JPH02142045A - Scan type electron microscope and similar device thereof - Google Patents

Abstract

PURPOSE:To achieve a high resolution in a low acceleration range, and obtain a high detection sensitivity for secondary electrons by using a filter of an in-lens type where a sample is disposed inside a lens, and of an EXB type which decelerates a primary electron beam by applying a negative voltage to the sample while crossing an electric field with a magnetic field. CONSTITUTION:An electron beam 2 generated from an electron gun 1 is throttled through an acceleration lens 3, a capacitor lens 4, and an objective lens 5, for example, to be thin and radiated on a sample 6. The electron beam 2 is scanned on the sample 6 two-dimensionally by a deflector 7, and a secondary electron 8 generated from the sample 6 is detected by a secondary electron detector 9 to be an image signal. A negative voltage VR is then applied to the sample 6 for decelerating the electron beam 2, and the generated secondary electron 8 is accelerated by the decelerating voltage VR inversely, so it cannot be deflected to the detector 9 sufficiently only by the electric field of the detector 9. A filter 10 of a so-called EXB type where an electric field is made to cross with a magnetic field is disposed between the objective lens 5 and the detector 9 to eliminate the effects on the route of the electron beam 2. A high resolution and a high detection sensitivity for secondary charged particles can thus be obtained in a low acceleration range.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to a scanning charged particle microscope and similar devices thereof, and particularly to a charged particle optical system suitable for high resolution in a low acceleration region and high detection efficiency of secondary electrons. 2. Description of the Related Art In order to improve the resolution of a scanning electron microscope, an optical system as described in Japanese Patent Application No. 136004/1983 has been used. That is, it is a combination of a field emission (FE) electron gun with high brightness and a small energy width, and an in-lens type objective lens in which the sample is placed inside the lens to minimize aberrations. Even in such an optical system, the resolution decreases in the low acceleration/velocity region. On the other hand, in order to reduce chromatic aberration,
An optical system as described in 8 has been proposed. This optical system maintains a high accelerating voltage until just before the electron beam irradiates the sample, and decelerates the electron beam when irradiating the sample to lower the accelerating voltage. In this case, since the energy of the electron beam when passing through the lens is high, lens aberration can be reduced. In other words, high resolution can be achieved. From the above point of view, it is possible to obtain a higher resolution than the conventional one in the low acceleration region by combining the two optical systems described above. That is, the sample may be placed inside the lens, and a negative voltage may be applied to the sample to decelerate the sample. However, the problem in this case is the detection of secondary electrons. In the conventional case where the sample is outside the lens, the
As shown in No. 34588, it was sufficient to configure the secondary electron detector to detect the secondary electrons in the electric field of the secondary electron detector before the secondary electrons are accelerated by the deceleration electric field of the -order layer beam. However, with the in-lens type, in which the sample is placed inside the lens, the secondary electrons are not only strongly bound by the strong magnetic field of the lens, but also the secondary electron detector cannot be placed inside the lens. A problem arises.

Problem 1 to be Solved by the Invention An object of the present invention is to provide an electron optical system that achieves high resolution in a low acceleration region and provides high detection sensitivity for secondary electrons. [Means for solving the problem 1: In order to obtain high resolution with low accelerating voltage, the sample is placed inside the lens in an in-lens type, and a negative voltage is applied to this sample to decelerate the primary electron beam. I have already mentioned what you should do. In order to achieve high detection efficiency of secondary electrons with this optical system, it is sufficient to deflect the secondary electrons accelerated by the deceleration electric field of the -th layer beam toward the detector after passing through the lens. However, in this case, it is necessary to deflect only the secondary electrons toward the detector so as not to affect the -order beam. This can be achieved by using a so-called EXB type filter in which the electric field (E) and the magnetic field (B) are orthogonal to each other. [Effect 1] First, it is clear from the prior art that high resolution can be obtained even at a low acceleration voltage if the electron beam is decelerated immediately before irradiation of the sample. On the other hand, for secondary electron detection, an EXB type filter is used between the sample and the detector. -If the secondary electron beam is made to travel straight, secondary electrons with different energies will be naturally deflected. That is, the acceleration voltage V of the electron beam 2 as shown in FIG. If E and B are applied so as to satisfy the linear equation, the trajectory of the electron beam 2 will not be affected. E/V, = 2kB ・・・・・・・・・
...(1,) where k=φf2mV, r
e/m: Electron charge/mass. At this time, the energy of the secondary electrons 8 to be detected is the deceleration voltage V
R and the direction is opposite to that of the electron beam 2, so the deflection angle θ of the secondary electrons 8 is: tanθ=EL o+, /V ﾁｲﾞﾞ■ ・・・・・・
...(2). If this deflection direction is made to match the direction of the detector, the secondary electrons will proceed toward the detector, thereby improving detection efficiency. [Embodiment] An embodiment of the present invention will be explained with reference to FIG. Electrons 11A2 emitted from the electron gun 1 are focused narrowly by several lenses (in this embodiment, an accelerating lens 3, a condenser lens 4, and an objective lens 5) and are irradiated onto a sample 6. This electron IwI2 is two-dimensionally scanned on the sample 6 by the deflector 7. Further, secondary electrons 8 emitted from the sample 6 are detected by a secondary electron detector 9 and become a video signal. Here, the sample 6 is applied with a negative voltage V to decelerate the electron beam 2.
R is applied. At this time, the secondary electrons that have come out are accelerated by the deceleration voltage VR, and cannot be sufficiently deflected toward the detector 9 by the electric field of the detector 9 alone. Therefore, a deflector may be placed to deflect the emitted secondary electrons 8 toward the detector 9, but the electric field E and magnetic field B are made perpendicular to each other so as not to affect the trajectory of the electron beam 2. A so-called EXB type filter 0 is arranged between the objective lens 5 and the detector 9. At this time, if E and B are applied as in equation (1), only the secondary electrons 8 can be deflected toward the detector without affecting the trajectory of the electron beam 2, improving detection efficiency. . However, in this case, chromatic aberration due to filter 0 becomes a problem. The deflection angle β due to this chromatic aberration is β=ΔVEL/4V. =tan θAVVR/2Vo (1+ nm)−
・−・−(3) Here, ΔV is the electron beam 2
This is an energy book. In other words, as shown in Figure 2, this chromatic aberration causes the object point 1 to
2, it will have a spread of Sβ, and if the magnification of the objective lens is M, a spread of MSβ will occur on the sample. A typical example of specific numerical values is θ=30@, ΔV=
0.3eV, Vo=1. 3, β for VR is as shown in FIG. From this figure, β is estimated to be 5×10+5, S=200mm, M=1150
Then, the spread is 0.2 μm. This value is much larger than the desired value (~nm) for the electron beam 2. Therefore, in the present invention, as shown in FIG. 4 and FIG. 1, an EXB type filter 11 is arranged so as to be able to self-eliminate this chromatic aberration. In other words, as can be seen from FIG.
Operate 1. The deflection angle β' of this filter 11 is: β'=sβ/T ・・・・・・・・・・・・
・(4) may be used. With the above, it is possible to deflect only the secondary electrons 8 toward the detector 9 without increasing the diameter of the electron beam 2. In other words, high resolution and high secondary electron detection efficiency can be obtained even in the low acceleration region. A small example of the results of implementing the present invention shown in FIG. 1 is shown below. The filter 11 is placed approximately midway between the object point 12 and the filter 10, so that the length of action of the electric field E and the magnetic field B is approximately 20 mm.
The configuration is set so that V0=1kV and vR=
The voltage was varied from 0 to 900v. At this time, filter 10.
The strength of each E and B of 11 is E=0 to 25v/mm
, 0~50V/mm, B=O~14 Gauss (Gauss
), 0 to 28 Gauss was changed in conjunction with VR, and a high resolution of 4 to 6 nm was achieved. The present invention was made with the purpose of obtaining nanometer-order resolution at a low accelerating voltage of 1 kV or less, so the filter is configured in two stages, but depending on the purpose, it may be configured with one stage to achieve high secondary electron detection efficiency. As described in this embodiment, this is possible. In addition, in this example, the sample was placed inside the lens, but
The present invention can also be applied to an optical system 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 on the -L side of the objective lens as shown in FIG. In short, this can be realized if there is an EXB type filter between the sample and the secondary electron detector. Furthermore, although the present invention has been described with respect to a scanning electron microscope,
It goes without saying that the present invention is not limited to this, and can be applied to similar electron beam application devices in general, and can also be applied to charged particle beam application devices such as ion beams in general. However, in the case of a charged particle beam that has a positive charge, the deceleration voltage needs to be a positive value.

【Effect of the invention】

According to the present invention, it is possible to deflect secondary charged particles toward the detector without increasing the charged particle beam diameter even in a low acceleration region, resulting in high resolution and high detection efficiency of secondary charged particles. There is an effect that can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a charged particle optical system showing an embodiment of the present invention, Fig. 2 is an explanatory diagram regarding the chromatic aberration of the EXB type filter, and Fig. 3 is a diagram showing the deflection angle caused by the chromatic aberration of the EXB type filter and the effect on the sample. Figure 4 is a longitudinal cross-sectional view of the basic optical system for self-cancelling the chromatic aberration of the filter; Figure 5 is the trajectory of the primary electron beam and secondary electrons in the EXB type filter. FIG. Explanation of symbols 1: Electron gun, 2: Electron beam, 3: Accelerating lens, 4: Condenser lens, 5: Objective lens, 6: Sample. 7: Deflector, 8: Secondary electron, 9: Secondary electron detector. 10.11: EXB type fi/L/Yu, 12: object point' finger 7th 2nd item

Claims (1)

[Scope of Claims] 1. An electron gun, a lens means for narrowing the electron beam emitted from the electron source and irradiating it onto the sample, a scanning means for two-dimensionally scanning the electron beam on the sample, and the sample. A device comprising a detection means for detecting secondary electrons emitted from the sample, in which a negative voltage is applied to the sample, and between the sample and the detection means and on the electron source side with respect to the detection means. The electric field (E
) and a magnetic field (B) are arranged in a so-called EXB type filter. 2. A charged particle source, a lens means for narrowing the charged particle beam emitted from the charged particle source and irradiating it onto the sample, a scanning means for two-dimensionally scanning the charged particle beam on the sample, and a lens means for irradiating the charged particle beam onto the sample. and a detection means for detecting secondary charged particles coming from the sample, a negative voltage is applied to the sample when the charged particles are negatively charged particles, and a positive voltage is applied to the sample when the charged particles are positively charged particles. A so-called EXB type filter is placed between the sample and the detection means and on the side of the charged particle source with respect to the detection means, in which an electric field (E) and a magnetic field (B) are applied orthogonally, respectively. A scanning charged particle microscope and similar devices characterized by: 3. A scanning charged particle microscope and its similar apparatus according to claim 1, wherein the sample placement section is arranged inside the lens. 4. The scanning charged particle microscope and its similar apparatus according to claim 1 or 2, wherein the direction of the electric field of the EXB type filter is made to coincide with the direction of the detection means.