JPS59154732A - Magnetic field type deflector - Google Patents

Abstract

PURPOSE:To simultaneously eliminate 3rd order and 5th order aberrations without concentration of coil opening angle by fixing the optical axis and making constant a distance between the axis and coordinate point setting cylindrical coordinate with a rotating angle of theta to the coordinate point of particular first and second groups. CONSTITUTION:Considered here is a quadrilateral PQRS where the opposing sides indicated by a broken line are parallel each other to the theta1 and theta2 axes and the corners are placed on a solid line 4 and a dash-dot-dash line 5. When two pairs of opening half angles at the points P and Q are considered respectively as thetaa, thetab and thetac and thetad, since the point P combining thetaa and thetab and the point R combining thetac and thetad exist on the solid line 4, it is apparent that there is no deflected four-fold aberration of third order. When thetaa, thetad and thetac, thetab are selected as two pairs of selections from the coil having these four opening half angles thetaa, thetad, the points Q and S existing on the dash-dot-dash line can be obtained respectively and in such a combination, the deflected four-fold aberration of fifth order can also be eliminated.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a magnetic field type deflector that controls the traveling direction of a charged particle beam using a magnetic field generated by passing a current through a deflection coil. The present invention is intended to reduce deflection aberrations, and can be used, for example, in ion beam exposure equipment and equipment for forming semiconductor IC patterns, electron beam exposure equipment, and the like.

[Prior art]

Generally, when a charged particle beam emitted from a charged particle source is deflected by a deflector, various four-fold aberrations related to deflection occur in addition to normal deflection aberrations.

The present invention focuses on the third-order and fifth-order four-fol
This invention relates to a magnetic field type deflector that simultaneously removes the d aberration component.

Usually, a saddle-type coil or a toroidal-type coil is used for a magnetic field type deflector, except for special ones. Figures 1 and 2 each illustrate a pair of coils that deflect charged particles in the y-axis direction by passing a current through the coils (arrows indicate the direction of the current) (hereinafter referred to as this). (referred to as the X coil). Here, 1 is the central axis of the coil (hereinafter referred to as the Z axis), which is usually made to coincide with the optical axis. Also, 2 and 3 are each 2 axes (center axis of the coil)
The two orthogonal coordinate axes X and Y axes are also 7
In both figures, (a) is a plan view of a pair of coils viewed from the axial direction, and ■ indicates the flow of current from the front to the back of the paper. , ■ is the opposite. Further, the broken line is an auxiliary line indicating that r is constant. In the following explanation, 1 is shown in the figure a++<, h is the length of the coil in the direction of the central axis, and r is the radius from the - point of the central axis of the coil to the coil on the plane perpendicular to the central axis including that point. Let it represent the distance in the direction, and also as the opening half angle θ.

In the case of an X coil, it is defined as the maximum angle between the windings that are symmetrical in the x-z plane or the center axis.

A conceptually clear four-fol, deflector without d aberrations.

This is achieved by overlapping the coils in Fig. 1 or 2 (so-called cosine winding) so that the density distribution of the number of turns of the coils constituting it is proportional to sin θ in the θ direction. Deflection of order four-fol
It has been revealed that d aberration does not occur [H, Oh
iwa, E, Goto, and A, Ono,
Electr:on, Com・mun, in J
apan p54-B, No, 12.44 (19
71)']. However, since the winding has a finite thickness and the coils are actually wound discretely, it is difficult to make a continuous cosine-wound deflector.

As an alternative to this, the most basic four-fo
ld aberration is the third-order deflection four-fo1. Since this is a d aberration, it may be possible to create a deflector that removes only this aberration. To do this, the length of the coil in the axial direction and the distance in the radial direction of the coil are equal, and Σsin color = 0...
・・・・・・・・・・・・Opening half-angle θ that satisfies (1)
By integrating one coil on the same two axes so that they perform a deflection action in the same direction (for example, all as an Are known. However, 1 set (
In 1), it is assumed that the current flowing through each fill is equal.

Here, if we limit θ to one angle (i=1), equation (1) holds true at θ1-60, which means that
This is equivalent to saying that third-order deflection four-fold aberration does not occur in a concentrated winding coil with an opening angle of 120°.

Next, considering two coils with different half-angles of opening (θI and θ2), Equation 2 (1) is sin 3θ1-1- sin 3θ220...
・・・・・・・・・・・・・・・・・・(2+, and there are countless combinations of 21 open half angles θ1 and θ2 that satisfy this. Indicated by solid line 4.

Here, the horizontal axis is θ and the vertical axis is θ2, and 0°≦θ1. θ2
The range of ≦90° is shown. That is, by selecting an appropriately large number of two pairs of coils each having an opening half angle that satisfies Equation 2 (2), the third-order deflection four-fo1. In order to produce a deflector without d aberration, it is possible to wind a coil with dispersed opening half angles. For example, if θ] is 0°<θ]<30°, θ2 becomes 60°<θ2<90°.

The opening half-angle of all the coils can be set to different values. This is important in the production of a highly accurate deflector, since overlapping of the windings can be avoided. However, the above matters only for the third-order deflection fouro1
This is a condition for a deflection coil without d aberration, and in an optical system that requires large deflection, only the third order is insufficient.

Therefore, if we obtain the conditional expressions corresponding to Equation (1) and Equation (2) for removing the fifth-order deflection four-fold aberration, we obtain Σsin 5θ, -0, respectively.・・・
・・・・・・・・・・+3+sin 5θ1+5in
5θ2-0 ・・・・・・・・・・・・・・・(4) Expressed as (E, Munro, Advances
in Electronics and Electro
n Physics, Supplement 13B
, pp73-131). Two opening half angles θ1 that satisfy this equation (4). There are also an infinite number of combinations of θ2, which are shown by the dashed-dotted line 5 in FIG.

Therefore, if the only condition is to remove the fifth-order deflection four-four-o-ld aberration, the coils can be appropriately distributed and wound as in the third-order case.

However, the condition that does not cause both third- and fifth-order deflection four-fold aberrations is to simultaneously satisfy Equation 1 (2) and Equation (4), which immediately results in (θ1.θ2)
= (6°.

66°) and (θ1.θ2)−(42°, 78°) (Here, θJ is set to θ2). These are the intersection points A of the solid line 4 and the dashed-dotted line 5 in FIG.
and B (corresponding. However, there are only two conditions that do not cause both the third-order and fifth-order deflection four-fo1.d aberrations, F-, notes A and B, so the specific In order to obtain a deflector with a constant deflection direction, two conditions are not satisfied and the opening angle is fixed and the coils are concentrated at these angular positions, which is not realistic.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and prevent the opening angles of the coils from concentrating.

Moreover, it is an object of the present invention to provide a magnetic field type deflector that can simultaneously eliminate third-order and fifth-order deflection four-rold aberrations.

[Summary of the invention]

Summary of the present invention is to achieve the above objects.

The placement position of the deflection coil and the optical axis of the charged particle beam are z I
'llll + Using a cylindrical coordinate system (z, r, θ) where r is the radial distance from the Z axis to the coil coordinate point and θ is the rotation angle around the z axis, calculate r and z. When the angle θ is constant and Δθ is an arbitrary angle, the coordinate points of the first group of 8 points determined by 42 degrees Δθ degrees, 78 J degrees Δθ degrees, 102 ± Δθ degrees, and 138 ± Δθ degrees, and r, z is the above r,
The same as the z value, the angle θ is 222 ± Δθ degrees, 258 ± Δθ degrees,
282 ± Δθ degrees, 16 coordinate points with the second group of 8 coordinate points determined by 318 ± Δθ degrees, or r,
When z is constant and angle θ: Δθ is an angle of 6 degrees or less, 6 ± Δθ degrees, 66 ± Δθ degrees, 114 ± Δθ degrees, 17
The coordinate points of the first group of 8 points determined by 4±Δθ degrees and 186±
Δθ degrees, 246±Δθ degrees, 294±Δθ degrees.

354" 1 with the coordinate points of the second group of 8 points determined by 2 Δθ degrees
The coordinate point positions of 6 points, and the positions of the 8 points of the first group □
All the currents existing at the gauge points have current element vectors equal to δi, ``all the currents existing at the eight coordinate points of the second group of paragraph 2 have current element vectors equal to −δ1, and furthermore, ``
The 16 coordinate points mentioned above allow for a tolerance corresponding to the thickness of the coil conducting wire through which the current flows.

[Embodiments of the invention]

Now, in FIG. 3, a quadrilateral P Q RS is assumed whose opposite sides are parallel to the θ1 axis and the θ2 axis, respectively, and whose sides are at the 2nd point of the solid line 4 and the dashed-dotted line 5, as shown by the broken lines in FIG. P
The opening half angle of the two pairs at the point is θ3. θb(θ]=θ3.
θ2−θl)), and the opening half angle of the two pairs at point R is θ
. , θd (θ1=θ., θ2−θd). Then (
Point P consisting of the combination of θa, θb) and (θC9θd)
Since the R point consisting of the combination is on the solid line 4'2, it is cubic 1
It is clear that there is no deflection four-fold aberration, but these four half-angles θ2. θb, θ0.
As a combination of two pairs from the coil with θd, (θ3.
If we choose θd) and (θ., θb), they become point Q and point 8, which are on the dashed line 5, respectively, and follow □
This is a combination in which the fifth-order deflection four-fold aberration also disappears. In other words, if a series of quadrilaterals can be drawn in Fig. 3, the four pairs of coils consisting of the opening half angle determined by the corner will have the third and fifth order deflections fo.
This deflector does not cause any ur-fold aberration. This is synonymous with what will be described in the second section. In other words, assuming that Equation 5 (2) and Equation (4) hold true, for any Δθ, 5in3(θl + 5in3(θ1−Δθ) of Δθ)4−5
in3 (θ2+Δ+5in3(θ2−Δ=O15
) sin5(θl+Δ1-5in5 (θ1−Δ−1sin5(θ2−Δ+5in5(θ2−Δ−0−
It is clear from the formula of trigonometric functions that =+61 holds true. Moreover, these equations (5) and 2 equations (6) both satisfy equation (1) and equation (3) when each becomes 4.
It is also clear that the solution is the 3rd and 5th order deflection r
This shows that a deflector that does not cause our-fold aberration can be obtained. The four opening half angles mentioned here are 6 + Δθ degrees, 66 ± Δθ degrees, assuming that equations (2) and (4) hold true.
... (7) or 42-1=Δθ degrees, 78±Δθ degrees...
(8). Therefore, these equations (7) or (8)
Accordingly, it is possible to obtain a deflector consisting of four coils for one Δθ, and it is also possible to obtain a deflector consisting of another four pairs of coils depending on the value of Δθ. and.

All of these are [3rd and 5th order deflection four
fo1. This is a deflector that does not produce d aberration. In addition.

The opening half angle θ determined by equation (7) or equation (8) is Δ
Depending on how θ is selected, θ may be 9o°, but in that case, by adopting 180°-θ as the opening half-angle θ, four pairs of deflections without third- and fifth-order four-fol and d aberrations can be obtained. It is obvious that it is a set. In particular, the first rule is to avoid opening half angles that are negative or greater than 90°.
In Equation 2 (7), oo〈Δθ〈6° Equation 2 (
In 8), all opening half angles of the coils included in each cent can be made different from each other by setting the range Oo<Δθ<12°. For example, Δθ
Assuming 1°, 2°, and 3°, the opening half angle 1 of each coil is (41°, 43°, 7
7°, 79°), (4044°, 76°, 80'),
(39°, 45°, 75°, 81°), and the opening half angles do not have the same value. FIG. 4 shows a plan view of a deflector made up of four pairs of coils viewed from the axial direction at an angle of Δθ-3°.

It is also important to note that there is no restriction on the length h (coil radius r) of the coils in the axial direction between the deflectors made up of four pairs of coils that satisfy the above conditions. That is, although deflectors are often manufactured with a constant coil radius r, in this case, by varying the length h of the coil of each deflector, even in the case of a saddle-type deflector, the arc portion can be made heavier. (To be precise, in the case of saddle-type coils, the arc parts overlap only for the four pairs of coils included in one deflector, but
The manufacturing problem can be eliminated by using printed coils.

Next, it should be mentioned that the above two points are not limited to deflectors such as saddle type or troital type, but also apply to general deflectors.

In the following explanation, the coordinate system is a cylindrical coordinate system (r+θ, z
), 2 is the axis of the cylindrical surface, r is the radial direction,
Let θ indicate the direction of rotation. Let the unit vectors in the r, θ, and r axis directions be n, to, and c. Further, assuming that a current flows through one coordinate point of the cylindrical coordinates, each direction component of the current at that coordinate point is δ14. δ] When θ and δ12, δ1-a・δir+b・δiθ0C・δ12
・ ・・・・ ・・・+91 will be called the current element vector flowing through that coordinate point.

Then, the deflector has the same r and z values, and θ is 18o.

Two different points (rO'+θo+Zo) and (ro, θ.+1
80. The current element vectors at Z□U and are respectively δ
Although it can be defined as consisting of a pair of currents 1 and -δ1, FIG. 5 is shown for ease of explanation.

An example of a deflector consisting of two pairs of current element vectors is shown. That is, U(ro, θI + zO) + U'(r
O'+θr)18Q, Zo)V (ro, -θ]+
ZO), V'(ro+-θ, -180.Z(+), 2 points U8, 7 points V', 7 points U', 1 δ1 current flowing at 2 points V'. In this way, 4
The angle θ (here δ1) defining the coordinate point has the same meaning as the opening half angle defined in FIG. Here, the arrow indicates the direction of the current, and the broken line is an auxiliary line to indicate the cylindrical coordinate system. The solid line indicated by 6 in the figure is added as a reference for the rotation angle θ. Figure 5 t
al is a perspective view, and +b+ in the same figure is Z seen from the two-axis direction.
``This is a plan view at ZO. Here ■ and ■ are the same as the definitions in Figure 1, but in this case □ does not mean that they are perpendicular to the plane of the paper. By changing only θ of the deflector consisting of a pair of current elements (θ−θ1°θ
2. ...) When multiple current elements are superimposed, the total potential (magnetic potential in this case) 6M created by these current elements is δφ−Σ(δφ) Sinθ, +δφ3S1n3θ1.
-δφ5sin5θF mountain...') -(11JI. Here, δφm (m=1.3.5...) is r, θ,
As a function of Z, δφ1 is a rotationally invariant deflection component, and δφ
3.delta..phi.5... are components that cause four-fold aberrations that are affected by third-order, fifth-order, etc. deflections, respectively. The conditional expressions for a deflector with no four-fol and d aberrations in the third- and fifth-order deflections obtained from this second (10) are isomorphic to equations (1) and (3), respectively. .

Therefore, to summarize the following, the conditions for obtaining a deflector in which the four-fold aberrations related to third- and fifth-order deflections both disappear and currents with the same vector do not occupy the same coordinate points are: Basically, in a cylindrical coordinate system where the Z axis is the axis of the cylindrical surface, r is the radial direction, and θ is the rotation direction, when r and z are constant and the angle θ is an arbitrary angle, Δθ is an arbitrary angle. .

42±Δθ degrees, 78±Δθ degrees, 1o2±Δshi degrees, 138
When all the current element vectors of the current existing at the eight coordinate points determined by Δθ degrees are equal and this current element hector is defined as
r and z are the same as the r and z values, and the angle θ is 222 ± Δθ degrees, 258 ± Δθ degrees, 282 ± Δθ degrees, 3
The currents at the eight coordinate points determined by +s-+-Δθ degrees...(I2) are all equal to one electric current M
[It has an element vector, or r and z are - constant, and the angle θ is 6 ± Δθ degrees, 66 ± Δθ degrees, 114 ± Δθ degrees, 174L
The current element vectors of the current existing at the eight coordinate points determined by Δθ degrees are all equal, and when this current element vector is δ1, r, ziiJ2 r, z values and the angle θ is 186 ± Δθ degrees, 246 ± Δθ degrees, 294 ± Δθ degrees, 3
It can be seen that the currents at the eight coordinate points determined by 54±Δθ degrees (14) all have current element vectors equal to −δ1. Also,
Is it clear that this can also be applied to the arc portion of a saddle-type deflector? As 4/S,
By using the position shown by the solid line 7 rotated by 90 degrees from the solid line 6 in FIG. 5 fbl as a reference.

The meaning can be clarified. In this way, the reference for the rotation angle θ can be arbitrarily adopted as shown in equations (1 to 04
), it is more general to set θ to θ→−α (α is an arbitrary angle). Note that by continuously changing the 16 coordinate points that have been explained so far, a concrete deflector can be obtained, but due to the saddle-shaped arc portion, overlapping of the windings may occur in some cases. . In this case, in order to actually construct a deflector, it is a matter of course that a deviation in coordinate values of the thickness of the conductor through which the current flows or several times the thickness of the conductive wire is allowed.

In addition, normally a deflector exhibits a deflection effect by a continuous current flowing through the winding, but from what has been said above, at different r and z, there is no difference between the angle θ and the current element vector. 2 or r value may also be changed arbitrarily, so the shape of the coil may be a cone shape as shown in Figure 6 (here - only one pair of coils is shown as an example). Needless to say, it's fine to do so.

〔Effect of the invention〕

As explained above, two aspects of the present invention can be applied to four-dimensional optical systems that are related to both third-order and fifth-order deflection in general charged particle optical systems.
Since a magnetic field type deflector without -fold aberration can be made by integrating coils with discrete opening angles, a high-precision deflector can be manufactured without overlapping a large number of windings. There is a publication that can provide an optical system with low aberration deflection performance by applying it to a deflector of an optical system that requires large deflection.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional saddle type coil, ta+ is a perspective view, and crest) is a plan view. Fig. 2 is an explanatory diagram of a conventional lo ital type coil, +a+ is a perspective view, [bl is a plan view] , 3rd
The figure shows 3rd and 5th order four-folds in the present invention.
Figure 4 shows the conditions for removing aberrations. Figure 4 shows an embodiment of the present invention, as seen from the axial direction of a saddle-type deflection coil consisting of four pairs of coils. Figure 5 shows the conditions for eliminating two pairs of currents according to the present invention. A] is a perspective view, (bl is a plan view, and FIG. 6 shows another embodiment of the present invention. The distance from the central axis of the coil to the coil is 1 to 1. is 2
FIG. 3 is a perspective view of a pair of coils that change with the axis. Explanation of symbols■・Coil center axis (2 axes) 2,,, x-axis 3- Y jM114・
- Third-order deflection four-fo1. Condition 5 for removing d aberration...Condition 6.7 for removing fifth-order deflection four-fold aberration...Reference line middle 2A (b) 1'F3 Figure 4 Figure 5 ~~~--- -,,/

Claims (4)

[Claims] (1) In a magnetic field type deflector that controls the traveling direction of a charged particle beam using a magnetic field generated by passing a current through a deflection coil, the position of the deflection coil is set so that the optical axis of the charged particle beam is aligned with the optical axis of the charged particle beam. Using a cylindrical coordinate system (z + r + θ) in which the radial distance from these two axes to the coil coordinate point is r, and the rotation angle around the z axis is θ, r and z are constant, and the angle θ is When Δθ is an arbitrary angle, 42d: Δθ degrees,
78±Δθ degrees, 102±Δθ degrees. The coordinate points of the first group of 8 points determined by 138 ± Δθ degrees, and r,
z is the same as the r and z values above, and the angle θ is 222 ± Δθ degrees, 2
16 coordinate point positions with the second group of 8 coordinate points determined by 58±Δθ degrees, 282±Δθ degrees, and 318±Δθ degrees, or r. 2 is constant and the angle θ is 6± when Δθ is an arbitrary angle.
Δθ degrees, 66±Δθ degrees, 114±Δθ degrees, 174±Δθ
The coordinate points of the first group of 8 points determined by degrees, and 186 ± Δθ degrees,
246 ± Δθ degrees, 294 ± Δθ degrees, 354 ± Δθ degrees, and 16 coordinate points with the second group of 8 coordinate points,
-1- The currents existing at the eight coordinate points of the first group all have a current element hector equal to ml, and -''2, the second
■The currents existing at the 8 coordinate points of ¥ all have a current element vector equal to 1 δl, and furthermore, the above 16 coordinate points allow an error corresponding to the thickness of the coil conductor wire through which the current flows. A magnetic field type deflector characterized by: (2) In the magnetic field type deflector according to claim 1, the current element vector is a current element vector that changes with continuous changes of one or more of the r, z, and θ values. A magnetic field type deflector characterized in that the current element vector maintains a certain or constant vector value. (3) In the magnetic field type deflector according to claim 1, the 16 coordinate points and one Δθ determine: A complete set of deflection coils and the 16 coordinate points are the same and the Δθ is determined by the 16 coordinate points and one Δθ. and at least 11 or more deflection coils determined by Δθ different from Δθ. (4) In the magnetic field type deflector according to claim 1, the magnetic field type deflector is characterized in that it is a deflection coil as described in +1iii above, or a deflection coil having a round shape or a toroidal shape. vessel.