JPS586266B2 - Lens current setting device for electron microscopes, etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens current setting device that controls the lens current supplied to an electron lens used in an electron microscope or the like using a digital signal, and in particular does not require refocusing even when switching functions. The present invention relates to the above device.

A plurality of electromagnetic lenses such as a focusing lens, an objective lens, and a projection lens are used in an electron microscope, and each lens is supplied with a predetermined lens current corresponding to a designated magnification.

For example, as shown in FIG. 1, an objective lens 1, an intermediate lens 2,
The projection lens 3 includes a reference power source 4 provided for each lens.
A plurality of types of reference voltages from amplifiers 10, 11, and 12 are sent to amplifiers 10, 11, and 12 through interlocking changeover switches 7, 8, and 9, which are provided for each lens. Supplied.

However, regarding the objective lens 1, due to the delicate focus adjustment, a highly variable power supply 13 is inserted in series between the selector switch 7 and the amplifier 10, and a variable voltage is superimposed on the reference voltage to enable adjustment. .

However, in addition to the function of obtaining a normal transmission image, an electron microscope also has the function of a selected area diffraction camera, a high dispersion diffraction camera, etc., and each function is selected by a function selection switch.

Then, it is necessary to adjust the focus by operating the variable power supply for each function.

For this reason, once a normal transmission image is obtained in a focused state, the function is switched so that, for example, a diffraction image is obtained in a focused state, and the function is switched again to obtain a normal transmission image. When the function is restored, focusing must be performed again, which is disadvantageous in that the operation becomes complicated.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a lens current setting device that does not require focusing every time a function is switched.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 21, 22, and 23 are an objective lens, an intermediate lens, and a projection lens, respectively, which constitute an imaging lens system of an electron microscope.

Amplifiers 24, 25, 26 provided for each lens are connected to DA converters 27, 28 provided for each lens.
．． A lens current corresponding to the reference voltage from 29 is supplied to each of the lenses.

A digital signal specifying the reference voltage to be sent to the amplifier is sent to the register 3 in the D-A converters 27, 28, and 29.
It is sent from the computer 33 via 0, 31, and 32.

The computer 33 includes a function switching circuit 34,
It is interconnected with a magnification setting circuit 35', a focus adjustment circuit 36, a read-only fixed storage device (hereinafter referred to as ROM) 37, and a writable and readable storage device (hereinafter referred to as RAM) 38, respectively.

The function switching circuit 34 is composed of a changeover switch having a selector corresponding to each function of the electron microscope, and a code generator that generates a code corresponding to the function selected by the switch, and the magnification setting circuit 35 is also similar. It is composed of a designation switch that can specify dozens of magnification levels realized by an electron microscope, and a code generator that generates a code corresponding to the magnification specified by the switch.

The focus adjustment circuit 36 has an adjustment knob, and when the knob is rotated, an up-count pulse is generated when the knob is rotated clockwise, and a down-count pulse is generated when the rotation is counterclockwise. and sends it to the computer 33.

The discrimination circuit 39 discriminates whether the pulse generated from the adjustment circuit 36 is an up-count pulse or a down-count pulse, and sends a signal to the computer 33 to distinguish between the up-count pulse and the down-count pulse.

If the magnification of the electron microscope can be varied over 24 steps in the above configuration, the combination of lens current values to be supplied to the intermediate lens 22 and the projection lens 23 to achieve each magnification corresponds to each magnification in the ROM 37. The address is stored in advance.

Furthermore, as for the current value of the objective lens 21, unlike the intermediate and projection lenses mentioned above, the absolute current value corresponding to each magnification is not determined, but the current value that should be increased or decreased between each magnification when changing the magnification is measured in advance. It is also stored in the ROM 37.

Here, if the operator uses the function switching circuit 34 and the magnification setting circuit 35 to specify 100,000x for normal transmission image observation, the computer 33 stores the intermediate lens 22 and projection lens 23 corresponding to 100,000x from the ROM 37. The lens current values A i 1 2 Ap 1 are read out and sent to the registers 31 and 32 and held therein.

The digital current value held in the register is sent to the lens via the DA converter and amplifier, so the intermediate lens 2
2 and the projection lens 23 are supplied with lens currents having the above-mentioned predetermined values A 1 1 and Apl corresponding to 100,000 times magnification.

In this state, the lens current of the objective lens 21 is not adjusted, so a focused image cannot be obtained.

The operator then operates the adjustment knob of the focus adjustment circuit 36 to change the objective lens current and focus the image.

That is, each time a pulse is generated as the adjustment knob is rotated, the computer 33 determines whether the generated pulse is an up-count pulse or a down-count pulse.
In the former case, a constant minute current value is added to the objective lens current value, and in the latter case, it is subtracted to change the lens current.

After focusing in this manner, image observation is performed, and in order to further observe a diffraction image of the same sample, it is assumed that the function switching circuit 34 is used to switch to the function of, for example, a high dispersion diffraction camera.

At this time, the computer 33 saves the digital current value Ao1 held in the register 30 immediately before switching to the RAM 38.

Then, the computer 33 selects the intermediate lens current value A i 2 and the projection lens current value Ap stored in the ROM 37 in advance according to the function of the high dispersion diffraction camera that has been switched.
2 and sends it to registers 31 and 32, intermediate lens 2
2 and the above read value A I 2 to the projection lens 23
Provide a lens current with tA-p2.

Next, the operator operates the focus adjustment knob to focus the diffraction image.

Therefore, the digital current value held in the register 30 will be different from the previous value Ao1.

Therefore, even if the function switching circuit 34 is used to return to the previous function of obtaining a transmitted image, only an out-of-focus image will be obtained and refocusing will be required.

However, in the present invention, the current value A in the focused state is
o1 has been saved in the key 38, and the computer 33 confirms that it has returned to the function of obtaining a transmitted image, reads out the current value Ao1 from the RAM 38, and sends it to the register 30.

Therefore, a focused image can be immediately obtained again without the need for further adjustment.

In this embodiment, when the magnification is changed in this state, the computer 33 adds the objective lens current value to be increased or decreased to change the magnification from the ROM 37 to the readout current value Aol and sends it to the register 30.

Therefore, even if the magnification is changed, a focused image is always obtained, and there is no need to adjust the focus every time the magnification is changed.

In the embodiment described above, the value of the register immediately before switching the function was saved to the RAM, but if the value of the register was always sent to the RAM, the value of the RAM when switching the function could be saved. Just hold it.

Further, although the value saved in the RAM is the objective lens current value in the above embodiment, it is not necessarily necessary, and any value corresponding to the above current value may be used.

Furthermore, in the above embodiment, the objective lens current value is saved in the RAM only when observing a transmitted image, but each function that can be switched by the function switching circuit is saved in the RAM.
If you allocate different addresses within and save the objective lens current value in the focused state for each function,
Even when switching functions, a focused image is always obtained, eliminating the need for refocusing.

As described in detail above, according to the present invention, it is not necessary to perform focusing each time the function is switched, so that the operability of the electron microscope can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the conventional drawbacks, and FIG. 2 is a configuration diagram showing an embodiment of the present invention. 21: Objective lens, 22: Intermediate lens, 23: Projection lens, 27, 28, 29: D-A converter, 30, 31, 3
2: Register, 33: Computer, 34: Function switching circuit, 35: Magnification setting circuit, 36: Focus adjustment circuit, 37: ROM, 38: RAM○

Claims (1)

[Claims] 1. A device for digitally setting the current supplied to the lens via a D-A converter, characterized in that a storage means is provided for storing a digital value corresponding to the lens current value immediately before the function is switched. Lens current setting device for electron microscopes, etc.