JP5244730B2 - Low vacuum scanning electron microscope - Google Patents

Description

  The present invention relates to a scanning electron microscope, and more particularly to a low vacuum scanning electron microscope that observes the vicinity of a sample in a low vacuum atmosphere.

  Some conventional low-vacuum scanning electron microscopes have a vacuum exhaust system configuration as described in Patent Document 1 and Patent Document 2. FIG. 3 schematically shows a conventional exhaust system configuration. With reference to this figure, the configuration of a vacuum exhaust system of a conventional low vacuum electron microscope will be described.

  In FIG. 3, an electron gun chamber 1 for accommodating an electron gun, an intermediate chamber 23 for accommodating an electron optical system, an objective lens 5 for narrowing an electron beam to irradiate a sample, and a sample chamber 7 for accommodating a sample are provided. The electron gun chamber 1 and the intermediate chamber 23 are connected to the main intake port 21 of the composite turbo molecular pump 10 through the vacuum exhaust pipe 8 and the vacuum exhaust pipe 9 and are evacuated to a high vacuum.

  A vacuum gauge 12 a is disposed in the vacuum exhaust pipe 8 and monitors the degree of vacuum in the electron gun chamber 1. An orifice 6 is disposed in the objective lens 5, and differential exhaust is performed upstream of the sample chamber 7 and the intermediate chamber 23. The exhaust port of the composite turbo molecular pump 10 and the sample chamber 7 are connected to the auxiliary vacuum pump 11, and the back pressure exhaust of the composite turbo molecular pump 10 and the low vacuum exhaust of the sample chamber 7 are performed together. The degree of vacuum in the sample chamber 7 is monitored by a vacuum gauge 12b, and a variable flow valve 13 for adjusting the amount of gas introduced into the sample chamber 7 in order to vary the low degree of vacuum in the sample chamber 7 is disposed.

JP 2007-141633 A JP 2008-226521 A

  In the conventional low-vacuum scanning electron microscope described above, the sample chamber, the intermediate chamber, and the electron gun chamber are generally opened to the atmosphere when the sample is exchanged. In this case, the valve is switched after preliminary evacuation with the auxiliary vacuum pump, and high vacuum evacuation of the electron gun chamber and the intermediate chamber is performed with the composite turbo molecular pump, so it takes several minutes to obtain the required degree of vacuum. It cost. On the other hand, in order to change the sample while maintaining the vacuum of the electron gun chamber, a separate exhaust chamber such as a sample changer is required. In this case, the preliminary exhaust chamber can be evacuated in about several tens of seconds, so that the throughput is improved. Cost increases are inevitable.

  Since the electron gun chamber and the intermediate chamber are connected to the main inlet of the turbo molecular pump, when the amount of gas blown from the sample chamber through the orifice is increased during low vacuum, i.e., when the orifice diameter is increased, When the degree of vacuum in the sample chamber is set to a lower vacuum, the degree of vacuum in the electron gun chamber is lowered. For this reason, the orifice diameter and the degree of vacuum in the sample chamber are limited to such an extent that they do not affect the degree of vacuum in the electron gun chamber in practice. As a result, for example, in the case of X-ray analysis and the like, particularly when a large amount of probe current is required, the amount of probe current is limited by the orifice, so it is necessary to remove the orifice.

  In view of the above problems, an object of the present invention is to improve the throughput from sample exchange to observation, and at the time of electron beam irradiation, an exhaust system capable of expanding the orifice diameter so as to obtain a necessary probe current amount. It is providing the low vacuum electron microscope provided with.

  To achieve the above object, the present invention provides an electron gun, a sample chamber in which a sample irradiated with an electron beam emitted from the electron gun is disposed, an electron gun chamber including the electron gun, and the sample chamber In an electron microscope equipped with an exhaust system for evacuating a vacuum chamber, the electron microscope has a plurality of intermediate chambers through which an electron beam passes between the electron gun chamber and the sample chamber, and a valve at an opening between the plurality of intermediate chambers. An electron microscope comprising: an exhaust system for exhausting so that the pressure in the intermediate chamber and the sample chamber on the sample chamber side from the valve is higher than the pressure in the intermediate chamber and the electron gun chamber on the electron source side from the valve. I will provide a.

  In addition, an electron gun, a sample chamber in which a sample irradiated with an electron beam emitted from the electron gun is arranged, an electron gun chamber including the electron gun, and an exhaust system for evacuating the sample chamber are provided. The electron microscope has an intermediate chamber through which an electron beam passes between an electron gun chamber and a sample chamber, and has a valve at an opening between the intermediate chamber and the electron gun chamber, and the intermediate chamber and the sample chamber It may be an electron microscope characterized by having an exhaust system that exhausts the air so that the pressure becomes higher than the pressure of the electron gun chamber.

  According to the present invention, it is possible to improve throughput from sample exchange to observation by maintaining the vacuum degree upstream of the electron gun chamber and the valve (on the electron gun side) at a high vacuum. In addition, by making the degree of vacuum downstream of the valve (sample chamber side) lower than the degree of vacuum upstream of the valve, the amount of gas blown up from the sample chamber can be suppressed, and the orifice diameter can be increased compared to the conventional case. it can.

The figure which shows one Embodiment of the low vacuum scanning electron microscope which is this invention. The figure which showed the flow of the exhaustion sequence at the time of sample replacement | exchange of the low vacuum scanning electron microscope which is this invention. The figure which shows the vacuum exhaust system of the conventional low vacuum scanning electron microscope. The figure which shows one Embodiment of the low vacuum scanning electron microscope which is this invention. The figure which shows one Embodiment of the low vacuum scanning electron microscope which is this invention.

  The principle of the present invention will be described.

  In the present invention, with the air lock valve as a boundary, the electron source side is connected to the main intake port of the composite turbo molecular pump, and the sample chamber side is connected to the intermediate intake port of the composite turbo molecular pump to perform exhaust. Accordingly, if the air lock valve is closed at the time of sample exchange, the upstream (electron source side) from the air lock valve can be maintained at a high vacuum, and throughput from sample exchange to observation can be improved.

  Further, since the downstream side of the air lock valve (sample chamber side) is connected to the intermediate intake port, it blows up from the sample chamber even if the orifice diameter is enlarged compared to the case where it is connected to the conventional main intake port. The amount of gas can be suppressed. Thereby, the electron gun chamber can expand the orifice diameter while maintaining a high vacuum.

  Furthermore, when there are a plurality of intermediate chambers, the high vacuum of the electron gun chamber can be better maintained by differential exhaust.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing an embodiment of a low vacuum scanning electron microscope of the present invention.

  The low-vacuum scanning electron microscope of the present invention houses an electron gun chamber 1 that houses an electron gun, an intermediate chamber that houses an electron optical system, an objective lens 5 that narrows the electron beam and irradiates the sample, and a sample. A sample chamber 7 is provided. The intermediate chamber is vacuum-separated into a first intermediate chamber 2 and a second intermediate chamber 4 by an air lock valve 3.

  The objective lens 5 includes an orifice 6 for limiting the amount of gas blown from the sample chamber 7 in order to perform differential exhaust between the sample chamber 7 and the second intermediate chamber 4. The electron gun chamber 1 and the first intermediate chamber 2 are connected to the main intake port 21 of the composite turbo molecular pump 10 through a vacuum exhaust pipe 8 and are evacuated to a high vacuum. A vacuum gauge 12 a is disposed in the vacuum exhaust pipe 8 and monitors the degree of vacuum in the electron gun chamber 1. The second intermediate chamber 4 is connected to the intermediate intake port 22 of the composite turbo molecular pump 10 through the vacuum exhaust pipe 9 and exhausts the gas blown up from the sample chamber 7 through the orifice 6. The exhaust port of the composite turbo molecular pump 10 and the sample chamber 7 are connected to an auxiliary vacuum pump 11, and the auxiliary vacuum pump 11 performs low vacuum exhaust of the sample chamber 7 and back pressure exhaust of the composite turbo molecular pump 10. The degree of vacuum in the sample chamber 7 is monitored by a vacuum gauge 12b, and the amount of gas introduced into the sample chamber 7 is adjusted by a variable flow valve 13 in order to vary the degree of vacuum in the sample chamber 7.

  The sample chamber has a pressure of 1 to 3000 Pa, and the pressure can be adjusted.

  FIG. 2 shows the flow of the exhaust system sequence control from the opening of the sample chamber 7 to the atmosphere in the low vacuum scanning electron microscope according to the present invention until the low vacuum observation. In the air release mode, the air lock valve 3 is first closed, and the electron gun chamber 1 and the first intermediate chamber 2 are vacuum-sealed. Next, the valves AV2, AV3, AV5 and AV7 are closed, the leak valve LV2 is opened, and the sample chamber 7 and the second intermediate chamber 4 are opened to the atmosphere.

  After the sample exchange, the low vacuum evacuation mode is started, the valves LV2 and AV1 are closed, the valves AV2 and AV6 are opened, and the sample chamber 7 and the second intermediate chamber 4 are evacuated. When the vacuum gauge 12b reaches the lower limit of the set vacuum level, for example, 500 Pa, the AV6 valve is closed. Next, the valves AV 1 and AV 5 are opened, and the second intermediate chamber 4 is evacuated at the intermediate intake port 22 of the composite turbo molecular pump 10. Next, the valve of AV7 is opened and control of the variable flow valve 13 is started to adjust the degree of vacuum in the sample chamber 7. Although not shown in the present example, the value of the vacuum gauge 12b may always be read and the flow rate adjustment of the variable flow valve 13 may be automatically controlled.

  Finally, the air lock valve 3 is opened and low vacuum observation is started.

  With the above configuration, the sample can be exchanged by holding the vacuum in the electron gun chamber 1 and the first intermediate chamber 2 by the air lock valve 3, and the sample chamber 7 and the second intermediate chamber 4 can be connected by the auxiliary vacuum pump 11. Since preliminary evacuation is sufficient, the evacuation time can be shortened, and throughput can be improved from sample exchange to low vacuum observation.

  FIG. 4 is a diagram showing an embodiment of the low vacuum scanning electron microscope of the present invention.

  In this embodiment, there is one intermediate chamber, but an air lock valve is provided between the electron gun chamber 1 and the intermediate chamber 24 with the air lock valve 3 as a boundary, and the electron gun chamber is the main of the composite turbo molecular pump. The intermediate chamber is connected to the intake port, and the intermediate chamber is connected to the intermediate intake port 22 of the composite turbomolecular pump. Also in the present embodiment, the effect of the present application can be achieved. Since there is only one intermediate chamber, the structure is easy and can be produced at low cost.

  FIG. 5 is a diagram showing an embodiment of the low vacuum scanning electron microscope of the present invention.

  In this embodiment, the intermediate chamber is separated into three chambers, a first, a second and a third vacuum chamber. An air lock valve 3 is provided between the second intermediate chamber 26 and the third intermediate chamber 27. In the electron gun chamber 1, an extra high vacuum pump such as an ion pump 28 is separately attached. As in the previous embodiment, the electron gun chamber 1 may be exhausted from the main intake port of the composite turbomolecular pump.

  Further, in the present embodiment, exhaust is performed by connecting the orifice 6 directly above the intermediate intake port of the composite turbo molecular pump. Thereby, the gas molecules rising from the sample chamber can be effectively exhausted. The downstream side of the air lock valve 3 is connected to the intermediate intake port 22 of the composite turbo molecular pump. The closer to the main intake port, the higher the degree of vacuum can be achieved at the intermediate intake port, so the side closer to the sample chamber is connected to the intermediate intake port far from the main intake port.

  In the above embodiment, the effect of the present invention can be obtained by connecting the upstream side of the air lock valve to a pump capable of exhausting with high vacuum and connecting the downstream side to a pump having a lower degree of vacuum. Can do. By using the main intake port and the intermediate intake port of the composite turbo molecular pump, the effect of the present invention can be achieved with a single pump.

  According to the present invention, when the sample is exchanged, the upstream side of the valve is kept in vacuum, and the downstream side of the valve is opened to the atmosphere. After exchanging the sample, the pre-evacuation time can be shortened without providing a pre-exhaust chamber by pre-exhausting the sample chamber to several hundreds Pa, which is the lower limit of vacuum that can be set for the sample chamber. In addition, since the electron gun section is maintained at a high vacuum, it is possible to irradiate an electron beam in a relatively short time after preliminary evacuation, thereby improving throughput from sample exchange to observation.

  In addition, the intermediate chamber where the upstream side of the valve is evacuated from the main intake port and the gas blows up through the orifice arranged in the objective lens is an intermediate intake port that can be evacuated in a lower vacuum range than the main intake port By evacuating from the bottom, it is possible to suppress a decrease in the degree of vacuum in the electron gun chamber due to the effect of the gas blowing up from the orifice. Therefore, since the amount of gas blown up to the second intermediate chamber can be reduced, the electron gun chamber can expand the orifice diameter while maintaining a high vacuum. As a result, it is possible to increase the amount of probe current applied to the sample. As a result, during X-ray analysis that requires a relatively large probe current, the conventional operation of removing the orifice is involved, but the necessary probe current can be obtained without removing the orifice. The troublesome work is eliminated. Further, when the orifice diameter is the same as that of the prior art, the sample chamber can be set to a lower degree of vacuum. Therefore, when observing a sample that is susceptible to damage such as shrinkage or drying due to vacuum, the damage can be reduced.

  Furthermore, since the present invention can be achieved by the configuration of one composite turbo molecular pump and one auxiliary vacuum pump, a differential pumping function can be added without adding a vacuum pump. Accordingly, the increase in the space in the apparatus required for the exhaust system can be minimized and the function of the exhaust system can be improved, and the maintenance cost required for the vacuum pump can be suppressed.

DESCRIPTION OF SYMBOLS 1 Electron gun chamber 2 First intermediate chamber 3 Air lock valve 4 Second intermediate chamber 5 Objective lens 6 Orifice 7 Sample chamber 8, 9 Vacuum exhaust pipe 10 Composite turbo molecular pump 11 Auxiliary vacuum pump 12a, 12b Vacuum gauge 13 Variable flow valve 21 Main intake ports 22, 22a, 22b Intermediate intake ports 23, 24 Intermediate chamber 25 First intermediate chamber 26 Second intermediate chamber 27 Third intermediate chamber 28 Ion pump

Claims (3)

An electron gun, and a sample chamber in which a sample irradiated with an electron beam emitted from the electron gun is disposed;
In an electron microscope including an electron gun chamber including the electron gun and an exhaust system for evacuating the sample chamber,
It has a plurality of intermediate chambers through which electron beams pass between the electron gun chamber and the sample chamber, and has a valve at the opening between the plurality of intermediate chambers,
Having an orifice between the sample chamber side intermediate chamber and the sample chamber from the valve;
The pressure in the intermediate chamber and the sample chamber of the sample chamber side of the valve, have a exhaust system for exhausting to be higher than the intermediate chamber and the pressure of the electron gun chamber of the electron source side of the valve,
The exhaust system is composed of a composite turbo molecular pump, the intermediate chamber and the sample chamber on the sample chamber side from the valve are connected to the intermediate intake port of the composite turbo molecular pump, and the intermediate chamber on the electron source side from the valve and An electron microscope characterized in that an electron gun chamber is connected to a main inlet of the composite turbo molecular pump . In claim 1 ,
An electron microscope characterized in that an intermediate chamber and a sample chamber closer to the sample chamber than the valve are connected to a side closer to the main intake port of the intermediate intake port in order from the sample chamber. Oite to claim 1,
The sample chamber is 1 to 3000 Pa, and has a valve for adjusting the pressure of the sample chamber.

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