Method and measuring device for inspecting a photomask and an EUV camera

Abstract

To provide a method for inspecting photomasks, in which a photomask (17) is illuminated by EUV radiation emitted by an EUV radiation source (14).SOLUTION: EUV radiation reflected at a photomask (17) is guided via a projection lens (22) to an image sensor (24) of an EUV camera (23) such that the photomask (17) is imaged on the image sensor (24). The EUV radiation passes through a pellicle (30) which is arranged between the projection lens (22) and the image sensor (24). The invention also relates to an EUV camera and to a measuring device for inspecting photomasks.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and a measurement device and an EUV camera for inspecting a photomask. [Background technology]

[0002] In microlithography projection exposure apparatus, which are used to manufacture integrated circuits, particularly with very small structures, photomasks are used that are irradiated with very short-wave extreme ultraviolet radiation (EUV radiation) and imaged onto the lithography object in order to transfer the mask structure onto the lithography object.

[0003] To ensure the high quality of the image formed on the lithography object, it is necessary that the photomask is precisely to size and not marred by contaminants. It is known practice to subject the photomask to inspection before operation in a microlithography projection exposure apparatus or during interruptions in operation. For this purpose, a so-called aerial image of the photomask, or of a part of the photomask, is created, and the photomask in process is imaged onto an image sensor rather than onto the lithography object. Using the image on the image sensor as a basis, it is possible to evaluate the photomask for defects and contaminants.

[0004] Mask inspection must be performed in such a way that the measurement results are not altered by contaminants, specifically, the photomask must be prevented from becoming contaminated as a result of the mask inspection procedure. Summary of the Invention

[0005] The present invention is based on the object of providing a method and a measurement device for mask inspection where the risk of contamination is reduced, and of providing an EUV camera. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0006] In a method for mask inspection according to the present invention, a photomask is irradiated with EUV radiation emitted by an EUV radiation source. The EUV radiation reflected from the photomask is directed through a projection lens to an image sensor of an EUV camera so that the photomask is imaged on the image sensor. The EUV radiation passes through a pellicle disposed between the projection lens and the image sensor.

[0007] The pellicle placed between the EUV camera and the image sensor has the effect of firstly preventing contaminants and particles coming from the EUV camera from passing into the projection lens or other areas of the measurement device, and secondly preventing contaminants and particles coming from the projection lens or other areas of the measurement device from passing into the EUV camera and onto the image sensor, thereby reducing the risk of the measurement being corrupted by contamination.

[0008] The pellicle can be positioned between the image sensor and the last mirror of the projection lens, in other words, EUV radiation between the last mirror of the projection lens and the image sensor does not reflect off further mirrors of the projection lens.

[0009] According to one aspect of the invention, the pellicle is positioned in a section of the EUV beam path where the EUV radiation passes through the pellicle exactly once between the EUV radiation source and the image sensor. This differs from conventional measurement devices where the pellicle is configured in a reflective manner to cover the entire surface of the EUV photomask. In this case, the EUV radiation passes through the pellicle twice, specifically once before reflection on the photomask and once after reflection on the photomask. The loss of EUV radiation power is twice as high as when passing through the pellicle only once.

[0010] A pellicle is a membrane designed to allow EUV radiation to pass through but block particles. Because materials are generally highly absorptive of EUV radiation, the pellicle material and structure must be carefully adapted for use in measurement devices for mask inspection. For example, unlike with visible light, a glass plate cannot be used as protection against contamination. The EUV radiation would be absorbed by the glass plate and would not reach the image sensor with sufficient intensity.

[0011] In one embodiment, the pellicle is a CNT (carbon nanotube) pellicle, i.e., a membrane made of carbon nanotubes. The density and bundle structure of the carbon nanotubes can be selected so that the membrane is transparent to EUV radiation on the one hand, but particles are stopped at the membrane and cannot pass through the membrane on the other hand. To make the membrane sufficiently resistant to radical ions and molecules, the membrane can be coated.

[0012] In another embodiment, the pellicle comprises a membrane made of silicon, silicon nitride, or any other silicon-containing material. When sufficiently thin, such a membrane made of silicon material also exhibits sufficient transparency to EUV radiation. Again, the ability to block the passage of gaseous contaminants is more pronounced for a pellicle made of silicon material than for a CNT pellicle.

[0013] The pellicle can be a component of an EUV camera. The EUV camera can include a camera housing that carries an image sensor and to which the pellicle is attached. The camera housing can include a pressure equalization channel so that the same pressure exists both inside the camera and in other areas of the measurement device. The projection lens, illumination system, and / or EUV radiation source can be located in a vacuum chamber in which vacuum pressure exists during operation of the measurement device.

[0014] The camera housing can have an opening that allows EUV radiation to enter the interior of the EUV camera and impinge on the image sensor, and the camera housing can be completely sealed except for the opening and the pressure equalization channel so that the interior of the camera is protected from particles entering from the environment.

[0015] The pellicle can be fitted over the opening such that all EUV radiation entering the interior through the opening passes through or travels through the pellicle. The pellicle can be sealingly flush with the housing edge surrounding the opening to prevent the passage of particles between the interior and surroundings of the EUV camera at the transition between the pellicle and the housing.

[0016] The pellicle can be attached to a frame. The pellicle can be fixed to the frame such that the pellicle covers an opening spanned by the frame. The connection with the EUV camera housing can be established through the frame. To allow for replacement of the pellicle, the connection between the frame and the EUV camera housing can be a detachable connection. The pellicle may need to be replaced if it becomes contaminated after a certain period of use. The pellicle can be a consumable item designed to be replaced periodically within repair limits. Pellicle replacement can be done manually. A motor-driven mechanism for pellicle replacement is also possible.

[0017] The pellicle can extend in a plane parallel to the plane of the image sensor. The distance between the image sensor and the pellicle can be such that particles adhering to the pellicle only insignificantly impair the image recorded by the image sensor. In this context, there is a trade-off: it is advantageous for the pellicle to be at a large distance from the image sensor so that the recorded image is not impaired. A pellicle arranged close to the image sensor is advantageous for a compact construction of the EUV camera or measurement device.

[0018] EUV cameras can be used in a face-down configuration, where the image sensor faces downwards and EUV radiation is incident on the image sensor from below. In the face-down configuration, a pellicle is placed below the image sensor. It is also possible to use EUV cameras in a face-up configuration, where the image sensor faces upwards and EUV radiation is incident on the image sensor from above. In the face-up configuration, a pellicle is placed above the image sensor.

[0019] In the face-up configuration, gravity assists in the movement of particles toward the image sensor. However, particle movement toward the image sensor can also occur in the face-down configuration, again resulting in a risk of contamination of the image sensor. In both cases, the pellicle protects the image sensor from particles from the EUV camera's environment that can deposit on the image sensor.

[0020] Conversely, it is also necessary to prevent contaminants of other components of the measurement device emanating from inside the EUV camera. Specifically, contaminants separated from the EUV camera must not be deposited on the surface of the photomask. This risk exists when the EUV camera is operated in a vacuum atmosphere and there is outgassing of materials used in the camera. In general, the structure of the pellicle is not designed to prevent the passage of gaseous contaminants. The present invention recognizes that a pellicle made of a silicon material has a superior effect on the passage of gaseous contaminants compared to a CNT pellicle. For this reason, in one embodiment, the pellicle is made of a silicon material.

[0021] The projection lens of the measurement device can have a high magnification, for example, at least 50, preferably at least 100, and more preferably at least 200. Therefore, an image sensor with a large area compared to the imaged portion of the photomask is required. The EUV camera can include an image sensor with a uniform sensor area that is completely populated with pixels. The pellicle can be sized to cover the area of ​​the uniform sensor area, so that EUV radiation can reach the entire sensor area through the pellicle.

[0022] In other embodiments, the image sensor is configured as a sensor array with multiple sensor elements spanning the sensor area of ​​the image sensor. Each individual sensor element can have a sensor area that is entirely populated with pixels. The sensor area of ​​the image sensor can have pixel-free areas that can be located between the sensor areas of two sensor elements.

[0023] The EUV camera can include a pellicle that is smaller than the sensor area of ​​the image sensor, such that not all of the EUV radiation incident on the image sensor passes through a single pellicle. The EUV camera can include multiple pellicles that together cover the sensor area of ​​the image sensor, such that all of the EUV radiation incident on the image sensor passes through one of the pellicles, preferably exactly one of the pellicles. The multiple pellicles can be arranged in a plane.

[0024] Multiple pellicles can be held on a frame. The frame of the pellicle can be placed in front of the pixel-free sensor area of ​​the image sensor. In that case, the frame does not interfere with image recording, but merely blocks EUV radiation where it does not impinge on the pixels of the image sensor in any case. The pellicle can cover the sensor area of ​​one or more sensor components. In one embodiment, each sensor component is assigned its own pellicle.

[0025] For sensor arrays that are not entirely populated by pixels, there will be areas of the imaged portion of the photomask for which no image information can be obtained from a single EUV image record. Therefore, provision can be made for the position of the photomask to be changed relative to the incoming EUV beam path and for a second EUV image record to be recorded. For the second EUV image record, the photomask can be positioned such that image information is obtained from areas of the imaged portion of the photomask for which the first image record did not provide image information. This method can be performed with more than two positions of the photomask and more than two EUV image records. An image of the imaged portion of the photomask can be calculated from the multiple EUV image records available.

[0026] In one embodiment, the device includes an XY positioning mechanism that can change the position of the photomask relative to the incoming EUV beam path in an XY plane. The XY plane can correspond to the plane of the photomask. The XY positioning mechanism can be implemented to linearly displace the photomask in the XY plane. This can be used for a scanning procedure in which multiple EUV image records belonging to the same portion of the photomask are recorded during linear movement of the photomask.

[0027] Additionally or alternatively, the XY positioning mechanism can be used to displace the photomask relative to the incident EUV beam path so that aerial images of different portions of the photomask can be created. Specifically, the XY positioning mechanism can be designed to enable inspection of each portion of the photomask.

[0028] Additionally or alternatively, the XY positioning mechanism can be used to obtain information about the condition of the pellicle. To this end, a reference mask with a known surface structure, such as a uniform surface structure, can be introduced into the measurement device. Depending on how the image recording changes when the reference mask is displaced in the XY plane, an indication of the pellicle condition can be obtained.

[0029] The projection lens of the measurement device can include multiple EUV mirrors through which EUV radiation is reflected between the photomask and the image sensor. The optical region of the EUV mirrors can be formed by a highly reflective coating. This can be a multilayer coating, particularly a multilayer coating with alternating layers of molybdenum and silicon. Using such a coating, approximately 70% of the incident EUV radiation can be reflected. The term "EUV radiation" is used to refer to electromagnetic radiation in the extreme ultraviolet spectral range, having wavelengths between 5 nm and 100 nm, specifically between 5 nm and 30 nm.

[0030] A projection lens can be used to direct EUV radiation coming from the photomask to the image sensor so that an image of the photomask, specifically a portion of the photomask, appears on the image sensor. The portion of the photomask imaged onto the image sensor can correspond to a small portion of the photomask.

[0031] For example, the photomask may have an edge length between 100 mm and 200 mm and / or a width of 100 cm 2 and 400cm 2 The portion to be inspected may have an area between 0.1 mm and 5 mm, preferably between 0.5 mm and 3 mm. If the portion is not square, this specification relates to the longer of these edge lengths. If the portion is not rectangular either, this specification relates to the largest dimension of the portion. The sensor area of ​​the image sensor is preferably larger than the portion to be inspected of the photomask, corresponding to the magnification of the projection lens. The dimensions of the sensor area of ​​the image sensor, which are defined in the same way as the portion to be inspected, may be, for example, between 50 mm and 500 mm, preferably between 100 mm and 200 mm.

[0032] The measurement device according to the invention can include further pellicles arranged in one or more other sections of the EUV beam path, such that the EUV radiation passes through multiple pellicles in succession. The measurement device can include further pellicles through which the EUV radiation passes exactly once. Additionally or alternatively, the measurement device can include a pellicle arranged such that the EUV radiation passes through it twice.

[0033] The present invention also relates to an EUV camera having a camera housing and an image sensor, the image sensor being held within the camera housing, the image sensor being sensitive to EUV radiation. The camera housing spans an entrance aperture provided for the entrance of EUV radiation. The EUV camera includes a pellicle such that EUV radiation entering the EUV camera through the entrance aperture passes through the pellicle.

[0034] The pellicle of the EUV camera can be made of a silicon material. The pellicle can be hermetically flush with the housing edge surrounding the aperture. The pellicle can be mounted on a frame, where the pellicle is connected to the camera housing via the frame, and the frame is removably connected to the camera housing. The image sensor can be configured as a sensor array, where multiple sensor components span the sensor area of ​​the image sensor. The EUV camera can include a pellicle that is smaller than the sensor area of ​​the image sensor. Multiple pellicles can be held on a frame, where components of the frame are positioned in front of pixel-free areas of the sensor area of ​​the image sensor.

[0035] The present invention further relates to a measurement device for inspecting a photomask. The measurement device includes an illumination system, a projection lens, and an EUV camera. EUV radiation emitted by an EUV radiation source is directed to the photomask via the illumination system. EUV radiation reflected from the photomask is directed to an image sensor of the EUV camera via the projection lens so that the photomask is imaged on the image sensor. The measurement device includes a pellicle disposed between the projection lens and the image sensor. The measurement device may include an EUV camera according to the present invention.

[0036] The illumination system can be configured to illuminate a portion of the photomask. The illumination system can be configured such that the intensity of the EUV radiation is substantially uniform within the illuminated portion. The illumination system can include one or more EUV mirrors by which the EUV radiation is reflected on a path between the EUV radiation source and the photomask. The EUV radiation source can be a plasma radiation source in which a plasma that emits EUV radiation is formed. For example, the medium in which the plasma is formed can be tin. The plasma is formed by directing a laser beam at droplets of the medium. The projection lens can include multiple EUV mirrors by which the EUV radiation is reflected between the photomask and the pellicle. The measurement device can include an EUV radiation source.

[0037] The present disclosure encompasses the development of methods with features described in the context of an EUV camera according to the present invention or a measurement device according to the present invention.The present disclosure encompasses the development of EUV cameras and measurement devices with features described in the context of a method according to the present invention.

[0038] The invention will now be described by way of example only with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 shows a schematic diagram of a measuring device according to the invention. [Figure 2] 1 is a diagram showing a schematic cross-sectional view of an EUV camera according to the present invention; [Figure 3] FIG. 3 illustrates an embodiment of the EUV camera of FIG. 2. [Figure 4] FIG. 1 is a diagram showing a schematic diagram of a photomask. [Figure 5] 3 is a view from the viewpoint according to FIG. 2 in another embodiment of the EUV camera. [Figure 6] FIG. 6 illustrates an embodiment of the EUV camera of FIG. 5. [Figure 7] FIG. 1 shows a schematic diagram of a measuring device according to the invention. [Figure 8] 3 is a view from the viewpoint according to FIG. 2 in a further embodiment of the EUV camera; [Figure 9] FIG. 9 illustrates an embodiment of the EUV camera of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0040] The measurement device according to the present invention can be used to inspect a microlithography photomask 17 .

[0041] Typically, the microlithography photomask 17 is provided for use in a microlithography projection exposure apparatus (not shown here). In the microlithography projection exposure apparatus, the photomask 17 is irradiated with extreme ultraviolet radiation (EUV radiation), for example at a wavelength of 13 nm, in order to image structures formed on the photomask 17 onto the surface of a lithography object in the form of a wafer. The wafer is coated with a photoresist that is sensitive to EUV radiation. A measuring device is used to check that the measuring device meets requirements and is free of contaminants.

[0042] According to FIG. 1 , the photomask 17 is arranged in the measurement device such that an EUV beam path 15 emanating from an EUV radiation source 14 is guided to the photomask 17 via an illumination system 16. The illumination system 16 is used to shape the EUV radiation to form a beam that is used to illuminate an inspection field 20 on the surface of the photomask 17 with uniform brightness. A small inspection field 20 compared to the area of ​​the photomask 17 is shown not to scale in FIG. 4 . For example, the illumination area 20 may have dimensions of 0.5 mm × 0.8 mm. The edge length of the photomask 17 may be, for example, between 100 mm and 200 mm. A field stop 21 is arranged between the first illumination mirror 17 and the second illumination mirror 18 and is used to delimit the illumination area into inspection fields 20 on the surface of the photomask 17. To bring different inspection fields 20 into the area of ​​the EUV beam path, the photomask can be moved in the XY plane using an XY positioning mechanism 37.

[0043] The EUV beam path 15 reflected from the photomask 17 continues through a projection lens 22 to an EUV camera 23 equipped with an image sensor 24. The projection lens 22 is used to image the inspection field 20 of the photomask 17 onto the image sensor 24 of the EUV camera 23. An aperture stop 25, whose aperture corresponds to the first mirror M1, is disposed between the photomask 17 and the first mirror M1. The EUV radiation source 14, illumination system 15, photomask 17, projection lens 22, and EUV camera 23 are disposed within a vacuum housing 40, which is under negative pressure during operation of the measurement device.

[0044] The EUV radiation source 14 is a plasma radiation source in which EUV radiation is emitted from the plasma at a wavelength of 13 nm. Tin is a medium that can be used to generate a plasma suitable for emitting such EUV radiation. A laser beam can be directed at droplets of the medium to generate the plasma.

[0045] 2 , the EUV camera 23 includes a housing 26 in which the image sensor 24 and an electronic circuit unit 27 are disposed. The electronic circuit unit 27 is used to control the image sensor 24 and process EUV image data acquired by the image sensor 24. A connecting flange 29 is formed on the housing 26 and extends around the entrance aperture 31 of the EUV camera 23. A frame 28, on which a pellicle 30 is stretched, is connected to the connecting flange 29. The connection between the frame 28 and the connecting flange 29 is detachable so that a pellicle unit 32, including the frame 28 and the pellicle 30, can be removed from the housing 26 and replaced with a new pellicle unit. For example, the pellicle unit 32 can be replaced during maintenance procedures that the measurement device undergoes at appropriate intervals.

[0046] Together with pellicle unit 32, housing 26 completely encloses the interior of EUV camera 23. EUV radiation coming from projection lens 22 passes through pellicle 30 into the interior of EUV camera 23 and is incident on image sensor 24. The schematic diagram of Figure 3 shows a view of image sensor 24 as seen through pellicle 30. Image sensor 24 is fully pixelated, and includes a sensor area entirely viewable through pellicle 30 and entirely available for recording an image of test field 20 on photomask 17.

[0047] The projection lens 22 has a magnification of more than 100. In order to be able to record the entire resulting image of the inspection field 20 of the photomask 17, the area of ​​the image sensor 24 is accordingly larger than the area of ​​the inspection field 20. For example, the image sensor 24 may have dimensions on the order of 100 mm to 200 mm.

[0048] Together with the pellicle unit 32, the housing 26 is designed such that mass exchange between the interior of the EUV camera 23 and the surroundings is largely inhibited, while pressure equalization remains possible. Operation of the measurement device occurs within the vacuum housing 40. During operation of the measurement device, the vacuum pressure within the EUV camera 23 is the same as in other areas of the vacuum housing 40.

[0049] The pellicle 30 is an extremely thin membrane made of a silicon material that is highly transparent to EUV radiation but prevents particles from passing through. The pellicle 30 ensures that particles contained in the atmosphere of the measurement device cannot penetrate into the interior of the EUV camera 23. Such particles are particularly troublesome when they land on the image sensor 24. Particles on the image sensor 24 alter the recorded image of the inspection field 20 of the photomask 17.

[0050] Conversely, pellicle 30 also prevents contaminants from leaving the interior of EUV camera 23 and from adhering to other components of the measurement device. In particular, contamination of photomask 17 itself must be avoided, as this could result in unusable semiconductor components fabricated using photomask 17 at a later stage.

[0051] Such contamination can result in outgassing, which can occur in the EUV camera 23, especially when a vacuum exists inside the EUV camera 23. The EUV camera 23 includes, for example, an adhesive for connecting the electronics unit 27 and the image sensor 24 to the housing 26. The pellicle 30, made of a silicon material, acts to confine such outgassing to the interior of the EUV camera 23, allowing only a small fraction of it to escape to the outside. The function of the EUV camera 23 is not impaired by outgassing. Outgassing can cause damage if the gas cloud comes into contact with other components of the measurement device outside the EUV camera 23.

[0052] FIG. 5 shows another embodiment of the EUV camera 23 in which the pellicle unit 32 is connected to a mechanism 33 that allows for semi-automatic replacement of the pellicle unit 32. The mechanism 33 includes a motor 34 that can rotate a rotating element 35. The pellicle unit 32, which is attached to the rotating element 35 via an arm, pivots laterally relative to the housing 26 of the EUV camera 23 when the rotating element 35 is rotated. In this manner, the pellicle unit 32 can be moved to an easily accessible position where a used pellicle unit 32 can be replaced with a new one. The vacuum housing of the measurement device can include a flap that allows access to the used pellicle unit 32. Before the flap is opened, the vacuum in the vacuum housing is released.

[0053] 6, image sensor 24 includes a plurality of sensor elements 36, nine in total in this embodiment. Each sensor element 36 has a sensor area entirely populated with pixels. At the transitions between two adjacent sensor elements 36, there are narrow pixel-free regions. The pixel-free regions form a checkerboard pattern on image sensor 24.

[0054] If the sensor area of ​​the image sensor 24 is formed from multiple sensor elements 36, this is advantageous in that it allows for the assembly of a large area image sensor 24 with conventional CCD chips that are sensitive to EUV radiation. It is acceptable in this embodiment that there are pixel-free areas between the sensor elements 36 from which EUV image information cannot be obtained.

[0055] 7, the photomask 17 is placed on an XY positioning mechanism 37, which allows the photomask 17 to be displaced in the XY plane. By displacing the photomask 17 in the XY plane, the effect is that not always the same area of ​​the inspection field 20 on the photomask 17 is incident on a pixel-free area of ​​the image sensor 24. By recording multiple EUV image records using slightly different positions of the photomask 17 in the XY plane, EUV image information for each point in the inspection field 20 can be obtained. By appropriate combination of the EUV image records by computation, a complete view of the inspection field 20 can be obtained.

[0056] 8 and 9 show an example embodiment in which the EUV camera 23 includes multiple pellicles 30, each smaller than the image sensor 24, but which together span the sensor area 38 of the image sensor 24. Each sensor element 36 is assigned a pellicle 30 that is held in a frame piece that extends around the sensor element 36. Together, this forms a frame 39 that extends in a grid pattern over the area of ​​the image sensor 24, with its frame posts each located in the pixel-free areas between the sensor elements 36.

[0057] According to FIG. 8, first, the pellicle element consisting of multiple pellicles 30 is positioned at a shorter distance from the image sensor 24 so that the EUV image recorded by the image sensor 24 is not corrupted by contaminants adhering to the pellicle 30, and second, EUV radiation passing through the support pillars of the frame 28 is blocked primarily by the pixel-free areas between the sensor elements 36 rather than by the sensor elements 36.

[0058] The pellicle component placed in front of the image sensor 24 prevents particles and outgassing from escaping from inside the EUV camera 23 and damaging other components of the measurement device. Conversely, particles present in the measurement device are prevented from entering the interior of the EUV camera 23 and depositing on the image sensor 24. Particles on the image sensor 24 would interfere with EUV image recording.

[0059] If a situation arises in which a defect is visible in the EUV image record, it cannot be easily determined whether it is a contaminant on image sensor 24, a contaminant or defect on photomask 17, or a defect at some other point in projection lens 22. Provision can be made to impart slight movement to photomask 17 in the XY plane so that different sources of error can be distinguished. A defect that moves on image sensor 24 with photomask 17 can be attributed to photomask 17. A defect that remains unchanged on image sensor 24 despite movement of photomask 17 is likely to be located in image sensor 24.

[0060] It is also possible to replace the photomask 17 with a reference mask whose surface may, for example, be free of structures. An EUV image created using such a reference mask should have uniform brightness values ​​over the area of ​​the image sensor 24. The state of the projection lens 22 can be inferred based on deviations from the expected brightness distribution. [Explanation of symbols]

[0061] 14 EUV radiation source 15 EUV beam path 16 Irradiation system 17 Photomask 20 Inspection Fields 21 Field diaphragm 22 Projection lens 23 EUV camera 24 image sensors 26 Housing 27 Electronic Circuit Unit 28 frames 29 Connection flange 30 Pellicle 31 Entrance aperture 32 Pellicle unit 33 Mechanism 34 Motor 35 Rotating Parts 36 Sensor Components 37 Positioning mechanism 38 Sensor Area 39 frames 40 Vacuum housing M1 First Mirror

Claims

1. 1. A method for inspecting a photomask using an EUV camera (23) comprising: a housing (26) having an entrance opening (31) through which EUV radiation is incident; an image sensor (24) held within the housing (26); and a pellicle (30) mounted on the housing (26) to cover the entrance opening (31), wherein the photomask (17) is irradiated with EUV radiation emitted by an EUV radiation source (14); EUV radiation reflected from the photomask (17) is directed to the image sensor (24) of the EUV camera (23) via a projection lens (22) so as to image the photomask (17) on the image sensor (24); the EUV radiation passes through the pellicle (30) and the entrance opening (31) disposed between the projection lens (22) and the image sensor (24); A method in which a first EUV image record is recorded by the EUV camera (23), the photomask (17) is displaced relative to the incident EUV radiation, and thereafter a second EUV image record is recorded.

2. The method of claim 1, wherein the EUV radiation passes through the pellicle (30) exactly once between the EUV radiation source (14) and the image sensor (24).

3. The method according to claim 1 or 2, wherein the pellicle (30) is a component of the EUV camera (23).

4. An EUV camera having a camera housing (26) and an image sensor (24), wherein the image sensor (24) is held within the camera housing (26), the image sensor (24) is sensitive to EUV radiation, the camera housing (26) spans an entrance opening (31) designed for the incidence of EUV radiation, the EUV camera (23) includes a pellicle (30) provided on the camera housing (26) to block the entrance opening (31), and EUV radiation enters the EUV camera (23) through the pellicle (30) and the entrance opening (31).

5. 5. The EUV camera of claim 4, wherein the pellicle (30) is made of a silicon material.

6. 6. An EUV camera according to claim 4 or 5, wherein the pellicle (30) is sealingly flush with a housing edge surrounding the entrance aperture (31).

7. 6. The EUV camera of claim 4, wherein the pellicle is attached to a frame, the pellicle is connected to the camera housing via the frame, and the frame is removably connected to the camera housing.

8. 6. The EUV camera according to claim 4, wherein the image sensor (24) is configured as a sensor array in which a plurality of sensor elements (36) are spread across a sensor area (38) of the image sensor (24).

9. 9. The EUV camera of claim 8, wherein the EUV camera (23) includes a pellicle (30) that is smaller than the sensor area (38) of the image sensor (24).

10. The EUV camera of claim 8, wherein the EUV camera (23) comprises a plurality of pellicles (30).

11. The EUV camera of claim 10, wherein the plurality of pellicles (30) are arranged in a plane.

12. 11. The EUV camera of claim 10, wherein the plurality of pellicles (30) are held on a frame (39), and a part of the frame (39) is positioned in front of a pixel-free area of ​​the sensor area (38) of the image sensor (24).

13. 1. A measurement device for inspecting a photomask, comprising: an illumination system (16); a projection lens (22); an EUV camera (23); The EUV camera (23) a housing (26) having an entrance opening (31) through which EUV radiation is incident; an image sensor (24) held within said housing (26); a pellicle (30) provided in the housing (26) so as to cover the entrance opening (31); a positioning mechanism for displacing the photomask (17) relative to the incident EUV beam path; Equipped with a pellicle (30) disposed between the projection lens (22) and the image sensor (24); a measurement device in which EUV radiation emitted by an EUV radiation source (14) is guided to the photomask (17) via the illumination system (16); EUV radiation reflected from the photomask (17) is guided to the image sensor (24) of the EUV camera (23) via the projection lens (22) so that the photomask (17) is imaged on the image sensor (24); a first EUV image recording is recorded by the EUV camera (23); and the positioning mechanism displaces the photomask (17) relative to the incident EUV radiation, and then a second EUV image recording is recorded.

Images