JPH01187753A - Superposed field energy analyzing device utilizing uneven electric field - Google Patents

Abstract

PURPOSE:To attain image focusing condition without astigmatism by giving the first and second terms of electric field such factors as in linear relation in a certain slope. CONSTITUTION:A superposed field type analyzer device includes a uniform magnetic field and an electrode and magnetic pole giving an electric field whose third term and higher in the electric field direction x orthogonally intersecting the mentioned magnetic field is ignorable, wherein the factors to the first and second terms of electric field are in linear relation in a certain slope. Magnetic field distribution according to this shape is for ex. such that the electrode is in cylindrical form, and the radius of curvature in its center is Re, and the shape of magnetic pole is not specifically restricted but uniform, and the first and second terms are small enough to ignore. The interelectrode distance Se is related to the distance between magnetic poles Sm as Se=Sm to give the relation Se>he, where he is the width of the electrode. This allows attainment of an image focusing condition without astigmatism even in case the interpolar gap is approx. equal to the gap between magnetic poles with lesser influence of the edge field.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a superimposed field energy analyzer, and particularly to a superimposed field energy analyzer that utilizes a non-uniform electric field to achieve astigmatism-free imaging conditions. It is related to.

[Conventional technology]

In the superimposed field energy analyzer (ExB type energy filter), which performs energy analysis by making the electric field and magnetic field orthogonal and making charged particles move straight in the direction perpendicular to the superimposed field, there is no lens effect in the direction of the magnetic field. The beam spreads according to the aperture angle of incidence, and even if a round beam is incident, the output beam becomes elongated and forms an astigmatic image.

On the other hand, various ideas have been proposed for EXB type energy filters that form images without astigmatism.

For example, use gradient magnetic poles as shown in Figure 4 to apply B to the magnetic field.
A gradient expressed by the formula y = Bw (1+ x/Rm) is provided to perform a convergence effect, and by making the electric field uniform, astigmatism-free imaging is performed. However, Rm is E
The radius of curvature of the magnetic field at the center of the ffi plane, which is approximately equal to the distance between the point where the extensions of the magnetic pole surfaces intersect and the magnetic pole center line.

Furthermore, as shown in Fig. 5, a cylindrical electrode is used in addition to the tilted magnetic pole, and E x = E w (1+ x / Re )
A method has also been proposed in which a nonuniform electric field expressed by the following equation is also added. However, Re is the radius of curvature of the cylindrical electrode. In this case, astigmatism-free imaging conditions are found by combining Rm and Re. Note that FIG. 4 is a special case of Re=■ in FIG. 5.

[Problem to be solved by the invention]

By the way, the things shown in Figures 4 and 5 are both S
There is a relationship b>Se, and the electric field is generally expressed as Ex-Ew (1+a, x+b, x" +c, x2 +
・・・・・・）・・・When expressed as in (1), b
The absence of terms a, C, . . . was an implicit premise of the astigmatism-free imaging condition. Conventionally, no consideration has been given as to whether the astigmatism-free imaging condition is violated when the terms of second order or higher cannot be ignored, or whether these higher order terms can be ignored. Furthermore, in electrodes where Se is much smaller than sb and therefore the electrode gap is much smaller than the width of the electrode, the terms of second order or higher are usually extremely small, and there is no need to consider their effects.

However, in this type of filter, one effective method for reducing the influence of the edge field is the Sb#Se filter as shown in FIG.
e, it becomes extremely difficult to control the electric field distribution. That is, in addition to the difficulty of adjusting the first-order coefficient a to an appropriate value, it is almost impossible to reduce the second-order and higher-order terms to zero.

The present invention is intended to solve the above-mentioned problems.
The present invention aims to provide a superimposed field energy analyzer using a non-uniform electric field that can eliminate the above-mentioned difficulties and provide astigmatism-free imaging in a filter.

(Means for Solving the Problems) For this purpose, the superimposed field energy analyzer using a non-uniform electric field of the present invention has a --like magnetic field and third-order or higher-order terms in the electric field direction X orthogonal to this can be ignored. A superimposed field analyzer having magnetic poles and electrodes that provide an electric field is characterized in that the JJJ coefficients of the !° order and the second order of the electric field are in a linear relationship with a predetermined slope.

[Effect]

The superimposed field energy analyzer using a non-uniform electric field of the present invention makes the magnetic field uniform, and when the electric field perpendicular to the magnetic field can ignore terms of third order or higher order, the first and second order terms of the electric field can be analyzed. By forming a linear relationship with a predetermined slope, it is possible to easily provide an astigmatism-free imaging condition even when the magnetic pole gap and the electrode gap are approximately equal.

〔Example〕

Examples will be described below with reference to the drawings.

Fig. 1 is a diagram showing the relationship between the first and second order coefficients of the non-uniform electric field in the present invention, Fig. 2 is a diagram showing the electron trajectory obtained in the present invention, and Fig. 3 is a diagram showing the superimposed field energy of the present invention. FIG. 2 is a diagram showing an example of the shape of electrodes and magnetic poles of an analyzer.

In Fig. 3, the electrode is cylindrical, and the radius of curvature at its center is Re.Although the shape of 11'M is not particularly limited here, it is cylindrical and has linear and quadratic terms. The electrode has a shape that gives an extremely small and negligible magnetic field distribution, and the distance Ss and the magnetic pole opening #Sm are Se=Sm, and therefore, when the width of the electrode is he, The relationship is Se>he. In other words, the magnetic pole shape does not create a term linearly proportional to X in the magnetic field distribution as in the case of Figures 4 and 5, and the electrode shape has a concentric circular shape so as to create terms a and x. do. However, since the width he of the electrode is small, the b0x2 term in equation (1) inevitably occurs. That is, in the present invention, the first-order terms aox and 2
The conditions for astigmatism-free imaging are realized by combining the following items x and x''.

Conventionally, the conditions for providing astigmatism-free imaging are as follows: 1 of the magnetic or electric field.
The following gradient (i.e., reverse the sign at the positive and negative points of X)
It has been thought that it is given by However, by calculating the orbits of electrons under various electric and magnetic fields, it is possible to create conditions for astigmatism-free imaging using the quadratic terms of the electric and magnetic fields (same sign regardless of whether X is positive or negative). I understand.

That is, when we set x=Ew (1+a, x+b, x''), we investigated the combinations of ao and , which perform astigmatism-free imaging, and found that the coefficient a is as shown in the following equation.

It has been found that it is sufficient to give , and by a linear relationship with a predetermined slope.

a,=a,. +'Q, 224 b, -(2) Here, the constant term aaa is the condition when there is no quadratic term, a, o=-(1/2Ro 1/Rv)"' (3
) can be expressed as Ro is the cyclotron radius, expressed as RO=t-/nπ, and is determined by the effective filter length. In the case of filter length = 70 Tsuru, 2Ro = 31.51, a,, -1/3
4, and Rr is a small correction term due to the presence of edge groups. FIG. 2 shows equation (2) in the case of filter length L = 70 mm. In the case of the filter used here, Rr=428 (Ryu-1).

In addition, when calculating for the case of L=4o*, /H, it becomes ago'''-1/27, and b,=o.

Assuming 2, a,. --0,0324.

When the electron trajectory was calculated using this value, as shown in FIG. 2, the trajectory in both directions was focused at Z=67m. Therefore, it can be seen that the coefficient of b, 0.224, is a constant that is independent of the filter length.

Therefore, if conditions are set to give the first and second coefficients of the electric field so as to satisfy equations (2) and (3), astigmatism can be achieved even under conditions where the magnetic pole gap and the electrode gap are almost equal. You can give images.

〔Effect of the invention〕

As described above, according to the present invention, when the magnetic field distribution is uniform and the electric field distribution cannot be ignored up to the second order term of
By selecting the following coefficients in a linear relationship with a predetermined slope, it is possible to perform astigmatism-free imaging, and there is no astigmatism even when the magnetic pole gap and the electrode gap are almost equal, reducing the influence of edge groups. It becomes possible to provide the following imaging conditions.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the conditions for astigmatism-free imaging;
The figure shows the trajectory, Figure 3 shows an example of the shape of the electrodes and magnetic poles of the superimposed field energy analyzer using a non-uniform electric field of the present invention, and Figure 4 shows the conventional superposition using gradient magnetic poles. Figure 5 shows a conventional energy analyzer using a non-uniform electric field; Figure 6 shows a conventional energy analyzer in which the distance between electrodes and the distance between magnetic poles are approximately equal. It is. Se...electrode gap, Sm...magnetic pole gap, he...
Electrode width. Applicant JEOL Ltd. Agent Patent Attorney Masanobu Hirukawa (4 others) Figure 1 Figure 2 Figure 3 S Figure 5 Figure 4 Figure 6

Claims (1)

[Claims] In a superimposed field analyzer that has magnetic poles and electrodes that provide a uniform magnetic field and an electric field in which third-order or higher-order terms in the electric field direction x perpendicular to this can be ignored, the coefficients of the first- and second-order terms of the electric field are A superimposed field energy analysis device using a non-uniform electric field, characterized in that the is a linear relationship with a predetermined slope.