JPS5842937B2 - Stigma correction device for electron microscopes and similar devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an astigmatism correction device for electron microscopes and similar devices, and particularly to astigmatism correction devices that change over time due to the inherent astigmatism of an electromagnetic lens and dirt in an electron beam path. The present invention relates to an astigmatism correction device that can independently correct aberrations.

In order to obtain good images with an electron microscope, it is necessary to correct the inherent astigmatism of the electromagnetic lens used and the astigmatism that changes over time due to dirt in the electron beam path, aperture, etc. be.

The inherent astigmatism of an electromagnetic lens is greatly affected by the processing precision of the lens, and it is very difficult to reduce the astigmatism to zero, but if you focus on this only, you only need to correct it once.

Astigmatism, which changes over time due to dirt, varies depending on the usage time and needs to be corrected each time.

By the way, conventional electron microscopes use an astigmatism correction device that corrects astigmatism using a single correction means without distinguishing between the inherent astigmatism of the electromagnetic lens and the astigmatism that changes over time. Since it is used, the amount of correction increases,
The disadvantage is that the correction operation is difficult, and in some cases, the astigmatism may even increase.

SUMMARY OF THE INVENTION An object of the present invention is to provide an astigmatism correction device for an electron microscope and similar devices, which eliminates the drawbacks of the prior art described above and improves the operability of astigmatism correction.

A feature of the present invention is that a correction signal for correcting inherent astigmatism and a correction signal for correcting astigmatism that changes over time are independently supplied to each of the pair of astigmatism correction lenses. be.

The figure is a block diagram showing an embodiment of the astigmatism correction device of the present invention.

In the figure, 1 is an electron beam accelerated to several +KV to several hundred KV, and the electron beam diameter a of the electron beam 1 is reduced or expanded by an electromagnetic lens 2 depending on the purpose.

3a and 3b are X-direction and Y-direction astigmatism correction lenses each consisting of a four-pole coil of the device of the present invention;
The correction current signal set in step b and the correction current signal set in the second X-direction astigmatism correction signal setter 5a and Y-direction astigmatism correction signal setting device 5b are respectively added, and these correction signals are respectively accelerated. Voltage correction circuit 5a.

After passing through 6b, the current is amplified by current amplifiers 7a and 7b, and is supplied to the X-direction and Y-direction astigmatism correction lenses 3a and 3b.

The acceleration voltage correction circuits 6a and 6b include astigmatism correction lenses 3a,
The astigmatism correction signal setters 4a and 4b set the current for correcting the inherent astigmatism of the electromagnetic lens 2. Astigmatism correction signal setting devices 5a, 5
b is used to set a correction current signal for correcting astigmatism that changes over time due to dirt in the electron beam path, aperture, etc., and the astigmatism correction signal setting devices 5a and 5b are incorporated in the operation panel 8. ing.

9 is a lens power source for changing the focus of the electromagnetic lens 2.

A spot 10 is obtained when the electron beam 1 passes through an electromagnetic lens 2, but generally it is not a perfect circle due to astigmatism and is a'Nb', but in the embodiment of the present invention. According to , when the cause is due to the inherent astigmatism of the electromagnetic lens 2, the first astigmatism correction signal setters 4a and 4b
The astigmatism correction current signal i can be applied to the astigmatism correction lenses 3a and 3b using the above method to correct the current signal b'.

Note that since the inherent astigmatism of the electromagnetic lens 2 is fixed, once the astigmatism corrections 4a and 4b are set, there is usually no need to readjust them thereafter.

After that, when using an electron microscope for a long time, r)b'
If this happens, it is due to astigmatism that changes over time due to dirt in the electron beam path, etc. In that case, use the second astigmatism correction signal setter 5a, 5b. Astigmatism correction can be performed independently and separately from intrinsic astigmatism correction.

Therefore, when the electron beam path etc. are not contaminated, it is not necessary to operate the second astigmatism corrections 5a and 5b, and the correction of the inherent astigmatism is performed in advance by the first astigmatism correction signal setting device 4a.
, 4b, so no further operation is required.

In addition, when astigmatism occurs due to contamination in the electron beam path, only the astigmatism is detected by the second astigmatism correction signal setting device 5a,
5b, the amount of correction is small, the operation is simple, and it is rare to accidentally increase astigmatism.

In short, the operability of astigmatism correction can be improved.

In addition, in the embodiment shown in the figure, acceleration voltage correction circuits 5a, 5
b is provided, but it can be omitted if the acceleration voltage is constant.

Moreover, although the number of electromagnetic lenses is one, in the case of a plurality of electromagnetic lenses, the number of astigmatism correction devices of the present invention may be increased accordingly.

As described above, the present invention has the remarkable effect of improving the operability of astigmatism correction.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of the astigmatism correction device of the present invention. 1... Electron beam, 2... Electromagnetic lens, 3
a, 3b... Astigmatism correction lens, 4a, 4b...
...First astigmatism correction signal setter, 5a, 5b...
...Second astigmatism correction signal setter, 6a, 6b...
...Acceleration voltage correction circuit, 7a, 7b...Current amplifier.

Claims (1)

[Claims] 1. A correction signal for correcting inherent astigmatism and a correction signal for correcting astigmatism that changes over time for each of a pair of astigmatism correction lenses arranged around an axis through which an electron beam passes. Astigmatism correction device for electron microscopes and similar devices configured to independently supply 2 A signal for correcting inherent astigmatism and a correction signal for correcting astigmatism that changes over time are independently supplied to each of a pair of astigmatism correction lenses arranged around the axis through which the electron beam passes. An astigmatism correction device for an electron microscope and similar devices thereof, wherein the correction signal for correcting the inherent astigmatism is changed in accordance with the accelerating voltage of the electron beam.