Optical inspection devices

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 the priority of German Patent Application No. DE102023131119.0 filed on November 9, 2023, the content of which is hereby incorporated by reference in its entirety into this specification.

[0002] The present invention relates to an optical inspection device, and more particularly to a mask inspection system for a photomask related to semiconductor lithography.

Background Art

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

[0004] Such a system usually includes an imaging device, whereby a mask placed on a holding device, a so-called mask holder, is recorded section by section, process by process, or in a scanning manner.

[0005] With the spread of the popularity of EUV lithography, that is, semiconductor lithography using extremely short wavelengths, especially wavelengths in the order of a few nanometers, special means for inspection and for handling photomasks are required.

[0006] In particular, mask inspection needs to be usually carried out in a vacuum environment. In this case, usually, the imaging device and the mask to be inspected are placed in two different partial volumes that are each conditioned independently, and only a small aperture for the passage of electromagnetic waves used to inspect the mask remains between the partial volumes.

[0007] However, for reliable imaging of the mask, the relative position of the imaging device to the mask under inspection must be known as precisely as possible, or controlled as precisely and quickly as possible. This requires detecting the position of each relevant element as accurately as possible. In this case, for example, position-measuring devices such as interferometers are typically used. Generally, these position-measuring devices 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 positional information of both the imaging device and the mask being examined 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 simultaneous measurement becomes more difficult due to the placement of the imaging device and mask in different volumes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The objective of the present invention is to provide a device that ensures the relative position between the imaging device and the mask or element to be inspected is determined as simply and accurately as possible.

[0010] The above objective is achieved by a device having the features of independent claim 1. The independent claim relates to beneficial developments and variations of the present invention. [Means for solving the problem]

[0011] The optical inspection device according to the present invention comprises an imaging device for generating an image of an element, wherein the imaging device is located in a first fractional volume, and a second fractional volume comprising a holding device for receiving the element. In this case, the separation element is located between the two fractional volumes. Furthermore, the inspection device comprises at least one position measuring device for confirming the position and orientation of the imaging device and the holding device, the position measuring device comprising a reference mask for the emission of electromagnetic waves used in the position measuring device. Within the scope of the present application, emission should be understood to also mean, in particular, 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 wall having an opening, which functions for image recording by an imaging device, and electromagnetic waves radiated from a reference mask mounted on the imaging device and traveling through the position measuring device pass through the opening.

[0013] In this way, the opening between fractional volumes can be kept small, thereby facilitating the maintenance of different atmospheric conditions within the fractional volumes. Overall, the design can also be significantly more compact by the disclosed means, simplifying the replacement of imaging devices in the field, i.e., at the point of use.

[0014] In one beneficial variation of the present invention, there are at least two position-measuring devices and at least two reference masks mounted on imaging devices, wherein the beam paths of electromagnetic waves radiated from the reference masks and traveling through the position-measuring devices are oblique to each other.

[0015] In particular, the beam paths of electromagnetic waves emitted from the reference mask and traveling through the positioning device may intersect with each other.

[0016] The elements described above may also be photomasks for semiconductor lithography, such as EUV lithography, and in particular, the optical inspection device may be a mask inspection system for photomasks related to EUV lithography.

[0017] The photomask may have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and 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) in length and width. 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) in width and 12 inches (30.48 cm) in length.

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

[0019] In this case, the interferometer may operate in particular at wavelengths different from those of the radiation used for image recording, such as 200 nm to 1700 nm, preferably 400 nm to 800 nm. In this case, the electromagnetic waves emitted from the reference mask are generated by the reference mask, which is embodied as a reflector being irradiated in the interferometer, and reflect the incident radiation in the manner known in the beampath of the interferometer.

[0020] Furthermore, at least one position measuring device can be embodied such that electromagnetic waves are emitted from a reference mask on an imaging device and reach the position measuring device, and the imaging device also enters the position measuring device within the volume in which it is located.

[0021] In modifications of the present invention not asserted herein, 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 the holding device also travels entirely within the volume in which it is located.

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

[0023] Exemplary embodiments and variations of the present invention are detailed below with reference to the drawings.

Brief Description of the Drawings

[0024] [Figure 1] It is a diagram showing a mask inspection system for inspecting a photomask. [Figure 2] It is a diagram showing an alternative to the configuration shown in FIG. 1. [Figure 3] It is a diagram showing a further embodiment of the present invention. [Figure 4] It is a diagram showing a further embodiment of the present invention.

Mode for Carrying Out the Invention

[0025] FIG. 1 schematically extracts and shows an optical inspection device embodied as a mask inspection system 100 for inspecting a photomask for EUV lithography, which is not claimed in this case and is shown in the example. In such a system, unlike inspection systems for masks for longer wavelengths, the photomask is not stationary and recorded in segments, but generally a scan of the entire mask surface is performed. In this case, the mask 1 is moved so as to scan below the imaging device 2, which is indicated by the double-headed arrow (reference numeral not given) in FIG. 1. In this case, the mask 1 is arranged on a movable holding device 20, a so-called mask holder.

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

[0027] In this case, the imaging device 2 and image sensor 3 are located in a first fractional volume embodied as a vacuum chamber 4, while the mask 1, placed on the mask holder 20, is located in a further fractional volume embodied as a vacuum chamber 5, and the mask 1 is separated from the vacuum chamber 5 by a separating element embodied as a partition wall 11. The vacuum chamber 5 may also be embodied in the form of a box, in contrast to the figure shown, in which case this box may be located inside the vacuum chamber 4. A decoupling element 8 is placed between the imaging device 2 and the vacuum chamber 4 to decouple the imaging device 2 from the vacuum chamber 4 at least partially.

[0028] These separate vacuum chambers 4 and 5 are necessary in this case to minimize contamination, and furthermore, chambers 4 and 5 typically contain different atmospheres or media. An opening 6 is located between the two vacuum chambers 4 and 5, through which light emitted from mask 1 passes to imaging device 2.

[0029] Mechanical dispersion occurs due to the scanning movement of mask 1 and environmental influences such as vibrations of the hall's floor. If no further measures are taken, this leads to an offset of imaging device 2 relative to mask 1 during the scanning process. Image quality may be negatively affected by such offsets; therefore, it is desirable that imaging device 2 and mask 1 maintain a fixed spatial relationship with respect to each other during scanning, rather than undergoing scanning movement. Thus, it is necessary to track mask 1 relative to imaging device 2. For this purpose, it is necessary to know the positions of mask 1 and imaging device 2 in a common coordinate system. To determine these positions, an interferometer 7 is used as a position measuring device, which can be embodied, for example, as a differential interferometer.

[0030] Reference element 9 is further recognizable in the figure, which is fixedly connected to imaging device 2, shown as a rod in the figure, protruding toward vacuum chamber 5 through partition 11 between two vacuum chambers 4 and 5, and includes a reference mask which is embodied as sensor target 15, which is embodied as a mirror reflecting surface and can function as a reference for interferometer 7. The measurement beam advances in interferometer 7, passes through radiation window 16, which is shown in the figure by a double-headed arrow (no reference numeral is given), in this case reaches sensor target 15 of interferometer 7, and after reflection at sensor target 15, also through radiation window 16, enters the transmitting / receiving unit 10 of interferometer 7, which may include, for example, a radiation source (not shown separately in Figure 1) and a receiving device for interferometer 7 (similarly not shown in Figure 1).

[0031] Similar to the imaging device 2, the mask holder 20 is also provided with a sensor target 15, which similarly functions to reflect the measurement beam of the interferometer 7. This allows for the determination and control of the relative position between the mask holder 20 (and therefore the mask 1) and the imaging device 2.

[0032] As an alternative to the configuration shown in Figure 1, this alternative, which is not asserted in this case, is also shown in Figure 2. In Figure 2, a portion of the interferometer 7 is fixedly connected to the imaging device 2 and is involved in its movement. In this way, the relative position of the imaging device 2 with respect to the mask 1 can be determined relatively easily.

[0033] Figure 3 shows one embodiment of the present invention, in which the 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 an example shown by the measurement beam of the interferometer 7, which travels obliquely between vacuum chambers 4 and 5 and passes through the aperture 6 of the partition wall 11, and this measurement beam is also used for image recording by the imaging device 2. The beam paths of electromagnetic waves emitted from or reflected in the sensor target 15 intersect each other in the illustrated example. Distorted propagation of the beam paths is also possible. The aperture 6 between vacuum chambers 4 and 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 characteristics and makes higher performance achievable in controlling the relative position of the imaging device 2 and the mask 1.

[0034] Overall, the design is also significantly more compact by the disclosed means, and the replacement of the imaging device 2 in the field, i.e., at the site of use of the corresponding mask inspection device 100, is simplified.

[0035] In the example shown, the measurement beam of the interferometer 7 is guided at an angle, so it may be necessary to perform intermediate calculations to confirm the accurate relative movement of the imaging device 2 and the mask 1 relative to each other.

[0036] Figure 4 shows a modification not asserted in this case, in which the interferometer is embodied so that the measurement beam reaching the imaging device 2 travels entirely through the vacuum chamber 4. In this case, the transmitting and receiving unit 10 of the interferometer 7 is inserted into the partition wall 11, the radiation window 16 for the measurement beam for the mask 1 is located in the associated vacuum chamber 5, while the radiation chamber 16' for the measurement beam for the imaging device 2 is located in the associated vacuum chamber 4. In this case, it may be necessary to implement special sealing of the transmitting and receiving unit 10 of the interferometer 7. [Explanation of symbols]

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

Claims

1. An optical inspection device (100) for an element (1) related to semiconductor lithography, - An imaging device (2) for generating an image of an element, wherein the imaging device (2) is located in a first volume (4), - A second volume (5) having a holding device (20) for receiving the element (1), - The separation element (11) is positioned between the two aforementioned volumetric parts (4, 5), - It includes at least one position measuring device (7) for confirming the position and orientation of the imaging device (2) and the holding device (20), - The position measuring device (7) is equipped with a reference mask (15) for the emission of electromagnetic waves used in the position measuring device (7), - The reference mask (15) is connected to the imaging device (2) and the holding device (20), respectively. - The separation element (11) comprises a partition having an aperture (6), the aperture (6) functioning for image recording by the imaging device (2), and the electromagnetic waves radiated from the reference mask (15) mounted on the imaging device (2) and traveling through the position measuring device (7) pass through the aperture (6), the optical inspection device (100).

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

3. The 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) intersect with each other.

4. The optical inspection device (100) according to claim 1, characterized in that the optical inspection device (100) is a mask inspection system for a photomask related to EUV lithography.

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

Images