JPS5986141A - Method of detecting axial shift of diaphragm in electron beam irradiation system - Google Patents

Abstract

PURPOSE:To accurately and easily detect axial shift by switching the focusing condition of an electron lens into two steps or more, line-scanning an electron beam on the specific area of a sample in the X or Y direction, detecting diffused electrons and x-rays, and plotting line profiles on a cathode-ray tube. CONSTITUTION:A switch is connected to a terminal (a) and a sample area B with an exceeding contrast is focused on a CRT screen. Then, the switch is changed over into a terminal (b) and excitation intensity is switched into two steps by the power supply 14 of an objective lens every horizontal scanning. In addition, the line-scanning is made on specific area B in the X direction indicated by a line L and a sample information signal is sent to the y deflector 13y of the cathode-ray tube and then a focal point profile P1 and a non-focal point profile P2 are displayed on the cathode-ray tube. When the axis of a diaphragm is aligned, both P1 and P2 appear in the center of the screen and the left and right skirts are intersected symmetrically. When the axis is not aligned, they are not intersected symmetrically. In this case, the axis must be aligned by actuating a drive mechanism 9. Furthermore, the axial alignment of the diaphragm in the Y direction is performed by changing the switch to a terminal (c).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting axis deviation of an aperture of an electron beam irradiation system in a scanning electron microscope, a transmission electron microscope, an Auger electron spectrometer, or the like.

For example, the electron beam irradiation system of a scanning electron microscope consists of an electron gun, multiple stages of focusing lenses, an electron beam deflection system for scanning the electron beam on the sample, etc. In order to reduce the size, it is necessary to provide a diaphragm for limiting the opening angle of the electron beam in or near the final stage focusing lens (objective lens). The size of this diaphragm is very small, and a diameter of several tens of microns to several hundred microns is usually used, making it extremely difficult to align the aperture with the optical axis.

In the conventional alignment method, an electron beam is scanned over a sample while repeatedly changing the excitation intensity of the objective lens, that is, the focal length 1llII, from the under side to the over side in multiple steps, and at this time, the electron beam scattered from the sample, e.g. Secondary electrons are detected and the signal is introduced into a cathode ray tube as a brightness modulation signal to form a sample image, and the aperture position is adjusted to minimize movement of the image projected on the cathode ray tube. Figures 1 and 2 explain the alignment of the aperture. Figure 1 shows the movement of the sample 1'+1 image on the cathode ray tube, and Figure 2 (zl).
is an optical diagram of the electron beam when the aperture is adjusted, Figure 2 (b
) is an optical diagram C when the aperture C is not included. In FIG. 1, 8 is an image of a specific area of the sample when the objective lens is excited to the top focus, and A' and A'' are images of the same sample when the objective lens is set to underfocus and A-bar focus. This is an image of a region.As can be seen from the figure, the image will be blurred and its position will change depending on the excitation conditions of the objective lens, such as when the aperture is not aligned with the optical axis.

Figure 2 hazono j1]! (a)
When the axis of the diaphragm AP is aligned with the optical axis as shown in the figure, the excitation of the objective lens OL is switched and the electron beam is focused on the di-1 cysteine force [after changing from EB+ to A-bar focus EB2, it lands on the i3I S. The central beams of both types of beams coincide with the optical axis. However, as shown in figure (b), if the aperture is not aligned with the optical axis, when switching from VS1 to focus E[3+ to A-bar focus EB2, not only the spot diameter will change on sample S. The position of the central beam is changing. This change in the position of the electron beam spot on the sample causes a change in the position of the image shown in FIG. 1.

Therefore, all you have to do is observe the changes (fluctuations) in the image shown in Figure 1 and adjust the aperture position by 11λ so that the fluctuations disappear, but in reality, as described above, the image A ′
and A II cause blurring as the position changes, so
There is a contradiction that if you increase the position change to make L't easier, the blur will increase, and if you reduce the blur, the position change will become smaller. This makes it very difficult to check the axis misalignment, and it is difficult to confirm the accuracy in operation and accuracy. There is a problem on the top.

The present invention aims to eliminate the above-mentioned drawbacks.
Its configuration is such that an aperture is inserted into the electron beam path of the electron beam irradiation system, and an electron lens is used to focus the electron beam and irradiate it onto the sample. A line is scanned across the direction, and electrons and X-rays scattered from the sample are detected by the scanning to detect the λ pole I! the electron beam is supplied to an Il tube to draw a line profile on the cathode ray tube, and the focusing conditions of the electron lens are switched in at least two stages, in each case to draw a line profile on the cathode ray tube. The feature lies in the method of detecting the axis deviation of the aperture in the electron beam irradiation system, which is displayed and compared with each other in an overlapping manner.

An embodiment of the present invention will be explained in detail below based on the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention.
indicates an electron gun. Iζ electron beam 2 emitted from the electron gun 1
is narrowly focused by the focusing lens 3 and objective lens 4 and projected onto the sample 5. 5x.

6■ is an electron beam deflection coil, 7x horizontal signal generator and 8 vertical scanning signals! It is connected to the single device 7y, and serves to direct the electron beam onto the sample 5 in a secondary manner. The deflection coils 6X and 6V may be placed behind the objective lens like an eyepiece, or they may be placed between the objective lens 4 and the focusing lens 3.1. A diaphragm 8 is disposed near the objective lens 4, and its position can be varied by 1 in every 9 directions of the drive I. The drive! e11Whatt:k It has a mechanism in the x and Y directions, and its movement direction is the deflection coil (3x
, 6y should match the deflection direction of the electron beam. For example, a secondary electron detector 10 is installed near the test 1'31.
is installed to detect secondary electrons scattered from the sample by electron beam irradiation.

Its output is supplied to the brightness modulation grid of the cathode ray tube 12 via the amplifier 11 and the a terminal of the switch S1. The electron beam deflectors 13x and 13y of the cathode ray tube 12 are supplied with switches S2 and S3 a from the scanning signal generators 7x and 7V, respectively.
A signal synchronized with the scanning of the irradiated electron beam is supplied via the terminal. As a result, a secondary electron scanned image of the sample 5 is displayed on the cathode ray tube. The B terminal of the switch S1 is connected to the Y deflector 13y of the cathode ray tube, and the C terminal is connected to the X deflector. The a terminal and the C terminal of the switch S2 are commonly connected to the deflector 13y of the cathode ray tube, and the b terminal is an open end. Further, the a terminal and the b terminal of the switch S3 are commonly connected to the deflector 13x of the cathode ray tube, and the C° terminal is an open end. These switches are operated in conjunction with each other; when the a terminal is selected, a secondary electron image of the sample is displayed on the cathode ray tube, and when the b terminal is selected, a video signal is supplied to the y deflector 13y. C
A line pronoisle in the X direction is displayed on Yin Jii line tube 1. Furthermore, when the C terminal is selected, the video signal from the detector is supplied to the X deflector 13
A line profile in the X direction is displayed on the line tube. Reference numeral 14 denotes a power supply for the objective lens, which is configured to supply a desired DC current and to switch the excitation intensity to a plurality of stages, for example, two stages, in synchronization with the scanning of the father-son beam.

1!11 The loading operation will be explained below with reference to FIG.

First, connect the switch to the a terminal, and try to irradiate the sample L with the electron beam. 1
Secondary electrons emitted from each part of the detector 10 are detected by the detector 10. The secondary electron signal is supplied to a brightness modulation grid of a cathode ray tube, and a sample image is displayed on the cathode ray tube. Therefore, while observing the image 1 (z), search for the sample area B (Fig. 4 (a)) with the extreme 1 to last 1, and move the sample area B to the center of the cathode FA tube video screen. Focus and set the appropriate A8 ratio.Next, switch the switch from terminal a to terminal b, and at the same time supply a current from the power supply 14 of the objective lens so that the excitation intensity can be switched to, for example, two levels every horizontal scan. In this state, the specific area B of the sample
(a) Line scanning is performed in the X direction as shown by line L in the figure, and the sample information signal obtained at that time is the yg of the cathode ray tube.
4 (b) on the cathode ray tube because it is sent to the
), the cured profile P1 is displayed on line L. (b) shows a line profile in the case of just focus, and the signal change due to region B is extreme, and this portion appears in the center of the screen. Then, in the next line scan, the excitation current of the objective lens is changed, and the focus of the electron beam scanning over the rotating line is moved, for example, to the under side. The line profile P2 at that time is displayed on the cathode ray tube superimposed on the line profile P1 at the time of 0IJ just-off A-cass (FIGS. 4(c) and 4(d)). The line profile can be seen as 114 display U9A due to the afterglow of the cathode ray tube if the scanning of the electron beam is fast to a certain extent. ll'l i:d line pronoisle P2 is a line that shows broad changes because the irradiated electron beam is in a defocused state compared to Pl. If the axes of the apertures are not aligned, P2 will appear at a position shifted from the center of Pl, as shown in Figure (C), and the intersection of Pl and P2 will not be symmetrical. On the other hand, when the axes of the diaphragm are aligned as Jζ shown in FIG. 3(C), both Pl and P2 appear at the center of the screen, and the left and right tails intersect symmetrically. Just by observing this condition, you can check whether the axis of the aperture is aligned, and if the condition is as shown in Fig. 4 (C), operate the aperture drive mechanism 9 shown in Fig. 3 to adjust the line pronoisle P1. P2 is the fourth
Adjust so that it becomes the state shown in figure (d). Once the adjustment in the X direction is completed in this way, if you change the switch to the C terminal and perform the same observation as above, the line pronoisle in the Y direction will be displayed on the cathode ray tube, and the same The axis alignment V of the aperture in the Y lj direction can be performed by operation and adjustment.

With the configuration described above, the alignment of the axis of the aperture can be easily and accurately detected by the state of intersection of the line pronoisles on the ζ447 tube, and the alignment of the aperture can be accurately determined. Be able to do it.

Note that the above is an example of the present invention, and various changes can be made when implementing the present invention. For example, in the above explanation, the excitation condition of the objective lens is switched to two stages: just focus and A-bar focus, but it is also possible to display a line profile by switching to three stages or more, up to under focus. You can also do it. Furthermore, in the embodiment shown in FIG. 3, the X-direction profile and the Y-direction profile are displayed in orthogonal directions on the cathode ray tube, but the Y-direction profile I is also the same as the X-direction profile in FIG. It can also be configured to be displayed in the same direction. Furthermore, the cathode ray tube for image display and the cathode ray tube for line profile display are separate; H) is good. Furthermore,
Information from the sample is not limited to secondary electron beams, but also reflected electron beams,
Transmission electron beams, X-rays, etc. can also be used in the same way.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams for explaining the outline of conventional aperture axis alignment, and Figure 3 is a block diagram of a device implementing the method of the present invention.
4 is an explanatory diagram of the operation of the device shown in FIG. 3. 1: Electron gun 2: Electron beam 3: Focusing lens 42 Objective lens 5: Sample 5x, 6y: Deflection coil 8
: Aperture 9 Two-aperture drive mechanism 10: Secondary electron detector 12: Cathode I! Jl tubes 13x, 13y: Electron beam deflector 14: Objective lens power supply Patent applicant: Ito Denshi Co., Ltd. Representative Mr. Ito

Claims (1)

[Claims] An aperture is inserted into the electron beam path of the electron beam irradiation system, and an electron lens focuses the electron beam onto the sample so that the electron beam crosses a specific area on the sample in the X or Y direction. The electrons and X-rays scattered from the sample are detected by the scanning and supplied to the cathode ray tube, so that a line profile is drawn on the cathode ray tube, and the electrons are focused. Change the conditions to at least two stages” (
A method for detecting aperture deviation in an electron beam irradiation system characterized by displaying and mutually comparing line profiles in each case superimposed on a cathode ray tube.