JPH0447943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for efficiently aligning the axis of an electron beam with respect to an electron lens of an electron optical column.

[Technical background of the invention and its problems]

The axis of the electron beam with respect to the electron lens of the conventional electron optical column is appropriately determined by a deflection means provided in the front stage of the electron lens so that the incident position of the electron beam on the electron lens is approximately at the center.
Next, the current of the electron lens is changed. When the incident position of the electron beam is shifted from the center of the electron lens, the direction of the electron beam exiting from the electron lens changes due to a change in the current of the electron lens. Therefore, a beam position detection means provided after the electron lens measures the positional deviation of the emitted beam due to the change in the current of the electron lens.
Change the incident position of the electron beam appropriately in a direction that reduces this positional deviation, change the current of the electron lens again, measure the positional deviation of the emitted beam at that time, and if there is any positional deviation, repeat the above operation. Repeat this to make the positional deviation zero. Conventional axis alignment like this requires several tens of thousands of steps using an electronic computer.
It usually takes about a minute, and it takes a long time to align the axis of one electron optical lens barrel having multiple stages of electron lenses.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for aligning the axis of an electron optical lens barrel by which the axis of an electron beam with respect to an electron lens can be more rationally aligned in a short time.

[Summary of the invention]

The gist of the present invention is that the positional deviation of the emitted beam when the current of the electron lens is changed is
This is based on the knowledge that the direction component u and the Y direction component v are related to the incident position (Ax, Ay) of the electron beam on the electron lens, and are expressed by the following formula. Measure the positional deviation of the emitted beam due to the current change of the electron lens at each incident position selected at three locations, calculate k ₁ to _{k 6} of the following formula from these measured values, and calculate the components u, v. The incident position (Ax ₀ , Ay ₀ ) at which the value becomes zero is determined by calculation.

u=k ₁ ·Ax+k ₂ ·Ay+k ₃ v=k ₄ ·Ax+k ₅ ·Ay+k ₆ [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. Figure 1 shows an electron optical system for axis alignment, where 11 is an electron beam, 12
is an electronic lens. Deflection means 13 is provided in front of the electron lens 12 (upper side in FIG. 1) for setting the incident position of the electron lens 11 with respect to the electron lens 12. This deflection means 13 includes a pair of deflection coils 13x for deflecting the electron beam 11 in the X direction in a plane perpendicular to the electron beam 11, and a pair of deflection coils 13y for deflecting the electron beam 11 in the Y direction. It's summery.

An aperture mask 15 having an aperture 14 is provided downstream of the electron lens 12 (lower in FIG. 1). An electronic lens 12 is provided between the electronic lens 12 and the aperture mask 15.
A deflection means 1 consisting of deflection coils 16x and 16y for scanning the electron beam 11 emitted from the aperture mask 15 in the X and Y directions.
6 is provided.

Further, an electron detector 17 is provided above the aperture mask 15 to detect reflected electrons when the electron beam 11 hits the aperture mask 15, and the output signal of this detector 17 is sent to an amplifier. It is adapted to be incorporated into an electronic computer 19 via a cable 18.

The output from the detector 17 is the electron beam 11
is passing through aperture 14
It becomes OFF, and when it misses the aperture 14 and hits the aperture mask 15, it becomes ON.
The position of the aperture 14 is measured from the relationship between OFF and the input to the deflection means 16.

In this device, when the electron beam 11 passes through the center of the electron lens 12, even if the current of the electron lens 12 is changed, the electron beam 11 will not be bent and the emission direction will not change. The measured value of the position of the aperture 14 by the subsequent deflection means 16 does not change due to changes in the current of the electron lens 12.

However, if the electron beam 11 is off the center of the electron lens 12, the emitted beam will be bent due to the change in the current of the electron lens 12. Therefore, the measured value of the position of the aperture 14 by the deflection means 16 differs before and after the change in the current of the electron lens 12. The amount of this difference is called the positional deviation of the emitted beam.

FIG. 2 shows an electron beam 11 directed to an electron lens 12.
The incident position is represented by the horizontal axis Ax and the vertical axis Ay, and when the current of the electron lens 12 is changed by a predetermined ΔI at each incident position (Ax, Ay), the positional deviation vector D→ of the output beam is expressed as The obtained experimental results are shown in bold lines.

The vector D→ of this positional shift is expressed by the following formula.

D→=u・x→+v・y→... However, x and y are unit vectors in the X and Y directions.

Figure 3 shows the change in the amount of positional deviation when changing Ay with Ax as a parameter, and Figure 4 shows the change in the amount of positional deviation when changing Ax with Ay as a parameter. . As is clear from these figures 3 and 4, the above-mentioned Ax
It has been found that the X-direction component u and Y-direction component v of the displacement vector D→ exhibit linearity with respect to and Ay. That is, the components u and v can be expressed by the following formula.

u=k ₁・Ax+k ₂ Ay+k ₃ ... v=k ₄・Ax+k ₅・Ay+k ₆ ... Since each coefficient k ₁ to k ₆ in the above equation exists three times in each equation, it is applied to the electron lens 12. The incident position of the electron beam 11 is (Ax ₁ , Ay ₁ ), (Ax ₂ ,
Set at three locations: Ay ₂ ) and (Ax ₃ , Ay ₃ ),
The amount of positional deviation in the X and Y direction components at that time u ₁ to _{u 3} ,
If v ₁ to _{v 3} are obtained by actual measurement, k ₁ to _{k 6} can be calculated mathematically.

Once k ₁ to _{k 6} have been determined in this way, substitute these values into the equations to obtain the components u,
Ax and Ay when v becomes zero, that is, (Ax ₀ ,
If we find the incident position (Ax ₀ , _{Ay 0 )}
is the center of the electronic lens 12.

X and Y direction components of the positional deviation u ₁ to u ₃ , v ₁ to _{v 3}
can be automatically measured by the electronic computer 19, and the calculation of k ₁ to _{k 6} based on these values, the calculation of Ax ₀ and Ay ₀ based on them, and the input to the deflection means 13 are all performed. Since it can be performed automatically by the electronic computer 19, the above-mentioned axis alignment can be performed fully automatically.

Note that the incident position (Ax ₀ , Ay ₀ ) when the positional deviation obtained as described above becomes zero may deviate slightly from the above formula depending on the characteristics of the electron optical system, and it can be determined by one operation. Although it may not be possible to completely eliminate the positional deviation, by repeating the above operation several times, the positional deviation can be reduced to almost zero.

In the above-described embodiment, the aperture mask 15, the detector 17 for detecting reflected electrons, etc. are used to measure the position of the beam emitted from the electron lens 12, but various other known beam position measuring means may be used. Needless to say, it is also possible to use

〔Effect of the invention〕

As described above, according to the present invention, it is possible to rationally align the axis of the electron beam to the center of the electron lens, which conventionally took several tens of minutes for a single-stage electron lens. I was able to shorten the time to about 1 minute.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a partial configuration of an electron optical column to which the method of the present invention is applied, and Fig. 2 is a diagram showing the positional deviation vector D→ of the emitted beam at each incident position (Ax, Ay) of the electron beam with respect to the electron lens. A diagram showing an actual measurement example with thick lines, Figure 3 is the X-direction component Ax of the incident position
Figure 4 shows an actual measurement example of the amount of positional deviation when changing the Y-direction component Ay with the Y-direction component Ay of the incident position as a parameter.
FIG. 7 is a diagram showing an example of actual measurement of the amount of positional deviation when changing the directional component Ax. 11...electron beam, 12...electron lens, 1
3... Deflection means (for axis alignment), 14... Aperture, 15... Aperture mask, 16... Deflection means (for position detection), 17... Electronic detector, 18
...Amplifier, 19...Electronic computer.

Claims (1)

[Scope of Claims] 1. When aligning the axis of the electron beam to the center of the electron lens by the deflection means for alignment provided in the front stage of the electron lens, the incident position of the electron beam on the electron lens by the deflection means ( Ax, Ay) are selected at least three locations, and the current of the electron lens is changed at each incident position, and the X-direction component u and the Y-direction of the vector D→ of the positional deviation of the electron beam emitted from the electron lens. Detect the component v, calculate k ₁ to _{k 6} of the following formula from these components u and v, calculate the incident position (Ax ₀ , Ay ₀ ) where the components u and v become zero, and calculate the incident position Position (Ax ₀ ,
A method for aligning the axis of an electron optical lens barrel, characterized in that an input corresponding to Ay ₀ ) is applied to the deflection means. u=k ₁・Ax+k ₂・Ay+k ₃ v=k ₄・Ax+k ₅・Ay+k ₆