Method and apparatus for qualifying a mask in a lithography system

Abstract

To provide a method and device for qualifying a mask of a lithography system.SOLUTION: There is provided a method for qualifying a mask, comprising: a first detection (101), wherein the first detection (101) takes place sequentially; determining a plurality of reference measurement points (24) from the plurality of measurement points (22); second detection (103) of the at least one critical dimension (20) of the mask at the reference measurement points (24) in each case at a temporal distance from the first detection (101) at the measurement points (22) determined as reference measurement points (24); determining a deviation between the first and the second detected critical dimension (20) at each of the reference measurement points (24); determining, depending on the determined deviation, a temporal profile of a correction factor over the measurement time period; and applying a determined temporal profile of the correction factor to the at least one critical dimension (20).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method and also to an apparatus for qualifying a mask for a lithography system. [Background technology]

[0002] Lithography systems in microlithography are used, for example, in the fabrication of finely structured components, such as integrated circuits, having particularly small structures. In a lithography system, an image of a mask (also called a "reticle") illuminated by an illuminator with deep or extreme ultraviolet (DUV or EUV) radiation having a very short wavelength is imaged by a projection system onto a lithography object to transfer the mask structure onto the lithography object.

[0003] To achieve high imaging quality, the mask structure must already have a high degree of precision. To ensure that the mask meets these precision requirements and that the lithography object produced thereby also has the desired characteristics and functions, the mask is checked by a qualification method for deviations from the actual desired structure before use in the lithography system. For this qualification to be as accurate as possible, the mask structure must be tested, for example, by an interferometric method, at as many measurement points as possible. Furthermore, the mask structure is tested several times in succession to determine the deviations between the results ascertained in the measurement passes, so that any influences of the test equipment used for this purpose, such as those due to drifts occurring during the test (e.g., temperature drift or damper drift), can be taken into account by appropriate corrections. Therefore, such qualification methods are associated with a significant time consumption. Summary of the Invention

[0004] It is therefore an object of the present invention, against the background of the problems mentioned above, to provide an improved method and an improved device that allows qualification of masks of a lithography system to be carried out as accurately as possible with minimal time expenditure.

[0005] The solution according to the invention resides in the features of the independent claims. The independent claims relate to advantageous developments.

[0006] The present invention relates to a method for qualifying a mask for a lithography system, the mask having a plurality of predefined measurement points for detecting one or more critical dimensions of the mask at each measurement point, the method comprising: - first detections of at least one critical dimension of the mask at the measurement points, the first detections being performed sequentially and the duration of the first detections defining a measurement time period; - determining a plurality of reference measurement points from the plurality of measurement points, the number of reference measurement points being less than the number of measurement points; - a second detection of at least one critical dimension of the mask at a reference measurement point, in each case at a time distance from the first detection at the measurement point determined as the reference measurement point; - determining a deviation between the first and second detected critical dimensions at each of the reference measurement points; - determining a temporal profile of a correction factor over the measurement time period in response to the determined deviation; - applying the determined temporal profile of the correction factor to at least one critical dimension to obtain a corrected critical dimension of the mask; A method is disclosed, comprising:

[0007] First, some terms used in connection with the present invention are explained below.

[0008] "Critical dimension" refers to the dimension of a critical feature of a mask's structure, such as the minimum linewidth of an individual line, the minimum linewidth of closely spaced lines, and the minimum size of a circular area. The uniformity of the critical dimension has a significant impact on the imaging quality of the lithography process and therefore on the quality of the structure transferred to the lithography object. Critical dimensions can be detected, for example, by interferometric methods. Critical dimensions can be expressed, for example, as values ​​having the unit [nm].

[0009] "Measurement point" should be understood to mean such an area of ​​the mask where at least one critical dimension of the object to be detected can be ascertained. If, for example, the minimum line width of an individual line is intended to be the object to be detected, the measurement point can have at least a range that covers the entire line width. Therefore, a measurement point for detecting the minimum line width of adjacent lines can also further cover the intermediate area between the two lines.

[0010] In particular, "detecting at least one critical dimension" may also include detecting multiple critical dimensions. In each case, the critical dimension to be detected may depend, for example, on the configuration and suitability of predefined measurement points. For example, measurement points may be predefined such that all critical dimensions of the mask required for mask qualification can be detected.

[0011] The method according to the invention is, for example, part of an alignment method for a mask for an EUV lithography system.

[0012] The present invention includes a useful method for qualifying a mask of a lithography system, which takes into account the time profile of the correction factor for at least one critical dimension of the mask to obtain a corrected critical dimension. To determine the correction factor, the critical dimension to be considered is sequentially detected at all measurement points of the mask at a first time, and then at selected reference measurement points constituting a subset of the measurement points at a second time. Based on the detected critical dimensions, a deviation between the first and second detected critical dimensions for these reference measurement points can be determined, and the time profile of the correction factor over the measurement time period of the first detection can be ascertained therefrom and applied to the critical dimension to be considered in each case. Due to the fact that only some of the measurement points need to be considered in the further detection process required to determine the deviation in the method according to the present invention, the time required for the second detection can be significantly shorter. As a result, the overall time required for the qualification method can be significantly reduced.

[0013] In one embodiment, determining the plurality of reference measurement points depends on the temporal distribution of the measurement times of the measurement points within the measurement time period. Preferably, the measurement times of the measurement points determined as reference measurement points are at the same temporal distance from one another so as to be uniformly distributed in time within the measurement time period. This allows the deviation between the first and second detected critical dimensions to be determined in a uniformly distributed manner across the plurality of measurement points, thereby allowing the temporal profile of the correction factor to be determined particularly accurately.

[0014] Preferably, determining the time profile of the correction factor comprises determining a reference curve passing through the deviations determined for each reference measurement point, in this way the deviation of the critical dimension under consideration can be estimated sufficiently accurately even for measurement points that are not determined as reference measurement points, which makes it possible to determine the time profile of the correction factor with higher accuracy.

[0015] As an example, the method further includes a third detection of at least one critical dimension of the mask at at least some of the reference measurement points at a position a certain temporal distance from the second detection, wherein determining the deviation further depends on the further detected critical dimension. As an example, an average value is formed from the values ​​of the detected critical dimensions ascertained during the second and third detections, and a deviation between the first detected critical dimension and the average value of the second and third detected critical dimensions is determined. By the third detection, and further taking the third detected critical dimension into account when determining the deviation, the temporal profile of the correction factor can be determined more accurately.

[0016] Advantageously, the mask has at least 500 measurement points, preferably at least 700 measurement points. Alternatively or additionally, the plurality of reference measurement points comprises at most 10%, preferably at most 5%, of the measurement points. With these numbers of measurement points and reference measurement points, the method constitutes a particularly efficient possibility for sufficiently accurate qualification of masks for lithography systems.

[0017] In particular, the first detection, the second detection and / or the third detection may in each case comprise multiple detection of at least one critical dimension, wherein the detected critical dimension in each case may here be obtained by averaging over the multiple detected critical dimensions in each case.

[0018] According to one embodiment, the method further comprises outputting a signal if the deviation determined at the reference measurement point exceeds a predefined threshold. By way of example, a threshold for still acceptable deviations is predefined for the critical dimensions, preferably for all detectable critical dimensions in each case. If determining the deviation of the critical dimension considered for one reference measurement point or for a minimum number of reference measurement points in each case results in a value exceeding the predefined threshold, a signal can be output at a suitable user interface. This signal can be an acoustic signal, for example, a warning sound, or a visual signal, for example, a message on a display. Potential malfunctions of an apparatus used to perform the method for qualifying a mask of a lithography system, such as incorrect setting of environmental conditions during the execution of the method, or incorrect setting of an imaging unit of the apparatus, can be signaled in this way.

[0019] The present invention further discloses an apparatus for qualifying a mask for a lithography system, the mask having a plurality of predefined measurement points for detecting one or more critical dimensions of the mask at each measurement point, the apparatus comprising a mask holder, an image capture unit, a processing unit and an evaluation unit, the evaluation unit being configured to perform the method according to the present invention by means of the mask holder, the image capture unit and the processing unit.

[0020] The apparatus according to the invention is for example a correspondingly configured mask metrology apparatus for aligning masks for EUV lithography systems.

[0021] For a more detailed description of further advantageous developments of the device, reference is made to the development of the method described above, which in turn can be developed with further features described in connection with the device.

[0022] The above-described embodiments and configurations should be understood as examples only and are not intended to limit the present invention in any way.

[0023] The invention is explained in more detail below by way of example on the basis of advantageous embodiments with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows a schematic diagram of an exemplary embodiment of a lithography system; [Figure 2] 1 shows a schematic flow diagram of the method according to the present invention according to an exemplary embodiment; [Figure 3] 10 shows a diagram of critical dimensions detected at a number of measurement points and a reference measurement point, respectively, according to an exemplary embodiment; [Figure 4] 10 is an illustration of a diagram of critical dimension deviations determined for a number of reference measurement points in accordance with an illustrative embodiment; [Figure 5] 10 is an illustration of a spatial distribution of critical dimension deviations determined in accordance with an illustrative embodiment; [Figure 6] 1 shows a schematic diagram of an apparatus according to the present invention according to an exemplary embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0025] 1 shows a schematic representation of an exemplary embodiment of a lithography system, an EUV lithography system 1. The EUV lithography system 1 comprises an illumination apparatus 10 and a projection apparatus 11. A mask 13, which is arranged at an object plane 12 in an object field, is illuminated using the illumination apparatus 10.

[0026] The illumination device 10 comprises an illumination radiation source 14 which emits electromagnetic radiation in the EUV range, i.e. in particular with a wavelength between 5 nm and 100 nm. The illumination radiation emitted by the illumination radiation source 14 is first focused by a collector 15 into an intermediate focal plane 16.

[0027] The illumination device 10 comprises a deflection mirror 17, by means of which the illumination radiation emitted by the illumination radiation source 14 is deflected onto a first facet mirror 18. A second facet mirror 19 is arranged downstream of the first facet mirror 18. The first facet mirror 18 and the second facet mirror 19 each comprise a number of micromirrors which are in each case individually pivotable about two axes extending perpendicular to each other. The individual facets of the first facet mirror 18 are imaged into the mask 13 by means of the second facet mirror 19.

[0028] Using the projection device 11, a mask 13 is imaged via a plurality of mirrors 8 onto a photosensitive layer of a wafer arranged in an image plane 9. Various mirrors of the EUV lithography system 1, from which the illumination radiation is reflected, are embodied as EUV mirrors. The EUV mirrors are provided with a highly reflective coating, for example in the form of a multilayer coating, in particular in the form of a multilayer coating having alternating layers of molybdenum and silicon. The method according to the invention relates to the qualification of such a mask 13 in order to verify whether its quality is sufficient for use in the lithography system 1.

[0029] 2 shows a schematic flow diagram of an exemplary embodiment of a method 100 according to the present invention for qualifying a mask 13 for a lithography system 1. The mask 13 has a plurality of predefined measurement points 22 for detecting one or more critical dimensions 20 at each measurement point 22 of the mask 13.

[0030] Step 101 comprises performing a first detection of at least one critical dimension 20 of the mask 13 at a measurement point 22. This is done sequentially by an interferometric method. The duration of the first detection 101 defines a measurement time period.

[0031] 3, the critical dimension 20 detected in each case for the measurement points 22 in step 101 is plotted with values ​​between 47.6 nm and 48.4 nm. The number of measurement points 22 is 786. The duration of the first detection 101 is 7 hours.

[0032] In step 102, a plurality of reference measurement points 24 are determined from the plurality of measurement points 22. In this case, the number of reference measurement points 24 is less than the number of measurement points 22, in this example 30, and therefore less than 5% of the number of measurement points 22. The reference measurement points 24 determined from the plurality of measurement points 22 are similarly shown in FIG.

[0033] In this embodiment, the determining step 102 depends on the temporal distribution of the measurement times of the measurement points 22 within the measurement time period. In this way, the reference measurement points 24 can be determined from among the measurement points 22 by taking into account their respective measurement times within the duration of the first detection 101. In the described embodiment, the reference measurement points 24 are determined such that the measurement times of the measurement points 22 determined as reference measurement points 24 are at the same temporal distance from one another and are therefore uniformly distributed in time within the measurement time period.

[0034] At the reference measurement points 24, a second detection 103 of at least one critical dimension 20 of the mask 13 is in each case carried out at a certain temporal distance from the first detection 101 at the measurement point 22 determined as the reference measurement point 24. The values ​​of these second detected critical dimensions 20 are also plotted for the individual reference measurement points 24 in Figure 3. The duration of the second detection 103 is 20 minutes, which is therefore significantly shorter than the duration of the first detection 101.

[0035] Step 104 involves determining the deviation 21 between the first and second detected critical dimensions 20 at each of the reference measurement points 24. To this end, for each measurement point 22 determined as a reference measurement point 24, the deviation 21 of the value of the second detected critical dimension 20 at that measurement point 22 from the value of the critical dimension 20 previously detected in step 101 is determined. In the illustrated embodiment, the deviation 21 is determined by subtracting the value of the first critical dimension 20 detected at the measurement point 22 determined as the reference measurement point 24 from the value of the second critical dimension 20 detected at this reference measurement point 24.

[0036] 4, where the value of the deviation 21 between the first and second detected critical dimensions 20, determined in step 104, is in each case plotted for a reference measurement point 24 (of the plurality of measurement points 22). In this example, the illustrated deviation 21 assumes values ​​from the range of -0.03 nm to 0.15 nm.

[0037] Step 105 involves determining a time profile of a correction factor over the measurement time period that depends on the deviation 21 between the first and second detected critical dimensions 20 determined in step 104 .

[0038] In the example presented, step 105 of determining the temporal profile of the correction factor comprises determining a reference curve passing through the deviations 21 determined for the reference measurement points 24 of the critical dimension 20 considered in each case. To determine the reference curve, a curve passing through the deviations 21 determined for the reference measurement points 24 in step 104 can be provided by an n-th degree polynomial.

[0039] Since the first detections 101 at the measurement points 22 are performed sequentially over a measurement time period defined by the duration of the first detections 101, in this example 7 hours, the temporal profile of the deviation 21 can be ascertained from the profile of the deviation 21 determined at the reference measurement points 24. It is then possible to determine the temporal profile of the correction factor based on the change in the deviation 21 determined in this temporal profile.

[0040] In the described embodiment, in step 106 the determined temporal profile of the correction factor is applied to at least one critical dimension 20, such that the correction factor and its temporal profile for the considered critical dimension 20 of the mask 13 are taken into account in the method for aligning the mask 13 used in the lithography system 1. Thus, alignment of the mask 13 can be performed depending on the critical dimension of the mask 13 corrected as described above.

[0041] Furthermore, the method 100 may further comprise, as a further step 303, a third detection of the at least one critical dimension 20 of the mask 13 at the reference measurement points 24 or at least some of the reference measurement points 24, the third detection being performed at a time distance from the second detection 103. Thus, the step 104 of determining the deviation 21 of the at least one critical dimension 20 may additionally be performed in a manner dependent on the at least one critical dimension 20 additionally detected in step 303.

[0042] Similar to the critical dimensions detected in step 103, for each additional critical dimension detected in step 303 at each measurement point 22 determined as a reference measurement point 24, a deviation 21 can be determined between the first critical dimension 20 detected (step 101) at that measurement point 22 and the third detected (step 303) critical dimension 20. These additional determined deviations 21 are similarly illustrated in FIG. 4 as a profile 304 across the reference measurement point 24.

[0043] Taking into account the deviation 21 of the at least one critical dimension 20 determined respectively at each of the reference measurement points 24, an averaging can be performed, and an averaged deviation 21 of the critical dimension 20 considered in each case can be determined for each of the reference measurement points 24. A profile 306 of such an averaged deviation 21 across the reference measurement points 24 is also shown in Figure 4. Accordingly, step 105 of determining the temporal profile of the correction factor can be performed depending on the averaged deviation 21 determined as described above.

[0044] The method 100 further provides a step 401 of outputting a signal if the deviation 21 determined for the reference measurement point 24 is above a predefined threshold. In this case, depending on the available user interface, an alarm sound is output and / or a corresponding alarm message is displayed.

[0045] 5 shows a diagram of deviations 21 determined according to an exemplary embodiment between first and second detected critical dimensions 20 that exceed a predefined threshold in a spatial distribution over an area of ​​mask 13 extending in each case by 140 mm in the x and y directions. The x and y axes show the respective coordinates of measurement points 22 and reference measurement points 24 on the area of ​​mask 13. In the areas highlighted in black, the deviations 21 determined in each case exceed the threshold.

[0046] A first detection 101 of the critical dimension 20 at the measurement points 22 is performed line by line, proceeding from the bottom left to the top right. In the region of the mask 13 at the bottom left, there is a larger region of the reference measurement points 24, where, compared to further regions of the area of ​​the mask 13, the determined deviation 21 exceeds a threshold. It can be derived that the deviation 21 is larger at the beginning of the detection 101 than towards the end of the detection 101, which is reflected by a decrease in the deviation 21 in the temporal profile. Therefore, in step 105, a correction factor and its temporal profile are also determined and applied to the critical dimension 20 considered, in such a way that its influence decreases with increasing duration of the lithography process.

[0047] 6 shows an apparatus 30 for qualifying a mask 13 for a lithography system 1, the mask 13 having a plurality of predefined measurement points 22 for detecting one or more critical dimensions 20 of the mask 13 at each measurement point 22. The apparatus 30 comprises a mask holder 32, a processing unit 34, an imaging unit 36, and an evaluation unit 38, the evaluation unit 38 being operatively connected to the mask holder 32, the processing unit 34, and the imaging unit 36. The evaluation unit 38 is configured to perform the method 100 described above with the aid of the mask holder 32, the imaging unit 36, and the processing unit 34.

[0048] In this case, the mask holding part 32 is controlled to enable the imaging unit 36 ​​to perform a first detection 101 of at least one critical dimension 20 of the mask 13 held by the mask holding part 32 at the measurement point 22. The imaging unit 36 ​​then performs such first detections 101, the first detections 101 being performed sequentially and the duration of the first detections 101 defining a measurement time period.

[0049] Furthermore, the processing unit 34 determines a plurality of reference measurement points 24 from the plurality of measurement points 22 (step 102 ), the number of reference measurement points 24 being less than the number of measurement points 22 .

[0050] Subsequently, the imaging unit 36 ​​performs a second detection 103 of at least one critical dimension 20 of the mask 13 at a position at a certain temporal distance from the first detection 101 at the measurement point 22 determined as the reference measurement point 24, in each case at the reference measurement point 24, and for that purpose the mask 13 is positioned accordingly by the mask holder 32.

[0051] The processing unit 34 determines a deviation 21 between the first and second detected critical dimensions 20 at each of the reference measurement points 24 (step 104) and determines a temporal profile of a correction factor over the measurement time period (step 105) depending on the determined deviation 21. The evaluation unit 38 then performs a step 106 of applying the determined temporal profile of the correction factor to the at least one critical dimension 20 in order to obtain a corrected critical dimension of the mask 13 by the processing unit 34.

[0052] The embodiments of the invention described herein, and the optional features and characteristics each mentioned in connection therewith, are also to be understood as being disclosed in all combinations with each other. In particular, in this case, the description of a feature included in an embodiment should not be understood as being essential or essential for the functioning of that embodiment, unless expressly stated to the contrary. [Explanation of symbols]

[0053] 1 Lithography System 10. Lighting equipment 13 Mask 14 Illumination Radiation Source 15 Light Concentrator 16 Intermediate focal plane 20 Critical dimensions 21 Deviation 22 measurement points 24 Reference measurement points 30 equipment 32 Mask holder 34 Processing Unit 36 Imaging unit 38 evaluation units

Claims

1. 1. A method (100) for qualifying a mask (13) for a lithography system (1), the mask (13) having a plurality of predefined measurement points (22) for detecting one or more critical dimensions (20) of the mask (13) at each measurement point (22), the method (100) comprising: - first detections (101) of at least one critical dimension (20) of said mask (13) at said measurement points (22), said first detections (101) being performed sequentially and the duration of said first detections (101) defining a measurement time period; - determining (102) a number of reference measurement points (24) from said number of measurement points (22), the number of reference measurement points (24) being less than the number of measurement points (22); a second detection (103) of the at least one critical dimension (20) of the mask (13) at a position at a certain time distance from the first detection (101) at the measurement point (22) determined as a reference measurement point (24), in each case at the reference measurement point (24); determining (104) the deviation (21) between said first and said second detected critical dimensions (20) at each of said reference measurement points (24); determining (105) a temporal profile of a correction factor over the measurement time period as a function of the determined deviation (21); applying (106) said determined temporal profile of said correction factor to said at least one critical dimension (20) to obtain a corrected critical dimension of said mask (13); A method (100) comprising:

2. The method (100) of claim 1, wherein determining (102) the plurality of reference measurement points (24) depends on a temporal distribution of measurement times of the measurement points (22) within the measurement time period.

3. 3. The method (100) according to claim 1 or claim 2, wherein determining (105) the temporal profile of the correction factor comprises determining a reference curve passing through the deviations (21) determined for each of the reference measurement points (24).

4. a third detection (303) of the at least one critical dimension (20) of the mask (13) at at least a portion of the reference measurement points (24) at a time distance from the second detection (103), the determination (104) of the deviation (21) being further dependent on the third detected critical dimension (20); The method (100) of claim 1 or claim 2, further comprising:

5. 3. The method (100) of claim 1 or claim 2, wherein the mask (13) has at least 500 measurement points (22).

6. The method (100) of claim 1 or claim 2, wherein the plurality of reference measurement points (24) includes up to 10% of the measurement points (22).

7. 3. The method (100) according to claim 1 or claim 2, wherein the first detection (101) and / or the second detection (103) in each case comprises multiple detection of the at least one critical dimension to form an average value.

8. The method (100) of claim 4, wherein the first detection (101), the second detection (103) and / or the third detection (303) in each case include multiple detection of the at least one critical dimension to form an average value.

9. 3. The method (100) according to claim 1 or claim 2, wherein the measurement points (22) are predefined such that all critical dimensions of the mask (13) required for the qualification of the mask (13) are detectable.

10. - outputting a signal (401) if said deviation (21) determined at a reference measurement point (24) exceeds a predefined threshold value; The method (100) of claim 1 or claim 2, further comprising:

11. 1. An apparatus (30) for qualifying a mask (13) for a lithography system (1), the mask (13) having a plurality of predefined measurement points (22) for detecting one or more critical dimensions (20) of the mask (13) at each measurement point (22), the apparatus (30) comprising: a mask holder (32), an imaging unit (36), a processing unit (34), and an evaluation unit (38), the evaluation unit (38) being configured to perform the method (100) of claim 1 or claim 2 by means of the mask holder (32), the imaging unit (36), and the processing unit (34).

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