JPS6171539A - Irradiation system of electron beam equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an improvement in a lens system for an electron beam device, particularly a focusing lens system in an electron beam device.

(2) Prior art and its problems In electron beam equipment, especially transmission electron microscopes, the basic role of the focusing lens is to create illumination with high magnification, strong illumination intensity, and high coherence, and to illuminate the sample. It plays a variety of roles, including creating nanometer-sized electronic globes for performing microanalysis, and creating wide, well-parallel illumination for low-magnification, wide-field observation. A conventional example of an imaging system incorporating a focusing lens having such a role is shown in FIG. 1, for example.

This consists of a 1'fkL sub-ray source (hereinafter referred to as a light source for convenience) 1, a first-stage focusing lens 2 and a second-stage focusing lens 3 placed behind this light source 1, and a It has a focusing lens diaphragm (hereinafter simply referred to as diaphragm) 4 arranged therein, and a sample 5 is arranged behind the diaphragm 4 in the objective lens section. A light source 1 is installed at a position S on an electron beam axis (hereinafter referred to as optical axis) 6 of the irradiation system, and emits an electron beam from here. The illumination diameter of the electron beam incident on the sample 5 can be changed by adjusting the excitation of the second stage focusing lens 3.

That is, as is clear from FIG. 1, the illumination diameter on the sample 5 is determined by determining the light source image formed by the second stage focusing lens 3, indicated by Q1...Qn in the same figure. . In order to vary the illumination diameter, the second stage focusing lens 3
The light source image (this is especially referred to as the second light source image) Q formed by the lens 3 is changed to Ql on the optical axis 6.
This is done by moving from to Qn. During this time, the first stage focusing lens 2 is excited and fixed so as to keep its light source image P at one of the positions Pl to Pn. The first stage focusing lens 2 has the role of controlling the flow of electrons passing through the aperture 4 and reaching the sample 5.

Then, the position of the light source image (hereinafter referred to as the first light source image) P formed by the first stage focusing lens 2 changes from Pl to P.
As the distance from the first-stage focusing lens 2 to n is increased, the cut of the electron flow emitted from the light source 1 by the aperture 4 decreases, and the electron flow increases. The illumination intensity of the electron beam was
It is calculated by dividing the total electron flow reaching the surface by the illuminated area.

Normally, the illumination intensity is changed by keeping the excitation intensity of the first stage focusing lens 2 unchanged (that is, the electron flow is constant), and by changing only the excitation of the second stage focusing lens 3, the irradiation area on the surface of the sample 5 is changed. In the case of an illumination system that performs continuous illumination, it is impossible to limit the illumination to only a portion corresponding to the observation field, and if the illumination intensity is too strong, it is necessary to significantly increase the illumination diameter. Due to this increase in the illumination diameter, the sample 5 is irradiated beyond the observation field of view on the sample 5 surface.
Irradiation of unobserved areas should be avoided as much as possible. Because,
In particular, for specimens that are easily damaged by electron beam irradiation, such as living organisms and polymeric materials, the non-observation area should be irradiated with the electron beam in advance.
This is because if the non-observation part comes into the observation field by changing the observation part to the arrow, this part may be damaged.

In this way, the sample 5 is extremely sensitive to electron beam irradiation.
When observing, please adjust the brightness of the electron gun.
Although the irradiation intensity can be changed without changing the illumination diameter of the electron beam, it is necessary to change the constants of the high-voltage circuit in order to adjust the brightness of the electron gun, which requires frequent operations.

An alternative method for adjusting the illumination intensity is to widen the illumination diameter using the second stage focusing lens 3, while minimizing irradiation outside the observation field of view by reducing the diameter of the aperture 4.

However, the diaphragm 4 is usually only available in a maximum of four different diameters, and it is difficult to accommodate changes in illumination intensity over many stages. Furthermore, accurate alignment of the aperture holes is required each time the aperture 4 is switched, which is troublesome in operation.

Furthermore, as a method for adjusting the pond, in the irradiation system shown in FIG. If the imaging position of the first light source image P is changed to Pn in order to increase the imaging position, it is impossible to change the illumination intensity while the imaging position of the second light source image Q remains Qn.

Looking at the adjustment of the irradiation system up to f'L, the brightness setting of the electron gun, the selection of the hole diameter of the aperture 4, and the excitation setting of the first focusing lens 2 are all set as the initial settings of the observation conditions. Once the appropriate value has been set, the settings are not changed much. Therefore, normally, the illumination diameter is changed only by variable excitation of the second stage focusing lens 3, and the illumination intensity is controlled. This occurs because when observing sample 5, emphasis is placed on speeding up the operation, and as a result, they are unable to take care of the preservation of the sample (preventing spider damage). is the reality.

(3) Purpose of the Invention The present invention has been made in view of the above-mentioned problems in the past, and the purpose is to smoothly adjust the illumination diameter and illumination intensity of the electron beam on the sample surface without causing unnecessary damage to the sample. The object of the present invention is to solve the above-mentioned conventional problems by providing an irradiation system for an electron beam device that can be used without any problems.

(4) Structure of the invention In order to achieve the above object, the invention includes at least two stages of focusing lenses as a focusing lens system, and the first focusing lens has an image of the electron beam source located at a position S on the electron beam axis. In order to form the L′-th sclerotic source image at arbitrary n positions PI, P2゜..., PnK, SPI, SPz,...*・'', SP
While the excitation can be varied so that n satisfies a conjugate relationship in terms of the element theory, the second focusing lens converts the first electron beam source image to a predetermined position 1fQ1 . Qz.

. . . +QmK 2' The main purpose of this article is to make it possible to vary the excitation in response to changes in the first electron beam source image in order to obtain a second electron beam source image.

(5) Description of examples FIGS. 2 to 4 are diagrams showing one embodiment of the present invention.

Similar to the irradiation system mentioned in the conventional example above, the irradiation system at the head of the forest in this example includes a light source 1, a first converging lens 2 arranged behind the light source 1, and a first focusing lens 2 disposed behind the light source 1. A two-stage focusing lens 3 and an aperture 4 located behind the second-stage focusing lens 3
A sample 5 is placed behind the aperture 4 and in the objective lens portion. The light source 1 is installed at a position S on the optical axis G of the irradiation system, and emits electrons a from here.

In this embodiment, the light source image formed by the second stage focusing lens 3 cannot be set continuously as in the conventional case, but is set in m pieces as Qiv Q21 -e---, Qm in the figure. The excitation is adjusted so that it takes only a fixed position. In the example shown in FIG. 2, the first light source image P is first formed at the position Pt by the first focusing lens 2, and the second stage focusing lens 3
forms the second light source image Q at the Q1 position. Next, the excitation of the first focusing lens 2 is changed to the position of the first light source image.
2゜P3. ..., encourage FI to become Pn! 1, and even if the excitation 5g of the first focusing lens 2 is changed in this way, the imaging position of the second light source image remains at 91 points. Between the image P and the second light source image Q, Initially, PIQ1 was in a conjugate relationship, but from then on, conjugate relationships such as PzQl, P3Q1, 1''''@, and PnQl are established.

In the conventional example shown in FIG. 1, the excitation k of the second stage focusing lens,
Since it remains fixed so that PIQi, when the imaging position of the first light source image P is moved from Pl to Pn K, the imaging position of the second light source image Q moves from Ql to Qll. be.

With the above-described aspect of this embodiment, only the illumination intensity is variably controlled while the illumination diameter is kept strictly constant. The illumination intensity is such that the imaging position of the first light source image P is P
It increases as you move from l to Pn. This is because the ratio of the electron flow passing through the aperture to the total electron flow emitted from the light source 1 gradually increases.

In the example of FIG. 3, contrary to the example of FIG. 2, the imaging position of the first light source image P is fixed to Pn, and the imaging position of the second light source Q is
The excitation of the second stage focusing lens is varied so as to vary sequentially from 1 to 2.

According to this electron beam irradiation mode, the first stage focusing lens 2
Since the imaging position of the first light source image P has not changed,
The electron flow passing through the diaphragm 4 does not change at all, and as the imaging position of the second light source image moves from Ql to Qm, the illumination diameter of the electron beam hitting the sample 5 gradually decreases. ing.

Therefore, in the example of FIG. 3, the first stage focusing lens 2
are PnQl, PnQ for the excitation with (S, Pn) conjugated.
21..., PnQm, the excitation is sequentially changed so that a conjugate relationship such as PnQm is established.

In the example of FIG. 2, the imaging position of the second light source image Q is fixed at Ql, and the imaging position of the first light source image P is moved arbitrarily to change the irradiation intensity, and in the example of FIG. The imaging position of the image P is fixed at Pn, and the imaging position of the second light source image is moved arbitrarily to change the illumination diameter, but the Q imaging point is changed to QI I Qz +・
...+ Select any one of QmO and fix it and move the P imaging point, or conversely, move the P imaging point to Pl, Pz,...
・To select and fix any one of Pn and move the Q imaging point, proceed as follows.

Table 1 M I M 2 Stored in a storage device in which a matrix M2 of 1 row and m columns as shown in Table 1 was formed, and a matrix of n rows and 1 column of the excitation 'i current value of the first focusing lens. Store it in the storage device where M1 was created. Then, P imaging point t−Pl
When changing from Pn to Pn, address is specified in the direction of changing the row by 110th, the excitation current values of the first-stage focusing lens 2 and the second-stage focusing lens 3 are read, and the Q imaging point is changed from Ql to Qm. When changing to , addresses are specified in the direction of sequentially changing the columns, and the excitation current values of the first stage focusing lens 2 and the second stage focusing lens 3 are read out. Based on the nine excitation current values thus read out, the excitation of the first-stage focusing lenses 2 and W and the second-stage focusing lens 3 is controlled.

In this way, the illumination diameter or illumination intensity can be adjusted with full efficiency.

FIG. 4 is a diagram showing a modification of the irradiation system of the electron beam apparatus shown in FIGS. 2 and 3. In this modification, an additional focusing lens 1o is provided above the first stage focusing lens 2 in the above embodiment. This additional focusing lens 10 is S
SR1 so as to connect the image of the light source 1 at the position R1, Rz, "., Rn determined as the front stage light source image.
, SRz, SR3, . . . , SRn are variable in excitation so that they form a conjugate pair.

On the other hand, the first stage focusing lens 2 has RIP, RzP, R3 regardless of which point the front stage light source image is formed at.
Excitation is synchronously variable so that P, . . . , RnP form a conjugate pair.

If this method is adopted, the excitation of the second stage focusing lens 3 and the imaging position of the second light source image Q can have a one-to-one correspondence relationship since the imaging point P does not move.

In the examples shown in Figures 2 and 3, in order to change the illumination intensity, the P imaging point must be moved back and forth, so the position of the P imaging point is not specified in addition to the position of the Q imaging point. Therefore, the excitation value of the second lens cannot be determined. That is, for example, for the Q1 position, PIQI, P2 Ql, ”・, n of PnQs
The excitation values of flist correspond to each other and do not have a simple relationship of l to l.

However, in the example of FIG. 4, although the P imaging point is fixed, the illumination intensity can be changed freely. In this example, the closer the R imaging point is to the front-stage focusing lens 10, the more the electron flow that is blocked by the aperture 4 increases, and the more the electron flow that passes through it decreases. Therefore, the illumination intensity can be reduced. Further, the second stage focusing lens 3 is connected to the front stage focusing lens 10.
Alternatively, since no excitation operation is performed in relation to any of the first stage focusing lenses 2, the excitation can be freely varied. Therefore, the imaging position of the second light source image Q formed by the second stage focusing lens 3 is set as in the above example <Ql, Q2.
...+ It is not necessary to limit the number to m as in Qm, and it is possible to move it finely to the extreme state. As a result, the diameter of the beam can be varied continuously. It is also possible to set the illumination diameter to an arbitrary size and quickly switch the intensity in n steps without changing the diameter at all.

Furthermore, another great advantage is that the Q imaging point can be precisely aligned on the sample.

Regarding this point, in the examples shown in Figures 2 and 3, the shift kJJ of the Q imaging point is relatively rough, so it is extremely difficult to make the Qti imaging point coincident on the entire sample surface. Become.

Table 2 M3 M4 Table 2 above shows the excitation control method for the electron beam irradiation system shown in Fig. 4, where M3 is a storage device for controlling the front-stage focusing lens 10. IJ sock M4 is the first-stage focusing lens. Represents a storage matrix for lens 2 control. Both are n rows 1
The illumination intensity can be changed by reading out the M3 and M4 matrices simultaneously in the vertical direction and giving the instruction to the power supply unit to control the front-stage focusing lens 10 and the first-stage focusing lens 2. The configuration of the storage device is further simplified.

(6) As described in detail, according to the present invention, an electron beam device is provided with at least two stages of focusing lenses, and these focusing lenses are excitation-variable in conjunction with each other, and each focusing lens forms an image. Since the light source image can be set at a plurality of positions, it is possible to adjust the illumination intensity and the illumination diameter with extremely simple operations.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a conventional example of an electron beam irradiation system of an electron beam device, and FIG. FIG. 3 is a schematic diagram showing another example of operation in a configuration similar to that of FIG. 2, and FIG. 4 is a schematic diagram showing another configuration of an electron beam irradiation system to which the present invention is applied and an example of its operation. 1.--Light source (electronic Y) 2.-1st stage focusing lens 3..2nd stage focusing lens 4..Aperture 5..Sample P..1st light source image Q..・Second light source image

Claims (1)

[Claims] 1) At least two stages of excitation variable focusing lenses, a first stage and a second stage adjacent to the upper side of the focusing lens aperture that limit the electron beam irradiated onto the sample, in order from the light source side. The first stage focusing lens first focuses an image of the electron beam source at a position S on the electron beam axis at an arbitrary number n of positions P_1, P_2, ..., Pn.
In order to form an electron beam source image, SP_1, SP_2, SP_3, . In order to focus the source image as a second electron beam source image at a predetermined position Q_1Q_2...Qm of an arbitrary number of meters, the imaging position of the first electron beam source image is set to P_
When it is 1, P_1Q_1, P_1Q_2, P_1Q
_3,...P_2Q_1, P_2Q_2, P_2Q_3 so that P_1Qm satisfies the electron-optical conjugate relationship, and when the imaging position of the first electron beam source image is P_2.
,...In such a way that P_2Qm satisfies the electron-optical conjugate relationship, and in the same manner, when the imaging position of the first electron beam source image is Pn, PnQ_1, PnQ_2, PnQ_3, ...Pn
An irradiation system for an electron beam apparatus, characterized in that excitation can be varied in response to changes in the first electron beam source image so that Qm satisfies an electron-optical conjugate relationship. 2) The first stage focusing lens converts the first electron beam source image into P_1, P_
2, ..., Pn, while the second stage focusing lens focuses the second electron beam source image at any position Q_1, Q_2, ..., Qm. 2. The irradiation system of an electron beam apparatus according to claim 1, wherein the irradiation system is variable in excitation so as to be connected in a variable manner. 3) The first stage focusing lens converts the first electron beam source image into P_1, P_
2, ..., Pn, while the second stage focusing lens focuses the second electron beam source image at any of the positions Q_1, Q_2, ..., Qm. 2. The irradiation system of an electron beam apparatus according to claim 1, wherein the irradiation system is variable in excitation so as to connect to any one position. 4) Adjacent to the upper side of the focusing lens aperture that limits the electron beam irradiated onto the sample, the front stage, first stage, and second stage are arranged in order from the light source side.
and at least three stages of variable excitation focusing lenses;
The front-stage focusing lens focuses an image of the electron beam source located at a position S on the electron beam axis at an arbitrary number of positions R_1, R_2, . . . , Rn as a front-stage electron beam source image SR_1, SR_2, SR_3,... ..., while the excitation can be varied so that SRn satisfies an electron-optical conjugate relationship, the first-stage focusing lens is capable of controlling the first-stage electron beam source at any imaging position of the previous-stage electron beam source image. An irradiation system for an electron beam apparatus, characterized in that excitation can be varied so that R_1P, R_2P, R_3P, .