JPS628438A - Scanning type electron microscope - Google Patents

Abstract

PURPOSE:To eliminate distortion of the scanning face thus to improve the detection efficiency of secondary electron by arranging a meshed electrode while surrounding a detector then making the underface of electrode flush with the underface of objective lens and varying the potential of electrode with correspondence to the working distance. CONSTITUTION:The light pipe 5 or the corona ring 7 constituting a detector is surrounded by a meshed electrode 9 and the electrons will advance from the underface of the meshed electrode toward a scintillator 6. The detector is arranged along the sideface of an objective lens pointed toward a sample 1. The underface of meshed electrode is arranged approximately in flush with the underface of the objective lens and positive D.C. voltage for accelerating secondary electrons is applied from D.C. power source 10 onto the electrode, Position detector 14 will detect the working distance and feed to control means 15 which will control D.C. power source on the basis of the working distance informations. Consequently, secondary electrons can be detected with quite high efficiency while distorsion on the scanning face can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a scanning electron microscope equipped with a detector that has high secondary electron detection efficiency and less distortion of the electron beam scanning plane.

[Prior Art] In a scanning electron microscope, observation of secondary electron images is the most important function, and for this purpose, various studies have been made regarding the structure and arrangement of the secondary electron detector. FIGS. 5 and 6 do not show the configuration of conventional secondary electron detection, but are illustrative;
In the example shown in FIG. 5, 1 indicates a sample and 2 indicates an objective lens. Sample 1
is placed on the sample moving mechanism 3, and X is moved by a drive mechanism (not shown).

It can be moved arbitrarily in the Y and Z directions. A focusing lens and further an electron gun are arranged above the objective lens 2, and the electron beam from this electron gun is narrowly focused by the focusing lens and the objective lens 2, and is irradiated onto the sample 1. An electron beam deflector is installed in or near the objective lens, and the focused electron beam EB scans a certain area on the sample 1 two-dimensionally. 4
is a secondary electron detector, which is arranged perpendicular to the optical axis of the electron beam and consists of a light vibrator 5, a scintillator 6, a corona ring 7, a collector 8, and a photomultiplier tube connected to a light pipe. ing. The secondary electrons generated from the sample 1 by the irradiation with the electron beam EB are accelerated by the potential gradient caused by the high voltage applied to the corona ring 7, and collide with the surface of the scintillator 6. Also, in Fig. 6, the detector 4 is placed along the side of the objective lens that is pointed toward the sample surface, and in order to prevent the detector 4 from interfering with the sample, it is placed away from the sample surface as in Fig. 5. It is arranged as follows.

[Problems to be Solved by the Invention] In the above-exemplified apparatus, in order to prevent the detector 4 from interfering with the sample, it is necessary to place the detector 4 at a large distance from the sample. When the detector is moved away from the sample, the accelerating electric field distributed near the sample becomes significantly weaker2.
The detection efficiency of secondary electrons is greatly deteriorated. Therefore, a configuration in which an auxiliary accelerating electrode is placed in front of the detector as shown in the example in Figure 6 has been proposed, but although the electric field at the sample surface can be made stronger and the detection efficiency can be improved, the working distance When the distance becomes long, the electric field on the electron beam path becomes extremely strong, causing distortion in the scanning plane of the electron beam, resulting in the observation of a distorted scanning electron microscope image.

Therefore, in view of the above-mentioned drawbacks of the conventional apparatus, the present invention aims to improve the detection efficiency of secondary electrons without distorting the scanning plane of the electron beam.

[Means for Solving the Problems] The configuration of the present invention has an objective lens that is pointed toward the sample surface, and an electron beam detector for capturing electron beams emitted from the sample is connected to the objective lens. A mesh-like electrode is arranged to surround the detector, and the lower surface of the mesh-like electrode is made substantially flush with the lower surface of the objective lens, and the potential of the electrode is A scanning electron microscope is characterized by a means for changing the working distance according to the working distance.

[Operation] In the present invention, the detector is arranged along the side surface of the inclined objective lens, and the detector is surrounded by a mesh-shaped electrode whose lower surface is substantially flush with the lower surface of the objective lens.
The electric potential of this mesh-shaped electrode is linked to the working distance so that it is low when the working distance is large and high when the working distance is small, so that the electric field extending over the sample surface is independent of the working distance. None so as to be kept properly.

[Example] FIG. 1 is a schematic diagram of main parts showing an example of the present invention,
The same reference numerals as in FIG. 5 indicate similar members. In FIG. 1, a light vibrator 5 and a corona ring 7 constituting a detector are surrounded by a mesh-like electrode 9, and electrons enter the scintillator 6 from the lower surface of the mesh-like electrode. Further, as in the case of FIG. 6, the detector is arranged along the side of the objective lens which is pointed toward the sample 1. The lower surface of the mesh-like electrode is disposed approximately on the same plane as the lower surface of the objective lens, and a DC voltage for positive secondary electron acceleration is applied to the sample from a DC power supply 10 to the electrode. The applied voltage varies depending on the actual device, but is on the order of several tens of volts to one thousand volts. The moving mechanism 3 is moved in the X and Y directions by a driving device 11, and the moving mechanism is placed on a vertical moving device 12, and the position in the optical axis direction, that is, the working distance, is changed by a driving device 13. .

A position detector 14 detects the working distance and supplies it to the control means 15. This control means controls the DC power supply 10 based on information regarding the working distance from the position detector. That is, when the working distance is small, a relatively high voltage is applied to the mesh-like electrode, and an electric field is extended to the sample surface.
Further, in the case of a knife having a large working distance, the voltage of the mesh electrode is controlled to be low so that the electric field on the electron beam path does not become too strong. Figure 2 shows the relationship between the working distance WD and the voltage applied to the electrodes. When WD is 81III, a voltage of 500V is applied, and the voltage decreases relatively steeply until approximately WD reaches 20nua, and then WD increases. If the voltage increases, the voltage is controlled according to the curve that gradually decreases.Of course, Fig. 2 is just an example, and this characteristic differs depending on the device, and the working distance may be changed in several stages, for example. When changing the voltage, the applied voltage may be changed in steps according to the stage.

Figures 3 and 4 depict the outline of the electric field distribution near the sample and how secondary electrons are detected when the working distance is changed. is when the working distance is large. As is clear from the figure, when the working distance is small, a relatively high voltage is applied to the mesh-like electrode 9, but the mesh-like electrode
Since the working distance is large, the attenuation of the electric field is relatively small (the electric field can be sufficiently extended even in the narrow space between the sample 1 and the objective lens. easily extends over the path of the electron beam, so even if the voltage applied to the electrode 9 is suppressed, the
The secondary electrons are accelerated and focused and captured by a detector. The reason why the lower surface of the mesh electrode is placed on a horizontal plane that is approximately the same as the lower surface of the objective lens is to strongly bend the secondary electrons toward the detector.
This is to gain efficiency.

[Effect] As explained above, in the present invention, the secondary electron detector arranged along the inclined side surface of the objective lens is surrounded by a mesh-like electrode, and at the same time, the voltage applied to the electrode is changed when the working distance is small. Since the working distance is controlled to be high and low when the working distance is large, a sufficient electric field can be extended over the sample surface even when the working distance is small and secondary electrons cannot be extracted. If the distance is large and the electric field easily overhangs the electron beam path and affects the trajectory of the electron beam, the electric field can be weakened. Therefore, secondary electrons can be detected with high efficiency at all times, and at the same time, there is no problem such as the electric field extending too strongly over the electron beam path and distorting the scanning plane.

[Brief explanation of drawings]

FIG. 1 is a schematic view of the main parts showing an embodiment of the present invention, FIGS. 2 to 4 are explanatory diagrams of the operation of the device shown in FIG. 1, and FIGS. 5 and 6 are illustrations of a conventional device. . 1: Sample 2: Objective lens 3: Movement mechanism
5 Nilight pipe 6: Scintillator 7:
Corona ring 9: mesh electrode 10: DC power supply 11: drive device 12: sample up/down device 13: drive device 14: position detector 15: control means

Claims (1)

[Claims] 1) It has an objective lens that is pointed toward the sample surface, and an electron beam detector for capturing electron beams emitted from the sample is placed along the inclined side surface of the objective lens. A mesh-like electrode is arranged surrounding this detector, and the lower surface of the mesh-like electrode is made approximately flush with the lower surface of the objective lens, and the potential of the electrode is changed according to the working distance. 1. A scanning electron microscope characterized by comprising means for causing 2) The scanning electron microscope according to claim 1, wherein the voltage applied to the mesh electrode is controlled to be low when the working distance is large, and to be high when the working distance is small.