JPS5847825B2 - electronic microscope - Google Patents

Description

Detailed Description of the Invention The present invention provides an electron gun that generates an irradiation electron beam, an objective lens device that directs the electron beam toward an object surface, a projection lens device that directs the electron beam from the object surface to an image surface, and an electron gun that directs the electron beam toward an object surface. The present invention relates to an electron microscope comprising a device for apparently expanding the beam aperture.

Electron microscopes with extremely high resolving power have a relatively small aperture for the irradiating electron beam, resulting in a very deep image focal depth, which can therefore be adjusted so that the object image is precisely projected onto the image plane. It has the disadvantage of being extremely difficult.

In the electron microscope described in British Patent Specification No. 687,207, an attempt was made to eliminate the above-mentioned drawbacks by superimposing an alternating image with a relatively high frequency on the focal plane of the condenser lens.

In this method, the focal point of the condenser lens moves along a predetermined trajectory in the optical axis direction of the electron microscope.

As a result, the object distance of the objective lens changes, and therefore the aperture of the irradiated electron beam changes, so that the optimum focus position can be adjusted more easily.

However, such a solution increases the contribution of spherical aberration and
This limits the freedom to select the intensity of electron beam irradiation on the sample, and actually changes the aperture of the electron beam irradiated onto the sample.

Furthermore, since this method changes the brightness and darkness of the image, it cannot be applied to cases such as recording the size of an object.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electron microscope in which the aperture of the electron beam can be made considerably large in appearance without causing the above-mentioned drawbacks.

The present invention provides an electron gun having a radiation source for generating an irradiation electron beam, an objective lens device that directs the irradiation electron beam toward an object plane, and a projection lens device that projects the electron beam from the object plane toward an image plane. and a device for apparently expanding the aperture of the electron beam,
A device for apparently expanding the aperture of the electron beam tilts the irradiated electron beam around a point located on the object plane to equate the electron beam over the entire interior of a cone with the point as the apex. The present invention is characterized in that it includes a beam deflection device including a power supply device formed as a beam deflector.

In the electron microscope according to the present invention, the size of the cross section of the electron beam on the object plane is always kept constant;
Due to the apparently large aperture, the magnitude of the electron beam current does not change at all, and the irradiation point of the irradiated electron beam on the sample does not shift in the optical axis direction.

The locus of the irradiation beam when viewed from the horizontal direction perpendicular to the optical axis draws an arbitrary figure that is symmetrical with respect to the optical axis.

Similar to the shape of this figure, the size of this figure can be almost arbitrarily selected as long as the focus of the electron beam is always located on the object plane.

Furthermore, since no beam defocus occurs, the irradiation intensity at the image plane remains constant, and by increasing the apparent aperture of the irradiation beam as desired, it is possible to record and study object images.

In a preferred embodiment, for an electron beam passing off the optical axis of the objective lens, a predetermined modification can be made to the excitation of the objective lens system depending on the degree of deviation of the beam in the transverse direction.

Next, the present invention will be explained in detail with reference to the drawings.

The drawing is a diagram showing the configuration of an electron microscope of the present invention, which includes an electron gun 1, and the electron gun 1 includes a radiation source 2 that generates an electron beam with a relatively small cross section and a relatively high current density. It is preferable that

Opposed to the radiation source 2, an anode 3, an objective lens device 7 comprising, in order as viewed in the traveling direction of the electron beam, a beam alignment device 4, a condenser lens device 5, a beam deflection device 6, a pole shoe 8, and a sample position adjustment. A sample stage 9 having a device 10, an intermediate lens device 11, and a projection lens device 12 are arranged.

A camera 14 and a fluorescent screen 15 are provided in the image space 13 of the electron microscope, and the fluorescent screen 15 can be observed through a window 16.

All electro-optical elements are installed in the outer case 1T, and the outer case 17
In addition, a window 16, a passage 18 for applying the necessary potential, and a vacuum duct 19 are provided, and the vacuum duct 19 is provided with a connection 20 to a pump device.

In the present invention, the power supply device 21 for the deflection device 6 is designed to be able to tilt the electron beam around a point 22 on the sample.

Preferably, the power supply is also controlled by the high voltage to be applied.

This is illustrated diagrammatically by connecting line 23.

The beam deflection device 6 usually comprises two sets of electromagnetic coils, by means of which the beam can first be deflected in a known manner from the optical axis 24 and then again at a given point on the optical axis, As a result, the electron beam can be tilted.

The latter point on the optical axis is the convergence point when the electron beam is projected from all directions inside the cone.

The entire bottom surface of this cone is scanned by the beam.

As a result, over time, the electron beam completely fills the interior of the cone, covering the entire bottom surface even if the sample is such that weak electron beam irradiation would not provide sufficient image information. By scanning, sufficient image information can be obtained.

Furthermore, in the present invention, the shape of the electron beam is not limited to a cone, but can take any shape.
It is preferable to use a cone or a pyramid whose bottom surface has a symmetrical shape such as a circle or a rectangle.

Particularly when scanning a circular base, for example, a power supply with two slightly out-of-phase sine wave generators can be used to scan the circular base in a spiral manner with the electron beam. The electron beam can be deflected to

On the other hand, when scanning a rectangular bottom surface, it is possible to use a power supply device that deflects the electron beam so as to scan the rectangular bottom surface in a rask-like manner, in the same way that a scanning beam is deflected in a television system. can.

Operating the deflection device in this way, when viewed over a period of time, is equivalent to irradiating the sample with a single electron beam with a large aperture defined by the apex angle of the cone; The aperture is as large as, for example, 1000 times the aperture of the electron beam itself.

During this beam deflection, the magnitude of the electron beam current is not affected, and the irradiation point on the sample corresponding to the apex of the cone does not move in the axial direction.

It is also possible to correct spherical aberrations as in the device described in British Patent Specification No. 687207 mentioned above.

For this purpose, in the electron microscope according to the invention, it is only necessary to control a suitable lens arrangement, in this case for example an objective lens arrangement, as a function of the transverse position of the electron beam.

In known electron microscopes, the diameter of the electron beam widens when spherical aberration is corrected, but in the electron microscope of the present invention, the diameter of the electron beam does not widen, but simply passes outside the optical axis of the objective lens device. .

However, the possible spherical collection caused by this deflection can be completely corrected with reference to the off-axis path of the undeflected electron beam.

In a preferred embodiment of the electron microscope according to the invention, adjustable control means are added to the power supply of the deflection device so that the electrons can be supplied from a fixed point or from a series of fixed points outside the optical axis. It is also possible to irradiate with a beam.

In this way, the electron beam irradiation mode can be selected depending on the characteristics of the object to be tested.

As explained above, according to the present invention, not only can the depth of focus be made shallow without producing aberrations, but also
Since the entire interior of the cone is irradiated with the electron beam, it is possible to obtain a sufficiently high luminance signal even when using an electron beam in a weak energy range.

[Brief explanation of the drawing]

The drawing is a diagram showing the configuration of an example of the electron microscope of the present invention. 1... Electron gun, 2... Radiation source, 6...
... Beam deflection device, 9 ... Sample stage, 21
...Power supply device, 22... Point on the sample surface.

Claims (1)

[Claims] 1. An electron gun having a radiation source for generating an irradiation electron beam, an objective lens device that directs the irradiation electron beam toward an object plane, and a projection lens device that directs the electron beam from the object plane to an image plane. and a device for apparently enlarging the aperture of the electron beam, the device for apparently enlarging the aperture tilting the irradiation beam about a point located on the object plane. An electron microscope comprising a beam deflection device including a power supply device that equivalently forms an electron beam that is deflected throughout the entire interior of a cone having the point as its apex. 2% The electron microscope according to claim 1, further comprising an aberration correction device that is controlled according to the degree of deflection of the electron beam in the horizontal axis direction and that acts on an electron optical lens downstream of the beam deflection device. An electron microscope characterized by: