EP4158424A1

EP4158424A1 - Damping arrangement for vibration damping of an element in an optical system

Info

Publication number: EP4158424A1
Application number: EP21709624.7A
Authority: EP
Inventors: Marwene Nefzi; Stefan Hembacher; David SCHOENEN; Jens Kugler
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2020-05-27
Filing date: 2021-02-18
Publication date: 2023-04-05
Also published as: KR20230017779A; US20230104921A1; DE102020206589A1; WO2021239277A1

Abstract

The invention relates to a damping arrangement for vibration damping of an element in an optical system, in particular in a microlithography exposure system. A damping arrangement according to the invention comprises an element (101, 401, 501), a fluid (120, 220, 420, 520) located in a cavity and at least one channel (130, 230, 430, 530) connected to the cavity, wherein a vibration of the element causes a dissipation of vibration energy of the element by the partial displacement of the fluid from the cavity into the at least one channel.

Description

Damping arrangement for vibration damping of a

Element in an optical system

The present application claims the priority of the German patent application DE 10 2020 206 589.6, filed on May 27, 2020. The content of this DE application is incorporated by reference into the present application text.

BACKGROUND OF THE INVENTION

Field of invention

The invention relates to a damping arrangement for damping vibrations of an element in an optical system, in particular in a microlithographic projection exposure system.

State of the art

Microlithography is used to manufacture microstructured components such as integrated circuits or LCDs. The microlithography process is carried out in what is known as a projection exposure system, which has an illumination device and a projection lens. The image of a mask (= reticle) illuminated by the lighting device is projected by means of the projection lens onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to create the mask structure on the light-sensitive Transfer coating of the substrate. In a projection exposure system designed for EUV (ie for electromagnetic radiation with a wavelength below 30 nm, in particular below 15 nm), mirrors are used as optical components for the imaging process due to the lack of transparent materials.

A problem that arises in the operation of a projection exposure system, in particular with EUV systems, is that mechanical disturbances caused by vibrations have a detrimental effect on the positional stability of the components (such as EUV mirrors) of the system and the optical performance of the system. Weakly damped mechanical resonances in the system lead to a local increase in the interference spectrum in the area of the resonance frequencies and to an associated deterioration in the positional stability of passive components mounted as well as actively controlled components. Furthermore, in the case of regulated systems, resonances can lead to instability of the control loop.

Since the materials permitted in EUV systems with regard to the required vacuum resistance (e.g. metallic or ceramic) themselves only have a low intrinsic damping, further damping measures are necessary to overcome or alleviate the above-mentioned problems.

Various damping concepts are known in the prior art, reference being made to US Pat. No. 9,593,733 B2 by way of example only.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a damping arrangement for damping vibrations of an element in an optical system, in particular in a microlithographic projection exposure system, which is effective even in the case of higher-frequency vibration excitations Allows damping with a compact design.

This object is achieved by the damping arrangement according to the features of independent claim 1.

A damping arrangement for damping vibrations of an element in an optical system comprises

- an element;

a fluid located in a cavity; and

- At least one channel connected to the cavity;

- wherein an oscillation of the element causes a dissipation of oscillation energy of the element by partially displacing the fluid from the cavity into the at least one channel.

The invention is based, in particular, on the concept of realizing an energy dissipation for damping vibrations of an element (such as an EUV mirror, for example) in that a fluid located in a cavity is used in such a way that the vibration of the element to be damped with a partial Displacement of this fluid is associated with a channel connected to the cavity. The liquid displacement taking place in said channel has the particular consequence that - due to the intensification of the energy dissipation due to the friction occurring on the channel wall - efficient damping can also be achieved when the fluid itself has only a low or medium viscosity (see above that e.g. water can also be used as a fluid).

Furthermore, the increase in energy dissipation achieved by said channel means that - depending on the size of the (resonance) frequency of the respective element to be damped - the further use of a damper mass or auxiliary mass is either unnecessary or significantly lower masses (in Compare to a fluid-based energy dissipation without the one according to the invention Displacement in a channel) can be limited. In this way, among other things, the installation space required for the damping arrangement can in turn be significantly reduced and, as a result, a particularly compact system design can be implemented.

In the context of the present application, a “channel” is understood to mean an elongated hollow structure, the length of which is preferably at least five times, in particular at least ten times, the mean diameter.

According to one embodiment, the damping arrangement has at least one auxiliary mass located within the cavity, which when the element vibrates partially displaces the fluid into the at least one channel.

According to one embodiment, this auxiliary mass is mounted in a stable manner with respect to the element.

According to one embodiment, the stable mounting of the auxiliary mass has a resonance frequency which corresponds to a resonance frequency of the element to be damped.

However, the invention is not limited to the use of such an auxiliary mass. Thus, depending on the size of the (resonance) frequency of the element to be damped, it may also be sufficient to use only the fluid itself or its vibrating mass fraction in the cavity for vibration damping. In this case, this oscillating mass fraction of the fluid is then possibly to be matched to the resonance frequency of the optical element to be damped.

According to one embodiment, the damping arrangement is designed for damping a resonance frequency of the element of more than 50 Hz, in particular more than 100 Hz, further in particular more than 500 Hz. According to one embodiment, the damping arrangement has a plurality of auxiliary masses located within the cavity which, when the element vibrates, partially displace the fluid into the at least one channel.

The use of a plurality of “counter-oscillating” auxiliary masses or particles located within the cavity has the particular advantage that a spatial distribution of the damping effect achieved is achieved (compared to punctual damping), which results in particularly effective damping even with comparatively complex ones Geometries of each element to be damped can be achieved.

According to one embodiment, the at least one channel forms a cooling channel for cooling the element when the optical system is in operation.

In this way, a double functionality of the fluid according to the invention can be implemented by the fluid causing a cooling effect (e.g. to compensate for thermal loads occurring during operation of the element or an optical system having this element) in addition to the energy dissipation described above. Here, the invention can in particular also make use of the fact already mentioned above that, according to the invention, a fluid with only medium viscosity (e.g. cooling water) can also be used for vibration damping.

According to one embodiment, the at least one channel has, at least in some areas, a meandering geometry.

According to one embodiment, the damping arrangement also has at least one magnet and / or at least one coil that can be charged with electrical current.

According to one embodiment, the element is an optical element, in particular a mirror. In further embodiments, the element can also be, for example, an actuator component or a support or measuring frame.

The invention also relates to a projection exposure system with at least one damping arrangement according to the invention. The projection exposure system can in particular be designed for operation in the EUV or for operation at an operating wavelength of less than 30 nm, in particular less than 15 nm. In further applications, the projection exposure system can also be designed for operation in the VUV range, for example for wavelengths less than 200 nm, in particular less than 160 nm.

Further embodiments of the invention can be found in the description and the subclaims.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Show it:

Figure 1a-1b schematic representations to explain the basic structure and function of a damping arrangement according to the invention according to one embodiment;

2a-2b are schematic representations to explain further embodiments of a damping arrangement according to the invention;

FIG. 3 shows a diagram to explain a vibration suppression which can be achieved by way of example with a damping arrangement according to the invention; Figure 4-6 are schematic representations to explain further embodiments of a damping arrangement according to the invention;

FIG. 7-10 are schematic representations to explain further embodiments of a damping arrangement for damping comparatively low-frequency vibrations; and

FIG. 11 shows a schematic illustration to explain the possible

Construction of a microlithographic projection exposure system designed for operation in the EUV.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Furthermore, a damping arrangement according to a first embodiment of the invention will first be explained with reference to FIGS. 1a-1b. The damping arrangement according to FIG. 1 a is used to dissipate vibration energy of an element in an optical system, in particular in a microlithographic projection exposure system.

In the application examples described below, the element to be damped with regard to vibrations (not illustrated in FIG. 1 a) is a mirror which forms an oscillating mass-spring system with a predetermined resonance frequency in relation to a support structure. However, the invention is not restricted to this. In other applications, the element to be damped with regard to vibrations can also be, for example, an actuator component of an actuator used to actuate such an optical element, a joint element, a reaction or filter mass or any structural element, for example a support or measuring frame , Act. As can be seen from FIG. 1 a, the damping arrangement according to the invention has, in particular, a fluid 120 located within a cavity and a channel 130 connected to the cavity. The cavity for its part can be provided in the element to be damped or also formed separately from this (for example in a housing enclosing the cavity). Furthermore, according to FIG. 1 a, an auxiliary mass 110 is located within the cavity, the value of the mass of this auxiliary mass being rri2 and a stable mounting of the auxiliary mass 110 being symbolized by a spring labeled “115”.

The functional principle of the damping arrangement of Fig. 1a is that an oscillation of the element to be damped with regard to its oscillation energy leads to the fluid 120 being partially displaced into the channel 130 connected to the cavity, which results in energy dissipation and an accompanying damping effect Has. According to the invention, this energy dissipation is amplified by the said fluid displacement in the channel 130, with the result that vibration damping of comparatively high resonance frequencies of the element to be damped, for example of more than 50 Hz (in particular more than 100 Hz, further in particular more than 500 Hz), even below Use of a fluid 120 of only medium or lower viscosity and / or with a comparatively low value of the mass rri2 of the auxiliary mass 110 can be achieved.

In particular, water can be used as fluid 120, for example. In further embodiments, however, highly viscous liquids such as water silicones, silicone oils, magnetorheological liquids or ferrofluids can also be used as the fluid 120.

Depending on the specific application or the size of the resonance frequency to be damped, the use of an auxiliary or damper mass 110 can optionally be dispensed with entirely by only using the fluid 120 itself (which then does not completely fill the cavity) or its oscillating mass Energy dissipation is used. The at least one channel 130 used according to the invention to increase the energy dissipation can in particular, as indicated in FIG. 1a, have a meandering geometry. Such a geometry is advantageous for achieving a high level of friction or energy dissipation on the duct wall with a particularly compact design at the same time. However, the invention is not restricted to this, so that embodiments with any other channel configuration or geometry are also to be considered as encompassed by the invention.

Suitable (joining) technologies for implementing the channel 130 in the damping arrangement according to the invention (e.g. within the element to be damped or a frame structure) include, in particular, silicate bonding, fusion bonding and direct bonding.

1b shows an equivalent circuit diagram for the damping arrangement explained above with reference to FIG. Furthermore, the disturbing force acting on the element 101 to be damped with regard to vibrations is denoted by Fi and the movement of this element 101 or the mass to be damped rrn is denoted by xi.

The transfer function from the disturbing force, Fi, to the movement, xi, of the mass to be damped is

(1 )

On the basis of equation (1), the degree of damping C2 required to achieve optimal damping of the mass mi can be determined in accordance with Table 1 below. Table 1:

2a-2b show schematic representations to explain further embodiments of the invention, with components that are analogous or essentially functionally identical in comparison to FIG. 1 with reference numbers increased by “100”. According to FIG. 2a, instead of just a single filling compound 110, a plurality of auxiliary compounds 210 can also be provided within the cavity connected to the channel 230. Such a configuration has the particular advantage that instead of punctual damping, a spatial distribution of the damping effect is achieved with the result that an effective damping effect can be achieved even with comparatively complex shapes of the respective element to be damped with regard to vibrations.

Furthermore, as indicated in Fig. 2b, a further amplification of the energy dissipation he aimed can also be achieved in that a magnetic field (indicated by field lines 240) is generated via permanent magnets or via coils charged with electrical current, with the Viscosity of the fluid 220 can be increased by using, for example, magnetorheological particles or ferrofluids.

Additionally or alternatively, an increase in the energy dissipation can also be achieved by attaching one or more diaphragms within the flea space and / or within the duct connected to the flea space.

3 shows a diagram for the transfer function to explain an exemplary possible damping effect achieved with the damping arrangement according to the invention. In the exemplary embodiment shown, the element to be damped with regard to vibrations has an undesirable resonance at a frequency of about 1000Flz (= curve “A”), with a significant suppression (= curve “B”) being achieved according to the invention for this resonance frequency.

Table 2 shows quantitative data for a possible embodiment. The fluid with a suitable dynamic viscosity can be a commercially available water silicone ^{(for example available under the name Wacker® 1000000).}

Table 2:

FIG. 4 shows a schematic illustration to explain a further possible embodiment of a damping arrangement according to the invention, where in comparison to FIG. 1 analog or essentially functionally identical components are denoted by reference numbers increased by “300”. In Fig.

4 the element to be damped with regard to vibrations is also shown and labeled “401”. This can be, for example, an EUV mirror with an optical active surface 405.

In the embodiment of FIG. 4, the channels 430 used according to the invention to amplify the energy dissipation (and, analogously to the embodiments described above, each connected to a flea chamber receiving a fluid 420) form additional cooling channels for the element 401 to be damped or the EUV- Mirrors. In other words, the fluid 420 used for energy dissipation (e.g. water) in this embodiment also takes on the function of a cooling fluid to reduce thermal loads occurring during operation of the element 401 or EUV mirror (for example, as a result of electromagnetic loads hitting the EUV mirror Radiation).

5-6 show a possible application scenario of a damping arrangement according to the invention, with components that are analogous or essentially functionally identical in comparison to FIG. 1 with reference numbers increased by “400”. The element 501 to be damped with regard to vibrations is shown in FIG.

5 is shown in a perspective view and in FIG. 6 in a top view. In FIG. 6, a mechanical suspension of the element 501 is also indicated and denoted by “502”.

According to FIGS. 5-6, four auxiliary masses are used in three areas offset azimuthally in the circumferential direction (shown in FIG. 6) in such a way that in each of these three azimuthally offset areas (in which, according to FIG. 6, a damping element 511, 512 and 513 is formed by the mentioned auxiliary masses) each vibrations are damped in two directions of vibration. Of the mentioned auxiliary masses for each of the three azimuthally offset areas or for each of the damping elements 511, 512 and 513, two auxiliary masses (labeled “510” in FIG. 5) oscillate in the x direction, and the other two Auxiliary masses (labeled “511” in FIG. 5) in the z-direction. Overall, vibration damping is achieved in six degrees of freedom in this way. The auxiliary masses 510, 511 each have a natural frequency which corresponds to a resonance frequency to be damped of the element or mirror 501. In addition, the energy dissipation takes place analogously to the embodiments described above by displacing a respective fluid 520 surrounding the respective auxiliary mass 510, 511 into a channel 530 (also here, for example, with a meandering shape).

In addition, with reference to FIGS. 7-10, embodiments are described in which damping of low-frequency vibrations (typically with a frequency of less than 10 Hz) is to be implemented. In particular, the disturbance excitations to be attenuated according to these embodiments can be shock excitations, which can occur e.g. during transport or handling of the element to be damped or the associated system (e.g. a projection lens) or also during an earthquake. In the case of such low-frequency interference excitations, according to the embodiments of FIGS. 7-10, the previously described amplification of the energy dissipation by the fluid displacement in at least one channel and / or the use of a highly viscous fluid can be dispensed with.

Fig. 7 shows a schematic representation of an embodiment in which a fluid 720 used for energy dissipation is arranged in a cavity located within the element 701 which is to be dampened and which has the mass mi. An interfering force acting on element 701 or its mass mi is denoted by “F”. The natural frequency of element 701 (as a more rigid Body) is in the order of magnitude of 1 Hz. The rigidity of the suspension of the element 701 or the corresponding actuator units is symbolized by a spring 715. In the embodiment of FIG. 7, instead of the channel present in each of the above-described embodiments, only a diaphragm 750 serves to intensify the energy dissipation can carry out corresponding counter-vibrations within the flea space when the element 701 is vibrated to realize the energy dissipation.

Since the use of an additional damper mass in the form of a rigid body is thus dispensed with according to the embodiment of FIG. 7, the mass rri2 relevant for vibration damping or energy dissipation is that of the fluid 720 performing the corresponding counter-vibration.

FIG. 8 shows a schematic representation of the use of a damping arrangement with the functional principle described above with reference to FIG. 7 in a mirror forming the element 801 to be damped with an optical active surface 805, with a diaphragm used to amplify the energy dissipation denoted by “850” is. “820” denotes the fluid which, upon shock excitation of the element 801 to be damped, is forced through the opening (s) of the said diaphragm 850 with energy dissipation.

According to FIG. 9, such a diaphragm 950, which is set to increase the energy dissipation, can also have a plurality of openings or bores, in which case increased energy dissipation is achieved when the fluid 920 passes through said openings or bores.

The liquid movement within the optical element can be described by the following differential equation where x _{r is} the running coordinate along the liquid line, p is the density of the liquid and A = cd is the total cross-sectional area of the channel. The meaning of the parameters c and d can be seen from FIG. 9. X denotes the loss factor of the diaphragm 950 that is dependent on the diaphragm geometry. G is the acceleration of gravity. The movement of the mass m _t can be described by where F denotes the disturbing force acting on the mass rrn.

Table 3 shows quantitative data for a possible embodiment. Table 3: According to FIG. 10, depending on the size of the (resonance) frequency to be damped, only the fluid located within the flea space (labeled “1020” in FIG. 10) can be used for vibration damping, dispensing with a diaphragm. The element to be damped with regard to vibrations is designated here with “1001”. The arrow symbolizes the direction of a possible shock excitation to be dampened.

11 shows a schematic illustration of an exemplary projection exposure system 1100 designed for operation in the EUV.

According to FIG. 11, an illumination device of this projection exposure system 1100 has a field facet mirror 1103 and a pupil facet mirror 1104. All of the mirrors in the projection exposure system 1100 can be freeform surfaces. The light from a light source unit, which comprises a plasma light source 1101 and a collector mirror 1102, is directed onto the field facet mirror 1103. A first telescope mirror 1105 and a second telescope mirror 1106 are arranged in the light path after the pupil facet mirror 1104. A deflecting mirror 1107 is arranged in the light path, which deflects the radiation striking it onto an object field in the object plane of a projection objective comprising six mirrors 1151-1156. At the location of the object field, a reflective structure-bearing mask 1121 is arranged on a mask table 1120, which is imaged with the aid of the projection objective in an image plane in which a substrate 1161 coated with a light-sensitive layer (photoresist) is located on a wafer table 1160.

The element to be damped with regard to vibrations according to the present invention can be, for example, any of the mirrors 1151-1156 of the projection lens.

If the invention has also been described on the basis of specific embodiments, numerous variations and alternative embodiments are accessible to the person skilled in the art, for example by combining and / or exchanging Features of individual embodiments. Accordingly, it is understood by a person skilled in the art that such variations and alternative embodiments are also encompassed by the present invention, and the scope of the invention is limited only within the meaning of the attached patent claims and their equivalents.

Claims

1. Damping arrangement for damping vibrations of an element in an optical system, with

• an element (101, 401, 501);

• a fluid (120, 220, 420, 520) located in a cavity; and

• at least one channel (130, 230, 430, 530) connected to the cavity;

• wherein an oscillation of the element (101, 401, 501) by partial displacement of the fluid (120, 220, 420, 520) from the cavity into the at least one channel (130, 230, 430, 530) results in a dissipation of oscillation energy of the element (101, 401, 501) causes.

2. Damping arrangement according to claim 1, characterized in that it has at least one auxiliary mass (110, 210, 410, 510, 511) located inside the cavity, which when the element (101, 401, 501) vibrates, the fluid (120, 220 , 420, 520) partially displaced into the at least one channel (130, 230, 430, 530).

3. Damping arrangement according to claim 2, characterized in that this auxiliary mass (110, 210) is mounted in a stable manner with respect to the element (101, 401, 501).

4. Damping arrangement according to claim 3, characterized in that the stable mounting of the auxiliary mass (110, 210) has a resonance frequency which corresponds to a resonance frequency of the element (101, 401, 501) to be damped.

5. Damping arrangement according to one of the preceding claims, characterized in that it is used for damping a resonance frequency of the element (101, 401, 501) of more than 50Hz, in particular of more than 100Hz, further in particular of more than 500Hz.

6. Damping arrangement according to one of the preceding claims, characterized in that it has a plurality of auxiliary masses (210, 410) located within the cavity, which when the element (101, 401) vibrates, the fluid (220, 420) partially in the at least displace a channel (230, 430).

7. Damping arrangement according to one of the preceding claims, characterized in that the at least one channel (430) forms a cooling channel for cooling the element (401) when the optical system is in operation.

8. Damping arrangement according to one of the preceding claims, characterized in that the at least one channel (130, 230, 530) has a meandering geometry at least in some areas.

9. Damping arrangement according to one of the preceding claims, characterized in that it further comprises at least one magnet and / or at least one coil which can be charged with electrical current.

10. Damping arrangement according to one of claims 1 to 9, characterized in that the element (101, 401, 501) is an optical element, in particular a special mirror.

11. Damping arrangement according to one of claims 1 to 9, characterized in that the element is an actuator component.

12. Damping arrangement according to one of claims 1 to 9, characterized in that the element is a support or a measuring frame.

13. Damping arrangement according to one of the preceding claims, characterized in that the optical system is a microlithographic projection exposure system.

14. Attenuation arrangement according to claim 13, characterized in that the projection exposure system is designed for operation at an operating wavelength of less than 30 nm, in particular less than 15 nm.

15. Microlithographic projection exposure system, characterized in that it has at least one damping arrangement according to one of the preceding claims.