JPH09167588A - Scanning type electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe a sample in a low vacuum state without affecting the degree of vacuum in an electron gum chamber by arranging a sample box in a sample chamber, and differentially exhausting the sample chamber and the sample box. SOLUTION: A sample box 2 is detachably fixed to a sample chamber 1. The sample box 2 has an orifice 3 in the upper wall and a sample stage 4 on the inside. In low vacuum observation, a main valve 21 is closed, the inside of an electron gun 5 is exhausted with a main pump 20, and the electron gun 5 and a primary electron beam path 6 are kept in high vacuum. The sample chamber 1 is exhausted with a rotary pump 23, the degree of vacuum is varied with a needle valve 19, the sample box 2 is exhausted with a rotary pump 15, and the degree of vacuum is varied with a needle valve 16. Thereby, the portion between the high vacuum part and the sample chamber 1 is differentially exhausted with an orifice 8, and the portion between the sample chamber 1 and the sample box 2 is differentially exhausted with the orifice 3. A sample 9 can be observed as its vicinity is kept in low degree of vacuum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope, and more particularly, it relates to a scanning electron microscope capable of observing a sample containing a large amount of water at a high magnification with minimal deformation of tissue.

[0002]

2. Description of the Related Art FIG. 6 shows a general exhaust system structure of a conventional scanning electron microscope capable of observing a low vacuum, which is provided between an electron gun section 5 and a sample chamber 1 by an orifice 8 provided on the lower surface of an electron lens. Differential exhaust. During low-vacuum observation, the main valve 21 connected to the sample chamber 1 is closed, and the main pump 20 evacuates the electron gun 5. On the other hand, the sample chamber 1 is evacuated by the rotary pump 23, and the needle valve 19 adjusts the amount of air introduced into the sample chamber 1 to adjust the degree of vacuum in the sample chamber 1. The shaded portion in the drawing indicates the high vacuum portion, and the gas is differentially exhausted through the orifice 8 provided under the objective lens.

Further, in Japanese Unexamined Patent Publication No. 6-215716, an intermediate chamber partitioned by an electron gun chamber and an orifice is provided above the objective lens, and the intermediate chamber is evacuated by an oil rotary pump so that the pressure in the sample chamber is 1000 Pa. It is described that it is enlarged to a degree.

[0004]

In the scanning electron microscope shown in FIG. 6, it is necessary to maintain the electron gun 5 in a high vacuum state, so that there is a limit in making the sample chamber 1 low vacuum. . That is, when the degree of vacuum in the sample chamber 1 is lowered, the amount of air leaked from the orifice 8 is increased and the degree of vacuum in the high vacuum portion is lowered. As a result, the discharge of the electron gun portion and the inside of the primary electron beam passage Deterioration of image quality due to phenomena such as increase in scattering at 6
It causes a decrease in resolution. Although it is possible to maintain the vacuum of the high vacuum part by replacing the main pump 20 with a high-performance pump having a pumping speed several times to several tens of times of the current one,
New problems arise such as an increase in manufacturing cost and an increase in size of the device.

As described above, in the conventional apparatus, since there was a limit to the reduction of the degree of vacuum in the sample chamber, it is difficult to observe a sample containing a large amount of water. There was a problem that was changed. In addition, when the sample chamber 1 is evacuated to a low vacuum, the sample from the orifice 8 to the sample 9
There are many air molecules between. The mean free path of electrons is about 100 m at a vacuum degree of 10 ^-3 Pa and 1.3 Pa.
Is about 100 mm, and about 270 Pa is about 0.5 mm
However, there is a problem that as the degree of vacuum gets worse, the primary electron beam and the reflected electron signal are scattered more, the detection efficiency of the reflected electron signal detected by the reflected electron detector 10 is lowered, and the resolution is lowered.

The method disclosed in Japanese Patent Laid-Open No. 6-215716 is
Since the vacuum level of the intermediate system adjacent to the electron gun is lowered, the vacuum level of the electron gun chamber is affected, and the field emission type electron gun or LaB
_It cannot be applied to a scanning electron microscope equipped with an electron gun that requires an ultra-high vacuum of 10 ⁻⁵ to 10 ⁻⁸ Pa like ₆ filaments. An object of the present invention is to provide a scanning electron microscope capable of observing a sample in a lower vacuum state without affecting the vacuum degree of the electron gun chamber. Further, the present invention provides a scanning electron microscope capable of observing a sample containing a large amount of water by reducing drying due to vacuum, and further increasing the amount of backscattered electron signals during low-vacuum observation to enable high-resolution observation. The purpose is to do.

[0007]

In the present invention, a sample box which can be kept in a vacuum state lower than that of the sample chamber is provided in the sample chamber, and the orifice provided in the sample box allows the sample chamber and the sample box to be differentiated from each other. The above object is achieved by exhausting. That is, in the scanning electron microscope of the present invention, a closed container having an orifice on one side surface, a sample stage arranged in the closed container for positioning a sample with respect to the orifice, a driving unit for driving the sample stage, and an exhaust unit are provided. The sample box for a scanning electron microscope which is used by inserting into the sample chamber of the scanning electron microscope is used.

The orifice diameter of the sample box can be changed according to the observation conditions and the like. The sample stage may have a sample cooling means, and a backscattered electron detector may be provided on the inner wall of the closed container. The sample box includes an electron gun, an electron lens, a sample chamber, and an orifice provided below the electron lens, and is used as a sample chamber of a scanning electron microscope capable of differentially exhausting the electron gun to a high vacuum and the sample chamber to a low vacuum. The sample box is attached so that the orifice of the sample box is located on the optical axis. By differentially evacuating the sample chamber and the sample box through the orifice of the sample box, the vicinity of the sample can be observed in a vacuum lower than that of the sample chamber while the electron gun is maintained in a high vacuum.

The sample box is provided with the first vacuum gauge and the first outside air introducing means, and the sample chamber is provided with the second vacuum gauge and the second outside air introducing means, respectively, and the outputs of the first and second vacuum gauges are provided. If a control means for controlling the first and second outside air introduction means is provided based on
It is possible to automatically control the sample chamber and the sample box to a set degree of vacuum. According to the present invention, since the sample is placed in the sample box having a vacuum degree lower than the vacuum degree in the sample chamber, it is possible to observe the sample containing a large amount of water as compared with the conventional case. Further, the drying of the sample due to the vacuum is also reduced, so that the surface shape of the sample is not deformed even during long-term observation.
Furthermore, since the low vacuum state is only in the very vicinity of the sample, the scattering of reflected electrons by air molecules is reduced, the reflected signal amount is increased, and the resolution is also improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an exhaust system configuration of a scanning electron microscope according to an example of the present invention, and FIG. 2 shows an enlarged cross-sectional view near a sample. The electron lens and the scanning deflector for the primary electron beam, which are not shown in detail, have well-known configurations.

A sample box 2 is detachably attached to the sample chamber 1. The sample box 2 has an orifice 3 on the upper wall and a sample stage 4 inside. The primary electron beam 40 emitted from the electron gun 5 passes through the primary electron beam passage 6 and the orifice 8 provided in the lower part of the electron lens 7, the orifice 3 provided in the sample box 2, and the sample stage 4. The sample 9 is scanned. The backscattered electrons 41 generated from the sample 9 are
It is detected by the backscattered electron detector 10 arranged in the sample chamber 1 after passing through the orifice 3 of the sample box 2 in the opposite direction. The output of the backscattered electron detector 10 is input to an image display device 11 such as a CRT, and a sample image is displayed on the image display device 11.

In the sample box 2, a rotary pump 15 for exhausting the inside, a needle valve 16 for adjusting the amount of outside air introduced to control the degree of vacuum inside, and a vacuum gauge 17 such as a Pirani gauge for measuring the degree of vacuum inside. Are connected. A vacuum gauge 18 and a needle valve 19 are also provided in the sample chamber 1 of the scanning electron microscope. The degree of vacuum in the high vacuum section is monitored by a vacuum gauge 22.

During low vacuum observation, the main valve 21 is closed and the main pump 20 evacuates the electron gun 5.
High vacuum (about 10 ^-3 P) inside the electron gun 5 and the primary electron beam passage 6
Keep in a). In FIG. 1, a hatched portion indicates a high vacuum area. The inside of the sample chamber 1 is evacuated by the rotary pump 23, and the degree of vacuum can be changed by the needle valve 19. The inside of the sample box 2 is evacuated by the rotary pump 15, and the degree of vacuum can be changed by the needle valve 17. The orifice 8 is differentially evacuated between the high vacuum portion and the sample chamber 1, and the orifice 3 provided in the sample box 2 is differentially evacuated between the sample chamber 1 and the sample box 2. Needle valve 1
The opening control of 6 and 19 is performed by motor control. The controller 25 receives the outputs of the vacuum gauges 17 and 18 and controls the opening degrees of the needle valves 16 and 19 so that the insides of the sample chamber 1 and the sample box 2 have a preset degree of vacuum.

The diameters of the orifices 3 and 8 are variable. The orifice 8 provided at the lower end of the primary electron beam passage 6 also has a function as a diaphragm for the primary electron beam 40, and in order to keep the electron gun 5 and the primary electron beam passage 6 in a high vacuum, it is preferable that the diameter be small. . The diameter of the orifice 3 of the sample box 2 is, for example, as shown in FIG. 3, the orifice plate 30 provided with a plurality of orifices 3a to 3d having a diameter of about 0.1 mm to several mm on the outside of the sample box 2. Movably, and the orifice plate 30 is moved to select an orifice located on the optical axis of the primary electron beam 40, thereby making it variable.

When a large-diameter orifice is used, the primary electron beam 40 and the backscattered electron 41 are used when observing at a low magnification such as a field of view.
Does not block. However, since the vacuum difference between the sample box 2 and the sample chamber 1 cannot be increased, the degree of vacuum of the sample box 2 cannot be lowered so much. On the other hand, by using an orifice having a small diameter, it is possible to increase the vacuum difference between the sample box 2 and the sample chamber 1. Therefore, even when the vacuum degree in the sample box 2 is set to, for example, 270 Pa or more, the vacuum in the sample chamber 1 is reduced. It becomes possible to maintain the degree at about 1.3 Pa. Therefore, only the atmosphere of the sample 9 can be made low vacuum while the electron gun 5 and the primary electron beam passage 6 are maintained at high vacuum. On the other hand, when observed at a low magnification, the field of view becomes narrow because the primary electron beam 40 is blocked by the orifice 3.

From the above, the diameter of the orifice 3 is made smaller when observing the sample 9 at high magnification while suppressing the evaporation of water, and made larger when observing a wide range at a low magnification. The diameter of the orifice 3 may be selected according to the type of sample or observation conditions.
By changing the orifice diameter and controlling the opening / closing of the needle valves 16 and 19, the vacuum degree of the sample chamber 1 and the sample box 2 can be set to an optimum value for the sample to be observed.

The sample stage 4 provided in the sample box 2 is provided with a cooling means 43 using a Peltier element or the like so that the sample 9 can be cooled. When the cooling means 43 is operated to freeze the water in the sample containing a large amount of water, the drying speed of the sample becomes slow, and the sample can be observed for a long time without deformation. The sample stage 4 is configured to be movable up and down in the sample box 2,
By moving the sample stage 4 up and down, the distance between the orifice 3 and the sample 9 can be changed. The sample stage 4 can be moved in the vertical direction by external screw drive or the stage 4
This can be performed by vertically moving only the portion of the sample stage 4 on which the sample 9 is placed, as shown by the arrow in FIG. 2, by the small motor provided inside.

Alternatively, as shown in FIGS. 4 and 5, a slit 44 is provided on the wall surface of the sample box 2, and the member 4 movable along the wall surface of the sample box 2 while hermetically covering the slit 44.
The support 45 of the sample stage 4 is fixed to 7. Sample box 2
The airtightness of the slit 44 is secured by the O-ring 46. By rotating the Z knob 48 and moving the member 47 and the support body 45 integrally by the feed screw 49, the sample stage 4 can be integrally moved up and down from the outside of the sample box 2.

When the distance between the orifice 3 and the sample 9 is reduced, the backscattered electron signal detected by the backscattered electron detector 10 arranged in the sample chamber 1 is increased, so that the image quality and the resolution are improved, and Observation at low magnification is possible. On the other hand, since the degree of vacuum in the sample atmosphere is high, the sample is easy to dry. On the contrary, if the distance between the orifice 3 and the sample 9 is increased, the drying of the sample is suppressed, but since the reflected electrons 41 are cut by the orifice 3, the image quality and the resolution are deteriorated, and the orifice 3 is observed at the low magnification observation. The shadow of. Therefore, by moving the sample stage 4 up and down, the distance between the orifice 3 and the sample 9 is adjusted to realize optimum observation conditions.

The problem that the backscattered electrons 41 from the sample 9 are blocked by the orifice 3 and do not reach the backscattered electron detector 10 is that a semiconductor type backscattered electron detector 50 or the like is installed inside the sample box 2, for example, around the orifice 3. Can be solved by doing. The detection signal from the backscattered electron detector 50 provided in the sample box 2 and the detection signal from the backscattered electron detector 10 arranged in the sample chamber 1 may be used independently or may be used by adding. . When the semiconductor backscattered electron detector 50 is divided around the orifice 3 in the azimuth direction and an image is formed by the backscattered electron detection signals in a specific azimuth angle direction or a plurality of selected azimuth directions, the unevenness of the sample is obtained. It is possible to obtain a sample image that reflects

For example, the inside of the sample chamber 1 is 1.3 Pa, the sample box 2 is
When the inside is set to 270 Pa, the vicinity of the sample is 270 Pa.
Since it is in the vacuum degree of 1, the damage of the sample due to drying can be reduced even if the sample has a lot of water, the deformation of the sample is small even during long-term observation, and the sample can be cooled for a longer time. It becomes possible to observe time. Further, between the orifice 8 and the sample 9, the degree of vacuum in the sample chamber 1 is set to 1.3 Pa (mean free path 100 mm), so that the scattering of the primary electron beam 40 by air molecules is suppressed, and the orifice 3 and the backscattered electron are detected. Since the degree of vacuum is the same between the chambers 10, scattering of the reflected electrons 41 is also suppressed, and the amount of reflected electron signals increases and the resolution increases as compared with the conventional case where the entire sample chamber is set to 270 Pa. The image quality can be improved.

Further, if the degree of vacuum in the sample chamber is 1.3 Pa, the amount of air leaked from the orifice 8 to the primary electron beam passage 6 is also small, and the influence on the high vacuum portion is reduced, so that the main pump 20 is also reduced. A conventional pumping speed is sufficient.

[0023]

According to the present invention, a sample containing a large amount of water can be observed because the vicinity of the sample can be observed while maintaining a lower degree of vacuum, and the drying of the sample surface is suppressed, so that the sample can be observed for a long time. It will be possible. In addition, the amount of backscattered electron signals is increased and the resolution is expected to be improved because the vacuum is provided only in the very vicinity of the sample.

Furthermore, since the influence on the high vacuum portion is small,
It is possible to perform low-vacuum observation with a LaB ₆ electron gun, which requires an ultrahigh vacuum in the electron gun chamber, or a scanning electron microscope equipped with a field emission electron gun.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an exhaust system according to the present invention.

FIG. 2 is a detailed view around the sample.

FIG. 3 is an explanatory view of an orifice plate having a plurality of orifices.

FIG. 4 is an explanatory diagram of an example of a sample stage moving mechanism.

FIG. 5 is a perspective view of a slit portion of a sample box.

FIG. 6 is an explanatory view showing a conventional exhaust system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sample chamber, 2 ... Sample box, 3 ... Orifice, 4 ... Sample stage, 5 ... Electron gun, 6 ... Primary electron beam passage, 7 ... Electron lens, 8 ... Orifice, 9 ... Sample, 10 ... Reflection electron detector , 11 ... Image display device, 15 ... Rotary pump, 1
6 ... Needle valve, 17 ... Vacuum gauge, 18 ... Vacuum gauge, 1
9 ... Needle valve, 20 ... Main pump, 21 ... Main valve, 22 ... Vacuum gauge, 23 ... Rotary pump, 2
5 ... Control device, 30 ... Orifice plate, 40 ... Primary electron beam, 41 ... Reflected electron, 43 ... Cooling means, 44 ... Slit, 45 ... Support, 46 ... O ring, 48 ... Z knob,
49 ... Lead screw, 50 ... Semiconductor type backscattered electron detector

Claims (6)

[Claims] 1. A closed container having an orifice on one side surface, a sample stage arranged in the closed container for positioning a sample with respect to the orifice, a driving means for driving the sample stage, and a connection to an exhaust means. Section and
A sample box for a scanning electron microscope, which is used by being inserted into a sample chamber of a scanning electron microscope. 2. The sample box for a scanning electron microscope according to claim 1, further comprising means for changing a diameter of the orifice. 3. The sample box for a scanning electron microscope according to claim 1, wherein the sample stage has a sample cooling means. 4. The sample box for a scanning electron microscope according to claim 1, 2 or 3, wherein a backscattered electron detector is provided on the inner wall of the closed container. 5. A scanning electron microscope including an electron gun, an electron lens, a sample chamber, and an orifice provided below the electron lens, capable of differentially exhausting the electron gun to a high vacuum and the sample chamber to a low vacuum, wherein the sample The sample box according to any one of claims 1 to 4 is installed in a room so that the orifice is located on the optical axis, and the sample box and the sample box are connected via the orifice of the sample box. A scanning electron microscope, characterized in that it is dynamically evacuated and the vicinity of the sample in the sample box is evacuated to a lower vacuum than the sample chamber for observation. 6. The sample box is provided with a first vacuum gauge and a first outside air introducing means, and the sample chamber is provided with a second vacuum gauge and a second vacuum gauge.
External air introduction means, and controls the first and second outside air introduction means based on the outputs of the first and second vacuum gauges to automatically control the sample chamber and the sample box to a set vacuum degree. The scanning electron microscope according to claim 5, wherein