SU1084912A1 - Immersion system for focusing charged particle beam - Google Patents

Abstract

IMMERSION SYSTEM FOR FOCUSING A BUNCH OF CHARGED PARTICLES, containing in series electrodes arranged on one axis, made in the form of surfaces, forming which are parallel to the system's axis, characterized in that, in order to reduce aberrations and extend the range of beam shape adjustment, at least one of The electrodes are made of four parts, while the opposite parts are equal to each other, and the neighboring parts are different, and all parts are located at the same distance from the axis of the system. (ABOUT

Description

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The invention relates to electron optics, namely, electrostatic lenses, and can be used in the development of electrostatic analyzers, accelerators of charged particles, and beam transport systems.

. A known immersion system for focusing a beam of charged particles, containing several cylinders of the same diameter arranged in series on the same axis L.

In the known device, the beam is focused as a result of applying the difference in potential to the cylinders, which leads to the appearance of radially directed electric fields acting on the beam.

The disadvantage of the device is that it only works with a beam of circular cross section at the entrance and exit | And has large aberrations.

The closest technical solution to the invention is an immersion system for focusing a beam of charged particles, containing successively arranged on one axis electrodes, made in the form of surfaces, which form parallel to the axis of the system.

In the known device, the beam is focused by applying a potential difference to the electrodes, which leads to the appearance of radially directed: electric fields acting on the beam.

A disadvantage of the known device is the large amount of spherical aberration, which cannot be eliminated without the use of additional corrective electron-optical elements.

In addition, in the known device, the range of adjustment of the beam shape is limited. one

The aim of the invention is to reduce aberrations and expand the range of adjustment of the beam shape.

The goal is achieved by the fact that in an immersion system for focusing a beam of charged particles containing successively arranged on one axis electrodes, made in the form of surfaces, forming which are parallel to the axis of the system, at least one of the electrodes is made of four parts, with

In this case, the opposite parts are equal to each other, and the neighboring parts are different, and all parts are located at the same distance from the axis of the system.

Figures 1 and 2 depict an immersion system with round electrodes; in FIG. 3, sections A-A, B-B and B-B in FIG. G. in FIG. 4 — sections of GG and DD in FIG. 2, in FIG. 5 — the proposed system with square electrodes J in FIG. 6 —E-E sections of FIG. And 3-3 in FIG. 3.

. The device contains located on a common axis electrodes 1-3

at least one of which is made of four parts.

The device works as follows.

Electrodes 1 and 2 are supplied

the potentials Ф, and which determine the beam energy at the input and output of the system, i.e. they slow down or accelerate the beam of charged particles, and at the same time participate in focusing. On

the middle four electrode cut into 3 parts (for the 1st and Sh variants) the potentials are supplied so that two identical opposite parts have potential j and the other two

. the same opposite parts have potential Vj where Fa is axisymmetric and V is quadrupole component. Potentials. are selected in such a way that the beam of charged particles of a given shape is focused at a certain place. All this remains true even if the first or third electrodes are cut.

For G) -th option proposed

the system (Fig. 3), in which both electrodes are cut, the potentials are supplied as follows: a potential is applied to electrode 1: Φ i V to an electrode ± 2. When the beam energy Yag / P is changed, the potentials Vj and Vg are chosen so that the beam with the given initial conditions was focused in the required

place :

The lengths of the adjacent sides of the cut electrodes are chosen from the conditions of minimizing third order aberration coefficients. Angular clearance of

(FIG. 3) or the distance between adjacent flat d-d electrodes should be small (о С О, 1 rad 0.8 і f. 0.9 оО, 1,0). In the opposite case, the interfering fields will penetrate into the area occupied by the beam and violate the conditions of focusing and correction. The third order spherical aberration coefficients in the X O Z plane of the proposed system are calculated using the following formulas with ,,, Al ;;,. 27 ..) - 0 total coefficients of spherical aberration, Ships. spherical aberration coefficients of individual lenses, 1Г (nl-l, linear increases in the part of the system, located frn-h in front of the h-th lens in the plane), respectively. The expressions for the coefficients of aberration in the plane y O t; are obtained from the expression (1) by replacing the X and Y indices. Below are the results of calculating the operating modes of the system under consideration, which converts a round beam into a wedge-shaped one (beam parallel to axis 2 in the plane, WHERE is a quadrupole; It is collecting) and elliptical, o Option 1. The system consists of three cylinders of the same diameter D, the last of which (electrode 2, Fig. 1) is cut into four parts, the length of the average electric p is the distance between adjacent cylinders Oh oh, ID. Potential ratios of a are chosen as follows: 1) π / 10. 10. It. The distance from the object to the center of the middle electrode in the planes, the quadrupole component is collecting (O (c) and scattering) () equal to (3c - D, the distance from the center of the middle electrode to the image in the same planes. 5D , oo., Parameters characterizing the first-order electron-optical properties are given in Table 1. Table 1

Here, 1o and io (Fo) HZ (the focal lengths and focal positions of the axisymmetric component in the object and image space, respectively, fp and Z (fc), the focal lengths and positions of the quadrupole component foci in the collecting plane, IQC is the focal distance

3here MO. An increase in the axisymmetric component;

 (i is the angular size of the opposite parts of the cut-off system as a whole. All the electron-optical parameters here and hereinafter are given in units of D

The coefficients characterizing the spherical aberration of the third order of the system in the plane, where the quadrupole component is collecting, are given in Table 2.

table 2

whom cylinder

aJ is the angular distance between adjacent parts (Fig. 1). At angle jf, the spherical aberration coefficient of the proposed system is 7-8 times less than at | 90, when the last electrode is cut into equal parts, i.e. octupole component missing. The spherical aberration of the proposed system is less than the aberration of the axisymmetric lens C.j of the known system more than twice. Option And, The system consists of two cylinders, each of which is cut into a four-piece part. The ratios of potentials 2 of the second cylinder and TI - Yervoi are selected as follows: 1) 92 / Pi 0.5, 2) The lengths of both cylinders are 1, bD is the distance between the cylinders O, ID. The following geometrical parameters remained constant in both cases; the distance from the object to the first cylinder is 2.5 D, the distance from the second cylinder to the image (101). The calculation of the potentials V and V, ensuring the formation of an elliptical beam with the given parameter mp, carried out on a computer by numerical solution of the motion equation aal 1), 5, V, №, 0.042,, Of8; 2) 2W 0.2, v; (9.0.019, 0.004. In a system containing two cylinders cut into four unequal parts, you can reduce (and for the Hi section) K modes and completely correct) two spherical aberration coefficients that determine li Fg / g. 2 linear images along the entire length of the line. So at angles y, 68 and y 94 °, the coefficients of spherical aberration Shg. 1 0.2 in absolute value less than at) f, 2 90 ° by 5.3 times and 2.3 times, respectively. , 5 both coefficients Cd and are zero at 5f 68 ° and f2 94 Spherical aberration of the proposed system is less than the aberration known more than 4 times in both cases. Option 111. The system consists of three square electrodes. Cut on the chip part of the last electrode. At the same initial values of the geometric and electrical parameters that were taken for option I, the first-order focusing properties remain unchanged (Table O. The aberration properties of the system change. The spherical aberration coefficient Cxjr of the proposed system is less consisting of three square electrodes (4 1), 1.7 times at 91 / F1 2 and 1.2 times at 10). Thus, the proposed immersion system forms beams of various shapes (round, elliptical, wedge-shaped, etc.) and, at the same time, has 1.2-4 times less aberrations compared to the known system.

Claims (1)

IMMERSION SYSTEM FOR FOCUSING A BEAM OF CHARGED PARTICLES, comprising sequentially arranged on one axis electrodes made in the form of surfaces, the generatrix of which is parallel to the axis of the system, characterized in that, in order to reduce aberrations and expand the range of adjustment of the beam shape, at least one of the electrodes made of four parts, while the opposite parts are equal to each other, and the neighboring ones are different, and all parts are located at the same distance from the axis of the system. SU „„ 1084912 ί