Control device for controlling at least one manipulator of a projection lens

Abstract

The disclosure provides a control device for controlling at least one manipulator of a microlithographic projection lens by generating a travel command, which defines a change to be undertaken, of an optical effect of at least one optical element of the projection lens by manipulating a property of the optical element via the at least one manipulator along a travel. The control device is configured to generate the travel command for the at least one manipulator from a state characterization of the projection lens by optimizing a merit function. Here, the merit function includes a linear combination of at least two exponential expressions, a setting of the at least one manipulator defining the manipulation of the property of the optical element is represented via a travel variable and the respective base of the at least two exponential expressions contains a function of the travel variable.

Claims

1. A control device, wherein: the control device is configured to control a manipulator of a microlithographic projection lens by generating a travel command; the travel command defines a change to be undertaken of an optical effect of an optical element of the microlithographic projection lens by manipulating a property of the optical element via the manipulator along a travel; the control device is configured to generate the travel command for the manipulator from a state characterization of the microlithographic projection lens by optimizing a merit function; the merit function comprises a linear combination of at least two exponential expressions; a setting of the manipulator defines the manipulation of the property of the optical element is represented via a travel variable and a respective base of the at least two exponential expressions contains a function of the travel variable; and exponents of the at least two exponential expressions have different values.

2. The control device of claim 1, wherein the at least two exponential expressions have different bases.

3. The control device of claim 1, wherein each of the exponents of the at least two exponential expressions has a value of at least two.

4. The control device of claim 1, wherein, for each base of the at least two exponential expressions: the base comprises a quotient comprising a numerator and a denominator; the numerator of the base comprises a term comprising the function of the travel variable; and the denominator of the base comprises a target value for the term of the numerator and a weighting factor for the target value.

5. The control device of claim 1, wherein a difference in the values of the at least two exponents is at least five.

6. The control device of claim 1, wherein: the control device is configured to control a plurality of manipulators; the state characterization comprises a plurality of state parameters characterized by a state vector; and each of the exponential expressions comprises a sensitivity matrix defining a relationship between the travels of the manipulators and the state vector.

7. The control device of claim 1, wherein one of the exponential expressions comprises a term which describes an image aberration of the microlithographic projection lens.

8. The control device of claim 1, wherein one of the exponential expression comprises a term which describes a fading aberration of a microlithographic step-and-scan projection exposure apparatus.

9. The control device of claim 1, wherein one of the exponential expression comprises a term which describes a root mean square of a selection of image aberrations of the microlithographic projection lens.

10. The control device of claim 1, wherein one of the exponential expression comprises a term which describes a pure overlay error.

11. The control device of claim 1, wherein one of the exponential expressions includes a term which describes an error correctable by means of mechanical post-processing of an optical element of the microlithographic projection lens.

12. The control device of claim 1, wherein the merit function contains at least one implicit constraint for the travel.

13. An adjustment apparatus, the adjustment apparatus comprising: a measurement system; and a control device according to claim 1, wherein: the adjustment apparatus is configured to adjust the microlithographic projection lens; and the measurement system is configured to establish the state characterization of the microlithographic projection lens.

14. The adjustment apparatus of claim 13, wherein the measurement system comprises a wavefront measurement device.

15. An apparatus, comprising: a control device according to claim 1; and the microlithographic projection lens.

16. The apparatus of claim 15, further comprising an illumination device configured to provide radiation to the microlithographic projection lens.

17. The apparatus of claim 15, further comprising a measurement system configured establish the state characterization of the microlithographic projection lens.

18. An apparatus, comprising: an illumination optical unit configured to illuminate an object plane; a projection lens configured to image the object plane into an image plane; and a control device, wherein: the projection lens comprises an optical element and a manipulator; the control device is configured to control the manipulator by generating a travel command; the travel command defines a change to be undertaken of an optical effect of the optical element by manipulating a property of the optical element via the manipulator along a travel; the control device is configured to generate the travel command for the manipulator from a state characterization of the projection lens by optimizing a merit function; the merit function comprises a linear combination of at least two exponential expressions; a setting of the manipulator defining the manipulation of the property of the optical element is represented via a travel variable and a respective base of the at least two exponential expressions contains a function of the travel variable; and exponents of the at least two exponential expressions have different values.

19. The apparatus of claim 18, further comprising a measurement system configured establish the state characterization of the microlithographic projection lens.

20. A method of controlling a manipulator of a microlithographic projection lens, the method comprising: generating a travel command for the manipulator by carrying out an optimization of a merit function, wherein: the merit function comprises a linear combination of at least two exponential expressions; a setting of the manipulator defines a manipulation of a property of an optical element of the microlithographic projection lens is represented via a travel variable, and a respective base of the at least two exponential expressions contains a function of the travel variable; and exponents of the at least two exponential expressions have different values; and manipulating the property of the optical element via the manipulator along the travel variable defined by the generated travel command to change an optical effect of the optical element of the microlithographic projection lens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and further advantageous features of the disclosure are illustrated in the following detailed description of exemplary embodiments according to the disclosure with reference to the accompanying schematic drawings.

(2) FIG. 1 shows a visualization of an embodiment of a control device according to the disclosure, for controlling manipulators of a microlithographic projection lens and a post-processing device.

(3) FIG. 2 shows a visualization of an embodiment of a microlithographic projection exposure apparatus according to the disclosure, including a projection lens and a control device for controlling manipulators of the projection lens, and

(4) FIG. 3 shows a diagram visualizing the profile of a merit function component which is part of a merit function of an optimization algorithm running in the control device.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(5) In the exemplary embodiments or embodiments or embodiment variants described below, elements which are functionally or structurally similar to one another are provided with the same or similar reference signs as far as possible. Therefore, for understanding the features of the individual elements of a specific exemplary embodiment, reference should be made to the description of other exemplary embodiments or the general description of the disclosure.

(6) In order to facilitate the description, a Cartesian xyz-coordinate system is indicated in the drawing, from which system the respective positional relationship of the components illustrated in the figures is evident. In FIG. 1, the y-direction runs perpendicular and into the drawing plane, the x-direction toward the right, and the z-direction upwardly.

(7) FIG. 1 shows an adjustment apparatus 10 for adjusting a projection lens 16 of a microlithographic projection exposure apparatus. The adjustment apparatus 10 includes a measurement system 12 for establishing a state characterization 34 of the projection lens 16 and a control device 14 in the form of a so-called travel establishing device for generating a travel command 38 from the state characterization 34.

(8) The projection lens 16 serves to image mask structures from an object plane 24 into an image plane 28 and it can be designed for exposure radiation at different wavelengths, such as e.g. 248 nm or 193 nm. In the present exemplary embodiment, the projection lens 16 is designed for a wavelength in the EUV wavelength range, e.g. 13.5 nm.

(9) The measurement system 12 is configured to measure wavefront errors of the projection lens 16 and it includes an illumination device 18 and a measurement mask 22 on the entrance side of the projection lens 16 and a sensor element 26, a detector 30 and an evaluation device 32 on the exit side of the projection lens. The illumination device 18 is configured to generate measurement radiation 20 at the operating wavelength of the projection lens 16 to be tested, in the present case in the form of EUV radiation, and to radiate the radiation onto the measurement mask 22, which is arranged in the object plane 24. Within the scope of this application, EUV radiation should be understood to mean electromagnetic radiation with a wavelength of less than 100 nm, in particular a wavelength of approximately 13.5 nm or approximately 6.7 nm. The measurement mask 22, which is often also referred to as a “coherence mask”, has a first periodic structure. The sensor element 26 in the form of an image grating, which has a second periodic structure, is arranged in the image plane 28. It is also possible to combine chequerboard structures on the measurement mask 22 with chequerboard structures in the sensor element 26. It is also possible to use other combinations of periodic structures known to a person skilled in the art from the field of shearing interferometry or point diffraction interferometry.

(10) A detector 30 in the form of a camera, which resolves in two dimensions, is arranged below the sensor element 26, to be precise in the plane conjugate to the pupil plane of the projection lens 16. Together, the sensor element 26 and the detector 30 form a sensor module. The measurement mask 22 and the sensor module form a shearing interferometer or point diffraction interferometer, known to a person skilled in the art, and serve to measure wavefront errors of the projection lens 16. To this end, phase shifting methods, which are known to a person skilled in the art, are applied in particular.

(11) The evaluation device 32 establishes the state characterization 34 of the projection lens 16 from the intensity patterns recorded by the detector 30. In accordance with the present embodiment, the state characterization 34 includes a set of Zernike coefficients b.sub.j characterizing the wavefront errors of the projection lens 16.

(12) In the present application, the Zernike functions Z.sub.m.sup.n, as known from e.g. Chapter 13.2.3 in the textbook “Optical Shop Testing”, 2.sup.nd Edition (1992) by Daniel Malacara, pub. John Wiley & Sons, Inc., are denoted by Z.sub.j in accordance with the so-called fringe sorting, as described in e.g. paragraphs [0125]-[0129] in US 2013/0188246A1, with b.sub.j then being the Zernike coefficients assigned to the respective Zernike polynomials (also referred to as “Zernike functions”). The fringe sorting is visualized, for example, in Table 20-2 on page 215 of the “Handbook of Optical Systems”, Vol. 2 by H. Gross, 2005 Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim. The wavefront deviation W(ρ,Φ) at a point in the object plane of the projection lens is then developed as follows in a manner dependent on the polar coordinates (ρ,Φ) of the pupil plane:

(13) $\begin{array}{cc}W\left(\rho ,\Phi \right)=\underset{j}{.Math.}{b}_j.Math.Z_j\left(\rho ,\Phi \right)& \left(1\right)\end{array}$

(14) While the Zernike functions are denoted by Z.sub.j, i.e. with the subscript index j, the Zernike coefficients are denoted by b.sub.j within the scope of this application. It should be noted here that the Zernike coefficients b.sub.j are often also denoted by Zj, i.e. with a normally written index, in the specialist world, such as e.g. Z5 and Z6 representing astigmatism.

(15) The state characterization 34 established by the evaluation device 32 of the measurement system 12 is transferred to the control device 14, which generates the travel command 38 therefrom. The travel command 38 includes travels x.sub.i and travels x.sub.n.sup.L. These travels x.sub.i serve to control manipulators M.sub.s of the projection lens 16, while the travels x.sub.n.sup.L serve to control a post-processing device 36 for mechanical post-processing of optical elements of the projection lens 16. Within the scope of this application, both the manipulators M.sub.s and the post-processing device 36 are understood to be manipulators of the projection lens 16 in the general sense.

(16) The projection lens 16 only has four optical elements L1 to L4 in the embodiment in accordance with FIG. 1. All optical elements are mounted in a movable manner. To this end, a respective manipulator M.sub.s, namely respectively one of the manipulators M1 to M4, is assigned to each one of the optical elements L1 to L4. The manipulators M1, M2 and M3 each enable a displacement of the assigned optical elements L1, L2 and L3 in the x- and y-direction and therefore substantially parallel to the plane in which the respective reflecting surface of the optical elements lies.

(17) The manipulator M4 is configured to tilt the optical element L4 by rotation about a tilt axis 40 arranged parallel to the y-axis. As a result, the angle of the reflecting surface of L4 is changed in relation to the incident radiation. Further degrees of freedom for the manipulators are conceivable. Thus, for example, provision can be made for a displacement of the relevant optical element transversely to the optical surface thereof or for a rotation about a reference axis perpendicular to the reflecting surface.

(18) In general terms, each one of the manipulators M1 to M4 illustrated here is provided to bring about a displacement of the assigned optical element L1 to L4 while performing a rigid body movement along a predetermined travel. By way of example, such a travel can combine translations in different directions, tilts and/or rotations in any manner. Alternatively or additionally, it is also possible to provide manipulators which are configured to undertake a different mannered change of a state variable of the assigned optical element by an appropriate actuation of the manipulator. In this respect, an actuation can be carried out by e.g. applying a specific temperature distribution or specific force distribution to the optical element. In this case, the travel can be as a result of a change in the temperature distribution of the optical element or the application of local tension to an optical element embodied as a deformable lens or as a deformable mirror.

(19) In the shown case, the travels x.sub.i included by the travel command 38 contain the travels x.sub.1, x.sub.2, x.sub.3 and x.sub.4, which specify changes to be carried out by the manipulators M1 to M4 and which therefore serve to control the manipulators M1 to M4 of the projection lens 16. The established travels x.sub.1 to x.sub.4 are transferred to the individual manipulators M1 to M4 by way of travel signals and they provide the manipulators with respective correction travels to be carried out. These define corresponding displacements of the assigned optical elements L1 to L4 for correcting wavefront errors of the projection lens 16 that occurred. In the case where a manipulator has a plurality of degrees of freedom, it is also possible to transfer a plurality of travels x.sub.i thereto.

(20) The travels x.sub.n.sup.L furthermore included by the travel command 38 contain the travels x.sub.n.sup.1, x.sub.n.sup.2, x.sub.n.sup.3 and x.sub.n.sup.4 in the shown case, which travels serve to control the post-processing device 36 for the respective mechanical post-processing of the optical elements L1, L2, L3 and L4 of the projection lens 16. Therefore, like the travels x.sub.1 to x.sub.4, the travels x.sub.n.sup.1 to x.sub.n.sup.4 serve to correct wavefront errors of the projection lens 16 that occurred. The post-processing device 36 should be understood to mean a device for mechanical ablation of material at an optical surface of an optical element in the form of a lens or mirror. This ablation is subsequent to the production of the optical element and it serves, in particular, to change a spherical surface into an aspherical surface. Therefore, a correspondingly post-processed optical element is referred to as an intrinsically corrected asphere (ICA). In particular, an ablation device usually used for the mechanical processing of ICAs can be used as a post-processing device 36. Therefore, the ablations are also referred to as “ICA ablations” below. By way of example, an ion beam can be used for mechanical processing. Using this, it is possible to work any correction profile into a post-processed optical element.

(21) The functionality of the control device 14 is illustrated below in an exemplary manner. It is configured to carry out a travel-generating optimization algorithm. The optimization algorithm serves to optimize a merit function H, which is also referred to as figure-of-merit function.

(22) Below, the travels of the travel command 38 which is to be generated by the optimization algorithm are described using one travel variable, the travel variable including a travel vector x and a further travel vector x.sup.L. The vector components of the travel vector x are the aforementioned individual travels x.sub.i of the manipulators provided in the projection lens 16. The vector components of the travel vector x.sup.L are the travels serving to control the ICA post-processing device 36 and x.sub.n.sup.L. The travels x.sub.i and x.sub.n.sup.L are also referred to as travel variables. The state characterization 34 is described by a state vector b, the vector components of which are the aforementioned Zernike coefficients b.sub.j. The Zernike coefficients b.sub.j are also referred to as state parameters. The sensitivities of the manipulators, in the present case the manipulators M1 to M4, in relation to the degrees of freedom thereof in the case of a state change are described via a sensitivity matrix M in accordance with one embodiment variant. Here, the sensitivity matrix M describes the relationship between an adjustment of a degree of freedom i of a manipulator by a standard travel x.sub.i.sup.0 and a change, resulting therefrom, of the state vector b of the projection lens 16.

(23) In accordance with one embodiment, the travel-generating optimization algorithm according to the disclosure is configured to solve the following optimization problem:
min(H)  (2)

(24) Further details in respect of the basic solution of such an optimization problem can be gathered from, for example, WO2010/034674A1, in particular from pages 38 to 45.

(25) In accordance with one embodiment, the merit function H is composed as follows from a plurality of merit function components:
H=H.sub.b+H.sub.f+H.sub.ovl+H.sub.x+H.sub.ica+H.sub.rms  (3)

(26) Here, the component H.sub.b contains the weighted individual Zernike coefficients b.sub.j. H.sub.f contains specifications in respect of so-called fading aberrations. A fading aberration is understood to mean a specification as to how an image aberration changes in the scanning direction of a projection exposure apparatus, i.e. in the direction of the relative movement between the mask and the wafer during the exposure. H.sub.ovl contains specifications in respect of so-called overlay errors. An overlay error specifies a local image position displacement of an imaged mask structure in relation to the setpoint position thereof on the substrate. H.sub.x describes the boundary conditions of the manipulators M.sub.s. H.sub.ica describes boundary conditions of the ICA ablations to be carried out via the post-processing device 36. Since the boundary conditions described via H.sub.x and via H.sub.ica are described within the scope of the merit function H, these are so-called implicit constraints. H.sub.rms contains grouped RMS values of the Zernike coefficients b.sub.j. As a person skilled in the art knows, an RMS value of coefficients should be understood to mean the square root of the sum of the squares of the coefficients.

(27) An exemplary embodiment for the merit function component H.sub.b is described below. The condition for the individual Zernike coefficients b.sub.j is:
|(Mx−b).sub.j|≦S.sub.j.sup.b  (4)

(28) Here, S.sub.j.sup.b is the target value or the predetermined specification for the Zernike coefficients b.sub.j. M is the sensitivity matrix, already described above, and x is the travel vector relating to the manipulators M.sub.s. The merit function component H.sub.b describing the contribution of the Zernike coefficients b.sub.j in the merit function H is as follows:

(29) $\begin{array}{cc}{H}_b=\underset{j}{.Math.}{\left(\frac{{\left(\mathrm{Mx}-b\right)}_j}{t_j^b*S_j^b}\right)}^{2n_j^b}& \left(5\right)\end{array}$

(30) Here, t.sub.j.sup.b and n.sub.j.sup.b denote parameters that are freely selectable by the user. The respective target value S.sub.j.sup.b for the corresponding Zernike coefficient is a so-called “hard” target value in accordance with one exemplary embodiment. This is taken into account when selecting the respective parameter t.sub.j.sup.b by virtue of a value in the range from 0.6 to 0.95 being assigned to the parameter t.sub.j.sup.b. The parameter t.sub.j.sup.b is also denoted a weighting factor for the target value S.sub.j.sup.b. A “hard target value” should be understood to mean a target value which may only be slightly overshot or undershot.

(31) If the substitutions δb.sub.j=(Mx−b).sub.j and sb.sub.j=t.sub.j.sup.b*S.sub.j.sup.b are carried out, H.sub.b can be expressed as follows:

(32) $\begin{array}{cc}{H}_b=\underset{j}{.Math.}{\left(\frac{\delta b_j}{s{b}_j}\right)}^{2n_j^b}& \left(5^{\prime }\right)\end{array}$

(33) Hence, H.sub.b is a linear combination of the exponential expressions

(34) ${\left(\frac{\delta b_j}{s{b}_j}\right)}^{2n_j^b}.$
The base

(35) $\left(\frac{\delta b_j}{s{b}_j}\right)$
of the exponential expressions contains a function of the travel vector x and hence of the travel variable x.sub.i. The aforementioned freely selectable parameters n.sub.j.sup.b are the associated exponents of the aforementioned exponential expressions. Since the target value S.sub.j.sup.b is a “hard” target value in the present exemplary embodiment, a value greater than 10, in particular greater than 18 is assigned to the respective exponent n.sub.j.sup.b. In accordance with one exemplary embodiment, the value assigned to the respective exponent n.sub.j.sup.b is in the range from 10 to 30 in each case.

(36) The diagram depicted in FIG. 3 shows the merit function component H.sub.b as a function of the base

(37) $\left(\frac{\delta b_j}{s{b}_j}\right).$
What is possible to read off from the diagram is that, as a result of the selection of the exponent n.sub.j.sup.b, the function becomes very steep when δb.sub.j is close to the weighted target value sb.sub.j in respect of magnitude. Although outliers in the Zernike coefficients b.sub.j, i.e. values of b.sub.j above or below the target value, are admitted, they are weighted so strongly that they hardly appear in practical terms.

(38) An exemplary embodiment for the merit function component H.sub.f is described below. The so-called fading aberrations b.sub.f.sup.j can be calculated from the measured Zernike aberrations b.sub.j. The condition for the fading aberrations b.sub.f.sup.j is as follows:
δf.sub.j≦S.sub.j.sup.f  (6)
wherein

(39) $\begin{array}{cc}\delta f_j=\sqrt{\underset{m}{.Math.}{w_m\left(M_f^{j}x-b_f^j\right)}_m^2}& \left(7\right)\end{array}$

(40) Here, S.sub.j.sup.f is the target value or the predetermined specification for the fading aberration b.sub.f.sup.j. The sum m runs over all field points along the scanning direction of the projection exposure apparatus. The parameter w.sub.m denotes so-called scan weightings, i.e. weightings of the image aberrations which can be traced back to the scanning movement. M.sub.f.sup.j denotes a sensitivity matrix for the fading aberrations b.sub.f.sup.j and therefore defines the change in the state vector b of the projection lens due to fading aberrations when adjusting the manipulators M.sub.s by one standard travel x.sub.0.

(41) The merit function component H.sub.f describing the contribution of the fading aberrations in the merit function H is as follows:

(42) $\begin{array}{cc}{H}_f=\underset{j}{.Math.}{\left(\frac{\delta f_j}{t_j^f{S}_j^f}\right)}^{2n_j^f}& \left(8\right)\end{array}$

(43) Here, t.sub.j.sup.f and n.sub.j.sup.f denote parameters that are freely selectable by the user. The respective target value S.sub.j.sup.f for the corresponding fading aberration is a so-called “hard” target value in accordance with one exemplary embodiment. This is taken into account when selecting the respective parameter t.sub.j.sup.f by virtue of a value in the range from 0.6 to 0.95 being assigned to the parameter t.sub.j.sup.f. The parameter t.sub.j.sup.f is also denoted a weighting factor for the target value S.sub.j.sup.f.

(44) Hence, H.sub.b is a linear combination of the exponential expressions

(45) ${\left(\frac{\delta f_j}{t_j^f{S}_j^f}\right)}^{2n_j^f}.$
The base

(46) 0$\left(\frac{\delta f_j}{t_j^f{S}_j^f}\right)$
of the exponential expressions contains a function of the travel vector x and hence of the travel variable x.sub.i. The aforementioned freely selectable parameters n.sub.j.sup.f are the associated exponents of the aforementioned exponential expressions. Since the target value S.sub.j.sup.f is a “hard” target value in the present exemplary embodiment, a value greater than 10, in particular greater than 18 is assigned to the respective exponent n.sub.j.sup.f. In accordance with one exemplary embodiment, the value assigned to the respective exponent n.sub.j.sup.f is in the range from 10 to 30 in each case.

(47) The profile of the merit function component H.sub.f as a function of the base

(48) $\left(\frac{\delta f_j}{t_j^f{S}_j^f}\right)$
corresponds substantially to the profile of the merit function component H.sub.b depicted in FIG. 3. The explanations made above in respect of the profile of the diagram in accordance with FIG. 3 can therefore be transferred to the profile of H.sub.f.

(49) An exemplary embodiment for the merit function component H.sub.ovl is described below. Overlay errors are determined for different structure types, such as e.g. isolated lines, lines arranged in a grid, circular structures, etc. The different structure types are denoted by the index p. An overlay error as a function of the structure type p and the field point m is denoted by the product (SZ.sup.pb).sub.m. Here, SZ.sup.p is a matrix which includes field point-dependent weightings for the individual Zernike coefficients b.sub.j. An overlay error (SZ.sup.pb).sub.m is therefore formed by linear combinations of individual Zernike coefficients b.sub.j.

(50) The condition for the overlay errors (SZ.sup.pb).sub.m in the optimization algorithm is as follows:
OVL.sub.p≦S.sub.p.sup.ovl,  (9)
wherein
OVL.sub.p=max.sub.m((SZ.sup.pMx−SZ.sup.pb).sub.m)  (10)

(51) Here, S.sub.p.sup.ovl is the target value or the predetermined specification for the overlay error of the structure type p. The matrix M is the sensitivity matrix already described above in relation to the merit function component H.sub.b. The max function determines the maximum over all field points m.

(52) The merit function component H.sub.ovl describing the contribution of the overlay errors in the merit function H is as follows:

(53) $\begin{array}{cc}{H}_{\mathrm{ovl}}=\underset{m}{.Math.}\underset{p}{.Math.}{\left(\frac{{\left({\mathrm{SZ}}^p\mathrm{Mx}-{\mathrm{SZ}}^{p}b\right)}_m}{t_p^{\mathrm{ovl}}*S_p^{\mathrm{ovl}}}\right)}^{2n_p^{\mathrm{ovl}}}& \left(11\right)\end{array}$

(54) Here, t.sub.p.sup.ovl and n.sub.p.sup.ovl denote parameters that are freely selectable by the user. The respective target value S.sub.p.sup.ovl for the corresponding overlay error is a so-called “hard” target value in accordance with one exemplary embodiment. This is taken into account when selecting the respective parameter t.sub.p.sup.ovl by virtue of a value in the range from 0.6 to 0.95 being assigned to the parameter t.sub.p.sup.ovl. The parameter t.sub.p.sup.ovl is also denoted a weighting factor for the target value S.sub.p.sup.ovl.

(55) Hence, H.sub.ovl is a linear combination of the exponential expressions

(56) ${\left(\frac{{\left({\mathrm{SZ}}^p\mathrm{Mx}-{\mathrm{SZ}}^{p}b\right)}_m}{t_p^{\mathrm{ovl}}*S_p^{\mathrm{ovl}}}\right)}^{2n_p^{\mathrm{ovl}}}.$
The base

(57) $\left(\frac{{\left({\mathrm{SZ}}^p\mathrm{Mx}-{\mathrm{SZ}}^{p}b\right)}_m}{t_p^{\mathrm{ovl}}*S_p^{\mathrm{ovl}}}\right)$
of the exponential expressions contains a function of the travel vector x and hence of the travel variable x.sub.i. The aforementioned freely selectable parameters n.sub.p.sup.ovl are the associated exponents of the aforementioned exponential expressions. Since the target value S.sub.p.sup.ovl is a “hard” target value in the present exemplary embodiment, a value greater than 10, in particular greater than 18 is assigned to the respective exponent n.sub.p.sup.ovl. In accordance with one exemplary embodiment, the value assigned to the respective exponent n.sub.p.sup.ovl is in the range from 10 to 30 in each case.

(58) The profile of the merit function component H.sub.ovl as a function of the base

(59) $\left(\frac{{\left({\mathrm{SZ}}^p\mathrm{Mx}-{\mathrm{SZ}}^{p}b\right)}_m}{t_p^{\mathrm{ovl}}*S_p^{\mathrm{ovl}}}\right)$
corresponds substantially to the profile of the merit function component H.sub.b depicted in FIG. 3. The explanations made above in respect of the profile of the diagram in accordance with FIG. 3 can therefore be transferred to the profile of H.sub.ovl.

(60) An exemplary embodiment for the merit function component H.sub.x is described below. The travels x.sub.i of the manipulators M.sub.s have lower limits x.sub.i.sup.min and upper limits x.sub.i.sup.max, and so the following applies:
x.sub.i.sup.min≦x.sub.i≦x.sub.i.sup.max  (12)

(61) As already explained above, an individual x.sub.i denotes one degree of freedom of a manipulator M.sub.s, wherein the individual manipulators may have one or more degrees of freedom. If the following substitutions are used:

(62) $\begin{array}{cc}{y}_i=\left(m_i{x}_i+c_i\right)& \left(13\right)\\ m_i=\frac{2}{x_i^{\max }-x_i^{\min }}& \left(14\right)\\ c_i=\frac{x_i^{\max }+x_i^{\min }}{x_i^{\min }-x_i^{\max }},& \left(15\right)\end{array}$
equation (12) can be expressed in the following form:
−1≦y.sub.i≦1  (16)

(63) The merit function component H.sub.x relating to the limits of the manipulators is then expressed as:

(64) $\begin{array}{cc}{H}_x=\underset{i=1}{\overset{\mathrm{DOF}}{.Math.}}{\left(\frac{y_i}{t_i^y}\right)}^{2n_i^y}& \left(17\right)\end{array}$

(65) Here, the sum of the index i runs over all degrees of freedom of all manipulators M.sub.s. The parameters freely selectable by the user are t.sub.i.sup.y and n.sub.i.sup.y. The limits x.sub.i.sup.min and x.sub.i.sup.max are so-called “hard” target values. This is taken into account when selecting the corresponding parameter t.sub.i.sup.y by virtue of a value in the range from 0.6 to 0.95 being assigned to the parameter t.sub.i.sup.y.

(66) Hence, H.sub.x is a linear combination of the exponential expressions

(67) ${\left(\frac{y_i}{t_i^y}\right)}^{2n_i^y}.$
The parameter y.sub.i and hence the base

(68) $\left(\frac{y_i}{t_i^y}\right)$
of the exponential expressions contains a function of the travel vector x and hence of the travel variable x.sub.i. The aforementioned freely selectable parameters n.sub.i.sup.y are the associated exponents of the aforementioned exponential expressions. Since the limits x.sub.i.sup.min and x.sub.i.sup.max are “hard” target values in the present exemplary embodiment, a value greater than 10, in particular greater than 18 is assigned to the respective exponent n.sub.i.sup.y. In accordance with one exemplary embodiment, the value assigned to the respective exponent n.sub.i.sup.y lies in the range from 10 to 30 in each case.

(69) The profile of the merit function component H.sub.x as a function of the base

(70) 0$\left(\frac{y_i}{t_i^y}\right)$
corresponds substantially to the profile of the merit function component H.sub.b depicted in FIG. 3. The explanations made above in respect of the profile of the diagram in accordance with FIG. 3 can therefore be transferred to the profile of H.sub.x.

(71) An exemplary embodiment for the merit function component H.sub.ica is described below. As already mentioned above, H.sub.ica describes boundary conditions of the ICA ablations to be undertaken via the post-processing device 36 on individual optical elements, such as the optical elements L1 to L4 of the projection lens 16 in accordance with FIG. 1. The profiles F.sub.L(x.sup.K,y.sup.K) generated in an optical element via ICA ablations can be described as follows as a sum of n base functions f.sub.n.sup.L(x.sup.K,y.sup.K):

(72) $\begin{array}{cc}{F}_L\left(x^K,y^K\right)=\underset{o}{.Math.}{f}_o^L\left(x^K,y^K\right)x_n^L& \left(18\right)\end{array}$

(73) Here, x.sup.K and y.sup.K denote the Cartesian x- and y-coordinates on a relevant optical element L. In accordance with one exemplary embodiment, the base functions f.sub.o.sup.L(x.sup.K,y.sup.K) are calculated from the measured Zernike coefficients b.sub.j of the projection lens 16 using a conversion matrix containing the sensitivities for ICA ablations. In this case, the base functions f.sub.o.sup.L(x.sup.K,y.sup.K) contain a sum of Zernike polynomials. Alternatively, the base functions f.sub.o.sup.L(x.sup.K,y.sup.K) can also be built up from spline functions, Legendre polynomials, etc.

(74) A peak-to-Valley function PV.sub.L of the ICA ablations is defined as follows:

(75) $\begin{array}{cc}{\mathrm{PV}}_L=\underset{x^K,y^K}{\max }{F}_L\left(x^K,y^K\right)-\underset{x^K,y^K}{\min }{F}_L\left(x^K,y^K\right)& \left(19\right)\end{array}$

(76) The limit condition for the resulting profile F.sub.L(x.sup.K,y.sup.K) is as follows:
PV.sub.L≦S.sub.L.sup.pv  (20)

(77) Here, the target value S.sub.L.sup.pv is a value which is determined by the ion beam production process. Equation (20) ensures that variations in the profile cannot become arbitrarily large. In accordance with the described exemplary embodiment, the corresponding target value S.sub.L.sup.pv is a so-called “soft” target value, which need not be observed as precisely as a “hard” target value.

(78) The merit function component H.sub.ica relating to the limits of ICA ablations is as follows:

(79) $\begin{array}{cc}{H}_{\mathrm{ica}}=\underset{L}{.Math.}\underset{n}{.Math.}{\left(\frac{2f_n^L\left(x^K,y^K\right)x_n^L}{t_L^{\mathrm{pv}}*S_L^{\mathrm{pv}}}\right)}^{2n_L^{\mathrm{pv}}}& \left(21\right)\end{array}$

(80) The sum of the index L runs over all optical elements in the case of which ICA ablations are undertaken and the sum over k runs over all base functions used to describe the relevant optical element.

(81) Furthermore, t.sub.L.sup.pv and n.sub.L.sup.pv denote parameters that are freely selectable by the user. Since the target value S.sub.L.sup.pv for the corresponding profile of the ICA ablation is a “soft” target value, a value in the range from 0.5 to 2.0 is assigned to the parameter t.sub.L.sup.pv. The parameter t.sub.L.sup.pv is also denoted a weighting factor for the target value S.sub.L.sup.pv.

(82) Hence, H.sub.ica is a linear combination of the exponential expressions

(83) ${\left(\frac{2f_n^L\left(x^K,y^K\right)x_n^L}{t_L^{\mathrm{pv}}*S_L^{\mathrm{pv}}}\right)}^{2n_L^{\mathrm{pv}}}.$
The base

(84) $\left(\frac{2f_n^L\left(x^K,y^K\right)x_n^L}{t_L^{\mathrm{pv}}*S_L^{\mathrm{pv}}}\right)$
of the exponential expressions contains a function of the above-described travel vector x.sup.L and hence of the travel variable x.sub.n.sup.L. The aforementioned freely selectable parameters n.sub.L.sup.pv are the associated exponents of the aforementioned exponential expressions. Since the target value S.sub.L.sup.pv is a “soft” target value in the present exemplary embodiment, a value from 3 to 10 is assigned to the exponent n.sub.L.sup.pv.

(85) The profile of the merit function component H.sub.ica as a function of the base

(86) $\left(\frac{2f_n^L\left(x^K,y^K\right)x_n^L}{t_L^{\mathrm{pv}}*S_L^{\mathrm{pv}}}\right)$
differs from the profile of the merit function component H.sub.b, depicted in FIG. 3, substantially in that the approach to the vertical lines arranged at −1 and +1 is less steep and the lines are exceeded more strongly.

(87) An exemplary embodiment for the merit function component H.sub.rms is described below. To this end, grouped RMS values RMS.sup.r are defined as follows:

(88) $\begin{array}{cc}{\mathrm{RMS}}^r=\underset{m}{\max }\sqrt{\underset{j}{.Math.}\left({{\alpha }_j^r\left(\mathrm{Mx}-b\right)}_{j,m}^2\right)}& \left(22\right)\end{array}$

(89) Here, r is an index of the grouped RMS value RMS.sup.r. By way of example, the grouping is carried out by classifying the corresponding Zernike coefficients b.sub.j into the categories “spherical aberrations”, “coma”, “astigmatism”, etc. The sum over j is a sum over Zernike orders, α.sub.j.sup.r are the weightings of the individual Zernike contributions b.sub.j to the RMS value with the index r and the maximum is established over all field points m of the image field of the projection lens 16. In accordance with different embodiments, the grouped RMS values RMS.sup.r include all Zernike coefficients Zj with j≦10, with j≦25, to with j≦49, with j≦64 or with j≦100.

(90) The conditions for the RMS values are as follows:
RMS.sup.r≦S.sub.r.sup.rms  (23)

(91) Here, S.sub.r.sup.rms is the target value or the predetermined specification for the RMS value with the index r. The merit function component H.sub.rms describing the contribution of the RMS values in the merit function H is as follows:

(92) $\begin{array}{cc}{H}_{\mathrm{rms}}=\underset{r}{.Math.}\underset{m}{.Math.}{\left(\underset{j}{.Math.}\frac{{{\alpha }_r^j\left(\mathrm{Mx}-b\right)}_{j,m}^2}{{\left(t_r^{\mathrm{rms}}{S}_r^{\mathrm{rms}}\right)}^2}\right)}^{n_r^{\mathrm{rms}}}& \left(24\right)\end{array}$

(93) Here, t.sub.r.sup.rms and n.sub.r.sup.rms denote parameters that are freely selectable by the user. The respective target value S.sub.r.sup.rms for the corresponding RMS value is a so-called “hard” target value in accordance with one exemplary embodiment. This is taken into account when selecting the respective parameter t.sub.r.sup.rms by virtue of a value in the range from 0.6 to 0.95 being assigned to the parameter t.sub.r.sup.rms. The parameter t.sub.r.sup.rms is also denoted a weighting factor for the target value S.sub.r.sup.rms.

(94) Hence, H.sub.rms is a linear combination of the exponential expressions

(95) ${\left(\underset{j}{.Math.}\frac{{{\alpha }_r^j\left(\mathrm{Mx}-b\right)}_{j,m}^2}{{\left(t_r^{\mathrm{rms}}{S}_r^{\mathrm{rms}}\right)}^2}\right)}^{n_r^{\mathrm{rms}}}.$
The base

(96) 0$\left(\underset{j}{.Math.}\frac{{{\alpha }_r^j\left(\mathrm{Mx}-b\right)}_{j,m}^2}{{\left(t_r^{\mathrm{rms}}{S}_r^{\mathrm{rms}}\right)}^2}\right)$
of the exponential expressions contains a function of the travel vector x and hence of the travel variable x.sub.i. The aforementioned freely selectable parameters n.sub.r.sup.rms are the associated exponents of the aforementioned exponential expressions. Since the target value S.sub.r.sup.rms is a “hard” target value in the present exemplary embodiment, a value greater than 20, in particular greater than 36 is assigned to the respective exponent n.sub.r.sup.rms. In accordance with one exemplary embodiment, the value assigned to the exponent n.sub.r.sup.rms is in the range from 20 to 60.

(97) The profile of the merit function component H.sub.rms as a function of the base

(98) $\left(\underset{j}{.Math.}\frac{{{\alpha }_r^j\left(\mathrm{Mx}-b\right)}_{j,m}^2}{{\left(t_r^{\mathrm{rms}}{S}_r^{\mathrm{rms}}\right)}^2}\right)$
corresponds substantially to the profile of the merit function component H.sub.b depicted in FIG. 3. The explanations made above in respect of the profile of the diagram in accordance with FIG. 3 can therefore be transferred to the profile of H.sub.rms.

(99) The parameters n.sub.j.sup.b, n.sub.j.sup.f, n.sub.p.sup.ovl, n.sub.i.sup.y, n.sub.L.sup.pv and n.sub.r.sup.rms are selected in such a way that the exponents 2n.sub.j.sup.b, 2n.sub.j.sup.f, 2n.sub.p.sup.ovl, 2n.sub.i.sup.y, 2n.sub.L.sup.pv and 2n.sub.r.sup.rms emerging thus in the individual merit function components have at least two different values. In other words, there is at least one exponent, the value of which differs from that of the other exponents. In accordance with further exemplary embodiments, the aforementioned exponents have a multiplicity of different values; in particular, each one of the exponents has a different value. As a result, the weightings of the different optimization variables can be set individually in a targeted manner during the optimization and hence the optimization result can be adapted ideally to the boundary conditions present.

(100) FIG. 2 shows an embodiment according to the disclosure of a microlithographic projection exposure apparatus 50. The present embodiment is designed for operation in the EUV wavelength range. All optical elements are embodied as mirrors as a result of this operating wavelength. However, the disclosure is not restricted to projection exposure apparatuses in the EUV wavelength range. Further embodiments according to the disclosure are designed, for example, for operating wavelengths in the UV range, such as e.g. 365 nm, 248 nm or 193 mm. In this case, at least some of the optical elements are configured as conventional transmission lens elements.

(101) The projection exposure apparatus 10 in accordance with FIG. 2 includes an exposure radiation source 52 for generating exposure radiation 54. In the present case, the exposure radiation source 52 is embodied as an EUV source and it can include, for example, a plasma radiation source. The exposure radiation 54 initially passes through an illumination optical unit 56 and it is guided onto a mask 58 thereby. The illumination optical unit 56 is configured to generate different angle distributions of the exposure radiation 54 incident on the mask 58. Depending on an illumination setting desired by the user, the illumination optical unit 56 configures the angle distribution of the exposure radiation 54 incident on the mask 58. Examples for selectable illumination settings include a so-called dipole illumination, annular illumination and quadrupole illumination.

(102) The mask 58 has mask structures to be imaged on a substrate 64 in the form of a wafer and it is displaceably mounted on a mask displacement stage 60. As depicted in FIG. 2, the mask 58 can be embodied as a reflection mask or, alternatively, it can also be configured as a transmission mask, in particular for UV lithography. In the embodiment in accordance with FIG. 2, the exposure radiation 54 is reflected at the mask 58 and it thereupon passes through the projection lens 16, which was already described with reference to the adjustment apparatus 10 in accordance with FIG. 1. The projection lens serves to image the mask structures of the mask 58 on the substrate 64. The exposure radiation 54 is guided within the projection lens 16 via a multiplicity of optical elements, presently in the form of mirrors. The substrate 64 is displaceably mounted on a substrate displacement stage 66. The projection exposure apparatus 50 can be designed as a so-called scanner or a so-called stepper.

(103) In the case of an embodiment is a scanner, which is also referred to as a step- and scan projection exposure apparatus, the mask displacement stage 60 and the substrate displacement stage 66 are moved in opposite directions during each instance of imaging the mask 58 on the substrate 64, i.e. each instance of exposing a field on the substrate 64. As shown in FIG. 2, in this case, for example, the mask displacement stage 60 moves in a scanning direction 62 pointing to the left and the substrate displacement stage moves in a scanning direction 68 pointing to the right. The fading aberrations, described above in the context of the description of the merit function component H.sub.f, can be traced back to the scanning movements during the field exposure of such a scanner.

(104) The projection exposure apparatus 50 furthermore includes a central controller 72 for controlling the exposure process, including the mask displacement stage 60 and the substrate displacement stage 66. The projection exposure apparatus 10 furthermore includes a control device 114 for controlling the manipulators M1 to M4. The control device 114, in turn, includes a state encoder 80 and a travel establishing device 86. The state encoder 80 transmits current state characterisations 34a of the projection lens 16 to the travel establishing device 86, which generates a travel command 138 therefrom. The travel command 138 includes travels x.sub.i, in the shown case the travels x.sub.1, x.sub.2, x.sub.3 and x.sub.4.

(105) These travels serve to control the manipulators M1 to M4, as described in more detail above in relation to the adjustment apparatus 10 in accordance with FIG. 1.

(106) The travel command 138 generated by the travel establishing device 86 includes changes to be carried out by the manipulators M1 to M4 in the form of state variables of the optical elements L1 to L4 corresponding to travels x.sub.i. The established travels x.sub.i are transferred to the individual manipulators M1 to M4 by way of travel signals and they provide the manipulators with respective correction travels to be carried out. These define corresponding displacements of the assigned optical elements L1 to L4 for correcting wavefront errors of the projection lens 16 that occurred. In order to establish the travels x.sub.i, the travel establishing device 86 receives respectively updated state characterisations 34a in the form of Zernike coefficients b.sub.j characterizing the wavefront from the state encoder 80, in particular when the exposure process is carried out.

(107) In accordance with one embodiment, the travel establishing device 86 generates travels x.sub.i which are updated a number of times during the exposure of the substrate 64. In accordance with one embodiment, the state encoder 80 has a memory 82 and a simulation device 84. State characterisations 34 in the form of aberration parameters, which were established at the projection lens 16 via a wavefront measurement, are stored in the memory 82. These measurement results can be gathered via an external wavefront measurement system, such as the measurement system 12 described with reference to FIG. 1. However, alternatively, the state characterisations 34 can also be measured by a wavefront measurement device 70 which is integrated into the substrate displacement stage 66. By way of example, such a measurement can take place regularly after each exposure of a wafer or in each case after exposing a complete set of wafers. Alternatively, it is also possible to undertake a simulation or a combination of a simulation and a reduced measurement instead of a measurement.

(108) The measurement values of the state characterization 34 in the form of aberration parameters in the form of Zernike coefficients, stored in the memory 82, are adapted to the updated conditions during the exposure process in each case by way of the simulation device 84 where desired. In accordance with one embodiment variant, the central controller 72 regularly transfers the current irradiation intensity 74 to the simulation device 84. From this and on the basis of the respective illumination setting, the simulation device 84 calculates changes, caused by lens element heating, in the aberration parameters. Furthermore, the simulation device continuously obtains measurement values from a pressure sensor 76 monitoring the ambient pressure of the projection exposure apparatus 10. Effects of changes in the ambient pressure on the operation parameters are taken into account by the simulation device 84.

(109) The control device 114 of the projection exposure apparatus 50 in accordance with FIG. 2 differs from the controller 14 of the adjustment apparatus 10 in accordance with FIG. 1 in that, by way of the state encoder 80, the control device 114 converts the state characterization 34 measured by a wavefront measurement device into a current state characterization 34a using the current illumination intensity 74. The function of the travel establishing device 86 of the control device 114 corresponds to the function of the controller 14, but with the constraint that the travel command 138 generated by the control device 114 only includes the travel vector x with the travels x.sub.i of the manipulators, but not the travel vector x.sup.L for controlling the ICA post-processing device 36.

(110) The present description of exemplary embodiments is to be understood to be exemplary. The disclosure effected thereby firstly enables the person skilled in the art to understand the present disclosure and the advantages associated therewith, and secondly encompasses alterations and modifications of the described structures and methods that are also obvious in the understanding of the person skilled in the art. Therefore, all such alterations and modifications, in so far as they fall within the scope of the disclosure in accordance with the definition in the accompanying claims, and equivalents are intended to be covered by the protection of the claims.

LIST OF REFERENCE SIGNS

(111) 10 Adjustment apparatus 12 Measurement system 14 Control device 16 Projection lens 18 Illumination device 20 Measurement radiation 22 Measurement mask 24 Object plane 26 Sensor element 28 Image plane 30 Detector 32 Evaluation device 34 State characterization 34a Current state characterization 36 Post-processing device 38 Travel command 40 Tilt axis 50 Projection exposure apparatus 52 Exposure radiation source 54 Exposure radiation 56 Illumination optical unit 58 Mask 60 Mask displacement stage 62 Scanning direction of the mask displacement stage 64 Substrate 66 Substrate displacement stage 68 Scanning direction of the substrate displacement stage 70 Wavefront measurement device 72 Central controller 74 Current radiation intensity 76 Pressure sensor 80 State encoder 82 Memory 84 Simulation device 86 Travel establishing device 114 Control device 138 Travel command L1-L4 Optical elements M1-M4 Manipulators b State vector x.sub.i Travels for manipulators x.sub.n.sup.L Travels for the ICA post-processing device

(112) The claims of the disclosure follow below.