AT520964B1 - Apparatus and method for optically detecting a peripheral area of a flat object - Google Patents

Abstract

The invention relates to a device (1) for optically detecting an edge region of a flat object (15), in particular a wafer, comprising at least one detector (3) and a plurality of optical devices each comprising a lighting unit (4), between which at least one detector (3) and the optical devices, a measuring range is spanned in a measuring plane, wherein the at least one detector (3) and the optical devices on a rigid support (2) are arranged and with the optical devices in each case a rectilinear beam path through the Measuring range to at least one detector (3) can be generated and wherein the at least one detector (3) and the cooperating with this optical devices are arranged on opposite sides of the measuring range. Furthermore, the invention relates to a use of such a device (1) in an inspection of an edge and / or determination of a geometric edge condition of an object (15). Moreover, the invention relates to a method for optical measurement of an edge of a flat object (15), in particular of a wafer, wherein the edge of the object (15) is illuminated with a plurality of light sources and whose projection is detected by at least one detector (3), wherein the edge of the object (15) is illuminated sequentially with in each case at least one light source (9) whose projections are detected by the at least one detector (3) and diffraction phenomena are evaluated, their positions being determined on the at least one detector (3) ,

Description

DEVICE AND METHOD FOR OPTICALLY DETECTING AN EDGE AREA OF A FLAT OBJECT The invention relates to an apparatus for optically detecting an edge area of a flat object, in particular a wafer, comprising at least one detector and a multiplicity of optical devices, each comprising an illumination unit, wherein A measurement area is spanned in a measurement plane between the at least one detector and the optical devices, the at least one detector and the optical devices being arranged on a rigid support.

[0002] The invention further relates to the use of such a device.

Furthermore, the invention relates to a method for the optical measurement of an edge of a flat object, in particular a wafer, the edge of the object being illuminated with a multiplicity of light sources and the projection of which is detected by at least one detector.

Various devices and methods for the optical measurement of edge areas of flat objects and for evaluating defects on them are known from the prior art.

[0005] An example of such a device is described in DE 10 2007 024 525 A1. In such a device, a large number of optical devices for illuminating a wafer are provided. In addition, at least three cameras are provided, which are directed from different sides onto the edge area of the wafer and with which the edge area is recorded in each case, a defect to be recorded being illuminated in the bright field.

US 2006/0115142 A1 describes a device and a method for inspecting an edge of a wafer, wherein at least one image of the edge is also recorded.

[0007] AT 510 605 B1 describes a device and a method for the optical measurement of at least one dimension of a flat object. In such a device, punctiform light sources and at least one detector opposite the light sources are provided.

[0008] DE 10 2005 014596 B3 discloses a device for detecting an edge region of a wafer, with several detectors being provided which are arranged above and below the wafer, so that a light can be detected which reflects on the surface of the wafer becomes.

[0009] Devices for optical inspection are also known from documents US 5,781,649 A, WO 2015/196163 A1 and DE 10 2007 047352 A1, in which it is provided that a light beam reflected on an object surface is detected.

Such devices and methods, however, have the disadvantage that a measurement of an object edge or assessment of the defects on the object edge is dependent on a shape and on optical material properties of the object, such as reflection, absorption or transparency ,

The object of the invention is to provide a device of the type mentioned, which enables a shape and material-independent inspection of object edges.

Another aim is to specify a use for such a device.

Furthermore, it is an object of the invention to provide a method of the type mentioned, which enables a shape and material-independent inspection of object edges.

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AT 520 964 B1 2019-11-15 Austrian Patent Office [0014] The first object is achieved if, in the case of a device of the type mentioned at the beginning, a straight beam path can be generated with the optical devices through the measuring area to at least one detector, and the at least one a detector and the optical devices interacting with it are arranged on opposite sides of the measuring range.

An advantage achieved with the invention can be seen in particular in that the arrangement on a, in particular common, rigid support fixes a geometric relationship between the at least one detector and the optical devices. Such a fixed geometric relationship allows a simple mathematical modeling of the edge area from recorded measurement values. A position of the projection on the detector can be determined here by exposure of an object edge and tangential projection of a beam from an optical device on the object edge onto the at least one detector. This can be done for each optical device separately and in succession, in a so-called sequential single exposure, or in each case for several optical devices simultaneously, in a so-called simultaneous multiple exposure.

[0016] The carrier expediently has a recess which is open to one side. The carrier can in particular be C-shaped. This makes it easy to insert an object to be measured into the device.

[0017] The at least one detector and the optical devices are advantageously at least partially positioned on opposite sides of the recess. This ensures that the object can be inserted between the at least one detector and the optical devices.

[0018] The at least one detector and / or the optical devices are preferably fixed in the measurement plane and / or adjustable perpendicular to the measurement plane. This ensures that the geometric relationship between the at least one detector and the optical devices is fixed in the measurement plane. Adjustments perpendicular to the measuring plane can compensate for positional deviations caused by production and / or increase the measuring accuracy.

It is advantageous if the at least one detector is designed as a multi-line optoelectronic sensor. As a result, light from the optical devices, in particular from tangential projection beams, can be detected as an electrical signal in a positionally accurate manner and on an area which is enlarged in comparison to a single-line sensor. It is particularly to be seen as an advantage if the position of the signal or the tangential projection beams on the detector is known, since an increased measurement accuracy can thus be achieved. With the multi-line sensor, the position of the signal can also be determined with improved accuracy.

In order to ensure homogeneous illumination or a homogeneous distribution of the light intensity on the detector, it is advantageous if one or more optical devices have a device for beam expansion and / or beam focusing. It is particularly advantageous if each optical device has a device for beam expansion and / or beam focusing. A lens system, for example, can be provided as the device for beam expansion and / or beam focusing. In particular, a beam expansion in the measuring plane and / or a beam bundling can take place normal to the measuring plane.

The optical devices preferably each have at least one fixed and / or adjustable diaphragm. As a result, lighting can be restricted to a specific partial area of the detector.

Furthermore, it can be provided that the optical devices each comprise at least one light source which has a narrow-band wavelength spectrum, for example with a half-value width of at most 10 nm, in particular less than 5 nm, for example 3 nm. if the wavelength spectrum is so narrow-band that diffraction patterns are retained or diffraction phenomena in particular

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AT 520 964 B1 2019-11-15 Austrian patent office arise especially when illuminating an object edge at the detector.

It is useful if the optical devices each have highly focusable light sources, in particular lasers, laser diodes and / or superluminescent diodes.

It is advantageous if a mirror is provided in at least one optical device, which is positioned so that the beam path is deflected by the respective optical device and is guided in a straight line through the measuring plane to the detector. In this way, for example, virtual light sources can be positioned in locations that would be difficult to access for real light sources or that space is insufficient for them. Such locations can be outside the carrier, for example. Thus, a small carrier can be used and a compact design can be ensured, even if positioning of a light source in an area for which an enlarged carrier would otherwise be necessary is desired.

[0025] It is preferably provided that the support at least partially comprises a material having a thermal conductivity greater than 100 W / (m K) and / or a thermal expansion coefficient of less than 100Ί0 ^'6 K ^-1. A thermal conductivity can preferably be at least 300 W / (m K), in particular up to 2000 W / (m K). The thermal expansion coefficient of the material is preferably less than 50ΊΟ ^'6 K' ^1, especially about 10Ί0 ^'6 K' ¹ to 20 · 10 ^-6 K ^-1. It can be provided here that the carrier itself is made of such a material or is coated, covered or coated with such a material. Alternatively, the carrier can be in good thermal contact with a heat sink. Such a condition of the support ensures thermal stability of the support or resistance to deformation, as a result of which temperature influences on a geometry of the device, in particular on a relative position of the at least one detector to the optical devices, and on the measurement accuracy are minimized. As an alternative or in addition to this, such temperature influences can be distributed over the entire carrier and thereby homogenized due to a high thermal conductivity of the material.

[0026] A housing for housing the device is advantageously provided. As a result, the device is protected against environmental influences such as dust or similar contaminations. Furthermore, the detector can thereby be isolated from ambient or scattered light.

In order to achieve a high measuring accuracy, which is independent of vibration or other movement or deformation of the device, it can be provided that the carrier is mechanically decoupled from the housing. This reduces or minimizes external forces on the carrier. Forces such as those that occur when the device is fastened, for example, can cause permanent deformation of the support if it is firmly connected to the housing. This would also result in reduced measurement accuracy. In order to mechanically decouple the carrier from the housing and thus reduce the influence of external forces or limit it to a minimal area, the carrier can be mounted on or connected to the housing in only a small area, for example. For this purpose, at least one fixation, in particular several fixations, can be provided, with a distance from a first fixation to a last fixation or a longitudinal extension of an individual fixation being as small as possible and preferably being less than 50 mm, in particular a maximum of 20 mm. A fixation can comprise, for example, one or more screws, glue points and / or weld seams. Alternatively, the carrier can be mechanically decoupled, for example, by the carrier being connected to the housing via spring elements or other elastic or movable elements. The carrier could, for example, be connected to the housing with wires or rod-shaped connecting elements which are movably mounted on the housing.

Advantageously, components of the device, which are positioned in a beam path, at least partially have a low-reflection, in particular a diffuse surface. This ensures that the detector does not detect light from unwanted reflections. Furthermore, it is also advantageous if components of the device, which

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AT 520 964 B1 2019-11-15 Austrian patent office before they are positioned directly in the beam path, for example the housing, the carrier, the optical devices themselves or optional positioning devices for the object to be measured at least partially have a low-reflection surface. Such a surface can be achieved, for example, by a matt and / or black surface coating and / or appropriate shaping. It goes without saying that each optional mirror must have a reflective surface on at least one side.

The further object of the invention is achieved when using such a device for an inspection of an edge and / or determination of a geometric edge condition of an object. The object can preferably be designed as a wafer.

The procedural object is achieved in that in a method of the type mentioned, the edge of the object is sequentially illuminated with at least one light source, the projections of which are detected with the at least one detector and any diffraction phenomena are evaluated, the positions of which are evaluated the at least one detector can be determined.

By detecting the diffraction phenomena, a position on the at least one detector can be determined precisely and with a high positional accuracy.

Advantageously, the edge of the object is illuminated simultaneously with several optical devices. As a result, several tangential projection beams for calculating measuring points can be recorded simultaneously and a measuring time can be reduced.

It is particularly preferably provided that a smaller number of calculated measurement points is selected than a number of optical devices. This increases the robustness of the measurement, since existing redundancies can be used to improve reliability and / or automatic measurement error detection. A maximum number of measuring points is limited by the number of optical devices.

It is advantageous if a beam of the at least one light source is widened in a measurement plane and bundled perpendicular to the measurement plane. This enables an elliptical illumination profile to be created. In particular, illumination can be homogenized by beam expansion in the measuring plane, with exposure energy being maximized on the respective sensor array and maximized by bundling perpendicular to the measuring plane. With the elliptical illumination profile, very short exposure times and a correspondingly high measuring rate can be achieved. For this purpose, the beam is preferably expanded by means of a device for beam expansion in the measuring plane and bundled perpendicular to the measuring plane.

[0035] The invention is explained in more detail below. In the drawings, to which reference is made, show:

Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 7, and Figure 8 9 [0045] FIG. 10 shows an embodiment of a device with a detector;

an embodiment of a device with two detectors;

a further embodiment of a device with two detectors;

an embodiment of a device with a virtual light source;

a side view of the device;

a lighting unit;

a device with a disk-shaped object;

a detailed view of an edge area with a corresponding signal;

a detailed view of an exposed edge area;

Detector signals with sequential single exposure and simultaneous double exposure.

An embodiment of a device 1 is shown in Fig. 1. Such a pre

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AT 520 964 B1 2019-11-15 Austrian patent office direction 1 comprises a detector 3 and a large number of optical devices which are positioned on a carrier 2. In this embodiment, the optical devices each comprise an illumination unit 4. The carrier 2 is designed here as a plate with a recess 5 that is open to one side. As shown in FIG. 1, the recess 5 can be essentially rectangular, but can also be shaped differently, for example round or oval. It is advantageous if the recess 5 is positioned centrally in the carrier 2. Sometimes a decentralized arrangement of the recess 5 can also be useful. Furthermore, it is expedient if the recess 5 is designed such that an object 15, for example a wafer, can be introduced into the recess 5.

In this embodiment, the detector 3 and the optical devices are arranged on opposite sides of the recess 5. In addition, the lighting units 4 are aligned with a front side essentially in the direction of the detector 3, as a result of which a beam path runs in a straight line and without deflection to the detector 3. The detector 3 and the optical devices define a measurement plane 12, which lies essentially parallel to the carrier 2 and in which a measurement area 6 lies. The measuring range is flat.

The optical devices are arranged essentially along an arc of a circle, so that a light of the optical devices hits the edge region of the object 15 at a different angle or strikes it. 1 shows two enveloping rays 7 of a light cone for each lighting unit 4. In order to ensure a uniform measurement, it is useful if the optical devices are arranged at a uniform distance from one another. A tangential projection beam corresponds to each optical device along an edge point on the object 15, which is why a measurement accuracy can be increased with an increasing number of optical devices. A measuring point is usually calculated for each optical device. If, however, a smaller number of calculated measurement points is selected for several optical devices or if several tangential projection beams are processed into a single calculated measurement point, the robustness of the measurement can be increased. The exemplary embodiment shown in FIG. 1 has six optical devices. However, any number of optical devices can be provided, in particular three to one hundred, particularly preferably five to fifty. A number of optical devices is essentially limited by the space available on the carrier 2. In order to be able to position a large number of optical devices on the carrier 2, it can be advantageous if these are arranged offset to one another.

A further exemplary embodiment is shown in FIG. 2, such a device 1 having two detectors 3 and also six optical devices. These are combined in groups of three optical devices, one group and one detector 3 interacting. Accordingly, a group of optical devices and an associated detector 3 are positioned on opposite sides of the recess 5. Of course, the groups can each comprise any number, in particular three to fifty, optical devices. It can further be provided that a group comprises more than one detector.

A further embodiment is shown in FIG. 3, only the positions of the lighting units 4 and the detectors 3 being exchanged in comparison to FIG. 2.

4 shows a detailed view of a device 1 with a large number of optical devices and a detector 3. In contrast to the embodiment shown in FIG. 1, an illumination unit 4 of an optical device is positioned facing away from the detector 3, this optical device comprising a mirror 8, which is positioned in such a way that it emits a light that comes from the remote lighting unit 4 , deflected to the detector 3. As a result, a virtual light source 9 'is generated, which is positioned on the other side of a carrier edge and along a rectilinear beam path from the detector 3. A further angle of illumination can thus be achieved, which

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AT 520 964 B1 2019-11-15 Austrian patent office cannot be achieved by positioning a real light source 9. This can be done at different positions on the carrier 2 by arranging a mirror 8, in particular if there is insufficient space for a lighting unit 4 or a real light source 9 at the desired position.

FIG. 5 shows a side view of the device 1, an illumination unit 4 and a detector 3 being shown. The lighting unit 4 shown comprises a light source 9, a field diaphragm 11 and a device for beam expansion 10. The lighting unit 4 and the detector 3 are arranged opposite one another on the carrier 2, a measuring plane 12 running parallel to the carrier 2. The lighting unit 4 shown is adjustable perpendicular to the measuring plane 12. A degree of freedom for a movement is indicated by double arrows.

6 shows an illumination unit 4, which also has a light source 9, a field diaphragm 11 and a device for beam expansion 10. The device for beam expansion 10 is in particular designed such that it widens the beam 7 in the measurement plane 12 and bundles it perpendicular to the measurement plane 12. For this purpose, the lighting unit 4 can have, in addition to the device for beam expansion 10, a device for beam focusing. This essentially leads to a strongly elliptical illumination profile 13. In a particularly simple embodiment, the lighting unit 4 can also be designed without a field diaphragm 11 or devices for beam expansion 10 and / or beam focusing. In order to limit the illumination profile 13 to a certain area, the field diaphragm 11 is provided, which essentially limits the beam 7 to a narrow band 14. Scattered light can thereby be reduced, which can cause undesired effects, such as interference at the detector 3. It can also be advantageous for a mathematical evaluation if only certain partial areas of the detector 3 are illuminated. Alternatively, a plurality of field diaphragms 11 can be provided in order to further restrict the illumination profile 13. In addition, envelopes of the expanded beam 7 are shown in FIG. 6.

FIG. 7 shows a device 1 with a disk-shaped, flat object 15 to be measured, which is partially introduced into the recess 5. The object 15 is introduced into the recess 5 such that an object edge is essentially positioned in a measuring area 6. As a result, light emanating from the illumination units 4 is diffracted at the object edge. Such diffraction phenomena 17 appear in an electrical signal 16 from the detector 3. The detector 3 can be designed as an optoelectronic sensor for this purpose.

A detailed view of an illumination of the object edge with the rays 7 incident on the detector 3 is shown in FIG. 8. The detector 3 detects projections of the light sources 9 and supplies a detector signal 16. The detector signal 16 is also shown in FIG. 8, a position on the detector 3 on an abscissa axis and a measured value, for example a voltage, detected by the detector 3 on an ordinate axis. a current or an intensity is plotted. The detector signal 16 shown here was recorded in the case of sequential individual exposure, that is to say in the case of a successive exposure of one edge point in each case by an optical device in each case. Light which is diffracted at the object edge produces a characteristic diffraction phenomenon 17 in the detector signal 16. From this diffraction phenomenon 17 an exact position of the respective projection on the detector 3 can be determined. As a result, a shape and a nature of the object edge can be determined from the positions determined on the detector 3. An evaluation can take place, for example, using a mathematical model. In order to increase the measuring accuracy or to ensure the reliability of the mathematical model, it is useful if device parameters are calibrated beforehand. A measurement accuracy is improved with an increasing number of optical devices and an increased number of tangential projection beams, which can be used to calculate a selected number of measurement points. The number of measurement points can be selected to be the same as the number of tangential projection beams or less than this.

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AT 520 964 B1 2019-11-15 Austrian Patent Office [0056] FIG. 9 shows a detailed image of an edge profile scan of an object 15 with the rays 7 or projections, each of which corresponds to an optical device.

10 shows a detector signal 16 with sequential single exposure in the upper representation and a detector signal 16 with simultaneous double exposure in the lower representation. Simultaneous double exposure here means that simultaneous exposure of two edge points is carried out by one optical device each. Depending on the number of optical devices, simultaneous triple, quadruple or any multiple exposures can also be carried out in this sense.

Claims (19)

1. Device (1) for optically detecting an edge region of a flat object (15), in particular a wafer, comprising at least one detector (3) and a large number of optical devices, each of which comprises an illumination unit (4), between which at least one Detector (3) and the optical devices a measuring area (6) is spanned in a measuring plane (12), the at least one detector (3) and the optical devices being arranged on a rigid support (2), characterized in that with the optical devices each have a rectilinear beam path through the measuring area (6) to the at least one detector (3) and the at least one detector (3) and the optical devices interacting with it are arranged on opposite sides of the measuring area (6). 2. Device (1) according to claim 1, characterized in that the carrier (2) has a recess (5) open to one side. 3. Device (1) according to claim 2, characterized in that the at least one detector (3) and the optical devices are at least partially positioned on opposite sides of the recess (5). 4. Device (1) according to one of claims 1 to 3, characterized in that the at least one detector (3) and / or the optical devices in the measuring plane (12) fixed and / or adjustable perpendicular to the measuring plane (12). 5. Device (1) according to one of claims 1 to 4, characterized in that the at least one detector (3) is designed as a multi-line optoelectronic sensor. 6. Device (1) according to one of claims 1 to 5, characterized in that one or more optical devices have a device for beam expansion (10) and / or beam focusing. 7. Device (1) according to one of claims 1 to 6, characterized in that the optical devices each have at least one fixed and / or adjustable diaphragm. 8. Device (1) according to one of claims 1 to 7, characterized in that the optical devices each comprise at least one light source (9) which has a narrow-band wavelength spectrum. 9. Device (1) according to one of claims 1 to 8, characterized in that the optical devices each have highly focusable light sources (9), in particular lasers, laser diodes and / or superluminescent diodes. 10. The device (1) according to one of claims 1 to 9, characterized in that a mirror (8) is provided in at least one optical device, which is positioned such that the beam path is deflected by the respective optical device and rectilinear through the measuring plane (12) is guided through to the detector (3). 11. The device (1) according to any one of claims 1 to 10, characterized in that the carrier (2) at least partially comprises a material which has a thermal conductivity of more than 100 W / (m K) and / or a coefficient of thermal expansion of less than 100 · 10 ' ⁶ Κ' ¹ . 12. The device (1) according to one of claims 1 to 11, characterized in that a housing for housing the device (1) is provided. 13. The device (1) according to any one of claims 1 to 12, characterized in that the carrier (2) is mechanically decoupled from the housing. 14. Device (1) according to one of claims 1 to 13, characterized in that components of the device (1), which are positioned in a beam path, at least partially have a low-reflection, in particular a diffuse surface. 8.15 AT 520 964 B1 2019-11-15 Austrian patent office 15. Use of a device (1) according to one of claims 1 to 14 for an inspection of an edge and / or determination of a geometric edge condition of an object (15). 16. A method for the optical measurement of an edge of a flat object (15), in particular a wafer, the edge of the object (15) being illuminated with a plurality of light sources (9) and the projection of which is detected by at least one detector (3) characterized in that the edge of the object (15) is illuminated sequentially with in each case at least one light source (9), the projections of which are detected by the at least one detector (3) and diffraction phenomena (17) that occur are evaluated, their positions on the at least one detector (3) can be determined. 17. The method according to claim 16, characterized in that the edge of the object (15) is illuminated simultaneously with several optical devices. 18. The method according to claim 16 or 17, characterized in that a smaller number of calculated measurement points is selected as a number of optical devices. 19. The method according to any one of claims 16 to 18, characterized in that a beam (7) of the at least one light source (9) is expanded in a measurement plane (12) and bundled perpendicular to the measurement plane (12).