JPS62184750A - Electron beam device - Google Patents

Abstract

PURPOSE:To achieve display of a low magnification image without expansion and contraction or distortion of a sample image, by deflecting electron beams to be passed near the midway between the main face of an object lense and the front focus of it, in a low magnification image observation mode. CONSTITUTION:When a selection signal S which selects a low magnification image observation mode is applied to a mode switching gain control 7, gains of amplifiers 3a and 3b are controlled by the control 7 so as to change deflection ratio of deflection coils 2a and 2b and to deflect electron beams 1 to be passed near the midway between main face A of an objective lense and front focus B of it. Consequently, as an electron beam 1c is not passed through a cross point between the front focus B and an optical axis Z like an electron beam 1b is, an effect caused by spherical aberration is lessened and subsequently, extension of the electron beam scanning width or deformed scanning such as a barrel formed scanning on a sample are also lessened to a negligible degree. Thus, expansion and contraction or distortion of an image at displayed screen edges as shown by C in the figure may not happen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for observing scanned images, and particularly to an electron beam apparatus that prevents image expansion/contraction and distortion when observing low magnification images.

[Prior art] In a scanning electron microscope or the like, a sample is scanned with an electron beam, and secondary electrons generated from the sample during the scanning are detected and supplied to a cathode ray tube or the like to observe a secondary electron image of the sample. There is. Third
The figure is a schematic configuration diagram of such a conventional device, in which 1 is an electron beam;
Denoted at 2a and 2b are upper and lower two stages of deflection coils for deflecting the electron beam 1, to which a deflection signal is supplied from a deflection signal generation source 4 via amplifiers 3a and 3b. 5 is an objective lens, and 6 is a sample.

In such a device, electrons 111 are always deflected by upper and lower deflection coils 2a and 2b provided above the objective lens so as to pass through the intersection of the main surface A of the objective lens and the light @Z, and are irradiated onto the sample 6. be done.

[Problems to be Solved by the Invention] By the way, when a sample is observed in a low magnification image observation mode with such an apparatus, the electron beam 1 is oriented at a large angle with respect to the sample surface, as shown in the electron beam 1a in FIG. (As shown in FIG. 5(a), the width of the electron beam scanning area differs for scanning at the same angle θ in the vicinity of the optical axis Z and in the part away from the optical axis. In other words, from the optical axis The scanning width of the electron beam on the sample increases as it moves away from the sample.Also, considering a rectangular scanning area, the distance from the optical axis increases in the diagonal direction, as shown in Fig. 5(b).
A pincushion-shaped scan as shown by the solid line A is performed. Therefore, at the edges of the display screen, image shrinkage occurs due to an increase in the electron beam scanning width, and barrel-shaped distortion as shown by the solid line opening in FIG. 6 occurs due to the pincushion-shaped scanning described above. Furthermore, as shown by the electron beam 1b in FIG. Therefore, the sample is irradiated perpendicularly to the sample, but due to spherical aberration, it is deflected back to the optical axis Z direction. Therefore, contrary to the above, the electron beam scanning width is reduced and barrel-shaped scanning is performed on the sample, resulting in image expansion and pincushion-shaped distortion at the edges of the display screen. Therefore, when creating a stitched photo of an IC or the like using low-magnification images using such a device, it is difficult to synthesize the images with high precision because the images are expanded, contracted, and distorted at the stitched portions of the photos. It was difficult to create a composite photo.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide an apparatus that can display a low-magnification image without stretching or distortion of a sample image, and can also display an extremely low-magnification image.

[Means for Solving the Problems] The present invention achieves the above object by directing an electron beam irradiated onto a sample to a two-stage electron beam deflector disposed above an objective lens at a predetermined ratio. In a device that observes a scanned image by supplying a deflection signal with The present invention is characterized in that means is provided for supplying a deflection signal to the electron beam deflector so that the electron beam passes through the intersection of the main surface of the objective lens and the optical axis in the observation mode.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a schematic diagram of an embodiment of the present invention.

In the embodiment shown in FIG. 1, the same components as those in the conventional device shown in FIG. 3 are given the same numbers and their explanations are omitted. In FIG. 1, 7 is connected to amplifiers 3a and 3b, for example, the amplifier 3a is
, 3b is a gain control for mode switching.

The device configured in this way has a low magnification image observation mode (
For example, when the selection signal S for selecting 100x) is supplied to the mode switching gain control 7, the mode switching gain control 7 controls the gain of the amplifiers 3a and 3b and changes the deflection ratio of the deflection coils 2a and 2b. The electron beam 1 is deflected so as to pass approximately midway between the main surface A of the objective lens and the front focal point B, as shown by the electron beam 1C.

Therefore, unlike the electron beam 1b described above, the electron beam 1C does not pass through the intersection of the front focal point B and the optical axis Z, so the influence of spherical aberration is reduced, and accordingly, the electron beam scanning width on the sample is elongated. Modified scans such as barrel scans become negligible. Therefore, there is no expansion/contraction or distortion of the image at the edge of the display screen as shown by the dotted line in FIG. Therefore, even when creating stitched photos of ICs, for example, it is possible to create stitched composite photos with high accuracy. or,
When the extremely low magnification image observation mode (for example, 20x) is selected, the mode selection signal S- causes the mode switching gain control 7 to control the gains of the amplifiers 3a and 3b and change the deflection ratio of the deflection coils 2a and 2b. . By this deflection, the electron beam 1 is deflected so as to pass through the intersection of the optical axes toward the main surface of the objective lens, as shown by electron beam 1d, and an extremely low magnification image observation is performed.

Here, the minimum magnification in the very low magnification image observation mode is determined by blocking the electron beam by the electron beam passage hole of the objective lens lower magnetic pole piece 5a, if there is margin in the gain adjustment of the amplifiers 3a and 3b.

On the other hand, if the electron beam passage hole of the objective lens lower magnetic pole piece 5a is made too large, the leakage magnetic field of the objective lens to the sample surface increases, reducing the detection efficiency of secondary electrons generated from the sample. Therefore, the electron beam passage hole of this embodiment is formed to a size that does not cause the electron beam to be blocked even during extremely low magnification image observation. Therefore, even in the very low magnification image observation mode, it is possible to observe the movement M@ without so-called vignetting, which is caused by the shielding of the electron beam by the lower magnetic pole piece of the objective lens.

It should be noted that the embodiments described above are merely illustrative. In the above embodiment, an example in which the present invention was applied to a scanning electron microscope was explained.
The present invention may be applied to an apparatus that requires linearity of electron beam scanning on a wafer, such as at the opening of an electron beam exposure bag.

[Effects of the Invention] As described in detail above, according to the present invention, the electron beam that irradiates the sample during low-magnification image observation can be passed approximately halfway between the main surface of the objective lens and the front focal point, and the electron beam that irradiates the sample during low-magnification image observation can be Since the electron beam is deflected to pass through the main surface of the objective lens, the electron beam scanning width is not expanded or contracted or deformed during low-magnification image observation, which may cause image expansion, contraction or distortion at the edges of the display screen. In addition, an electron beam device is provided which displays an extremely low magnification image without vignetting in extremely low magnification image WA observation.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, FIG. 2 is a diagram for explaining the display state based on the present invention, FIG. 3 is a schematic configuration diagram of a conventional device, and FIG. 4 is a conventional device Ray diagram of, No. 5
The figure is a diagram for explaining the scanning state on a sample, and FIG. 6 is a diagram for explaining the display state of the conventional apparatus. 1: Electron beam, 2a, 2b: [l? i-direction coil, 3a
. 3b: Amplifier, 4: 11 signal @ source, 5: Objective lens, 6: Sample, 7: Gain control for mode switching.

Claims (1)

[Claims] In a device that observes a scanned image by supplying a deflection signal at a predetermined ratio to a two-stage electron beam deflector placed above an objective lens, the electron beam irradiating the sample is The electron beam is deflected so as to pass approximately midway between the main surface of the objective lens and the front focal point of the objective lens, and in the extremely low magnification image observation mode, the electron beam is deflected so as to pass through the intersection of the main surface of the objective lens and the optical axis. An electron beam device comprising means for supplying a deflection signal to a beam deflector.