JPH0228601Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electron beam apparatus such as a scanning electron microscope.

In a scanning electron microscope, when aligning the axis of a focusing lens with respect to an objective lens, it is conventionally done as follows. In other words, while the excitation polarity of the objective lens is positive, observe the image displayed on the cathode ray tube, pay attention to a point in the image where the movement of that position is easy to discern, and then Supply an excitation current with opposite polarity to find the position of the point of interest after the movement, and then switch between the forward and reverse of the excitation current that exists near the midpoint of the position before and after the movement of this point. Find a point that does not move along with the polarity reversal (this point is usually called the center of polarity reversal), and then move the focusing lens while checking the position of the center of polarity reversal 4 to 5 times so that this center of polarity reversal is displayed in the center of the screen. The axes are aligned by mechanically moving the position each time. In such work, it is essential to accurately know the position of the center of polarity reversal, but to do so, it is necessary to accurately focus on the sample regardless of whether the excitation polarity of the objective lens is forward or reverse. There must be. However, since the yoke of an electron lens such as an objective lens has hysteresis, switching the polarity causes the focus to shift as described below. That is, when the horizontal axis represents the excitation current of the coil and the vertical axis represents the magnetic flux density generated in the yoke, the hysteresis curve of the yoke is as shown in FIG. 1. In this figure, when the excitation current takes a negative value, this corresponds to passing the excitation current through the coil in the opposite direction. Now, when the exciting current is flowing through the coil in the positive direction, the exciting current ₁
As a result, a magnetic flux density B ₁ is generated and the object is focused (corresponding to point A on curve A of the hysteresis curve). After this, when the same value of excitation current is passed through the coil in the opposite direction (i.e. _-1 ),
Since the magnetic flux density of the yoke changes along the curve A, the magnetic flux density becomes -B ₁ ', and its absolute value differs from the initial magnetic flux density. Therefore, in the past, when the polarity was switched, the focus became out of focus and the image became blurred, so each time the polarity was switched, the excitation current value supplied to the objective lens had to be adjusted and the focus adjustment had to be performed again. It was crowded and hot.

It is an object of the present invention to provide an electron beam device that can solve these conventional drawbacks and perform axis alignment easily and in a short time.

The present invention consists of a lens system consisting of multiple stages of electron lenses for narrowing the electron beam from an electron gun and irradiating it onto a sample, and a scanning system for two-dimensionally scanning the electron beam narrowed by the lens system. means, a display device for displaying a sample image based on the supply of a detection signal scanned in synchronization with the scanning, means for aligning the axes of the plurality of stages of electron lenses, and for aligning the axes. is a device equipped with a polarity reversing means for switching the direction of the current supplied from the excitation power source to the electron lens, and the excitation power source is for supplying an arbitrary excitation current to focus the objective lens. Consisting of a first power source and an auxiliary second power source that generates a constant excitation current to make the excitation history of the electronic lens the same, the electronic lens is switched between the first and second power sources. It is characterized by having means for connection.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 2 showing an embodiment of the present invention, 1 is an electron gun, and the electron beam EB from this electron gun 1 is
It is focused by a focusing lens 2, and is further focused by an objective lens 3.
is focused and irradiated onto the sample 4. 5 is a deflector, and the deflector 5 includes a scanning signal generation circuit 6.
A scanning signal is supplied from the This scanning signal is also supplied to the cathode ray tube 7, and the cathode ray tube 7
The scan is performed in synchronization with the scan on the sample 4 of the EB. 8 is a secondary electron detector, and a detection signal from this detector 8 is supplied to the cathode ray tube 7 as a brightness signal. 9 is an excitation power source for the objective lens;
The excitation current value output from the excitation power supply 9 is controlled based on an excitation designation signal from an auxiliary signal generation circuit 11 or an excitation current adjustment circuit 13, which will be described later.
The current from the excitation power source 9 can be supplied to the positive side introduction terminal a or the negative side introduction terminal b of the objective lens 3 via the first switch circuit 10. Reference numeral 11 denotes an auxiliary signal generation circuit that generates an excitation designation signal corresponding to a constant current indicated by ₀ in FIG. 1, which is larger than the excitation current during observation of the objective lens 3. The output signal of the auxiliary signal generating circuit 11 can be supplied to the excitation power source 9 via the a terminal of the second switch circuit 12. 13 is a potentiometer 13a that changes the excitation current output from the excitation power supply 9 in conjunction with the acceleration voltage.
The output signal from the excitation current adjustment circuit 13 can also be supplied to the excitation current adjustment circuit 13 via the b terminal of the switch circuit 12. 1
4 is a first switching signal generation circuit that can generate a switching signal at any timing as shown in FIG. .
Reference numeral 16 indicates a period T (for example, 1
a second generating a switching signal having a pulse width of
The output signal from the second switching signal generating circuit 16 is supplied to the second switching circuit 12 via an on/off switch 17. This on/off switch 17 and the on/off switch 15 are designed to work together. Further, the first and second switch circuits 10 and 12 can also be switched manually.

In such a configuration, first, with the on/off switches 15 and 17 open, the excitation power source 9 is manually connected to the terminal a of the switch circuit 10, and the terminal a of the switch circuit 12 is connected. Do it like this. As a result, an excitation current indicated by ₀ in FIG. 1 from the excitation power supply 9 generated based on the output signal from the auxiliary signal generation circuit 11 is supplied to the objective lens 3. Next, after a sufficient time has elapsed for the magnetic response to be completed, the switch circuit 12 is switched to the b terminal so that the output signal from the excitation current adjustment circuit 13 is supplied to the excitation power supply 9. Therefore, by operating the potentiometer 13a, the current output from the excitation power source 9 is adjusted, and the objective lens 3 is adjusted so that a sharp screen can be observed.
Adjust the focus. Assuming that the magnitude of the excitation current in the focused state is ₁ , at this time, a magnetic flux indicated by _B1 in FIG. 1 is generated in the yoke of the objective lens 3. Then,
At a certain time t, the on/off switches 15 and 17 are closed, and the first switching signal generating circuit 14 generates a switching signal as shown in FIG. 3a. As a result, the switch circuit 10 is switched to the b terminal, and the second switching signal generating circuit 16 generates a switching signal as shown in FIG. 3b based on the switching signal from the first switching signal generating circuit 14. Therefore, the switch circuit 12 is connected to the a terminal only while this signal is at a high level. Therefore, as the switch circuit 10 is switched by the switching signal from the first switching signal generation circuit 10, the excitation power supply 9 outputs an excitation current based on the output signal from the auxiliary signal generation circuit 11 for a period T. As a result, when switching from a positive excitation state (a state in which current is supplied from the a terminal of the excitation coil) to a negative excitation state (a state in which current is supplied from the b terminal), the objective lens 3 is temporarily In Figure 1, after the excitation current indicated by _-0 is applied, a current _{of -0 is} applied, and when switching to a positive excitation state, _the magnetic flux is It is possible to switch between the state shown at point A and the excitation state shown at point B in FIG. 1, where the absolute values of the densities are equal. Therefore, as the excitation polarity is switched, the focal length of the objective lens does not change.
It is possible to align the axes of each lens while tracking the position of the center of polarity reversal without having to perform the troublesome focus alignment work associated with polarity switching.

In the embodiment described above, the switching circuit for connecting the excitation power source to either the auxiliary signal generation circuit or the excitation current adjustment circuit is connected to the signal from the switching signal generation circuit for switching the excitation polarity of the objective lens. Although the switching is performed automatically in synchronization with the above, it is also possible to switch manually.

Further, in the above-described embodiment, the switching signal from the first switching signal generating circuit is generated at an arbitrary timing, but it may be generated periodically.

Furthermore, in the embodiments described above, an example was explained in which the present invention was applied to a device that aligns the axis by mechanically moving the lens.
The present invention can be similarly applied to a device that performs axis alignment by electromagnetic deflection.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the hysteresis characteristics of the magnetic flux density in the yoke due to forward/reverse switching of the lens current.
Figure 2 is a diagram showing an embodiment of the present invention;
This figure is a diagram for illustrating output signals from each circuit of the embodiment shown in FIG. 2. 1: Electron gun, 2: Focusing lens, 3: Objective lens, 4: Sample, 5: Deflection coil, 6: Scanning signal generation circuit, 7: Cathode ray tube, 8: Secondary electron detector,
9: Excitation power supply, 10, 12: Switch circuit, 1
1: Auxiliary signal generation circuit, 13: Excitation current adjustment circuit, 14, 16: Switching signal generation circuit, 15, 1
7: On-off switch.

Claims (1)

[Claims for Utility Model Registration] (1) A lens system consisting of a multi-stage electron lens for narrowing the electron beam from an electron gun and irradiating it onto a sample; and a scanning means for two-dimensional scanning; a display device for scanning in synchronization with the scanning and displaying a sample image based on the supply of a detection signal; and alignment of mutual axes between the plurality of stages of electron lenses. and a polarity reversing means for switching the direction of the current supplied from the excitation power source to the electron lens during the axis alignment. a first power supply for supplying an excitation current of;
and an auxiliary second power source that generates a constant excitation current to make the excitation history of the electronic lens the same, and means for switching and connecting the electronic lens between the first and second power sources. An electron beam device characterized by comprising: (2) A practical device comprising a means for automatically connecting the electronic lens to the second power source for a certain period of time and then connecting it to the first power source as the polarity is reversed by the polarity reversing means. Scope of patent registration request No.
Electron beam device described in (1). (3) The electron beam device according to claim (1) of the utility model registration, comprising means for periodically operating the polarity reversing means.