JP2001312989A - Sample stage for electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample stage for an electron microscope, capable of setting an eucentric position around the visual field of the electron microscope at all times during a large inclination of a sample. SOLUTION: The sample stage comprises a mechanism for adjusting the direction of an overall stage system eucentrically adjusted and passing a rotating shaft through the center of the electron microscope, namely, an adjusting mechanism containing second spherical seat for adjusting the direction of mounting the whole stage eucentrically adjusted on the electron microscope. The whole stage is rotated on the second spherical seat, without marring the eucentric conditions of a rotating cylinder and a sample holder, so that the direction of the rotating shaft of the cylinder can be set to pass the center of the visual field of the electron microscope. Three-dimensional observation of the sample from all directions is ensured, irrespective of the shape of the sample, observing magnification and inclination angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In an electron microscope, a sample position can be finely moved with high accuracy on the order of nanometers, and a sample with a small visual field shift and a small focus shift even when the sample is greatly inclined to observe the sample from various angles. About the stage.

[0002]

2. Description of the Related Art Transmission Electron Microscope (TEM)
The ctron microscope) irradiates the sample with an electron beam accelerated to 100 to 300 kV, and forms an enlarged image of the transmitted electron beam by interacting with the sample. Since a TEM image is a projection image of an electron beam transmitted through a sample, information in the thickness direction is added and cannot be separated from one image. Therefore, attempts have been made to extract information in the thickness direction from a plurality of images obtained by tilting the sample. However, if the sample stage that tilts the sample in the past is not a eucentric structure, the field of view shift when the sample is tilted is several hundred μm, which not only impairs operability but also limits the viewable field of view to several μm square. There is a problem and the sample that can be observed is very limited. To address these problems, a eucentric sample stage has been devised and already available on the market. Here, the eucentric structure is
This is a rotating structure having a mechanism for finely moving an object in a plane perpendicular to the rotation axis. Therefore, since the object can always be moved on the rotation axis, the sample does not rotate around the rotation axis during rotation,
The stationary position can be maintained.

A typical example of a sample stage for an electron microscope is a two-axis tilt sample fine-movement apparatus and an image relief correction method described in Japanese Patent Application Laid-Open No. 08-017380. The operation principle of this conventional example will be described with reference to FIG. Here, the direction perpendicular to the paper is z
The directions, left and right and up and down directions on the paper are referred to as x and y directions, respectively. The rotation angle with the x direction as the rotation axis is referred to as θ. This figure is a principle diagram of the operation of the apparatus viewed from above the electron microscope body. Specimen is usually 3m like electron microscope
It is fixed to a mesh of about mφ and installed at the tip of the sample holder. The sample holder 1 is inserted and fixed in a sample holder sheath 2. The tip of the sample holder sheath 2 is spherical, and is structured to be housed in the spherical seat 3. Therefore, the sample holder 1 can perform precession with respect to the x-axis with the center of the spherical seat 3 as a fixed point, and can move the sample to arbitrary y and z positions. Further, the entire sample holder 1 can be rotated by θ. Here, in order to control the sample position to the y and z positions with high precision, a fine movement actuator 5 which is usually fixed in the y and z2 directions is provided on a rotating cylinder 4 provided on the outer layer of the sample holder sheath 2 and the fine movement is performed. It is sandwiched by a push-back spring 6 installed on the opposite side of the actuator 5. The fine movement actuator 5 can be moved in and out by an electric pulse input, and can be moved by several nanometers. The position restoring force is generated by the return spring 6. The sample holder 1 is rotated around the x axis by a θ motor 7 via a rotary cylinder 4. The fine actuator 5 is installed on the rotary cylinder 4 so as to have a eucentric function.
Rotate around an axis. This is because the one on the cylinder rotation axis of the rotary cylinder 4 does not move in any of the x, y, and z directions although the direction changes during rotation. Therefore, if the fine movement actuator 5 is fixed on the rotating body, that is, the rotating cylinder 4, and the sample is constantly moved on the rotation axis by the fine movement actuator 5, there is no visual field shift and focus shift during rotation. This is because The fine movement of the sample in the x direction is realized by an x fine movement lever 9 fixed to the electron microscope body 8 at a position facing the rotary cylinder 4 with the sample interposed therebetween. That is, the sample 10 can be finely moved by the x fine movement of the tip of the sample holder 1 back and forth in the x direction. As the restoring force in the opposite direction, a force is used in which the sample holder 1 is sucked toward the mirror body by a pressure difference between the atmosphere and vacuum. Now, since the sample holder 1 is configured to rotate using the rotary cylinder 4 as a guide and also using the spherical seat 3 as a guide, the positional relationship between the two is adjusted so that the cylinder rotation axis passes through the center of the spherical seat 3. There is a need. If this adjustment is not made, the sample holder 1 causes a swinging rotation phenomenon with the radius of the eccentric distance between the cylinder rotation axis and the center of the spherical seat 3 at the contact portion with the fine movement actuator 5, and the sample 10 also moves around the cylinder rotation axis. Cause a differential movement. Therefore, a rotating cylinder position fine adjustment mechanism 11 for passing the cylinder rotating shaft through the center of the spherical seat 3 is provided in the y and z2 directions. Now, this adjustment process is called eucentric adjustment. By this adjustment, an immovable rotation axis can be formed, and the target portion of the sample can be moved by the fine movement actuator 5 on this axis, so that it is possible to suppress a visual field shift and a focus shift during sample rotation. In addition to this, an application for a sample stage for an electron microscope has been acknowledged.
36744. In this application, the point that the x fine movement lever that creates the fine movement of the sample in the x direction is not at the position facing the sample stage with the sample interposed therebetween as shown in FIG. The principle of the eucentric adjustment function, which is the purpose of the application, is disclosed in Japanese Patent Application Laid-Open No. 08-01738.
It is the same as 0, and also has the problems described in the items.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 08-017380.
The problem with the described sample stage is that, since the direction of the rotation axis is determined by the positional relationship between the rotating cylinder and the electron microscope body, it does not always pass through the center of the electron microscope, that is, the center of the visual field. At the time of low-magnification observation, there is a high probability that the rotation axis is included somewhere in the visual field, but it is extremely difficult to use a tens of thousands or more. In other words, it can be said that eucentric observation at high magnification is difficult in the conventional method. Similarly, when the sample tilt angle is large, the probability that the sample falls out of the visual field increases, and it is practically difficult to perform eucentric observation with a large tilt. Summarizing the above, the realization of a positive mechanism for adjusting the rotation axis adjusted eucentrically to the center of the electron microscope is required for large-magnification oblique observation and omnidirectional three-dimensional observation at high magnification, which is a feature inherent in electron microscopes. It is an issue.

[0005]

In order to address the above-mentioned problem, the present application proposes a new mechanism for adjusting the direction of the eucentrically adjusted stage system as a whole and passing the rotation axis through the center of the electron microscope. That is, a second cylinder for holding the rotary cylinder, fixing the rotary cylinder guide including the spherical seat to the electron microscope body at the second spherical seat, and adjusting the relative positional relationship between the electron microscope body and the rotary cylinder guide. An adjustment mechanism was provided. As a result, the entire stage can be rotated by the second spherical seat without breaking the eucentric conditions of the rotating cylinder and the sample holder, and the setting can be made so that the direction of the cylinder rotation axis passes through the center of the objective lens.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 shows the principle of the apparatus as viewed from above the electron microscope body of the stage devised. As in the conventional example of FIG. 2, the sample holder 1 is inserted and fixed to the sample holder sheath 2. Since the tip of the sample holder sheath 2 is spherical and has a structure that can be accommodated in the spherical seat 3, the sample holder 1 has the center of the spherical seat 3 as a fixed point and x
It can precess about the axis and move the sample to any y, z position. Further, the entire sample holder 1 can be rotated by θ. Here, in order to control the sample position to the y and z positions with high accuracy, a fine actuator 5 fixed in the y and z2 directions is provided on a rotary cylinder 4 provided on the outer layer of the sample holder sheath 2. 5 is sandwiched by a push-back spring 6 installed on the opposite side. The fine movement actuator 5 can be moved in and out by an electric pulse input, and the position restoring force is generated by the push-back spring 6. The sample holder 1 is rotated around the x axis by a θ motor 7 via a rotary cylinder 4. The fine movement actuator 5 is mounted on the rotary cylinder 4 to have a eucentric function, and rotates around the x-axis together with the rotary cylinder 4. This is because the one on the cylinder rotation axis of the rotary cylinder 4 does not move in any of the x, y, and z directions although the direction changes during rotation. Therefore, if the fine movement actuator 5 is fixed on the rotating body, that is, the rotating cylinder 4, and the sample 10 is constantly moved on the rotation axis by the fine movement actuator 5, there is no visual field shift or focus shift during rotation. It is because it can be in a state. Also, x
The fine movement of the sample in the direction is realized by the x fine movement lever 9 fixed to the electron microscope body 8 at a position facing the rotary cylinder 4 with the sample 10 interposed therebetween. That is, the sample can be finely moved by the x fine movement of the tip of the sample holder 1 in the x direction. As the restoring force in the opposite direction, a force is used in which the sample holder 1 is sucked toward the mirror body by a pressure difference between the atmosphere and vacuum. Now, since the sample holder 1 is rotated by using the rotary cylinder 4 as a guide and also has a rotational speed structure using the spherical seat 3 as a guide, the positional relationship between the two is adjusted so that the cylinder rotation axis passes through the center of the spherical seat 3. There is a need. Without this adjustment,
The sample holder 1 causes a swinging rotation phenomenon with the radius of the eccentric distance between the cylinder rotation axis and the center of the spherical seat 3 at a contact portion with the fine movement actuator 5, and the sample 10 also causes precession about the cylinder rotation axis. Therefore, a rotating cylinder position fine adjustment mechanism 11 for passing the cylinder rotating shaft through the center of the spherical seat 3 is provided in the y and z2 directions. This adjustment process is called eucentric adjustment. By this adjustment, an immovable rotation axis can be formed, and the target portion of the sample 10 can be moved by the fine movement actuator 5 on this axis, so that it is possible to suppress a visual field shift and a focus shift during sample rotation. However, since the rotation axis direction is determined by the positional relationship between the rotation cylinder 4 and the electron microscope body 8, it does not always pass through the center of the electron microscope (that is, the center of the visual field). Therefore, a new mechanism that adjusts the direction of the eucentrically adjusted stage system as a whole and passes the rotation axis through the center of the field of view (center of the objective lens) of the electron microscope was newly devised and manufactured. That is, the rotary cylinder guide 12 holding the rotary cylinder 4 and including the spherical seat 3 is moved to the second spherical seat 13.
And a rotary cylinder guide position fine adjustment mechanism 14 for adjusting the relative positional relationship between the electron microscope mirror 8 and the rotary cylinder guide 12 is provided.
Thereby, the entire stage is rotated by the second spherical seat 13 without breaking the eucentric conditions of the rotary cylinder 4 and the sample holder 1 and irrespective of the shape of the sample, the mounting position of the sample in the sample holder in the z direction, and the observation magnification. It is now possible to set so that the direction of the cylinder rotation axis passes through the center of the field of view of the electron microscope.

(Embodiment 2) In Embodiment 1, since the x fine movement is an x fine movement mechanism for pushing the holder toward the atmosphere at the tip of the sample holder, it is not a cantilever structure of the holder, but a rotation of the sample holder. Since the frame crosses over the electron beam, it becomes impossible to perform, for example, omnidirectional observation of a cylindrical sample suitable for three-dimensional observation. Therefore, a combination of the dual eucentric adjustment function shown in the first embodiment and the shape of the cantilever sample holder was devised, and shown in FIG. That is, the fine movement of the sample in the x direction is realized by the fine movement lever 9 fixed to the sample holder sheath 2. The sample can be finely moved by pushing up the sample holder handle 15 to the right side of the paper by an actuator with a lever. The restoring force in the opposite direction utilizes the force of the sample holder being sucked toward the mirror body by the pressure difference between the atmosphere and vacuum. In this method, since the operation of the x-fine movement is performed in the atmosphere, some O-rings serving both as a vacuum seal and forming a slip surface can be eliminated, and there is an advantage of improving the degree of vacuum. Further, in the method of FIG. 1, since the pushing direction of the x fine movement and the moving direction of the sample holder are not arranged in a straight line, there is a possibility that meandering may occur when the x fine movement is changed between the + direction and the − direction. It is thought that this can be solved.

[0008] Consideration is given to rigidly joining the fine movement actuator and the lever and the sample holder by adopting a structure in which the gap is reduced as much as possible and the rotation shaft is suppressed. For example, a sapphire pivot is used at the joint side between the x fine movement lever 9 and the sample holder handle 15 and a carbide tip is embedded in the sample holder side to suppress the elastic deformation of both. Apply a thin layer of vacuum grease (Homblin) to the slip surface of the O-ring between sample holder 1 and sample holder sheath 2.
The lost motion in the x direction due to sliding friction is suppressed as much as possible. For example, if the force required for loading and unloading the sample holder 1 is 300 g or less in the atmosphere, the x-direction driving force is 1 kg of atmospheric pressure (when the sample holder O-link is 12 mm in center diameter, the atmospheric pressure is 1 kg / cm ^{2 or} less. Therefore, the differential pressure can be set to a value sufficiently smaller than 1130 g), and it is considered that a smooth x fine movement can be obtained.

(Embodiment 3) In this embodiment, the x fine movement lever shown in Embodiment 2 will be examined in detail. A rotary motor 20 was used for the drive system at the lever in FIG. This rotation is transmitted to the gear B22 via the gear A21. The contact surfaces of the gear B22 and the holder pressing jig 23 are also engaged with each other by gears. As a result, the rotation of the rotary motor 20 causes the holder pressing jig 23 to move back and forth in the z direction, and the holder handle 24
For example, the holder can be moved in the x direction because the contact is made through the x fine movement pivot 25 made of sapphire. This method has the feature of being compact because it does not use a lever that requires a large space. On the other hand, although the fine movement is transmitted by two gear contacts, there is a disadvantage that the gears generate a backlash (immobile area) when the operation is reversed. In the system shown in FIG. 4B, the same linear motion actuator 26 as the y and z fine movement is used for the drive system. The linear movement of the actuator 26 is transmitted to the holder pushing jig 23 via the x fine movement lever 27 that rotates around the lever fulcrum 28. The restoring force of the x fine movement lever 27 is the pushback spring 2
9 is generated. Note that the x fine movement lever 27 and the holder pressing jig 23 are in two-point contact with each other at the arm portion of the holder pressing jig 23. Since no gear is used in this method, backlash is greatly reduced. However, on the other hand, since there is a slight gap between the holder pressing jig 23 and the sample holder 1, when receiving a force from a lever, the holder pressing jig 23 does not move in the x-axis direction, and the direction slightly tilts. It is expected that there is a problem and the precision of the fine movement is insufficient. Then, the structure of FIG. 4C was devised. In the method shown in FIG. 4B, since the lever fulcrum 28 is located below the sample holder 1, when the tip of the actuator 26 comes out, the sample holder 1 is pulled out from the vacuum toward the atmosphere. In the c) method, the lever fulcrum 28 is present on the sample holder 1, and therefore, when the tip of the actuator 26 is protruded, the sample holder 1 is pulled by the vacuum force and moves from the atmosphere to the vacuum side. An x-fine movement pivot 27 made of sapphire is installed at the tip of the x-fine movement lever 27, and the tip of the x-fine movement lever 27 is inserted into the notched sample holder handle 24, and is a cemented carbide part attached to the inner wall of the handle. Press to make the structure. Further, the pivot shaft of the lever fulcrum 28 has a pivot structure without play. Therefore, the rigid connection is entirely performed from the distal end of the actuator 26 to the sample holder 1 to prevent the rattle from occurring. Therefore, the movement of the actuator 26 can be immediately transmitted as the fine movement of the sample holder 1. The restoring force of the x fine movement lever 27 is the same as the method shown in FIG.
Generated by

(Embodiment 4) In the case of Embodiments 2 and 3, since the x fine movement mechanism is provided on the rotating body, the weight burden on the fine movement actuator 5 for controlling the sample holder sheath 2 and the push-back spring 6 increases, and the stage Depending on the angle of inclination, malfunction of the stage is expected. The solution to this problem will be described with reference to FIG. FIG. 5 is a diagram showing the positional relationship between the tilt angle, the actuator in each direction, and the return spring as viewed from the x-axis direction for this sample stage. The problem of this stage is that when the inclination is increased in the minus direction, the operation in the minus direction of the actuator, that is, the pushing direction by the y-return spring may stop at a certain angle or more. this is,
This is because if the weight of the stage increases, the stage cannot be pushed back by the spring having the specified strength. On the other hand, the z pushback spring is constantly above the sample stage and its force is working well. Fig. 6 (a) shows the relationship between the y-return spring force and the preload applied to the actuator by the stage weight when the stage weight is 4kg, the return spring force is 3kg, and the tilt angle is changed from -90 ° to + 90 °. Indicated. Here, the direction of the force applied to the actuator is defined as plus. Stage weight exerts maximum force on actuator at + 90 °
4 kg, which is in a sine function relationship according to the angle. On the other hand, since the push-back spring rotates together with the actuator, the applied force does not change. (Spring force + stage weight) is the pressure applied to the actuator. When the spring force is 3 kg, the preload is negative when the inclination is less than 40 °. This indicates that the pushback spring force is weak, a gap is generated between the actuator and the sample stage, and fine movement control becomes impossible. On the other hand, in the positive tilt, the spring force and weight are all on the spring, and the force is up to 7 kg. In order to increase the spring force at the negative inclination, a method of using a strong spring, for example, a 7.5 kg spring shown in the drawing can be considered. However, in this case, although about 1 kg of pressurization can be obtained at −90, the pressurization reaches 11.5 kg at + 90 °. To achieve the fine movement accuracy of the actuator, it is necessary to apply a pressure of at least about 1 kg.
When the above preload is applied, the life is shortened, and the precision of the fine movement is not guaranteed. Therefore, a strong spring cannot be simply employed, and a structure in which the spring force is strengthened when the inclination is negative and reduced when the inclination is positive must be considered. To cope with this problem, a y-return spring mechanism with variable spring force shown in FIG. 7 has been devised. In this mechanism, a fixed force is applied from the fixed spring 40 (adjustable to 1 to 3 kg) to the spring tip 41 irrespective of the inclination angle, and the force by which the weight 43 is reduced by gravity via the lever 42 is applied to the fixed spring 40. The force can be exerted on the spring tip 41 by being superimposed on the force. Therefore, at θ = 0 °, the mechanism is in the horizontal plane with respect to gravity, and is at position A, and its spring force is only the force of the fixed spring 40. At the time of minus inclination, the weight 43 of this mechanism is at the position B, and the weight 4
A gravity of 3 is added. At the time of plus inclination, the weight 43 is at the position C, and at this time, the lever 42 is structured so as not to push the spring tip 41, so that only the force of the fixed spring 40 is applied to the spring tip 41 regardless of the angle. it can. This time, the force of the fixed spring 40 was 1 kg, the weight was 780 g, and the lever ratio was 1: 6, so the added force was (1 + 0.78 ×
6) kg, that is, 5.68kg. In this way, as shown in FIG. 6B, the y-return spring force changes by a sine function according to the angle at a fixed inclination of 1 kg at a plus inclination and at a maximum inclination of 5.67 kg at a minus inclination. Eventually, from the relation with the stage weight, the pressurization of the actuator became 1 kg at the minimum and 5 kg at the maximum, and the operation conditions of the actuator could be satisfied, and the sample could be finely moved in all directions.

[0011]

The rotation axis can always be set at the center of the electron microscope body regardless of the sample shape, observation magnification, and tilt angle. Three-dimensional observation becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration and an operation principle of a sample stage of the present application.

FIG. 2 is a diagram showing a schematic configuration and operation principle of a conventional sample stage.

FIG. 3 is a diagram showing a configuration in which x fine movement is placed on a sample holder sheath on the sample stage of the present application.

FIG. 4 is a diagram illustrating this configuration by x fine movement.

FIG. 5 is a diagram showing a positional relationship between a y, z actuator and a return spring when the sample is tilted at a large angle.

FIG. 6 is a diagram showing a force relationship between a y, z actuator and a return spring when the sample is tilted at a large angle.

FIG. 7 is a diagram showing a configuration of a y-return spring.

[Explanation of symbols]

1: sample holder, 2: sample holder sheath, 3: spherical seat,
4: rotating cylinder, 5: fine actuator, 6: pushback spring, 7: θ motor, 8: electron microscope body, 9: x
Fine movement lever, 10: sample, 11: adjustment mechanism for fine adjustment of rotary cylinder position, 12: rotary cylinder guide, 13: second spherical seat, 14: adjustment mechanism for fine adjustment of rotary cylinder guide position, 1
5: sample holder handle, 20: rotary motor, 21: gear A, 22: gear B, 23: holder pressing jig, 24: holder handle, 25: x fine movement pivot, 26: actuator, 27: x fine movement lever, 28: Lever fulcrum, 29: Push-back spring, 40: Fixed spring, 41: Spring tip, 42: Lever, 43: Weight

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masanari Takaguchi 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. Hitachi, Ltd. Central Research Laboratory (72) Inventor Ruriko Tsuneda 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5C001 AA03 AA05 CC03

Claims (3)

[Claims] 1. A sample stage for inserting a sample into an electron microscope and controlling a position and an angle of the sample with respect to an electron beam, and transmitting a force of a sample holder for holding the sample and a rotation mechanism to the sample holder. A rotating member, a first spherical seat for guiding the operation of rotating the sample holder, a fine movement function fixed on the rotating member and adjusting a relative position between the rotating member and the sample holder, and rotation of the rotating member A first adjusting function of moving the position of the rotating member in a plane perpendicular to the rotation axis in order to adjust a relative position between the shaft and the center of the spherical seat of the first spherical seat; A sample stage for an electron microscope, comprising: a second spherical seat for changing an angle of attachment to a microscope body and a position of the rotation axis; and a second adjustment function for adjusting an angle. 2. The sample stage for an electron microscope according to claim 1, wherein the sample holder is finely moved in the direction of the rotation axis, and is fixed on the rotating member while being in direct contact with the sample holder via an intermediate member. A sample stage for an electron microscope, comprising a fine movement mechanism capable of adjusting a relative position between the rotating member and the sample holder. 3. The fine movement mechanism according to claim 1, wherein the sample holder is fixed by a spring mechanism and a device for generating an electric translational movement on the rotating member, and the spring mechanism has a weight. A sample stage for an electron microscope, characterized in that a gravity caused by the weight is added to the spring via an intermediate member, so that a spring force is variable depending on a direction of a spring mechanism with respect to a direction of gravity.