JPH0345859B2 - - Google Patents

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. It is designed to reduce deflection aberrations, and is used, for example, in ion beam exposure equipment when forming semiconductor IC patterns,
Can be used for electron beam exposure equipment, etc.

[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-
This invention relates to a magnetic field type deflector that simultaneously removes fold aberration components.

Generally, a saddle-type coil or a toroidal-type coil is used in 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. Further, 2 and 3 are two orthogonal coordinate axes x and y axes, respectively, which are perpendicular to the z-axis (center axis of the coil). In both figures, a is a perspective view of a pair of coils, b is a plan view of the same coil as seen from the axial direction, and indicates the flow of current from the front to the back of the paper. , ○ is the opposite. Furthermore, the broken line is an auxiliary line indicating that r is constant. In the following explanation, as shown in the figure, h is the length of the coil in the direction of the central axis, and r is the distance in the radial direction from one point on the central axis of the coil to the coil on a plane perpendicular to the central axis including that point. In addition, the opening half angle θ is defined as 1/2 of the maximum angle that the windings, which are symmetrically located in the xz plane, extend around the central axis in the X coil.

A conceptually clear deflector without four-fold aberration has a density distribution of the number of turns of the coil θ.
This is achieved by overlapping the coils shown in Figures 1 or 2 (so-called cosine winding) so that the direction is proportional to sinθ, and in this case, deflection four-fold aberrations of all orders do not occur. It has been revealed [H.Ohiwa, E.Goto, and A.Ono,
Electron.Commun.in Japan p54-B, No.12, 44
(1971)]. However, the winding has a finite thickness,
Furthermore, since the coils are actually wound discretely, it is difficult to create a deflector with continuous cosine winding.

As an alternative, the most basic four−
Since the fold aberration is a third-order deflection four-fold aberration, it is first possible to create a deflector that removes only this aberration. To do this, the length in the axial direction of the coils and the distance in the radial direction of the coils are equal, and the coils with an opening half angle θi that satisfies 〓 ⁱ sinθi=0 ...(1) are placed on the same z-axis and moved in the same direction. It is known that a deflector free from third-order deflection four-fold aberration can be obtained by integrating the coils so as to have a deflection effect (for example, as an X coil). However, equation (1) assumes that the current flowing through each coil is equal. Here, θi
If we limit it to one angle (i=1), equation (1) holds true when θi=60, which means that the opening angle
In a 120° concentrated winding coil, the third-order deflection four
This is equivalent to saying that -fold aberration does not occur.

Next, considering two coils (θ ₁ and θ ₂ ) with different opening half angles, equation (1) becomes sin3θ ₁ + sin3θ ₂ = 0 ...(2), and the two opening half angles θ ₁ that satisfy this, There are countless combinations of θ ₂ . This is shown by solid line 4 in FIG. Here, the horizontal axis is θ ₁ and the vertical axis is θ ₂ ,
The figures are shown in the range of 0°≦θ ₁ and θ ₂ ≦90°. In other words, by selecting an appropriately large number of two pairs of coils with half-angle openings that satisfy equation (2), it is possible to create a deflector without third-order deflection four-fold aberration by using coils with dispersed half-angle openings. You can turn it up. For example, if θ ₁ is 0° < θ ₁ < 30°, θ ₂ is 60° < θ ₂ < 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-mentioned matters are conditions for a deflection coil having no four-fold aberration, and only the third order is insufficient in an optical system that requires a large deflection.

Therefore, if we obtain the conditional expressions corresponding to equations (1) and (2) for removing the fifth-order deflection four-fold aberration, we obtain the following, respectively: 〓 ⁱ sin5θi=0 ……(3) sin5θ ₁ + sin5θ ₂ =0 …… (4) (E. Munro, Advances in
Electronics and Electron Physics.Supplement
13B, pp73−131). There are countless combinations of the two half-opening angles θ ₁ and θ ₂ that satisfy this equation (4), and these are shown by the dashed-dotted line 5 in FIG. Therefore, the fifth-order deflection four
If the only condition is to remove the −fold aberration, then
As with the tertiary case, all you have to do is distribute the coils appropriately and wind them.

However, the condition that does not cause both third- and fifth-order deflection four-fold aberrations is to simultaneously satisfy equations (2) and (4), which immediately leads to (θ ₁ , θ ₂ )=
It can be seen that only (6°, 66°) and (θ ₁ , θ ₂ )=(42°, 78°) (here, θ ₁ <θ ₂ ). these are,
In FIG. 3, they correspond to the intersections A and B of the solid line 4 and the dashed-dotted line 5, respectively. However, since there are only two conditions, A and B, that do not cause both third- and fifth-order deflection four-fold aberrations, if you want to obtain a specific deflector with a constant deflection direction, the conditions must be met. The opening angles to be satisfied are fixed and the coils have to be concentrated at those 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 to prevent the opening angle of the coil 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-fold aberrations.

[Summary of the invention]

The summary of the present invention is to achieve the above objects.
The deflection coil is arranged in a cylindrical coordinate system (the optical axis of the charged particle beam is the z-axis, the radial distance from the z-axis to the coil coordinate point is r, and the rotation angle around the z-axis is θ). z, r, θ), r, z are constant, angle θ is an arbitrary angle, Δθ is an arbitrary angle,
The coordinate points of the first group of 8 points are determined by 42±Δθ degrees, 78±Δθ degrees, 102±Δθ degrees, and 138±Δθ degrees, and r and z are the same as the above r and z values, and the angle θ is 222±Δθ degrees. degree, 258±Δθ
The second of eight points determined by degrees, 282±Δθ degrees, and 318±Δθ degrees
When the coordinate points of the group are 16 coordinate points, or r and z are constant, and the angle θ is Δθ less than 6 degrees, 6 ± Δθ degrees, 66 ± Δθ degrees, 114 ±Δθ
The coordinate points of the first group of eight points determined by 174±Δθ degrees, 186±Δθ degrees, 246±Δθ degrees, 294±Δθ degrees, and 354±
16 coordinate points are located between the coordinate points of the second group of eight points determined by Δθ degrees, and the currents existing at the eight coordinate points of the first group all have current element vectors equal to δi →. , the currents existing at the eight coordinate points of the second group all have current element vectors equal to -δi→,
Furthermore, the above-mentioned 16 coordinate points are configured to allow a tolerance corresponding to the thickness of the coil conducting wire through which the current flows, in a magnetic field type deflector.

[Embodiments of the invention]

Now, assume a quadrilateral PQRS whose opposite sides are parallel to the θ ₁ axis and θ ₂ axis and whose corners are on the solid line 4 and the dashed-dotted line 5, as shown by the broken lines in FIG. 3. The two pairs of opening half angles at point P are θ _a , θ _b (θ ₁
= θ _a , θ ₂ = θ _b , and the two pairs of opening half angles at point R are θ _c and θ _d (θ ₁ =θ _c , θ ₂ =θ _d ). Then (θ
_a ,
Since point P consisting of the combination of θ _b ) and point R consisting of the combination of (θ _c , θ _d ) are on the solid line 4, it is clear that there is no third-order deflection four-fold aberration.
However, as a combination of two pairs of coils with these four opening half angles θ _a , θ _b , θ _c , θ _d , (θ _a , θ _d )
If and (θ _c , θ _b ) are selected, they become point Q and point S, respectively, which are on the dashed-dotted line 5, and are therefore a combination in which the fifth-order deflection four-fold aberration also disappears. In other words, if we can draw a quadrilateral as described above in Fig. 3, the four pairs of coils with half-angle openings determined by the corners will produce both third- and fifth-order deflection four-fold aberrations. There is no deflector. This is synonymous with what will be described next. That is, assuming that equations (2) and (4) hold, sin3 (θ ₁ + Δθ) + sin3 (θ ₁ − Δθ) + sin3 (θ ₂
+Δθ)+sin3(θ ₂ −Δθ)=0……(5) sin5(θ ₁ +Δθ)+sin5(θ ₁ −Δθ)+sin5(θ ₂
+Δθ)+sin5( _θ2 −Δθ)=0...(6) It is clear from the trigonometric formula. In addition, these equations (5) and (6) each have i=4
It is also clear that this is one solution that satisfies both equations (1) and (3) when
This shows that a deflector that does not produce four-fold aberration can be obtained. The four opening half angles mentioned here are 6±Δθ degrees, 66±Δθ degrees...(7) or 42±Δθ degrees, based on the premise that equations (2) and (4) hold true. , 78±Δθ degrees...(8). Therefore, by these equations (7) or (8),
A deflector consisting of four pairs of coils can be obtained for one Δθ, and another deflector consisting of four pairs of coils can be obtained depending on a different value of Δθ. All of these are deflectors that do not produce the desired third- and fifth-order deflection four-fold aberrations. Note that the opening half angle θ determined by equation (7) or equation (8) may be θ > 90° depending on how Δθ is selected, but in that case, the opening half angle θ is 180°−θ.
By adopting as
It is clear that the result is a four-pair deflection set with no fold aberration. In particular, with the condition that the opening half-angle is not negative or 90° or more, in equation (7),
By setting the range to be 0°<Δθ<6°, and 0°<Δθ<12° in equation (8), all the opening half angles of the coils included in each set can be made different from each other. For example, if Δθ is 1°, 2°, and 3°, the opening half angle of each coil is (41°, 43°, 77°, 79°), (40°, 44°), respectively in equation (8). , 76°,
80°),
(39°, 45°, 75°, 81°), and the opening half angles do not have the same value. Figure 4 shows 4 due to Δθ=3°.
A plan view of a deflector consisting of a pair of coils as seen from the axial direction is shown.

It is also important to note that there are no restrictions on the axial coil length h (and coil radius r) between the deflectors made up of four pairs of coils that satisfy the above conditions. That is, the coil radius r
There are many cases in which deflectors are manufactured with a constant value, but in this case, by varying the length h of the coil of each deflector, even in the case of a saddle-type deflector, it is possible to prevent the arcuate parts from overlapping. (To be exact, in the case of saddle-type coils, the arc parts overlap only for the four pairs of coils included in one deflector, but manufacturing problems can be eliminated by using printed coils etc.) be able to).

Next, it should be mentioned that the above-mentioned matters are not limited to deflectors such as saddle type or toroidal type, but also apply to general deflectors. In the following explanation, a cylindrical coordinate system (r, θ, z) will be used as the coordinate system,
It is assumed that z indicates the axis of the cylindrical surface, r indicates the radial direction, and θ indicates the rotation direction. Let the unit vectors in the r, θ, and z axes directions be 〓, 〓, and 〓. Also, assuming that a current flows through one coordinate point in the cylindrical coordinates, and let the components in each direction of the current at that coordinate point be δi _r , δi〓, δi _z, then δi→=〓・δi _r +〓・δi〓 +〓・δi _z ...(9) will be called the current element vector flowing through that coordinate point.

Then, the deflector has equal r and z values and θ is
Two points different by 180° (r ₀ , θ ₀ , z ₀ ) and (r ₀ , θ ₀ +180,
z ₀ ) and the current element vectors are δi→ and −
Although it can be defined as consisting of a pair of currents δi→, for the sake of simplicity, FIG. 5 shows an example of a deflector consisting of two pairs of current element vectors. That is, U(r ₀ , θ ₁ , z ₀ ), U′(r ₀ , θ
₁
+180, z ₀ ), V(r, ₀ −θ ₁ , z ₀ ), V′(r ₀ , −θ ₁
−
180, z ₀ ), point U and point V′ have δi→,
It is assumed that a current of −δi→ flows through point U′ and point V. The angle θ (here, θ ₁ ) that defines the four coordinate points in this way 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 5a is a perspective view, and Figure 5b is a perspective view of z as viewed from the z-axis direction.
It is a plan view at =z ₀ . Here, and ○ are the same as the definitions in FIG. 1, but in this case they do not mean perpendicular to the plane of the paper. When a large number of deflectors consisting of two pairs of current elements as shown in Fig. 5 are superimposed by changing only θ (θ = θ ₁ , θ ₂ , etc.), the total amount produced by each of these current elements is The potential (magnetic potential here) δφ is δφ= 〓 〓 ⁱ (δφ ₁ sinθ _i +δφ ₃ sin3θ _i +δφ ₅ sin5θ _i +……)
...(10) becomes. Here, δφ _n (m=1, 3, 5...) is r,
As a function of θ and z, δφ ₁ is a rotationally invariant deflection component, and δφ ₃ , δφ ₅ , . . . are components that cause four-fold aberrations related to third-order, fifth-order, . The conditional expressions for a deflector free of four-fold aberrations related to third-order and fifth-order deflections obtained from equation (10) are the same as equations (1) and (3), respectively.

Therefore, to summarize the above, 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 as follows. 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 rotational direction, r and z are constant, and the angle θ and Δθ are arbitrary angles. When, 42±Δθ degrees, 78±Δθ degrees, 102±
Δθ degrees, 138±Δθ degrees...(11) The current element vectors of the currents at the eight coordinate points determined by are all equal, and this current element vector is expressed as δi→
When, r and z are the same as the above r and z values, and the angle θ is 222±Δθ degrees, 258±Δθ degrees, 282±
Δθ degrees, 318 ± Δθ degrees...(12) The currents at the eight coordinate points determined by all have current element vectors equal to -δi→, or r, z
is constant, and the angle θ is 6±Δθ degrees, 66±Δθ degrees, 114±
Δθ degrees, 174±Δθ degrees... (13) The current element vectors of the currents existing at the eight coordinate points determined by are all equal, and this current element vector is expressed as δi→
When, r and z are the same as the above r and z values, and the angle θ is 186±Δθ degrees, 246±Δθ degrees,
It can be said that the currents at the eight coordinate points determined by 294±Δθ degrees, 354±Δθ degrees (14) all have current element vectors equal to −δi→. It is clear that this can also be applied to the arcuate portion of a saddle-type deflector, but the reference for the rotation angle θ is the position indicated by the solid line 7 rotated by 90 degrees from the solid line 6 in Fig. 5b. By doing,
The meaning can be clarified. As described above, since the reference for the rotation angle θ can be arbitrarily adopted, it is more general to set θ in equations (11) to (14) to θ+α (α is an arbitrary angle). In addition, by continuously changing the 16 coordinate points that have been explained so far, a concrete deflector can be created.
In some cases, such as a saddle-shaped arc portion, overlapping windings may occur. 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, a normal deflector exhibits a deflection effect due to a continuous current flowing through the winding, but in this case, the above-mentioned changes cannot be made except for the angle θ at different r and z. Since the z or r value is not specified, the z or r value may also be changed arbitrarily, and therefore the shape of the coil may be a cone shape as shown in Fig. 6 (here, only one pair of coils is shown as an example). Needless to say, it's fine to do so.

[Effects of the Invention] As explained above, the present invention provides a magnetic field type deflector that is free from four-fold aberrations related to both third- and fifth-order deflection in a general charged particle optical system by using a discrete aperture. Since it can be made by accumulating coils with corners, it is possible to manufacture highly accurate deflectors without overlapping many windings, and by applying this to optical system deflectors that require particularly large deflections. This has the advantage of providing an optical system having deflection performance with low aberrations.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional saddle type coil, where a is a perspective view, b is a plan view, Fig. 2 is an explanatory diagram of a conventional toroidal coil, a is a perspective view, b is a plan view, and Fig. 3 is an explanatory diagram of a conventional toroidal coil. Third-order and fifth-order four-fold 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. 6 shows a deflection coil composed of element vectors, a is a perspective view, b is a plan view, and FIG. 6 is another embodiment of the present invention, in which the distance r from the central axis of the coil to the coil changes with the z-axis. FIG. 3 is a perspective view of a pair of coils. Explanation of symbols, 1... Central axis of the coil (z-axis),
2...x axis, 3...y axis, 4...3rd order deflection four
-Conditions for removing fold aberration, 5...5th order deflection
Conditions for removing four-fold aberration, 6, 7...Reference line.

Claims (1)

[Claims] 1. In a magnetic field type deflector that deflects and controls the running direction of a charged particle beam using a magnetic field generated by passing a current through a deflection coil, the arrangement position of the deflection coil is
A cylindrical coordinate system (z, r,
θ), and when r and z are constant and the angle θ and Δθ are arbitrary angles, 42 ± Δθ degrees, 78 ± Δθ degrees, 102
The coordinate points of the first group of 8 points determined by ±Δθ degrees and 138 ±Δθ degrees, and r and z are the same as the above r and z values, and the angle θ is
222±Δθ degrees, 258±Δθ degrees, 282±Δθ degrees, 318±Δθ
16 coordinate points with the second group of 8 coordinate points determined by degrees, or r and z are constant and the angle θ
However, when Δθ is an arbitrary angle, 6±Δθ degrees, 66±
The coordinate points of the first group of 8 points determined by Δθ degrees, 114 ± Δθ degrees, 174 ± Δθ degrees, and 186 ± Δθ degrees, 246 ± Δθ degrees, 294
±Δθ degrees, 354±Δθ degrees with the coordinate points of the second group of 8 points, and the coordinate points of 16 points, and the above-mentioned first
The currents existing at the eight coordinate points of the group all have current element vectors equal to δi→, and the currents existing at the eight coordinate points of the second group all have current element vectors equal to −δi→, Furthermore, the magnetic field type deflector is characterized in that the 16 coordinate points allow an error corresponding to the thickness of the coil conducting wire through which the current flows. 2. In the magnetic field type deflector according to claim 1, the current element vector has the r, z,
A magnetic field type deflector characterized by having a current element vector that changes with one or more continuous changes in θ value or a current element vector that maintains a constant vector value. 3. In the magnetic field type deflector according to claim 1, a set of deflection coils is determined by the 16 coordinate points and one Δθ, and the 16 coordinate points are the same and have a Δθ different from the Δθ. 1. A magnetic field type deflector comprising at least one set of other deflection coils determined by: 4. The magnetic field type deflector according to claim 1, wherein the deflection coil is a deflection coil having a saddle shape or a toroidal shape.