JPH0236209Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of an electron beam device for obtaining scanning electron microscope images using secondary electrons.

[Prior art]

BACKGROUND ART Recently, in order to observe large samples such as semiconductor wafers, scanning electron microscopes equipped with large sample chambers in which these large samples can be mounted and moved have been used. An example of such a device is shown in FIG. In FIG. 5, 1 is an electron beam emitted along the optical axis C from an electron gun (not shown), and the electron beam 1 is directed to a sample 3 (not shown) placed under a magnetic pole piece 2 forming an objective lens. The beam is two-dimensionally scanned and irradiated by a deflection coil. The sample 3 is placed on the sample stage 11 via the sample holder 10,
It is movable in the X, Y and Z axis directions. When the sample 3 is irradiated with the electron beam 1, secondary electrons e are generated from the sample surface. The secondary electron detector D for detecting the secondary electrons e from the sample 3 includes a light guide 5 having a scintillator 4 attached to its tip, and a photomultiplier tube 6 disposed at its rear end.
Consists of etc. A conductive thin film is deposited on the front surface of the scintillator 4 at the tip of the light guide. A high positive voltage (for example, 10 KV) is applied to this conductive thin film and a ring-shaped electrode 8 for capturing secondary electrons e by a DC power supply (not shown). Further, a collector electrode 7 to which a variable potential of, for example, about +100V is applied is provided around the light guide 5, and the secondary electron detector D configured in this way is aligned with respect to the optical axis of the objective lens. It is attached to the lens barrel 9 along the inclined side surface. Therefore, unlike the case where the detector is inserted and placed perpendicular to the optical axis, the detector can be placed very close to the sample without impairing the movement of the sample 3, and the secondary electron It is possible to improve the detection efficiency and increase the image resolution.

[Problem that the invention attempts to solve]

However, in the apparatus configured in this way, when the working distance W is large as shown in FIG. 6, that is, when the distance between the secondary electron detector D and the sample becomes long, the A relatively large electric field formed by the electrode 8 enters the space between the sample 3 and the magnetic pole piece 2, deflecting the electron beam 1 and causing distortion in the image. The present invention solves the above problems by deflecting the electron beam by the electric field of the extraction electrode when the working distance W is increased, without impairing the detection efficiency when the working distance W is decreased. The purpose is to prevent the resulting image distortion.

[Means for solving problems]

In order to solve such problems, the present invention irradiates an electron beam onto a sample movably placed under an objective lens, and directs secondary electrons from the sample at an angle tilted with respect to the optical axis of the objective lens. A secondary electron detector is provided along the side, and the secondary electron detector includes a scintillator and at least several kilovolts or more arranged in the vicinity of the scintillator for capturing secondary electrons and accelerating them toward the scintillator. A device having an electrode to which a high voltage of The present invention is characterized in that it is provided with means for selectively arranging the mesh-like electrode between the high-voltage electrode and the sample depending on the setting of the working distance.

〔Example〕

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

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and the same components as in FIG. 5 are given the same numbers and their explanations are omitted. In FIG. 1, 12 is a mesh-shaped electrode to which a variable positive voltage is applied from a power source (not shown), and 13 is a metal rotating rod that holds the mesh-shaped electrode 12. The rotating rod 13 is supported by a metal fitting 14 on the collector electrode 7, and therefore the mesh electrode 12 is also maintained at about +100V like the collector electrode. The rotating rod 13
passes through the lens barrel 9 through an insulating member 15 while maintaining a vacuum, and by operating the handle 16, the mesh-shaped electrode 1 held on the rotary rod 13 is released.
2 can be placed between the secondary electron detector and the sample 3 or removed.

In the apparatus configured as described above, when observing with a small working distance W as shown in FIG. 1, that is, with a relatively short distance between the secondary electron detector D and the sample, use the handle 1
Rotate 6 in the direction of arrow A. By this operation, the mesh-shaped electrode 12 held on the rotating rod 13
are removed from the front of the secondary electron detector D as shown in FIG. In this state, the secondary electrons e generated from the sample 3 enter the scintillator 4 with a trajectory as shown in FIG. 1 and are detected. Further, as shown in FIG. 3, when the working distance W is large, that is, when the sample 3 and the secondary electron detector are far apart, the handle 16 is rotated in the direction of arrow B. By this operation, the mesh electrode 12 held by the rotary rod 13 is rotated and placed in front of the secondary electron detector, as shown in FIG.
By placing the mesh-shaped electrode 12 to which this positive voltage is applied in front of the detector, the relatively large electric field of the electrode 8 that enters the space between the sample 3 and the magnetic pole piece 2 is shielded by the mesh-shaped electrode 12. be done.
Therefore, since the electron beam 1 is not deflected by the electric field of the electrode 8, image distortion can be prevented. On the other hand, +100V is applied to the mesh electrode 12.
Since a certain potential is applied, an electric field corresponding to an equipotential surface as shown in FIG. 3 is formed in the space between the mesh electrode 12 and the sample 3. Due to this electric field, the secondary electrons enter the scintillator 4 with a trajectory as shown in FIG. 3(b) and are detected. Incidentally, although the electric field is weakened by arranging the mesh-shaped electrode 12, the electric field, which was conventionally unnecessarily large, is only weakened, so that the detection efficiency is hardly reduced compared to the conventional technique.

Note that the mesh electrode 12 is used as a secondary electron detector D.
For example, if the distortion of the image is measured in advance and a tolerance value is determined, then if the working distance W is changed and the tolerance value is exceeded, the distortion can be determined manually or automatically. Further, the working distance W
It is also possible to improve the detection efficiency by varying the voltage applied to the mesh electrode according to the value of .

[Effects of the invention] As described above, according to the invention, in an electron beam apparatus in which the secondary electron detector is arranged close to the sample along the objective lens magnetic pole piece, when the working distance is large, the secondary electron detector Image distortion can be prevented by reducing the influence of the electric field of the electrodes on the entire surface of the detector without impairing electron detection efficiency.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the device of the present invention;
3, and 4 are diagrams for explaining the operating state of the invented device, and FIG. 5 is a configuration diagram of the conventional device,
FIG. 6 is a diagram for explaining the operating state of the conventional device. 1... Electron beam, 2... Magnetic pole piece, 3... Sample, 4
...Scintillator, 5...Light guide, 6...
... Photomultiplier tube, 7 ... Collector electrode, 8 ... Extraction electrode, 9 ... Lens barrel, 10 ... Sample holder,
DESCRIPTION OF SYMBOLS 11...Sample stage, 12...Mesh-shaped electrode, 13...Metal rotating rod, 14...Support fitting, 1
5...Insulating member, 16...Handle, D...Secondary electron detector.

Claims (1)

[Claims for Utility Model Registration] (1) A specimen movably placed under an objective lens is irradiated with an electron beam, and secondary electrons from the specimen are emitted from a side surface inclined with respect to the optical axis of the objective lens. a secondary electron detector arranged along the
The secondary electron detector includes a scintillator and at least several kilovolts disposed in the vicinity of the scintillator to capture secondary electrons and accelerate them toward the scintillator.
In an apparatus having an electrode to which a high voltage is applied, a mesh-shaped electrode is provided for shielding the electric field from the high-voltage electrode from the electron beam, and a positive voltage that is extremely smaller than the high voltage is applied to the mesh-shaped electrode. and an operating means for selectively arranging the mesh-like electrode between the high-voltage electrode and the sample depending on the setting of the working distance. (2) The electron beam device according to claim 1, wherein the potential of the mesh electrode is variable.