Device for electrostatic deflection of a particle beam

Details Device for electrostatic deflection of a particle beam Device for electrostatic deflection of a particle beam

2000-02-22

2003-04-01

Lee, John R. (Department: 2881)

Radiant energy

With charged particle beam deflection or focussing

Magnetic lens

C250S492200

Reexamination Certificate

active

06541776

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Reference is made to the German Patent Application 199 07 858.0-33 from which the present application claims piority.
FIELD OF THE INVENTION
This invention relates a device for electrostatic deflection of a particle beam out of a primary beam direction for the purpose of scanning a plane spanned by two coordinates X, Y, in which multiple electrodes configured as deflection wires are connected to an activation circuit and are acted upon, depending on the activation, by modifiable deflection voltages. In this context the “primary beam direction” is to be understood as the direction of the undeflected particle beam which intersects the origin of the coordinates X, Y; the deflection voltages are an equivalent for the deflection of the particle beam out of the primary beam direction in the direction of coordinate X or coordinate Y.
BACKGROUND OF THE INVENTION
In particle beam equipment, for example in electron-beam and ion-beam exposure systems for exposing wafers, devices are necessary for deflecting the particle beam over the surface that is to be exposed.
In deflection devices of this kind, which are often also called deflection systems, the change in the direction of the particle beam is accomplished, in principle, by the influence of magnetic or electrostatic forces. Also known are deflection devices in which both principles are utilized in succession in the beam direction.
If the deflection of the particle beam is to take place quickly and accurately, electrostatic deflection systems are preferred. In such systems, multiple deflection electrodes are acted upon by different voltage potentials, thereby generating an electrostatic field that, depending on the change in voltage potentials and the activation of the deflection electrodes, acts on the particle beam so as to change its direction. Activation is accomplished in such a way that the particle beam is deflected out of a primary beam direction (which corresponds to the undeflected beam path) into a desired direction, and is guided as a function of the change in activation over a plane spanned by the coordinates X, Y.
Electrostatic deflection systems in which the deflection electrodes are configured in the form of wires that extend, over part of their length, parallel to the primary radiation direction, have recently been developed. One such deflection system is described in the German Patent Application DE 31 38 898 A1. In this, eight wires are arranged in radially symmetrical fashion around the primary beam direction. The wires are attached at their ends to insulators. The attachment positions on the insulators determine the location and orientation of the wires relative to the particle beam. The arrangement disclosed in DE 31 38 898 A1 of the wires with respect to the primary radiation direction is illustrated in
FIG. 1
of the present specification.
One disadvantage of this device as compared to previously known deflection systems, in which electrodes were arranged distributed in the form of cylindrical or circular segments around the primary beam direction, is the fact that deflection sensitivity is lower, and moreover that greater complexity is involved in activating the electrodes, since mixed deflection potentials must be generated (cf. page 4 of DE 31 38 898 A1, lines 5 through 7). The mixed deflection potentials, for example U
4
=(U
y
+U
x
)/v2, are necessary so that the electrostatic field is at least approximately homogeneous.
The wire deflection system described above thus exhibits poorer practical value characteristics than the previously known existing art. As a result, its actual advantage—namely simplicity of manufacture—cannot be effectively utilized, especially for applications in which rapid and accurate deflection of the particle beam is desired.
SUMMARY OF THE INVENTION
Proceeding therefrom, it is the object of the invention to develop deflection systems of the kind described above in such a way that practical value characteristics are improved while retaining the advantages in terms of production engineering.
According to the invention, in deflection systems of this kind multiple deflection wires are linked into deflection grids, the deflection wires being joined to one another and to the activation circuit in such a way that an equivalent deflection voltage is always applied to all deflection wires belonging to one and the same deflection grid.
In a preferred embodiment of the invention, provision is made for multiple deflection grids to be allocated to the X coordinate and for the deflection wires of those deflection grids to be arranged symmetrically with respect to the Y coordinate; and/or for multiple deflection grids to be allocated to the Y coordinate and for the deflection wires of those deflection grids to be arranged symmetrically with respect to the X coordinate.
It has thereby been advantageously possible to achieve high field homogeneity even without the complex provision of mixed deflection potentials. It has moreover been possible, by suitable positioning of multiple deflection wires as will be explained in further detail below, to suppress in simple fashion the higher-order Fourier harmonics of the electrostatic potential, thus improving the field homogeneity even further. The application of the same potential to multiple deflection wires has advantageously resulted in an elevated deflection sensitivity for the entire deflection system.
A particularly preferred embodiment of the invention provides for two deflection grids to be allocated in each case to the X coordinate and to the Y coordinate. The deflection grids allocated to the X coordinate are located opposite one another symmetrically with respect to the Y coordinate; the deflection grids allocated to the Y coordinate are located opposite one another symmetrically with respect to the X coordinate. A voltage potential ±U
X
is provided between the deflection grids allocated to the X coordinate, and a voltage potential ±U
Y
is provided between the deflection grids allocated to the Y coordinate. The deflection of the particle beam out of the primary radiation direction is effected as a function of the change in the voltage applied to the deflection grids.
In further embodiments of the invention, at least two deflection wires of one and the same deflection grid are arranged at different spacings from the origin of the X and Y coordinates. In other words, the spacings between the deflection wires and the undeflected particle beam are of different magnitudes for at least two deflection wires of a deflection grid. In this context, provision can advantageously be made for the cross-sectional center points of all the deflection wires to be distributed on circumferential lines of multiple concentric circles k
1
, k
2
through k
n
, these circles also being oriented concentrically with respect to the coordinate origin or the undeflected particle beam. As a result, the spacings of the deflection wires that belong to one and the same deflection grid are defined with respect to the undeflected particle beam via the radii r
1
, r
2
through r
n
of circles k
1
, k
2
through k
n
.
An embodiment that is particularly favorable in terms of field homogeneity results, for example, if a total of four deflection grids are provided, each deflection grid being constituted from six deflection wires, the deflection wires of all the deflection grids being arranged distributed on circumferential lines of three circles k
1
, k
2
, k
3
having radii r
1
<r
2
<r
3
, and each of circles k
1
, k
2
and k
3
being occupied by two deflection wires of each grid.
In this context, the ratio of the radii r
1
:r
2
:r
3
should be approximately 1:1.1:1.21. The arc length b
1
between the two deflection wires of a grid on circle k
1
, the arc length b
2
between the two deflection wires of a grid on circle k
2
, and the arc length b
3
between the two deflection wires of a grid on circle k
3
should be related to one another as 8:1:14.
It is advantageous in this context to embody arc length b
1
wi

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