Optical inspection device

Abstract

To provide an optical inspection device.SOLUTION: Disclosed is an optical inspection device for elements pertaining to semiconductor lithography, comprising: an imaging device for generating an image of an element, the imaging device being arranged in a first partial volume; and a second partial volume comprising a holding device for receiving the element. In this case, a separating element is arranged between the two partial volumes. Further included is a position measuring device for ascertaining the position and orientation of the imaging device and the holding device, the position measuring device comprising reference masks for radiation of an electromagnetic wave used in the position measuring device, the reference masks being respectively connected to the imaging device and the holding device. The separating element comprises a partition wall having an opening. The opening serves for image recording by the imaging device, and the electromagnetic wave which emanates from the reference mask mounted on the imaging device and proceeds in the position measuring device passes through the opening.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] This application claims priority to German patent application DE102023131119.0, filed November 9, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to optical inspection devices, and more particularly to mask inspection systems for photomasks associated with semiconductor lithography. [Background technology]

[0003] Such inspection devices are also used to check the condition of photomasks used in semiconductor lithography, in particular to identify defects that occurred during the production or use of the corresponding masks, so as to enable subsequent repair of the masks.

[0004] Such systems usually comprise an imaging device, by means of which the mask, which is arranged on a holding device, a so-called mask holder, is recorded in a section-by-section, step-by-step or scan manner.

[0005] The growing popularity of EUV lithography, a form of semiconductor lithography using extremely short wavelengths, specifically wavelengths of a few nanometers, requires special measures for the inspection and handling of photomasks.

[0006] In particular, the inspection of the mask must usually be performed in a vacuum environment, where the imaging device and the mask to be inspected are typically placed in two different, independently conditioned volumes, leaving only a small aperture between the volumes for the passage of the electromagnetic waves used to inspect the mask.

[0007] However, for reliable imaging of the mask, the relative position of the imaging device with respect to the mask to be inspected must be known as precisely as possible or must be controllable as precisely and quickly as possible. This requires that the respective positions of the relevant elements be detected as precisely as possible. In this case, for example, position measuring devices such as interferometers are typically used. These position measuring devices generally detect the position of the mask holder and thereby indirectly detect the position of the mask.

[0008] In this situation, it is beneficial if the position information of both measured components, i.e. the imaging device as well as the mask being inspected, is recorded by the same measuring device, so that the relative positions of the imaging device and the mask can be determined as simply as possible. However, this collective measurement is made more difficult by the arrangement of the imaging device and the mask in different volumetric volumes. Summary of the Invention [Problem to be solved by the invention]

[0009] It is an object of the invention to specify a device which ensures that the relative position of the imaging device and the mask or element under inspection is determined as simply and as accurately as possible.

[0010] This object is achieved by a device having the features of the independent claim 1. The independent claims relate to advantageous developments and modifications of the invention. [Means for solving the problem]

[0011] The optical inspection device according to the invention comprises an imaging device for generating an image of an element, said imaging device being arranged in a first portion volume, and a second portion volume with a holding device for receiving said element. In this case, a separation element is arranged between the two portions volumes. Furthermore, the inspection device comprises at least one position measuring device for checking the position and orientation of the imaging device and the holding device, the position measuring device comprising a reference mask for the radiation of electromagnetic waves used in the position measuring device. Within the meaning of the present application, radiation is understood to mean in particular also the reflection of incident radiation by the reference mask. The reference mask is connected to the imaging device and the holding device, respectively.

[0012] In this case, the separation element comprises a partition having an opening which serves for image recording by the imaging device, through which electromagnetic waves emitted from a reference mask mounted on the imaging device and traveling within the position measuring device pass.

[0013] In this way, the openings between the compartments can be kept small, which facilitates maintaining different atmospheric conditions in the compartments. Overall, the design can also be made significantly more compact by the disclosed means, simplifying replacement of the imaging device in the field, i.e., at the point of use.

[0014] In one advantageous variant of the invention, there are at least two reference masks mounted on the at least two position measuring devices and the imaging device, and the beam paths of the electromagnetic waves emitted from the reference masks and traveling through the position measuring devices extend obliquely relative to each other.

[0015] In particular, the beam paths of the electromagnetic waves emanating from the reference mask and traveling within the position measuring device may cross each other.

[0016] The element as described may be a photomask for semiconductor lithography, for example for EUV lithography, and in particular the optical inspection device may be a mask inspection system for a photomask associated with EUV lithography.

[0017] The photomask may have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, particularly preferably 1:1 or 1:2, and may be substantially rectangular in design. The photomask may preferably have a length and width of 5 to 7 inches (12.7 to 17.78 cm), particularly preferably 6 inches (15.24 cm). Alternatively, the photomask may have a width of 5 to 7 inches (12.7 to 17.78 cm) and a length of 10 to 14 inches (25.4 to 35.56 cm), preferably 6 inches (15.24 cm) and 12 inches (30.48 cm).

[0018] In an advantageous embodiment of the invention, the position measuring device may be an interferometer.

[0019] In this case, the interferometer may in particular operate at a wavelength different from the radiation used for image recording, for example between 200 nm and 1700 nm, preferably between 400 nm and 800 nm, In this case, the electromagnetic waves emitted from the reference mask are generated by the reference mask being embodied as a reflector which is illuminated in the interferometer and reflects the incident radiation in a known manner in the beam path of the interferometer.

[0020] Furthermore, at least one position measuring device may be embodied such that electromagnetic waves emanate from a reference mask on the imaging device, reach the position measuring device and enter the position measuring device within a volume in which the imaging device is also located.

[0021] In a variant of the invention not claimed here, at least one position measuring device may be embodied such that it radiates from a reference mask on the holding device, travels within the position measuring device and travels completely within the volume in which the holding device is also located.

[0022] This can be achieved, for example, by inserting at least a part of the position measuring device into the separation element so that a radiation entrance aperture for electromagnetic waves emitted from a reference mask on the holding device and traveling through the position measuring device is arranged in the same volume as the holding device, while a radiation entrance aperture for electromagnetic waves emitted from a reference mask on the imaging device and traveling through the position measuring device is arranged in the same volume as the imaging device.

[0023] Exemplary embodiments and variants of the invention are described in detail below with reference to the drawings. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 illustrates a mask inspection system for inspecting a photomask. [Diagram 2] FIG. 2 illustrates an alternative to the configuration shown in FIG. [Diagram 3] FIG. 1 illustrates a further embodiment of the present invention. [Figure 4] FIG. 1 illustrates a further embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 1 shows a schematic excerpt of an optical inspection device, which is not claimed here and is embodied in the illustrated example as an element, namely a mask inspection system 100 for inspecting photomasks for EUV lithography. In such systems, unlike inspection systems for masks for longer wavelengths, the photomask is not recorded stationary in segments, but rather a scan of the entire mask surface is generally performed. In this case, the mask 1 is moved to scan under the imaging device 2, which is indicated by a double-headed arrow (no reference number is given) in FIG. 1. In this case, the mask 1 is arranged on a movable holding device 20, a so-called mask holder.

[0026] 1 further shows an image sensor 3 onto which the imaging device 2 images the surface of the mask 1. In this case, the image sensor 3 may be embodied as a TDI sensor similar to sensors used in linear array cameras.

[0027] In this case, the imaging device 2 and the image sensor 3 are located in a first compartment, which is embodied as a vacuum chamber 4, whereas the mask 1 arranged on a mask holder 20 is located in a further compartment, which is embodied as a vacuum chamber 5, from which the mask 1 is separated by a separating element, which is embodied as a partition 11. In contrast to the shown figure, the vacuum chamber 5 can in particular also be embodied in the form of a box, which box can then be located within the vacuum chamber 4. A decoupling element 8 is arranged between the imaging device 2 and the vacuum chamber 4 and at least partially decouples the imaging device 2 from the vacuum chamber 4.

[0028] The separated vacuum chambers 4 and 5 are necessary in this case to minimize contamination, and furthermore, the chambers 4 and 5 usually contain different atmospheres or media. Located between the two vacuum chambers 4 and 5 is an opening 6 through which the light emitted from the mask 1 passes to reach the imaging device 2.

[0029] Due to the scanning movement of the mask 1 and also due to environmental influences such as vibrations of the associated floor of the hall, mechanical dispersions are caused which, in the absence of further measures, lead to an offset of the imaging device 2 relative to the mask 1 during the scanning process. The image quality may be adversely affected by such offsets and it is therefore desirable to have the imaging device 2 and the mask 1 in a fixed spatial relationship relative to each other also during scanning, rather than a scanning movement. It is therefore necessary to track the mask 1 relative to the imaging device 2. For this purpose, the positions of the mask 1 and the imaging device 2 in a common coordinate system need to be known. To determine these positions, an interferometer 7 is used as a position measuring device, which may for example be embodied as a differential interferometer.

[0030] Further visible in the figure is a reference element 9, which is fixedly connected to the imaging device 2, is shown in the figure as a rod, protrudes through a partition 11 between the two vacuum chambers 4 and 5 towards the vacuum chamber 5 and includes a reference mask embodied as a sensor target 15, which is embodied as a mirror-reflecting surface and may serve as a reference for the interferometer 7. A measurement beam advances in the interferometer 7, passes through an emission window 16, which is indicated in the figure by a double-headed arrow (no reference number is given), in this case reaches the sensor target 15 of the interferometer 7 and, after reflection at the sensor target 15, again through the emission window 16, enters the transceiver 10 of the interferometer 7, which may include, for example, a radiation source (not shown separately in FIG. 1) and a receiving device of the interferometer 7 (likewise not shown in FIG. 1).

[0031] Like the imaging device 2, the mask holder 20 is also provided with a sensor target 15, which also serves to reflect the measurement beam of the interferometer 7. This allows the relative position of the mask holder 20 (and thus the mask 1) and the imaging device 2 to be determined and controlled.

[0032] As an alternative to the configuration shown in Figure 1, this alternative, which is not claimed here, is likewise shown in Figure 2. In Figure 2, a partial area of ​​the interferometer 7 is fixedly connected to the imaging device 2 and participates in its movement. The relative position of the imaging device 2 with respect to the mask 1 can thus be determined relatively easily.

[0033] FIG. 3 shows an embodiment of the present invention, in which a sensor target 15 assigned to the imaging device 2 is located in the same vacuum chamber 4 as the imaging device 2. This is achieved in the example shown by a measurement beam of an interferometer 7 running obliquely between the vacuum chambers 4 and 5 and passing through an opening 6 in the partition 11, which measurement beam is also used for image recording by the imaging device 2. The beam paths of the electromagnetic waves emitted from the sensor target 15 or reflected at it cross each other in the example shown. A distorted progression of the beam paths is also possible. The opening 6 between the vacuum chamber 4 and the vacuum chamber 5 can thus be kept relatively small. Furthermore, in this way the sensor target 15 can be mounted close to the imaging device 2, which provides advantages in terms of dynamic properties and higher performances become achievable in the control of the relative positions of the imaging device 2 and the mask 1.

[0034] Overall, the design is also significantly more compact by the disclosed measures, simplifying the replacement of the imaging device 2 in the field, ie at the place of use of the corresponding mask inspection device 100 .

[0035] Since the measurement beam of the interferometer 7 is directed obliquely in the example shown, it may be necessary to carry out intermediate calculations to be able to ascertain the exact relative movement of the imaging device 2 and the mask 1 with respect to one another.

[0036] 4 shows a variant not claimed here, in which the interferometer is embodied in such a way that the measurement beam, having reached the imaging device 2, travels completely inside the vacuum chamber 4. In this case, the transceiver 10 of the interferometer 7 is inserted into the bulkhead 11, the radiation window 16 for the measurement beam for the mask 1 is arranged in the associated vacuum chamber 5, while the radiation window 16' for the measurement beam for the imaging device 2 is arranged in the associated vacuum chamber 4. In this case, it may be necessary to carry out a special sealing of the transceiver 10 of the interferometer 7. [Explanation of symbols]

[0037] 1 element, mask 2 Imaging Device 3 Image Sensor 4. First portion volume 5 Second portion volume 6 aperture 7 Interferometer 8 Decoupling Elements 9. Criteria Elements 10 Transmitter / receiver 11 Bulkhead 15 Reference mask, sensor target 16, 16' Radiation window 100 Optical Inspection Device

Claims

1. An optical inspection device (100) for an element (1) related to semiconductor lithography, comprising: an imaging device (2) for generating an image of the element, said imaging device being arranged in a first portion (4); a second portion volume (5) comprising a holding device (20) for receiving said element (1), a separating element (11) is arranged between the two said compartments (4, 5), - at least one position measuring device (7) for ascertaining the position and orientation of said imaging device (2) and said holding device (20); - said position measuring device (7) comprises a reference mask (15) for the radiation of the electromagnetic waves used in said position measuring device (7), said reference mask (15) being connected to said imaging device (2) and to said holding device (20), an optical inspection device (100), in which the separation element (11) comprises a partition having an opening (6) which serves for image recording by the imaging device (2), and in which the electromagnetic waves emitted from the reference mask (15) mounted on the imaging device (2) and traveling within the position measuring device (7) pass through the opening (6).

2. 2. The optical inspection device (100) of claim 1, characterized in that there are at least two position measuring devices (7) and at least two reference masks (15) mounted on the imaging device (2), and the beam paths of the electromagnetic waves emitted from the reference masks (15) and traveling through the position measuring devices (7) extend obliquely with respect to each other.

3. 3. Optical inspection device (100) according to claim 2, characterized in that the beam paths of the electromagnetic waves emitted from the reference mask (15) and traveling through the position measuring device (7) cross each other.

4. The optical inspection device (100) according to any one of claims 1 to 3, characterized in that the optical inspection device (100) is a mask inspection system for photomasks related to EUV lithography.

5. Optical inspection device (100) according to any one of claims 1 to 4, characterized in that the position measuring device (7) is an interferometer.

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