US-20260126731-A1 - METHOD FOR REDUCING ABERRATIONS OF AN OPTICAL ELEMENT, OPTICAL ELEMENT AND SEMICONDUCTOR SYSTEM

Abstract

A method for reducing aberrations of an optical element (Mi) e.g., in a lithography system includes: determining a temporal change in an optical property of the optical element (Mi), e.g., a temporal change of a surface FIGURE(P(x,y)) of a surface ( 24 a) of a substrate ( 24 ) of the optical element (Mi), that is expected over the operational life of the optical element (Mi), with the temporal change in the optical property over the operational life (T) of the optical element (Mi) causing varying aberrations, and reducing the aberrations that vary over the operational life of the optical element (Mi) by generating an allowance, in particular a surface figure allowance (∆P V ), which compensates at least a portion of the total temporal change in the optical property (P(x,y)) that is expected over the operational life.

Inventors

• Robert Harmes
• Felix Waeldchen
• Malte Langenhorst
• Werner Weiss

Assignees

• CARL ZEISS SMT GMBH

Dates

Publication Date

20260507

Application Date

20251229

Priority Date

20230627

Claims (20)

1. 1 . A method for reducing aberrations of an optical element, comprising: determining a temporal change in an optical property of the optical element that is expected over an operational life of the optical element, whereby the temporal change in the optical property over the operational life of the optical element causes varying aberrations, and reducing the aberrations that vary over the operational life of the optical element by generating an allowance, which compensates at least a portion of a total temporal change in the optical property that is expected over the operational life.
2. 2 . The method as claimed in claim 1 , wherein the optical element is in a lithography system, wherein the temporal change is a temporal change of the surface figure of a surface of a substrate of the optical element and wherein the allowance is a surface figure allowance.
3. 3 . The method as claimed in claim 1 , wherein the allowance compensates a predetermined portion of the total temporal change in the optical property that is expected over the operational life of the optical element.
4. 4 . The method as claimed in claim 3 , wherein the allowance compensates at least a 50 % portion of the total temporal change in the optical property that is expected over the operational life of the optical element.
5. 5 . The method as claimed in claim 2 , further comprising: generating the surface figure allowance by processing the surface of the substrate, wherein said processing comprises material-removing processing of the surface of the substrate and/or irradiating the substrate.
6. 6 . The method as claimed in claim 2 , wherein the surface figure allowance is generated by surface-processing of a further surface of a further substrate of a further optical element of the lithography system.
7. 7 . The method as claimed in claim 1 , wherein the temporal change in the optical property that is expected over the operational life of the optical element is determined based on at least one measurement.
8. 8 . The method as claimed in claim 7 , wherein the allowance is generated once a waiting time of at least 10 days since a last processing of the optical element has elapsed, and wherein the measurement of the temporal change in the optical property is performed once the waiting time has elapsed and a size of the allowance is determined based on the measurement.
9. 9 . The method as claimed in claim 8 , wherein the allowance is generated once a waiting time of at least 100 days since the last processing of the optical element has elapsed.
10. 10 . The method as claimed in claim 7 , wherein the allowance is generated once a waiting time of at least 10 days since a last processing of the optical element has elapsed, and wherein a respective measurement of the temporal change in the optical property is implemented at a time before and at a time after the waiting time has elapsed and a size of the allowance is determined based on a difference between the two measurements and on a model-based expected temporal change in the optical property.
11. 11 . The method as claimed in claim 10 , wherein the allowance is generated once a waiting time of at least 100 days since the last processing of the optical element has elapsed.
12. 12 . The method as claimed in claim 1 , wherein the temporal change in the optical property that is expected over the operational life of the optical element is determined based on a model-based simulation.
13. 13 . The method as claimed in claim 2 , wherein the optical element forms one of three optical elements in the lithography system having larger-volume substrates relative to remaining substrates in the lithography system.
14. 14 . The method as claimed in claim 2 , wherein the allowance compensates a portion of at least 20 % of the aberrations that vary over the operational life of the optical element.
15. 15 . The method as claimed in claim 1 , wherein the temporal change in the optical property is caused by at least one of the following effects: thermal hysteresis, mechanical hysteresis, volume shrinkage, relaxing material compaction and radiation-induced compaction.
16. 16 . The method as claimed in claim 1 , wherein the optical property varies spatially dependently, wherein the expected temporal change in the optical property is determined spatially dependently, and wherein the allowance corrects the change in the optical property spatially dependently.
17. 17 . The method as claimed in claim 1 , wherein the optical element forms an extreme ultraviolet (EUV) mirror, and wherein the substrate of the EUV mirror consists at least partly of a zero-crossing material.
18. 18 . An optical element exhibiting aberrations that vary in time over an operational life of the optical element, wherein the aberrations reduce from a start of the operational life until a predetermined time at which the aberrations are minimal, and increase after the predetermined time.
19. 19 . The optical element as claimed in claim 18 , wherein the predetermined time is between 100 days and 8 years.
20. 20 . The optical element as claimed in claim 18 , wherein the aberrations have a value of 100 pm or less at the predetermined time.

Description

CROSS-REFERENCE TO RELATED APPLICATION This is a Continuation of International Application PCT/EP2024/067117, which has an international filing date of June 19, 2024, and the disclosure of which is incorporated in its entirety into the present Continuation by reference. This Continuation also claims foreign priority under 35 U.S.C. §119(a)-(d) to and also incorporates by reference, in its entirety, German Patent Application DE 102023 206 062.0 filed June 27, 2023. FIELD The invention relates to a method for reducing aberrations of an optical element, in particular of an optical element in a lithography system, to an optical element, preferably a mirror, in particular an EUV mirror, and to an apparatus for semiconductor technology having at least one such optical element. BACKGROUND Optical elements in the form of lens elements or mirrors represent the core elements of projection lenses, for example as used in microlithography. In such optical elements, the requirements for the imaging quality are becoming increasingly stringent and ensure that new processes and materials have to be developed for the production of these optical elements. However, depending on the material used and the process applied, the various effects may lead to a deterioration in the imaging quality over the lifetime or operational life of a respective optical element, i.e. the aberrations of the optical element typically increase irreversibly over the operational life of the optical element. The practice of correcting surface figure errors on a surface of an optical element, i.e. deviations of a surface shape from a target surface shape of the surface, by surface processing is known. For example, DE102018211596A1 describes a method for producing a reflective optical element for a projection exposure apparatus, with the optical element comprising a substrate. The method comprises measuring the substrate surface, irradiating the substrate with the aid of electrons or with photons and annealing the substrate. Irradiation leads to local compaction of the substrate, and this can be used for correcting surface defects. Since annealing partially reverses the compaction produced during the irradiation, the decompaction by annealing may already be kept available during the compaction in the irradiation step. Using such an allowance makes it possible to attain the target surface shape by irradiation and the subsequent annealing. The method described in DE102018211596A1 can also be used to create protection for the substrate against progressive compaction over the service life of the substrate that is caused by irradiation with extreme ultraviolet (EUV) radiation during the operation of the reflective optical element. In order to gain this protection, irradiation is performed during the production of the optical element until compaction saturation is reached, i.e. until a state is reached in which substrate compaction no longer increases or still increases only to a negligible extent in the event of further irradiation. It is possible in the long term hereby to prevent impermissible surface deformations and associated aberrations due to the compaction of the material by EUV radiation. In principle, time-varying aberrations or image errors that occur over long time scales can be divided into two classes: A first class of image errors that are distinguished in that their future size increases by a non-negligible amount after a constant time period, and a second class of image errors that, after reaching a threshold value, only still grow by a negligible amount after every further time period. DE102012212758A1 proposes adjusting both classes of image errors in parallel in time with the aid of manipulators of the projection lens. The first or second image error can be determined by measurement or by prediction from a prediction model. However, it is typically not possible to use manipulators to correct all aberrations of a projection lens or a lithography system that arise over the operational life of the optical elements. SUMMARY One object addressed by the invention is that of providing a method for reducing aberrations that vary over the operational life of the optical element, an optical element and an apparatus of semiconductor technology having at least one such optical element. According to a first aspect and in one formulation, this object is addressed by a method for reducing aberrations of an optical element, comprising: determining a temporal change in an optical property of the optical element – in particular a temporal change in a surface figure of a surface of a substrate of the optical element – that is expected over the operational life of the optical element, with the temporal change in the optical property over the operational life of the optical element causing varying aberrations, and reducing the aberrations that vary over the operational life of the optical element by generating an allowance, in particular a surface figure allow