 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 An object of the present invention is to provide an electron optical system capable of achieving high resolution in a low acceleration region and obtaining high sensitivity for detecting secondary electrons.

[0009]

According to an aspect of the present invention, a charged particle source, a condenser lens for narrowing a first charged particle beam emitted from the charged particle source, and a sample stage for holding the sample are provided. Scanning means for scanning the first charged particle beam, and means for applying a negative voltage to the sample, wherein the first charged particle beam irradiated on the sample by the scanning means is generated on the charged particle beam side from the sample. A second charged particle beam,
A first deflector for deflecting the charged particle beam, a second deflecting unit for reducing aberration of the first charged particle beam, and the first deflector.
And a detector for detecting the second charged particle beam is provided between the deflector and the second deflector.

First, it can be seen from the prior art that if the electron beam is decelerated immediately before sample irradiation, high resolution can be obtained even at a low acceleration voltage.

On the other hand, regarding secondary electron detection, since an E × B type filter is used between the sample and the detector, secondary electrons having different energies can be obtained by moving the primary electron beam straight. You will be naturally deflected. That is,
As shown in FIG. 5, with respect to the acceleration voltage Va 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.

[0012]

(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

[0014]

(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.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG.

The electron beam 2 emitted from the electron gun 1 is narrowed down by a number of lenses (accelerating lens 3, condenser lens 4, and objective lens 5 in this embodiment) to irradiate 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 due to the filter 10 becomes a problem. The deflection angle β due to this chromatic aberration is

[0021]

(Equation 3)

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

That is, as shown in FIG. 2, the 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 °, ΔV = 0.3 eV and V0 = 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 such 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

[0025]

(Equation 4)

It is sufficient to set

As described above, only the secondary electrons 8 can be deflected 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, nm is obtained at a low accelerating voltage of 1 kV or less.
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 also 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.

Further, the present invention has been described with respect to a scanning electron microscope. However, it is needless to say that the present invention is not limited to this, but can be applied to similar electron beam application devices in general and further to charged particle beam application devices such as ion beams. No. However, in the case of a charged particle beam having a positive charge, the deceleration voltage needs to be a positive value.

[0032]

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 (4)

(57) [Claims] 1. A charged particle source, a condenser lens for narrowing a first charged particle beam emitted from the charged particle source, a sample stage for holding a sample, and a scanning unit for scanning the narrowed charged particle beam Means for applying a negative voltage to the sample,
A second charged particle beam generated on the charged particle beam side from the sample by the first charged particle beam irradiated on the sample by the scanning unit, and a first deflector for deflecting the second charged particle beam;
A second deflecting unit that reduces aberration of the first charged particle beam, and the second deflecting unit is disposed between the first deflector and the second deflector.
A charged particle beam application apparatus comprising a detector for detecting a charged particle beam. 2. An apparatus according to claim 1, wherein said first deflector and said second deflector comprise an electric field and a magnetic field. 3. An apparatus according to claim 2, wherein said electric field and said magnetic field intersect with each other. 4. The charged particle beam application apparatus according to claim 1, wherein said first and second deflectors are E × B filters.