SU1557603A1 - Electrostatic deflecting system - Google Patents

Abstract

The invention relates to electron optics and can be used in the development of instruments with a scanned beam across the surface in two mutually perpendicular directions. The purpose of the invention is to increase the sensitivity of the deviation and expand the functionality — it is achieved by deflecting the particles in two mutually perpendicular directions. The deviating system contains an even or an odd number of pairs of opposite electrodes 1, 2, 3, 4, 5, 6 having two mutually perpendicular antisymmetry planes, along the intersection line of which the longitudinal axis of the device is directed, in the direction of which the deflected particles are shifted. The electrodes that are opposite in each pair are connected to voltage sources 7 and 8 of opposite polarity, thereby ensuring that particles are deflected in a vertical plane. In addition, for each pair of electrodes opposite to the vertical plane of antisymmetry, additional displacements of potentials of opposite sign are applied, which ensure the deflection of particles in the horizontal plane. The invention is characterized by increased deviation sensitivity and small aberrations. 4 hp f-ly, 3 ill.

Description

+ vs; jarctg Lth (5

(1) ifr.

ft-x,, b v p l; I

„....) tg (.r rj | i

where A;., 1, + la + ... 1,;

   ;, + 1 ;.

Sizes 1 and d are shown in FIG. 1. Potentials and +; Vij, symmetrical with respect to the XOZ and YOZ planes and antisymmetric with respect to the YOZ and XOZ planes, respectively, provide deflection in the horizontal and vertical directions. The coefficients at the first harmonic in the decomposition of the potential (1) in the form of r yes in powers of m x, y, are responsible

The deviations for sensitivity are:

0

k - z: g

.v .....

i / and "

CM V,

fl,

to

five

 but

 ,,

(2)

The coefficients at higher harmonics in the potential decomposition (1), which determine the inhomogeneity of the deflecting field, are equal to:

 Jx

Coefficients K ss KT, etc. recorded in the same way. As the number of harmonics increases, the magnitudes of the coefficients decrease.

The sensitivity of the deviation in the direction perpendicular to the plates is equal to the sensitivity of the plane capacitor at 1.4 ... and 1 and for large i

width of the plates. So for - 3

, a 0.9998; KZU 2, B5-Yu dl

-jj- 5 K, at 1,0000, K 1.14.105

Thus, starting with -: - 3,

but

component field E and almost constant. Therefore, the supply of potentials + Vu to each pair of opposite electrodes ensures a high uniformity of the field in the direction perpendicular to the electrodes,

Consider the deviation in the direction parallel to the electrodes. For the simplest design and power, i.e. for the case of two pairs of electrodes, we have: V + V c - Vj - on the opposite electrodes to the left of the vertical symmetry plane and V + V u + + V, (- on the right, this means that Ј - 1. At the same time, 0.996; K3lf - 0.413; Ksx 0.254. The introduction of additional pairs of electrodes with a width of

varying between 0.2 --- i 1,

allows to obtain the conditions for vanishing coefficients at the third, fifth, etc. harmonics in the decomposition potential. So, with three pairs of elec

Trodes with a width of -t- 0.57 and -j- - aa

 2 ,, either at -Ј 0.56 and -y-aa

 4.44 (i.e., at 0.56 ± 0.01,

but"

-t-2,4 -4,4) from formula (3) we have Kjjt 0 at JT, 0, g 1. At four

five

0,

rex pairs of electrodes with a width

d

 0.85 and -1- 2.15, we have K, x - K5A

5 0 at jf4 0.19 and fft- 1 and t, d. Thus, with an increase in the number of pairs of electrodes, it is possible to reach the field of any desired uniformity.

Going beyond these limits affects the uniformity of the floor, the sensitivity of the deviation. With medium width

electrodes --- from 0.2 the heterogeneity of the field increases greatly. So, at - 0.16 and - 3.84 in order

in order for K) s to be zero, you must have -0.91 and | ° 2 1, with 0.80, the residual coefficient is large (K5 -0.35), and the number of pairs of electrodes is four instead of three, as in mode. When the width of the medium5 of these electrodes --1 1 decreases

deviation sensitivity. So, with --- 1.5 and --- 2.5, the uniformity of the floor is high, K3 0, Ku 0.04, but the coefficient K, - 0.32, i.e. deviation sensitivity is two times lower than in the proposed modes.

5 Power mode, in which | O is of the greatest interest, since in this case both pairs of middle electrodes, adjacent to the vertical plane of symmetry to the left and right of it, have the same potential ± Vu, i.e. can be performed as a unit. The power supply mode „1 is rational, providing the supply to the extreme pairs of the same 5 potentials for any number of electrode pairs as a sum of | (difference) of the main stresses defining the required voltage deviation (± Vu VX). Overshoot

71

() degrades the sensitivity of the deviation in the parallel direction, since in order to achieve the same intrinsic sensitivity instead of 1, it is necessary to apply} B. Going below the lower limit worsens the uniformity of the field (see, for example, example 4 to 0.91). Thus, with the observance of the indicated limits of variation of electrical and geometrical parameters, the best positive effect is achieved. With the same effective lengths of the deflection systems and the same accelerating voltages, the intrinsic sensitivity of the deflection is determined as follows:

to Јikb (

0 Sdif l;

w

where 2d is the distance between the opposite electrodes;

L is the length of the system along the longitudinal axis;

tf is the accelerating voltage;

K - coefficient of the main

harmonics determined by the shape and arrangement of the electrodes.

Comparison () taking into account the value - „-, Ј .а

with known deflecting systems with the same dimensions, it shows that the sensitivity of deviation of new systems with the proposed feeding methods is 1.6-6.6 times greater, i.e. a positive effect is achieved, with the number of pairs of electrodes in the new systems being less or equally, and the homogeneity of the floor is higher (residual coefficients in the decomposition of the potential) compared with the known ones.

Claims (1)

Invention Formula 1 "Electrostatic deflection system containing a pair of flat pro- opposing electrodes arranged in parallel to one another and possessing a plane of antisymmetry, which is so wise that, in order to increase the sensitivity of deviation and enhancement of functionality by deflecting particles in two mutually perpendicular directions, additional / pair of planar opposite electrodes with an additional antisymmetry plane perpendicular to the first antisymmetry plane. 2, The system of claim 1, wherein the conditions are met 3 Ј - {- 65; 0.2 P1 1 where 0 s 0 2L is the total length of the deflecting system, and 1 {is the length of a pair of electrodes with the sequence number i along the first antisymmetry plane; 2d is the distance between plane-parallel electrodes along the additional antisymmetry plane,, 2, 3, ..., n is the sequence number of electrode pairs when counting to the left and to the right of the additional antisymmetry plane. 3. The system according to claims 1 and 2, characterized in that the total number of pairs of electrodes is equal to three conditions: 1.12  1.16. k. A system according to claims 1 and 2, characterized in that the total number of electrode pairs is four and conditions are met: 0.8 ---- 0.86, d 5. A system according to claims 1 and 2, characterized in that the total number of pairs of electrodes is equal to five and the following conditions are met: 0.8. ---- 0.52; 0.78 -Ј from 0.80. f1 / FIG. 2 one -X Pi / e.Z