KR20180104022A - Beam measurement system, lithography system, and method - Google Patents

Abstract

A beam measurement system (30), a lithography system, and a method are disclosed. In one arrangement, the beam measurement system 30 is for determining at least one of the characteristics of the plasma 7 of the laser-generated plasma radiation source, the image of the plasma, and the collectors 5, The beam measurement system includes at least one sensor (32) configured to receive at least a portion of the radiation beam (B) output from the collector. Each sensor unit includes a first patterned element 34, a second patterned element 36, and a detector 38 configured to detect radiation that has passed through the first patterned element and the second patterned element. . The first patterned element and the second patterned element are each positioned with respect to one another to provide a combined transmittance that is patterned with a spatially non-uniform transmittance and has a non-uniform angular dependence on the direction of incidence of radiation on the sensor unit.

Description

Beam measurement system, lithography system, and method

Cross-reference to related application

This application claims priority of EP Application No. 16151638.0, filed on January 18, 2016, the entire contents of which are incorporated herein by reference.

The present invention relates to a beam measurement system, a lithography system and a method. In particular, the present invention relates to determining the performance or alignment of a radiation source.

A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. The lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). The lithographic apparatus may, for example, project a projection pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

The wavelength of the radiation used by the lithographic apparatus to project a pattern onto a substrate may be determined by a combination of factors such as the refractive index of the material through which the radiation passes and the numerical aperture of the projection system, Determine the size. Lithographic apparatus employing EUV radiation, which is electromagnetic radiation having a wavelength in the range of 5-20 nm, can be used to reduce features smaller than conventional lithographic apparatus (e.g., can use electromagnetic radiation having a wavelength of 193 nm) Lt; / RTI >

If a plasma is used to produce EUV radiation, the lithographic performance can be evaluated by measuring the intensity of an image of the plasma formed at the intermediate focus between the collector used to focus the radiation emitted by the plasma and the illumination system that conditions the radiation beam output from the collector Location, size, or shape. The nature of the image of the plasma depends on the plasma itself and the alignment between the collector and the illumination system. Prior art systems for measuring alignment between a collector and a lighting system are relatively complex and may not be effective when there is a large deviation in alignment. Also, if the prior art system relies on the imaging of the target formed on the collector, the contamination of the collector during use may reduce the reliability or accuracy of the measurement.

It is an object of the present invention to provide a device for determining the characteristics of an image of a plasma, a plasma, and / or an alignment between a collector and an illumination system, more simply, more reliably and / And a method thereof.

According to one aspect, a beam measurement system for determining at least one characteristic of a plasma of a laser-generated plasma radiation source, an image of a plasma, and a collector,

And at least one sensor unit configured to receive at least a portion of the radiation beam output from the collector, each sensor unit comprising a first patterned element, a second patterned element, and a second patterned element, And a detector configured to detect radiation that has passed through the patterned element, wherein the first patterned element and the second patterned element are each patterned with a spatially non-uniform transmittance, and wherein the radiation pattern on the sensor unit And are positioned relative to one another to provide a combined transmittance that is non-uniformly angularly dependent on the direction of incidence.

Thus, a beam measurement system is provided that can accurately determine the characteristics of an image, plasma, or collector of a plasma using relatively simple component and analysis techniques. The image of the plasma and the characteristics of the plasma do not necessarily depend on the pattern formed on the collector. In this case, even if the collector is contaminated, it does not interfere with the measurement. This approach is effective even when there is a relatively large deviation in alignment.

In one embodiment, the beam measurement system comprises a group of sensor units, wherein each sensor unit in the group comprises a first patterned element and a second patterned element having an angularly dependent combined transmittance, The angular dependencies for the group of sensor units are different from each other.

In one embodiment, different angular dependencies are obtained by providing different relative positioning between the same patterns in the first patterned element and the second patterned element in each sensor unit.

In one embodiment, the beam measurement system includes an array comprising a plurality of groups of sensor units. In one embodiment, the beam measurement system includes a plurality of arrays, each array being positioned to receive a different portion of the radiation beam.

In one embodiment, each of the first patterned element and the second patterned element is patterned into a periodic array of regions of high transmittance separated by a region of lower transmittance.

In one embodiment, the first patterned element and the second patterned element are substantially planar, and the first patterned element and the second patterned element are separated from each other in a direction perpendicular to the plane of the first patterned element do.

In one embodiment, the determined characteristics of the plasma, the image of the plasma, and the at least one of the collectors are determined by the shape of the image of the plasma at the intermediate focus, the size of the image of the plasma at the intermediate focus, Wherein the intermediate focus is a focus formed by the collector between the collector and the illumination system configured to condition the beam of radiation. Optionally, at least one of the at least one sensor unit is positioned in the far field relative to the intermediate focus.

In one embodiment, the at least one determined characteristic of the plasma, the image of the plasma, and the collector includes at least one of the shape of the plasma, the size of the plasma, and the location of the plasma.

In one embodiment, the collector includes a patterned area, and the beam measurement system includes at least one sensor unit positioned to receive radiation modulated by the patterned area, wherein the modulation detected by the detector The ratio of the emitted radiation being dependent on at least one of the position of the collector relative to the illumination system configured to condition the beam of radiation and the orientation of the collector relative to the illumination system. Optionally, the patterned region comprises a portion of a plurality of concentric rings.

In one embodiment, the first patterned elements are patterned in a periodic array with a first pitch, of a region of high transmittance separated by a region of lower transmittance. The second patterned element is patterned in a periodic array having a second pitch that is different from or equal to the first pitch of the regions of high transmittance separated by the regions of lower transmittance. The received radiation modulated by the patterned area of the collector periodically has a pitch different from either or both of the first pitch and the second pitch.

In one embodiment, the beam measurement system further comprises a sensor unit mounting system configured to cause at least one of the sensor units to be moved so as to selectively receive radiation modulated by one of a plurality of different patterned areas of the collector .

In one embodiment, at least one of the determined characteristics of the plasma, the image of the plasma, and the collector includes at least one of the position of the collector relative to the illumination system and the orientation of the collector relative to the illumination system.

In one embodiment, the patterning of the first patterned element and the second patterned element allows the diffraction effect to be ignored. Optionally the minimum characteristic dimension of the patterning in the first patterned element and the minimum characteristic dimension of the patterning in the second patterned element are at least 10 times greater than the wavelength of the radiation generated by the laser-generated plasma radiation source.

In one embodiment, the measurement system further comprises a control device configured to control the laser-generated plasma radiation source based on an output from the at least one sensor unit.

According to an embodiment of the present invention, there is provided a lithographic apparatus comprising:

(a) a radiation source configured to collect radiation emitted from a plasma using a collector and output a radiation beam from the collector; And

(b) a beam measurement system configured to determine a plasma, an image of the plasma, and at least one characteristic of the collector,

Wherein the beam measurement system includes at least one sensor unit configured to receive at least a portion of the radiation beam,

Each sensor unit including a first patterned element, a second patterned element, and a detector configured to detect radiation that has passed through the first patterned element and the second patterned element,

Within each sensor unit, the first patterned element and the second patterned element are each patterned with a spatially non-uniform transmittance, and the combined transmittance, which has a non-uniform angular dependence on the direction of incidence of radiation on the sensor unit, Wherein the lithographic apparatus is positioned relative to one another to provide a lithographic projection apparatus.

According to one aspect, the method includes determining at least one characteristic of a plasma in a laser-generated plasma radiation source, an image of the plasma, and a collector by measuring a characteristic of the beam of radiation output by the laser-generated plasma radiation source Wherein measuring the characteristics of the radiation beam comprises receiving at least a portion of the radiation beam using at least one sensor unit, each sensor unit comprising a first patterned element, a second patterned element, And a detector configured to detect radiation that has passed through the first patterned element and the second patterned element, wherein the first patterned element and the second patterned element each have a spatially non-uniform transmittance And a non-uniform angular dependence on the direction of incidence of radiation on the sensor unit Are positioned relative to each other to provide a combined transmittance.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:
- Figure 1 depicts a lithography system comprising a lithographic apparatus and a radiation source according to an embodiment of the invention;
Figure 2 schematically shows a radiation source according to an embodiment of the invention;
Figure 3 shows an exemplary light beam incident on the sensor unit;
4 shows an exemplary light ray incident on different relative positions between the first and second patterned elements in a sensor unit of the type shown in Fig. 3; Fig.
Figure 5 shows the angular dependence of the combined transmittance through the first and second patterned elements in the sensor unit;
- Figure 6 shows the angular dependence of the combined transmittance through the first and second patterned elements in the sensor unit according to another embodiment;
7 shows an array of groups of sensor units according to one embodiment (figure above) and one of the groups in more detail (lower drawing);
8 is a schematic side view showing the capture of the radiation output from the collector on the array of groups of sensor units; Fig.
Figure 9 shows four arrays of groups of sensor elements mounted on a sensor unit mounting system;
10 shows an array of the groups of sensor units according to another embodiment (figure above) and one of the groups in more detail (figure below);
11 shows the relative alignment between the patterned area on the collector mapped on the far field and the first and second patterned elements of the 3x3 grid of nine sensor units;
12 shows the arrangement of FIG. 11 after a transition of the position of the far field-mapped patterned area caused by a change in position and / or alignment of the collector; And
Figure 13 shows an exemplary pattern on a collector comprising a plurality of concentric rings.

Figure 1 illustrates a lithography system including a radiation system with a beam measurement system 30 in accordance with an embodiment of the present invention. The lithography system includes a radiation source (SO) and a lithographic apparatus (LA). The radiation source SO is configured to generate an extreme ultra-violet (EUV) radiation beam B. The lithographic apparatus LA includes a support structure MT configured to support an illumination system IL, a patterning device MA (e.g., a mask), a projection system PS, and a substrate And a table WT. The illumination system IL is configured to condition the radiation beam B prior to entering the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. [ The substrate W may comprise a previously formed pattern. In this case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W.

Therefore, both the radiation source SO, the illumination system IL, and the projection system PS can be constructed and implemented such that they can be isolated from the external environment. At a pressure below atmospheric pressure, a gas (e.g., hydrogen) may be provided in the radiation source SO. Vacuum may be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure can be provided in the illumination system IL and / or the projection system PS.

The radiation source SO shown in Fig. 1 is a type that can be called a laser-generated plasma (LPP) source. A laser 1, for example a CO ₂ laser, is implemented to transfer energy through a laser beam 2 to a fuel such as tin Sn provided from a fuel emitter 3. Although the annexes are referred to in the following description, any suitable fuel may be used. The fuel may be in the form of, for example, a liquid, for example a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct the tin, for example in the form of a droplet, along the trajectory into the plasma forming region 4. The laser beam 2 is incident on the tin in the plasma forming region 4. When the laser energy is transmitted to the tin, the plasma 7 is generated in the plasma forming region 4. [ The radiation containing the EUV radiation is emitted from the plasma 7 while the de-excitation and the recombination of the ions of the plasma take place.

The EUV radiation is focused and focused by an incident radiation collector 5 (more generally commonly referred to as a normal incidence radiation collector), which is nearly vertical. The collector 5 may have a multilayer structure implemented to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm or 6.4-7.2 nm). The collector 5 may have an elliptical configuration with two elliptical focus points. The first focus may be in the plasma forming region 4 and the second focus may be in the middle focus 6 discussed below.

The laser 1 may be separated from the radiation source SO. When separated, the laser beam 2 is directed from the laser 1 to a radiation source (not shown), for example, with the aid of a beam delivery system (not shown) comprising a suitable directing mirror and / or a beam expander, SO). The laser 1 and the radiation source SO can be collectively considered as a radiation system.

The radiation reflected by the collector (5) forms a radiation beam (B). The radiation beam B is focused at point 6 to form an image of the plasma-forming region 4, which now operates as a source of virtual radiation for the illumination system IL. The point 6 at which the radiation beam B is condensed may be referred to as intermediate focus. The radiation source SO is embodied such that the intermediate focus 6 is located at or close to the opening 8 in the sealing structure 9 of the radiation source.

The radiation beam B is transmitted from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a polyhedral pupil mirror device 11. The faceted field mirror device 10 and the polyhedral pupil mirror device 11 together provide a radiation beam B having a desired cross-sectional shape and a desired angular distribution. The radiation beam B is incident on the patterning device MA, which is transmitted from the illumination system IL and held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the polyhedral field mirror device 10 and the polyhedral type pupil mirror device 11.

After being reflected from the patterning device MA, the patterned beam of radiation B enters the projection system PS. The projection system includes a plurality of mirrors configured to project a radiation beam B onto a substrate W held by a substrate table WT. The projection system PS applies a reduction factor to the radiation beam to form an image with a smaller feature than the corresponding feature on the patterning device MA. For example, a reduction factor of 4 may be applied. Although the projection system PS has two mirrors in Figure 1, the projection system may include any number of mirrors (e.g., six mirrors).

Fig. 2 shows a laser-generated plasma (LPP) radiation source SO2 having a configuration different from that of the radiation source shown in Fig. The radiation source (SO2) comprises a fuel emitter (3) configured to deliver fuel to the plasma forming region (4). While any suitable materials may be used, the fuel may be, for example, tin. The pre-pulsed laser 16 emits a pre-pulsed laser beam 17 impinging on the fuel. The pre-pulsed laser beam 17 serves to change characteristics such as its size and / or shape by pre-heating the fuel. The main laser 18 emits a main laser beam 19 incident on the fuel after the pre-pulse laser beam 17. The main laser beam transfers energy to the fuel to convert the fuel to EUV radiation that emits the plasma 7. The mechanism of operation up to now can also be applied to the radiation source SO described above with reference to Fig. However, the radiation collector 20 of FIG. 2 is different from the radiation collector 5 of FIG. 1 as described later.

The radiation collector 20, which may be a so-called grazing incidence collector, is configured to focus the EUV radiation and focus the EUV radiation to a point 6, which may be called an intermediate focus. Thus, the image of the radiation-emitting plasma 7 is formed at the intermediate focal point 6. [ The enclosure structure 21 of the radiation source SO2 comprises an aperture 22 which is at or near the intermediate focal point 6. The EUV radiation passes through the aperture 22 and is transmitted to the illumination system of the lithographic apparatus (e.g., as shown schematically in Figure 1).

The radiation collector 20 may be a nested collector with a plurality of grazing incidence reflectors 23, 24 and 25 (e.g., as schematically shown). The grazing incidence reflectors 23, 24 and 25 may be arranged axially symmetrically about the optical axis O. [ The illustrated radiation collector 20 is merely shown as an example, and other radiation collectors may be used.

 The contamination trap 26 is located between the plasma forming region 4 and the radiation collector 20. Contamination trap 26 may be, for example, a rotating foil trap, or any other suitable form of contaminant trap. In some embodiments, the contamination trap 26 may be omitted.

The enclosure 21 of the radiation source SO includes a window 27 through which the pre-pulse laser beam 17 can pass and which can be transmitted to the plasma forming region 4, and a main laser beam 19, As shown in FIG. The mirror 29 is used to direct the main laser beam 19 through the openings in the contamination trap 26 to the plasma forming region 4.

The radiation source SO shown in Figures 1 and 2 may comprise a component not shown. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transmissive for EUV radiation but substantially blocky for other wavelengths of radiation, such as infrared radiation.

The operation of the lithography system depends on the characteristics of the image of the plasma 7 formed in the intermediate focus 6 (e.g., one or more of the shape of the image, the size of the image, and the position of the image). The image of the plasma is now transmitted to the plasma 7 (7), which includes the relative alignment between the collectors 5, 20 and the illumination system IL and the shape of the plasma 7, the size of the plasma 7, ) Depending on its own characteristics. The prior art method for measuring the alignment of the collectors 5, 20 works fairly well if there are small variations in alignment. However, larger deviations may occur, especially during initial setup of the lithography system. Larger deviations may cause the prior art system to fall into a less accurate operating range, e.g., a non-linear operating range. Further, when a larger deviation occurs, the image of the plasma 7 can be clipped by the openings 8 and 22 of the radiation source SO. Because of this clipping, the prior art measurement accuracy may be lower. Moreover, the measurement of the prior art may vary depending on the imaging of the pattern on the collector (SO). As the collector SO is contaminated during use, the signal intensity may drop or the radiation distribution from the pattern may change, leading to poor accuracy or measurement errors.

In one embodiment, a beam measuring system 30 is provided, for example as described below with reference to FIG. 1 and with reference to FIGS. 3-13. The radiation source SO condenses the radiation emitted from the plasma 7 by using the collectors 5 and 20. The collectors (5, 20) output the condensed radiation as a radiation beam (B). The beam measuring system 30 determines the characteristics of the plasma 7, the image of the plasma 7 and the collector 5, 20 by measuring the characteristics of the radiation beam B.

The beam measuring system 30 includes at least one sensor unit 32. The sensor unit 32 receives at least a part of the radiation beam B. Each sensor unit 32 includes a first patterned element 34, a second patterned element 36, and a detector 38. The detector 38 detects radiation that has passed through the first patterned element 34 and the second patterned element 36. Thus, the first patterned element 34, the second patterned element 36, and the detector 38 may form a stack. The first patterned element 34 and the second patterned element 36 are each patterned with a spatially non-uniform transmittance. The first patterned element 34 and the second patterned element 36 are positioned relative to each other to provide an associated transmittance that varies as a function of the angle of incidence of the radiation on the sensor unit 32.

In one embodiment, patterning the first patterned element 34 may be patterned to provide a non-uniform spatial variation in the transmittance within the plane of the first patterned element 34 (i.e., perpendicular to the plane when viewed) . In one embodiment, patterning the second patterned element 36 may be patterned to provide a non-uniform spatial variation in the transmittance in the plane of the second patterned element 36 (i.e., perpendicular to the plane when viewed) . Exemplary patterns are shown schematically in Figs. 3 and 4. Fig.

In one embodiment, each of the first patterned element 34 and the second patterned element 36 has a high transmissivity of the region 62 of high transmittance separated by a region 64 of lower transmittance, for example, In a periodic arrangement.

In one embodiment, a first set of regions 62 and a second set of regions 64 are provided. Each first set of regions 62 has a first transmittance for EUV radiation. Each second set of regions 64 has a second transmittance for EUV radiation. The first transmittance is higher than the second transmittance. In one embodiment, the first set of regions 62 is substantially transparent to EUV radiation (e.g., has a transmissivity of greater than 80%). In one embodiment, the second set of regions 64 substantially shields the EUV radiation (e.g., has a transmissivity of less than 20%). In one embodiment, all of the first set of regions 62 have substantially equivalent transmittance (e.g., within 5%). In one embodiment, all of the second sets of regions 64 have substantially equivalent transmittance (e.g., within 5%).

In one embodiment, the first set of regions 62 includes a plurality of elongated regions when viewed perpendicularly to the plane of the first patterned elements 34. The plurality of elongated regions may comprise a plurality of parallel elongated regions. The plurality of parallel elongated regions may comprise a plurality of straight, parallel, elongated regions. In one embodiment, the second set of regions 64 includes a plurality of elongated regions when viewed perpendicularly to the plane of the second patterned elements 36. The plurality of elongated regions may include a plurality of parallel regions. The plurality of parallel elongated regions may comprise a plurality of straight, parallel, elongated regions.

In one embodiment, the patterning of the first patterned element 34 and the second patterned element 34 allows the diffraction effect to be ignored. The diffraction effect is negligible when the angular dependence of the combined transmittance through the first patterned element 34 and the second patterned element 36 is dominated by a geometric effect rather than a diffraction effect. In one embodiment, the minimum characteristic dimension of the patterning in the first patterned element 34 is at least 10 times greater than the wavelength of the radiation (e.g., EUV radiation) produced by the laser-generated plasma radiation source, alternatively at least 25 Fold, optionally at least 50 times greater. In one embodiment, the minimum characteristic dimension of the patterning in the second patterned element 36 is at least 10 times, preferably at least 25 times, alternatively at least 50 times, more preferably at least 50 times the wavelength of the radiation generated by the laser- It is bigger. In this context, it is understood that the minimum feature dimension is the minimum dimension of the patterning that is associated with the transmission of radiation through the patterning. The minimum feature dimension may include, for example, the minimum spacing between areas 64 of lower transmittance. If the patterning is periodic, the minimum feature dimension may comprise the period or pitch 40,41 of the patterning. If the minimum characteristic dimension is much larger than the wavelength of the radiation, the diffraction effect is guaranteed to be very small. In one embodiment, the minimum feature dimension is between 0.5 microns and 5 microns, optionally about 1 micron.

In one embodiment, the first set of regions 62 are irregularly spaced from one another. In this embodiment, the first set of regions 62 is optionally spaced apart by a distance that is much greater than the wavelength of radiation (e.g. EUV), alternatively at least 10 times, alternatively at least 25 times, alternatively at least 50 times do. In another embodiment, the first set of regions 62 are evenly spaced from one another by the pitch 40,41. In such an embodiment, pitch 40,41 is optionally implemented to be at least 10 times, optionally at least 25, alternatively at least 50 times greater, such that it is much larger than the wavelength of radiation (e.g. EUV). In one embodiment, pitch 40,41 is between 0.5 microns and 5 microns, and optionally is about 1 micron.

The first set of regions 62 in the first patterned element 34 is spaced by a first pitch 40 and the first set of regions 62 in the second patterned element 36 Is spaced at a second pitch 41. The first pitch 40 may be the same as or different from the second pitch 41 (as in the example of FIGS. 3 and 4) or the second pitch 41. Providing a pattern with a different pitch increases the flexibility of angular variation of the combined transmittance of the first patterned element 34 and the second patterned element 36.

 In the example of Figures 3 and 4, the first set of regions 62 are arranged in a plurality of straight parallelograms oriented perpendicularly to the page (i.e., in the direction of entering the paper) and spaced from each other by pitch 40, And includes an elongated area. The second set of regions 64 includes a corresponding plurality of linearly parallel elongated regions interposed between the first sets of regions 62 to form a lattice structure.

In one embodiment, the first patterned element 34 and the second patterned element 36 are substantially planar. In one embodiment, the first patterned element 34 and the second patterned element 36 are separated from each other by a distance 42 in a direction perpendicular to the plane of the first patterned element 34. In one embodiment, the distance 42 is at least 50 microns, alternatively at least 100 microns, alternatively at least 500 microns, alternatively at least 1 mm. In any of these embodiments, the distance 42 may be less than 10 mm, alternatively less than 5 mm, alternatively less than 3 mm.

The pitches 40 and 41 and the distance 42 are implemented such that the second set of regions 64 cross the incident rays 51-54 in different ways depending on the incident angles 72-74 (see FIG. 3) . This geometric effect provides the desired angular variation in the combined transmittance.

3, an exemplary ray 51 is incident on the sensor unit 32 at a relative zero radian relative to normal incidence. At such an angle of incidence the light beam 51 is incident on one or more areas of the first set of regions 62 (i.e., regions of relatively high transmittance) of both the first patterned element 34 and the second patterned element 36 Lt; / RTI > Exemplary light rays 54 enter the sensor unit 32 at an oblique incident angle 74 but are incident on the first set of regions 62 of both the first patterned element 34 and the second patterned element 36 Lt; RTI ID = 0.0 > through < / RTI > Therefore, the combined transmittance (the combined transmittance of the first patterned element 34 and the second patterned element 36) is similar and is maximum at 0 radian and angle 74. At an intermediate angle, the combined transmittance is lower because the rays can not reach the detector 38 at least partially without encountering one or more regions of the second set of regions 64 (i.e., regions of relatively low transmittance). An exemplary light beam 52 is incident on the sensor unit 32 at an oblique angle 72 and partially meets an area of the second set of areas 64 in the second patterned element 36. The exemplary light ray 53 is incident on the sensor unit 32 at an oblique angle 73 and is more direct than the exemplary light ray 52 in one region of the second set of regions 64 in the second patterned element 36 . Therefore, the combined transmittance for a ray incident at angle 72 is higher at angle 73, but lower at 0 radian and angle 74.

4, the first patterned element 34 and the second patterned element 36 have the same pattern as in the configuration of Fig. 3, but are parallel to the plane of the first patterned element 34 and in an elongated region (The second patterned element 36 is transited upward to the orientation shown in Figure 4 for the first patterned element 34). If a transition occurs at a relative position, a corresponding transition also occurs in the angular dependence of the combined transmittance of the first patterned element 34 and the second patterned element 36. In the configuration of FIG. 4, the combined transmittance for the exemplary rays 51 and 54 is now minimum (similar to the combined transmittance for the exemplary ray 53 in FIG. 3). The combined transmittance for ray 53 is at a maximum (similar to the combined transmittance for rays 51 and 54 in FIG. 3). The combined transmittance for ray 52 is intermediate between the combined transmittance for rays 51 and 54 and the combined transmittance for ray 53. [

3 and 4, the combined transmittance through the first patterned element 34 and the second patterned element 36 will vary continuously as a function of the angle of incidence. In this embodiment, the continuous variation is periodic. It may be convenient because the periodic variation provides a repeating feature (e.g., maximum and minimum values) that has a simple angular positional relationship to each other (angle separation is a constant). This repeating feature can make it easier to analyze the variation of the output from the individual sensor units 32 and / or the difference of the output from the different sensor units 32. [ In other embodiments, continuous fluctuations that are not periodic are provided. Such a continuous variation may or may not include a repeating feature (e.g., maximum or minimum values). If there is a repeating feature and the angular position of the repeating feature is known, the repeating feature makes it easier to make the difference in the output from the individual sensor unit 32 and / or the output from the different sensor unit 32 Analysis.

In the examples of Figures 3 and 4, the combined transmittance has a peak corresponding to the direction of light rays, such as exemplary rays 51 and 54 in Figure 3 and ray 53 in Figure 4. The combined transmittance has a trough corresponding to the direction of the light beam, such as the exemplary light ray 53 of FIG. 3 and the exemplary light rays 51 and 54 of FIG. The periodicity will vary depending on the ratio of the distance 42 to the pitch 40,41. As this ratio increases, the period (the angular distance between adjacent peaks) will decrease.

Figures 5 and 6 illustrate two exemplary examples. In each graph, the vertical axis is the combined transmittance through the first patterned element 34 and the second patterned element 36. In each graph, the horizontal axis is the incident angle in mrad relative to the perpendicular incidence. In FIG. 6, the ratio of distance 42 to pitch 40, 41 is 2000 (e.g., distance 42 = 2 mm and pitch 40, 41 = 1 micron achievable). In FIG. 7, the ratio of distance 42 to pitch 40, 41 is 1000 (e.g., distance 42 = 1 mm and pitch 40, 41 = 1 micron achievable). The solid curve represents the variation of the combined transmittance to the angle of incidence when the pattern of the first patterned element 34 is aligned with the pattern of the second patterned element 36 (e.g., as in FIG. 3). The dashed curve shows the angle of incidence when the pattern of the first patterned element 34 is shifted by the pitch 40, 41 relative to the pattern of the second patterned element 36 (e.g., as in FIG. 4) Lt; RTI ID = 0.0 > transmittance < / RTI >

Figure 5 shows a separation of 0.5 mrad between peaks. When the sensor unit 32 is used to measure the position of the image of the plasma 7 at the intermediate focus located at 1.5 m from the sensor unit 32, if the incident angle changes by 0.5 mrad, the corresponding 750 micron plasma The position of the image of the image 7 will be shifted. Fig. 6 shows a separation of 1.0 mrad between the peaks, which would correspond to the position of the image of the plasma 7 being shifted by 1.5 mm. Distance 42 and / or pitch 40,41 may be adjusted as needed to provide appropriate sensitivity to the particular characteristic at which the angular variation is measured.

In one embodiment, the beam measurement system 30 comprises a group (including a plurality) of sensor units 32. Each sensor unit 32 in the group includes a first patterned element 34 and a second patterned element 36 having an angularly dependent combined transmittance. The angular dependencies for the groups of sensor units 32 are different. Thus, for radiation incident on the plurality of sensor units 32 in the group from the common direction, a corresponding plurality of different output levels are expected to emanate from the corresponding plurality of detectors 38. [ Even if the overall intensity of the radiation incident on the detector changes (e.g. radiation is derived from a pattern formed on the collectors 5, 20 and the signal level is affected by contamination of the collectors 5, 20) It is possible to accurately deduce the incidence direction of the radiation beam by comparing the output levels.

In one embodiment, the different angular dependencies may result in different relative positioning between identical patterns, except for the locations within the first patterned element 34 and the second patterned element 36 in each sensor unit 32 . Figures 3 and 4 show an exemplary configuration in which the relative positions of the first patterned element 34 and the second patterned element 36 are shifted by half pitch in the configuration of Figure 4 for the configuration of Figure 3. In one embodiment, the set of n sensor units 32 includes a first patterned element 34 and a second patterned element 36 that are relatively shifted from each other by 1 / n times the pitch of the first patterned element 34 and the second patterned element 36 / RTI > For example, when four sensor units 32 are provided, the second sensor unit 32 is shifted by 1/4 of the pitch relative to the first sensor unit 32, Is shifted by 1/2 of the pitch relative to the first sensor unit 32 and the fourth sensor unit 32 is shifted by 3/4 of the pitch relative to the first sensor unit 32. [ Many other configurations are possible.

In one embodiment, the beam measurement system includes an array 37 that includes a plurality of groups of sensor units 32.

Figure 7 shows a configuration in which the beam measuring system 30 comprises a 2D array 37 (8x8 array in this particular example) of the group 35 of sensor units 32. [ In this example, each group 35 is sensitive to the angle of incidence of the varying radiation in the first plane (this angle is obtained, for example, by obtaining the angle of incidence of the component parallel to the first plane of the vector representing the radiation) (This angle being obtained by obtaining, for example, the angle of incidence of the component parallel to the second plane of the vector representing the radiation) in the first set and the second plane of the sensor unit 32, And a second set of sensor units 32 oriented in a sensitive manner. The second plane is not parallel to the first plane. In one embodiment, the second plane is perpendicular to the first plane. In the example of Figure 7, the first plane is horizontal and perpendicular to the ground, and the first set of sensor units 32 are the four sensor units 32 (shown in the expanded exemplary group 35 shown at the bottom of Figure 7) ). ≪ / RTI > The second plane is perpendicular and orthogonal to the ground and the second set of sensor units 32 is the lowermost set of the four sensor units 32 shown in the expanded exemplary group 35 shown at the bottom of Figure 7 . The signals output from the detectors 38 of the sensor unit 32 of each group 35 cause the direction of incidence of the radiation onto the group 35 to be accurately and reliably determined. Providing the array 37 of groups 35 allows for spatial variations in the direction of radiation incidence to be detected, so that the characteristics of the incident radiation beam can be measured in detail. The plasma 7 or the collectors 5 and 20 when the incident radiation beam is dependent on the characteristics of the plasma 7 or the plasma 7 or the collectors 5 and 20, Can also be accurately and reliably derived.

In one embodiment, the beam measurement system 30 comprises a plurality of arrays 37, each array 37 being positioned to receive a different portion of the beam of radiation. An exemplary embodiment including such a plurality of arrays 37 is described below with reference to Figures 8-10.

One or more of the characteristics of the plasma 7 determined by the beam measuring system 30, the image of the plasma 7 and the collector 5 may be used to determine the image of the plasma 7 at the intermediate focus 6. [ Size, and position of the substrate. Alternatively, or in addition, in one embodiment, at least one of the characteristics of the plasma 7, the image of the plasma 7, and the collector 5 determined by the beam measurement system 30 is such that the shape of the plasma 7 itself , Size, and position of the object.

Figure 8 is a schematic side view illustrating how the measurement system 30 can be positioned relative to an exemplary radiation system. In this example, the plasma 7 emits EUV radiation that is condensed by the collector 5. The EUV radiation is emitted from different locations spanning a three-dimensional volume occupied by the plasma 7. The volume occupied by the plasma 7 is indicated by the circular black region in FIG. 8, but such volume is not necessarily spherical. The collector 5 forms an intermediate focus 6 at or near the aperture 8 in the sealing structure 9 of the radiation source SO. The beam measurement system 30 is configured such that the sensor unit 32 is configured to receive at least a portion of the radiation beam at a relatively long field position (i.e., a position where the radiation beam has a substantially planar- do. In this embodiment, the array 37 of sensor units 32 is provided to determine the shape of the image of the plasma 7 at the intermediate focus. Each array 37 samples a portion of the beam of radiation and provides information about a corresponding portion of the image of the plasma 7 therethrough. The presence of the plurality of arrays 37 can determine the shape of the large portion of the image of the plasma 7 or the shape of all of the image of the plasma 7. For example, each of the arrays 37 may be as shown in FIG. 7 or may have a different shape. The sensor unit 32 does not necessarily have to be provided in the far field with respect to the intermediate focus 6. [ One or more of the sensor units 32 may be provided closer to the intermediate focus. The cross section of the radiation beam becomes smaller at a location closer to the intermediate focus 6 than at the far field position. Therefore, the sensor unit 32 of a certain size can sample a larger proportion of the radiation beam at a position closer to the intermediate focus 6. [ In such a situation, it may be desirable for the sensor unit 32 to occupy the area of the radiation beam that contributes to the patterned radiation beam projected onto the substrate W. [ In this case, the measurement system 30 can be configured such that the sensor unit 32 is not permanently positioned within the radiation beam. One or more of the sensor units 32 may be configured to be positioned within the radiation beam only while the plasma 7, the image of the plasma 7, and at least one of the properties of the collectors 5, 20 are being determined. In one embodiment, the light intensity at the intermediate focus is reduced while one or more of the sensor units 32 does not damage such a sensor unit 32 in the radiation beam at a location close to the intermediate focus 6. Alternatively or additionally, a filter may be provided on the one or more sensor units 32 to reduce the intensity of the radiation reaching the sensor unit 32. In one embodiment, one or more arrays 37 of sensor units 32 are provided in a single unit that covers most or all of the radiation beam. The beam measuring system 30 can then use such a single unit to obtain detailed information about the image of the plasma 7 including, for example, the total anisotropy of the image of the plasma 7. The size of the single unit will depend on the position relative to the intermediate focus 6. In one particular embodiment where the aperture 8 in the sealing structure 9 of the radiation source, in which the image of the plasma 7 is located, is about 6.5 mm in diameter, the diameter of a single unit comprising one or more arrays 37 Can be about 10 mm to 20 mm.

In one embodiment, one or more of the sensor units 32 are connected to and / or positioned directly close to the facetted field mirror device 10 of the illumination system IL. Relative to an axis representing the average direction of incidence of radiation onto the multi-faceted field mirror device 10, one or more sensor units 32 are arranged in a radial direction within the area where the radiation is received by the multi-faceted field mirror device 10 (If there is space), positioned radially outwardly of the area, or both. Alternatively or additionally, one or more of the sensor units 32 may be located adjacent to and / or directly adjacent to other elements of the illumination system IL, such as a multi-faceted pupil mirror device 11. Relative to the axis representing the average incidence direction of the radiation onto the polyhedral pupil mirror device 11, one or more sensor units 32 are arranged in the radial direction within the area where the radiation is received by the polyhedral pupil mirror device 11 (If there is space), positioned radially outwardly of the area, or both. The sensor unit 32 interferes with the functionality of the elements of the illumination system (e.g., the multi-faceted field mirror device 10 or the multi-facetted pupil mirror device 11) to obtain almost all information about the plasma, plasma image or collector It is beneficial to sample as many radiation beams as possible.

In an alternative embodiment, a plurality of sensor units 32 are provided in the plurality of arrays 37 and all of the sensor units 32 have the same orientation within each of the plurality of arrays 37. [ Examples of this type are shown in Figs. 9 and 10. Fig. In this example, the beam measuring system 30 includes four arrays 37, but alternatively, three or less arrays 37 or five or more arrays 37 may be provided. Each of the arrays 37 comprises a plurality of groups 35 of sensor units 32. Both the group 35 and the sensor unit 32 in the array 37 all have the same orientation. The sensor unit 32 in a given group 35 is different from each other by having different relative transitions between the first patterned element 34 and the second patterned element 36. 10, the orientation of the sensor unit 32 is made sensitive to the angle of incidence of the varying radiation in a plane perpendicular and perpendicular to the plane of the paper. In the extended exemplary group 35 shown below in Fig. 10, . In this example, each of the four arrays 37 is aligned as shown in Fig. 9 so as to be located at a different position in the circumference parallel to the direction of the circumference of the circular path. The orientations of the sensor units 32 in the nearest neighbor array 37 are aligned perpendicular to each other in this particular example. Taken together, the output from all of the arrays 37 allows the incidence direction of the radiation beam to be determined in three dimensions.

In one embodiment, the determined properties of the plasma 7, the image of the plasma 7, and one or more of the collectors 5, 20 are determined by the position of the collectors 5, 20 relative to the illumination system IL, IL) of the collector (5, 20).

In one embodiment, a control device (not shown) controls the radiation source SO based on the characteristics determined by the plasma 7, the image of the plasma 7, and the beam measuring system 30 of at least one of the collectors 5, (110) is provided. For example, the control device 110 may change the characteristics of one or more of the plasma 7, the image of the plasma 7, and the collector 5, 20 or change the characteristics of the plasma 7, the image of the plasma 7, The operation of the radiation source may be modified in response to the output from the beam measurement system 30 to compensate for deviations of one or more of the characteristics of the radiation source 5, 20 from the target state.

In one embodiment, the collector 5, 20 includes a patterned region 94. An example of the patterned area 94 is shown in FIG. 13 and described below. If the collector is, for example, a vertical incidence collector 5 as shown in Fig. 1, the patterned region 94 may be formed on the existing surface of the collector 5, for example (only the patterned region 94) is not provided). If the collector is, for example, a grazing incidence collector 20 as shown in FIG. 2, the patterned region 94 is formed as an additional element, for example, mounted at the exit of the collector 20. The beam measurement system 30 includes at least one sensor unit 32 that is positioned to receive radiation modulated by the patterned area 94. In this embodiment, the modulated radiation detected by the detector 38 of the sensor unit 32 depends on at least one of the position and orientation of the collectors 5, 20 relative to the illumination system IL. The patterned area 94 may have any shape. In one embodiment, the patterned region 94 comprises a plurality of elongated elements forming a lattice. In one embodiment, the patterned region 94 includes a portion of a plurality of concentric rings.

Figure 13 shows an exemplary pattern 96 on the collector 5,20, including a plurality of concentric rings. The diameter of the ring is not particularly limited. In one embodiment, the diameter ranges from 400 mm to 800 mm, alternatively from 550 mm to 650 mm. An exemplary patterned area 94 is shown surrounded by a dashed line. The patterned regions 94 of Figure 13 may be imaged separately on an array 37 of sensor units 32, for example, as shown in Figure 9. The patterned region 94 may be sufficiently small such that the parallelism of the concentric rings is substantially straight and the parallel lines in each patterned region 94 resemble a lattice. There will be a transition in the far field image of each patterned area 94 onto the array 37 of sensor units 32 if there is a transition in the orientation of the collectors 5 and 20 relative to the illumination system IL. If a transition occurs in the far-field image, there will be a corresponding change in the amount of light reaching the detector 38 of each sensor unit 32. Therefore, the output from this array of sensor units 32 provides a measurement of the transitions in the orientation of the collectors 5,20.

The operating principle is schematically illustrated in Figs. 11 and 12. Fig. In each of these figures, the top-most series of elongated regions 102 represents the mapping of the patterned regions 94 onto the 3x3 array 37 of nine sensor units 32. In Fig. The elongated region 102 represents the region of low reflectivity onto the collectors 5,20 and thus corresponds to the region of low radiation beam intensity on the sensor unit 32 in the far field. The low transmittance region 64 of the first patterned element 34 of each sensor unit 32 is represented as an empty square. The low transmittance area 64 of the second patterned element 36 of each sensor unit 32 is indicated as a cross-hatched square. For clarity, a 3x3 array 37 of sensor units 32 is displayed below the series of elongated regions 102, but will actually be positioned at the overlapping position. The signal output from each sensor unit 32 is thus between the regions outside the low transmittance region 64 of both the first and second patterned elements 34,36 and the overlapping long regions 102 (The three representative examples of which are indicated by arrows in Figs. 11 and 12).

Thus, in the example of Fig. 11, it can be seen that the output of the central sensor unit 32 will be the maximum and the output of all the other sensor units 32 will have a lower value. In this embodiment, this represents a state in which the collectors 5 and 20 are aligned as desired.

Conversely, in Fig. 12, the arrangements of the collectors 5 and 20 have transitioned and now the maximum output occurs in the upper left sensor unit 32 and the output of all other sensor units 32 including the central sensor unit 32 It has a lower value. It can be seen that in the upper left sensor unit 32 the area 104 does not overlap any lower transmittance area 64 in the sensor unit 32. [ In all other sensor units 32 there is at least a partial overlap between the region 104 and the low transmittance region 64. In the sensor unit 32 at the lower right side, for example, the region 104 has a low transmittance region 64 of the first patterned element 34 and a low transmittance region 64 of the second patterned element 36. [ And provides a minimum output from the sensor unit 32 through the sensor unit 32.

In this type of configuration, the collectors 5 and 20 are operated until the output from the central sensor unit 32 in each of the arrays 37 of the sensor unit 32 has a maximum value (for example, 32) by adjusting the collector (5, 20).

In the embodiment described above with reference to Figures 11 and 12, the patterned region 94 comprises a periodic array of elongated regions 102. The pitch 95 of the elongated region 102 is greater than the pitch 40 of the periodic arrangement of the low transmissivity regions 64 in the first patterned element 34 and the pitch 40 of the second patterned element 34. [ Is equal to the pitch 41 of the periodic array of low transmissivity regions 64 in the region 36. This is not necessary. In other embodiments, pitch 95 may be different from either pitch 40 or pitch 41 or both. If the pitch 95 is configured to be different from either the pitch 40 or the pitch 41 or both, the sensitivity with which the rotation of the patterned region 94 can be detected can be increased due to the formation of the moire pattern . The rate at which the slope angle of the moire pattern changes as a function of the rotation of the patterned area 94 is increased, compared to when the pitch 95 is equal to the pitches 40 and 41. [ Therefore, detecting a change in the angle of the moire pattern can provide a sensitivity measurement for the change in the rotational position of the patterned area 94, and thus of the collectors 5, 20.

In one embodiment, the beam measuring system 30 includes at least one of the sensor units 32 to selectively receive modulated radiation from one of a plurality of different patterned regions 94 on the collectors 5, And a sensor unit mounting system (90) for moving the sensor unit (90). One example in which the sensor unit mounting system 90 can move the array 37 along the circular curved path 92 is shown in Fig. The sensor unit 32 can therefore be moved to a different location if the contamination in the collectors 5 and 20 compromises the measurement based on the patterned area 94 aligned with the current position of the array 37 have.

Although an embodiment of the present invention has been specifically referred to in the context of a lithographic apparatus herein, embodiments of the present invention may be used in other apparatuses as well. Embodiments of the present invention may be part of any device that measures or processes an object, such as a mask inspection device, a metrology device, or a wafer (or other substrate) or a mask (or other patterning device). Such an apparatus can generally be referred to as a lithography tool. Such a lithography tool may use vacuum conditions or ambient (non-vacuum) conditions.

The term "EUV radiation" may be considered to encompass electromagnetic radiation having a wavelength in the range of 5-20 nm, for example in the range of 13-14 nm. The EUV radiation may have a wavelength in the range of less than 10 nm, for example in the range of 5-10 nm, for example 6.7 nm or 6.8 nm.

Although Figures 1 and 2 illustrate the radiation source SO as a laser-generated plasma (LPP) source, any suitable source may be used to generate the EUV radiation. For example, the EUV emission plasma may be generated using an electrical discharge to convert the fuel (e.g., tin) to a plasma state. A radiation source of this type may be referred to as a discharge produced plasma (DPP) source. The electrical discharge may form part of the radiation source or may be generated by a power supply, which may be a separate entity connected through an electrical connection to the radiation source SO.

Although particular reference may be made in this text to the use of lithographic apparatus in the art for manufacturing ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

Although specifically mentioned above with respect to the use of embodiments of the present invention in the context of optical lithography, it is to be understood that the invention may be used in other applications, for example imprint lithography, and limited to optical lithography, It will be recognized that it is not. In imprint lithography, the topography of a patterning device defines a pattern created on a substrate. The topography of the patterning device may be pressed onto a layer of resist supplied to the substrate on which the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is moved out of the resist after the resist is cured so as to leave a pattern therein.

Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. The machine-readable medium may comprise any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, the machine-readable medium may comprise read only memory (ROM); A random access memory (RAM); Magnetic disk storage media; Optical storage media; Flash memory devices; (E. G., Carrier waves, infrared signals, digital signals, etc.), and the like, as well as electrical, optical, acoustical or other types of signals. Further, firmware, software, routines, and instructions may be described as performing certain operations herein. It should be appreciated, however, that such descriptions are merely for convenience and that these operations result from a computing device, processor, controller, or other device executing firmware, software, routines, instructions, and the like.

Although specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is provided by way of example and not limitation. It will therefore be apparent to those skilled in the art that changes may be made to the invention as described without departing from the scope of the following claims.

Claims (20)

A beam measurement system for determining at least one characteristic of a plasma of a laser-generated plasma radiation source, an image of a plasma, and a collector,
And at least one sensor unit configured to receive at least a portion of the radiation beam output from the collector,
Each sensor unit including a first patterned element, a second patterned element, and a detector configured to detect radiation that has passed through the first patterned element and the second patterned element,
Wherein the first patterned element and the second patterned element are each patterned with a spatially non-uniform transmittance and are arranged to provide a combined transmittance with a non-uniform angular dependence on the direction of incidence of radiation on the sensor unit Is positioned relative to the beam. The method according to claim 1,
Wherein the beam measurement system comprises a group of sensor units,
Wherein each sensor unit in the group comprises a first patterned element and a second patterned element having an angularly dependent combined transmittance,
Wherein the angular dependencies for the group of sensor units are different from each other. 3. The method of claim 2,
Wherein the different angular dependencies are obtained by providing different relative positioning between the same patterns in the first patterned element and the second patterned element in each sensor unit. The method according to claim 2 or 3,
Wherein the beam measurement system comprises an array comprising a plurality of groups of sensor units. 5. The method of claim 4,
Wherein the beam measurement system comprises a plurality of the arrays, each array being positioned to receive a different portion of the radiation beam. 6. The method according to any one of claims 1 to 5,
Wherein each of the first patterned element and the second patterned element is patterned into a periodic array of regions of high transmittance separated by a region of lower transmittance. 7. The method according to any one of claims 1 to 6,
Wherein the first patterned element and the second patterned element are substantially planar and wherein the first patterned element and the second patterned element are separated from each other in a direction perpendicular to the plane of the first patterned element, system. 8. The method according to any one of claims 1 to 7,
Wherein at least one of the plasma, the image of the plasma, and the collector has at least one of a shape of the image of the plasma at the intermediate focus, a size of the image of the plasma at the intermediate focus, and a position of the image of the plasma at the intermediate focus, Wherein the intermediate focus is a focus formed by the collector between the collector and an illumination system configured to condition the beam of radiation. 9. The method of claim 8,
Wherein at least one of the at least one sensor unit is positioned in a far field relative to the intermediate focus. 10. The method according to any one of claims 1 to 9,
Wherein the at least one determined characteristic of the plasma, the image of the plasma, and the collector comprises at least one of a shape of the plasma, a size of the plasma, and a position of the plasma. 11. The method according to any one of claims 1 to 10,
The collector including a patterned region,
The beam measurement system comprising at least one sensor unit positioned to receive radiation modulated by the patterned area,
Wherein the ratio of modulated radiation detected by the detector depends on at least one of the position of the collector relative to the illumination system configured to condition the beam of radiation and the orientation of the collector relative to the illumination system. 12. The method of claim 11,
Wherein the patterned area comprises a portion of a plurality of concentric rings. 13. The method according to claim 11 or 12,
The first patterned elements are patterned into a periodic array with a first pitch of regions of high transmittance separated by regions of lower transmittance,
The second patterned element is patterned into a periodic array having a second pitch that is different from or equal to the first pitch of regions of high transmittance that are separated by a region of lower transmittance,
Wherein the received radiation modulated by the patterned area of the collector has a periodicity and has a different pitch from either or both of the first pitch and the second pitch. 14. The method according to any one of claims 11 to 13,
Wherein the beam measurement system further comprises a sensor unit mounting system configured to cause at least one of the sensor units to be moved so as to selectively receive radiation modulated by one of a plurality of different patterned areas of the collector, Measuring system. 15. The method according to any one of claims 11 to 14,
Wherein the determined characteristics of the at least one of the plasma, the image of the plasma, and the collector include at least one of the position of the collector relative to the illumination system and the orientation of the collector relative to the illumination system. 16. The method according to any one of claims 1 to 15,
Wherein the patterning of the first patterned element and the second patterned element is implemented such that the diffraction effect is negligible. 17. The method of claim 16,
Wherein the minimum characteristic dimension of the patterning in the first patterned element and the minimum characteristic dimension of the patterning in the second patterned element are at least 10 times greater than the wavelength of the radiation generated by the laser generated plasma radiation source. 18. The method according to any one of claims 1 to 17,
Wherein the beam measurement system further comprises a control device configured to control the laser generated plasma radiation source based on an output from the at least one sensor unit. A lithographic system,
(a) a radiation source configured to collect radiation emitted from a plasma using a collector and output a radiation beam from the collector; And
(b) a beam measurement system configured to determine a plasma, an image of the plasma, and at least one characteristic of the collector,
Wherein the beam measurement system includes at least one sensor unit configured to receive at least a portion of the radiation beam,
Each sensor unit including a first patterned element, a second patterned element, and a detector configured to detect radiation that has passed through the first patterned element and the second patterned element,
Within each sensor unit, the first patterned element and the second patterned element are each patterned with a spatially non-uniform transmittance, and the combined transmittance, which has a non-uniform angular dependence on the direction of incidence of radiation on the sensor unit, Wherein the lithographic apparatus is positioned relative to one another to provide a lithographic projection apparatus. As a method,
Determining the at least one of the plasma in the laser-generated plasma radiation source, the image of the plasma, and the collector by measuring a characteristic of the radiation beam output by the laser-generated plasma radiation source,
Wherein measuring the characteristics of the radiation beam comprises receiving at least a portion of the radiation beam using at least one sensor unit,
Each sensor unit including a first patterned element, a second patterned element, and a detector configured to detect radiation that has passed through the first patterned element and the second patterned element,
Wherein the first patterned element and the second patterned element are each patterned with a spatially non-uniform transmittance and are positioned relative to each other to provide a combined transmittance with a non-uniform angular dependence on the direction of incidence of radiation on the sensor unit How.

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