JPH0845454A - Alignment adjusting method - Google Patents

Abstract

PURPOSE:To adjust the alignment of an electron gun in a short time. CONSTITUTION:An alignment coil 3 is provided between a Wehnelt electrode 2 and a diaphragm 4, and a collector 5 is laid under the aperture of the diaphragm 4. In this condition, an electron beam is scanned and a position giving maximum beam current is detected. In this case, the electron beam is scanned from a position keeping the highest probability of alignment toward the surrounding area. For example, the electron beam is vector scanned concentrically in a direction parting from an origin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment adjusting method for an electron microscope or the like.

[0002]

2. Description of the Related Art An electron gun is provided in an apparatus using an electron beam such as an electron microscope. Then, as shown in FIG. 4A, the cathode 1 of the electron gun and the Wehnelt electrode 2 are assembled so that their axes coincide with each other. That is, the tip of the cathode 1 and the center of the opening of the Wehnelt electrode 2 are assembled so as to be positioned on the optical axis set mechanically. This is the state of being mechanically aligned.

However, due to the mechanical assembling accuracy,
As shown in FIG. 4B, mechanical displacement of the cathode 1 and the Wehnelt electrode 2 may occur. Such mechanical displacement between the cathode 1 and the Wehnelt electrode 2 may occur when the cathode 1 is replaced.

Therefore, conventionally, an alignment coil is provided, and an electron beam is deflected by the alignment coil to adjust the alignment. A schematic configuration example thereof is shown in FIG.

In FIG. 5, the Wehnelt electrode 2 and the diaphragm 4 are shown.
An alignment coil 3 is arranged between the and.
Although only one set of the alignment coils 3 is shown in FIG. 5, actually two sets of the alignment coils 3 are provided in orthogonal directions so that the electron beam can be deflected in two directions of orthogonal X and Y axes. Is. Further, the diaphragm 4 is not specially provided for the alignment adjustment, and a normally used diaphragm may be used. However, here, it is assumed that the diaphragm 4 has no mechanical displacement.

When performing the alignment adjustment, FIG.
As shown in, a collector 5 such as a Faraday cup that collects an electron beam is arranged below the aperture of the diaphragm 4. Then, the control device 7 outputs a series of digital scanning current values for scanning the electron beam. This digital scanning current value is converted into an analog scanning current value by the DAC 8,
It is supplied to the drive circuit 9.

When the driving circuit 9 receives the analog scanning current value from the DAC 8, the driving circuit 9 generates the scanning current value and supplies it to the alignment coil 3. As a result, the electron beam is scanned.

At this time, the controller 7 fetches the beam current value from the beam ammeter 6 every predetermined period. This beam current value naturally corresponds to the electron dose collected by the collector 5.

When the controller 7 detects that the beam current value fetched from the beam ammeter 6 has reached the maximum, it stores the scanning current value at that time. Then, the controller 7 stops outputting a series of digital scanning current values for scanning the electron beam, and stores the stored scanning current value, that is, the beam ammeter 6
The digital deflection current value that maximizes the beam current detected at is output. This digital deflection current value is converted into an analog value by the DAC 8 and is supplied to the drive circuit 9, and the deflection current is supplied to the alignment coil 3, so that the electron beam has an electron dose collected by the collector 5. It will be deflected to its maximum, which will bring it into alignment. The control device 7 is composed of a CPU and its peripheral circuits.

[0010]

However, in the conventional alignment adjustment, since the electron beam was raster-scanned as shown in FIG. 6, there was a problem that the alignment adjustment took a long time. In FIG. 6, reference numeral 10 denotes the aperture of the diaphragm 4.

A concrete explanation is as follows. Now, suppose XY coordinates are taken on a plane orthogonal to the mechanically set optical axis, the origin (0, 0) is the position of the optical axis, and the maximum deflection distance of the electron beam by the alignment coil 3 is a. In the conventional alignment adjustment, as shown in FIG. 7, P (a, -a), Q (a, a), R (-is centered on the origin (0,0) of the XY coordinate system. a,
Raster scanning is performed within the range of the rectangle surrounded by the four points a) and S (-a, -a). The scanning start point and the scanning direction are arbitrary. For example, if scanning is performed from the point P in FIG. 7 in the Y direction, the scanning end point is the point R.
It turns out that.

By the way, there is a possibility that mechanical displacement may occur when the cathode 1 is replaced as described above. However, when assembling, it is tried to visually check the mechanical displacement as much as possible. Therefore, even if a mechanical displacement occurs due to the assembling accuracy, the amount of the displacement is very small. Therefore, the intensity of the beam current detected by the beam ammeter 6 becomes maximum near the origin as shown in FIG. The probability is very high.

However, if the alignment adjustment is performed as described above, the raster scan must be performed from the scan start point to at least the vicinity of the origin, that is, the half scan range of the entire scan range. .
Moreover, since the beam current was originally a very small current, alignment adjustment took a long time.

An object of the present invention is to solve the above problems and to provide an alignment adjusting method capable of performing alignment adjustment based on a mechanical displacement of an electron gun, a diaphragm or the like in a short time. To do.

[0015]

In order to achieve the above object, the alignment adjusting method of the present invention is an alignment adjusting method in which an electron beam is scanned and the position where the electron beam current becomes maximum is the alignment position. It is characterized in that the electron beam is sequentially scanned from a position having a maximum probability of being an alignment position to a direction having a low probability by a predetermined scanning shape.

[0016]

[Advantageous Effects and Effects of the Invention] When the alignment is adjusted, the electron beam is scanned. This scanning is performed at the alignment position,
That is, scanning is sequentially performed from the position having the highest probability of being in the aligned position to the direction having the lowest probability. The scanning shape at this time can be various shapes such as a circular shape, a polygonal shape, and a spiral shape.

Therefore, the position where the beam current is maximum, that is, the alignment position can be found quickly. Therefore, by ending the scanning when the position where the beam current is maximized is detected, alignment adjustment can be performed as compared with the prior art. The time required can be greatly reduced.

[0018]

Embodiments will be described below with reference to the drawings.
The hardware configuration for performing the alignment adjusting method of the present invention may be the same as the conventional configuration shown in FIG. 5, but the mode of scanning the electron beam is different.

Now, assuming that the XY coordinates are set on the plane orthogonal to the mechanically set optical axis, and the origin (0, 0) is the position of the optical axis, the operator is required to assemble the cathode when assembling the electron gun. Since the mechanical misalignment between 1 and the Wehnelt electrode 2 is minimized, the probability of being mechanically aligned is the highest at the origin, and the probability decreases as the distance from the origin increases.

Therefore, in the present invention, the electron beam is made to scan toward the periphery from the position where the probability of alignment is the maximum, in this case the origin. Although various scanning modes are possible, an example thereof is shown in FIG.

FIG. 1A is a diagram showing a mode in which an electron beam is vector-scanned in a circular shape in a direction away from the origin. First, the electron beam is positioned at the origin, and then a circle indicated by 11 and a circle indicated by 12. , 13 and 14 are sequentially scanned in the direction of the arrow.
In other words, scanning is performed concentrically from the origin toward the periphery.

Here, how to set the intervals of the circles to be scanned is arbitrary. For example, all the intervals may be the same, or the intervals near the origin have a high probability of being alignment positions, so the intervals may be narrowed and the intervals may be increased as the distance from the origin increases.

Those skilled in the art will understand that in order to perform the scanning shown in FIG. 1A, it is sufficient to supply the scanning currents having the waveforms shown in FIGS. 2A and 2B to the X and Y alignment coils, respectively. Is.

By performing such scanning, the position where the beam current is maximum, that is, the alignment position can be found in a short time.

FIG. 1B is a diagram showing a mode in which the electron beam is vector-scanned in a rectangular shape in the direction away from the origin. First, the electron beam is positioned at the origin, and then 1
The rectangle indicated by 1 ', the rectangle indicated by 12', the rectangle indicated by 13 ', and the rectangle indicated by 14' are sequentially scanned in the arrow direction. That is, scanning is performed in a concentric rectangular shape from the origin toward the periphery. Since the scanning current waveform for performing such scanning is well known, its description is omitted.

Further, it is a diagram showing a mode in which the electron beam is vector-scanned into an octagonal shape in a direction away from the origin. Octagon shown, 13 "octagon,
Scanning is performed in the direction of the arrow in the order of the octagon indicated by 14 ″. That is, scanning is performed in a concentric octagonal shape from the origin toward the periphery. The scanning current waveform for performing such scanning is also included. It is well known.

It will be apparent to those skilled in the art that the alignment position can be found in a short time by such scanning as shown in FIGS. 1B and 1C.

As described above, the electron beam can be scanned in any polygonal shape, and can also be spirally vector-scanned from the origin toward the periphery. Further, a vector scan may be performed by approximating the spiral shape with a polygonal line.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications can be made. For example, in the above embodiment, the electron beam is deflected by the alignment coil 3, but it may be electrostatically deflected by the electrostatic deflection plate.

Further, in the above embodiment, the case of the alignment adjustment based on the mechanical displacement between the cathode 1 and the Wehnelt electrode 2 of the electron gun has been described, but the present invention is a condenser lens diaphragm, an objective diaphragm, or another diaphragm. It can also be applied to the alignment adjustment based on the position shift of. An example of the configuration is shown in FIG.

FIG. 3 is a diagram showing an example of the configuration in the case where the alignment adjustment based on the mechanical displacement of the objective diaphragm is performed by the alignment adjusting method according to the present invention. In the figure, 20 denotes the objective diaphragm. It should be noted that the same components as those shown in FIG. 5 are designated by the same reference numerals to omit redundant description.

In FIG. 3, the alignment coil 3 is arranged on the electron gun side of the objective diaphragm 20. Further, when performing the alignment adjustment, the collector 5 is arranged below the aperture of the objective aperture 20. Then, in this state, the electron beam may be scanned as shown in FIG. 1A, FIG. 1B, or FIG. 1C, for example.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a scanning mode of an electron beam in the present invention.

FIG. 2 is a diagram showing a scanning current waveform supplied to an alignment coil when performing the scanning shown in FIG. 1A.

FIG. 3 is a diagram showing a configuration example when the present invention is applied to alignment adjustment based on a mechanical displacement of an objective diaphragm.

FIG. 4 is a diagram for explaining alignment adjustment of the electron gun.

FIG. 5 is a diagram showing a configuration example in the case of performing alignment adjustment of the electron gun.

FIG. 6 is a diagram for explaining a raster scan performed in the alignment adjustment of the electron gun.

FIG. 7 is a diagram for explaining the problem of the present invention.

[Explanation of symbols]

1 ... Cathode, 2 ... Wehnelt electrode, 3 ... Alignment coil, 4 ... Aperture, 5 ... Collector, 6 ... Beam ammeter, 7 ... Control device, 8 ... DAC, 9 ... Driving circuit.

Claims (1)

[Claims] 1. An alignment adjusting method in which an electron beam is scanned and the position where the electron beam current is maximized is used as an alignment position. An alignment adjusting method characterized by scanning in a direction with a low probability.