Arrangement for actuating an element in a microlithographic projection exposure apparatus

Abstract

The invention relates to arrangements for actuating an element in a microlithographic projection exposure apparatus. In accordance with one aspect, an arrangement for actuating an element in a microlithographic projection exposure apparatus comprises a first number (n.sub.R) of degrees of freedom, wherein an adjustable force can be transmitted to the optical element in each of the degrees of freedom, and a second number (n.sub.A) of actuators, which are coupled to the optical element in each case via a mechanical coupling for the purpose of transmitting force to the optical element, wherein the second number (n.sub.A) is greater than the first number (n.sub.R). In accordance with one aspect, at least one of the actuators is arranged in a node of at least one natural vibration mode of the optical element.

Claims

1. An arrangement configured to actuate an optical element of a microlithographic projection exposure apparatus, the optical element configured so that an adjustable force is transmittable to the optical element in a first number of degrees of freedom, the arrangement comprising: a second number of actuators; wherein: the second number is greater than the first number; for each of the second number of actuators, the actuator is coupled to the optical element via a mechanical coupling to transmit force to the optical element; the actuators are arranged so that, when at least one natural vibration mode of the optical element is actuated, a magnitude of a transfer function of an open control loop at a frequency of the at least one natural vibration mode is reduced by at least six dB compared with an arrangement in which the second number is not greater than the first number.

2. The arrangement of claim 1, wherein the actuators are arranged so that, when the at least one natural vibration mode of the optical element is actuated, the magnitude of the transfer function of the open control loop at the frequency of the at least one natural vibration mode is reduced by at least 12 dB compared with the arrangement in which the second number is not greater than the first number.

3. The arrangement of claim 1, wherein the actuators are arranged so that, when the at least one natural vibration mode of the optical element is actuated, the magnitude of the transfer function of the open control loop at the frequency of the at least one natural vibration mode is reduced by at least 20 dB compared with the arrangement in which the second number is not greater than the first number.

4. The arrangement of claim 1, wherein the optical element comprises a mirror.

5. The arrangement of claim 4, wherein the mirror is actively deformable to compensate for an undesirable disturbance in the microlithographic projection exposure apparatus.

6. The arrangement of claim 4, wherein the mirror is a non-actively deformable mirror.

7. The arrangement of claim 1, further comprising a third number of sensor elements configured to determine at least one parameter selected from the group consisting of a location of the optical element and a position of the optical element.

8. The arrangement of claim 7, wherein the third number is greater than the first number.

9. The arrangement of claim 1, wherein at least one actuator comprises a Lorentz actuator.

10. The arrangement of claim 1, wherein the first number of degrees of freedom is at least three.

11. The arrangement of claim 1, wherein the first number of degrees of freedom is six.

12. The arrangement of claim 1, wherein the arrangement is configured so that the optical element is actively deformed by the adjustable forces.

13. The arrangement of claim 1, wherein the arrangement is configured so that a position of the optical element is manipulated via the adjustable forces.

14. The arrangement of claim 1, wherein the microlithographic projection exposure apparatus comprises an EUV microlithographic projection exposure apparatus.

15. An apparatus, comprising: an optical element; and an arrangement configured to actuate the optical element, the optical element configured so that an adjustable force is transmittable to the optical element in a first number of degrees of freedom, the arrangement comprising a second number of actuators; wherein: the second number is greater than the first number; for each of the second number of actuators, the actuator is coupled to the optical element via a mechanical coupling to transmit force to the optical element; the actuators are arranged so that, when at least one natural vibration mode of the optical element is actuated, a magnitude of a transfer function of an open control loop at a frequency of the at least one natural vibration mode is reduced by at least six dB compared with an arrangement in which the second number is not greater than the first number; and the apparatus is a microlithographic projection exposure apparatus.

16. The apparatus of claim 15, comprising an illumination device, wherein the optical element is in the illumination device.

17. The apparatus of claim 15, comprising a projection lens, wherein the optical element is in the projection lens.

18. The apparatus of claim 15, wherein the optical element comprises a mirror.

19. An apparatus, comprising: an illumination device; a projection lens; a mirror; and an arrangement configured to actuate the mirror, the mirror configured so that an adjustable force is transmittable to the mirror in a first number of degrees of freedom, the arrangement comprising a second number of actuators; wherein: the second number is greater than the first number; for each of the second number of actuators, the actuator is coupled to the mirror via a mechanical coupling to transmit force to the mirror; the actuators are arranged so that, when at least one natural vibration mode of the mirror is actuated, a magnitude of a transfer function of an open control loop at a frequency of the at least one natural vibration mode is reduced by at least six dB compared with an arrangement in which the second number is not greater than the first number; the mirror is in the illumination system or the projection lens; and the apparatus is a microlithographic projection exposure apparatus.

20. The apparatus of claim 19, wherein the microlithographic projection exposure apparatus comprises an EUV microlithographic projection exposure apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the figures:

(2) FIGS. 1A-1B show schematic illustrations for elucidating one approach according to the invention in conjunction with a non-actively deformable mirror;

(3) FIG. 2 shows a schematic illustration for elucidating one approach according to the invention in conjunction with an actively deformable mirror;

(4) FIGS. 3-4A-4C show schematic illustrations for elucidating one embodiment on the basis of the example of positional control of a vibratory body;

(5) FIG. 5 shows a diagram for elucidating a control loop on the basis of the example of an actively deformable mirror with realization of the over-actuation according to the invention;

(6) FIG. 6 shows a diagram for elucidating a control loop on the basis of the example of an actively deformable mirror with realization of the over-sensing according to the invention;

(7) FIG. 7 shows a diagram for elucidating a control loop on the basis of the example of an actively deformable mirror with realization of a statically determinate I-controller; and

(8) FIG. 8 shows a schematic illustration of an exemplary construction of a microlithographic projection exposure apparatus which is designed for operation in the EUV and in which the present invention can be realized.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(9) FIGS. 1A-1B firstly show schematic illustrations for elucidating one approach according to the invention in conjunction with a non-actively deformable mirror.

(10) In accordance with FIG. 1A, a mirror 100 to be held in a defined position is conventionally mounted isostatically by virtue of the fact that three actuators 111, 112 and 113 having a force direction or drive direction perpendicular to the mirror 100 are used to position the mirror 100 in the three degrees of freedom z, R.sub.x and R.sub.y (i.e. with regard to displacement in the spatial direction z and rotation about the x- and y-axis, respectively). With exactly these three actuators 111, 112 and 113, the three degrees of freedom z, R.sub.x and R.sub.y are statically determinate. As likewise explained here with reference to FIGS. 3 and 4, however, these three actuators 111, 112 and 113 can excite elastic natural frequencies or natural vibration modes of the mirror 100.

(11) As indicated in FIG. 1B, a higher number (in the example n.sub.A=4) of actuators 111, 112, 113 and 114 relative to the number of degrees of freedom (in the example the three degrees of freedom z, R.sub.x and R.sub.y) is now used according to the invention, as likewise explained in even greater detail with reference to FIGS. 3 and 4, the actuators 111-114 being positioned in such a way that no undesired excitation or associated disturbance of the positional control takes place for some natural frequencies or natural vibration modes of the mirror 100.

(12) FIG. 2 serves for clarifying the concept according to the invention in conjunction with an actively deformable mirror 200, likewise merely indicated schematically. In accordance with FIG. 2, a comparatively high number (e.g. 10, 100 or more) of deformation actuators 211, 212, . . . serve for actively deforming the deformable mirror 200, wherein the mirror 200 is simultaneously designed to be comparatively elastic in order to enable an active deformation. According to the invention, the deformation actuators 211, 212, . . . are used doubly insofar as firstly they serve for deforming the mirror 200 and secondly they serve, by way of the over-actuation described above, to configure the positional control of the mirror 200 in such a way that an undesired excitation of natural frequencies or natural frequency modes of the mirror 200 as far as possible does not occur.

(13) The principle and the functioning of the over-actuation applied according to the invention to an optical element such as a mirror, for example, are explained below on the basis of a specific exemplary embodiment with reference to the schematic illustrates in FIGS. 3 and 4. In this case, the movement of the optical element in FIGS. 3 and 4 is restricted to a translational and a rotational degree of freedom, for the sake of simplicity, and the system is subdivided or discretized into three nodes 310, 320, 330 for describing the vibration capability, wherein each of the nodes 310, 320, 330 has a respective translational degree of freedom q.sub.1, q.sub.2 and q.sub.3 and a respective rotational degree of freedom .sub.1, .sub.2 and .sub.3.

(14) Furthermore, in accordance with FIG. 3, the same mass m is assigned to each node 310, 320, 330, wherein the nodes 310, 320, 330 are associated with the same stiffness k.

(15) The system discretized in a simplified manner in accordance with FIG. 3 shows, as illustrated schematically in FIGS. 4A-4C, three vibration modes, wherein a first vibration mode is the translation of the rigid body (FIG. 4A), a second vibration mode is the rotation of the rigid body (FIG. 4B) and a third vibration mode is a first bending vibration of the rigid body (FIG. 4C).

(16) $\begin{array}{cc}\left(\begin{array}{c}{q}_1\\ q_2\\ q_3\end{array}\right)=\left(\begin{array}{c}1\\ 1\\ 1\end{array}\right)=q_{m1}& \left(1\right)\\ \left(\begin{array}{c}{q}_1\\ q_2\\ q_3\end{array}\right)=\left(\begin{array}{c}+1\\ 0\\ -1\end{array}\right)=q_{m2}& \left(2\right)\\ \left(\begin{array}{c}{q}_1\\ q_2\\ q_3\end{array}\right)=\left(\begin{array}{c}+1\\ -1\\ +1\end{array}\right)=q_{m3}& \left(3\right)\end{array}$

(17) Conventionally, two actuators could then be chosen for a statically determinate actuation, via which actuators the rigid-body translation and the rigid-body rotation can be actuated, for which purpose, in the specific case, one actuator (for applying the force F.sub.1) can be arranged at the node 310 and the other actuator (for applying the force F.sub.3) can be arranged at the node 330. For the control of the translation and respectively rotation by a controller, a transformation matrix T.sub.a can usually be used which generates a desired translational force f and a desired torque M, via these two actuators:

(18) $\begin{array}{cc}\left(\begin{array}{c}{f}_1\\ f_2\\ f_3\end{array}\right)=T_a\left(\begin{array}{c}f\\ M\end{array}\right),\mathrm{where}{T}_a=\left(\begin{array}{cc}\frac{1}{2}& \frac{1}{2l}\\ 0& 0\\ \frac{1}{2}& \frac{1}{2l}\end{array}\right)& \left(4\right)\end{array}$
wherein the following holds true:

(19) $\begin{array}{cc}{q}_{m1}^T.Math.T_a=\left(\begin{array}{cc}1& 0\end{array}\right),q_{m2}^T.Math.T_a=\left(\begin{array}{cc}0& \frac{1}{l}\end{array}\right),q_{m3}^T.Math.T_a=\left(\begin{array}{cc}1& 0\end{array}\right)& \left(5\right)\end{array}$

(20) Upon checking how the vibration modes of the system are excited in the case of such a statically determinate actuation via the chosen actuators and using the abovementioned transformation matrix, it is then evident that the force f excites the translational rigid-body mode (mode 1) as desired and the torque M excites the rotational rigid-bodied mode (mode 2), but the force f also additionally excites the bending mode (mode 3) (since, as can be seen from (5), the bending mode (=mode 3) is visible in the translational axis). Consequently, the bending mode is also visible in the transfer function of the control loop for the translational movement and may possibly lead undesirably to a limitation of the bandwidth that can be set.

(21) The problem described above can now be rectified via the over-actuation according to the invention as follows. For this purpose, an additional actuator is provided in the exemplary embodiment, the additional actuator being arranged at the node 320 for applying the force F.sub.2 in accordance with FIG. 3. Consequently, three actuators are available for generating the forces for translation and rotation, such that compared with the above-described statically determinate actuation via two actuators, additional freedom is obtained with regard to the design of the transformation matrix Ta, since the transformation matrix Ta is now no longer uniquely determinate. In order to use the freedom additionally obtained as a result, the elements of the transformation matrix Ta are preferably chosen such that the force f and the torque M still actuate only the corresponding (translational or rotational) rigid-body degree of freedom, but the force f can no longer excite the bending mode.

(22) In the specific exemplary embodiment, the transformation matrix Ta can be chosen as follows:

(23) $\begin{array}{cc}\left(\begin{array}{c}{f}_1\\ f_2\\ f_3\end{array}\right)=T_a\left(\begin{array}{c}f\\ M\end{array}\right),\mathrm{where}{T}_a=\left(\begin{array}{cc}\frac{1}{3}& \frac{1}{2l}\\ \frac{1}{3}& 0\\ \frac{1}{3}& \frac{1}{2l}\end{array}\right)& \left(6\right)\end{array}$
wherein the following holds true:

(24) $\begin{array}{cc}{q}_{m1}^T.Math.T_a=\left(\begin{array}{cc}1& 0\end{array}\right),q_{m2}^T.Math.T_a=\left(\begin{array}{cc}0& \frac{1}{l}\end{array}\right),q_{m3}^T.Math.T_a=\left(\begin{array}{cc}0& 0\end{array}\right)& \left(7\right)\end{array}$

(25) As can be seen from (7), the bending mode (=mode 3) is no longer visible in the translational axis.

(26) FIG. 5 shows a diagram for elucidating the construction and function of a control loop for the case of an actively deformable mirror with the realization of the above-explained concept of over-actuation according to the invention. In this case, n.sub.R denotes the number of positionally controlled rigid-body degrees of freedom and n.sub.A denotes the number of positionally controlled actuators, wherein the number of actuators exceeds the number of degrees of freedom, that is to say n.sub.A>n.sub.R holds true.

(27) In accordance with FIG. 5, the desired values for the mirror position are fed to a position controller 510, which generates a static transformation matrix T.sub.a for the n.sub.R positionally controlled rigid-body degrees of freedom. On the basis of the transformation matrix T.sub.a and a driving signal for the mirror deformation, actuators 520 for actuating the mirror 530 are driven with position determination via the position sensors 540. The resultant static transformation matrix T.sub.a is in turn fed to the position controller 510, etc.

(28) FIG. 6 shows an analogous diagram for elucidating a control loop for the case of an actively deformable mirror with the realization of the concept of over-sensing according to the invention, likewise explained above. In this case, n.sub.R denotes the number of positionally controlled rigid-body degrees of freedom and n.sub.S denotes the number of sensors, wherein the number of sensors exceeds the number of degrees of freedom; n.sub.S>n.sub.R holds true.

(29) FIG. 7 shows a further exemplary embodiment of the invention, wherein components that are analogous or substantially functionally identical to FIG. 5 are designated by reference numerals increased by 200. In this case, once again n.sub.R denotes the number of positionally controlled rigid-body degrees of freedom and n.sub.A denotes the number of positionally controlled actuators, wherein the following holds true: n.sub.A>n.sub.R.

(30) The exemplary embodiment in FIG. 7 takes account of the circumstance that the over-actuation applied according to the invention can lead to undesired deformations of the optical element. The cause of the undesired deformations is that the position controller generally exerts both dynamic and small static forces in order to keep the optical element stably in position. The static forces can be position- and time-dependent. The overdeterminate application of the variable static forces to an overdeterminate number of force application points (actuators) can then lead to undesired deformations of the optical element.

(31) This problem can be solved as follows by the concept described with reference to FIG. 7: The position controller is typically a PID-like controller, i.e. a controller whose dynamic behavior has a proportional component (P component), a derivative component (D component) and an integral component (I component). The I component generates the static forces, whereas the P component and the D component generate the dynamic forces. If the I component is then separated from the PD component and applied statically determinately to a smaller statically determinate subset (n.sub.R) of actuators, the static forces are always applied statically determinately to a statically determinate number of force application points, with the result that the undesired deformations described above are avoided.

(32) FIG. 8 shows a schematic illustration of a microlithographic projection exposure apparatus which is designed for operation in the EUV and in which the present invention can be realized, for example.

(33) The projection exposure apparatus in accordance with FIG. 8 comprises an illumination device 6 and a projection lens 31. The illumination device 6 comprises, in the light propagation direction of the illumination light 3 emitted by a light source 2, a collector 26, a spectral filter 27, a field facet mirror 28 and a pupil facet mirror 29, from which the light impinges on an object field 4 arranged in an object plane 5. The light emerging from the object field 4 enters into the projection lens 31 with an entrance pupil 30. The projection lens 31 has an intermediate image plane 17, a first pupil plane 16 and a further pupil plane with a stop 20 arranged therein. The projection lens 31 comprises a total of 6 mirrors M1-M6. M6 denotes the last mirror relative to the optical beam path, the mirror having a through-hole 18. M5 denotes the penultimate mirror relative to the optical beam path, the mirror having a through-hole 19. A beam emerging from the object field 4 or reticle arranged in the object plane passes onto a wafer, arranged in the image plane 9, after reflection at the mirrors M1-M6 in order to generate an image of the reticle structure to be imaged.

(34) The arrangement according to the invention can be used for positioning and/or actively deforming one or a plurality of mirrors in the projection lens 31 and/or in the illumination device 6.

(35) Even though the invention has been described on the basis of specific embodiments, numerous variations and alternative embodiments are evident to a person skilled in the art, e.g. via combination and/or exchange of features of individual embodiments. Accordingly, it goes without saying for a person skilled in the art that such variations and alternative embodiments are concomitantly encompassed by the present invention, and the scope of the invention is restricted only within the meaning of the accompanying patent claims and the equivalents thereof.