JPH0518840Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an objective lens for a scanning electron microscope.
More specifically, the present invention relates to an objective lens for a scanning electron microscope that enables observation of high-resolution scanning electron microscope images, observation of large samples, large-angle oblique observation, etc. with a single lens.

[Prior art] Recently, objective lenses for scanning electron microscopes have been developed to enable observation of high-resolution scanning electron microscope images and observation of large samples and large tilted angles using a single lens (1986). −155162).

In such a device, an upper magnetic pole piece and a lower magnetic pole piece that form a magnetic pole piece gap are arranged at the lower end of the lens yoke, and the central part of the lower magnetic pole piece is divided from the other parts to form a movable magnetic pole piece. An electron beam passing hole is formed in the movable magnetic pole piece, and the movable magnetic pole piece is movably arranged between the upper and lower magnetic pole pieces. I try to bring it into contact with. In such conventional devices, by magnetically bringing the movable magnetic pole piece into contact with the lower magnetic pole piece, the lens magnetic field constituting the lens is prevented from leaking from the electron beam passage hole, and the working distance is lengthened. This allows us to observe large samples and to observe scanning electron microscope images by tilting the sample greatly. In addition, by magnetically bringing the movable magnetic pole piece into contact with the upper magnetic pole piece, the lens magnetic field constituting the lens can be greatly extended below the lower magnetic pole piece, and the working distance can be shortened to enable scanning electrons with high resolution. We are also observing microscopic images.

[Problems to be solved by the invention] By the way, in the conventional device configured as described above, the drive mechanism (screw body, bevel gear, etc.) for moving the movable magnetic pole piece up and down is evacuated to a high vacuum. Since the drive mechanism is placed near the sample, the gas emitted from the drive mechanism may contaminate the vicinity of the sample, and the emitted gas may adhere to the sample surface, causing contamination of the sample and impeding high resolution. There was a problem in which scanning electron microscope images could not be obtained.

The present invention was developed in view of the above points, and is an apparatus that prevents contamination of the sample by keeping the vicinity of the sample clean by providing a drive mechanism for moving the movable magnetic pole piece up and down outside the vacuum. is intended to provide.

[Means for Solving the Problems] The present invention for achieving the above objects includes a lens yoke, an excitation coil, upper and lower magnetic pole pieces connected to the yoke, and electronics provided on the upper and lower magnetic pole pieces. An objective lens for a scanning electron microscope comprising a beam passage hole and a cylindrical member inserted into the electron beam passage hole of the upper magnetic pole piece, the inside of the cylindrical member communicating with the vicinity of an evacuated sample. , a central part of the lower magnetic pole piece is divided from other parts to form a movable magnetic pole piece, the movable magnetic pole piece is attached to the lower end of the cylindrical member, and the cylindrical member faces toward the atmosphere. The cylindrical member is movable along the electron beam optical axis while being kept airtight, and a drive mechanism for the cylindrical member is disposed on the atmosphere side, and the cylindrical member is moved up and down by the drive mechanism. The movable magnetic pole piece is characterized in that the movable magnetic pole piece selectively comes into magnetic contact with other parts of the upper magnetic pole piece or the lower magnetic pole piece.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view of the structure of an embodiment of the present invention, and FIGS. 2 and 3 are diagrams for explaining the operating state of the present invention. In FIG. 1, reference numeral 1 denotes a lens yoke within which an excitation coil 2 is wound. 3 is an upper magnetic pole piece, 4 is a lower magnetic pole piece, and 5 is a movable magnetic pole piece formed by dividing the center part of the lower magnetic pole piece 4 from other parts, and the movable magnetic pole piece 5 is attached to the lower magnetic pole piece 4. It is formed to fit into the formed hole 4a. 6
is a fixing fitting for the excitation coil 2 made of a non-magnetic material, and this fixing fitting 6 is attached to the upper magnetic pole piece 3 and the lower magnetic pole piece 4 by soldering etc. It works to contain it. 7 is a pipe inserted into the hole 3a of the upper magnetic pole piece 3, through which the electron beam EB passes and which is evacuated to a high vacuum. The pipe 7 is made of a non-magnetic material, and the lower end is thinner than the other parts.
The movable magnetic pole piece 5 is attached to the lower end. 8 is a lens barrel, and the pipe 7 is connected to the lens barrel 8.
O-rings 9 and 10 disposed at the upper magnetic pole piece 3 and an O-ring 11 disposed at one end of the upper magnetic pole piece 3 allow the upper magnetic pole piece 3 to be movably arranged in an airtight state. Reference numeral 12 denotes a rack attached to the upper end of the pipe 7 outside the vacuum, and the rack 12 includes:
A pinion 13 for moving the pipe 7 along the electron beam optical axis Z is engaged with the pinion 1.
3 is arranged so that it can rotate from the atmospheric side. 14 and 15 are limit switches for detecting the upper and lower positions of the pipe 7. 16,1
6' is a sample irradiated with electron beam EB. 17,
18 is 2 attached to the lens barrel 8 while maintaining a vacuum.
It is a secondary electron detector. In FIG. 1, the left side of the page shows the case where the pipe 7 has moved to the specified position below, and the right side of the page shows the case where the pipe 7 has moved to the specified position above. This shows the case where the camera moves to the desired position.

In the device configured in this way, the pipe 7
The operation when the is moved upward or downward by a drive mechanism such as a motor will be described below.

First, when the pinion 13 is rotated by a drive mechanism not shown, the pipe 7 starts to move downward along the optical axis Z while maintaining a vacuum. This pipe 7
As a result of the movement of the lower magnetic pole piece 5 attached to the tip of the pipe 7, the hole 4 formed in the lower magnetic pole piece
It will be in a state where it is stuck in a. Eventually, the movable magnetic pole piece 5
When the rack 12 moves to a specified position, the lower end of the rack 12 hits the limit switch 14 and the limit switch 14 is opened, so that the rotation of the pinion 13 is stopped and the movement of the pipe 7 is stopped. In this state, the fitting between the hole 4a and the movable magnetic pole piece 5 is completed, and the movable magnetic pole piece 5 and the lower magnetic pole piece 4 are integrated. A relatively small excitation current is supplied to the excitation coil 2 from an excitation power source (not shown) which is driven in conjunction with the positional movement of the pipe 7, and the excitation coil 2 is weakly excited. FIG. 2 shows such a situation. In this state, since the tip of the movable magnetic pole piece 5 is formed into a conical shape, leakage magnetic flux from the lens is minimized. Therefore, the lens magnetic field φ does not leak from the electron beam passage hole a and project toward the sample 16, and the working distance can be increased. Furthermore, as is clear from the figure, the shape of the lower magnetic pole piece 4 is formed into a mortar shape so that even when the large sample 16 is tilted greatly, the tilt is not restricted. Therefore, even if the large sample 16 is tilted greatly, the 2
The secondary electrons e can be captured and detected by the focused electric field E of the secondary electron detector 18 disposed along the lower pole piece 4. Furthermore, in this state, since the lens magnetic field φ does not leak from the electron beam passage hole a and project toward the sample 16, it is possible to observe a magnetic sample and the like.

Next, the pinion 13 is rotated in the opposite direction to that described above,
The pipe 7 is moved upward along the electron beam optical axis Z. By this movement of the pipe 7, the lower magnetic pole piece 5
The movable magnetic pole piece 5 passes through the hole 4a and moves toward the hole 3a of the upper magnetic pole piece 3, and eventually the movable magnetic pole piece 5 comes into close contact with the tip portion 3b, and the upper magnetic pole piece 3 and the movable magnetic pole piece 5 are magnetically joined. In this position, the limit switch 15 is easily set.
2, the pinion 13 stops rotating and the pipe 7 stops moving. In conjunction with the movement of the pipe 7, a relatively large excitation current is supplied to the excitation coil 2 from an excitation power source (not shown), and the excitation coil 2 is strongly excited. FIG. 3 shows such a situation. In this state, the movable magnetic pole piece 5 acts as an upper magnetic pole piece, but since the tip of the movable magnetic pole piece 5 is formed into a conical shape,
A strong magnetic field is generated between the movable magnetic pole piece 5 and the tip 4b of the lower magnetic pole piece 4, and the magnetic field is concentrated to form a short focus lens. Further, the lens magnetic field φ constituting the lens extends largely below the lower magnetic pole end portion 4b, and the sample 16' is placed within the lens magnetic field φ. Of course, the sample 16' can also be placed between the movable magnetic pole piece 5 and the lower magnetic pole piece tip 4b if necessary. Therefore, the working distance becomes extremely short. In this state, when the sample 16' is scanned by the electron beam EB (the two-stage scanning coil of the electron beam EB is omitted), the secondary electrons e from the sample 16' are absorbed by the strong leakage of the lens. The electron beam moves upward while rotating spirally around the optical axis Z due to the magnetic field. Since the electrons pass through the opening 7a formed in the pipe 7 and are detected by the secondary electron detector 17, it becomes possible to observe a high-resolution scanning electron microscope image.

By the way, in the device configured as described above, the inside of the pipe 7 is evacuated to a high vacuum by an exhaust mechanism (not shown), but the drive mechanism for moving the movable magnetic pole piece 5 up and down is not on the vacuum side but on the atmosphere side. This eliminates the possibility of gas released from the drive mechanism adhering to the sample, unlike in conventional devices.
Furthermore, since the vicinity of the sample is evacuated to a clean atmosphere, contamination of the sample can be prevented.

Note that the above embodiments are merely illustrative. In the above embodiment, the excitation current of the excitation coil is changed according to the position of the movable magnetic pole piece, but the working distance may be changed according to the position of the movable magnetic pole piece.

[Effects of the invention] As detailed above, according to the invention, since the drive mechanism for moving the movable magnetic pole piece up and down is provided outside the vacuum, the vicinity of the sample can be kept clean, thereby reducing contamination of the sample. An objective lens for a scanning electron microscope or the like is provided which is designed to prevent the occurrence of irradiation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2 and 3 are diagrams for explaining the present invention. 1... Lens yoke, 2... Excitation coil, 3...
...Upper magnetic pole piece, 3a...hole, 3b...upper magnetic pole piece tip, 4...lower magnetic pole piece, 4a...hole, 4b...lower magnetic pole piece tip, 5...movable magnetic pole piece, 6... Fixing bracket, 7... Pipe, 7a... Opening, 8... Lens barrel, 9, 10, 11... O ring, 12... Rack, 13... Pinion, 14, 15... Limit switch, 16, 16 '... Sample, 17, 18...
...Secondary electron detector, a...Electron beam passage hole.

Claims (1)

[Scope of utility model registration request] A lens yoke, an excitation coil, upper and lower magnetic pole pieces connected to the yoke, an electron beam passage hole provided in the upper and lower magnetic pole pieces, and a cylindrical member inserted into the electron beam passage hole of the upper magnetic pole piece. In an objective lens for a scanning electron microscope, the interior of the cylindrical member being communicated with the vicinity of the evacuated sample, the central portion of the lower magnetic pole piece is separated from the other portion to form a movable magnetic pole piece. the movable magnetic pole piece is attached to the lower end of the cylindrical member, and the cylindrical member is movable along the electron beam optical axis while maintaining airtightness with respect to the atmosphere; A driving mechanism for the cylindrical member is disposed on the atmosphere side, and as the cylindrical member is moved up and down by the driving mechanism, the movable magnetic pole piece is selectively magnetically moved to the other part of the upper magnetic pole piece or the lower magnetic pole piece. An objective lens for a scanning electron microscope characterized by a contact lens.