Method for inspecting photomasks, as well as measuring devices and EUV cameras

Abstract

A photomask inspection method in which a photomask (17) is irradiated with EUV radiation emitted by an EUV radiation source (14). [Solution] EUV radiation reflected from the photomask (17) is guided through a projection lens (22) to the image sensor (24) of an EUV camera (23) so that the photomask (17) is imaged on the image sensor (24). The EUV radiation passes through a pellicle (30) placed between the projection lens (22) and the image sensor (24). The present invention relates to an EUV camera and also to a measuring device for inspecting a photomask.

Description

Technical Field

[0001] The present invention relates to a method for inspecting a photomask, a measuring device, and an EUV camera.

Background Art

[0002] In particular, in a microlithographic projection exposure apparatus used for manufacturing an integrated circuit having a particularly minute structure, a photomask is used. In order to transfer the mask structure onto a lithography object, a photomask irradiated with extreme ultraviolet radiation (EUV radiation) of ultra-short wavelength is imaged onto the lithography object.

[0003] In order to ensure the high quality of the image formed on the lithography object, it is necessary that the photomask is exactly the right size and is not impaired by contaminants. It is a known practice to subject the photomask to inspection before or during an operation in a microlithographic projection exposure apparatus. For this purpose, a so-called aerial image of the photomask or a part of the photomask is created, and the photomask during the process is imaged onto an image sensor instead of onto the lithography object. Based on the imaging onto the image sensor, it is possible to perform an evaluation regarding whether there are defects and contaminants in the photomask.

[0004] Mask inspection needs to be performed so that the measurement results are not modified by contaminants. Specifically, it is necessary to prevent the photomask from being contaminated as a result of the mask inspection procedure.

Summary of the Invention

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

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

[0007] The pellicle positioned between the image sensors has two effects: firstly, it prevents contaminants and particles emanating from the EUV camera from passing into the projection lens or other areas of the measuring device; and secondly, it prevents contaminants and particles emanating from the projection lens or other areas of the measuring device from passing into the EUV camera and onto the image sensors. This reduces the risk of measurements being impaired by contamination.

[0008] The pellicle can be placed 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 is not reflected by the further mirrors of the projection lens.

[0009] According to one aspect of the present 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 to be reflective across the entire surface of the EUV photomask. In that case, the EUV radiation passes through the pellicle twice, specifically once before reflection in the photomask and once after reflection in the photomask. The loss of EUV radiation output is twice as high as when it passes through the pellicle only once.

[0010] A pellicle is a film designed to allow EUV radiation to pass through but block the passage of particles. Because materials generally have high absorptive potential for EUV radiation, the material and structure of the pellicle must be carefully adapted for use in measuring 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 film made of carbon nanotubes. The density and bundle structure of the carbon nanotubes can be selected so that the film transmits EUV radiation on the one hand, but on the other hand, particles are trapped in the film and cannot pass through it. To give the film sufficient resistance to radical ions and molecules, the film can be coated.

[0012] In another embodiment, the pellicle comprises a film made of silicon, silicon nitride, or any other silicon-containing material. When sufficiently thin, such a film made of silicon material also exhibits sufficient permeability to EUV radiation. In this case as well, the ability to block the passage of gaseous contaminants is more pronounced in the case of a silicon material pellicle than in the case of a CNT pellicle.

[0013] The pellicle can be a component of the EUV camera. The EUV camera may include a camera housing that supports the image sensor and to which the pellicle is attached. The camera housing may 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 may be placed in a vacuum chamber where vacuum pressure exists during the operation of the measurement device.

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

[0015] The pellicle can be placed over the aperture so that all EUV radiation entering the interior through the aperture passes through the pellicle, i.e., travels through the pellicle. The pellicle can be flush with the housing edge surrounding the aperture so as 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 the frame. The pellicle can be secured to the frame such that the opening stretched across the frame is covered by the pellicle. The connection to the EUV camera housing can be established via the frame. To allow for pellicle replacement, 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 surface of the image sensor. The distance between the image sensor and the pellicle can be such that particles adhering to the pellicle only significantly impair the image recorded by the image sensor. In this context, there are conflicting aspects. To avoid damaging the recorded image, it is advantageous for the pellicle to be far from the image sensor. A pellicle positioned close to the image sensor is advantageous for a compact configuration of the EUV camera or measurement device.

[0018] EUV cameras can be used in a downward configuration, where the image sensor faces downwards and EUV radiation enters the image sensor from below. In this downward configuration, the pellicle is positioned below the image sensor. It is also possible to use an upward configuration EUV camera, where the image sensor faces upwards and EUV radiation enters the image sensor from above. In this upward configuration, the pellicle is positioned above the image sensor.

[0019] In an upward-facing configuration, gravity helps move particles toward the image sensor. However, particle movement toward the image sensor can also occur in a downward-facing configuration, and in this case as well, there is a risk of the image sensor being contaminated as a result. In both cases, the pellicle protects the image sensor from particles from the surroundings of the EUV camera that can adhere to the image sensor.

[0020] Conversely, it is also necessary to prevent contaminants from emanating from inside the EUV camera from contaminating other components of the measurement device. Specifically, contaminants separated from the EUV camera must not accumulate on the surface of the photomask. This risk exists specifically when the EUV camera is operated in a vacuum atmosphere and there is gas emission from the materials used in the camera. Generally, the structure of the pellicle is not designed to prevent the passage of gaseous contaminants. This invention acknowledges that a pellicle made of silicon material has a superior effect than a CNT pellicle in terms of the passage of gaseous contaminants. For this reason, in one embodiment, the pellicle is made of silicon material.

[0021] The projection lens of the measuring device can have a high magnification of, 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 may include an image sensor with a uniform sensor area that is entirely occupied by pixels. The pellicle can be sized to cover the area of ​​the uniform sensor area, and as a result, EUV radiation can reach the entire sensor area through the pellicle.

[0022] In other embodiments, the image sensor is configured as a sensor array in which multiple sensor components span the sensor area of ​​the image sensor. Each individual sensor component may have a sensor area entirely occupied by pixels. The sensor area of ​​the image sensor may have a pixel-free area that can be placed between the sensor areas of two sensor components.

[0023] An EUV camera may include pellicles smaller than the sensor area of ​​the image sensor, resulting in not all of the EUV radiation incident on the image sensor passing through a single pellicle. An EUV camera may include multiple pellicles that collectively cover the sensor area of ​​the image sensor, resulting in all of the EUV radiation incident on the image sensor passing through one of the pellicles, preferably exactly one of the pellicles. Multiple pellicles may be arranged in a plane.

[0024] Multiple pellicles can be held on a frame. The frame of the pellicle can be positioned in front of areas of the image sensor's sensor region that do not contain pixels. In this case, the frame does not interfere with image recording and merely shields EUV radiation in areas where EUV radiation does not occur to the pixels of the image sensor in any case. A pellicle can cover the sensor region of one or more sensor components. In one embodiment, each sensor component is assigned its own pellicle.

[0025] In the case of a sensor array that is not fully occupied by pixels, there is an area of the imaging portion of the photomask where image information cannot be obtained by a single EUV image recording. Therefore, provisions can be made to change the position of the photomask relative to the incoming EUV beam path and to enable a second EUV image recording to be made. In the case of the second EUV image recording, the photomask can be positioned such that image information can be obtained from the area of the imaging portion of the photomask where the first image recording does not supply image information. This method can be performed with more than two positions of the photomask and more than two EUV image recordings. The image of the imaging portion of the photomask can be calculated from the available multiple EUV image recordings.

[0026] In one embodiment, the device includes an XY positioning mechanism, whereby the position of the photomask in the XY plane can be changed relative to the incoming EUV beam path. The XY plane can correspond to the plane of the photomask. The XY positioning mechanism can be realized to linearly displace the photomask in the XY plane. This can be used for a scanning procedure in which multiple EUV image recordings belonging to the same portion of the photomask are recorded when the photomask moves linearly.

[0027] In addition to or instead of the above, the XY positioning mechanism can also be used to displace the photomask relative to the incoming EUV beam path so as to create aerial images of different portions of the photomask. Specifically, the XY positioning mechanism can be designed to be able to inspect each portion of the photomask.

[0028] In addition to or instead of the above, the XY positioning mechanism can be used to obtain information regarding the state of the pellicle. For this purpose, a reference mask having a known surface structure, such as a uniform surface structure, can be introduced into the measuring device. Information regarding the state of the pellicle can be displayed according to how the image recording changes when the reference mask is displaced in the XY plane.

[0029] The projection lens of the measurement device can include a plurality of EUV mirrors from which EUV radiation is reflected between the photomask and the image sensor. The optical region of the EUV mirror can be formed by a highly reflective coating. This can be a multilayer coating, particularly a multilayer coating having alternating layers of molybdenum and silicon. Using such a coating, about 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] The projection lens can be used to guide EUV radiation coming from the photomask to the image sensor so that an image of the photomask, specifically a part of the photomask, appears on the image sensor. The part of the photomask imaged on the image sensor can correspond to a small part of the photomask.

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

[0032] The measurement device according to the present invention may include additional pellicles positioned in one or more other sections of the EUV beam path, so that the EUV radiation passes through multiple pellicles in succession. The measurement device may include additional pellicles through which the EUV radiation passes exactly once. In addition to or instead of this, the measurement device may include pellicles positioned so that the EUV radiation passes through the pellicle twice.

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

[0034] The pellicle of an EUV camera can be made of silicon material. The pellicle can be flush with the housing edge surrounding the opening in a sealed manner. The pellicle can be mounted on a frame, in which case the pellicle is connected to the camera housing via the frame, and the frame is detachably connected to the camera housing. The image sensor can be configured as a sensor array, with multiple sensor components stretched across the sensor area of ​​the image sensor. The EUV camera can include a pellicle smaller than the sensor area of ​​the image sensor. Multiple pellicles can be held on a frame, with parts of the frame positioned in front of the pixelless areas of the image sensor's sensor area.

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

[0036] The illumination system may be configured to illuminate a portion of the photomask. The illumination system may be configured such that the intensity of the EUV radiation is substantially uniform within the illuminated portion. The illumination system may include one or more EUV mirrors that reflect the EUV radiation along the path between the EUV radiation source and the photomask. The EUV radiation source may 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 may be tin. The plasma is formed by directing a laser beam onto droplets of the medium. The projection lens may include multiple EUV mirrors that reflect the EUV radiation between the photomask and the pellicle. The measuring device may include an EUV radiation source.

[0037] This disclosure encompasses the development of a method having the features described in the context of the EUV camera or measurement device according to the present invention. This disclosure encompasses the development of an EUV camera and measurement device having the features described in the context of the method according to the present invention.

[0038] The present invention will be described below using advantageous embodiments as examples with reference to the accompanying drawings. [Brief explanation of the drawing]

[0039] [Figure 1] This figure shows a schematic diagram of the measuring device according to the present invention. [Figure 2] This figure shows a schematic cross-sectional view of the EUV camera according to the present invention. [Figure 3] This figure shows one configuration of the EUV camera shown in Figure 2. [Figure 4] This is a schematic diagram of a photomask. [Figure 5] This is a view from the perspective shown in Figure 2, in another embodiment of the EUV camera. [Figure 6] This figure shows one configuration of the EUV camera shown in Figure 5. [Figure 7] This figure shows a schematic diagram of the measuring device according to the present invention. [Figure 8] This is a view from the perspective shown in Figure 2, representing a further embodiment of the EUV camera. [Figure 9] This figure shows one configuration of the EUV camera shown in Figure 8. [Modes for carrying out the invention]

[0040] The microlithography photomask 17 can be inspected using the measuring device according to the present invention.

[0041] Generally, a 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) with a wavelength of, for example, 13 nm, in order to image the structure 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 reacts to EUV radiation. A measuring device is used to check that the measuring device meets the requirements and is free of contaminants.

[0042] As shown in Figure 1, the photomask 17 is positioned within the measurement device such that the EUV beam path 15 emitted from the EUV radiation source 14 is guided to the photomask 17 via the illumination system 16. The illumination system 16 is used to shape the EUV radiation to form a beam used to illuminate the inspection field 20 on the surface of the photomask 17 with uniform brightness. The inspection field 20, which is small compared to the area of ​​the photomask 17, is shown in Figure 4 in a diagram that is not scale-accurate. For example, the illumination area 20 may have dimensions of 0.5 mm × 0.8 mm. The edge length of the photomask 17 can be, for example, between 100 mm and 200 mm. A field aperture 21, used to demarcate the illumination area to the inspection field 20 on the surface of the photomask 17, is positioned between the first illumination mirror 17 and the second illumination mirror 18. To place different inspection fields 20 into the region of the EUV beam path, it is possible to move the photomask in the XY plane using the XY positioning mechanism 37.

[0043] The EUV beam path 15 reflected from the photomask 17 continues through the projection lens 22 to the 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 diaphragm 25, whose aperture corresponds to the first mirror M1, is positioned between the photomask 17 and the first mirror M1. The EUV radiation source 14, irradiation system 15, photomask 17, projection lens 22, and EUV camera 23 are all housed in a vacuum housing 40 that is under negative pressure during operation of the measurement device.

[0044] EUV radiation source 14 is a plasma radiation source that emits EUV radiation at a wavelength of 13 nm from the plasma. Tin is a medium that can be used to generate a plasma suitable for emitting such EUV radiation. A laser beam can be shone onto droplets of the medium for the purpose of generating the plasma.

[0045] As shown in Figure 2, the EUV camera 23 includes a housing 26 in which an image sensor 24 and an electronic circuit unit 27 are housed. The electronic circuit unit 27 is used to control the image sensor 24 and to process the EUV image data obtained by the image sensor 24. A connecting flange 29 is formed on the housing 26, extending 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 a detachable connection so that the 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 the pellicle unit 32, the housing 26 completely encloses the interior of the EUV camera 23. EUV radiation arriving from the projection lens 22 enters the interior of the EUV camera 23 through the pellicle 30 and is incident on the image sensor 24. A schematic diagram of the image sensor 24 as seen through the pellicle 30 is shown in Figure 3. The image sensor 24 includes a sensor area whose entire surface is occupied by pixels, which can be seen through the pellicle 30 and is available for recording an image of the inspection field 20 of the photomask 17.

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

[0048] Together with the pellicle unit 32, the housing 26 is designed so that mass exchange between the inside and outside of the EUV camera 23 is largely suppressed, while pressure equalization remains possible. The measurement device operates within the vacuum housing 40. During the operation of the measurement device, the vacuum pressure inside the EUV camera 23 is the same as in other areas of the vacuum housing 40.

[0049] The pellicle 30 is an extremely thin film made of silicon material that allows EUV radiation to pass through well but prevents the passage of particles. 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 problematic if they adhere to 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, the pellicle 30 prevents contaminants from escaping from inside the EUV camera 23 and from adhering to other components of the measurement device. Specifically, contamination of the photomask 17 itself must be avoided, as this could result in semiconductor components manufactured using the photomask 17 becoming unusable in later stages.

[0051] Such contamination can result in gas emissions, which can occur in the EUV camera 23, particularly when a vacuum is present inside the EUV camera 23. The EUV camera 23 includes an adhesive for connecting, for example, the electronic circuit unit 27 and the image sensor 24 to the housing 26. The pellicle 30, made of silicon material, has the effect of containing most of such gas emissions inside the EUV camera 23, allowing at most minute components to escape to the outside. The function of the EUV camera 23 is not impaired by the gas emissions. Gas emissions would cause damage if the gas cloud came into contact with other components of the external measuring device of the EUV camera 23.

[0052] Figure 5 shows another embodiment of the EUV camera 23 in which the pellicle unit 32 is connected to a mechanism 33 that enables semi-automatic replacement of the pellicle unit 32. The mechanism 33 includes a motor 34 that can rotate a rotating part 35. The pellicle unit 32, mounted on the rotating part 35 via an arm, pivots laterally relative to the housing 26 of the EUV camera 23 as the rotating part 35 rotates. In this way, the pellicle unit 32 can be moved to a position that is easily accessible, allowing the used-up pellicle unit 32 to be replaced with a new one. The vacuum housing of the measuring device may include a flap that allows access to the used-up pellicle unit 32. The vacuum in the vacuum housing is released before the flap is opened.

[0053] As shown in Figure 6, the image sensor 24 includes a total of nine sensor components 36 in this embodiment. Each sensor component 36 has a sensor area whose entire surface is occupied by pixels. There is a narrow pixelless area at the transition between two adjacent sensor components 36. The pixelless areas form a grid pattern on the image sensor 24.

[0054] When the sensor area of ​​the image sensor 24 is formed from multiple sensor components 36, this is advantageous in that a large-area image sensor 24 can be assembled on a conventional CCD chip that is sensitive to EUV radiation. In this embodiment, it is acceptable that there are pixel-free regions between the sensor components 36 from which EUV image information cannot be obtained.

[0055] In the exemplary embodiment shown in Figure 7, the photomask 17 is positioned on the XY positioning mechanism 37, thereby allowing the photomask 17 to be displaced in the XY plane. Displacing the photomask 17 in the XY plane results in the fact that the area of ​​the inspection field 20 on the photomask 17 that is incident on the pixelless area of ​​the image sensor 24 is not always the same area. By recording multiple EUV image recordings 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 appropriately combining the calculated EUV image recordings, an image showing the inspection field 20 without gaps can be obtained.

[0056] Figures 8 and 9 show an exemplary embodiment in which the EUV camera 23 includes a plurality of pellicles 30, each smaller than the image sensor 24 but combined to cover the sensor area 38 of the image sensor 24. Each sensor component 36 is assigned a pellicle 30 held by a frame component extending around the sensor component 36. Together, this forms a frame 39 that extends in a grid pattern over the area of ​​the image sensor 24, with its frame supports positioned in the pixel-free areas between the sensor components 36.

[0057] As shown in Figure 8, firstly, the EUV image recorded by the image sensor 24 is not impaired by contaminants adhering to the pellicle 30, and secondly, the pellicle component, consisting of multiple pellicles 30, is positioned at a shorter distance from the image sensor 24 so that the EUV radiation passing through the support pillars of the frame 28 is shielded not by the sensor component 36, but primarily by the pixelless areas between the sensor component 36.

[0058] The pellicle component positioned in front of the image sensor 24 prevents the release of particles and gases that could escape from inside the EUV camera 23 and damage other components of the measurement device. Conversely, it prevents particles present inside the measurement device from entering the EUV camera 23 and adhering to the image sensor 24. The presence of particles on the image sensor 24 would interfere with EUV image recording.

[0059] When a defect is visible in the EUV image recording, it is not easy to determine whether it is caused by contaminants on the image sensor 24, contaminants or defects on the photomask 17, or defects at any other point on the projection lens 22. To distinguish between different sources of errors, a mechanism can be provided to give the photomask 17 a slight movement in the XY plane. Defects that move on the image sensor 24 along with the photomask 17 can be attributed to the photomask 17. Defects that remain unchanged in position on the image sensor 24 despite the movement of the photomask 17 may be located on the image sensor 24.

[0060] The photomask 17 can also be replaced with a reference mask that does not necessarily have any structures on its surface. An EUV image created using such a reference mask should have uniform brightness values ​​across the area of ​​the image sensor 24. The state of the projection lens 22 can be inferred based on the deviation from the expected brightness distribution. [Explanation of Symbols]

[0061] 14 EUV radiation source 15 EUV beam path 16 Irradiation system 17 Photomasks 20 Inspection Fields 21 Field of View Aperture 22 Projection Lens 23 EUV cameras 24 Image sensors 26 Housing 27 Electronic Circuit Unit 28 frames 29 Connection flange 30 Pellicles 31 Entrance aperture 32 Pellicle Units 33 Mechanism 34 motors 35 Rotating parts 36 Sensor Components 37 Positioning mechanism 38 Sensor area 39 frames 40 Vacuum Housing M1 First Mirror

Claims

1. A method for inspecting a photomask, wherein the photomask (17) is irradiated with EUV radiation emitted by an EUV radiation source (14), and the EUV radiation reflected from the photomask (17) is guided through a projection lens (22) to the image sensor (24) of an EUV camera (23) so that the photomask (17) is imaged on the image sensor (24), and the EUV radiation passes through a pellicle (30) positioned between the projection lens (22) and the image sensor (24).

2. The method according to 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. The method according to any one of claims 1 to 3, wherein a first EUV image record is recorded by the EUV camera, the photomask (17) is displaced relative to the incident EUV radiation, and thereafter a second EUV image record is recorded.

5. An EUV camera having a camera housing (28) and an image sensor (24), wherein the image sensor (24) is held within the camera housing (28), the image sensor (24) is sensitive to EUV radiation, the camera housing (28) spans an entrance aperture (31) designed for the incidence of EUV radiation, and the EUV camera (23) includes a pellicle (30) such that EUV radiation incident on the EUV camera (23) through the entrance aperture (31) passes through the pellicle (30).

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

7. The EUV camera according to claim 5 or 6, wherein the pellicle (30) is flush with the housing edge surrounding the entrance opening (31) in a sealed manner.

8. The EUV camera according to any one of claims 5 to 7, wherein the pellicle (30) is attached to a frame (28), the pellicle (30) is connected to the camera housing (26) via the frame (28), and the frame (28) is detachably connected to the camera housing (26).

9. The EUV camera according to any one of claims 5 to 8, wherein the image sensor (24) is configured as a sensor array in which a plurality of sensor components (36) are stretched across the sensor area (38) of the image sensor (24).

10. The EUV camera according to any one of claims 5 to 9, wherein the EUV camera (23) includes a pellicle (30) smaller than the sensor area (38) of the image sensor (24).

11. The EUV camera according to any one of claims 5 to 10, wherein the EUV camera (23) includes a plurality of pellicles (30).

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

13. The EUV camera according to claim 11 or 12, wherein the plurality of pellicles (30) are held on a frame (39), and the components of the frame (39) are positioned in front of the pixelless area of ​​the sensor region (38) of the image sensor (24).

14. A measuring device for inspecting a photomask, comprising an illumination system (16), a projection lens (22), and an EUV camera (23), wherein EUV radiation emitted by an EUV radiation source (14) is guided through the illumination system (16) to the photomask (17), and the EUV radiation reflected from the photomask (17) is guided through the projection lens (22) to the image sensor (24) of the EUV camera (23) so that the photomask (17) is imaged on the image sensor (24), and the measuring device includes a pellicle (30) positioned between the projection lens (22) and the image sensor (24).

Images