Measuring head for an immersion lens and optical arrangement for lithography with such a measuring head

Abstract

The present invention relates to a measuring head for an immersion objective, comprising a measuring surface that can be arranged in the image plane of the immersion objective during operation of the measuring head (6) and against which the immersion liquid (5) rests. The measuring surface has an annular film (8) surrounding its edge, which film comprises a hydrophobic material at least on its side facing away from the measuring head (6). Furthermore, the invention relates to a method for producing a measuring head (6) for an immersion objective and to an optical arrangement, in particular a projection exposure system for immersion lithography, comprising at least one corresponding measuring head (6).

Description

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

[0001] The present invention relates to a measuring head for an immersion objective having a measuring surface which can be arranged in the image plane of the immersion objective during operation of the measuring head and against which the immersion liquid is applied, as well as to an optical arrangement, in particular a projection exposure system for immersion lithography, having at least one corresponding measuring head and a method for producing the same. STATE OF THE ART

[0002] Microlithographic processes are used to manufacture microstructured or nanostructured components in electrical engineering or microsystems technology. In these processes, structures present on a reticle are imaged onto a wafer at a reduced scale using a projection lens. To resolve ever smaller feature sizes, light with increasingly shorter wavelengths is used to image the structures in projection exposure systems. For example, projection exposure systems operate in the deep ultraviolet (DUV) wavelength spectrum, with wavelengths ranging from 100 nm to 250 nm.

[0003] In addition, immersion lenses are used, for example, in which immersion fluid is placed in a gap between the last optical element of the immersion lens and the image plane where the wafer to be exposed is located in order to increase the numerical aperture. With these immersion lenses, it is important to keep the immersion fluid within the desired area of ​​the gap and prevent it from leaving the gap, as escaping immersion fluid can impair neighboring components and, particularly in the case of evaporation, can lead to evaporative cooling, which in turn can cause mechanical stress due to the influence of temperature. Furthermore, unstable states of the immersion fluid negatively impact the imaging conditions.Accordingly, it is known, for example, from the German patent application DE 10 2014 224 717 A1 to provide a correspondingly hydrophobic material on the last optical element of an immersion lens, which keeps the immersion liquid in the area of ​​the gap.

[0004] In connection with projection exposure systems, it is also known to use measuring arrangements to monitor or check the imaging properties of the projection exposure system. Accordingly, for example, a measuring head is arranged in the area of ​​the image plane, where the wafer to be exposed is usually located, in order to record imaging properties in various ways. For reliable and efficient operation of such a measuring head, it is necessary, on the one hand, that conditions are as identical as possible to those for imaging onto a wafer, and, on the other hand, that the measuring head is as resistant as possible to environmental influences, such as existing radiation and the like. DISCLOSURE OF THE INVENTION OBJECT OF THE INVENTION

[0005] Accordingly, it is an object of the present invention to provide a measuring head which enables the reliable and efficient detection of imaging properties of an optical arrangement and in particular of a projection exposure system, wherein the measuring head should be as easy to operate and manufacture as possible and should have a long service life. TECHNICAL SOLUTION

[0006] This object is achieved by a measuring head having the features of claim 1 and an optical arrangement having the features of claim 14 and a method for producing a measuring head having the features of claim 16. Advantageous embodiments of the invention are the subject of the dependent claims.

[0007] The invention proposes a measuring head for an immersion objective, comprising a measuring surface that can be positioned in the image plane of the immersion objective during use, and against which the immersion fluid rests. To ensure stable measuring conditions, the measuring surface has an annular foil surrounding its edge. This foil, at least on the side facing away from the measuring head, comprises a hydrophobic material to keep the immersion fluid stable and symmetrical in the area of ​​the measuring surface. This prevents immersion fluid from escaping the gap between the measuring head and the immersion objective and causing evaporative cooling and associated mechanical stress, for example through evaporation. The formation of a foil with a hydrophobic material enables simple attachment and replacement, thus enabling both the manufacture and long-term operation of the measuring head.

[0008] The measuring surface can be arranged at least partially on a frustoconical and / or annular housing part, wherein the annular film can extend at least partially over the outer surface of the frustoconical housing part.

[0009] The measuring surface can have a hydrophilic surface within the ring formed by the annular foil to enable stable formation of an immersion droplet. Hydrophilic refers to a contact angle of the immersion liquid with the surface of less than 90°, whereas for hydrophobic materials, the contact angle is greater than 90°.

[0010] The film can be designed as an adhesive film or be connected to the measuring surface via at least one adhesive layer to ensure stable adhesion. In particular, the adhesive layer can be formed by an adhesive tape, especially double-sided adhesive tape.

[0011] A heat-conducting element can be arranged between the foil and the measuring surface in order to dissipate the heat generated by radiation or to distribute it homogeneously in order to avoid mechanical influences on the measuring head that could arise from uneven temperature distributions and the resulting forces due to different expansion.

[0012] The heat-conducting element can be formed as a heat-conducting layer, in particular as a metallic layer. The heat-conducting element can be arranged between a first adhesive layer and a second adhesive layer, which allows it to be attached to the annular foil on the one hand and to the measuring head on the other.

[0013] The hydrophobic material of the film can be polyolefins, especially polytetrafluoroethylene (PTFE), polypropylene, polyacrylates, (poly)methyl methacrylate, (poly)vinyl chlorides, polystyrenes, polysiloxanes, polycarbonates, and / or epoxy polymers. Polytetrafluoroethylene (PTFE) is preferred, as this material has proven to be highly resistant to radiation, especially UV radiation.

[0014] To enhance the hydrophobic effect, the hydrophobic material can be roughened on the side of the film facing away from the measuring head.

[0015] The hydrophobic material of the film can be applied in the film in the form of a coating on a carrier material or the film can be formed entirely from the hydrophobic material, wherein the film can have a thickness of less than 500 µm.

[0016] The measuring head can be used in an optical arrangement, in particular a projection exposure system for immersion lithography, so that according to a further aspect of the invention, an optical arrangement with at least one corresponding measuring head is additionally or alternatively claimed.

[0017] The optical arrangement can accordingly comprise an immersion liquid, in particular water, with which the measuring head has contact at least with the measuring surface.

[0018] The measuring head for an immersion objective can be manufactured in a simple manner. After providing a measuring head blank with a measuring surface that can be arranged in an image plane of the immersion objective during operation of the measuring head together with an immersion objective and against which the immersion liquid rests, a provided annular film comprising a hydrophobic material is connected circumferentially to the measuring surface of the measuring head blank at its edge, so that the hydrophobic material is present at least on the side facing away from the measuring head. The annular film can be easily exchanged and replaced. BRIEF DESCRIPTION OF THE CHARACTERS

[0019] The attached drawings show in a purely schematic manner in Fig. 1 a schematic representation of a projection exposure system for immersion lithography, Fig. 2 a lateral sectional view through a first embodiment of a measuring head and the end of an immersion objective, Fig. 3 a lateral sectional view through a second embodiment of a measuring head and the end of an immersion objective, Fig. 4 a partial sectional view through an annular foil, Fig. 5 is a partial sectional view through a second embodiment of an annular foil, Fig. 6 a partial sectional view through a third embodiment of an annular foil, Fig. 7 a partial sectional view through the second embodiment of an annular foil with a heat-conducting element, Fig. 8 a top view of a measuring surface with an immersion drop and in Fig. 9 a cross-sectional view through an immersion drop with different contact surfaces. EXAMPLES OF IMPLEMENTATION

[0020] Further advantages, characteristics, and features of the present invention will become apparent from the following detailed description of the embodiments. However, the invention is not limited to these embodiments.

[0021] In Fig. Figure 1 schematically shows an optical arrangement in the form of a projection exposure system for microlithography for the production of highly integrated semiconductor components. The optical arrangement comprises an excimer laser as light source 1 for generating radiation with a useful wavelength of 193 nm, although other useful wavelengths, such as 248 nm, are also possible. A downstream illumination system 2 generates an image field in its exit plane that is adapted to the requirements of a downstream projection lens 4. A photomask, a so-called reticle 3, is arranged in the image field such that it lies in the object plane of the projection lens 4.

[0022] This is followed by the projection lens 4, which in production mode projects an image of the photomask 3 with a reduced scale, for example, at a scale of 4:1 or 5:1 or 10:1, onto a wafer (not shown) coated with a photoresist layer. Fig. In the application shown in Figure 1, instead of the wafer, a measuring head 6 is arranged, with which the imaging properties of the optical arrangement can be monitored or checked by measuring system parameters.

[0023] The projection lens 4 has, as a terminal element adjacent to the image plane, an optical element 10, for example in the form of a plano-convex lens with a conical volume region, the end face of which forms the last optical surface of the projection lens 4 and which is arranged at a working distance above the measuring surface. An immersion liquid 5, in this case water, more precisely ultrapure water, is arranged between the end face of the projection lens 4 and the measuring surface of the measuring head 6 in order to increase the output-side numerical aperture of the projection lens 4. By means of the immersion liquid 5, the imaging of structures on the photomask 3 can take place with a higher resolution and depth of field than is possible if the space between the optical element 10 and the wafer is filled with a medium with a lower refractive index, e.g., air.The gap forming the intermediate space is typically between 2 mm and 4 mm in size. Accordingly, the gap with the immersion liquid 5 is also provided in the arrangement of the measuring head 6 in order to ensure identical imaging conditions.

[0024] The Fig. 2 shows in a purely schematic way a detailed view of the measuring head 6 and the last optical element 10 with a rinsing collar 9 of the projection lens 4. In the detailed view of the Fig. 2 shows the gap between the last optical element 10 of the projection lens 4 and the measuring surface of the measuring head 6, which is filled with an immersion liquid 5. The measuring surface of the measuring head 6 is located in the Fig. 2, on the top side of a frustoconical housing part 7, on which an annular film 8 is arranged circumferentially around the edge. The annular film 8 has a hydrophobic material facing away from the measuring head 6 and facing the last optical element 10 of the projection lens 4, while the surface of the measuring head 6 has a hydrophilic surface 15 in the inner region of the ring of the annular film 8. The measuring surface is formed by the area covered by the annular film 8 and the hydrophilic surface 15 enclosed by the ring of the annular film 8.

[0025] By designing the measuring surface with an annular, circumferential area with hydrophobic material and an inner area surrounded by the ring with hydrophilic material, the immersion liquid 5 is held in the inner area of ​​the annular film 8, as will be shown below.

[0026] The Fig. 3 shows a further embodiment of a measuring head 6 similar to the Fig. 2, wherein the embodiment of the measuring head 6 of Figure three differs from the embodiment of Fig. 2 only in that the annular foil 8 also extends into the area of ​​the lateral surface of the frustoconical housing part 7.

[0027] The Fig. 4 to 6 show various embodiments of an annular foil 8, as it can be arranged on the measuring head 6, in a partial sectional view.

[0028] In the Fig. Figure 4 shows the simplest embodiment of an annular film 8, in which the film 8 is made entirely of a hydrophobic material, such as polytetrafluoroethylene. Such a film 8 can be designed as an adhesive film and adhere to the measuring surface of the measuring head 6 without an additional adhesive layer.

[0029] The Fig. Figure 5 shows a second embodiment of an annular film 8 with an adhesive layer 11, such as a double-sided adhesive tape, and a hydrophobic material 12, which in turn can preferably be formed from polytetrafluoroethylene, as this has proven to be highly resistant to UV radiation. However, other hydrophobic materials are also conceivable.

[0030] The Fig. Figure 6 shows a third embodiment of an annular film 8, in which hydrophobic material 12 is again arranged on one side of a carrier layer 13, for example, by means of a coating. An adhesive layer for attachment to the measuring head 6 is arranged on the opposite side of the carrier layer 13.

[0031] The Fig. 7 shows the embodiment of the annular foil 8 from Fig. 5 in connection with the arrangement of a heat-conducting element 14, such as a metal foil. This can serve to dissipate the heat generated by the radiation at the measuring head 6 or to distribute it evenly in order to avoid mechanical stresses due to differential thermal expansion. The heat-conducting element 14, in turn, has an adhesive layer 11 with which the heat-conducting element 14 can be arranged on the measuring surface of the measuring head 6. The hydrophobic material 12 is also applied to the heat-conducting element 14 with an adhesive layer 11.

[0032] The Fig. 8 and Fig. 9 describe the operation of the measuring surface with a hydrophilic inner surface area 15 and a hydrophobic surface area 17, which is formed in the form of the annular film 8 on the measuring surface of the measuring head 6. As in the Fig. 8 and Fig.As shown in Figure 9, the different contact angles of the immersion liquid 5 in the hydrophilic surface area 15 and in the hydrophobic surface area 17 or the area of ​​the annular film 8 create a force equilibrium which holds the immersion liquid 5 within the ring of the annular film 8.

[0033] In the hydrophilic surface area 15, the contact angle of the immersion liquid 5 with the surface is less than 90°, while in the area of ​​the annular film 8, i.e., in the hydrophobic surface area 17, the contact angle of the immersion liquid 5 with the surface is greater than 90°. If the radius r i of the immersion drop 5 smaller than the radius r 1 of the hydrophilic surface area 15, the radial capillary force F 1 greater than the radial capillary force F 2 and the immersion liquid 5 fills the hydrophilic surface area 15. However, if the radius r iof the immersion drop 5 is larger than the radius r 1 of the hydrophilic surface area 15, a force equilibrium F 1 and F 2 so that the immersion drop 5 is concentrated to a radius r i in the order of magnitude of the radius r 1 of the hydrophilic surface area 15, since the hydrophobic surface area 17 of the annular film 8 prevents further expansion of the immersion droplet. This is particularly true when the measuring head 6 is moved. Due to inertia, the immersion droplet 5 is also displaced. In doing so, it can briefly spread onto the annular film 8. However, due to the buildup, the immersion droplet 5 will quickly retreat into the hydrophilic surface area 15. In this case, no immersion liquid remains on the annular film 8. This also has a positive effect on temperature stability, since no evaporative cooling occurs.

[0034] This results in stable drop edges of the immersion liquid 5, and the immersion liquid is reliably prevented from leaving the measuring surface, thus preventing spillage. This prevents evaporation of the immersion liquid 5 outside the hydrophilic region and the associated evaporative cooling as well as the resulting mechanical forces. Furthermore, it can be ensured that the immersion liquid 5 completely covers the measuring surface or its hydrophilic region and forms rotationally symmetrically, resulting in a symmetrical distribution of the drop forces, which positively influences the mechanical loads on the optical element 10 and the measuring head 6.In particular, the drop forces in a direction perpendicular to the measuring surface due to volume changes of the immersion liquid can be minimized, which has a positive effect on the imaging behavior, since the mechanical forces on the optical element 10 and the measuring head 6 in the direction of the optical axis can be minimized.

[0035] Since the annular film 8 can be easily applied and replaced due to the arrangement by adhesive bonding or by means of an adhesive layer, if the annular film 8 becomes damaged, it can be easily replaced directly in the area of ​​the optical arrangement, for example in the clean room of a projection exposure system, thus eliminating the need for complex work involving the insertion and removal of a measuring head 6. Furthermore, the hydrophobic material 12 of the annular film 8 can be formed from polytetrafluoroethylene, which has proven to be particularly resistant to the working radiation of the optical arrangement, such as a projection lens operating in the wavelength spectrum of deep ultraviolet light (DUV).

[0036] Although the present invention has been described in detail with reference to the exemplary embodiments, it will be understood by those skilled in the art that the invention is not limited to these exemplary embodiments, but rather that modifications are possible in such a way that individual features can be omitted or other combinations of features can be implemented without departing from the scope of the appended claims. In particular, the present disclosure includes all combinations of the individual features shown in the various exemplary embodiments, so that individual features that are only described in connection with one exemplary embodiment can also be used in other exemplary embodiments or in combinations of individual features not explicitly shown. LIST OF REFERENCE SYMBOLS 1 light source 2 Lighting system 3 Reticle or photomask 4 Projection lens or immersion lens 5 Immersion liquid or immersion drops 6 measuring head 7 truncated cone-shaped housing part 8 ring-shaped foil 9 Flush collar 10 optical element 11 Adhesive layer 12 hydrophobic material 13 Carrier layer 14 heat-conducting element 15 hydrophilic surface 16 upper contact surface 17 hydrophobic surface QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 224 717 A1

[0003]

Claims

Measuring head for an immersion objective with a measuring surface which can be arranged in the image plane of the immersion objective (4) during operation of the measuring head (6) and against which the immersion liquid (5) lies, characterized in that the measuring surface has an annular film (8) surrounding its edge, which film has a hydrophobic material (12) at least on its side facing away from the measuring head (6). Measuring head according to claim 1, characterized in that the measuring surface is arranged at least partially on a frustoconical and / or annular housing part (7). Measuring head according to claim 2, characterized in that the annular film (8) extends at least partially over the outer surface of the frustoconical housing part (7). Measuring head according to one of the preceding claims, characterized in that the measuring surface within the ring formed by the annular film (8) has a hydrophilic surface (15). Measuring head according to one of the preceding claims, characterized in that the film (8) is designed as an adhesive film or is connected to the measuring surface via at least one adhesive layer (11). Measuring head according to claim 5, characterized in that the adhesive layer (11) is formed by an adhesive tape. Measuring head according to one of the preceding claims, characterized in that a heat-conducting element (14) is arranged between the film (8) and the measuring surface of the measuring head (6). Measuring head according to claim 7, characterized in that the heat-conducting element is designed as a heat-conducting layer (14), in particular as a metallic layer. Measuring head according to claim 7 or 8, characterized in that the heat-conducting element (14) is arranged between a first adhesive layer (11) and a second adhesive layer (11). Measuring head according to one of the preceding claims, characterized in that the hydrophobic material (12) of the film (8) is selected from the group comprising polyolefins, in particular polytetrafluoroethylene (PTFE), polypropylene, polyacrylates, (poly)methyl methacrylate, (poly)vinyl chlorides, polystyrenes, polysiloxanes, polycarbonates and epoxy polymers. Measuring head according to one of the preceding claims, characterized in that the hydrophobic material (12) is roughened on the side of the film (8) facing away from the measuring head. Measuring head according to one of the preceding claims, characterized in that the hydrophobic material (12) of the film (8) is applied to the film (8) in the form of a coating or the film (8) is formed from the hydrophobic material (12). Measuring head according to one of the preceding claims, characterized in that the film (8) has a thickness of less than 500 µm. Optical arrangement, in particular projection exposure system for immersion lithography, with at least one measuring head (6) according to one of the preceding claims. Optical arrangement according to claim 14, characterized in that it further comprises an immersion liquid (5), in particular water, into which the measuring head (6) is immersed at least with the measuring surface. Method for producing a measuring head (6) for an immersion objective, in particular a measuring head according to one of claims 1 to 13, which comprises the steps of:providing a measuring head blank with a measuring surface which, during operation of the measuring head (6), can be arranged together with an immersion objective (4) in an image plane of the immersion objective (4) and against which the immersion liquid (5) rests,characterized by,providing an annular film (8) which has a hydrophobic material (12), connecting the annular film (8) to the measuring surface of the measuring head blank circumferentially at its edge, so that the hydrophobic material (12) is present at least on its side facing away from the measuring head (6).

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