JPH03105837A - Scanning electron microscope and similar device - Google Patents

Abstract

PURPOSE:To prevent an image from being lowered in quality in a range from a high to a low magnifying factor, and thereby keep the image high in quality by making a magnetic field changeable, which is generated by high voltage applied to a detector, while interlocking the deflection intensity of a polariscope. CONSTITUTION:A control electrode 73 controlling an electric field 8 is installed onto a shield electrode 71 (earthing potential) while an insulating spacer 72 is held. When a desired magnifying factor is set up by a magnifying setter 10, a deflection signal is given to a polariscope 5 by a deflection signal generator 11. Desired control voltage is concurrently applied to the control electrode 73 by a control voltage generator 12. The aforesaid control voltage is so set up as to respond the magnifying factor in such a way that no influence on primary electron beams is exerted in a range of high magnifying factors and also that the whole of secondary electron beams produced from a specimen is detected in a range of low magnifying factors. This thereby enables the electric field 8 to be controlled while being interlocked with change in magnifying factor, thereby making it possible to obtain a secondary electron image which is high in quality while an reduction in resolving power is prevented in a range from the high magnifying factors to the low magnifying factors.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention... This article relates to scanning electron microscopes and similar devices, and particularly to secondary electron detectors suitable for maintaining high image quality from low to high magnifications. [Prior art] Generally, a secondary electron detector consists of a scintillator that emits epsilon light upon which electrons collide, and a photomultiplier that detects this light with high sensitivity. A high voltage of approximately 10 KV is applied to this scintillator, and the electric field due to this high voltage leaks into the secondary electron path, attracts the secondary electrons, and detects them. However, since this electric field is asymmetrical with respect to the optical axis as shown in FIG. 2, the detection efficiency differs depending on the sample emission position of the secondary electrons. Therefore, when a secondary electron image is displayed, certain quadrants become dark. This phenomenon is not a problem at high magnifications because the scan area of the sample is narrow, but it becomes noticeable at low magnifications.

[Problems to be solved by the invention]

The purpose of the present invention is to provide a secondary electron detector that can maintain high image quality from low magnification to high magnification by preventing deterioration of image quality. [Means for solving the problem] In order to solve the above problem, it is necessary to make the electric field of the secondary electron detector that seeps into the path of the primary electron beam as uniform as possible. To do this, the electric field generated by the secondary electron detector can be strengthened to detect all secondary electrons coming out of the sample. However, in this case, the trajectory of the primary electron beam is affected, resulting in a decrease in resolution. This is because the trajectory of the primary electron beam changes due to the deflection effect of the detector electric field and is subject to off-axis aberrations of the lens.

This decrease in resolution is not a problem at low magnifications, but becomes a problem at high magnifications. Therefore, by making it possible to electrically control the electric field in conjunction with the magnification, the above problem can be solved by preventing a decrease in resolution at high magnifications and preventing differences in secondary electron efficiency depending on the quadrant at low magnifications. [Function] In order to control the electric field of the secondary electron detector that seeps into the path of the primary electron beam, it is necessary to control the high voltage applied to the detector or to use an electrode to control this electric field. This can be done by placing an electrode and controlling the voltage applied to this electrode. This objective can be achieved by controlling either of these voltages in conjunction with the observation magnification. [Example] An example of the present invention will be explained below with reference to FIG. l!
The primary electrons Ji2 emitted from the child gun 1 are focused narrowly by several lenses (other than the objective lens are omitted) 3 and are irradiated onto the sample 4. This primary electron beam 2 is scanned two-dimensionally over a sample 4 by a deflector 5. Secondary electrons 6 coming out of the sample 4 are accelerated by the electric field 8 of the secondary electron detector 7 and detected by the scintillator 74, resulting in a video signal.
In this embodiment, a control electrode 73 for controlling the electric field 8 is attached to a shield electrode 71 (ground potential) with an insulating spacer 72 in between.

In such a configuration, when a desired magnification is set by the magnification setter 10, a deflection signal is given to the deflector 5 by the deflection signal generator 11. At the same time, a desired control voltage is applied to the control electrode 73 by the control voltage generator 12. This control voltage is preset in correspondence with the magnification so that it does not affect the primary electron beam at high magnifications, and so that all secondary electrons emitted from the sample can be detected at low magnifications. Therefore, the electric field 8 can be controlled in conjunction with changes in magnification, and secondary electron images with high image quality and no reduction in resolution can be obtained from low to high magnifications.

The above is an embodiment of the present invention, but if the primary electron beam is affected to the extent that a decrease in resolution is noticeable at low magnification, this influence can be corrected. That is, by giving a signal from the correction signal generator 13 to the electron beam axis corrector 14 in conjunction with the magnification setting device 10 so that the primary electron beam always passes over the lens 3, a decrease in resolution can be prevented. I can do it. Note that this implementation can also be performed by the deflector 5 superimposed on the deflection signal generator 11.

As described in Section 6 [Operation], which is an embodiment of the present invention, the above is also possible by directly controlling the applied voltage 9 to the scintillator. In this case, the control electrode 73 becomes unnecessary. Although this embodiment has been described with respect to a configuration in which the sample 4 is placed inside the lens 3, the present invention is not limited to this, and the same can be done even if the sample 4 is placed below the lens 3, for example. Also, although we have discussed electron beams, it goes without saying that this method can be applied to charged particle beams in general, such as ion beams. [Effects of the Invention] As described above, according to the present invention, since the electric field generated by the voltage applied to the secondary electron detector is controlled in accordance with the accelerating voltage, there is an effect of preventing deterioration of image quality over a wide range of magnification.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram showing one embodiment of the present invention, and FIG. 2 is a conventional configuration diagram.

Claims (1)

[Claims] 1. A lens that narrows the electron beam emitted from the electron gun and irradiates it onto the sample, a deflector that scans the electron beam two-dimensionally on the sample, and a secondary beam emitted from the sample. A scanning electron microscope comprising an electron beam device comprising a secondary electron detector for detecting electrons, wherein an electric field generated by a high voltage applied to the detector is made variable in conjunction with the deflection intensity of the deflector. and similar devices. 2. When the electric field of the detector described in item 1 is made variable in conjunction with the deflection strength, a means for correcting the influence of the electron beam due to the electric field of the detector is provided, and this means is also made variable in conjunction with the deflection strength. 3. A scanning electron microscope and similar devices characterized in that the correction means according to item 2 uses a deflector to superimpose the deflection intensity. 4. Any one of items 1 to 3, wherein the sample described in item 1 is placed inside a lens, and the secondary electron detector is placed on the electron gun side of the lens. Scanning electron microscopes and similar devices described in