Optical inspection device

Abstract

The invention relates to an optical inspection device (100) for semiconductor lithography elements (1), comprising an imaging device (2) arranged in a first partial volume (4) for generating an image of an element (1) and a second partial volume (5) which includes a holding device (20) for receiving the element (1). A separating element (11) is arranged between the two partial volumes (4, 5). Furthermore, a position measuring device (7) is provided for determining the position and orientation of the imaging device (2) and the holding device (20), wherein the position measuring device (7) includes reference marks (15) for emitting electromagnetic radiation used in the position measuring device (7), and wherein the reference marks (15) are each connected to the imaging device (2) and the holding device (20).The separating element (11) comprises a partition wall with an opening (6), wherein the opening (6) serves for image acquisition by the imaging device (2) and wherein the electromagnetic radiation emanating from the reference mark (15) attached to the imaging device (2) and passing through the position measuring device (7) passes through the opening (6).

Description

[0001] The invention relates to an optical inspection device, in particular a mask inspection system for photomasks of semiconductor lithography.

[0002] Such inspection devices are used to determine the condition of photomasks used in semiconductor lithography; in particular, to identify defects that occurred during the production or use of the masks in order to enable subsequent repair of a mask.

[0003] Typically, such a system includes an imaging device that captures a mask arranged on a holding device, a so-called mask holder, section by section, step by step or by scanning.

[0004] With the increasing prevalence of EUV lithography, a form of semiconductor lithography using extremely short wavelengths, especially wavelengths of a few nanometers, special measures are required for the inspection and handling of photomasks.

[0005] In particular, the inspection of the masks usually has to take place in a vacuum environment. Typically, the imaging devices and the masks to be examined are arranged in two separate, independently conditioned subvolumes, with only a small opening between the subvolumes for the passage of the electromagnetic radiation used to examine the mask.

[0006] For reliable imaging of the mask, it is essential that the relative position of the imaging device to the mask under investigation is known as precisely as possible and can also be adjusted as quickly and accurately as possible. This requires accurately measuring the respective positions of the components involved. Typically, position measuring devices such as interferometers are used for this purpose. These devices usually measure the position of the mask holder and thus indirectly the position of the mask.

[0007] Interferometric measuring devices for determining the position of components of semiconductor lithography systems are already known from the prior art.

[0008] US patent application US 2011 / 0 026 006 A1 describes a projection exposure system for semiconductor lithography in which the position of a wafer stage is determined using an interferometric system. Furthermore, US patent application US 6 160 628 A shows a system in which the positions of a lens housing of a projection exposure system or a wafer stage are determined in a similar manner; a comparable device is also disclosed in Japanese publication JP 2004 153 092 A.

[0009] Another interferometric concept for position measurement is shown in German patent application DE 10 2005 052 758 A1. This document describes a position measuring device for determining the position of a substrate, which includes a laser interferometer system.

[0010] In this context, it is advantageous if the positional information of both components being measured—that is, the imaging device and the mask under investigation—is acquired using the same measuring device, in order to determine the relative position of the imaging device and the mask as simply as possible. However, this joint measurement is complicated by the arrangement of the imaging device and the mask in different subvolumes.

[0011] The object of the present invention is to provide a device which ensures the simplest and most precise determination possible of the relative position of an imaging device and a mask or element to be examined.

[0012] This problem is solved by a device having the features of independent claim 1. The dependent claims relate to advantageous further developments and variants of the invention.

[0013] An optical inspection device according to the invention comprises an imaging device arranged in a first partial volume for generating an image of an element and a second partial volume, which includes a holding device for receiving the element. A separating element is arranged between the two partial volumes. Furthermore, the inspection device comprises at least one position measuring device for determining the position and orientation of the imaging device and the holding device, wherein the position measuring device includes reference marks for emitting electromagnetic radiation used in the position measuring device. For the purposes of this application, emission is understood to include, in particular, the reflection of incident radiation by the reference marks. The reference marks are each connected to the imaging device and the holding device.

[0014] The separating element comprises a partition wall with an opening, the opening serving for image acquisition by the imaging device, and the electromagnetic radiation emanating from the reference mark attached to the imaging device and passing through the position measuring device passes through the opening.

[0015] In this way, the opening between the subvolumes can be kept small, making it easier to maintain different atmospheric conditions within each subvolume. Overall, the measures shown also allow for a significantly more compact design and simplify the replacement of the imaging device in the field, i.e., at the deployment site.

[0016] In an advantageous embodiment of the invention, at least two position measuring devices and at least two reference marks mounted on the imaging device are provided, wherein the beam paths of the electromagnetic radiation emanating from the reference marks and passing in the position measuring devices are inclined to each other.

[0017] In particular, the beam paths of the electromagnetic radiation emanating from the reference marks and passing through the position measuring devices can intersect.

[0018] As already mentioned, the element can be a photomask for semiconductor lithography, for example for EUV lithography; in particular, the optical inspection device can be a mask inspection system for photomasks of EUV lithography.

[0019] The photomask can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and particularly preferably between 1:1 or 1:2; it can be substantially rectangular. The photomask can preferably be 5 to 7 inches (12.7 to 17.78 cm) long and wide, and particularly preferably 6 inches (15.24 cm) long and wide. Alternatively, the photomask can be 5 to 7 inches (12.7 to 17.78 cm) wide and 10 to 14 inches (25.4 to 35.56 cm) long, and preferably 6 inches (15.24 cm) wide and 12 inches (30.48 cm) long.

[0020] In an advantageous embodiment of the invention, the position measuring device can be an interferometer.

[0021] The interferometer can operate, in particular, at a wavelength different from that of the radiation used for image acquisition, for example, at 200 nm to 1700 nm, preferably 400 nm to 800 nm. In this case, the electromagnetic radiation emitted by the reference marks is generated by the reference marks being designed as reflectors, which are illuminated within the interferometer and reflect the incident radiation back into the beam path of the interferometer in a known manner.

[0022] Furthermore, at least one position measuring device can be designed such that electromagnetic radiation emanating from a reference mark on the imaging device and reaching the position measuring device enters the position measuring device in the partial volume in which the imaging device is also arranged.

[0023] In an unclaimed variant of the invention, at least one position measuring device can be designed such that electromagnetic radiation emanating from a reference mark on the holding device and passing through the position measuring device passes completely within the partial volume in which the holding device is also arranged.

[0024] This can be achieved, for example, by inserting at least parts of a position measuring device into the separating element in such a way that a radiation inlet opening for electromagnetic radiation emanating from a reference mark on the holding device and passing through the position measuring device is arranged in the same partial volume as the holding device, whereas a radiation inlet opening for electromagnetic radiation emanating from a reference mark on the imaging device and passing through the position measuring device is arranged in the same partial volume as the imaging device.

[0025] Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. The drawing shows Fig. 1 A mask inspection system for examining photomasks, Fig. 2 an alternative to the one in Fig. 1 arrangement shown, Fig. 3 an embodiment of the invention, and Fig. 4 an alternative embodiment.

[0026] Fig. Figure 1 schematically and partially shows an optical inspection device, not claimed herein, designed as a mask inspection system 100 for examining elements, in the example shown, photomasks for EUV lithography. In such systems, the photomasks—unlike in inspection systems for masks for longer wavelengths—are not recorded in sections and while stationary, but rather a scan of the entire mask surface is generally performed. A mask 1 is moved under an imaging device 2 while scanning, which in the Fig. 1 is illustrated by the unlabeled double arrow. The mask 1 is arranged on a movable holding device 20, a so-called mask holder.

[0027] Also shown in the figure is an image sensor 3, onto which the imaging device 2 projects the surface of the mask 1. The image sensor 3 can be designed as a TDI sensor – similar to the sensors used in line scan cameras.

[0028] The imaging device 2 and the image sensor 3 are located in a first partial volume designed as a vacuum chamber 4, whereas the mask 1, arranged on the mask holder 20, is located in a further partial volume designed as a vacuum chamber 5, which is separated from the vacuum chamber 5 by a partition element designed as a baffle 11. The vacuum chamber 5 can – unlike the illustration – also be designed in the form of a box, which can be located inside the vacuum chamber 4. Decoupling elements 8 are arranged between the imaging device 2 and the vacuum chamber 4, which effect at least partial decoupling of the imaging device 2 from the vacuum chamber 4.

[0029] The separate vacuum chambers 4 and 5 are necessary to minimize contamination; furthermore, different atmospheres or media are typically present in chambers 4 and 5. An opening 6 is located between the two vacuum chambers 4 and 5, through which the light emanating from the mask 1 passes and reaches the imaging device 2.

[0030] However, the scanning movement of mask 1, as well as environmental influences such as vibrations of the associated hall floor or similar factors, introduce mechanical disturbances which, without further measures, would lead to an offset of the imaging device 2 relative to mask 1 during the scanning process. Such an offset would impair image quality; therefore, it is desirable that, even during the scan—apart from the scanning movement—the imaging device 2 and mask 1 maintain a fixed spatial relationship to each other. It is thus necessary to track mask 1 in relation to the imaging device 2. For this purpose, the positions of mask 1 and imaging device 2 must be known in a common coordinate system. Interferometers 7, which can be designed, for example, as differential interferometers, are used as position measuring devices to determine these positions.

[0031] Also visible in the figure are reference elements 9, depicted as rods in the figure and firmly connected to the imaging device 2. These elements project through the partition 11 between the two vacuum chambers 4 and 5 into vacuum chamber 5 and have reference marks designed as sensor targets 15. These reference marks can be designed as reflective surfaces and serve as references for the interferometer 7. The measuring beams, represented in the figure by unlabeled double arrows, which run through the interferometer 7 and pass through the radiation windows 16, reach the sensor targets 15 of the interferometer 7 and, after reflection at the sensor targets 15, re-enter the transmission / receiving section 10 of the interferometer 7 through the radiation windows 16. This transmission / receiving section may, for example, contain a sensor located in the interferometer 7. Fig. 1 radiation source not shown separately and one also shown in the Fig. 1 may contain a receiving device of the interferometer 7, which is not shown.

[0032] Like the imaging device 2, the mask holder 20 is also equipped with sensor targets 15, which likewise serve to reflect the measuring beams of the interferometer 7. This makes it possible to determine and, if necessary, control the relative position of the mask holder 20 (and thus of the mask 1) and the imaging device 2.

[0033] Another alternative to the one in which it is not claimed here is also Fig. The arrangement shown in 1 can be found in Fig. 2. There, a section of the interferometer 7 is rigidly connected to the imaging device 2 and moves with it. In this way, the relative position of the imaging device 2 to the mask 1 can be determined relatively easily.

[0034] Fig. Figure 3 shows an embodiment of the invention in which the sensor targets 15, which are associated with the imaging device 2, are located in the same vacuum chamber 4 as the imaging device 2. In the example shown, this is achieved by the measuring beams of the interferometers 7 being inclined and passing through the opening 6 in the partition 11 between the vacuum chambers 4 and 5, which is also used for image acquisition by the imaging device 2. The beam paths of the electromagnetic radiation emanating from and reflected by the sensor targets 15 thus intersect in the example shown. An oblique orientation of the beam paths is also conceivable. In this way, the opening 6 between the vacuum chamber 4 and the vacuum chamber 5 can be kept comparatively small.Furthermore, sensor targets 15 can be positioned closer to the imaging device 2 in this way, resulting in dynamic advantages and enabling higher performance in controlling the relative position of the imaging device 2 and mask 1.

[0035] Overall, the measures shown make the construction significantly more compact and simplify the exchange of the imaging device 2 in the field, i.e. at the deployment site of a corresponding mass inspection device 100.

[0036] Because the measuring beams of the interferometer 7 are guided at an angle in the example shown, it may be necessary to perform an intermediate calculation in order to determine the correct relative movement of imaging device 2 and mask 1 to each other.

[0037] Fig.Figure 4 shows an unclaimed embodiment in which the interferometers are configured such that the measuring beam reaching the imaging device 2 passes entirely within the vacuum chamber 4. The transmit-receive elements 10 of the interferometers 7 are inserted into the partition 11, and the radiation windows 16 for the measuring beam for the mask 1 are arranged in the associated vacuum chamber 5, whereas the radiation windows 16' for the measuring beam for the imaging device 2 are arranged in the associated vacuum chamber 4. In this case, it may be necessary to provide special encapsulation for the transmit-receive elements 10 of the interferometers 7. Reference symbol list 1 element, mask 2 Imaging device 3 Image sensor 4 First sub-volume 5 Second sub-volume 6 Opening 7 Interferometer 8 Decoupling element 9 Reference element 10 Transmit / Receive section 11 Partition wall 15 Reference mark, sensor target 16.16' radiation window 100 Optical Inspection Device

Claims

[1] Optical inspection device (100) for elements (1) of semiconductor lithography, - with an imaging device (2) arranged in a first partial volume (4) for generating an image of an element and - a second partial volume (5) which comprises a holding device (20) for receiving the element (1), -wherein a separating element (11) is arranged between the two partial volumes (4, 5), - and with at least one position measuring device (7) for determining the position and orientation of the imaging device (2) and the holding device (20), - wherein the position measuring device (7) comprises reference marks (15) for emitting electromagnetic radiation used in the position measuring device (7) - wherein the reference marks (15) are each connected to the imaging device (2) and the holding device (20), - wherein the separating element (11) comprises a partition wall with an opening (6), wherein the opening (6) serves for image recording by the imaging device (2) and wherein the electromagnetic radiation emanating from the reference mark (15) applied to the imaging device (2) and running in the position measuring device (7) passes through the opening (6). [2] Optical inspection device (100) according to claim 1, characterized by that at least two position measuring devices (7) and at least two reference marks (15) applied to the imaging device (2) are present, wherein the beam paths of the electromagnetic radiation emanating from the reference marks (15) applied to the imaging device (2) and running in the position measuring devices (7) run obliquely to one another. [3] Optical inspection device (100) according to claim 2, characterized bythat the beam paths of the electromagnetic radiation emanating from the reference marks (15) applied to the imaging device (2) and passing in the position measuring devices (7) cross each other. [4] Optical inspection device (100) according to one of claims 1 to 3, characterized by that the optical inspection device (100) is a mask inspection system for photomasks of EUV lithography. [5] Optical inspection device (100) according to one of claims 1 to 4, characterized by that the position measuring device (7) is an interferometer.

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