JP5232927B2 - Method for assigning a pupil facet of a pupil facet mirror of an illumination optical unit of a projection exposure apparatus to a field facet of a field facet mirror of the illumination optical unit - Google Patents

Description

  The present invention is for the definition of an illumination channel for a partial beam of illumination light traveling from a light source and reflected towards a field facet and an object field illuminated by an illumination optical unit at a pupil facet assigned using the method. The present invention also relates to a method of assigning pupil facets of a pupil facet mirror of an illumination optical unit of a projection exposure apparatus to a field facet of a field facet mirror of the illumination optical unit.

  A projection exposure apparatus including an illumination optical unit including a field facet mirror and a pupil facet mirror is disclosed in WO 2009/132 756 A1, DE 10 2006 059 024 A1, DE 10 2006 036 064 A1, WO 2010/037 453 A1, DE 10 2008. 042 876 A, DE 10 2008 001 511 A1, DE 10 2008 002 749 A1, and DE 10 2009 045 694 A1.

  In many cases, the field facet mirror and the pupil facet mirror of the illumination optical unit of the projection exposure apparatus have several hundred facets in each case. In the case of an illumination optical unit with N field facets and N pupil facets, in theory the number of candidates for the assignment of field facets to pupil facets is N! It changes with. When the number of facets of the facet mirror increases, the number of allocation candidates increases rapidly.

WO 2009/132 756 A1 DE 10 2006 059 024 A1 DE 10 2006 036 064 A1 WO 2010/037 453 A1 DE 10 2008 042 876 A DE 10 2008 001 511 A1 DE 10 2008 002 749 A1 DE 10 2009 045 694 A1 US 6 859 515 B2 EP 1 225 481 A2 US 6,658,084 B2 US 7.196,841 B2 DE 103 29 141 A1

  The object of the present invention is given at the beginning to ensure a reproducible selection of the assignment of pupil facets to field facets and thus a reproducible prejudgment of the illumination channel of the illumination optical unit based on the illumination parameters to be optimized It is to provide a method of assigning types.

  According to the invention, this object is achieved with a method comprising the steps specified in claim 1.

  In accordance with the present invention, it has been recognized that what is important is to specify an appropriate evaluation function that incorporates the effect of the properties of the beam guided through the individual illumination channels on the illumination parameters considered. This assignment method allows the assignment according to identified and optimized illumination parameters of all illumination channels of the illumination optical unit with field facets and pupil facets. The method can be flexibly adapted to each lighting task. This adaptation can be done by selecting the illumination parameters to be considered, selecting a pre-determined evaluation function, for example by adapting the evaluation function by inserting weighting terms and pre-defining the evaluation target range. it can.

  The allocation method as claimed in claim 2 further takes into account the stability of this evaluation variable with respect to the evaluated illumination channel, based on a predefined disturbance. Such an allocation method allows allocation with optimized stability of all illumination channels of an illumination optical unit having field facets and pupil facets. Furthermore, this adaptation is performed by selecting and adapting the respective disturbance variables used and predefining the disturbance variable fluctuation range.

  The evaluation variable can be pre-calculated for at least selected lighting channels of possible lighting channels based on a predefined evaluation function prior to the actual selection of lighting channels. In this way, the pre-selection of possible target configurations for the illumination channel can be performed with low computational complexity. Inappropriate configurations from the beginning can be ruled out especially by using preselection. Illustratively, symmetry considerations can be incorporated into the pre-selection, as an example, so that configurations having specific symmetric properties are first examined based on the evaluation function during the assignment method. Such a configuration can be used in particular as a starting configuration for disturbance variable fluctuations.

  The evaluation function according to claim 3 makes it possible in particular to predefine channel assignments with a predefined intensity distribution over the object field.

  The step of predefining the evaluation function according to claim 4 can take into account, in particular, the occlusion by adjacent field facets that may arise as a result of different facet tilt angles determined by the assignment.

  The evaluation function according to claim 5 has an effect that an undesirable reflectance reduction incident angle of the illumination light on the facet is avoided.

  The facet switching process can be incorporated into the evaluation function only if facets are provided that can be switched between different illumination positions.

  The evaluation function according to claim 6 can be used to record the systematic influence of the reflectivity of the optical components arranged downstream of the pupil facet mirror of the illumination optical unit.

  The shape of the light source image incorporated in the case of the evaluation function according to claim 7 is the light source image on the pupil facet, ie the size or shape of the image of the light source, the position of the light source image on the pupil facet, or otherwise It can be the energy centroid position of the light source image on the pupil facet.

  The imaging variables incorporated in the evaluation function according to claims 8 and 9 provide the possibility of predefining channel assignments that are optimized taking into account the respective imaging variables. Possible imaging aberrations incorporated into the evaluation function can be distortion, image rotation, image occlusion, faceted image deviation from the object plane (defocus), or else the depth of focus of the imaging.

  The symmetry variable evaluation function according to claim 10 is such that upon pre-selection of the illumination channel considered and the illumination channel complementary thereto, the superposition of object field illumination by both illumination channels falls within the evaluation target range. If there are additional complementary lighting channels, the preselection can be predefined to include lighting channels that deviate from the evaluation target range itself. Examples of such symmetrical or complementary field profiles are, for example, as a result of a facet assignment study on a point-symmetric array of illumination channel pairs having the same intensity and complementary field profile, or relative to each other about the pupil center This is especially true when investigating the presence of pairs of illumination channels that are rotated by 90 degrees in polar coordinates and have complementary profiles.

  The stray light variable according to claim 11 can be expressed, for example, as a neighborhood relationship between field facets on the one hand and a neighborhood relationship between pupil facets on the other hand. In this case, illumination channels that are formed by both adjacent field facets and adjacent pupil facets and that are then threatened by stray light profiles due to adjacent illumination channel profiles can thus be avoided.

  The evaluation functions according to claims 12 and 13 can be fully adapted to the corresponding lighting task.

  Exemplary embodiments of the invention are described in more detail below with reference to the drawings.

1 schematically shows a projection exposure apparatus for microlithography in a meridional section with respect to an illumination optical unit; FIG. It is a top view of the facet arrangement of the field facet mirror of the illumination optical unit of the projection exposure apparatus shown in FIG. It is a top view of the facet arrangement of the pupil facet mirror of the illumination optical unit of the projection exposure apparatus shown in FIG. FIG. 4 is a view similar to FIG. 2 showing a facet arrangement of yet another embodiment of a field facet mirror. FIG. 4 is a view similar to FIG. 2 showing a facet arrangement of yet another embodiment of a field facet mirror. Schematic of a method for assigning pupil facets of a pupil facet mirror of an illumination optical unit of a projection exposure apparatus for EUV lithography to a field facet of a field facet mirror of the illumination optical unit for defining an illumination channel for a partial beam of illumination light It is a flowchart. FIG. 3 is a perspective view of two adjacent field facets tilted with respect to each other directly joined to each other across the longitudinal facet sides of the field facet mirror in the embodiment described in FIG. 2. FIG. 8 shows the two field facets according to FIG. 7 arranged so that a gap remains between the longitudinal facet sides. FIG. 2 shows very schematically a field facet mirror on the left and a pupil facet mirror on the right of an illumination optical unit comprising two pupil facets and a field facet respectively assigned to each other for the definition of an illumination channel. FIG. 6 is a view similar to FIG. 1 showing still another embodiment of the illumination optical unit of the projection exposure apparatus. 1 is a side view corresponding to FIG. 1 showing the beam guidance between the intermediate focus and the object field along the illumination channel including exactly one field facet and exactly one pupil facet of the illumination optical unit according to FIG. FIG. 3 is not a schematic and accurate scale. FIG. 12 is a view from the object field location XII of the pupil facet of FIG. 11 where an EUV partial beam is applied through the illumination channel. FIG. 13 is a view from the object field location XIII of the pupil facet of FIG. 11 where an EUV partial beam is applied through the illumination channel. FIG. 14 is a view from the object field location XIV of the pupil facet of FIG. 11 where an EUV partial beam is applied through the illumination channel.

  The projection exposure apparatus 1 for microlithography functions to produce fine or nanostructured electronic semiconductor components. The light source 2 is used for illumination and emits EUV radiation in the wavelength range between 5 nm and 30 nm, for example. The light source 2 can be a GDPP (gas discharge generated plasma) light source or an LLP (laser generated plasma) light source. A synchrotron-based radiation source can be used for the light source 2. A person skilled in the art can find information on such light sources, for example in US 6 859 515 B2. In the projection exposure apparatus 1, EUV illumination light or illumination radiation 3 is used for illumination and imaging. The EUV illumination light 3 first passes downstream of the light source 2 through a collector 4 which can be a nested collector having a multi-shell configuration known in the prior art or alternatively an ellipsoidal collector. Corresponding collectors are known from EP 1 225 481 A2. Downstream of the collector 4, the EUV illumination light 3 first passes through an intermediate focal plane 5 that can be used to separate the EUV illumination light 3 from unwanted radiation or particle portions. After passing through the intermediate focal plane 5, the EUV illumination light 3 first enters the field facet mirror 6.

  In order to facilitate the expression of the positional relationship, an orthogonal wide area xyz coordinate system is shown in the drawing in each case. In FIG. 1, the x-axis extends so as to emerge from the drawing perpendicular to the drawing. The y-axis extends toward the right in FIG. The z-axis extends upward in FIG.

  In the following figures, orthogonal local xyz or xy coordinate systems are similarly used in each case in order to facilitate the description of the positional relationships in the individual optical components of the projection exposure apparatus 1. Each local xy coordinate is stretched to the respective main array plane of the optical component, eg, the reflection plane, unless otherwise described. The x-axis of the wide area xyz coordinate system and the x-axis of the local xyz or xy coordinate system extend parallel to each other. Each y-axis of the local xyz or xy coordinate system is at an angle corresponding to the tilt angle about the x-axis of each optical component with respect to the y-axis of the global xyz coordinate system.

  FIG. 2 exemplarily shows the facet arrangement of the field facet 7 of the field facet mirror 6. The field facet 7 is rectangular and has the same x / y aspect ratio in each case. The x / y aspect ratio can be, for example, 12/5, 25/4, or 104/8.

  The field facets 7 predefine the reflective surface of the field facet mirror 6 and are grouped into four columns, each consisting of six to eight field facet groups 8a, 8b. Each of the field facet groups 8 a has seven field facets 7. Each of the two additional peripheral field facet groups 8 b in the two central field facet rows has four field facets 7. Between the two central facet columns and between the third facet row and the fourth facet row, the facet arrangement of the field facet mirror 6 has a gap 9 where the field facet mirror 6 is shielded by the holding spokes of the collector 4. Have.

  After reflection at the field facet mirror 6, the EUV illumination light 3 divided into beam bundles or partial beams assigned to the individual field facets 7 is incident on the pupil facet mirror 10.

  The field facet 7 of the field facet mirror 6 can be tilted between a plurality of illumination tilt positions, whereby the beam path of the illumination light 3 reflected by the respective field facet 7 can be changed with respect to its direction. Therefore, it is possible to change the incident point of the illumination light 3 reflected on the pupil facet mirror 10. Corresponding field facets that can be displaced between different illumination tilt positions are known from US 6,658,084 B2 and US 7.196,841 B2.

  FIG. 3 shows an exemplary facet arrangement of the round pupil facet 11 of the pupil facet mirror 10. The pupil facet 11 is arranged around the center in a plurality of facet rings, one of which is inside of another. Each partial beam of EUV illumination light 3 reflected by one of the field facets 7 has a respective facet pair that receives an incident including one of the field facets 7 and one of the pupil facets 11. , At least one pupil facet 11 is assigned to predefine the object field illumination channel for the associated partial beam of EUV illumination light 3. The assignment of the pupil facets 11 to the field facets 7 by channel is performed in a manner depending on the desired illumination by the projection exposure apparatus 1.

  The field facet mirror 6 has several hundred field facets 7, for example 300 field facets 7. The pupil facet mirror 10 has as many pupil facets 11 as the number of field facets 7.

  Using a downstream transfer optical unit 15 composed of a pupil facet mirror 10 (see FIG. 1) and three EUV mirrors 12, 13, 14, the field facet 7 is placed on the object plane 16 of the projection exposure apparatus 1. Imaged. The EUV mirror 14 is embodied as a mirror for grazing incidence (a grazing incidence mirror). In the object plane 16, a reticle 17 is arranged that illuminates an illumination area in the form of an illumination field that is downstream and coincides with the object field 18 of the projection optical unit 19 of the projection exposure apparatus 1 with the EUV illumination light 3. The object field illumination channel is superimposed in the object field 18. The EUV illumination light 3 is reflected from the reticle 17.

  The projection optical unit 19 forms an object field 18 on the object plane 16 on an image field 20 on the image plane 21. Within this image plane 21 is disposed a wafer 22 carrying a photosensitive layer that is exposed using the projection exposure apparatus 1 during projection exposure. During projection exposure, both reticle 17 and wafer 22 are scanned synchronously in the y direction. The projection exposure apparatus 1 is embodied as a scanner. Hereinafter, the scanning direction is also referred to as an object displacement direction.

  The field facet mirror 6, the pupil facet mirror 10, and the mirrors 12 to 14 of the transfer optical unit 15 are part of the illumination optical unit 23 of the projection exposure apparatus 1. Together with the projection optical unit 19, the illumination optical unit 23 forms an illumination system of the projection exposure apparatus 1.

  The field facet mirror 6 constitutes a first facet mirror of the illumination optical unit 23. The field facet 7 constitutes a first facet of the illumination optical unit 23.

  The pupil facet mirror 10 constitutes a second facet mirror of the illumination optical unit 23. The pupil facet 11 constitutes a second facet of the illumination optical unit 23.

  FIG. 4 shows a further embodiment of the field facet mirror 6. Components corresponding to those described above with reference to the field facet mirror 6 described in FIG. 2 carry the same reference numerals, and only if the components are different from those of the field facet mirror 6 described in FIG. Give an explanation. The field facet mirror 6 described in FIG. 4 has a field facet arrangement including a curved field facet 7. These field facets 7 are arranged in a total of five rows, each having a plurality of field facet groups 8. The field facet arrangement is inscribed in the circular boundary of the carrier plate 24 of the field facet mirror 6.

  The field facets 7 of the embodiment described in FIG. 4 all have the same area, and in the embodiment described in FIG. 2 the width in the x direction and the height in the y direction corresponding to the x / y aspect ratio of the field facet 7. Have the same ratio.

  FIG. 5 shows a further embodiment of the field facet mirror 6. Components corresponding to those described above with reference to the field facet mirror 6 described in FIGS. 2 and 4 carry the same reference numerals, and the components are the same as those in the field facet mirror 6 described in FIGS. Will be explained only if they are different. The field facet mirror 6 described in FIG. 5 also has a field facet arrangement with a curved field facet 7. The field facets 7 are arranged in a total of five rows, each having a plurality of field facet groups 8a, 8b, 8c. This field facet array is inscribed in the circular boundary of the carrier plate 24 of the field facet mirror 6 described in FIG. 5 in a manner similar to the array of field facets 7 described in FIG. Here again, the field facet mirror 6 according to FIG. 5 has a central gap 9 extending parallel to the x-axis, in which the field facet mirror 6 according to FIG. 5 is shielded by the holding spokes of the collector 4. Is done. Furthermore, the boundary between the two illumination sections in which the field facet 7 of the field facet mirror 6 described in FIG. 5 is located is within the region of the central facet row with the field facet group 8 c towards the center of the field facet mirror 6. Is defined by a further circular shielding surface 25 in which the field facet mirror 6 is shielded at the center. Overall, the field facet 7 of the field facet mirror 6 described in FIG. 5 is in two generally circular segment-shaped illumination sections, which are predefined by the boundary of the carrier plate 24 and secondly by the boundary of the gap 9. Stuffed into.

  Referring to FIG. 6, each pupil facet 11 of the pupil facet mirror 10 of the illumination optical unit 23 of the projection exposure apparatus 1 is changed to the field of view of the illumination optical unit 23 in order to define each illumination channel for the partial beam of the illumination light 3. A description of how to assign to each one of the field facets of the facet mirror 6 is provided below. A partial beam of illumination light 3 traveling from the light source 2 and guided through the illumination channel is then applied to the assigned field facet 7 of the field facet mirror 6 and then to the pupil of the pupil facet mirror 10 assigned using this method. The light is reflected toward the object field 18 illuminated by the illumination optical unit 23 at the facet 11.

  In the context of the assignment method, initially at least one illumination parameter that can characterize the illumination of the object field 18 is identified in the identification step 26. Illustratively, illumination uniformity, telecentricity, or ellipticity can be used as illumination parameters. Definitions of these illumination parameters of uniformity, telecentricity and ellipticity are found, for example, in WO 2009/132 756 A1 and DE 10 2006 059 024 A1. Alternatively, the structural resolution that can be achieved by illumination during imaging of the illuminated object field 18 into the image field can be used as an illumination parameter. Instead of telecentricity or ellipticity, for example, the line width change of the imaging structure over the image field can be used as the illumination parameter.

  The imaging structure variable can be a critical dimension (CD). The object structure image variable is the magnitude of the distance value in the image plane of a general reference structure that is imaged in the image field using the projection optical unit. An example of an object structure image variable is the so-called “pitch”, ie the distance between two adjacent lines in the image field. Structural image variable change (ΔCD) is a line where the intensity of the imaging light exceeds the resist threshold intensity required to develop the photosensitive layer on the substrate or wafer when a linear object structure is imaged. The width can be changed. This line width, i.e. the imaging structure variable, is independent of the distance between two adjacent lines over the field height, i.e. independent of the pitch of the object structure as an example of yet another object structure variable. May change.

  The identification step 26 initially includes obtaining the nature of the requirements made from the illumination of the object field 18 for each exposure task. Based on this exposure task, a particularly uniform intensity distribution across the object field 18 may be desirable. In this case, uniformity is the illumination parameter identified in the identification step 26. Alternatively, for example, it may be necessary to set a predefined telecentric value in order to be able to control the overlay requirements during multiple exposures of the wafer 22 using the projection exposure apparatus 1. . In this case, telecentricity is identified as an illumination parameter in the identification step 26. The same applies correspondingly when an illumination angle distribution with a certain weight over the object field 18 is desired. In this case, the ellipticity is selected as an illumination parameter characterizing the illumination of the object field 18 in the identification step 26. Alternatively or additionally, the line width that can be imaged, the depth of focus, and / or the defocus of imaging into the object plane 16 of the field facet 7 can be used as illumination parameters.

  After the identifying step 26, a lighting channel dependent lighting function is pre-defined in the predefining step 27 for evaluating possible lighting channels based on the identified lighting parameters. Accordingly, the result of the evaluation function predefined in step 27 correlates with the illumination parameters identified in step 26. Thus, the evaluation function is a possible combination of one of the field facets 7 and one of the pupil facets 11 and is possible for guiding the partial beam of the illumination light 3 through the illumination channel defined thereby. Allows evaluation of combinations.

The following features of each evaluated illumination channel can be incorporated into the predefined evaluation function in the predefined stage 27.
-Non-uniform illumination in the case of a field facet 7 with illumination light 3; In this case, the deviation of the illumination intensity of the field facet 7 by the illumination light 3 from the uniform illumination intensity in each considered illumination channel can be incorporated into the evaluation function.
O shielding of field facets 7, in particular occlusion of a part of one of field facets 7 by adjacent field facets, especially when two adjacent field facets 7 are tilted to significantly different tilt positions (see FIG. 7 and the following description in connection with FIG. 8).
The reflectivity of the facets 7, 11 to the illumination light 3 depending on the angle of incidence of the illumination light 3 on the facets 7, 11 of the illumination channel to be evaluated. Thus, the incident angle of the respective partial beam of the illumination light 3 on the facets 7, 11 of the illumination channel to be considered can be incorporated into the evaluation function.
The reflectivity of the transfer optics unit 15 placed downstream of the facet mirrors 6, 10 depending on the illumination channel to be evaluated.
-Spot image or local geometric pupil aberration of field facets. In this case, the term spot image refers to the shape and intensity distribution of the partial beam guided just on the pupil facet along exactly one illumination channel, as will be explained further below.
The illumination channel dependent imaging scale, i.e. the dimension of the field facet 7 of the first evaluated illumination channel which is first parallel to the x direction and secondly parallel to the y direction and secondly the object plane; The ratio of this field facet 7 image size within 16.
In the object plane 16 as a result of, for example, grazing incidence on the mirror 14 and the effect caused by the deviation between the position of the pupil facet mirror 10 and the entrance pupil or entrance pupil image of the projection optical unit 19 Parameterization of the illumination channel dependent distortion of the imaging of the field facet 7 to the front.
-Illumination channel dependent changes in structural image variables, i.e. changes in imaging linewidth, for example. This line width change can be assessed differently for different profiles of the imaged line. Illustratively, the size of the difference between the imaging line widths of horizontally and vertically extending structural lines that are at the same distance from each other on the object side can be recorded. Alternatively or additionally, a structural variable change of the object line to be imaged diagonally, ie a change in line width, for example, can be considered as an evaluation function or a part thereof.
-Effects dependent on the illumination channel of the light source 2, e.g. due to varying shielding, due to incomplete imaging of the field facet 7 on the object field 18, or due to the varying radial center of gravity of the light source 2 depending on the radiation direction of the light source 2. The resulting illumination channel dependent non-uniformity of the radiation of the light source 2, for example.

  In addition to imaging aberrations introduced by the imaging optics unit, incomplete imaging of the field facet 7 on the object field 18 may result from the light source 2 not being a point light source. It therefore always results in an image of the field facet 7 which is ultimately blurred at the edges in the object plane 16. The quality of this imaging depends on the assignment of field facets 7 and pupil facets 11 to the respective illumination channels. Certain assignments result in better quality imaging than other assignments. Furthermore, in the case of light sources that are not point or spherical light sources, different field facets among these field facets 7 see the light source 2 in different shapes.

  The parameterizable aberration contribution using the evaluation function as a result of the distortion effect of the transfer optical unit between the field facet mirror and the object plane is illustratively described in WO 2010/037 453 A1. Similarly, pupil effects that can be illumination channel dependent and can be incorporated into the evaluation function are described, for example, in DE 10 2006 059 024 A.

  In the context of the assignment method, the evaluation target range of the evaluation variable representing the result of the evaluation function is predefined in a further predefined step 28. Accordingly, the pairing (field facet, pupil facet) associated with the illumination channel to be evaluated is incorporated into the evaluation function, and the evaluation variable is identified using the evaluation function accordingly. The predefining step 28 includes specifying the target range of this evaluation variable that should be achieved in order for the configuration of the lighting channel to be evaluated to be included in the further selection.

  In the context of the assignment method, then, in an optional calculation step 29, for at least selected lighting channels of possible lighting channels, evaluation variables are calculated by insertion into the evaluation function.

  Similarly, in the optional preselection step 30, pairing of the field facet 7 to the illumination channel with the evaluation variable calculated in step 29, ie the pupil facet 11, achieving the predefined evaluation target range in step 28. Is pre-selected.

  The assigning method identification step 31 comprises identifying at least one disturbance variable affecting the illumination of the object field 18 by the illumination optical unit or by an illumination system including the illumination optical unit and the light source.

  As an example, the position change of the light source 2 in the x direction, the y direction, or the z direction can be selected as a disturbance variable. The change of the light source variable of the light source 2 can be used as a disturbance variable. For example, a change in the type of the light source 2 between the LPP light source and the GDPP light source can be used as a disturbance variable. Furthermore, for example, a simulated lifetime effect on the time of use of the reflective layer of the component that provides the illumination light 3 can be used as a disturbance variable. The stray light increase resulting from the simulated aging of the illumination optical unit 23 can be used as a disturbance variable. Furthermore, the application of illumination light 3 not used for illumination to the pupil facet 11 of the illumination channel to be evaluated and thus the additional heating of the pupil facet 11 can be used as a disturbance variable.

  After the disturbance variable identification stage 31, the dependence of the evaluation function on the identified at least one disturbance variable is identified in a further identification stage 32.

  Next, the changing step 33 changes the disturbance variable identified for the preselected illumination channel in a predefined disturbance variable variation range, and the variation of the evaluation variable according to the evaluation function and the identification step 32. Computing with the dependencies identified in.

  The selection step 34 of completing the assignment method includes selecting an illumination channel having an evaluation variable that has undergone a variation that remains in the evaluation target range in the overall disturbance variable variation range.

  The assignment method including steps 27 to 34 is repeated until a predefined number of field facets 7 of the field facet mirror 6 are assigned each still free pupil facet 11 of the pupil facet mirror 10. The result of the assignment method is that these assignments of the field facets 7 to the other pupil facets 11 in each case if all assignments satisfy the evaluation criteria in the assignment method stages 27 to 34. be able to.

  Then, based on the result of the selection step 34, the tilted illumination position of the field facet 7 is adjusted, and the pupil facet 11 assigned through the selected illumination channel is adjusted accordingly. The field facet mirror 6 and the pupil facet mirror 10 can be equipped as having rigid components, ie facets 7, 11 that cannot be tilted by the actuator means, taking into account their respective tilted illumination positions. Alternatively, as described above at the beginning of the figure description, fine adjustment of the selected illumination channel and / or between different illumination channels possible in the range of selection of the selection stage 34 and thus of the field facet-pupil facet assignment. The facet mirrors 6, 10 can be designed to be tiltable by the actuator means so that variations between them are possible, in particular by predefining different illumination geometries.

  Selection of lighting channels using the assignment method can utilize a “simulated annealing” algorithm. In this case, the algorithm starts with a specific illumination channel, changes the disturbance variable in the change phase 33 and calculates the variation of the evaluation variable accordingly. Thereafter, further illumination channels that are hardly different from the illumination channels originally used for the guidance of the partial beam of the illumination light 3 are evaluated, for example, by replacing the pupil facets 11 to which the two field facets 7 are assigned. You can choose towards. Next, the modification step 33 is performed again for all of the lighting channels that are subsequently provided. If the evaluation criteria of the assignment method are fulfilled, the changes made, ie the exchange of pupil facets assigned to two specific field facets of the field facets 7 are accepted. Based on such a change stage, the evaluation variable is optimized in consideration of the sequential application of the fluctuation of the disturbance variable by the change stage 33.

  In the following, the assignment of the individual field facets 7 to the individual pupil facets 11 through the corresponding illumination channel at the start of carrying out the assignment method will also be referred to as the start assignment or otherwise the initial assignment.

  Symmetry considerations can have an impact when selecting the starting assignment of all lighting channels at the start of the assignment method or after predefining the change phase. Illustratively, the starting assignment can consider a pair of field facets 7 having field facet incident intensity profiles that are complementary to each other by the light source 2. Such a pair of field facets 7 can be incident on adjacent pupil facets of the pupil facets 11. In this context, the complementary field profiles compensate for each other when the field facet images are superimposed in the object field 18 so that the field dependence across the object field 18 can be minimized.

  In this case, the illumination channel assignment change in the process of searching for the optimum value of the evaluation variable is only carried out so that the corresponding pairing of facets with complementary field profiles is maintained. Changing the disturbance variable ensures, for example, that the desired complementarity is maintained even in the case of changing the light source 2.

  The starting assignment of the illumination channel that is optimized using the assignment method can proceed from a point-symmetric arrangement of illumination channels, so that the assigned illumination channel is on the one hand the carrier plate of the field facet mirror 6 and on the other hand the pupil. They are merged together by rotation of a predefined angle φ around the center of the carrier plate of the facet mirror 10. Again, the allocation change is performed so that symmetry is maintained. Thus, point symmetry constitutes a parameter that is incorporated into the evaluation function.

  The starting assignment, for example, rotates by 90 degrees in polar coordinates of the field facet with the same incident intensity profile by the light source 2 and with assigned pupil facets 11 arranged rotated by 90 degrees in polar coordinates relative to each other in the pupil. Position. In each case, two of such field facets can be present in the starting assignment, and the assigned pupil facets are arranged rotated 90 degrees in polar coordinates relative to each other in the pupil. Another assignment scheme that can be used as a starting assignment and that assigns four pupil facets arranged at 90 degrees in polar coordinates relative to each other to field facets having the same intensity profile is described in DE 10 2006 036 064 A1. Explained.

  The start assignment can take into account the drawing of this figure of the illumination optical unit 23 described in FIG. 1, ie the mirror symmetry with respect to the meridian plane. For example, in another design of the illumination optical unit 23 that is also at least approximately mirror-symmetric with respect to another plane in the design of the illumination optical unit according to DE 103 29 141 A1, this corresponding further mirror symmetry is This can be taken into account when predefining initial channel assignments.

  Yet another example of pairwise assignment that can be selected for the initial assignment of lighting channels prior to the start of the assignment method is described, for example, in WO 2009/132 756 A1.

  Alternatively, the assignment of the field facets 7 to the pupil facets 11 at the start of the assignment method is such that adjacent field facets 7 in the field facets 7 are not adjacent pupil facets 11, i.e. a predefined number of further separations. The pupil facets 11 separated from each other by the pupil facets 11 can be configured to illuminate. Such a starting assignment is brought about when the illumination channels have a generally close profile whereby the illumination light guided along one illumination channel is improperly scattered in the other illumination channel. Minimize possible stray light. Therefore, the stray light criterion can also be a criterion incorporated in the evaluation function.

  For example, when changing channel assignments in the context of a simulated annealing optimization method, yet another criterion associated with selecting an appropriate initial assignment of lighting channels or pre-defining a scheme is the individual facets 7, 11 Minimization of the switching angle in the case of the use of individual facets 7, 11 which can be displaced between at least two illumination tilt positions, or by minimizing the angle of incidence above.

  When predefining the initial assignment of the illumination channels at the start of the assignment method, the field facet 7 adjacent to the edge of the section in which the field facet 7 is arranged, for example the edge of the carrier plate 24, can be taken into account. In these peripheral field facets 7, the selection of the assigned pupil facets 11 permitted in the start assignment can be limited, for example, by prior judgment of a list of allowed pupil facets of the pupil facets 11. This selection can be made so that the imaging of the peripheral field facet 7 by the pupil facet 11 and the downstream transfer optics unit 15 does not suffer from undesired rotations or displacements, in particular it does not suffer from undesirable imaging aberrations. it can.

  Proper design of the arrangement of the field facets 7 on the field facet mirror 6 makes it possible to change, in particular to reduce, the influence of a particular disturbance variable on the evaluation function among the disturbance variables. This will be explained in more detail below with reference to FIGS. 7 and 8 for disturbance variables “shielding adjacent field facets 7”.

FIG. 7 shows in perspective view two adjacent field facets 7, denoted 7 ₁ and 7 ₂ in the following. The two field facets 7 ₁ , 7 ₂ are tilted with respect to each other about a tilt axis 35 parallel to the y-axis, so that a predefined pupil facet of the pupil facets 11 is assigned through the corresponding illumination channel. Take the corresponding lighting tilt position for. In the case of an arrangement of _two field facets 7 ₁ , 7 ₂ as described in FIG. 7, these field facets are joined directly to each other on the respective long sides of the reflective facet surface. Assuming a correspondingly inclined incidence of the illumination light 3 on the reflecting surface of the field facet 7 ₂ due to the different tilts of the _two field facets 7 ₁ , 7 ₂ around the tilt axis 35, the field facet 7 ₂ A triangular light-shielding region 36 having a maximum spread represented by d in FIG. 7 is provided in one region of the short side of the reflecting surface along the y-axis.

FIG. 8 shows two field facets 7 ₁ , 7 ₂ in a tilted arrangement about the tilt axis 35 corresponding to FIG. 7, this tilted array being the reflecting surface of the _two field facets 7 ₁ , 7 ₂ . Differs from the arrangement described in FIG. 7 only in that they are at a distance of d from each other along the y-axis. Accordingly, assuming the same incident angle of the illumination light 3 as in FIG. 7, the field facet 7 ₁ does not shield the facet 7 ₂ in the arrangement shown in FIG. 8.

  When calculating the evaluation function in the modification step 33, assuming a correspondingly separated arrangement of a particular pair of field facets 7, a relatively large relative in field facet tilt angle due to the distance present with respect to adjacent field facets. Even in the case of differences, it can be taken into account that a particular field facet of the field facets 7 does not provide exactly any occlusion with respect to the adjacent field facets of the field facets 7.

When choosing the initial assignment of the illumination channels, it can further be considered to avoid as much as possible a large difference in the tilt of the adjacent field facets 7 around the tilt axis parallel to the y-axis. This will be described below with reference to FIG. FIG. 9 very schematically shows yet another embodiment of the field facet mirror 6 and the pupil facet mirror 10. Two of the field facets 7 are highlighted with corresponding hatching of the same type, ie two of the field facets 7 ₁ , 7 ₂ and _two of the pupil facets 11, ie the pupil facets 11 ₁ and 11 ₂ . . The tilt adjustment of the _two field facets 7 ₁ , 7 ₂ is such that the field facet 7 ₁ is assigned to the pupil facet 11 ₁ and the field facet 7 ₂ is assigned to the pupil facet 11 ₂ through respective illumination channels. Since the two pupil facets 11 ₁ , 11 ₂ have approximately the same x-coordinate, two fields of view are provided to provide this assignment of the two illumination channels (7 ₁ , 11 ₁ ) and (7 ₂ , 11 ₂ ). The facets 7 ₁ , 7 ₂ are tilted with a good approximation by the same tilt angle around the respective tilt axis 35 of these field facets parallel to the y-axis. Thus, the discernable occlusion between _two adjacent field facets 7 ₁ , 7 ₂ that would be present in the case of a relatively large difference in tilt about tilt axis 35 is the initial assignment of FIG. The case does not occur.

  In order to reduce the influence of imaging aberrations on the object plane 16 of the field facet 7, it corresponds to the entrance pupil of the projection optical unit 19, ie a pupil in a plane that coincides with or is conjugated to the entrance pupil. The arrangement of the facet mirror 10 can be optimized. This is described in more detail below with reference to FIG. FIG. 10 shows a modification 37 of the illumination optical unit that can be used in the projection exposure apparatus 1 instead of the illumination optical unit 23. Components of the illumination optical unit 37 corresponding to those described above with reference to the illumination optical unit 23 are accompanied by the same reference numerals and will not be described again in detail.

  The illumination optical unit 37 has a collector 4 embodied as an ellipsoidal mirror. In the case of the illumination optical unit 37, the transmission optical unit 38 downstream of the pupil facet mirror 10 in the beam path of the illumination light 3 has a grazing incidence mirror equivalent to the mirror 14 of the illumination optical unit 23 as the only mirror. .

  In the case of the projection exposure apparatus 1 shown in FIG. 10, the projection optical unit 19 is illustrated in more detail. The projection optical unit 19 includes six imaging beam paths between the object field 18 and the image field 20 in order. It has EUV mirrors M1, M2, M3, M4, M5, and M6.

  In the case of the illumination optical unit 37, the pupil facet mirror 10 is located in a pupil plane 39 that arises from the entrance pupil plane 40 of the projection optical unit 19 as a result of the mirror image inversion. The pupil facet mirror 10 is accurately placed in the pupil plane 39 that results from the mirror image inversion. In this case, the mirror image inversion is achieved at the object plane 16 and the folding by the grazing incidence mirror of the transmission optical unit 38 is taken into account.

  If the plane approximation for the entrance pupil of the projection optical unit 19 is discarded, a spherical surface denoted 41 in FIG. 10 is produced in the shape of the entrance pupil. In FIG. 10, a mirror image of the spherical entrance pupil 41 is shown at 42.

  The deformation of the pupil facet mirror 10 can be concavely curved so that the support plate of the pupil facet mirror 10 on which the pupil facet 11 is disposed accurately follows the curvature of the spherical pupil plane 42. In this case, at the position on the object field 18 that one single pupil facet 11 will have the effect of appearing at one particular location in the object field 18 at different illumination angles with respect to another location in the object field 18. Distortion at certain locations on the dependent pupil facet mirror can be avoided. This makes it easier to comply with predefined values, especially for illumination parameters of telecentricity and ellipticity. Correspondingly curved facet mirrors are known from the field facet mirror example according to DE 10 2008 042 876 A.

  The channel dependent reflectivity of the optical component located between the pupil facet 11 and the object field 18 of the illumination channel to be considered can be incorporated into the evaluation function. In the case of the illumination optical unit 23, these optical components are mirrors 12 to 14. In the case of the illumination optical unit 37, this optical component is a mirror of the transmission optical unit 38.

  The shape of the light source image on the pupil facet 11 of the illumination channel considered can be incorporated into the evaluation function. The imaging scale of the imaging of the field facets of the illumination channels considered can be incorporated into the evaluation function.

  A variable representing the imaging of the field facet 7 of the illumination channel considered into the object field 18 can be incorporated into the evaluation function. This variable is in particular an imaging aberration, e.g. distortion, imaging tilt, image occlusion, deviation of the field facet image from the object plane 16, the entrance pupil of the projection optical unit 19, or the plane corresponding to this entrance pupil, In particular, it includes the deviation (defocus) of the pupil facet 11 of the illumination channel considered from the conjugate plane, or the depth of focus of the imaging.

  The symmetry variable, stray light variable, the imaged line width of the object placed in the object field 18, or the position in the far field of the light source 2 at the field facet mirror 6 location of the field facet 7 of the illumination channel considered. Can be incorporated into the evaluation function.

  As described above, the evaluation function that is determined in advance by the assigning method can be based on the spot image of the field facet. This feature will be described in more detail below with reference to FIGS.

  FIG. 11 is a very schematic representation of the beam path of the EUV partial beam 43 of the EUV illumination light 3 between the intermediate focus located in the intermediate focal plane 5 and the object field 18 corresponding to the side view described in FIG. Is shown in a typical figure. The course of three EUV illumination rays 44, 45, 46 is shown. The rays 44 and 46 constitute the peripheral rays of the EUV partial beam 43. The light ray 45 constitutes the central ray or principal ray of the EUV partial beam 43. In FIG. 11, the path of the EUV partial beam 43 is represented by 14 from another EUV mirror 12 upstream of the object field 18. Further, none of the size relationships or distance relationships for the illustrated single field facet 7, illustrated single pupil facet 11, and object field 18 are to scale.

  Along the beam path of the EUV partial beam 43, the intermediate focus is imaged in the intermediate focus image 47 after reflection at the field facet 7 and before reflection at the pupil facet 11. Since the intermediate focus image 47 is located in the beam path of the EUV partial beam 43 before reflection at the pupil facet 11, the rays 44 to 46 are incident at different locations 48, 49, 50 on the pupil facet 11, Also referred to as a spot. After reflection at spots 48-50, rays 44-46 are incident at different locations 51, 52, 53 on the object field 18, i.e. rays 44 and 46 are at the periphery and ray 45 is at the center.

  FIG. 12 shows the pupil facet 11 viewed from the location 51 of the object field 18. The spot 48 viewed from this location 51 is offset towards the left with respect to the center of the pupil facet 11, that is, in the negative x direction.

  FIG. 13 shows the pupil facet 11 viewed from a central location 52 of the object field 18. In this figure, the spot 49, that is, the place where the light ray 45 is incident on the pupil facet 11 is located at the center.

  FIG. 14 shows the pupil facet 11 viewed from a location 53 around the object field 18. In this figure, the spot 50 is offset to the right with respect to the center of the pupil facet 11, ie in the positive x direction.

  Due to the incomplete imaging of the light source 2 or the intermediate focus on the pupil facet 11, a slight deflection emanating from each considered pupil facet 11 based on the location considered on the object field 18. An illumination direction is provided.

  In addition to the cause of intermediate focus imaging in the beam path of the EUV partial beam 43 before reflection at the pupil facet 11 as revealed with reference to FIGS. There may also be other causes for the spot on the pupil facet being located differently on the pupil facet 11. Each spot image on the object field 18 can be accurately determined by geometric analysis of the optical design of the illumination optical unit 23. Each assignment of a particular field facet 7 to a particular pupil facet 11 results in a different spot image variation such that the spot image is appropriate as a feature in the evaluation function that is predefined in the predefined step 27 of the assignment method.

  As a result of the assignment method, the non-uniform illumination of the field facet 7 can be used to compensate for the displacement of the spot image described above with reference to FIGS. 11 to 14, resulting in the assignment of the field facet to the pupil facet. . The geometric displacement of the illumination angle distribution resulting from the superposition of the spot images on all pupil facets can be compensated by a corresponding adaptation of the intensity of the individual EUV partial beams 43 guided through the illumination channel. Since the product of the direction of each partial ray and its intensity, or the product of distance and intensity, is also incorporated into the telecentric value, the above compensation is equivalent to the telecentricity compensation.

Claims (12)

Reflected from the light source (2) towards the object field (18) illuminated by the illumination optics unit (23; 37) at the field facet (7) and at the pupil facet (11) assigned using the method. The pupil facet (11) of the pupil facet mirror (10) of the illumination optical unit (23; 37) of the projection exposure apparatus (1) for the definition of the illumination channel for the partial beam of the illumination light (3) 23; 37) the field facet mirror (6) of the field facet (7),
Identifying (26) at least one illumination parameter capable of evaluating the illumination of the object field (18);
Depending on the selected illumination parameter, possible illumination channels for guiding the partial beam of the illumination light (3), ie just one of the field facets (7) and the pupil facet (11) Predefining (27) an illumination channel dependent evaluation function for evaluating possible combinations with exactly one of
Pre-defining an evaluation target range of an evaluation variable as a result of the evaluation function;
Identifying (31) at least one disturbance variable affecting the illumination of the object field (18);
Identifying a dependence of the evaluation function on the at least one disturbance variable (32), changing the disturbance variable for a preselected illumination channel in a predefined disturbance variable variation range (33), Calculating each subsequent variation of the evaluation variable based on an evaluation function;
Selecting a lighting channel (34) having a modified evaluation variable that remains within the evaluation target range throughout the variation range;
A method comprising the steps of:   2. The deviation of the illumination intensity of the field facet (7) due to the illumination light (3) from the uniform illumination for each of the illumination channels to be considered is incorporated into the evaluation function. Method. Shielding (36) by other optical components of the partial beam of the illumination light (3) incident on the field facet (7) of the illumination channel to be considered is incorporated into the evaluation function. The method according to claim 1 or 2 , wherein: The incident angle of the partial beam of the illumination light (3) on the field facet (7) and / or the pupil facet (11) of the illumination channel to be considered is incorporated into the evaluation function The method according to claim 1 or claim 2 . The channel dependent reflectivity of the optical components (12 to 14; 38) located between the pupil facet (11) and the object field (18) of the illumination channel to be considered is incorporated into the evaluation function. The method according to any one of claims 1 to 4 , characterized in that: The method according to any one of claims 1 to 5, wherein the shape of the light source image of the pupil on the facets (11) of the illumination channels, characterized in that incorporated into the evaluation function to be considered. The imaging scale of the imaging onto the object field (18) of the field facets of the illumination channels are considered (7), of claims 1 to 6, characterized in that incorporated into the evaluation function The method according to any one of the above. Imaging aberration describing the imaging of the field facet (7) of the illumination channel under consideration into the object field (18) is incorporated in the evaluation function. 8. The method according to any one of items 7 . The method as claimed in any one of claims 8 to symmetry variable, characterized in that incorporated into the evaluation function. Stray variables, the method as claimed in any one of claims 9, characterized in that incorporated into the evaluation function. The method as claimed in any one of claims 10 to imaged by the structure width of the object field (18) in the arranged object (17), characterized in that incorporated into the evaluation function . Position of the field facets (7) in the far field of the light source at the location of the field facet mirror (6) (2), any one of claims 1 to 11, characterized in that incorporated into the evaluation function 2. The method according to item 1.

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