JP2014167660A - Method for manufacturing projection objective appliance and projection objective appliance manufactured by this method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a projection objective appliance and the projection objective appliance manufactured by this method.SOLUTION: A method for manufacturing a projection objective appliance includes a step of defining an initial design for a projection objective appliance and a step of optimizing the design using a merit function having a plurality of merit function components AB, IRRAD EFP, each of which reflects a specific quality parameter. One of that merit function components defines a maximum irradiance requirement requiring that a normalized effective irradiance value representing an effective irradiance AB, IRRAD EFF normalized to an effective irradiance in an image surface of the projection objective appliance does not exceed a predefined irradiance threshold value IRR TV on each optical surface of the projection objective appliance except for a last optical surface directly adjacent to an image surface of the projection objective appliance. Optical surfaces positioned within caustic regions and/or critically small effective sub-apertures on optical surfaces are thereby systematically avoided.

Description

  The present invention relates to a method of manufacturing a projection objective comprising the steps of defining an initial design for the projection objective and optimizing this design using a merit function. The method is used in the manufacture of projection objectives that can be used in microlithographic processes for manufacturing miniaturized devices. The invention also relates to a projection objective produced by the method.

  Microlithography processes are commonly used in the manufacture of small devices such as integrated circuits, liquid crystal elements, micropatterned structures, and micromechanical components. In this step, the projection objective achieves the role of projecting the pattern of a pattern structure (usually a photomask (mask, reticle)) onto a substrate (usually a semiconductor wafer). The substrate is coated with a photosensitive layer (resist) that is exposed by an image of the structure to be patterned using projection radiation.

  In order to create even finer structures, it is both necessary to increase the image side numerical aperture (NA) of the projection objective and to use ultraviolet radiation with shorter wavelengths, preferably shorter than 260 nm. . As a result, higher and higher requirements are imposed on the complexity of the projection objective. Projection objectives typically have at least 10, or 20, or even 25 or more multiple optical elements such as lenses and curved mirrors. The entire structure containing not only each single optical element, but also a plurality of optical elements arranged in a certain way, is the pattern structure on the substrate with a low level of aberrations into a large image field. It should be designed and manufactured with high precision so as to provide imaging.

Creating a new design of a projection objective is a complex task involving optimization of the structural and quality parameters of the projection objective. The structural parameters include the refractive index of the material forming the lens, the surface shape parameters of the lens and mirror (if applicable), the distance between the first and second surfaces of each lens, the surface of the different optical elements The distance between the object plane of the projection objective and the entrance surface of the front element on the object side of the projection objective, the distance between the exit surface of the front element on the image side of the projection objective and the image plane The refractive index of the medium disposed between adjacent optical elements, between the object plane and the object-side front element, and between the image plane and the image-side front element.
Quality parameters include, for example, parameters that represent the optical performance of the projection objective, such as by the selected aberration, image-side numerical aperture, and magnification of the projection objective.

  Today, optimization of designs to comply with the desired specifications of projection objective optical performance and other quality characteristics is a computerized method such as ray tracing that optimizes projection objective parameters while meeting certain boundary conditions. Is accompanied. “CODE V”, a lens analysis and design program sold by “Optical Research Associates, Inc.”, is a general-purpose software tool used for this purpose. This optimization includes minimizing or maximizing an appropriately selected merit function based on design parameters. In general, the merit function is constructed utilizing several merit function components that can represent optical aspects, manufacturability aspects, and other aspects that describe a particular design optimization goal.

  Due to the large number of design parameters, the solution space of the optimization process has a high dimension, and within this solution space, the calculation method is trapped and results far away from the design that meets the required specifications. There are many local minima and maxima that may be present. Thus, an optical instrument designer designing a projection objective for microlithography may determine a new design principle suitable for certain applications and / or based on the designer's intuition to meet predetermined boundary conditions. Sophisticated work should be satisfied. Therefore, the designer identifies an “initial design” that serves as a “starting point” that can be successful for computer-based optimization, and then based on that, improves the design through computerized optimization. Become. In general, one or more results will still be inadequate for the desired overall specification, and therefore it will be necessary to work a great deal until a satisfactory solution is found. become. Thus, the cost of a new design in the computer manufacturing stage will be high.

  With the proper design found, the optical elements of the projection objective must be manufactured and assembled in order to obtain the actual product of the manufacturing process. During these manufacturing steps, care must be taken to avoid as much as possible surface defects such as scratches and contamination of the optical surfaces. Low and medium aperture systems may be relatively tolerant with respect to such distortions, but typically for immersion operation in numerical aperture ranges where the image side numerical aperture NA is> 1.0. In the manufacturing process of lithographic projection objectives with very high numerical apertures, such as those designed for projection objectives, very strict specifications regarding surface defects are applied.

  At least one intermediate image, at least one concave mirror, and arranged to deflect radiation coming from the object surface towards the concave mirror or arranged to deflect radiation coming from the concave mirror towards the image surface Catadioptric projection objectives having at least one planar folding mirror that are applied frequently in these applications. Representative examples are shown, for example, in WO2004 / 019128A2 or JP2005-003982A.

  Surface defects on the optical surface can have a fatal effect on the optical performance of the projection objective by causing light loss due to essentially different loss mechanisms. For example, a relatively rough surface area on an ideally smooth surface will typically cause stray light, adversely affecting optical performance. Also, defects on the transmissive surface can act as phase objects, thereby causing light loss due to interference. Opaque contamination can occlude areas of the projection beam, which results in non-uniform intensity distribution within the image field. It is desirable to have a projection objective that is relatively insensitive to performance degradation caused by surface defects on the optical surface.

WO2004 / 019128A2 JP2005-003982A

One object of the present invention is to provide a method of manufacturing a projection objective that allows a compound projection objective for microlithography to be manufactured cost-effectively while maintaining a high standard in terms of optical performance. is there.
Another object of the invention is a projection objective that makes it possible to produce a projection objective for microlithography that has a relatively insensitive optical performance with respect to surface defects present on optical surfaces in the projection objective. It is to provide a method of manufacturing.
Another object of the present invention is to provide a method of manufacturing a projection objective having a low level of field change of intensity.
Another object of the present invention is to provide a projection objective that is relatively insensitive to surface defects and other effects caused by contamination on optical surfaces within the projection objective.

  As a solution to these and other objectives, the present invention includes a projection objective comprising the steps of defining an initial design for a projection objective according to one formalization and optimizing the design with a merit function. The method includes the step of defining a plurality of merit function components, each of which reflects a particular quality parameter, one of the merit function components being within the image surface of the projection objective The normalized effective illuminance value, which represents the effective illuminance normalized with respect to the effective illuminance, is a predetermined illuminance threshold on each optical surface of the projection objective except for the last optical surface closest to the image surface of the projection objective. Defining a maximum illumination requirement that does not exceed, the method calculates a numerical value for each of the merit function components based on corresponding features of the projection objective preliminary design, and the merit function And calculating the overall merit function, which can be expressed as a numerical value reflecting the quality parameter, and continuously changing at least one structural parameter of the projection objective so that the resulting overall merit function reaches a predetermined tolerance Recalculate the total merit function value that occurred using each successive change up to, and obtain the optimized projection objective structural parameters that have a predetermined tolerance for the resulting total merit function And manufacturing the projection objective by implementing the parameters.

In general, the term “illuminance” represents the power of electromagnetic radiation per unit area on the surface. Specifically, the term “illuminance” represents the power of electromagnetic radiation incident on the surface. As used herein, “effective illuminance” describes the contribution to the overall illuminance incident on the optical surface, and this contribution is derived from radiation emanating from a single object field point. Effective illuminance is alternatively referred to as “pinhole illuminance” in this application.
If a large value of effective illumination on the optical surface is avoided, the optical performance of the projection objective can be relatively insensitive with respect to surface defects present on the optical surface in the projection objective.

  In many cases, the “final optical surface”, ie the optical surface closest to the image surface of the projection objective, is subject to certain conditions that require the final optical surface to be excluded from the optimization process. The spatial distribution of the incident points of the radiation rays over the final optical surface is related to the concept of the involved projection process (dry projection or immersion projection) and the image side work space (between the final optical surface and the image surface on which the substrate surface is to be placed). Are greatly affected by the geometric conditions in the space. For example, if it is useful to provide a narrow gap (typically 1 millimeter or longer) between the final optical surface and the image surface to introduce immersion liquid for immersion exposure There is. In many cases, it is desirable to have a substantially planar final optical surface in terms of inflow and outflow of the immersion medium in the image space. Under these conditions, the intensity load of the final optical surface (e.g. expressed by effective illumination) is basically the image side working distance, the effective image field size, the refractive index of the medium after the last optical element, And the image-side numerical aperture NA. Therefore, the structural parameters representing the position of the final optical surface and the surface shape should not be free parameters and should be excluded from the optimization procedure.

  Various conditions are thought to cause or contribute to the maximum value of effective illumination on the optical surface. For example, if the optical surface is located within the fire surface area, a large effective illuminance value will occur. In an embodiment, these conditions calculate the position and extent of potential fire surface areas in the projection objective and optimize the structural parameters of the projection objective so that the optical surface is not positioned inside the fire area. Systematically avoiding it.

  Alternatively or additionally, the optical surface is considered critical if the actual partial aperture size of the beam bundle is extremely small. Thus, an embodiment of the method calculates several representative field points, calculates a ray bundle emanating from the field point and an intersection zone of the ray bundle optical surface, and the intersection zone of the ray bundle with the optical surface is Determining an actual partial aperture having a partial aperture size defined by the area of the intersection zone, determining a partial aperture size threshold, and determining the actual partial aperture size for the selected field point to be closest to the image surface of the projection objective. Optimizing the structural parameters of the projection objective so that it does not fall below the partial aperture size threshold for all optical surfaces of the projection objective except for the last optical surface of the projection objective.

  Method embodiments may include routines that consider more than one cause of extremely high effective illumination concentrations. For example, one merit function component can define the maximum illuminance requirement as described above, and another merit function component can have an actual partial aperture size on all optical surfaces (excluding the final optical surface) having a predetermined actual size. The minimum actual partial aperture requirement can be defined such that an optical design that can only obtain optical surfaces that exceed the partial aperture size threshold will automatically have.

  The method is used in various types of optical systems, in particular for projections used in microlithography with relatively high image side numerical apertures frequently found in projection objectives for immersion lithography capable of obtaining NA> 1. It can be applied to the design of objective instruments. Detailed analysis of many prior art projection objectives has shown that small effective and / or actual partial apertures and / or fire surface conditions are particularly suitable for at least one concave mirror and at least one intermediate image and concave mirror. It is shown that this may occur in a catadioptric projection objective having at least one planar deflecting mirror that separates the extending beam bundle from the beam bundle reflected from the concave mirror. These types of projection objectives do not have optical surfaces (except for final optical surfaces close to the image surface) where fire surface conditions occur and / or extremely small effective and / or actual partial apertures occur. Can be designed according to embodiments of the present invention.

  In some embodiments, the projection objective includes a plurality of optical elements arranged to image an off-axis object field arranged on the object surface onto an off-axis image field arranged on the image surface of the projection objective. An optical element that generates a first intermediate image from radiation coming from the object surface and includes a first refractive objective portion that includes the first pupil surface, and a second intermediate image. A second objective portion including a second pupil surface that is optically conjugate with the first pupil surface and includes at least one concave mirror that forms an image in the intermediate image; Forming a third refractive objective portion including a third pupil surface imaged on the surface and optically conjugate with the first and second pupil surfaces;

Embodiments may have exactly two intermediate images.
The second objective part can have exactly one concave mirror, the projection objective coming from the concave mirror and the first folding mirror for deflecting radiation coming from the object surface in the direction of the concave mirror And a second folding mirror for deflecting the radiation to be directed in the direction of the image surface. Both deflection mirrors can be planar. Projection objectives can be designed for immersion lithography with NA> 1.

FIG. 2 is a detailed view of a prior art catadioptric projection objective having exactly two intermediate images and a single concave mirror, with a relatively small real part aperture of the beam bundle at an optical surface close to the intermediate image. 1 is a detailed view of a prior art catadioptric projection objective having exactly two intermediate images and a single concave mirror, with a folding mirror positioned in the fire surface area. FIG. FIG. 3 is a schematic axial projection of a lens surface positioned on the pupil surface, illuminated by dipole illumination, and contaminated in one region of the pole. 2 is a schematic flow diagram illustrating a preferred embodiment of a manufacturing method that avoids optical surfaces having extremely high illuminance concentrations. FIG. 6 illustrates a pupil raster of pupil points that divides the pupil surface into raster fields having substantially the same raster field area in accordance with an embodiment of the present invention. FIG. 5 is a diagram showing an intersection on a selected optical surface separated from the pupil surface of a ray of the pupil raster shown in FIG. 4 and showing a region of relatively high effective illuminance (or pinhole illuminance). FIG. 5 is a diagram showing an intersection on a selected optical surface separated from the pupil surface of a ray of the pupil raster shown in FIG. 4 and showing a region having a fire surface condition. FIG. 6 shows an embodiment of a catadioptric projection objective having two intermediate images, one concave mirror, and two planar deflecting mirrors, with a fire surface condition systematically avoided on an optical surface close to the intermediate image. is there. FIG. 8 is a view showing a light receiving area of a field point selected around an edge of a rectangular field on the first and second folding mirrors of the embodiment of FIG. 7.

  As an introduction to some of the problems solved by the preferred embodiment of the present invention, consider a high aperture catadioptric projection objective NA> 1 adapted for immersion lithography. In many cases such designs provide a relatively small real partial aperture on the optical surface. As used herein, the term “real partial aperture” refers to a “light receiving area” (crossing zone) on the optical surface of a bundle of rays emanating from a specific object point (ie, a field point within the object surface). The small real part aperture in particular comprises at least one concave mirror and at least one intermediate image, in addition to at least one planar deflection mirror separating the beam bundle extending towards the concave mirror from the beam bundle reflected from the concave mirror. Can occur in catadioptric projection objectives.

  FIG. 1A shows details of a prior art catadioptric projection objective quoted from FIG. 2 of WO 2004/019128 A2 for illustrative purposes. This projection objective comprises a first refractive objective part OP1 that forms an object field from a planar object surface OS into a first intermediate image IMI1, and a first intermediate image IMI1 into a second intermediate image IMI2. A catadioptric objective part OP2 including a concave mirror CM for imaging and a refractive objective part OP3 (partial) for imaging the second intermediate image IMI2 on a planar image surface parallel to the object surface OS Only shown). The first plane folding mirror FM1 deflects the radiation coming from the object surface toward the concave mirror CM. A second plane folding mirror FM2 perpendicular to the first folding mirror deflects radiation coming from the concave mirror towards the image surface.

  The ray bundle RB emanating from the off-axis field point FP1 of the effective object field, which is positioned completely outside the optical axis AX, is the optical surface in the crossing zone whose size varies depending on the position of the optical surface in the optical system. Intersect. In the present application, these intersecting zones are represented by “real partial openings”. In FIG. 1, some representative intersection zones are highlighted with bold lines. The first real partial aperture SA1 on the incident side of the plane parallel plate immediately after the object surface is relatively close to the field surface (object surface) and is relatively small. The size of the second real partial aperture SA2 close to the first pupil surface P1 on the concave entrance side of the meniscus lens basically corresponds to the pupil size at that position and is relatively large. All real partial apertures substantially overlap at the pupil surface. In the actual partial aperture SA3 on the concave exit side of the positive meniscus lens immediately upstream of the first folding mirror FM1, the actual portion formed on the first folding mirror FM1 immediately upstream of the first intermediate image. As can be seen by the aperture SA4, the actual partial aperture becomes progressively smaller when the optical surface is positioned near the first intermediate image IMI1. In contrast, the fifth real partial aperture SA5 on the convex surface of the negative meniscus lens just before the concave mirror CM basically corresponds to the second pupil P2 size where the concave mirror CM is positioned. Has a large size.

  To obtain images without vignetting and pupil obscuration, these designs use off-axis object and image fields. When off-axis fields are used, the distance between the off-axis object field and the optical axis increases, thereby increasing the effort required to correct imaging aberrations when the “design object field” is enlarged. . The “design object field” includes all field points on the object surface that the projection objective can project with sufficient imaging fidelity in the targeted lithography process. Within the design object field, all imaging aberrations are sufficiently corrected for the target projection purpose, but at field points outside the design object field, at least one of the aberrations is less than the desired threshold. high. Thus, to facilitate correction, it may be desirable to keep the design object field size small, which requires minimizing the offset between the optical axis and the off-axis object field. The procedure that often minimizes this offset results in designs with mirror and / or lens surfaces that are relatively close to the field surface, thereby corresponding real parts present on these optical surfaces close to the field surface. The opening becomes smaller. For example, the actual partial apertures SA3 and SA4 on the lens and mirror immediately upstream of the first intermediate image IMI1 are relatively small.

  In general, small real partial apertures on the optical surface require strict requirements for the manufacturing process and the degree of decontamination of the resulting optical surface, and basically the optical surface must be free of significant surface defects. I must. Since the energy emitted from the selected field point is concentrated on a relatively small area in the region of the small real partial aperture, defects present in that region of the small partial aperture are present in the beam bundle. A portion of the light intensity will be shielded, thereby resulting in light loss. If the corresponding real part opening is small, simply the ratio between the area of the defect causing the perturbation and the area of the real part opening (light receiving area) becomes less favorable, so the surface defect of a given size is Causes a greater light loss effect than in an area with a large real part aperture. Local light loss caused by defects can cause uniformity errors that have direct problems with respect to the critical dimensions of structures produced by projection objectives. In particular, undesirable changes in critical dimensions (CD changes) may be caused in relation to the sensitivity level of the photosensitive coating (photoresist) on the substrate.

In addition, local light loss can cause telecentricity errors that typically result from a shift in the energy centroid of the pupil, typically towards a non-disturbed area. As a specific example, FIG. 2 schematically shows an axial projection of a lens surface LS positioned on a circular pupil surface in a projection objective. Projection exposure machines are operated with dipole illumination, for example, to improve depth of focus and / or contrast when printing densely bundled unidirectional lines. The intensity distribution of the projection radiation corresponding to this dipole illumination is on the side facing the optical axis AX and is characterized by two “poles” where the light energy is concentrated, the first pole PO1 and the second pole PO2. It is done. The light intensity does not exist on the optical axis. In the area of the first pole PO1 on the lens surface LS, there is a surface contamination CON. Since the contamination CON masks a significant portion of the light energy present in the first pole PO1, the energy centroid of the pupil will shift towards the second pole PO2, which is not disturbed. This eccentric energy centroid in the pupil corresponds to the propagation direction in which the intensity centroid of the image propagates in the image space where the wafer is positioned. Due to the contamination CON, the propagation direction is shifted from the optical axis and is directed at a finite angle with respect to the optical axis. For example, if the position of the substrate surface changes locally due to a position change caused by a high and low substrate surface and / or a wafer stage, it can lead to distortions induced by telecentricity. Image tilt occurs.
If it is assumed that the real part aperture is illuminated substantially uniformly so that there is no or very little difference in local radiation energy inflow between different locations within the real part aperture, The actual partial aperture size is considered to be a reasonable indicator of which optical surface is critical for surface defects.

  In many purely refractive optical systems, a substantially uniform distribution of illuminance within the real partial aperture can be a reasonable approximation. However, there can be significant changes in local illuminance within the real partial aperture, which can result in significant local illuminance differences within the real partial aperture. To address possible non-uniformities in local illuminance within the real partial aperture, it is advantageous to define an “effective partial aperture” that allows for local variations in illuminance within the real partial aperture. Is known. As indicated above, defects on the optical surface can be critical when relatively large radiation energy is concentrated in the defect area. Therefore, it is considered that a region having a relatively large value of local illuminance when compared with other portions of the actual partial aperture in the actual partial aperture is particularly decisive. To greatly avoid the problems associated with local concentration of radiation energy, identify the single area (or areas) where the maximum effective illuminance occurs by analyzing the real aperture area. Is considered advantageous. In geometric aspects, local illuminance can be characterized by a specified value of “geometric ray density” of rays emanating from a single field point in the object plane, and the maximum effective illuminance is Occurs when the maximum density occurs.

  Now consider the optimization of the system to deal with these local maxima of geometric ray density (or effective illuminance). Assuming that each real part aperture is illuminated uniformly, the system layout tolerance can have a certain value. However, the tolerance should be more stringent if a local concentration of radiation energy occurs within the real partial aperture. This effect can be addressed by defining an “effective partial aperture” that corresponds to the partial aperture that represents the location having the maximum geometrical light density (or maximum effective illuminance). In systems where the real partial aperture is illuminated uniformly with this concept, the “effective partial aperture” size is equal to the “real partial aperture” size. However, if a local concentration of radiation energy occurs within the real partial aperture, this local concentration is represented by the effective partial aperture size and is therefore smaller than the actual partial aperture size.

Illustratively, FIG. 1B shows details of another prior art catadioptric projection objective cited from embodiment 5 of WO 2004/019128 A2. Equal or similar features are indicated with reference numerals equal to those in FIG. 1A. One ray bundle RB exits from a selected field point FP1 in the object surface OS. The opening angle of the light beam on the object surface is determined by the object-side numerical aperture NA _OBJ . The trajectories of various selected rays including rays R1 and R2 are shown. As is apparent from the drawing, the geometric light density defined by the light rays of the light bundle RB is essentially uniform across the optical surface up to the region of the large positive meniscus lens ML upstream of the first folding mirror FM1. . However, when the light beam approaches the folding mirror FM1, the local density of the light beam (ie, the geometric light beam density) is the outer part of the light beam (the furthest away from the optical axis AX) when compared to the region close to the optical axis. It increases with. In other words, the geometric light density is non-uniform within the first folding mirror region at a short distance upstream of the first intermediate image IMI1. In particular, the light rays R1 and R2 emitted from the field point FP1 with different aperture values intersect in the area close to the first folding mirror FM1 or in the area of the first folding mirror FM1. (Note that these intersections of a single ray occur particularly in the region of the first and second folding mirrors FM1 and FM2 which are optically close to the intermediate images IMI1 and IMI2, respectively.) The intersection of rays emanating from a common field point at different apertures indicates the presence of a “fire surface” condition. From FIG. 1B, the first folding mirror and the second folding mirror FM1, FM2 are positioned in the region where the light beams of the light bundle RB intersect, that is, in the “fire surface region”. Is clear.

As described above, the geometric ray density corresponding to a particular field point can be considered as an expression for the contribution of a particular field point to the total illuminance on the optical surface.
In the present application, this contribution is expressed as “effective illuminance”. In an imaginary experiment, consider a pinhole (representing a single field point) that is illuminated in the object plane of the optical system. The ray bundle originates from this field point. The “effective illuminance” corresponding to this field point is the illuminance contribution on the selected optical surface with the light flux emanating from this field point. This contribution to the total illumination incident on the optical surface is a function of the position (or location) on the optical surface and is also a function of the position of the pinhole in the object surface. It is assumed that the maximum value of all values of effective illuminance (illuminance corresponding to a single object field point) must not exceed a predetermined “illuminance threshold”.

  Within the fire surface area, i.e., the area where the fire surface condition exists, the effective illuminance (pinhole illuminance) diverges and may actually cause a heavy concentration of light energy on a relatively small surface area. From the viewpoint of ray propagation, if different rays emitted from the object point with different numerical apertures intersect at or near the optical surface, a fire surface condition is given on the optical surface. A surface defect on an optical surface positioned in the fire surface area has an effect on rays emitted from the object plane at different aperture angles, thereby being substantially more than defects located outside the fire surface area Which greatly degrades imaging quality.

In an embodiment of the method of manufacturing a projection objective according to the invention, the fire surface conditions on the optical surface and / or the generation of extremely small effective partial apertures on the optical surface is a corresponding subroutine used in computer-based optical design. Systematically avoids and guides the typical layout of the optical elements of the projection objective. If these marginal conditions are systematically avoided, the process decontamination requirements can be relaxed without substantially compromising the optical performance of the resulting projection objective.
In this embodiment, one of the merit function components used in the calculation process defines a maximum illuminance requirement, which is the effective illuminance IRRDD that occurs on each optical surface (excluding the final optical surface closest to the image surface). It is requested that the maximum value of _EFF does not exceed a predetermined illuminance threshold value IRRTV.

As used herein, the term “illuminance” represents the power of electromagnetic radiation at the surface per unit area. In particular, the term “illuminance” represents the power of electromagnetic radiation incident on the surface. The SI unit of illuminance is watts per square meter (W / m ² ). Illuminance is sometimes called intensity, but should not be confused with radiation intensity having different units. “Effective illuminance” (also referred to as “pinhole illuminance”) represents the contribution from radiation emanating from a single object field point to the total illuminance incident on the optical surface. From the viewpoint of ray propagation, “effective illuminance” corresponds to the “geometric ray density” of different rays emanating from the common field point at equidistant aperture intervals. The effective illuminance can be uniform on the surface. Typically, the effective illuminance can vary across the surface, so that the region of maximum effective illuminance (corresponding to a large local geometric light density) and a small value of effective illuminance (small geometric light density) (Corresponding to) is formed.
If relatively large values of effective illuminance occur on the optical surfaces, these optical surfaces may be critical with respect to surface defects such as scratches and contamination. A relatively large value of effective illuminance can be caused, for example, by fire conditions on the optical surface and / or extremely small effective partial apertures on the optical surface.

  An embodiment of an optimization routine implemented in the software program used to calculate the optical design (layout) of the projection objective will now be described along the flow of the schematic flowchart shown in FIG. In the first stage S1 (optimization with respect to aberration “OPT AB”), the basic layout of the optical design is optimized with respect to aberration, and an optimized design D1 is obtained. For this purpose, a conventional subroutine of an appropriate optical design program can be used to change one or more structural parameters of the projection objective and to calculate the total aberrations of the resulting design. The resulting optimized design D1 may or may not have an optical surface where a large concentration of effective illuminance occurs locally on one or more optical surfaces.

In the second stage S2, the optimized design is analyzed and a normalized effective illuminance value IRRAD _EFF representing the effective illuminance normalized to the effective illuminance in the image surface of the projection objective is obtained for each optical surface of the projection objective. It is determined whether a predetermined illuminance threshold IRRTV is exceeded (excluding the final optical surface closest to the image surface of the projection objective).
If the normalized effective illuminance value IRRAD _EFF does not exceed the illuminance threshold IRRTV on any optical surface (with the possible exception of the final optical surface), a parameter representing the optimization design D1 is entered in the decision step S3. It is determined whether the aberration level AB is located above or below the predetermined aberration threshold ATV. If the aberration level is lower than the aberration threshold, the optimization design D2 is output as a result of the optimization procedure. The final design D2 can be equal to the optimized design D1 that functions as an input to the illumination determination in step S2.

  When the illuminance determination in step S2 determines that the normalized effective illuminance value IRRAD of the optimization design D1 exceeds the irradiation threshold IRRTV on at least one optical surface (excluding the final optical surface), the calculation routine Goes to the illuminance optimization stage S4 (OPT IRRAD), where the optimization design D1 is re-optimized to reduce local illuminance concentration on the optical surface that is decisive for effective illuminance. For this purpose, at least one structural parameter of the projection objective is changed and the full merit function is used, including the merit function component that defines the maximum illumination requirement. The resulting re-optimized design D1 ′ is then input into the illuminance determination step S2 through step S1, and whether the normalized illuminance value is lower than the illuminance threshold IRRTV for each of the optical surfaces of interest. Is determined. For this purpose, iterations involving two or more reoptimization steps can be used.

  If the illuminance determination step S2 determines that the resulting reoptimized design D1 ′ has been optimized with respect to the occurrence of the maximal value of illuminance, this optimized structure is input into the aberration determination step S3, It is determined whether re-optimization for illuminance has raised one or more critical aberrations above their respective aberration thresholds. If the reoptimized design is still acceptable with respect to aberrations, a final design D2 'is obtained and output in step S5.

If the design needs to be optimized with respect to aberrations, the structural parameters received from step S2 are input into step S1, and the optical design (already optimized for illumination) is also corrected for aberrations. . One or more iterations may be required to reoptimize the design with respect to aberrations and still obtain a normalized illuminance value that is lower than the critical illuminance threshold IRRTV on all critical optical surfaces . The final design D2 ′ is the result of the reoptimization procedure.
In some embodiments, the subroutine in the decision step S2 for determining illuminance involves the occurrence of fire conditions on all optical surfaces except the last optical surface closest to the image surface, and / or extremes on all optical surfaces. Makes it possible to avoid small partial openings.

A calculation routine for systematically avoiding the occurrence of fire surface conditions on the optical surface will now be described with reference to FIGS.
In the first stage of the manufacturing calculation part, several representative field points are defined. Ray tracing is performed on the rays of the bundle of rays emanating from these representative field points.
In the second stage, a pupil raster is defined in the pupil surface of the projection objective that represents an array of raster points that are separated from each other by a predetermined distance in a two-dimensional array.
In the third stage, ray trajectories of rays originating from the representative field points and passing through the raster points of the pupil raster are calculated for each representative field point. Commercially available design programs such as “CODE V”, OSLO, or ZEMAX can be used for this purpose.

に従う平方根関数に従って段階的に増大し、ここでｉ＝０、１、・・・、ｎであり、ＮＡは、投影対物器械の像側開口数であり、βは、物体視野と像視野の間の拡大係数である。そうすることにより、瞳表面は、実質的に同じラスタ視野面積を有するラスタ視野（ラスタセル）に細分化される。 Typically, the pupil raster covers the entire utilized aperture of the projection objective, and the aperture determines the opening angle of the beam bundle emanating from each representative field point. In the pupil raster embodiment schematically illustrated in FIG. 4, the coordinates of the raster points in the pupil surface are given in polar coordinates and are adjacent raster points (ie, nearest rasters having a predetermined distance between them). Point) have the same distance in the azimuth direction. In this embodiment, the angular interval width between raster points adjacent in the circumferential (azimuth) direction is 10/3 degrees. The coordinates of the raster point in the radial direction (radial coordinate) correspond to the aperture angle included between each light beam and the optical axis. In the present application, these angles are also referred to as “pupil angles”. The absolute value of the sine of the pupil angle is between the angle 0 and the maximum angle k _max = NA · β,

, Where i = 0, 1,..., N, NA is the image-side numerical aperture of the projection objective, and β is between the object field and the image field. Is an enlargement factor. By doing so, the pupil surface is subdivided into raster fields (raster cells) having substantially the same raster field area.

  In the fourth stage, for each optical surface, the intersection of these selected rays with the optical surface in the projection objective is calculated (in some cases the final optical surface closest to the image surface is Excluded as a possibility).

ここで、ｆは、それぞれの光学面の番号を表し、ｉ、ｊは、隣接する瞳ラスタ点のインデックスを表している。式（１）では、変数ｘ及びｋはベクトルである。ベクトルｘの成分は、光学面上の点の実空間での座標を表している。ベクトルｋの成分は、光学システムの入射瞳内（すなわち、瞳空間内）で光線の伝播方向を向く単位ベクトルのｘ、ｙ、及びｚ座標を表す方向正弦値である。従って、（１）における差分商は、瞳空間内で所定の間隔幅を有する間隔（変数ｋ）と光学面上の実空間内で対応する間隔幅（変数ｘ）の間の関係を示す基準値である。言い換えれば、式（１）の差分商によって定められる勾配パラメータｇ^f _ijは、瞳座標における所定の差分に対するそれぞれの表面上の交差点の変化程度を表している。（式（１）の差分商は、微分商の近似値であり、典型的に数値計算において有限間隔幅が用いられることを示している。式（１）の差分商は、間隔幅がゼロに近づく時に微分商になる。） At a later stage, pairs of raster points that are directly adjacent in the pupil surface are considered. Immediately adjacent raster points, both raster points in a pair have either the same azimuth coordinates or the same pupil angle coordinates, but each other coordinate has its own coordinate direction according to a preselected interval width It is characterized by being different by one coordinate interval. For each pair of adjacent raster points, the difference quotient of:

Here, f represents the number of each optical surface, and i and j represent the indices of adjacent pupil raster points. In equation (1), variables x and k are vectors. The component of the vector x represents the coordinates of a point on the optical surface in real space. The component of vector k is a directional sine value representing the x, y, and z coordinates of a unit vector that points in the direction of propagation of the ray within the entrance pupil of the optical system (ie, in pupil space). Accordingly, the difference quotient in (1) is a reference value indicating the relationship between an interval (variable k) having a predetermined interval width in the pupil space and a corresponding interval width (variable x) in the real space on the optical surface. It is. In other words, the gradient parameter g ^f _ij determined by the difference quotient of Equation (1) represents the degree of change of the intersection on each surface with respect to a predetermined difference in pupil coordinates. (The difference quotient in equation (1) is an approximation of the differential quotient, and typically indicates that a finite interval width is used in numerical calculations. The difference quotient in equation (1) has an interval width of zero. (It becomes a differential quotient when approaching.)

Note that the numerical criteria given by equation (1) above is determined using a linear gradient. More precisely, the ratio between the areas of the associated grid mesh elements on the surface corresponding to one grid mesh element in the direction space can be controlled. In practice, however, in most cases it is sufficient to control the linear gradient in a substantially orthogonal direction to avoid local peaks of light density.
In yet another step, a gradient threshold is defined that represents the minimum allowable gradient between adjacent intersections on the optical surface. For example, the gradient threshold value g ^f _ij (minimum) = 10 mm can be determined.

As yet another example of the meaning of the gradient parameter, FIG. 5 shows the intersection on a selected optical surface f of the pupil raster rays shown in FIG. 4 for a selected representative field point. The local density at the intersection is significantly higher in the high illumination area HIRAD in the lower right part of the optical surface than in other parts of the optical surface, such as the upper left part that is diametrically opposed to this high illumination area, so Obviously, the distribution of intersections and the resulting distribution of illuminance are not uniform. However, since the order of azimuth and radial intersections is the same as that in the pupil surface (the spacing between adjacent intersections indicating the amount of illuminance in each area is significantly different across the optical surface. However, there is no fire surface condition on the optical surface. The situation shown in FIG. 5 corresponds to a value of 4.7 mm in the gradient parameter g ^f _ij .

  In the next stage, the minimum value of the gradient parameter is calculated for each of the optical surfaces (optionally excluding the final optical surface). If the calculated minimum value for a particular optical surface is found to be less than the gradient threshold, the minimum gradient on each optical surface is reduced until the value is equal to or greater than the gradient threshold. In order to increase, the structural parameters of the projection objective are optimized. For example, the optimization procedure includes enlarging the distance between each optical surface and an adjacent field surface (such as an object surface, intermediate image, or image surface). Alternatively or additionally, the local tilt of the object surface within the minimum gradient region can be altered to increase the calculated gradient for adjacent intersections.

ここで、Ｍｉｎ（ｇ^f _ij）は、式（１）の差分商の最小値であり、ＮＡ_OBJは像側開口数である。勾配パラメータの最小値を有する領域は、最大幾何学的光線密度（及び最大有効照度）を有する領域に対応することに注意されたい。 The radius of the corresponding “effective partial opening” can be calculated according to the following equation:

Here, Min (g ^f _ij ) is the minimum value of the difference quotient of Equation (1), and NA _OBJ is the image-side numerical aperture. Note that the region having the minimum value of the gradient parameter corresponds to the region having the maximum geometric ray density (and the maximum effective illuminance).

  As a final result of the optimization procedure, all optical surfaces of the projection objective are positioned and shaped such that the gradient parameter is equal to or greater than the gradient threshold. From an illuminance standpoint, this requirement is that the normalized illuminance value IRRAD, which represents the illuminance normalized to the illuminance in the image surface of the projection objective, is close to each optical surface of the projection objective (close to the image surface of the projection objective). Corresponds to a condition that does not exceed a predetermined illuminance threshold value on the optical surface (excluding the final optical surface). If the illuminance does not exceed the allowable maximum of normalized illuminance, as described above, the optical performance of the projection objective is relatively insensitive to potential defects on the optical surface.

For comparison, FIG. 6 shows the intersection on the surface of the “virtual” system that is in the region where the fire surface condition of the ray of the pupil raster relative to the field point occurs. In the upper left part of the virtual surface, the intersection corresponding to the pupil coordinates of the outer edge of the pupil is more on the axis than the intersection corresponding to the raster point located somewhere between the optical axis and the outer edge of the pupil. It is clear that it is located near the intersection of rays. In other words, rays emanating from a given field point with different numerical apertures (represented by different radial coordinates in the pupil raster) intersect at or near their respective optical surfaces and are thereby large in the pupil surface The ray corresponding to the aperture value intersects the optical surface closer to the on-axis ray than the ray corresponding to the small aperture value. In this figure, the gradient parameter g ^f _ij reaches a minimum value of 0 mm in the optical surface area located in the fire surface area CAUSTIC (upper left part).
The systematic use of the above-described method leads to an optical design in which none of the optical surfaces is positioned in the fire surface region and / or in a region having a very small effective partial aperture. If such optical surfaces are avoided in the optical system, surface quality and / or contamination specifications can be relaxed, thereby facilitating the manufacture of the optical system.

  FIG. 7 shows an embodiment of a catadioptric projection objective 100 that satisfies these conditions. This projection objective is designed with a nominal UV operating wavelength λ = 193 nm. Specifications are provided in Tables 1 and 1A. The projection objective 100 divides a pattern image on a reticle arranged on a plane object surface OS (object plane) into a plane image surface IS (image plane) in exactly two real scales, for example with a reduction scale of 4: 1. It is designed to project while generating intermediate images IMI1, IMI2. The rectangular effective object field OF and image field IF are off-axis, i.e. completely outside the optical axis AX. The first refractive objective part OP1 is designed to image the pattern in the object surface to the first intermediate image IMI1 on an enlarged scale. The second catadioptric (refractive / reflective) objective instrument part OP2 forms the first intermediate image IMI1 in the second intermediate image IMI2 at a magnification close to 1: (− 1). The third refractive objective part OP3 images the second intermediate image IMI2 on the image surface IS with a large reduction ratio.

  In order to facilitate following the beam path of the projection beam, the path of the principal ray CR at the outer field point of the off-axis object field OF is indicated by a bold line in FIG. For the purposes of this application, the term “chief ray” (also known as the primary ray) is a ray that extends from the outermost field point (farthest from the optical axis) of the effective use object field OF to the center of the entrance pupil. Means. Due to the rotational symmetry of the system, the chief rays can be selected from comparable field points in the meridional plane shown for illustration purposes. In projection objectives that are essentially telecentric on the object side, the chief rays are emitted parallel to the object surface or at a very small angle with respect to the optical axis. Furthermore, the imaging process is characterized by the trajectory of the peripheral rays. As used herein, a “marginal ray” is a ray that extends from an axial object field point (field point on the optical axis) to the edge of the aperture stop. If off-axis effective object fields are used, this marginal ray cannot contribute to image formation due to vignetting. The chief and ambient rays are selected to characterize the optical performance of the projection objective. The angles included between such a selected ray and the optical axis at a given on-axis position are represented by “principal ray angle” (CRA) and “marginal ray angle” (MRA), respectively. The radial distance between such a selected light beam and the optical axis at a given on-axis position is represented by “principal ray height” (CRH) and “marginal ray height” (MRH), respectively.

At positions where the principal ray CR intersects the optical axis, pupil surfaces P1, P2, and P3 that are conjugate to each other are formed. A first pupil surface P1 is formed in a first objective part between the object surface and the first intermediate image, and a second pupil surface P2 is formed between the first intermediate image and the second intermediate image. Formed in the second objective part in between, a third pupil surface P3 is formed in the third objective part between the second intermediate image and the image surface IS.
The second objective part OP2 includes a single concave mirror CM. The first plane folding mirror FM1 is optically close to the first intermediate image IMI1 and arranged at an angle of 45 ° with respect to the optical axis so as to reflect the radiation coming from the object surface in the direction of the concave mirror CM. Is done. The second folding mirror FM2 having a plane mirror surface aligned perpendicular to the plane mirror surface of the first folding mirror reflects radiation coming from the concave mirror CM in the direction of the image surface parallel to the object surface. To do.

Each of the folding mirrors FM1 and FM2 is positioned optically close to the intermediate image so that etendue (geometric light beam) is kept small. The intermediate image is preferably not located on the planar mirror surface, thereby creating a finite minimum distance between the intermediate image and the optically closest mirror surface. This ensures that any obstructions in the mirror surface, such as scratches or impurities, are not clearly imaged on the image surface.
The first objective part OP1 includes two lens groups LG1, LG2 each having a positive refractive power on either side of the first pupil surface P1. The first lens group LG1 is designed to image the telecentric entrance pupil of the projection objective into the first pupil surface P1, thereby acting in the manner of a Fourier lens group that performs a single Fourier transform. To do. This Fourier transform yields a relatively small maximum chief ray angle CRA _P1 on the first pupil surface of the order of 17 °. As a result, the optically usable diameter of the first pupil is relatively large according to the Lagrangian invariant, and is indicated by the radiation beam diameter D ₁ = 145 mm of the first pupil surface.

  A relatively small chief ray angle with a large pupil diameter corresponds to a relatively large axial extent of the pupil space PS. For the purposes of this application, the pupil space is defined as a region where the marginal ray height MRH is substantially larger than the principal ray height CRH and RHR <| B | << 1 is satisfied at the ray height ratio RHR = CRH / MRH. Determined. The upper limit B of the beam height ratio can be, for example, smaller than 0.4, smaller than 0.3, or smaller than 0.2. If this condition is met, the correction applied in the pupil space will basically have a constant field of view effect. The axial extent of the pupil space increases when the chief ray angle at each pupil decreases. In this embodiment, the condition RHR <0.3 is satisfied.

In this embodiment, the pupil space PS includes the first lens L1-6 (biconvex lens) of LG2 immediately downstream of the pupil surface, and further up to the subsequent lens L1-7 on the image side of the pupil surface. It extends to a positive biconvex lens L1-5 immediately upstream of the pupil surface. Free spaces FS1 (= 41 mm) and FS2 (= 62 mm), each having an axial extension range of at least 40 mm and allowing one or more thin correction elements to be placed inside, are pupil surfaces It is formed in the pupil space PS on either side of P1, that is, optically close to the pupil surface. Thus, this embodiment provides one or more optically close proximity to the first pupil surface P1 in order to obtain a correction effect (constant field of view correction) that is essentially the same for all field points of the field of view. It also makes it possible to introduce many correction elements.
The parallel plate PP is positioned on the first pupil surface P1 that satisfies the condition RHR≈0 in the pupil space PS. The parallel plate is part of the original design of the projection objective and can serve as a placeholder for the correction element, which also has essentially the same thickness and material, at least One surface can be formed as a plane-parallel plate having an aspherical shape.

As mentioned above, in high aperture projection objectives typically used in microlithography, a relatively small real and / or effective partial aperture of the light bundle has a certain object surface, for example an object close to the field of view. It can occur at the surface. For example, in the embodiment of FIG. 7, the first folding mirror FM1 and the second folding mirror FM2 are both positioned optically close to the adjacent intermediate images IMI1 and IMI2, respectively, thereby a relatively small real part. An opening occurs on these folding mirrors. In general, the illuminance on the optical surface increases as the partial aperture size decreases. If relatively large values of illuminance occur on the optical surfaces, these optical surfaces may be critical with respect to surface defects such as scratches and contamination. Also, fire conditions may occur, especially on certain optical surfaces with optical systems close to the field of view. When the optical surface is located in the fire surface area, the illuminance is considered to diverge.
In optical systems having optical surfaces in areas of small partial apertures and / or areas where fire conditions occur, due to these effects, specifications regarding surface quality and contamination must be kept particularly strict. On the other hand, if such surfaces are avoided in the optical system, specifications regarding surface quality and / or contamination can be relaxed, thereby facilitating the manufacture of the optical system.

  In the manufacture of the embodiment of FIG. 7, the first and second folding mirrors FM1, FM2 are arranged sufficiently separated from the intermediate image to obtain a relatively large partial aperture and control of the fire surface conditions Special emphasis was placed on correcting the ray path so that no fire surface condition occurred on either of the folding mirrors FM1 and FM2. This is qualitatively illustrated in FIG. 8, which shows the light receiving areas of 18 selected field points around the edge of the rectangular field on the first and second folding mirrors FM1 and FM2. In each light receiving area, the light beam is indicated by 10 equidistant opening intervals. Obviously, the substantially elliptical lines corresponding to the beam bundles of different apertures emanating from the same field point do not intersect but overlap one another without intersecting the folding mirrors. This indicates that both the first and second folding mirrors are in a region without a fire surface condition, i.e., a "no fire surface" region. Similarly, a positive biconvex lens arranged geometrically relatively close to the first and second intermediate images in the geometrical folding mirror FM1, FM2 and the double path region between the concave mirrors, It is in an unfired area. As a result, the embodiment of FIG. 7 is relatively resistant to surface defects and / or contamination on the optical surface close to the intermediate images IMI1, IMI2.

The above description of preferred embodiments has been provided by way of example. Individual features can be implemented either alone or in combination as embodiments of the invention, or in other fields of application. Furthermore, these features may represent advantageous embodiments that can be protected on their own without depending on the other, and these embodiments are claimed for protection in this application at the time of filing, You will be asked for protection while you are pending. From the disclosure provided above, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find various changes and modifications to the disclosed structures and methods. Accordingly, Applicants desire that all such changes and modifications fall within the spirit and scope of the invention as defined by the appended claims and their equivalents.
The contents of all the claims are hereby incorporated by reference.

Table 1

Table 1A

S1 First stage D1, which is optimization “OPT AB” for aberrations D1 Optimization design IRRAD _EFF normalized effective illuminance value IRRTV illuminance threshold

Claims (14)

A method of manufacturing a projection objective comprising the steps of determining an initial design for the projection objective and optimizing the design using a merit function,
Defining a plurality of merit function components each reflecting a specific quality parameter;
Including
One of the merit function components is that the normalized effective illuminance value representing the effective illuminance normalized with respect to the effective illuminance at the image surface of the projection objective has a final optical value closest to the image surface of the projection objective. Defining a maximum illuminance requirement that requires a predetermined illuminance threshold not to be exceeded on each optical surface of the projection objective excluding the surface;
Calculating a numerical value for each of the merit function components based on corresponding features of a preliminary design of the projection objective;
Calculating an overall merit function that can be represented by a numerical value reflecting a quality parameter from the merit function component;
Continuously changing at least one structural parameter of the projection objective and recalculating the resulting overall merit function value with each successive change until the resulting overall merit function value reaches a predetermined tolerance; ,
Obtaining the structural parameters of an optimized projection objective having the predetermined tolerance for the resulting overall merit function;
Implementing the parameters to produce the projection objective; and
The method of further comprising. Calculating the position and extent of a potential fire surface area within the projection objective;
Optimizing the structural parameters of the projection objective such that an optical surface is not positioned within the fire surface area;
The method of claim 1, comprising: Defining several representative field points;
Defining a pupil raster representing an array of raster points spaced from each other on the pupil surface of the projection objective;
For each of the representative field points, calculating a ray trajectory of rays emanating from the representative field point and passing through the raster point of the pupil raster;
For each optical surface, calculating the intersection of the ray with the optical surface;
Calculating, for each optical surface, a plurality of gradient parameters representing respective gradients between intersections corresponding to adjacent raster points arranged in close proximity to each other;
Determining a slope threshold representing a minimum allowable slope between adjacent intersections;
Optimizing the structural parameters of the projection objective so that the gradient parameters do not fall below the gradient threshold for each optical surface of the projection objective except the final optical surface;
The method according to claim 1 or 2, characterized by comprising:   4. The method of claim 3, wherein the pupil raster is defined such that the pupil surface is subdivided into raster fields having substantially the same raster field area. In the pupil raster, adjacent raster points have the same distance in the azimuth direction, and the pupil angle k is

In accordance with a polar coordinate that changes stepwise between 0 and k _max = NA · β, where i = 0, 1,..., N, where NA is the image of the projection objective 5. A method according to claim 3 or claim 4, characterized in that it is the side numerical aperture and [beta] is the magnification factor between the object field and the image field. Defining several representative field points;
Calculating a ray bundle emanating from the field point and an intersection zone with an optical surface of the ray bundle defining an actual partial aperture having an actual partial aperture size defined by an area of the intersection zone;
Determining a partial opening size threshold;
The actual partial aperture size for the selected field point is not less than the partial aperture size threshold for all optical surfaces of the projection objective except the final optical surface closest to the image surface of the projection objective Optimizing the structural parameters of the projection objective;
The method according to any one of claims 1 to 5, comprising: A plurality of optical elements configured to image a pattern provided on the object surface of the projection objective onto the image surface of the projection objective;
Including
Manufactured according to the method of any one of claims 1 to 6,
A projection objective characterized by that. A catadioptric projection objective designed to image an off-axis object field arranged on the object surface into an off-axis image field arranged on the image surface, and at least one concave mirror;
At least one intermediate image;
At least one folding mirror arranged to deflect radiation coming from the object surface towards the concave mirror or arranged to deflect radiation coming from the concave mirror towards the image surface;
including,
The projection objective according to claim 7. The optical element is
A first refractive objective portion that generates a first intermediate image from radiation coming from the object surface and includes a first pupil surface;
A second objective including the at least one concave mirror for imaging the first intermediate image into a second intermediate image and including a second pupil surface optically conjugate with the first pupil surface; Instrument part,
A third refractive objective portion for imaging the second intermediate image on the image surface and including a third pupil surface optically conjugate with the first and second pupil surfaces;
Forming,
The projection objective according to claim 8. The projection objective has exactly two intermediate images, and / or the second objective part has exactly one concave mirror, and the projection objective emits radiation coming from the object surface A first folding mirror for deflecting in the direction of the concave mirror and a second folding mirror for deflecting radiation coming from the concave mirror in the direction of the image surface and / or a projection objective The instrument is designed for immersion lithography with NA>1;
A projection objective according to claim 9. A plurality of optical elements having an optical surface configured to image an off-axis object field arranged on the object surface into an off-axis image field arranged on the image surface of the projection objective;
And at least one concave mirror;
At least one intermediate image;
At least one folding mirror arranged to deflect radiation coming from the object surface towards the concave mirror or arranged to deflect radiation coming from the concave mirror towards the image surface;
Including
The structural parameters of the projection objective are adjusted so that the optical surface is not positioned in the fire surface area,
A catadioptric projection objective characterized by that. The optical element is
A first refractive objective portion that generates a first intermediate image from radiation coming from the object surface and includes a first pupil surface;
A second objective including the at least one concave mirror for imaging the first intermediate image into a second intermediate image and including a second pupil surface optically conjugate with the first pupil surface; Instrument part,
A third refractive objective portion for imaging the second intermediate image on the image surface and including a third pupil surface optically conjugate with the first and second pupil surfaces;
Forming,
The projection objective according to claim 11, wherein: The projection objective has exactly two intermediate images, and / or the second objective part has exactly one concave mirror, and the projection objective emits radiation coming from the object surface A first folding mirror for deflecting in the direction of the concave mirror and a second folding mirror for deflecting radiation coming from the concave mirror in the direction of the image surface and / or a projection objective The instrument is designed for immersion lithography with NA>1;
The projection objective according to claim 12, wherein:   14. Projection objective according to claim 11, 12, or 13, wherein the at least one folding mirror is a plane mirror.

Images