JP5854295B2 - Illumination optical system and optical system for microlithography - Google Patents

Description

  The present invention relates to an illumination optical system for microlithography. Furthermore, the invention relates to an optical system for microlithography, a projection exposure apparatus comprising these optical systems, a method for producing a microstructured component or a nanostructured component, and a microstructured produced by the method. Concerning components.

  An illumination optical system of the kind indicated at the beginning is known from US 2006/0132747 A1. In this document, the position of the facet mirror used to preset the illumination is required in other known illumination optics in the subsequent entrance pupil plane of the projection optics or a plane optically conjugate thereto. The concept of a specular reflector that is not so limited is described.

US 2006/0132747 A1 EP 1 905 594 A1

  The object of the present invention is to develop a specular reflector concept for illumination optics where special efficiency requirements are made with respect to the use of illumination light.

  According to the invention, this object is achieved by a first transfer optical system for guiding illumination light traveling from a light source and an illumination preset facet that is downstream of the first transfer optical system and has a plurality of illumination preset facets. An illumination preset facet mirror that generates preset illumination of the object field using an edge shape that can be illuminated by the illumination preset facet mirror and the individual tilt angle of the illumination preset facet; This is achieved by an illumination optics for microlithography for illuminating an object field having a first transfer optics and an array of illumination preset facet mirrors such that a telecentric illumination is provided.

  It was first recognized by the present invention that the design freedom provided by providing an illumination preset facet mirror according to the present invention enables telecentric illumination of the object field. In the case of having telecentric illumination of the object field, since the entrance pupil plane of the projection optical system that follows is not defined, the conventional system has a field facet mirror and a pupil facet mirror that is arranged in the entrance pupil plane of the projection optical system that follows. This type of telecentric illumination cannot be achieved with this illumination optical system. Thus, a conventional illumination optical system having a second facet mirror in the conjugate pupil plane needs to have an additional imaging optical element and therefore has low efficiency.

  Telecentric illumination of the object field reduces the requirement consisting of a structural design on the illuminated and imaged object. In particular, the need for field-dependent imaging correction is eliminated.

  An alternative to a specular reflector and basically a known illumination optical system in a field facet mirror and a pupil plane of a projection optical system located downstream of this type of illumination optical system or a plane conjugate thereto In contrast to the configuration of the illumination optical system with the pupil facet mirror arranged, the edge shape that can be illuminated by the illumination preset facet mirror in the illumination optical system according to the invention is that the preset illumination of the object field is Represents a substantive influence variable that depends on it. In a conventional illumination optical system with a field facet mirror and a pupil facet mirror, the edge shape of the pupil facet mirror in this case only affects the illumination angle distribution and affects the shape of the object field that can be illuminated. The edge shape that the pupil facet mirror can illuminate is in principle not critical with respect to the intensity distribution of the illumination of the object field. On the other hand, in the illumination optical system according to the present invention, the edge shape that can be illuminated by the illumination preset facet mirror has a direct influence on the illumination shape of the object field.

  A maximum of three reflective components can be placed between the light source array, which can include a collector for light source emission, and the object field. In this case, in other words, only three or even two reflective components are required between the light source array and the object field. Thereby, illumination light loss is reduced in illumination, particularly when EUV light with a wavelength between 5 nm and 30 nm is used, for example. There can be exactly two reflective components between the light source array and the object field.

  The illumination preset facet mirror has a plurality of transfer facets directed to be illuminated with a preset edge shape adapted to the shape of the object field and a preset assignment to the illumination preset facet; A transfer facet mirror located upstream of the illumination preset facet mirror again increases the design freedom when using the specular reflector principle. With the transfer facet mirror, the edge shape of the illuminated preset facet mirror can be illuminated, the illumination angle distribution of the illumination preset facet mirror, and the intensity distribution of the edge shape of the illumination preset facet mirror can be illuminated It can be strictly preset in the range.

  The transmission facets can be grouped into a plurality of transmission facets, one of the transmission facets directing the illumination light in each case towards full illumination of the object field. This kind of grouping of transmission facets allows a defined superposition of a plurality of facets that completely illuminate the object field. These facets need not be composed of spatially connected transmission facets. In the case of complete superposition of collector separation fields by transfer facets, form facets consisting of two or more complementary subgroups that complement each other to form a complete object field It is advantageous.

  The transfer facets may have a group edge shape that is geometrically similar to the edge shape of the object field. This kind of edge shape similarity improves the illumination quality of the object field.

  The transmission facets constituting the transmission facet group can be arranged in a plurality of columns, and the plurality of transmission facets are continuously arranged in the column direction in each of the columns. This type of tandem arrangement increases the number of individual transmission facets present in the transmission facet group. This ensures a very fine presetting of the angular distribution and the intensity distribution, in particular in the illumination of the illumination presetting facet mirror. In this case, the column direction extends in particular parallel to the object displacement device for which the illumination optical system is designed in the projection exposure apparatus.

  Adjacent columns of transmission facet mirrors can have transmission facets arranged offset relative to each other along the column direction. This type of transmission facet, which is arranged offset from one another in each column, allows in particular the fine adaptation of the group edge shape to the object field edge shape. In this case, the curvature of the group edge shape is not limited by the dimensions of the individual transmission facets.

  The transmission facets can be separated from each other by a cut extending at an angle different from zero with respect to the column direction. This kind of transmission facet extending in the longitudinal direction, in particular inclined with respect to the object displacement direction of the object illuminated by the illumination optical system, prevents intensity distortion of the object field illumination due to facet division.

  The illumination preset facet mirror can have a through opening through which illumination light is guided between the light source and the transfer facet mirror. This type of through-opening makes it possible to provide a very small angle of incidence on the mirrors of the illumination optics that do not operate with grazing incidence. Thereby, a small transmission loss is ensured especially when EUV light having a wavelength between 5 nm and 30 nm is used as illumination light in a projection exposure apparatus equipped with illumination optics.

  The illumination presetting facets on the one hand and the transmission facets optionally additionally present on the other hand can in particular be configured as tiltable facets that can be tilted by an actuator. Such tiltable facets can be designed in particular as facets that can be switched between at least two tilt positions. The small angle of incidence of the illumination light on the facet is specifically designed so that the facet for adjusting different illumination modes can be tilted, and due to the varying angle of incidence, the coating optimized for an angle It is important for high efficiency when it cannot be provided.

  The advantages of the optical system comprising the illumination optical system according to the invention and the projection optical system for imaging the object field into the image field correspond to those described above in relation to the illumination optical system according to the invention.

  According to a second aspect of the present invention, the purpose indicated at the outset is an illumination optical system for microlithography for illuminating an object field, and a first transfer optical system for guiding illumination light traveling from a light source, An illumination preset facet mirror disposed downstream of the first transfer optical system and having a plurality of illumination preset facets, wherein the illumination preset facet mirror can be illuminated with an edge shape and an illumination preset facet An illumination preset facet mirror that generates a preset illumination of the object field using the tilt angle, and a projection optical system for imaging the object field into the image field, the illumination preset facet mirror and the object field A first transfer optics in which the entrance pupil plane of the projection optical system is arranged between or after the object field to provide illumination of the object field adapted to the entrance pupil of the projection optical system And illumination preset sequence facet mirror is achieved by an optical system present.

  Implementing the adaptation of the object field illumination to the requirements of the entrance side of the projection optical system can be achieved by placing an optical component in the entrance pupil plane of the projection optical system or by relaying this entrance pupil plane It has been recognized that it is possible to use the principle of a specular reflector without being forced to displace to another position using. In this case, illumination optics for guiding the illumination light that can provide a particularly small angle of incidence of the illumination light on the reflective optical component, even in a projection optical system with an entrance pupil plane located immediately before or after the object field An arrangement of system components is possible. This type of entrance pupil plane located close to the object field will be found, for example, in pupil occluding projection optics. This results in a smaller reflection loss of the illumination light.

  The spacing ratio between the spacing of the entrance pupil plane from the object field and the spacing of the object field from the illumination preset facet mirror is less than 0.9, less than 0.8, less than 0.7, It can be smaller than 0.6, and further smaller than 0.5. With this kind of spacing ratio, the above-described advantages of the optical system according to the second aspect are particularly evident. In the optical system according to the invention, the distance of the entrance pupil plane from the illumination preset facet mirror can be greater than 800 mm independent of the distance of the entrance pupil plane from the object field.

According to a third aspect of the present invention, the purpose indicated at the outset is an illumination optical system for microlithography for illuminating an object field, and a first transfer optical system for guiding illumination light traveling from a light source, An illumination preset facet mirror disposed downstream of the first transfer optical system and having a plurality of illumination preset facets, wherein the illumination preset facet mirror can be illuminated with an edge shape and an illumination preset facet An illumination preset facet mirror that generates preset illumination of the object field using the tilt angle, and a projection optical system for imaging the object field into the image field, and the installation length of the projection optical system (B ) And object-image offset (d _OIS ) ratio is achieved by an optical system less than 20.

  Illumination light can be similarly guided through a large installation space requirement on the image side, no additional optical components are required for guiding the illumination light for this guidance, and yield is further reduced The degree of freedom of the specular reflector principle can be advantageously combined with projection optics having a large object-image offset so that extreme angles of incidence need not be selected. The above-mentioned ratio between the installation length of the projection optical system and the object-image offset can be smaller than 15 and even smaller than 10.

  According to the fourth aspect of the present invention, the purpose shown at the beginning is to provide a first transmission optical system for guiding the illumination light traveling from the light source, and a plurality of illumination pre-arrangements arranged downstream of the first transmission optical system. An illumination preset facet mirror having a setting facet, wherein the preset illumination of the object field is generated using an edge shape that can be illuminated by the illumination preset facet mirror and the tilt angle of the illumination preset facet A setting facet mirror, and a projection optical system for imaging the object field into the image field. The illumination optical system between the light source and the object field has an intermediate focus, and the installation length of the projection optical system (B ) And intermediate focus-image offset (D) ratio is achieved by an optical system with illumination optics for microlithography for illuminating an object field smaller than 5.

  With this kind of ratio between the installation length of the projection optics and the intermediate focus-image offset, the illumination light can be guided through a large installation space requirement on the image side and for this purpose the illumination light It can likewise be ensured that no additional optical components are required to guide the light and that it is not necessary to select extreme angles of incidence that reduce the yield. The ratio between the installation length of the projection optical system and the intermediate focus-image offset is smaller than 3, smaller than 2, smaller than 1.90, smaller than 1.80, smaller than 1.60. In particular, it can be smaller than 1.31.

  The general installation space requirement on the image side is about 1 m measured from the center of the image field in the image plane, especially about 1 m in the direction of the components of the illumination optics, and further projected perpendicular to the image plane. Even when measured away from the optical system, it is about 1 m.

  According to the fifth aspect of the present invention, the object shown at the beginning is to provide a first transmission optical system for guiding illumination light traveling from a light source, and a projection optical system for forming an object field into an image field. And an optical system having an illumination optical system for microlithography for illuminating an object field in which the ratio of the installation length (B) of the projection optical system to the illumination light beam-image offset (E) is less than 5 Achieved by:

  The advantages of the optical system according to the fifth aspect correspond to those described above in relation to the optical system according to the fourth aspect. In the optical system according to the fifth aspect, the intermediate focal point of the illumination optical system does not necessarily exist. The illumination preset of the object field can be designed separately from the illumination preset facet mirror of the optical system according to the fourth aspect. The ratio between the installation length of the projection optical system and the illumination light beam-image offset is smaller than 3, smaller than 2, smaller than 1.90, smaller than 1.80, smaller than 1.60. Especially in the 1.30 region.

  The optical system according to the second, third, fourth or fifth aspect can be combined with the above-mentioned features of the illumination optical system according to the invention, in particular with respect to the transfer facet mirror.

  Using a projection exposure apparatus having an optical system and a light source, in particular an EUV light source, and a reticle according to the present invention, a step of preparing a wafer having a coating sensitive to illumination light, and a projection exposure apparatus according to the present invention A production method for producing a microstructured component having the steps of projecting at least a portion of a reticle onto a wafer and developing a photosensitive layer exposed on the wafer with illumination light, and produced by the present invention. The advantages of the microstructured component or the nanostructured component correspond to those described above in relation to the illumination optics according to the invention and the optics according to the invention.

  The configuration of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a diagram schematically showing a projection exposure apparatus for EUV microlithography in the meridional section having an illumination optical system and a projection optical system. FIG. 2 is a diagram schematically showing a beam path of a typical individual beam in a meridional section in the illumination optical system shown in FIG. 1 from an intermediate focal point to a reticle arranged on the object plane of the projection optical system. . It is a figure which shows the transmission facet mirror of an illumination optical system in the figure which makes it possible to see dispersion | distribution of the transmission facet of a transmission facet mirror. FIG. 4 is a detailed enlarged view from FIG. 3 in the region of several transfer facets with each illumination light guiding the complete illumination of the object field in the object plane of the projection optics. It is an isointensity diagram of the intensity distribution of the illumination light on the illumination preset facet mirror of the illumination optical system arranged downstream of the transmission facet. It is a figure similar to FIG. 1 of the EUV projection exposure apparatus of another structure. It is a figure similar to FIG. 1 of the EUV projection exposure apparatus of another structure. It is a figure similar to FIG. 1 of the EUV projection exposure apparatus of another structure. A plurality of transfer facet groups of a further configuration of transfer facet mirrors for directing illumination light towards full illumination of the object field are shown in the enlarged view as before compared to FIG. It is a figure shown in detail respectively. FIG. 6 is a meridional cross-sectional view illustratively including an imaging beam path through a projection optical system configured for the above-described projection exposure apparatus. It is a figure of the projection optical system of another structure for the projection exposure apparatus of the above-mentioned structure. It is a figure of the projection optical system of another structure for the projection exposure apparatus of the above-mentioned structure. It is a figure of the projection optical system of another structure for the projection exposure apparatus of the above-mentioned structure.

  A projection exposure apparatus 1 for microlithography, shown very schematically in meridional section in FIG. 1, has a light source 2 for illumination light 3. The light source is an EUV light source that generates light in the wavelength range of 5 nm and 30 nm. The light source can be an LPP (laser generated plasma) light source or a DPP (discharge generated plasma) light source.

  A transmission optical system 4 is used to guide the illumination light 3 traveling from the light source 2. The transmission optical system 4 has a collector 5 which is only shown with respect to its reflection effect in FIG. 1 and a transmission facet mirror 6 which will be described in more detail below. Between the collector 5 and the transmission facet mirror 6, an intermediate focal point 5a of the illumination light 3 is arranged. The numerical aperture of the illumination light 3 in the region of the intermediate focus 5a is NA = 0.182. Arranged downstream of the transmission facet mirror 6 and thus downstream of the transmission optical system 4 is an illumination preset facet mirror 7 which will likewise be explained in more detail below. In the beam path of the illumination light 3 downstream of the illumination preset facet mirror 7, a reticle 8 disposed on the object plane 9 of the projection optical system 10 of the projection exposure apparatus is disposed downstream. The projection optical system 10 and the projection optical system having another configuration described below are a projection lens system in each case.

  In order to facilitate the display of the positional relationship, an orthogonal xyz coordinate system will be used below. The x direction extends in the direction perpendicular to the drawing in FIG. The y direction extends to the right in FIG. In FIG. 1, the z direction extends downward.

Optical components 5 to 7 are components of the illumination optical system 11 of the projection exposure apparatus 1. The object field 12 on the reticle 8 in the object plane 9 is illuminated by the illumination optical system 11 in a defined manner. The object field 12 has an arcuate or partial circular shape, two arcs parallel to the other and extending with a length y ₀ in the y direction and two straight lines having a distance x ₀ from each other in the x direction. Limited by side edges. The aspect ratio x ₀ / y ₀ is 13: 1. The inset of FIG. 1 shows a plan view of the object field 12 that is not to scale. The edge shape 12a is arcuate. In another similarly possible object field 12, the shape is rectangular.

  In FIG. 1, the projection optical system 10 is shown only partially and very schematically. The numerical aperture 13 on the object field side and the numerical aperture 14 on the image field side of the projection optical system 10 are shown. For example, between the optical components 15 and 16 shown in the projection optical system 10, which can be configured as a mirror having reflectivity with respect to the EUV illumination light 3, between these optical components 15 and 16. A further optical component of the projection optical system 10 for guiding the illumination light 3 is located.

  The projection optical system 10 focuses the object field 12 on an image field 17 in an image plane 18 on the wafer 19 which is held in the same way as the reticle 8 by a holder not shown in greater detail. The installation space requirement of the wafer holder is shown by a rectangular box 20 in FIG. The installation space requirement 20 is a rectangle having an extent that depends on the components accommodated in the installation space in the x, y, and z directions. The installation space requirement 20 originates from the center of the image field 17 and has a spread of 1 m in the x direction and the y direction, for example. In the z direction, the installation space requirement 20 emanates from the image plane 18 and likewise has a spread of, for example, 1 m. The illumination light 3 in the illumination optical system 11 and the projection optical system 10 should be guided in each case to be guided past the installation space requirement 20.

The transmission facet mirror 6 has a plurality of transmission facets 21. In the meridional section shown in FIG. 2, a line having a total of nine transmission facets 21 out of these transmission facets 21 is schematically shown, and in FIG. 2 these nine transmission facets 21 are shown from left to right. 21 ₁ to 21 ₉ . In practice, the transmission facet mirror has a substantially larger number of transmission facets 21, which will become apparent from FIGS. 3 and 4. The transmission facets 21 are grouped into a plurality of transmission facet groups 22. One of these transmission facets 22 is highlighted at the edge of FIG. 4 so that it can be more clearly recognized.

  The x / y aspect ratio of the transmission facet group 22 is at least as large as the x / y aspect ratio of the object field 12. In the illustrated configuration, the x / y aspect ratio of the transmission facet group 22 is larger than the x / y aspect ratio of the object field 12. The transmission facet group 22 has a partially circular curved group edge shape similar to the edge shape of the object field 12.

  Each of the transmission facet groups 22 is arranged by 16 columns, each having seven lines of transmission facets 21 arranged next to each other in the y direction and arranged offset in the x direction with respect to each other. The Each of the transmission facets 21 is rectangular. In particular, FIG. 4 does not show the x / y aspect ratio of the transmission facet 21 on the one hand in the x direction and on the other hand in the same y scale. Actually, an x / y aspect ratio of 1/1 can be selected for the transmission facet 21.

  Each of the transfer facets 22 provides part of the illumination light 3 for a respective complete illumination of the object field 12.

  As can be deduced from FIG. 3, there are a total of six group columns with several tens of facet groups 22 in each case. This column-by-column arrangement of the facet groups 22 is such that the illumination light beam 23, schematically illustrated by the annular distance field in FIG.

  As can be deduced from FIG. 4, these transmission facets 21 are arranged offset in the y direction with respect to each other in selected adjacent columns of transmission facets 21. This is illustrated in FIG. 4 using two columns S1 and S2. The transmission facets 21 of the transmission facets 22 which are adjacent to each other in these two columns S1, S2 are arranged offset in each case in the y-direction by about half the y-spread of the transmission facets 21. The In the case of other adjacent columns (see eg S3 and S4 in FIG. 4), the transmission facets 21 of the transmission facets 22 that are adjacent to each other in these columns are in each case relative to each other. The transmission facet 21 is offset in the y direction by almost the complete y spread. Due to this offset, a large preset radius of curvature of the transmission facets 22 can be provided, despite the size that can be handled with respect to the y-spread dimension of the individual transmission facets 21.

  The transmission facet 21 is configured such that the illumination preset facet mirror 7 has a preset edge shape 24 (see FIG. 5) and a preset assignment of the transfer facet 21 to the illumination preset facet 25 of the illumination preset facet mirror 7. Is directed to be illuminated.

An example of preset assignment of the transmission facet 21 to the illumination preset facet 25 is shown in FIG. An illumination preset facets 25 assigned to the transmission facets 21 ₁ to 21 ₉ in each case are shown in accordance with this assignment. The image field 25 is illuminated from left to right in the order of 25 ₆ , 25 ₈ , 25 ₃ , 25 ₄ , 25 ₁ , 25 ₇ , 25 ₅ , 25 ₂ , and 25 ₉ due to this assignment.

  The indices 6, 8, and 3 of the facets 21, 25 are the three illumination channels VI that illuminate the three object field points 26, 27, 28 numbered from left to right in FIG. 2 from the first illumination direction. , VIII, and III. The indices 4, 1, and 7 of the facets 21, 25 belong to three further illumination channels IV, I, VII that illuminate the three object field points 26 to 28 from the second illumination direction. The indices 5, 2, and 9 of facets 21, 25 belong to three further illumination channels V, II, IX that illuminate the three object field points 26 to 28 from the third illumination direction.

The illumination directions assigned below are equal in each case.
-Lighting channels VI, VIII, III
-Lighting channels IV, I, VII
-Lighting channels V, II, IX
Thus, the assignment of the transmission facet 21 to the illumination preset facet 25 is such that a telecentric illumination of the object field is provided.

  Illumination of the object field 12 using the transfer facet mirror 6 and the illumination preset facet mirror 7 occurs in a specular reflector manner. The principle of the specular reflector is known from US 2006/0132747 A1.

The projection optical system 10 has an object-image offset d _OIS of 930 mm. The object-image offset d _OIS is defined as the distance between the center point of the object field 12 from the penetration point where the normal on the center point of the image field 7 passes through the object plane 9. The projection exposure apparatus 1 having the projection optical system 10 has an intermediate focus-image offset D of 1280 mm. The intermediate focus-image offset D is determined as the distance from the penetration point on the image plane 18 of the normal line from the intermediate focus 5a to the center point of the image field 17. The projection exposure apparatus 1 having the projection optical system 10 has an illumination light beam-image offset E of 1250 mm. The illumination light beam-image offset E is defined as the distance of the center point of the image field 17 from the penetrating region where the illumination light beam 3 passes through the image plane 18.

On the one hand, due to a large object-image offset d _OIS and even due to a large intermediate focus-image offset D or a large illumination light beam-image offset E, the z direction between the light source 2 and the transfer facet mirror 6. In contrast, it is possible to guide the illumination light 3 traveling past the installation space 20 in parallel. This illumination light guidance ensures a small incident angle of the illumination light 3 at the facet mirrors 6 and 7. The average incident angle at the transmission facet mirror 6 is 3.5 °. The average incident angle at the illumination preset facet mirror 7 is 6.5 °.

  The incident angle is determined as half of the angle between the vicinity of each reflection of the main beam of the illumination light 3. In this case, the main beam is the beam of the illumination light 3 that connects the centers of the use reflecting surfaces of the facet mirrors 6 and 7 to each other. Due to the small angle of incidence, a correspondingly high reflection efficiency of the facet mirrors 6, 7 is brought about.

  Apart from the illumination edge shape 24 of the illumination preset facet mirror 7, FIG. 5 also illustrates the illumination intensity distribution of the illumination preset facet mirror 7 in the range of the edge shape 24. FIG. 5 shows this intensity distribution in an isointensity diagram. The outermost isointensity line reflecting the edge shape 24 corresponds to an illumination intensity of “100” in random units. Each adjacent isointensity line pointing inward indicates a position having the same intensity load, where there is an intensity increasing by the value 100 in the same unit in each case. An innermost illumination shape 29 having a generally American football shape corresponds to an illumination intensity having a value of 700. The overall edge shape 24 has a bean-shaped or kidney-shaped opening shape at the top, as already explained in principle in connection with the illumination of a specular reflector in US 2006/0132747 A1.

  The edge shape 24 depends on the desired illumination angle distribution over the object field 12 and further on the desired intensity distribution over the object field 12. The edge shape 24 becomes variable over the illumination preset facet 25 of the illumination preset facet mirror 7, in other words, depends on the respective preset value.

  The transmission facet 21 on the one hand and the illumination presetting facet 25 on the other hand can be made tiltable by means of an actuator, so that both the illumination angle distribution and the intensity distribution of the illumination light 3 over the object field 12 are preset. can do.

  The partial circular shape of the object field 12 illuminated by the illumination preset facet mirror 7 with the edge shape 24 described above also opens correspondingly. Thus, the preset illumination of the object field 12 is pre-illuminated on the other hand by means of an edge shape 24 that can be illuminated by the pre-set facet mirror 7 using a specular reflector arrangement having facet mirrors 6, 7. It is provided using the individual inclination angle of the setting facet 25.

  FIG. 6 shows a projection exposure apparatus 1 of still another configuration having an illumination optical system 30 that can be used in place of the illumination optical system 11 to illuminate the object field 12. Components corresponding to those described above with reference to FIGS. 1-5 have the same reference numerals and will not be described in detail again.

  In the illumination optical system 30, the illumination preset facet mirror 7 is provided with a central through opening 31. The illumination light 3 is guided through the through opening 31 between the light source 2 and the transmission facet mirror 6. The transmission facet 21 of the transmission facet mirror 6 not shown in detail in FIG. 6 is an illumination preset in which the illumination light 3 after the transmission facet 21 is arranged around the through-opening 31 of the illumination preset facet mirror 7. It is directed to be incident on facet 25. In this case, the illumination of the illumination preset facet mirror 7 and the tilt angle of the illumination facet 25 is such that the object field 12 is illuminated telecentric as described above in connection with FIG.

  This configuration of the illumination preset facet mirror 7 having the through opening 31 is also referred to as an occultation configuration.

  Due to the obscuration design of the illumination preset facet mirror 7, the illumination optical system 30 can be achieved with a smaller average incident angle on the facet mirrors 6, 7 compared to the illumination optical system 11. The average incident angle of the transmission facet mirror 6 is 0 °. The average incident angle on the illumination preset facet mirror 7 of the illumination optical system 30 is 6.5 °.

  The numerical aperture of the illumination light 3 in the region of the intermediate focus 5a is NA = 0.193.

  The projection exposure apparatus 1 having the illumination optical system 30 and the projection optical system 10 has an intermediate focus-image offset of 1070 mm. The projection exposure apparatus 1 having the illumination optical system 30 and the projection optical system 10 has an illumination light beam-image offset of 1030 mm.

  In the following, with reference to FIG. 7, a projection exposure apparatus 1 having still another configuration having an illumination optical system 32 that can be used in place of the illumination optical system 11 or 30 for illuminating the object field 12 will be described below. . Components corresponding to those described above with reference to FIGS. 1-6 have the same reference numerals and will not be described in detail again.

  Instead of the projection optical system 10 having the configuration shown in FIG. 1, the projection exposure apparatus 1 shown in FIG. 7 has a projection optical system 33.

  In addition to the transfer facet mirror 6 and the illumination preset facet mirror 7, the illumination optical system 32 is used to deflect the illumination light 3 between the illumination preset facet mirror 7 and the object field 12 toward the grazing incidence. The mirror 34 is further provided.

The projection optical system 33 has an object-imaging aberration compact disk read-only memory gate electrode offset d _OIS which is very small as 90 mm as compared with the projection optical system 10.

  When the illumination optical system 32 in the configuration shown in FIG. 7 is used, the object field 12 is also illuminated in a telecentric manner. This telecentric illumination is obtained by the corresponding orientation and illumination of the facet mirrors 6,7.

  The numerical aperture of the illumination light 3 in the region of the intermediate focus 5a is NA = 0.167.

  The projection exposure apparatus 1 having the illumination optical system 32 and the projection optical system 33 has an intermediate focus-image offset D of 930 mm. The projection exposure apparatus 1 having the illumination optical system 32 and the projection optical system 33 has an illumination light beam-image offset E of 1070 mm.

  8, the illumination optical system 35 that can be used in place of the illumination optical system 32 shown in FIG. 7 and the projection optical system 33 shown in FIG. 7 are used to illuminate the object field 12. A further configuration of the projection exposure apparatus 1 having the projection optical system 36 that can do this will be described below. Components corresponding to those described above with reference to FIGS. 1-7 have the same reference numerals and will not be described in detail again.

  The projection optical system 36 has an entrance pupil 37 located in the beam path of the illumination light 3 in front of the object field 12.

  The facets 21, 25 of the two facet mirrors 6, 7 are arranged to provide illumination of the object field 12 adapted to this position of the entrance pupil 37 of the optical projection system 36 relative to each other in the illumination optics 35. The In the entrance pupil 37, the cross-section shaping and divergence of the illumination light beam 3 correspond to an imaging light beam that can be guided on the incident side in the projection optical system 36.

  The entrance pupil 37 is located between the illumination preset facet mirror 7 of the illumination optical system 35 shown in FIG. 8 and the mirror 34 for grazing incidence. The ratio of the distance between the entrance pupil 37 from the object field 12 and the distance between the illumination preset facet mirror 7 from the object field 12 in the configuration shown in FIG. 8 is about 0.38, in other words, from 0.50. Is also small. Based on the configuration of the illumination optical system 35, this ratio is basically less than 1, for example, less than 0.9, less than 0.8, less than 0.7, or 0.6. Is also small. The spacing between the entrance pupil 37 and the illumination preset facet mirror 7 in the configuration described in FIG. 8 can be greater than 500 mm, in particular greater than 800 mm.

  For example, if the projection optics 36 is designed with central pupil obscuration, there is this type of entrance pupil 37 located near the object field 12. Examples of this type of projection optics can be found in the prior art cited in EP 1 905 594 A1. Therefore, due to the configuration of the illumination optical system 35 having a specular reflector formed by the facet mirrors 6, 7, the illumination preset facet mirror 7 is moved farther from the object field 12 than the entrance pupil 37. can do. This results in a small angle of incidence on the facet mirrors 6,7. An average incident angle of 4.7 ° exists on the transmission facet mirror 6. An average incident angle of 7.5 ° exists on the illumination preset facet mirror 7. The mirror 34 for grazing incidence is largely deviated from the vertical of the illumination light 3 from the collector 5 toward the transmitting facet mirror 6 through the intermediate focus 5a, despite these small average angles of incidence on the facet mirrors 6,7. Allows the direction of incidence. This ensures that the illumination light 3 is guided through the installation space 20 without the need for the projection optics 36 to have a significant object-image offset.

  The numerical aperture of the illumination light 3 in the region of the intermediate focus 5a is NA = 0.184.

  The projection exposure apparatus 1 having the illumination optical system 35 and the projection optical system 36 has an intermediate focus-image offset D of 880 mm. The projection exposure apparatus 1 having the illumination optical system 35 and the projection optical system 36 has an illumination light beam-image offset E of 910 mm.

  FIG. 9 shows an arrangement of transmission facets 38 different from the arrangement described in FIG. 4 and another grouping of these transmission facets 38 into transmission facets 39. In FIG. 9, the transmission facet group 39 is only partially shown in the x direction, and the transmission facet group 39 has an x / y aspect ratio corresponding to that of the transmission facet group 22 shown in FIG. In contrast to the transfer facet group 22, the transfer facet group 39 is rectangular in design. Each of these transfer facets 39 can be used to illuminate a rectangular object field in a design as a variation on the object field 12. A rectangular transmission facet group 39 can be used to illuminate the arcuate object field 12, in which case, for example, a grazing incidence on the corresponding field shape is ensured.

  Covering the transmission facet mirror 6 with the transmission facet 38 is similar to covering the house wall with a wooden shingles. Each of the transmission facet groups 39 has seven lines arranged above and below the transmission facet 38 positioned next to each other. The cut 40 between these lines extends horizontally, in other words, continuously in the x direction. The cut 41 between adjacent transmission facets 38 in one of the lines extends at an angle T with respect to the y direction, in other words with respect to the longitudinal direction of the arrangement of transmission facets 38. In the illustrated configuration, the angle T is about 12 °. Other cut angles T are possible, for example 5 °, 8 °, 19 °, 15 ° and 20 ° cut angles.

  The individual transmission facet 38 has an x / y aspect ratio corresponding to the x / y aspect ratio of the transmission facet group 39. The reason why it does not look so in the diagram of FIG. 9 is that the transmission facet 38 is shown very compressed in the x direction.

Installation length B of the projection optical system 10 by the configuration according to FIG. 1, in other words, the distance between the object plane 9 and the image plane 18, the object - the ratio B / d _OIS of the image offset d _OIS is about 1. 8. In guiding the illumination light 3 past the installation space 20, other ratios smaller than 20 based on the size of the installation space 20, for example, a ratio of 15, 12, 10, 8, 6, 4, or 3. B / d _OIS can be used. Smaller ratio ratios B / d _OIS are possible as well.

  The installation length B of the projection optical system described with reference to FIGS. 1, 6, and 7, in other words, the distance between the object plane 9 and the image plane 18 is 1800 mm.

  FIG. 10 shows a first configuration of the optical design for the projection optical system 42 that can be used in the projection exposure apparatus 1 in place of the projection optical system schematically described above. The path of the individual imaging beam 43 of the illumination light 3 traveling from two separate field points is shown. As one of the imaging beams 43, the main beam at the central field point, in other words, the main beam at the field point exactly located on the intersection of the diagonal lines connecting the corners of the object field 12 or the image field 17 is also shown. ing.

  In the projection optical system 42, the image plane 18 is the first field plane of the projection optical system 42 after the object plane 9. In other words, the projection optical system 42 does not have any intermediate image plane.

  The projection optical system 42 has a numerical aperture of 0.25 on the image side. The installation length B of the projection optical system 42, in other words, the distance between the object plane 9 and the image plane 18 is 1585 mm.

  In the case of a configuration of the projection optical system (not shown), which is possible in principle, where the object plane 9 is not arranged parallel to the image plane 18, the total length B is determined as the distance between the central object field points from the image plane. . For projection optics that have an odd number of mirrors, for example 7 or 9, and are also possible but not shown, the installation length is one of the mirrors and one of the field planes. Defined as the maximum interval between.

The object-image offset d _OIS of the projection optical system 42 is 1114.5 mm. In this case, the object-image offset d _OIS is defined as the distance between the vertical projection P of the central object field point on the image plane 18 and the central image point.

Therefore, the ratio between the installation length B and the object-image offset d _OIS in the projection optical system shown in FIG. 10 is about 1.42.

  The field size of the projection optical system 42 in the image plane 18 is 2 mm in the y direction and 26 mm in the x direction. In the object plane 9, the field size is 8 mm in the y direction and 108 mm in the x direction.

  The object field 12 and the image field 17 are rectangular. Basically, the field of view can be a partial ring shape with a corresponding xy aspect ratio, in other words, can exist as a curved field of view.

  The y dimension of the visual field is also called the slit height, and the x dimension is also called the slit width.

  On the object field 12, in other words, the incident angle β of the imaging beam 43 on the reflective mask or reticle is 6 °. Other angles of incidence β are possible.

  The projection optical system 42 has a total of six mirrors M1, M2, M3, M4, M5, and M6 that are numbered in the order of incidence by the illumination light 3 starting from the object field 12. The mirrors M3 and M6 are concave. The mirror M4 is convex. FIG. 10 shows only the reflecting surfaces of the mirrors M1 to M6, and does not show all the mirror bodies or related holders.

The mirrors M1 to M6 receive the illumination light 3 with an incident angle spectrum in each case. This incident angle spectrum is the difference between the minimum incident angle α _min and the maximum incident angle α _max on the respective mirrors M1 to M6. In FIG. 10, this is shown using the example of the last mirror M5 having the absolute maximum incident angle of the projection optical system 42.

The following table reflects the incident angle spectrum α _max −α _min at mirrors M1 to M6.

(table)

In the meridional section shown in FIG. 10, the minimum incident angle α _min occurs on the mirror M5 at its right hand edge and is about 14 °. In FIG. 10, the maximum incident angle α _max occurs at the left hand edge of the mirror M5 and is about 24 °. Therefore, the mirror M5 has an incident angle spectrum of 10 °. At the same time, this incident angle spectrum is the maximum incident angle difference at one of the mirrors M1 to M6. Accordingly, the incident angles on the mirrors M1 to M6 of the projection optical system 42 vary within a practically limited range where the small angle approximation (0 ° ≦ α ≦ 7 °) is very well satisfied. Thus, the mirrors M1 to M6 are each coated with a reflective coating of uniform thickness over the reflective surfaces of these mirrors.

The reflective coating, in particular the EUV reflective coating, is a known multilayer coating, in other words a stack of alternating molybdenum and silicon layers. Due to the small maximum incident angle spectrum of only 10 °, it is ensured that the reflections on all mirrors M1 to M6 of the projection optics 42 are almost constant over the mirror surfaces of these mirrors. Therefore, in the projection optical system 42, undesirable reflection paths or inappropriately large apodization on the respective mirror surfaces do not occur. Apodization is defined as a change in the intensity distribution of the illumination light 3 across the pupil. When the maximum intensity of the illumination light 3 in the pupil plane of the projection optical system 7 is represented by I _max and the minimum intensity of the illumination light 3 over the pupil plane is I _min , for example, the value of the following equation is a measure of apodization: It is.
A = (I _max −I _min ) / I _max

At least one of the mirrors M1 to M6 is configured as a reflection free-form surface having a biconical basic shape, and has a reflection surface that can be expressed by the following curved surface formula.

  In this case, x and y represent coordinates on the reflecting surface starting from a coordinate origin defined as a normal penetration point through the reflecting surface. This penetrating point may theoretically be located outside the reflective surface used.

  z represents the arrow height of the reflection free-form surface. The coefficients cvx and cvy represent the curvature of the reflection free-form surface in the xz section and the yz section. The coefficients ccx and ccy are cone parameters.

This free-form surface equation has an xy polynomial with a leading biconic term followed by a coefficient a _ji .

  The arrangement and shape of the optical surfaces of the mirrors M1 to M6 in the projection optical system 42 are specified by the following table.

  In Table 1, in the first column, the selection surfaces are defined by numbers. The second column provides the z-direction spacing from the respective next surface of each surface. The third column in Table 1 provides the y eccentricity of the local coordinate system of each surface relative to the global coordinate system.

  The last column in Table 1 allows for the assignment of defined surfaces to the components of the projection optics 42.

(Table 1)

  Table 2 shows data relating to the respective reflection free-form surfaces, M6 (surface 2), M5 (surface 3), M4 (surface 4), M3 (surface 5), M2 (surface 6), and M1 (surface 7) of the mirror. Represents. The coefficient not provided is equal to zero. Further, RDX = 1 / cvx and RDY = 1 / cvy are applied.

(Table 2)

(Table 2 continued)

  FIG. 11 shows a further configuration of the projection optical system 44 that can be used in the projection exposure apparatus 1 in place of the projection optical system 42. Components of the projection optical system 44 that correspond to those described above with reference to the projection optical system 42 have the same reference numerals and will not be described in detail again.

The projection optical system 44 has a numerical aperture of 0.25 on the image side. The installation length B of the optical projection system 44 is 1000 mm. The object-image offset d _OIS in the projection optical system 44 is 656.5 mm. Therefore, the ratio B / d _OIS is about 1.52.

  Also in the projection optical system 44, the maximum incident angle spectrum exists in the mirror M5 and is 12 ° in M5. In FIG. 11, the minimum incident angle in the mirror M5 exists at the right hand edge and is about 6 °. In FIG. 11, the maximum incident angle on the mirror M5 exists at the left hand edge and is about 18 °. Also in the projection optical system 44, the image plane 18 is the first field plane after the object plane 9.

  Also in the projection optical system 44, at least one of the mirrors M1 to M6 is configured as a biconic reflection free-form surface. The arrangement and shape of the optical surfaces of the mirrors M1 to M6 in the projection optical system 44 are specified by the following table.

  Table 3 defines the selection surface by number in the first column. The second column provides the z-direction spacing from the respective next surface of each surface. The third column in Table 3 provides the y eccentricity of the local coordinate system of each surface relative to the global coordinate system.

  The last column in Table 3 allows for the assignment of defined surfaces to the components of the projection optics 44.

(Table 3)

  Table 4 shows data regarding the respective reflection free-form surfaces, M6 (surface 2), M5 (surface 3), M4 (surface 4), M3 (surface 5), M2 (surface 6), and M1 (surface 7) of the mirror. Represents. The coefficient not provided is equal to zero.

  Further, RDX = 1 / cvx and RDY = 1 / cvy are applied.

(Table 4)

(Continued in Table 4)

(Continued in Table 4)

(Continued in Table 4)

  FIG. 12 shows a further configuration of the projection optical system 45 that can be used in the projection exposure apparatus 1 in place of the projection optical system 42. Components of the projection optical system 45 corresponding to those described above with reference to the projection optical system 42 have the same reference numerals and will not be described in detail again.

The projection optical system 45 has a numerical aperture of 0.32 on the image side. The installation length B of the optical projection system 45 is 1000 mm. The object-image offset d _OIS in the projection optical system 45 is 978 mm. Therefore, the ratio B / d _OIS is about 1.02.

  Also in the projection optical system 45, the maximum incident angle spectrum exists in the mirror M5 and is 13 ° in M5. In FIG. 12, the minimum incident angle in the mirror M5 exists at the right hand edge and is about 9 °. In FIG. 12, the maximum incident angle on the mirror M5 exists at the left hand edge and is about 22 °. Also in the projection optical system 45, the image plane 18 is the first field plane after the object plane 9.

  Also in the projection optical system 44, at least one of the mirrors M1 to M6 is configured as a biconic reflection free-form surface.

  The arrangement and shape of the optical surfaces of the mirrors M1 to M6 in the projection optical system 45 are specified by the following table.

  Table 5 defines the selection surface by number in the first column. The second column provides the z-direction spacing from the respective next surface of each surface. The third column in Table 1 provides the y eccentricity of the local coordinate system of each surface relative to the global coordinate system.

  The last column in Table 5 allows the assignment of defined surfaces to the components of the projection optics 45.

(Table 5)

  Table 6 shows data relating to the respective reflection free-form surfaces, M6 (surface 2), M5 (surface 3), M4 (surface 4), M3 (surface 5), M2 (surface 6), and M1 (surface 7) of the mirror. Represents. The coefficient not provided is equal to zero. Further, RDX = 1 / cvx and RDY = 1 / cvy are applied.

(Table 6)

(Continued in Table 6)

(Continued in Table 6)

(Continued in Table 6)

  FIG. 13 shows a further configuration of the projection optical system 46 that can be used in the projection exposure apparatus 1 instead of the projection optical system 42. Components of the projection optical system 46 corresponding to those described above with reference to the projection optical system 42 have the same reference numerals and will not be described in detail again.

The projection optical system 46 has a numerical aperture of 0.35 on the image side. The installation length B of the optical projection system 46 is 1500 mm. In the projection optical system 46, the object-image offset d _OIS is 580 mm. Therefore, the ratio B / d _OIS is about 2.59.

  In the projection optical system 46, a minimum incident angle of 0.15 ° and a maximum incident angle of 23.72 ° exist on the mirror M5. Therefore, the incident angle spectrum on the mirror M5 is 23.58 °, which is the maximum incident angle spectrum on one of the mirrors of the projection optical system 46.

  The projection optical system 46 has an intermediate image plane 47 between the mirrors M4 and M5. This intermediate image plane 47 exists near the position where the imaging beam 43 is guided past the mirror M6.

ここで、次式が成り立つ。

The reflection free-form surface of the mirrors M1 to M6 of the projection optical system 46 can be expressed mathematically by the following equation.

Here, the following equation holds.

Z is the arrow height of the free-form surface at the point x, y (x ² + y ² = r).

c is a constant corresponding to the vertex curvature of the corresponding aspherical surface. k corresponds to the conic constant of the corresponding aspheric surface. C _j is the coefficient of the monomial X ^m Y ⁿ . In general, the values of c, k, and C _j are determined based on desirable optical characteristics of the mirrors in the projection optical system 46. The monomial order m + n can be freely changed. Higher order monomials can guide the design of projection optics with better image error correction, but are more complex to calculate. m + n can use values between 3 and greater than 20.

  The free-form surface can be expressed mathematically by, for example, a Zernike polynomial described in the manual of the optical design program “CODE V (registered trademark)”. Alternatively, a free-form surface can be represented using a two-dimensional spline surface. Examples of two-dimensional spline surfaces are Bezier surfaces or non-uniform rational basis splines (NURBS). A two-dimensional spline surface can be represented, for example, by a point network in the xy plane and its associated z value, or by these points and the gradients associated with these points. Based on each type of spline surface, a complete surface can be obtained, for example, by interpolation between halftone dots using a polynomial or function that has unique properties with respect to continuity and differentiability. This example is an analytic function.

The optical design data of the reflecting surfaces of the mirrors M1 to M6 of the projection optical system 46 can be estimated from the following table. The first of these tables corresponds to the reciprocal value (radius) of the respective vertex curvature and the z-spacing of adjacent elements in the beam path starting from the object plane with respect to the optical surface and aperture stop of the optical component. The interval value (thickness) is provided. The second table provides the coefficient C _j of the monomial X ^m Y ⁿ in the free-form surface equation provided above for the mirrors M1 to M6. In this case, Nradius is a normalization coefficient. According to the second table, the amount of rotation (X rotation) of each mirror decentered (Y eccentricity) starting from the mirror reference design is also shown in units of mm. This amount corresponds to the parallel displacement and inclination in the above-described free-form surface design method. In this case, the displacement occurs in the y direction and the tilt is about the x axis. In this case, the rotation angle is provided in degrees.

(table)

(table)

(Table continued)

(table)

In FIG. 13, reference numeral 48 represents the main beam belonging to the central object field point. In FIG. 13, one normal to the object plane 9 is denoted by 49, and this normal extends through the central object field point. Therefore, the main beam 48 and the normal line 49 intersect in the object plane 9. The spacing of the main beam 48 from the normal 49 increases monotonically along the traveling beam path of the main beam 48 between the object plane 9 and the image plane 18. When the main beam 48 passes through the image plane 18, in other words, at the central image field point, this spacing is equal to the object-image offset d _OIS . A monotonic increase in the spacing of the main beam 48 from the normal 49 in the beam path between the object plane 9 and the image plane 18 indicates that this spacing does not decrease anywhere along the path of the beam path. means. In the projection optical system 46, this interval is constantly increased until the main beam 48 is incident on the last mirror M6. This spacing remains constant between the point of incidence of the main beam 48 on the mirror M6 and the image plane 18.

  In order to produce a microstructured component, in particular a highly integrated semiconductor component, for example a memory chip, using the projection exposure apparatus 1, a reticle 8 and a wafer 19 are first prepared. Next, the structure on the reticle 8 is projected onto the photosensitive layer on the wafer 19 by the projection optical system of the projection exposure apparatus 1. Thereafter, by developing the photosensitive layer, a microstructure is created on the wafer 19 from which microstructured or nanostructured components are generated.

3 Illumination light 7 Illumination preset facet mirror 12 Object field of view 25 Illumination preset facet

Claims (6)

Comprising illumination optics (35) for microlithography for illuminating the object field (12);
A first transfer optical system (4) for guiding illumination light (3) traveling from a light source (2);
An illumination preset facet mirror (7) disposed downstream of the first transfer optics (4) and having a plurality of illumination preset facets (25),
An edge shape (24) of the illumination preset facet mirror (7) that can be illuminated;
The angle of inclination of the illumination presetting facet (25);
An illumination preset facet mirror (7) for generating preset illumination of the object field (12) using
A projection optical system (36) for imaging the object field (12) into an image field (17);
An optical system,
An entrance pupil (37) of the projection optics (36) is arranged between the illumination preset facet mirror (7) and the object field (12) or after the object field (12);
The arrangement of the first transfer optics (4) and the illumination preset facet mirror (7) provides illumination of the object field (12) adapted to the entrance pupil of the projection optics (36) Exist in the way,
An optical system characterized by that. The distance of the entrance pupil (37) from the object field (12);
The distance of the object field (12) from the illumination preset facet mirror (7);
The optical system of claim 1, wherein the ratio is less than 0.9. Comprising illumination optics (11; 30) for microlithography for illuminating the object field (12);
A first transfer optical system (4) for guiding illumination light (3) traveling from a light source (2);
An illumination preset facet mirror (7) disposed downstream of the first transfer optics (4) and having a plurality of illumination preset facets (25),
An edge shape (24) of the illumination preset facet mirror (7) that can be illuminated;
The angle of inclination of the illumination presetting facet (25);
An illumination preset facet mirror (7) for generating preset illumination of the object field (12) using
A projection optical system (36) for imaging the object field (12) into an image field (17);
An optical system,
The ratio of the installation length (B) of the projection optical system (10) to the object-image offset (d _OIS ) is less than 20;
An optical system characterized by that. Comprising illumination optics (11; 30) for microlithography for illuminating the object field (12);
A first transfer optical system (4) for guiding illumination light (3) traveling from a light source (2);
An illumination preset facet mirror (7) disposed downstream of the first transfer optics (4) and having a plurality of illumination preset facets (25),
An edge shape (24) of the illumination preset facet mirror (7) that can be illuminated;
The angle of inclination of the illumination presetting facet (25);
An illumination preset facet mirror (7) for generating preset illumination of the object field (12) using
A projection optical system (36) for imaging the object field (12) to an image field (17); and the illumination optical system (11; 30) between the light source (2) and the object field (12). 32; 35) have an intermediate focus (5a);
An optical system,
The ratio of the installation length (B) of the projection optical system (10; 33; 36) to the intermediate focus-image offset (D) is less than 5;
An optical system characterized by that. The optical system according to any one of claims 1 to 4 , comprising:
With a light source (12),
A projection exposure apparatus. A method for producing a microstructured component, comprising:
Preparing the reticle (8);
Providing a wafer (19) with a coating sensitive to illumination light (3);
Projecting at least a portion of the reticle (8) onto the wafer (19) using the projection exposure apparatus (1) according to claim 5 ;
Developing the photosensitive layer exposed by the illumination light (3) on the wafer (19);
A method characterized by comprising:

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