JPH1040850A - Low vacuum atmosphere scanning electron microscope - Google Patents

Abstract

[PROBLEMS] To increase an orifice diameter and increase a beam current in an observation in a low vacuum atmosphere while keeping an electron gun chamber at a high vacuum. Alternatively, in the case of an exhaust system having the same orifice diameter as that of the conventional one, observation in a low vacuum atmosphere enables observation at a higher sample chamber pressure or prolongs the life of the electron gun filament. An intermediate chamber (8) is provided between an objective lens (7) and converging lenses (4) and (5), and a pipe for exhausting the intermediate chamber (8) is provided separately from a main pipe from an electron gun section (2) and near an inlet of an exhaust pump (22). Low vacuum atmosphere type scanning electron microscope connected by.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low vacuum atmosphere scanning electron microscope.

[0002]

2. Description of the Related Art By setting the pressure of the atmosphere around an observation sample to a low vacuum of several Pa to several hundred Pa, a charging phenomenon is prevented in the observation of an insulating sample, or a component containing a relatively high vapor pressure is contained. 2. Description of the Related Art Scanning electron microscopes that facilitate observation of a sample, that is, enable low-vacuum observation are used.

In general, the exhaust system of a conventional scanning electron microscope with a low vacuum atmosphere is provided with an intermediate chamber 8 or an objective lens 7 in order to keep the sample chamber 9 at a low vacuum during observation in a low vacuum atmosphere as shown in FIG. An orifice 13 is provided, and in order to maintain a high vacuum in the electron gun 3 and the intermediate chamber 8, the oil diffusion pump 2 is connected to the main exhaust pipe 16 from the electron gun 3 and the intermediate chamber 8.
1 and a rotary pump 22 for its back pressure. Further, it comprises a rotary pump 22 for maintaining the sample chamber 9 at a low vacuum level when the needle valve 20 for changing the pressure of the sample chamber 9 is opened, and both the low vacuum observation and the high vacuum observation are performed. It is configured as possible.

[0004] A problem with the conventional low vacuum atmosphere type scanning electron microscope is that the electron gun chamber, sample chamber, and intermediate chamber are evacuated due to the exhaust structure.
Since the main exhaust pipe and the convergent lens are connected via the electron beam path, if the pressure in the sample chamber is increased (poor degree of vacuum) during observation in a low vacuum atmosphere, the orifice in the objective lens will be removed. The passing gas passes through the lower part 16 "of the main exhaust pipe, causing a pressure drop. Therefore, the pressure of the electron gun chamber 3 connected to the upper part of the main exhaust pipe 16 becomes high (poor degree of vacuum). As a result, the high voltage of the electron gun 2 cannot be maintained and the function as the electron gun cannot be performed, and there is a problem that the diameter of the orifice cannot be increased due to the pressure limitation of the electron gun chamber 3.

In the present invention, it is desired to increase the diameter of the orifice in order to increase the beam current during observation in a low vacuum atmosphere, or to reduce the pressure in the electron gun chamber in order to extend the life of the filament (to improve the degree of vacuum). In order to prevent the pressure drop below the main exhaust pipe due to the inflow gas from the orifice, the exhaust conductance is increased without major modification of the apparatus.

[0006]

An object of the present invention is to increase the diameter of an orifice and increase the beam current while maintaining the electron gun chamber at a high vacuum in observation in a low vacuum atmosphere. Or, in the case of an exhaust system having the same orifice diameter as the conventional one and an exhaust system having the same, it is possible to perform observation at a higher sample chamber pressure in observation in a low vacuum atmosphere, or to improve the degree of vacuum of the electron gun section (lower pressure To extend the life of the electron gun filament.

[0007]

In order to achieve the above object, the present invention provides a method of evacuating a common portion between a main pipe and an intermediate pipe in order to reduce the influence of gas passing through an orifice on the degree of vacuum of an electron gun. An exhaust pipe for reducing the resistance, that is, for evacuating the intermediate chamber, is connected near the main exhaust pump.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a schematic view showing an exhaust structure of a general scanning electron microscope in a low vacuum atmosphere.

This apparatus comprises an electron gun chamber 3 having an electron gun 2 for taking out an electron beam 1 serving as a mirror body, an intermediate chamber 8 having a converging lens 4, a deflection coil 6, and an objective lens 7, a sample 1
2, a sample chamber 9 having detectors 10 and 11 and the like, and exhaust pumps 21 and 22 for keeping the inside of the apparatus at a vacuum and exhaust pipes 16 and 17 are constituted.

The electron beam 1 taken out of the electron gun 2 is converged into a thin electron beam by a converging lens 4 and an objective lens 7, and is scanned on a sample 12 by a deflection coil 6 connected to a scanning power supply 23. Signals such as secondary electrons and reflected electrons are generated from the sample by the irradiation of the electron beam. In a low-vacuum (6 Pa to 540 Pa) region where the pressure in the sample chamber is high, since the mean free path of electrons is extremely short, 250 μm to 2 cm, some of the electrons irradiating the sample collide with the residual gas near the sample. To produce electrons and ions. The ions are attracted to the negatively charged electric field of the sample by the irradiation of the electron beam and neutralize the charge on the sample surface, so that the charging phenomenon does not occur. Normally, secondary electrons are detected by the secondary electron detector 10 during observation in a high vacuum. However, during low vacuum observation, since a high voltage of the subsequent acceleration voltage used for the secondary electron detector cannot be applied, generally, a signal to be detected is used. Becomes reflected electrons. To detect this reflected electron signal, the objective lens 7
A backscattered electron detector 11 is provided between the sample and the sample 12. The detected backscattered electron signal is input to the luminance modulation terminal of the CRT 25 through the signal amplification circuit 24 so that a scanning image based on the backscattered electron signal can be observed.

During observation in a low-vacuum atmosphere, in order to maintain a low degree of vacuum in the sample chamber, a plurality of condensing lenses are used between the electron gun chamber 3 and the intermediate chamber 8, so-called a converging lens. A convergent lens having an orifice stop The orifice stop is provided between the electron beam path 5 and the lower part of the intermediate chamber 8 (objective lens section) and the sample chamber. These orifice diaphragms have both functions of preventing scattering of the electron beam by making the thickness as thin as possible, narrowing the electron beam as small as possible, and setting the exhaust conductance to an optimum value.

FIG. 4 shows the configuration of the exhaust path in FIG. 3 by a network of flow path resistance. Table 1 shows the calculated values of the pressures of the respective main parts using the flow path resistance.

[0014]

[Table 1]

In order to maintain the pressure (vacuum degree) (Pc ') of the sample chamber 9 at 270 Pa (2 Torr) when the orifice diameter is 0.2 mm, the vacuum degree of each vacuum chamber is determined by the flow path resistance shown in FIG. Means that the electron gun chamber 3 (Pg ') is 4.24 × 10 ^-2 Pa
(3.18 × 10 ⁻⁴ Torr), the intermediate chamber 8 (Pm ′) is about 0.1 mm.
42 Pa (3.14 × 10 ⁻³ Torr). This is the limit for the pressure (vacuum degree) of the electron gun chamber. If the diameter of the orifice is further increased in this exhaust path configuration, the pressure in the electron gun chamber will increase (the degree of vacuum will deteriorate), so that the Since the high voltage cannot be maintained, the function as an electron gun cannot be performed. The pressure in the electron gun chamber is limited such that the gas passing through the orifice (R1 ') is not restricted to the lower part of the main exhaust pipe 16 "(R
This is accompanied by the pressure drop that occurs when passing through 4 ').
To prevent this, the exhaust conductance of the lower part 16 ″ of the main exhaust pipe is increased, that is, the main exhaust pipe 16
This can be achieved by increasing the thickness of. However, it is not preferable in terms of space restrictions and costs.

According to the present invention, when it is desired to increase the diameter of the orifice or increase the pressure in the electron gun chamber (to improve the degree of vacuum) in order to increase the beam current during observation in a low vacuum atmosphere, the flow from the orifice is reduced. An object of the present invention is to increase the exhaust conductance without major modification of the apparatus in order to prevent a pressure drop below the main exhaust pipe due to gas.

FIG. 1 is a schematic view showing an exhaust structure of a scanning electron microscope of a low vacuum atmosphere type showing an example of the present invention. FIG. 2
FIG. 2 shows the exhaust path configuration of FIG. 1 by a network of flow path resistances. Table 2 shows the calculated pressure values obtained from the channel resistance.

[0018]

[Table 2]

The exhaust configuration of FIG. 1 is different from the conventional exhaust configuration of FIG. 2 in that the exhaust resistance of the double section (inner exhaust pipe) 18 of the main exhaust pipe of the intermediate exhaust pipe 17 and the exhaust resistance of the converging lens electron beam path 5 are different. Two points.

The pressure (degree of vacuum) in the electron gun chamber is limited by the pressure drop that occurs when the gas passing through the orifice R1 passes through the lower portion R4 of the main exhaust pipe. Therefore, when the diameter of the orifice is increased, the amount of inflow gas also increases, and the pressure in the electron gun chamber is reduced. In order to prevent the pressure drop in the electron gun chamber, it is necessary to increase the exhaust conductance of the lower portion 16 "of the main exhaust pipe.

Therefore, the intermediate exhaust pipe 1 from the intermediate chamber 8
7 is connected to the inner exhaust pipe 18 disposed in the main exhaust pipe 16, and the lower part of the inner exhaust pipe 18 is opened at the lowermost part of the main exhaust pipe 16 (near the opening of the oil diffusion pump 21),
The path length of the gas flowing from the sample chamber 9 in the main exhaust pipe, which was a problem, was shortened. The conductance becomes small and the pressure in the intermediate chamber becomes high because the exhaust path from the intermediate chamber 8 becomes long, but this reduces the gas flowing into the electron gun chamber 3 through the converging lens section, that is, the converging lens electron beam passage 5. The convergent lens aperture, that is, the conductance of the convergent lens electron beam path 5 may be designed to be small.

Another method of shortening the path length of the gas flowing from the sample chamber 9 in the main exhaust pipe is to extend the intermediate exhaust pipe 17 as shown in FIG.
Alternatively, it may be opened at the lowermost part of the main exhaust pipe 16 (near the opening of the oil diffusion pump 21). As shown in Table 1, FIG.
2 and the pressure (Pc) (degree of vacuum) of the sample chamber when the orifice diameter is 0.2 mm in the exhaust configuration of FIG.
Torr), the degree of vacuum in each vacuum chamber is 1.28 × 10 ⁻² Pa in the electron gun chamber (Pg) due to the flow path resistance shown in FIG.
(9.6 × 10 ^-5 Torr), the intermediate chamber (Pm) is about 0.82P
a (6.17 × 10 ⁻³ Torr), and a vacuum degree about 3.3 times higher than that of the exhaust configuration shown in FIGS. 3 and 4 can be obtained at the electron gun chamber pressure (vacuum degree).

In the exhaust configuration shown in FIGS. 3 and 4,
Electron gun chamber pressure (Pg ') (vacuum degree) when the orifice diameter is 0.2 mm and the pressure (vacuum degree) (Pc') in the sample chamber is 270 Pa (2 Torr), 4.24 × 10 ^-2 Pa
When the exhaust configuration shown in FIGS. 1 and 2 is replaced on the basis of (3.18 × 10 ⁻⁴ Torr), the orifice diameter can be increased to 0.36 mm, which is about 1.8 times the conventional value. Since the probe current ip has a square relationship with the size of the orifice diameter, the probe current ip can flow about 3.2 times as much as the exhaust current shown in FIGS. 3 and 4.

[0024]

According to the present invention, the orifice diameter can be reduced from the conventional hole diameter of about 0.1 mm to 0.2 mm to the hole diameter of 0.2 mm to 0.36 mm at the time of observation in a low vacuum atmosphere using a low vacuum atmosphere scanning electron microscope. The beam current can be increased to about 3.2 times as large. Alternatively, when the orifice diameter is about 0.1 mm to 0.2 mm, which is the same as the conventional one, the pressure in the sample chamber can be increased and the degree of vacuum in the electron gun chamber can be kept high (low pressure). Therefore, the life of the electron gun filament can be prolonged during observation in a low vacuum atmosphere.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an exhaust path configuration of a scanning electron microscope showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing the exhaust path configuration of FIG. 1 with a network of flow path resistances.

FIG. 3 is an explanatory view showing an example of a conventional exhaust system.

FIG. 4 is a circuit diagram showing the exhaust path configuration of FIG. 3 as a network of flow path resistance.

FIG. 5 is an explanatory diagram of an exhaust path configuration showing one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron beam, 2 ... Electron gun, 3 ... Electron gun room, 4 ... Converging lens, 5 ... Converging lens electron beam path, 6 ... Deflection coil, 7 ...
Objective lens, 8 intermediate chamber, 9 sample chamber, 10 secondary electron detector, 11 reflected electron detector, 12 sample, 13 orifice stop, 14 secondary electron, 15 reflected electron, 16
... Main exhaust pipe, 20 ... Needle valve, 21 ... Oil diffusion pump, 22 ... Rotary pump, 23 ... Scan power supply, 24 ...
Signal amplification circuit, 25 ... CRT.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Mitsuo Akatsu, Inventor Hitachi Science Systems, Inc., 1040, Oji, Hitachinaka-shi, Ibaraki Prefecture (72) Inventor, Noriyuki Yukita 1040, Ma-Ichi, Hitachi, Ibaraki, Hitachi Inside Science Systems (72) Inventor Hiroyuki Suzuki 1040 Ichige Ichige, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Science Systems Co., Ltd.

Claims (2)

[Claims] An intermediate chamber is provided between an objective lens and a converging lens, and a pipe for exhausting the intermediate chamber is provided separately from a main pipe from an electron gun section, and is connected near an exhaust pump inlet. A scanning electron microscope of a low vacuum atmosphere type characterized by the above. 2. The scanning electron microscope according to claim 1, wherein said intermediate pipe has a double structure passing through said main pipe.