Carl Zeiss SMT GmbH 1 METHOD FOR ANALYSING AND/OR PROCESSING A LITHOGRAPHY MASK AND REPAIR SYSTEM The present invention relates to a method for analysing and/or processing a lithog- raphy mask and to a repair system. The content of the priority application DE 10 2024 110 145.8 is incorporated in full by reference. Microlithography is used for producing microstructured component parts, for exam- ple integrated circuits. The microlithography process is carried out using a lithogra- phy apparatus, which comprises an illumination system and a projection system. The image of a mask (also "lithography mask" or "reticle" herein) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, in or- der to transfer the mask structure to the light-sensitive coating of the substrate. Driven by the desire for ever smaller structures in the production of integrated cir- cuits, EUV lithography apparatuses that use light having a wavelength in the range from 0.1 nm to 30 nm, in particular 13.5 nm, are currently under develop- ment. Since most materials absorb light at this wavelength, it is necessary in such EUV lithography apparatuses to use reflective optical units, i.e. mirrors, instead of refractive optical units, i.e. lens elements, as used previously. As the structure sizes of both masks used in the lithography process and microlitho- graphically structured wafers become ever smaller, the analysis and the processing or repair of such masks are becoming ever more of a demanding challenge in prac- tice. A respective lithography mask is used for the production of a large number of indi- vidual component parts, for example several hundred thousand or several million. If a lithography mask has a defect, which is to say a defined structure on the lithogra- phy mask is not located within a defined region, then this defect is transferred to the light-sensitive coating, and hence to the substrate, during each exposure proce- dure using the lithography mask. It is therefore immensely important that the li- thography masks used are defect-free. In this context, it is worthwhile to put great effort into the checking and repairing of lithography masks.
Carl Zeiss SMT GmbH 2 Known repair processes are based on particle-beam-induced etching or deposition processes, for example, which can be carried out purposefully with a high resolution by the particle beam. During the particle-beam-induced repair of defects on lithog- raphy masks, electrostatic charges of the lithography mask or mechanical drifts of system components and/or of the lithography mask can cause the particle beam or the electron beam to be incident not at a designated position of the lithography mask. In order to minimize these time-dependent drift effects of the particle beam or electron beam, the lithography mask and/or the sample stage during processing or imaging, reference structures are usually produced on the lithography mask in the periphery of the repair site before the start of the repair process. These refer- ence structures are periodically acquired by an image-recording device in order to measure a deviation with respect to at least one reference image. This deviation can be used to correct the position of the particle beam or electron beam in the form of drift correction. In particle-beam-based or electron-beam-based systems, such reference structures are produced by depositing material in the periphery of the site to be processed or repaired on the lithography mask. The reference structures are also referred to as drift correction marks (or DC marks) and are produced from point-type deposits of the precursors TEOS or Cr(CO)6. Usually, the deposited reference structures remain on the lithography mask after the repair process has been completed and are not reliably removed even by a mask cleaning that is carried out in principle. However, in particular due to increasingly smaller structure sizes on the lithogra- phy masks, in particular in EUV lithography and/or high NA-EUV lithography, this has the result that the remaining reference structures in the manufacture of compo- nent parts using the lithography mask form interference variables, which can dis- advantageously alter the optical properties of the lithography mask. Against this background it is an object of the present invention to provide an im- proved method for analysing and/or processing a lithography mask and an improved repair system. Accordingly, a method for analysing and/or processing a lithography mask for a li- thography apparatus is proposed. The method includes the steps of:
Carl Zeiss SMT GmbH 3 - providing a reference structure on the lithography mask in such a way that the reference structure is not imaged when the lithography mask is imaged on a wafer using the lithography apparatus; - generating an image representation of the reference structure using a parti- cle beam; and - controlling the particle beam for analysing and/or processing the lithogra- phy mask depending on the generated image representation of the refer- ence structure. The analysis and/or processing of the lithography mask preferably comprises a re- pair process during which at least one defect site of the lithography mask is re- paired by the particle beam by etching or particle accumulation at the defect site. The wording "image representation of the lithography mask" preferably refers to a result of the lithographic process in microelectronics or semiconductor production. This lithographic process is used in particular for the production of integrated cir- cuits (ICs). The "image representation" of the lithography mask preferably refers to the transfer of the pattern from the mask to the wafer during the exposure step. With reference to what was stated above, the at least one reference structure is de- signed such that it is not imaged on the wafer during the exposure step, which also includes: that the image representation of the at least one reference structure on the wafer has a maximum dimension or is describable by another parameter, wherein the maximum dimension or the other parameter is below a predetermined threshold value. The threshold value is such that the imaged at least one reference structure is non-critical for a predetermined imaging process in a predetermined li- thography apparatus (i.e. it is only marginally influenced). In order to achieve this, the at least one reference structure can preferably be optimized with respect to a plurality of design parameters, which will be explained in more detail below. The physical properties of the at least one reference structure are thus selected such that they are not imaged on the lithography mask or the reference structure does not change the optical properties of the lithography mask beyond a permissible limit value. The reference structure or the drift correction mark therefore does not at any time adversely alter the image representation in the lithography process. Examples of suitable masks are those used in lithography with UV, DUV or EUV light. In particular, binary masks, phase-shifting masks or hybrids from both vari- ants are used.
Carl Zeiss SMT GmbH 4 A "wafer" is a preferably flat, round and/or approximately round, in particular disc- shaped substrate made of a semiconductor material such as silicon, which is used in microelectronics and semiconductor production. Wafers are used as starting mate- rial for the manufacture of integrated circuits (ICs) and other electronic component parts. Wafers may have a multi-layer structure. As mentioned in the introductory part, during the particle-beam-induced repair of defects on lithography masks, electrostatic charges in the lithography mask or me- chanical drifts of system components and/or of the lithography mask can cause the particle beam or the electron beam to be incident not at a designated position of the lithography mask. In order to minimize these time-dependent drift effects of the particle beam or electron beam, the lithography mask and/or the sample stage dur- ing processing or imaging, reference structures are produced in the periphery of the repair site before the start of the repair process. The "reference structure" may be designed in embodiments as one or more so-called drift correction marks, which are used to correct an alignment of a particle beam, for example of an electron beam, of the lithography apparatus during an undesirable drift movement. The wording "image representation of the reference structure using the particle beam" is understood to mean: that the at least one reference structure is preferably captured or imaged by an image-recording device in order to thereby measure a de- viation with respect to at least one reference image in which the reference structure has been recorded, for example, at an earlier time step. The deviation that can be determined thereby can be used to correct the position of the particle beam or elec- tron beam in the form of drift correction. The controlling of the particle beam for an- alysing and/or processing the lithography mask is thus carried out "depending on the generated image representation of the reference structure by means of a particle beam". Providing a reference structure that is not or only insignificantly imaged during the imaging on the wafer can contribute to the prevention of incorrect image represen- tations on the wafer. This is particularly important because errors in the mask can lead to faulty chips or semiconductor component parts. The method contributes to quality assurance in semiconductor manufacturing by improving the accuracy and/or consistency of the lithography mask. This ultimately reduces manufacturing costs and improves chip yield. Since the reference structure is designed in such a way that it does not negatively affect the optical properties of the lithography mask, the reference structure can also be printed on a lithography mask before the lithog- raphy mask is used. If a defect site then occurs during use, or if an analysis of a
Carl Zeiss SMT GmbH 5 part of the lithography mask is required, then the already existing reference struc- ture can be used to enable repair and/or analysis by means of the particle beam us- ing drift correction. According to one embodiment, the provision is effected depending on at least one pa- rameter of the lithography apparatus, wherein the parameter is selected from a wavelength of operating light of the lithography apparatus and/or an intensity of operating light of the lithography apparatus and/or a numerical aperture of the li- thography apparatus. The at least one reference structure is configured and/or designed based on the at least one parameter, in particular in such a way that it is not imaged when the li- thography mask is imaged on a wafer in the lithography apparatus. For example, a size and/or at least one dimension and/or at least one refractive index of the reference structure can be determined depending on a wavelength used by the lithography ap- paratus in order to not be imaged on the wafer during the imaging step, since the reference structure is designed, for example, to absorb the light of this wavelength. Similarly, the reference structure can be designed based on the intensity and/or nu- merical aperture (NA). According to a further embodiment, the provision of the reference structure is ef- fected such that it is not imaged on the wafer, by selecting a volume and/or a basic geometry and/or a refractive index and/or a material and/or a material composition of the reference structure and/or a distance of the reference structure from at least one part of an imaging structure of the lithography mask which is imaged when the lithography mask is imaged on the wafer using the lithography apparatus. The "imaging structure" describes the pattern and/or structure which is produced on the lithography mask and is to be transferred to a substrate or semiconductor wafer. The imaging structure on the lithography mask preferably comprises various elements, which represent the structures and/or circuits to be transferred to the wa- fer. These structures may include, for example, conductor tracks, transistors, insu- lators, contacts and/or other microelectronic components. The nature of the imaging structure on the mask is crucial, as it directly affects the quality and/or perfor- mance of the microelectronic component parts or chips produced. At a defect site, the imaging structure deviates from a specified value and/or from a specification. In order to enable error-free use of the lithography mask, this defect site should be analysed and/or processed or repaired by the present method. In order
Carl Zeiss SMT GmbH 6 to enable the repair and/or analysis without error by means of the particle beam, the reference structure is arranged adjacent to the at least one part of the imaging struc- ture, in particular to an expected or existing defect within it, which is used for the drift correction of the particle beam. According to a further embodiment, the reference structure is formed on the lithog- raphy mask by depositing a material using a process gas. Alternatively, the refer- ence structure is formed by a depression and/or a notch in the lithography mask by way of etching using a process gas. A preferred minimum depth of the depression and/or notch is at least 10 nm. If the reference structure is provided in the form of a material application, a material is deposited on the lithography mask up to a height which is preferably above a topo- graphical level in the immediate vicinity of the reference structure. If the reference structure is provided in the form of a depression, a material is removed from the lithography mask down to a depth which is preferably below a topographical level in the immediate vicinity of the reference structure. The depression or notch should preferably not be deeper than 60 nm or not deeper than an absorption depth of the lithography mask. The amount of material missing from the native lithography mask is preferably se- lected in the case of the depression/notch such that the optical properties of the mask are not adversely affected. In this case, the depression/notch may remain in the mask, since it is not imaged on the wafer anyway. It is advantageous when providing a notch and/or a depression as the reference structure that no material needs to be deposited on the lithography mask. Furthermore, a secondary electron current of an SEM im- age is higher at edges than in a vicinity of the edges. On the other hand, a secondary electron current on an inside of the depression or notch is smaller than in the vicinity. Thus, the reference structure can be clearly identified as such by its contrast. The depression and/or notch can preferably be produced by gas-assisted electron-beam- induced etching and/or by a mechanical probe. According to a further embodiment, the imaging structure has at least one defect site to be repaired by means of the particle beam, wherein the reference structure is provided in the immediate periphery of the defect site. "At least one defect site to be repaired by means of the particle beam" preferably de- scribes a location and/or a site within, at or on the imaging structure at which at least one defect or error has occurred. This defect is to be repaired or corrected
Carl Zeiss SMT GmbH 7 using a particle beam. For example, the particle beam may comprise electrons, ions, or other charged particles. The "reference structure is provided in the immediate pe- riphery of the defect site" means that at least one reference structure is present in close proximity to the defect site. The reference structure can serve as a template or pattern to ensure that the defect can be repaired accurately. According to a further embodiment, a maximum dimension of the reference struc- ture, measured in particular parallel to a main plane of extent of the lithography mask, is less than or equal to 60 nm, preferably less than or equal to 50 nm, prefer- ably less than or equal to 40 nm, preferably less than or equal to 30 nm, preferably less than or equal to 20 nm. To select a maximum dimension of the reference structure, it is preferable to specify that particle defects up to a size of 52 nm (critical dimension, "CD") must be detected or that particles above this size are detected as optical defects of the lithography mask. Since the reference structure is not intended to be imaged on the wafer or at least not adversely affect the optical properties of the wafer, it is preferred if the maximum dimension of the reference structure is less than 52 nm. The use of such "small" reference structures has the advantage that the secondary electron current is increased due to a higher radius of curvature of the surface of the reference structure or the deposit. The "main plane of extent" of the lithography mask refers to the plane in which the essential structures of the lithography mask are aligned. This plane is crucial for the lithographic process, in which the pattern is transferred from the mask to a semicon- ductor wafer or a substrate. The main plane of extent of the lithography mask is preferably parallel to the surface of the mask. According to a further embodiment, a maximum dimension of the reference struc- ture, measured in particular parallel to the main plane of extent of the lithography mask, is selected to be smaller than a minimum dimension of the imaging structure, measured in particular parallel to the main plane of extent of the lithography mask. This is in line with the goal that the reference structure will not be imaged on the wafer at a later time, as it is smaller than the smallest imageable component of the lithography mask. According to a further embodiment, the refractive index of the reference structure has a phase-shifting component and an absorptive component, wherein the phase-
Carl Zeiss SMT GmbH 8 shifting component of the refractive index has a difference with respect to the vacuum of at most 0.045, and wherein the absorptive component of the refractive index has a difference with respect to the vacuum of at most 0.02. The "refractive index of the reference structure" refers to the optical property of the reference structure which indicates how light or electromagnetic radiation is re- fracted or diffracted in the structure. The refractive index is a dimensionless value that describes the change in the phase velocity of the light in the structure compared to the vacuum velocity. The "phase-shifting component" indicates that the refractive index of the reference structure has a part that changes the phase velocity of the light but does not cause significant absorption or energy loss. This phase-shifting compo- nent can be used to control the phase shift of the light, which can be important in optical applications. The "absorptive component" indicates that the refractive index of the reference structure has a component that can absorb light. This means that part of the incident light is absorbed in the structure and converted into heat instead of being passed on or reflected. According to a further embodiment, the material includes one or more of the following chemical elements Si, Ba, Ce, La, Br, Rb, Be, Sr, P, S, Ca, Y, B, Sc, Zr, Gd, Nd, C, Ti, Se, F, Cl. In principle, further materials or material compositions not mentioned here are also conceivable, if they are suitable for not being imaged on the wafer later in the form of the reference structure. According to a further embodiment, the material of the reference structure is selected such that a secondary electron current of the reference structure is greater than a secondary electron current of a region of the lithography mask surrounding the ref- erence structure. Alternatively or in addition (and/or), a backscatter electron current of the reference structure is smaller than or greater than a backscatter electron cur- rent of a, or the, region of the lithography mask surrounding the reference structure. Thus, for deposited structures, for example curved surfaces, the signal of the second- ary electron yield is preferably greater than that of the vicinity, for example a flat surface. The secondary electron current is preferably proportional to a secondary electron yield. The backscatter electron current is preferably proportional to a backscatter electron yield. The secondary electron current can be captured in the form of a meas- urement signal that can be measured by means of a detector. The backscatter electron
Carl Zeiss SMT GmbH 9 current can be captured in the form of a measurement signal, which can be measured by means of a detector. The respective detector signal is preferably proportional to the respective current. Due to the fact that the secondary electron yield of the reference structure is signifi- cantly greater or significantly smaller than the secondary electron yield at other sites of the lithography mask due to the material and/or geometry, the reference structure can be clearly identified as such and used for drift correction. It is therefore beneficial to maximize the secondary electron yield of the reference structure as much as possi- ble in order to be able to clearly distinguish it from the surrounding lithography mask. The same also applies to the backscatter electron current. An acceptable signal difference in the secondary electron yield or the corresponding proportional secondary electron current preferably corresponds to a greyscale value difference of 70. An ac- ceptable signal difference in the secondary electron yield or the corresponding pro- portional secondary electron current preferably corresponds to an image contrast of C = greyscale value(reference structure)-greyscale value(overall image)/greyscale value(overall image) = 184-116 / 116 = 0.59. Particularly preferably, the reference structure has an image contrast that is greater than 0.5, more preferably greater than 0.6, more preferably greater than 0.7 and most preferably greater than 0.8. According to a further embodiment, the reference structure has an auxiliary layer, which is used to amplify the secondary electron current and/or the backscatter elec- tron current of the at least one reference structure. The auxiliary layer acts, for example, as a kind of "amplifier" in order to amplify the signal of the secondary electron current and/or the backscatter electron current fur- ther relative to the respective signal of the lithography mask. The auxiliary layer is preferably disposed and/or applied between the lithography mask and the reference structure and preferably has a material that is different from the lithography mask and the reference structure. The auxiliary layer preferably has a maximum dimen- sion, which is measured in particular parallel to the main plane of extent of the li- thography mask and which is greater than a maximum dimension of the reference structure. The auxiliary layer is preferably produced with the aid of precursors such as TEOS, Cr(CO)6 or Mo(CO)6. Further precursors mentioned in this text are also possible as a material basis for the auxiliary layer. The respective electron yield of the auxiliary layer preferably differs more from the respective electron yield of the auxiliary structure than from the electron yield of the lithography mask.
Carl Zeiss SMT GmbH 10 According to a further embodiment, the depression and/or the notch is filled with a material deposited therein, preferably flush with a surface of the lithography mask. Before the depression and/or notch is used as a reference structure, the respective depression and/or notch can be filled with a material whose secondary electron yield at electron bombardment with the particle beam differs from the secondary electron yield of the vicinity around the depression and/or notch. Preferably, the filling mate- rial is selected in such a way that the optical properties of the lithography mask can be at least partially reconstructed. In this way, a reference structure is produced, which substantially provides a material contrast without changing the topography of the lithography mask in the region of the reference structure. According to a further embodiment, the operating light used in the imaging of the lithography mask on the wafer has a wavelength of between 0.1 nm and 30 nm, pref- erably between 13 and 14 nm, in particular 13.5 nm and/or the lithography apparatus has a numerical aperture greater than 0.3, in particular greater than 0.33, preferably greater than 0.5, for example 0.55, for example between 0.3 and 0.75, in particular greater than 0.6, preferably greater than 0.7. According to a further aspect, a repair system for carrying out a particle-beam-based repair process for a lithography mask is provided, wherein the repair system com- prises: - a repair device; and - the lithography mask, which can be analysed and/or processed by means of the re- pair device according to the method according to any of its embodiments. The repair system can also include the (predetermined) lithography apparatus. According to a further aspect, a method for analysing and/or processing a lithography mask is provided, the lithography mask comprising an imaging structure with at least one edge to be imaged on a wafer, wherein the method comprises the steps of: - capturing at least one portion of the at least one edge at a first time by way of an image-recording device or detector; - determining an edge position of the at least one portion of the at least one edge on the lithography mask based on at least one reference position at the first time; - determining (in particular pixel-by-pixel) an item of roughness information of the at least one portion of the at least one edge at the first time; - capturing the at least one portion of the at least one edge at a second time using the image-recording device;
Carl Zeiss SMT GmbH 11 - determining an edge position of the at least one portion of the at least one edge on the lithography mask based on at least one reference position at the second time; - determining (in particular pixel-by-pixel) an item of roughness information of the at least one portion of the at least one edge at the second time; - comparing the roughness information determined at the first time with the rough- ness information determined at the second time; and - tracking a particle beam used to repair the lithography mask based on the compar- ison. In the present case, instead of (or in addition to) a reference structure, an item of roughness information of an edge or an edge portion of the lithography mask can also be used for drift correction. In this case, an image of the respective edge or edge portion together with a surround- ing periphery of the lithography mask is acquired at a first time. From the image, the edge position is extracted and an item of roughness information is determined, in particular a roughness fingerprint, for example in the form of a roughness parameter, of the edge or the edge portion, preferably pixel-by-pixel. This can be effected, for example, by means of an edge roughness algorithm. The roughness information can be determined in real space and/or in the Fourier space. Subsequently, a further im- age of the respective edge or edge portion together with a surrounding periphery of the lithography mask is acquired at a second time. In turn, the edge position is ex- tracted and the roughness information is determined, in particular a roughness fin- gerprint. Based on this, a comparison of the roughness information between the first and the second image can be made. This comparison is used to calculate a particle beam drift or distortion. Based on the calculation, the particle beam can then be tracked. If there is an item of pronounced or highly resolved structure information or rough- ness information of the edge or edge portion, the drift correction can be carried out in a relevant spatial direction based on this information. Overall, the drift correction can be performed in two spatial directions, depending on the edge profile, by evalu- ating edge roughness information in each case. It is advantageous that the demands on the placement accuracy in the direction of the pronounced or highly resolved struc- ture information are generally higher than in the direction of an item of compara- tively weak structure information. According to a further embodiment, the at least one portion of the at least one edge is protected by a protective layer, in particular a protective layer that is removable
Carl Zeiss SMT GmbH 12 by a mask cleaning operation, wherein the protective layer preferably has a material containing Mo or C. It is also conceivable to protect the mask structures or edge information used for tracking in the manner described with a protective layer that can be removed by mask cleaning. Reference structures which have less deposited material than otherwise usual refer- ence structures or drift correction marks can be modified more by a particle beam and/or process gases during the repair process than is the case with reference struc- tures normally used. In order to compensate for a failure of individual reference struc- tures during a repair process, it may be preferable to produce a grid of small reference structures prior to repair. Since a material, a dimensioning and/or a refractive index of the reference structures is preferably selected in such a way that neither an indi- vidual reference structure nor a grid of reference structures completely or partially adversely affect the lithography process (imaging process), such reference structures may also remain on the lithography mask. During a repair process of a defect of a lithography mask, the condition of the refer- ence structures and/or the quality of the associated drift correction is checked at reg- ular intervals and provided with a quality criterion. As soon as the quality of the reference structures and/or the drift correction has fallen below a specific limit value, a new set of reference structures is preferably applied to the lithography mask or provided on the lithography mask. A site where the new reference structures are deposited and/or provided can prefera- bly be defined by a user prior to the start of the repair process as part of the produc- tion of a repair form. Thus, according to a further aspect, a method for analysing and/or processing a li- thography mask is provided, wherein the method comprises the steps of: - capturing and/or providing an SEM (Scanning Electron Microscope) image of a de- fect site, in particular including a periphery of the lithography mask present around the defect site, of an imaging structure of the lithography mask; - providing at least one reference structure and/or a reference structure grid, in par- ticular based on a repair plan for the repair of the defect site; and - tracking a particle beam used to repair the lithography mask based on the at least one reference structure and/or the reference structure grid.
Carl Zeiss SMT GmbH 13 The method particularly preferably comprises: - replacing at least one existing reference structure and/or providing at least one fur- ther reference structure on the lithography mask, if at least one existing refer- ence structure falls below a predetermined visibility threshold value or has been removed at least partially from the lithography mask by the particle beam or by process gases; and - tracking a particle beam used to repair the lithography mask also based on the at least one further reference structure. The at least one further reference structure can preferably be produced at a site of a previous reference structure or at another site of the lithography mask. The first case corresponds to a regeneration of the reference structure. Particularly preferred pre- cursors for the production of reference structures are TEOS and Cr(CO)6. It is also possible to use H2O or NO2 as additive gases. The following scenarios are preferably conceivable for the production of the further reference structures. As a rule, the quality of the drift correction is rated with a score of between 0 and 100 (100 stands for any absolute highest value). As soon as a quality value falls below a specific limit value, e.g.50, at least one further reference structure can be written or provided on the lithography mask. The production of at least one further reference structure can also be carried out in the form of an emergency mechanism, in which, for example, at least one further reference structure is produced, whenever a degradation of at least one reference structure is detected during a repair and/or the tracking of a reference structure is lost. It is also possible to provide the production of at least one further reference structure always at the end of a specific repair period. The production of the at least one further reference structure is then preferably carried out as a fixed step during the repair of a defect. The degradation behaviour of the reference structure can preferably be de- termined from previous test series. In particular, it can be estimated how long a ref- erence structure can perform its function with sufficient quality under given process conditions.
Carl Zeiss SMT GmbH 14 In order to switch from one reference structure to another reference structure prefer- ably without interruption during the repair process, a comparison between SEM im- ages of the two reference structures is preferred. In addition, a user can deposit a predetermined number of reference structures on the lithography mask and specify a position of at least one further reference structure to be produced during repair if necessary. If a repair is then carried out, the drift correction is initially carried out by the predetermined number of reference struc- tures. Further, during the repair, the quality of the predetermined number of refer- ence structures and/or the quality of the drift correction is preferably checked and/or assessed in intervals or continuously. If the quality of at least one of the predeter- mined number of reference structures and/or the quality of the drift correction falls below a specific limit value, the at least one further reference structure is produced based on the position previously defined by the user. A reference image of the at least one further reference structure is preferably recorded. Furthermore, a comparison with current SEM images of the predetermined number of reference structures can be made. The following drift correction is then preferably carried out first on a tran- sitional basis based on the predetermined number of reference structures and the at least one further reference structure, and then based on a correspondingly reduced number of previous reference structures with the at least one further reference struc- ture. It is also possible that a direct transfer to the at least one further reference structure takes place. The advantages of the described method can be summarized as follows: A functioning drift correction is ensured at all times. This minimizes the risk that a repair will have to be aborted or is carried out incorrectly due to the loss of at least one reference structure. The material for reference structures which is located on the lithography mask also remains below a limit value for undisturbed optical properties of the li- thography mask. The production of the at least one further reference structure is preferably carried out in such a way that the repair is impacted as little as possible. The production of the at least one further reference structure is preferably carried out with the same precursor with which the previous reference structure(s) was/were also produced. The production of the at least one further reference structure is preferably carried out with a different precursor than the previous reference structure(s). The process gas used for the repair is used to produce the at least one further reference structure.
Carl Zeiss SMT GmbH 15 If a precursor suitable for the electron-beam-induced deposition of material is used in the repair, it is possible to use the same precursor for producing the at least one further reference structure. If a precursor suitable for the electron-beam-induced re- moval of material is used in the repair, it is possible to use the same precursor for producing the at least one further reference structure. It is possible that the previous reference structures and the at least one further ref- erence structure are each produced using different precursors. The lithography mask is used in the lithography apparatus. For example, the lithog- raphy apparatus is an EUV or a DUV lithography apparatus. EUV stands for "ex- treme ultraviolet" and refers to a wavelength of the operating light in the range from 0.1 nm to 30 nm, in particular 13.5 nm. Furthermore, DUV stands for "deep ultravi- olet" and denotes a wavelength of the operating light of between 30 nm and 250 nm, in particular 193 nm or 248 nm. The EUV or DUV lithography apparatus comprises an illumination system and a projection system. In particular, using the EUV or DUV lithography apparatus, the image of a lithography mask (to which the previously described method was applied entirely or in parts) illuminated by means of the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer and arranged in the image plane of the projec- tion system, in order to transfer the mask structure to the light-sensitive coating of the substrate. According to a further embodiment of the method and/or the repair system, the analysis and/or processing of the lithography mask and/or the repair process com- prises a particle-beam-induced etching process and/or deposition process. Structures can be produced with a high accuracy, in particular a high spatial reso- lution, by means of particle-beam-induced processes. Therefore, edges can be pro- cessed with a high accuracy. The processing accuracy is in the atomic range in par- ticular, meaning that a spatial resolution of the process can be in the Angstrom and nanometre range. By way of example, it is possible to produce edges with a spacing of 1 nm. This is particularly advantageously possible by means of electron-beam-in- duced processes (EBIP). The respective particle-beam-induced process is preferably carried out under the supply of precursor gases. In this case, the precursor gases are supplied to the position on the lithography mask to be processed and the parti- cle beam is radiated and focused onto the position, which excites and/or decomposes
Carl Zeiss SMT GmbH 16 the precursor gases, wherein the excited species and/or decomposition products cause a deposition on or etching of the surface of the lithography mask. In particular, alkyl compounds of main group elements, metals or transition ele- ments can be considered as precursor gases suitable for the deposition or for grow- ing of elevated structures. Examples thereof include cyclopentadienyl(trime- thyl)platinum (CpPtMe3 Me = CH4), methylcyclopentadienyl(trimethyl)platinum (MeCpPtMe3), tetramethyltin (SnMe4), trimethylgallium (GaMe3), ferrocene (Cp2Fe), bisarylchromium (Ar2Cr), and/or carbonyl compounds of main group ele- ments, metals or transition elements, such as for example chromium hexacarbonyl (Cr(CO)6), molybdenum hexacarbonyl (Mo(CO)6), tungsten hexacarbonyl (W(CO)6), dicobalt octacarbonyl (Co2(CO)8), triruthenium dodecacarbonyl (Ru3(CO)12), iron pentacarbonyl (Fe(CO)5), and/or alkoxide compounds of main group elements, met- als or transition elements, such as for example tetraethoxysilane (Si(OC2H5)4), tetraisopropoxytitanium (Ti(OC3H7)4), and/or halide compounds of main group ele- ments, metals or transition elements, such as for example tungsten hexafluoride (WF6), tungsten hexachloride (WCl6), titanium tetrachloride (TiCl4), boron trifluo- ride (BCl3), silicon tetrachloride (SiCl4), and/or complexes with main group ele- ments, metals or transition elements, such as for example copper bis(hexafluoroa- cetylacetonate) (Cu(C5F6HO2)2), dimethylgold trifluoroacetylacetonate (Me2Au(C5F3H4O2)), and/or organic compounds such as carbon monoxide (CO), car- bon dioxide (CO2), aliphatic and/or aromatic hydrocarbons, and more of the same. By way of example, the precursor gas for an etching reaction may comprise: xenon difluoride (XeF2), xenon dichloride (XeCl2), xenon tetrachloride (XeCl4), steam (H2O), heavy water (D2O), oxygen (O2), ozone (O3), ammonia (NH3), nitrosyl chloride (NOCl) and/or one of the following halide compounds: XNO, XONO2, X2O, XO2, X2O2, X2O4, X2O6, where X is a halide. Further etching gases for etching one or more of the deposited test structures are specified in the applicant’s US patent applica- tion with the number 13/0103281. Further additional gases that can be used when producing the test structure com- prise, e.g., oxidizing gases such as hydrogen peroxide (H2O2), dinitrogen oxide (N2O), nitrogen oxide (NO), nitrogen dioxide (NO2), nitric acid (HNO3) and further oxygen-containing gases, and/or halides such as chlorine (Cl2), hydrogen chloride (HCl), hydrogen fluoride (HF), iodine (I2), hydrogen iodide (HI), bromine (Br2), hy- drogen bromide (HBr), phosphorus trichloride (PCl3), phosphorus pentachloride (PCl5), phosphorus trifluoride (PF3) and further halogen-containing gases, and/or re- ducing gases, such as hydrogen (H2), ammonia (NH3), methane (CH4) and further
Carl Zeiss SMT GmbH 17 hydrogen-containing gases. These additional gases can be used, for example, for etching processes, as buffer gases, as passivating media and the like. "A" or "an" in the present case should not necessarily be understood as being re- stricted to exactly one element. Rather, there may also be a plurality of elements, such as two, three or more. Any other numeral used here should also not be under- stood as being restricted to exactly the stated number of elements. Rather, unless indicated otherwise, numerical deviations upwards and downwards are possible. The embodiments and features described for the methods apply correspondingly to the proposed repair system, and vice versa. Further possible implementations of the invention also comprise non-explicitly mentioned combinations of features or embodiments described hereinabove or here- inafter with regard to the exemplary embodiments. A person skilled in the art will also add individual aspects as improvements or supplementations to the respective basic form of the invention. Further advantageous embodiments and aspects of the invention are the subject matter of the dependent claims and of the exemplary embodiments of the invention described below. The invention is explained in greater detail hereinafter based on preferred embodiments with reference to the accompanying figures. Fig.1 shows a repair system with a device for particle-beam-induced processing of a defect of a lithography mask according to an embodiment; Fig.2 shows a detail of an exemplary microstructured lithography mask; Fig.3 shows the detail of the lithography mask shown in Fig.2 in a cross-sectional view along line III-III; Fig.4 shows a schematic flowchart of a method for analysing and/or processing a li- thography mask according to an embodiment; Fig.5 shows three different reference structures with an improved signal-to-noise ratio in a secondary electron signal; Fig.6 shows reference structures produced by a depression in the lithography mask;
Carl Zeiss SMT GmbH 18 Fig.7 shows three top views of a lithography mask, wherein further reference struc- tures are applied in each case in order to at least partially replace unusable refer- ence structures; Fig.8 shows a schematic representation of a lithography mask in which a rough- ness fingerprint of an edge portion is used as a reference structure; Fig.9 shows a schematic flowchart of a further method for analysing and/or pro- cessing a lithography mask according to an embodiment; and Fig. 10 shows a schematic meridional section of a projection exposure apparatus for EUV projection lithography. In the figures, identical or functionally identical elements have been provided with the same reference signs, unless indicated otherwise. It should also be noted that the representations in the figures are not necessarily to scale. Fig.1 shows a repair system 1000 with a device 200 for particle-beam-induced anal- ysis and/or processing (e.g. etching, depositing) of a defect 126 (see Fig.2) of a li- thography mask 100. The lithography mask 100 in a lithography apparatus 1 is shown in Fig.10 (there also referred to as reticle 7). The device 200 shown in Fig. 1 represents e.g. a modified scanning electron micro- scope 200. In this case, an electron beam 202 is used as a particle beam for imaging, analysing and/or processing the lithography mask 100. The device 200 is largely ar- ranged in a vacuum housing 204. A space enclosed by the vacuum housing 204 is kept at a specific gas pressure by a vacuum pump 206. The lithography mask 100 to be repaired is arranged on a sample stage 208. For ex- ample, the sample stage 208 is designed to set the position of the lithography mask 100 accurately in three mutually perpendicular spatial directions x, y, z and, for ex- ample, additionally in three mutually perpendicular axes of rotation with an accu- racy of a few nanometres. The device 200 comprises an electron column 210. The electron column 210 com- prises an electron source 212 for providing the electron beam 202. The electron col- umn 210 also comprises an electron or beam optical unit 214. The electron source 212 generates the electron beam 202, and the electron or beam optical unit 214 fo- cuses the electron beam 202 and directs the latter to the lithography mask 100 at
Carl Zeiss SMT GmbH 19 the output of the column 210. The electron column 210 also comprises a deflection unit 216 (scanning unit 216) designed to guide (scan) the electron beam 202 over the surface of the lithography mask 100. Instead of the deflection unit 216 (scan- ning unit 216) arranged within the column 210, use can also be made of – not shown – a deflection unit (scanning unit) arranged outside of the column 210. The device 200 also comprises a detector 218 (here also "image acquisition device") for detecting the secondary electrons and/or backscattered electrons generated in the material of the lithography mask 100 by the incident electron beam 202. For ex- ample, as shown, the detector 218 is arranged around the electron beam 202 in ring-shaped fashion within the electron column 210. As an alternative and/or in ad- dition to the detector 218, the device 200 may also comprise other/further detectors for detecting secondary electrons and/or backscattered electrons (not shown in Fig. 1). The device 200 may optionally also comprise a gas provision unit 220 for supplying process gas to the surface of the lithography mask 100. For example, the gas provi- sion unit 220 comprises a valve 222 and a gas line 224. The electron beam 202 di- rected at a location on the surface of the lithography mask 100 by the electron col- umn 210 can carry out electron-beam-induced processing (EBIP) in conjunction with the process gas supplied by the gas provision unit 220 from the outside via the valve 222 and the gas line 224. In particular, said process comprises a deposition (depositing) and/or an etching of material. The device 200 moreover comprises a computing device 226, for example a com- puter, having a control device 228 and a generating device 230. In the example of Fig. 1, the computing device 226 is arranged outside of the vacuum housing 204. The control device 228 serves e.g. for controlling the device 200. For example, the control device 228 controls the provision of the electron beam 202 by controlling the electron column 210. In this case, the control device 228 inter alia controls the guid- ance of the electron beam 202 over the surface of the lithography mask 100 by con- trolling the scanning unit 216. The control unit 228 can also control the gas provi- sion unit 220 for providing process gas. Moreover, the generating device 230 receives measurement data from the detector 218 and/or other detectors of the device 200 and generates images from the meas- urement data, which images can be displayed on a monitor (not shown). For exam- ple, a spatial resolution of the generated images is of the order of a few nanometres.
Carl Zeiss SMT GmbH 20 Fig. 2 shows a detail of an exemplary microstructured lithography mask 100. Fig. 3 shows the detail of the lithography mask 100 shown in Fig.2 in a cross-sectional view along line III-III in Fig.2. The lithography mask 100 comprises a microstruc- ture 104. For example, the microstructure 104 comprises one or more raised imag- ing structures 106 with lower areas 108 (e.g. trenches 108) therebetween. The raised imaging structures 106 have edges 110, two of which are provided with a ref- erence sign in Fig.2. The lower areas 108 in particular have one or more first seg- ments 112 (if reference is made to a "segment", this could also be referred to as a "portion"). Furthermore, the raised imaging structures 106 comprise one or more second segments 114, which are raised with respect to the one or more first seg- ments 112. Fig.2 only shows two second segments 114 by way of example. Moreover, the microstructured lithography mask 100 has, for example, a flat shape with a main plane of extent E (xy-plane in Figures 2 and 4). A direction perpendicu- lar to the main plane of extent E is referred to as a height direction z of the lithogra- phy mask 100. As shown in the cross section in Fig.3, the at least one first segment 112 of the li- thography mask 100 has a first height H1 in relation to the height direction z of the lithography mask 100. Moreover, the at least one second segment 114 of the lithog- raphy mask 100 has a second height H2, greater than the first height H1, in rela- tion to the height direction z. In particular, the at least one second segment 114 rises by a height ΔH = H2 - H1 above a surface 116 of the at least one first segment 112. In other words, a surface 118 of the at least one second segment is arranged a height ΔH above the surface 116 of the at least one first segment 112. The edges 110 of the at least one second segment 114 each have in particular an edge wall 120 (Fig.3), which is arranged, for example, parallel to the height direc- tion z of the lithography mask 100 and perpendicular to the main plane of extent E (Fig.2) of the lithography mask 100. For example, the lithography mask 100 has a substrate 122 (Fig.3), on which the one or more raised elements 106 (imaging structure), which form the at least one second segment 114, are arranged. An exposed surface of the substrate 122 for ex- ample forms the surface 116 of the at least one first segment 112. Although not shown in the figures, one or more layers (coatings) can also be ar- ranged on the substrate 122 of the lithography mask 100. For example, if the
Carl Zeiss SMT GmbH 21 lithography mask 100 is an EUV lithography mask, then e.g. a protective layer (also referred to as a capping layer), such as a Ru capping layer, can be arranged on the substrate 122. Should one or more layers be arranged on the substrate 122, exposed regions of an uppermost layer of these one or more layers may form the surface 116 of the at least one first segment 112. The lower areas 108, e.g. the substrate 122, and the one or more raised elements 106 of the lithography mask 100 may include different materials from one another or the same material. In other words, the at least one first segment 112 and the at least one second segment 114 may include different materials from one another or the same material. For example, the exposed surface 116 of the at least one first segment 112 and the exposed surface 118 of the at least one second segment 114 may include different materials from one another or the same material. Furthermore, the at least one first segment 112 of the lithography mask 100 can in- clude a light-transmitting or light-reflecting material, and the at least one second segment 114 of the lithography mask 100 can include a light-absorbing material. The microstructured lithography mask 100 is, for example, an EUV or DUV lithogra- phy mask, i.e. it is suitable and intended for use in an imaging process in an EUV or DUV lithography apparatus (for example, the lithography apparatus 1 shown in Fig. 10). For example, the operating light used in the imaging of the lithography mask 100 on a wafer 13 (see Fig.10) with the aid of the lithography apparatus 1 may have a wavelength of between 0.1 nm and 30 nm, preferably between 13 and 14 nm, in particular 13.5 nm. In addition or alternatively, the lithography apparatus 1 may have a numerical aperture greater than 0.3, in particular greater than 0.33, prefera- bly greater than 0.5, for example 0.55, for example between 0.3 and 0.75, in particular greater than 0.6, preferably greater than 0.7. Furthermore, the lithography mask 100 has a reference structure 124 in the present case. The at least one reference structure 124 can be formed by depositing a material on the lithography mask 100 using a process gas. Alternatively, the at least one ref- erence structure 124 may be formed by providing a depression and/or a notch in the lithography mask 100, in particular by way of etching using a process gas. The reference structure 124 is provided in particular to enable drift correction of the particle beam 202 during a repair process. Such a repair process is to be carried out, for example, if the imaging structure 106 has at least one defect site 126 to be re- paired. The reference structure 124 is then preferably provided in the immediate
Carl Zeiss SMT GmbH 22 periphery of the defect site 126 in order to enable drift correction during the repair of the defect site 126 by the particle beam 202. The reference structure 124 is therefore preferably used to control the particle beam 202 according to the method described below with reference to Fig. 4, in particular to enable drift correction in at least one of the spatial directions x, y. Fig.4 shows a flowchart of the method for analysing and/or processing the lithogra- phy mask 100. In a step S1, the at least one reference structure 124 is provided on the lithography mask 100 in such a way that the reference structure 124 is not imaged when the lithography mask 100 is imaged on a wafer 13 in the lithography apparatus 1. The provision S1 can preferably be carried out depending on at least one parameter of the lithography apparatus 1, wherein the parameter is selected from a wavelength of op- erating light of the lithography apparatus 1 and/or an intensity of operating light of the lithography apparatus 1 and/or a numerical aperture (NA) in the lithography ap- paratus 1. In a step S2, an image representation of the reference structure 124 is generated with the aid of the particle beam 202 using the detector 218. In a step S3, the particle beam 202 is further controlled for analysing and/or pro- cessing the lithography mask 100 depending on the image representation of the ref- erence structure 124 generated by means of a particle beam 202. The provision S1 of the reference structure 124 is preferably carried out in depend- ence or under manipulation and/or adaptation and/or special design of a volume and/or a basic geometry and/or a refractive index and/or a material and/or a material composition of the reference structure 124 and/or a distance of the reference structure 124 from at least one part of the imaging structure 106 of the lithography mask 100. Exemplary reference structures 124, which are not imaged on the wafer 13, are shown in Figures 5 to 7 as examples and are explained in more detail below. The reference structure 124 preferably has a maximum dimension of less than or equal to 60 nm, preferably less than or equal to 50 nm, preferably less than or equal to 40 nm, preferably less than or equal to 30 nm, preferably less than or equal to 20 nm, measured in particular parallel to the main plane of extent of the lithogra- phy mask 100. The refractive index n + i*k of the reference structure 124 preferably
Carl Zeiss SMT GmbH 23 has a phase-shifting component n and an absorptive component k. The phase-shift- ing component n is different from the value for the vacuum by preferably at most 0.045. The absorptive component k is different from the value for the vacuum pref- erably by at most 0.02. Fig.5 shows three different reference structures 124 with in each case improved signal-to-noise ratio at least in the secondary electron signal in the detector 218. This improvement can be influenced, for example, by the material and/or the mate- rial composition of the respective reference structure 124. One or more of the follow- ing elements Si, Ba, Ce, La, Br, Rb, Be, Sr, P, S, Ca, Y, B, Sc, Zr, Gd, Nd, C, Ti, Se, F, Cl can be used as a material or in a material composition. According to Fig.5(a), the material of the reference structure 124 is selected such that a secondary electron current I(SE)2 of the reference structure 124 is greater than a secondary electron current I(SE)1 of a region 502 of the lithography mask 100 surrounding the reference structure 124. In addition, the material of the refer- ence structure 124 is chosen such that a backscatter electron current I(BSE)2 of the reference structure 124 is smaller or greater than a backscatter electron current I(BSE)1 of the region 502 surrounding the reference structure 124. The respective secondary electron signal is generated by the primary electron signal PE of the par- ticle beam 202. The material selection is preferably carried out in such a way that a work function of electrons from the two materials is selected differently if possible. According to Fig.5(b), a reference structure 124 has an auxiliary layer 500, which is used to amplify the secondary electron current I(SE)4 and/or the backscatter elec- tron current I(BSE)4 of the at least one reference structure 124. The auxiliary layer 500 is preferably a thin auxiliary layer, which has been deposited on the surface of the lithography mask 100. The reference structure 124 is deposited on the auxiliary layer 500. The material of the auxiliary layer 500 is selected in such a way that the difference in the secondary electron current I(SE)4 and/or the backscatter electron current I(BSE)4 of the reference structure 124 is maximized compared with the sec- ondary electron current I(SE)3 and/or the backscatter electron current I(BSE)3 of the auxiliary layer 500. Preferably: I(SE)3 << I(SE)4 and/or I(BSE)3 << I(BSE)4 or I(BSE)3 >> I(BSE)4. According to Fig.5(c), the geometry of the reference structure 124 is selected in such a way that the work function of the electrons is reduced and the yield of sec- ondary electrons is thereby increased, in particular in comparison with an underly- ing surface 502 provided by the lithography mask 100. For example, the reference
Carl Zeiss SMT GmbH 24 structure 124 is selected such that it has at least one tip and/or a cone shape. Pref- erably: I(SE)6 << I(SE)5. Fig.6 shows an embodiment in which the reference structure 124 is provided by providing a depression or notch 600. Fig.6(a) shows the case of a depression pro- duced by chemical or mechanical action with respect to a surface O of the lithogra- phy mask 100. Fig.6(b) shows an embodiment in which the depression and/or the notch 600 is filled with a material 602 deposited therein, preferably flush with a surface O of the lithography mask 100. Figures 7(a) to 7(c) each show a schematic representation of the lithography mask 100 in a top view, wherein Figures 7(a) to 7(c) each show the lithography mask 100 at different times of a repair process. At a first time, which is shown in Fig.7(a), four reference structures 124 are provided in the immediate periphery around the defect site 126 of the imaging structure 106. The four boxes 700 shown mark the lo- cation where new reference structures can be written or provided as required dur- ing the repair process. The boxes 700 can be set in position by a user on a user in- terface, for example, using software. During the repair process, one or more of the reference structures 124 may be re- moved due to the particle beam 202 and/or due to process gases, and thus are no longer available with sufficient accuracy for drift correction. This is shown schemat- ically in Fig.7(b), wherein the worn or defective reference structures are marked with the reference sign 124b. As a result, new or further reference structures 124c are provided on the lithography mask 100 in order to enable uninterrupted and ac- curate drift correction. According to Fig.7(c), the defective reference structures 124b are no longer shown. Alternatively or additionally, in order to analyse the lithography mask 100 and pro- cess and/or use it based on the analysis, it may be necessary to detect contours of the microstructures 104, i.e. for example the edges 110 of the second raised seg- ments 114. For example, it might be necessary to determine a position and/or an (e.g. two-dimensional) geometric shape of the edges 110 of the second segments 114. Fig.8 shows a top view of a lithography mask 100, in which at least one item of roughness information of an edge 110 or an edge portion 900 is used as a substitute for a reference structure 124 (then optionally not present) for drift correction. As an
Carl Zeiss SMT GmbH 25 example, a line-and-interspace structure is shown as an imaging structure 106 on a lithography mask 100. Such a method is explained in more detail with reference to the schematic flowchart in Fig.9. In a step S51, at least one portion 900 of the at least one edge 110 is detected at a first time by an image-recording device or a detector 218. The detected edge portion 900 contains a roughness fingerprint, i.e. individualizing roughnesses, which allow a unique localization of the edge portion 900. Roughness here is the (e.g. perpendic- ular) deviation from the edge that is specified by the mask design. The roughness is illustrated in Fig.8 by an arrangement of serrated structures with different spike sizes. In a step S52, an edge position of the at least one portion 900 of the at least one edge 110 on the lithography mask 100 is determined based on at least one reference position at the first time. In a step S53, an item of roughness information of the at least one portion 900 of the at least one edge 110 is determined at the first time. In this step, the roughness fingerprint mentioned above is determined in particular, e.g. depending on the spike sizes contained in the acquired image. In a step S54, the at least one portion 900 of the at least one edge 110 is detected at a second time by the image-recording device. In a step S55, an edge position of the at least one portion 900 of the at least one edge 110 on the lithography mask 100 is determined based on at least one reference position at the second time. In a step S56, an item of roughness information of the at least one portion 900 of the at least one edge 110 is determined at the second time. In a step S57, a comparison of the roughness information determined at the first time with the roughness information determined at the second time is carried out. The comparison of the roughness information or the roughness fingerprints can be carried out by pixel-by-pixel image comparison or by comparing a respective trans- formation of the roughness information at the first and second times.
Carl Zeiss SMT GmbH 26 In a step S58, a particle beam 202 used for the repair of the lithography mask 100 is tracked based on the comparison. The at least one portion 900 of the at least one edge 110 can be protected by a pro- tective layer, in particular a protective layer that is removable by a mask cleaning operation. The protective layer preferably has a material containing molybdenum (Mo) or carbon (C). Fig. 10 shows an embodiment of a projection exposure apparatus 1 (lithography ap- paratus), in particular an EUV lithography apparatus. An embodiment of an illumi- nation system 2 of the projection exposure apparatus 1 comprises, in addition to a light source or radiation source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3. A reticle 7 arranged in the object field 5 is exposed, the reticle also being referred to as the lithography mask 100. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable by way of a reticle displacement drive 9, in particular in a scanning direction. Fig. 10 shows, for explanation purposes, a Cartesian coordinate system with an x- direction x, a y-direction y, and a z-direction z. The x-direction x runs perpendicu- larly into the plane of the drawing. The y-direction y runs horizontally, and the z- direction z runs vertically. The scanning direction runs along the y-direction y in Fig. 10. The z-direction z runs perpendicularly to the object plane 6. The projection exposure apparatus 1 comprises a projection optical unit 10. The pro- jection optical unit 10 serves for imaging the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. Alter- natively, an angle different from 0° between the object plane 6 and the image plane 12 is also possible. A structure on the reticle 7 is imaged onto a light-sensitive layer of the wafer 13 ar- ranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable by way of a wafer dis- placement drive 15, in particular along the y-direction y. The displacement firstly of the reticle 7 by way of the reticle displacement drive 9 and secondly of the wafer 13
Carl Zeiss SMT GmbH 27 by way of the wafer displacement drive 15 can be implemented so as to be mutually synchronized. The light source 3 is an EUV radiation source. The light source 3 emits in particular EUV radiation 16, which is also referred to below as used radiation, illumination ra- diation or illumination light. The used radiation 16 has in particular a wavelength in the range between 5 nm and 30 nm. The light source 3 may be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge pro- duced plasma) source. It can also be a synchrotron-based radiation source. The light source 3 may be a free electron laser (FEL). The illumination radiation 16 emanating from the light source 3 is focused by a col- lector 17. The collector 17 can be a collector having one or more ellipsoidal and/or hyperboloidal reflection faces. The illumination radiation 16 may be incident on the at least one reflection surface of the collector 17 with grazing incidence (GI), i.e. at angles of incidence of greater than 45°, or with normal incidence (NI), i.e. at angles of incidence of less than 45°. The collector 17 can be structured and/or coated firstly to optimize its reflectivity for the used radiation and secondly to suppress extrane- ous light. Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optical unit 4. The illumination optical unit 4 comprises a deflection mirror 19 and, disposed downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 may be a plane deflection mirror or, in an alternative to that, a mirror with a beam-influencing effect going beyond the pure deflection effect. Alternatively or ad- ditionally, the deflection mirror 19 may be in the form of a spectral filter, which sep- arates a used light wavelength of the illumination radiation 16 from extraneous light of a different wavelength. Should the first facet mirror 20 be arranged in a plane of the illumination optical unit 4 which is optically conjugate to the object plane 6 as a field plane, this facet mirror is also referred to as a field facet mirror. The first facet mirror 20 comprises a multiplicity of individual first facets 21, which can also be referred to as field facets. Only some of these first facets 21 are illus- trated in Fig.10 by way of example.
Carl Zeiss SMT GmbH 28 The first facets 21 can be embodied as macroscopic facets, in particular as rectangu- lar facets or as facets with an arcuate or partly circular edge contour. The first fac- ets 21 can be embodied as plane facets or alternatively as convexly or concavely curved facets. As known for example from DE 102008009600 A1, the first facets 21 themselves can also be composed in each case of a multiplicity of individual mirrors, in particu- lar a multiplicity of micromirrors. The first facet mirror 20 can be designed in par- ticular as a microelectromechanical system (MEMS system). For details, reference is made to DE 102008009600 A1. The illumination radiation 16 propagates horizontally, i.e. along the y-direction y, between the collector 17 and the deflection mirror 19. In the beam path of the illumination optical unit 4, a second facet mirror 22 is dis- posed downsteam of the first facet mirror 20. Should the second facet mirror 22 be arranged in a pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a spec- ular reflector. Specular reflectors are known from US 2006/0132747 A1, EP 1614 008 B1, and US 6,573,978. The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets. The second facets 23 can likewise be macroscopic facets, which can for example have a round, rectangular or hexagonal boundary, or can alternatively be facets composed of micromirrors. For details, reference is likewise made to DE 102008 009600 A1. The second facets 23 may have plane or, alternatively, convexly or concavely curved reflection surfaces. The illumination optical unit 4 thus forms a doubly faceted system. This fundamen- tal principle is also referred to as a fly's eye integrator. It can be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optical unit 10. In
Carl Zeiss SMT GmbH 29 particular, the second facet mirror 22 can be arranged so as to be tilted in relation to a pupil plane of the projection optical unit 10, as described for example in DE 10 2017220 586 A1. With the aid of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-shaping mirror or actually the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5. In a further embodiment, which is not illustrated, of the illumination optical unit 4, a transfer optical unit may be arranged in the beam path between the second facet mirror 22 and the object field 5 and contributes in particular to the imaging of the first facets 21 into the object field 5. The transfer optical unit may have exactly one mirror or, in an alternative to that, two or more mirrors, which are arranged one be- hind another in the beam path of the illumination optical unit 4. The transfer opti- cal unit may in particular comprise one or two normal-incidence mirrors (NI mir- rors) and/or one or two grazing-incidence mirrors (GI mirrors). In the embodiment shown in Fig. 10, the illumination optical unit 4 has down- stream of the collector 17 exactly three mirrors, specifically the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22. In a further embodiment of the illumination optical unit 4, the deflection mirror 19 can also be omitted, and so the illumination optical unit 4 can then have exactly two mirrors downstream of the collector 17, specifically the first facet mirror 20 and the second facet mirror 22. The imaging of the first facets 21 into the object plane 6 by means of the second fac- ets 23 or using the second facets 23 and a transfer optical unit is, as a rule, only ap- proximate imaging. The projection optical unit 10 comprises a plurality of mirrors Mi, which are consec- utively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1. In the example illustrated in Fig. 10, the projection optical unit 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are likewise possible. The projection optical unit 10 is a doubly obscured optical unit. The penultimate mirror M5 and the last mirror M6 each have a
Carl Zeiss SMT GmbH 30 passage opening for the illumination radiation 16. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.5 and may also be greater than 0.6 and may be, for example, 0.7 or 0.75. Reflection surfaces of the mirrors Mi may be in the form of free-form surfaces with- out an axis of rotational symmetry. Alternatively, the reflection surfaces of the mir- rors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optical unit 4, the mirrors Mi can have highly reflective coatings for the illumina- tion radiation 16. These coatings can be designed as multilayer coatings, in particu- lar with alternating layers of molybdenum and silicon. The projection optical unit 10 has a large object-image offset in the y-direction y be- tween a y-coordinate of a centre of the object field 5 and a y-coordinate of the centre of the image field 11. This object-image offset in the y-direction y can be of approxi- mately the same magnitude as a z-distance between the object plane 6 and the im- age plane 12. In particular, the projection optical unit 10 can have an anamorphic configuration. It has in particular different imaging scales βx, βy in the x- and y-directions x, y. The two imaging scales βx, βy of the projection optical unit 10 are preferably (βx, βy) = (+/-0.25, +/-0.125). A positive imaging scale β means imaging without image inver- sion. A negative sign for the imaging scale β means imaging with image inversion. The projection optical unit 10 consequently leads to a reduction in size with a ratio of 4:1 in the x-direction x, i.e. in a direction perpendicular to the scanning direction. The projection optical unit 10 leads to a reduction in size with a ratio of 8:1 in the y- direction y, i.e. in the scanning direction. Other imaging scales are likewise possible. Imaging scales with the same sign and the same absolute value in the x-direction x and y-direction y are also possible, for example with absolute values of 0.125 or of 0.25. The number of intermediate image planes in the x-direction x and in the y-direction y in the beam path between the object field 5 and the image field 11 can be the same or can differ, depending on the embodiment of the projection optical unit 10. Exam- ples of projection optical units with different numbers of such intermediate images in the x-direction x and y-direction y are known from US 2018/0074303 A1.
Carl Zeiss SMT GmbH 31 In each case, one of the second facets 23 is assigned to exactly one of the first facets 21 for forming in each case an illumination channel for illuminating the object field 5. This can yield in particular illumination according to the Köhler principle. The far field is decomposed into a multiplicity of object fields 5 with the aid of the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 respectively assigned to them. The first facets 21 are each imaged onto the reticle 7 by an assigned second facet 23 and overlaid over one another for the purpose of illuminating the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It pref- erably has a uniformity error of less than 2%. Field uniformity may be achieved by overlaying different illumination channels. The illumination of the entrance pupil of the projection optical unit 10 can be de- fined geometrically by an arrangement of the second facets 23. The intensity distri- bution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channels, in particular the subset of the second facets 23, which guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling. A likewise preferred pupil uniformity in the region of portions of an illumination pupil of the illumination optical unit 4 which are illuminated in a defined manner can be achieved by a redistribution of the illumination channels. Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optical unit 10 are described below. The projection optical unit 10 can have in particular a homocentric entrance pupil. The latter may be accessible. It can also be inaccessible. The entrance pupil of the projection optical unit 10 regularly cannot be exactly illu- minated with the second facet mirror 22. In the case of an imaging process of the projection optical unit 10 that images the centre of the second facet mirror 22 tele- centrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find an area in which the spacing of the aperture rays that is determined in pairs becomes minimal. This area represents the en- trance pupil or an area conjugate thereto in real space. In particular, this area ex- hibits a finite curvature.
Carl Zeiss SMT GmbH 32 It may be the case that the projection optical unit 10 has different positions of the entrance pupil for the tangential beam path and for the sagittal beam path. In this case, an imaging element, in particular an optical structural element, of the trans- fer optical unit, should be provided between the second facet mirror 22 and the reti- cle 7. By means of this optical element, the different positions of the tangential en- trance pupil and the sagittal entrance pupil may be taken into account. In the arrangement of the components of the illumination optical unit 4 illustrated in Fig.10, the second facet mirror 22 is arranged in an area conjugate to the en- trance pupil of the projection optical unit 10. The first facet mirror 20 is in a tilted arrangement in relation to the object plane 6. The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged with a tilt in relation to an arrange- ment plane defined by the second facet mirror 22. The reference structure 124 (Fig.2) described above on the lithography mask 7, 100 is not apparent in the image representation on the wafer 13 (Fig.10), since the illu- mination radiation 16 is not influenced due to the reference structure 124 or influ- enced only uncritically for the imaging process. Although the present invention has been described with reference to exemplary em- bodiments, it is modifiable in various ways.
Carl Zeiss SMT GmbH 33 LIST OF REFERENCE SIGNS 1 Projection exposure apparatus 2 Illumination system 3 Light source 4 Illumination optical unit 5 Object field 6 Object plane 7 Reticle 8 Reticle holder 9 Reticle displacement drive 10 Projection optical unit 11 Image field 12 Image plane 13 Wafer 14 Wafer holder 15 Wafer displacement drive 16 Illumination radiation 17 Collector 18 Intermediate focal plane 19 Deflection mirror 20 First facet mirror 21 First facet 22 Second facet mirror 23 Second facet 100 Lithography mask 104 Microstructure 106 Imaging structure 108 Area 110 Edge 112 Segment 114 Segment 116 Surface 118 Surface 120 Wall 122 Substrate 124 Reference structure 124b Defective reference structure 124c Further reference structure
Carl Zeiss SMT GmbH 34 126 Defect site 200 Repair device 202 Particle beam 204 Housing 206 Pump 208 Sample stage 210 Electron column 212 Electron source 214 Electron or beam optical unit 216 Deflection unit 218 Detector or image-recording device 220 Gas provision unit 222 Valve 224 Gas line 226 Computing apparatus 228 Control device 230 Generating device 500 Auxiliary layer 502 Region or underlying surface 600 Depression or notch 602 Deposited material 700 Box 800 Threshold value 900 Edge portion 1000 Repair system D1-D5 Deposition height Main plane of extent H Height H1 Height H2 Height ΔH Height I(SE)1 Secondary electron current I(SE)2 Secondary electron current I(SE)3 Secondary electron current I(SE)4 Secondary electron current I(SE)5 Secondary electron current I(SE)6 Secondary electron current I(BSE)1 Backscatter electron current I(BSE)2 Backscatter electron current
Carl Zeiss SMT GmbH 35 I(BSE)3 Backscatter electron current I(BSE)4 Backscatter electron current I(BSE)5 Backscatter electron current I(BSE)6 Backscatter electron current M1 Mirror M2 Mirror M3 Mirror M4 Mirror M5 Mirror M6 Mirror O Surface S1-S3 Method steps S51-S58 Method steps x, y, z Direction