Device and method for evaluating defects in the edge area of a wafer and use of the device in inspection system for wafers

A device for evaluating defects in the edge area of a wafer (6) is disclosed. The evaluation may also be performed automatically. In particular, the device includes three cameras (25, 26, 27), each provided with an objective (30), wherein a first camera (25) is arranged such that the first camera (25) is opposite to an edge area on the upper surface (6a) of the wafer (6), wherein a second camera (26) is arranged such that the second camera (26) is opposite to a front surface (6b) of the wafer (6), and wherein a third camera (27) is arranged such that the third camera (27) is opposite to an edge area on the lower surface (6c) of the wafer (6).

FIELD OF THE INVENTION

The present invention relates to a device for visually evaluating defects in the edge area of a wafer. In particular, the device for visually evaluating defects in the edge area of a wafer includes a first camera arranged such that the first camera is opposite to an edge area on the upper surface of the wafer. A second camera is arranged such that the second camera is opposite to a front surface of the wafer. A third camera is arranged such that the third camera is opposite to an edge area on the lower surface of the wafer. Each camera has a field of view for acquiring images of the defects.

The present invention further relates to a method for visually evaluating defects in the edge area of a wafer. For the method for visually evaluating defects in the edge area of a wafer, a review of the defects in the area is performed with a first camera opposite to an upper edge area of the wafer, a second camera opposite to the front surface of the wafer, and a third camera opposite to a lower edge area of the wafer.

The invention further relates to the use of the device in an inspection system for wafers. The inspection system for wafers includes at least one unit for micro-inspection, transport means and alignment means. There is further provided at least one display, on which acquired and/or stored images of the defects may be displayed to a user.

BACKGROUND OF THE INVENTION

U.S. patent application 2005/0013474 discloses a device also inspecting or examining the edge area of a wafer with three cameras. For the inspection of the wafer edge, the wafer is rotated past the cameras more than two times. There is also provided a bright field arrangement for the illumination of the wafer. However, the cameras are not arranged on a common carrier, and the cameras are further not intended to be brought closer to the wafer edge in order to achieve a better positioning of the edge of the wafer with respect to the cameras. In addition, there is no indication that single defects may be directly approached by the device disclosed therein, so that an image of these defects may be acquired by the cameras.

U.S. patent application 2003/0169916 discloses a device using three cameras for acquiring an image of the front surface of the wafer edge and of the two bevels at the wafer edge, respectively. The cameras are arranged such that a first camera is opposite to the upper bevel of the wafer edge, that a second camera is opposite to the front surface of the wafer, and that a third camera is opposite to the lower bevel of the wafer edge. The cameras are oriented such that they face the respective associated surfaces at a right angle. However, the application does not disclose that the cameras are arranged on a common carrier movable in a perpendicular direction with respect to the edge of the wafer in order to position the cameras suitably for image acquisition. In addition, the first camera and the third camera are not arranged to image the upper surface and the lower surface, respectively, of the wafer edge nor to record defects there and display them to the user.

SUMMARY OF THE INVENTION

It is thus the object of the present invention to provide a device allowing the inspection of the defects on the upper surface, the front surface and the lower surface of the wafer edge in a simple way.

This object is achieved by a device including at least one illumination means designed such that the first, second and third cameras are arranged in bright field arrangement. The wafer is positionable in the field of view of each camera for acquiring the image of the defect.

It is a further object of the invention to suggest a method by which images of defects may be acquired, wherein the defects are located in the edge area of the wafer. The inventive method is supposed to allow displaying the selected defects to a user for inspection.

The method for evaluating defects in the edge area of a wafer with a first camera opposite to an upper edge area of the wafer, a second camera opposite to the front surface of the wafer, and a third camera opposite to a lower edge area of the wafer is characterized by the steps of:

depositing a wafer on a prealigner by means of a robot,

moving at least a first camera and a third camera in a radial direction with respect to the edge of the wafer so that the edge area of the wafer gets into the field of view of the respective camera,

positioning the wafer based on stored and/or determined position data such that the defects on the edge of the wafer are aligned with the field of view of the first and/or the second and/or the third camera for visual evaluation, and

beginning image acquisition with at least one of the cameras depending on the position of the defect opposite to the upper edge area of the wafer or the lower edge area of the wafer or the front surface of the wafer, wherein each defect to be captured is illuminated in the bright field.

It is a further object of the present invention to suggest the use of a device for visually evaluating defects in the edge area of a wafer in inspection system for wafers.

The use has the advantage that the alignment means is associated with the device for visually evaluating defects in the edge area of the wafer provided with three cameras. A first camera is arranged such that the first camera is opposite to an edge area on the upper surface of the wafer. A second camera is arranged such that the second camera is opposite to a front surface of the wafer. A third camera is arranged such that the third camera is opposite to an edge area on the lower surface of the wafer.

The device for visually evaluating defects in the edge area of the wafer is particularly advantageous because at least two of the three cameras are designed movable in the direction towards the wafer edge. Thus optimal positioning of the cameras with respect to the upper surface of the wafer edge and the lower surface of the wafer edge may be achieved. It is also contemplated that the camera opposite to the front edge area of the wafer, together with the two other cameras, is arranged on a common carrier, which is designed movable in a perpendicular direction with respect to the wafer edge. There is also provided an illumination device arranged such that a bright field arrangement is achieved together with the cameras. The first, second and/or third camera acquires an image of a defect in the edge area of the wafer with a defined field of view size. The position coordinates of the defect in the edge area of the wafer are known, so that the wafer is moved into position with respect to the cameras according to these coordinates, so that, depending on the position of the defect, the image of the defect is acquired either on the upper surface of the wafer edge or on the lower surface of the wafer edge or on the front surface of the wafer edge.

In an advantageous embodiment of the invention, the first camera and the third camera are arranged on a carrier arranged radially with respect to the wafer edge. The carrier is positionable with respect to the edge of the wafer such that the first camera is opposite to the upper surface of the wafer edge and the third camera is opposite to the lower surface of the wafer edge. The second camera is stationary with respect to the front surface of the wafer.

In another embodiment, all three cameras are arranged on a carrier movable in a perpendicular direction with respect to the wafer edge.

The illumination means forming a bright field arrangement together with the cameras may be designed, for example, as a calotte having a diffusely transparent screen or a diffuser. The calotte is essentially cylindrical and has at least one recess so that the calotte partially surrounds the edge of the wafer. Several light sources may be arranged on the calotte. Thus a diffuse and even and homogeneous illumination of the edge area of the wafer is achieved by the cooperation of the several light sources and the diffusely transparent screen or the calotte.

The light sources may be designed as white light LEDs. It is further possible to provide each camera with its own light source. When arranging the cameras and the light sources, care must be taken to meet the conditions for the bright field illumination (the cameras are arranged in the angle of reflection of the light from the light sources). It is also advantageous if the light sources for the cameras consist of LEDs.

It is further advantageous if the wafer is deposited on a prealigner, wherein the prealigner positions the wafer in the field of view of one of the cameras. It is further advantageous if the prealigner is designed to be movable in the Z-direction, so that the thickness and the position of the wafer in the Z-coordinate direction may be determined with the second camera.

The method is advantageous if a wafer is deposited on a prealigner by a robot. Furthermore, at least a first camera and a third camera are arranged to be movable in a perpendicular direction with respect to a front surface of the wafer, so that the edge area of the wafer gets into the field of view of the respective camera. The wafer is positioned based on stored and/or determined position data such that the defects on the edge of the wafer are aligned with the field of view of the first and/or the second and/or the third camera for visual evaluation. With at least one of the cameras, the image acquisition is performed depending on the position of the defect on the upper surface of the wafer edge or the lower surface of the wafer edge or the front surface of the wafer edge. The image acquisition is performed in the bright field. The images acquired by the cameras may be displayed to the user on a display for visual inspection.

In order to facilitate the deposition of the wafer on the prealigner by the robot, it is advantageous if at least the first camera and the third camera are designed to be movable in the direction towards the wafer edge. The movement of the cameras towards the wafer edge may achieve that the area for the deposition of the wafer by the robot is free of any obstacles and that damage to the wafer or misdeposition of the wafer on the prealigner is thus avoided to a maximum extent. The first camera and the third camera are mounted on a carrier that is positioned in a perpendicular direction with respect to the wafer edge by the movable carrier. In the embodiment suggested here, the second camera is arranged stationary with respect to the front surface of the wafer. It is also contemplated that all three cameras are arranged on a common and movable carrier.

The three cameras are arranged in one plane. Also, the LEDs on the cylindrical calotte are arranged in another plane. The two planes are arranged at an angle with each other so that the conditions for a bright field arrangement are met.

The light sources may be formed of several LEDs emitting light of different wavelengths so that light of any color may be mixed for illumination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1exemplarily shows a 3D representation of a substrate supply module1and a work station3. The general exterior view of the means also shows a monitor7(or display) helping the user to check the data input via an operator input11or to monitor the status of the handling of wafer6. Furthermore, the images acquired by the device for visually evaluating defects in the edge area of the wafer6may be displayed to the user on the display7. The system for wafer inspection is further provided with a microscope (not shown), with which micro-inspection of defects on the surface of the wafer6is possible. Furthermore, a microscope view unit8may be available to the user, where detailed images of the substrate may be observed by the user. Wafers may be input into the wafer inspection machine via two load ports2a,2b(any other number of load ports is conceivable, and the illustration inFIG. 1is not to be regarded as limiting).

FIG. 2schematically shows the inner structure of system for inspecting wafers6. A substrate supply module1is laterally associated with means3. Means3for wafer inspection includes several work stations9,10and12. In this embodiment, the substrate supply module1is oriented with respect to means3such that it may be loaded with substrates from its front2via one or more load ports2a,2b. Open design or closed cartridges4are used, which are inserted into the load ports2a,2bmanually by the user or by automation, e.g. by means of a robot. The cartridges4may be filled with wafers6, or they may also be empty, depending on the intended work process. For example, all cartridges4may be filled, and wafers6are first taken from one cartridge, inserted into means3and returned to the same cartridge4after processing and inspection there.

Predetermined examinations, checks and inspections of the wafer are performed at the work stations9,10and12. In the present embodiment, three work stations9,10and12are provided in means3. In the center between the work stations9,10and12, a changer14is provided distributing the wafer6to the various work stations9,10and12. The changer14has three arms14a,14band14c. The first work station9serves for receiving the wafers6from the substrate supply module. The wafers6from the system for wafer inspection may also be returned to the substrate supply module at the first work station9. The second work station10serves for aligning, for determining the positioning and/or for visually inspecting the wafers6. For the alignment of the wafers6, the second work station10is associated with measuring means detecting the markers applied to the wafer6and determining codings of the wafers. The measuring means15further determines the deviation from the exact positional deposition of the wafer6in the second work station10. This work station will be referred to as prealigner10in the following description. The measuring means15determines the lateral run-out of the wafer6resulting from the imprecise deposition of the wafer6on the prealigner10by the three-paddle handler14. The center offset of the wafer6is corrected by the prealigner10. The data thus determined are forwarded to a central processing unit (not shown). The third work station12is designed for micro-inspection of the wafers6. The third work station12has an X, Y table17supplying a microscope16for micro-inspection for the wafer6. Z-adjustment may also be allowed by the X, Y table. The second work station10is also associated with the device22for visually inspecting wafers in the edge area of the wafer6. As also shown inFIG. 2, the device22for visually inspecting wafers in the edge area of the wafer6may be moved towards the edge8of the wafer6or away from the edge8of the wafer in the direction of double arrow24.

FIG. 3shows a schematic representation of the device for visually evaluating defects in the edge area of a wafer6. The wafer6is deposited on the prealigner10. As already mentioned inFIG. 2, the prealigner is disposed in system for inspecting wafers6. A first camera25, a second camera26and a third camera27are arranged on a common carrier23. The common carrier23may be moved in a radial direction with respect to the wafer6. Each camera25,26and27is provided with an objective30. The direction of movement is indicated by double arrow24. The distance covered by the common carrier23ranges between 30 mm and 40 mm.

The cameras25,26and27are designed as CCD cameras. The optical resolution depends on the size of the aperture used. The upper edge area6aof the wafer6and the lower edge area6cof the wafer6have a width90in the range of some millimeters. The front surface6bof the wafer to be inspected has a wafer thickness of about 1 mm. The inventive device is used to capture the defects88located in the upper edge area6a, the lower edge area6cand on the front surface6bof the wafer6.

FIG. 4shows a representation of the inventive device, which is provided with a controller40regulating the mechanical movement of the arrangement of the three cameras25,26and27. The controller40is also responsible for the controlled rotation of the prealigner10. As already mentioned in the description forFIG. 2, the wafer6is deposited on the prealigner10by means of the three-paddle handler14. As shown inFIG. 2, the prealigner10is also associated with at least one measuring device15determining the lateral run-out of the wafer6. A center offset of the wafer6may be corrected by briefly lifting and correcting the wafer6by means of the three-paddle handler14. In the embodiment shown, the three cameras25,26and27of the device for visually observing defects in the edge area6a,6bor6cof the wafer6are arranged on a common carrier23. The common carrier23may be moved in a radial direction with respect to the wafer6in the direction of double arrow24by means of a translating unit45. In the case that all three cameras25,26and27are arranged on the common carrier23, these three cameras are correspondingly moved towards the wafer6or away from the wafer6. The prealigner10and the translating unit45are arranged on a common base plate41. The prealigner10is also movable in an axial direction, as illustrated by double arrow43. By the movement of the prealigner10, the position of the wafer6with respect to the objectives30of the cameras25,26and27may thus be set and/or changed. The drive assembly40is formed by the drive unit45, the drive electronics42and the software driver43. The raising and lowering movement of the prealigner10in the direction of double arrow43is also controlled by the drive electronics42. With the help of image processing, the front surface of the wafer6is moved into the image center of the second camera26by raising the prealigner10. At the same time, a predetermined position of the edge of the wafer6within a defined zone (6 mm width of the wafer edge) may be approached by rotating the prealigner10. In this way, the defect to be examined is moved into the field of view of the first, second and/or third camera25,26,27. The defect located at the position approached (on the upper surface of the edge of the wafer6, the front surface of the edge of the wafer6and/or the lower surface of the edge of the wafer6) may be captured by the first, second and/or third camera25,26and27. Each captured image may be presented for review on the display7. Storage for later review is also contemplated. When all positions of a wafer where there are defects have been visited, the common carrier23is moved into the home position in the direction of double arrow24by means of a translating unit45. The wafer may be removed from the prealigner10by the three-paddle handler14, so that the next wafer6may be supplied to review. It will also be possible to copy the acquired images into the network of the user.

FIG. 5shows an enlarged representation of the schematic arrangement of the three cameras25,26and27with respect to the edge area of the wafer6. In the embodiment shown, the three cameras25,26and27are attached to a common carrier23, which may be moved in a radial direction with respect to the edge of the wafer6in the direction of double arrow24shown inFIG. 5. By moving the common carrier23, each of the cameras25,26and27may be moved with respect to the wafer6so that it captures a particular area of the edge area of the wafer6with a field of view defined by the objective30(not shown). The first camera25is provided to capture an upper edge area6awith the objective30. The second camera26is designed with the objective30such that it captures the front surface6bof the wafer6. The third camera together with the objective30is designed such that it captures a lower edge area6cof the lower surface of the wafer6. As mentioned above, the viewing area of the first camera25and the third camera27for the upper edge area6aand the lower edge area6cis about 6 mm. The viewing area of the second camera26of the front surface6bof the wafer6is about 1 mm, essentially corresponding to the thickness of the wafer6.

FIG. 6shows a further embodiment of the arrangement of the three cameras25,26and27with respect to the edge area of the wafer6. In addition to the cameras25,26and27, there are provided several illumination means50illuminating the edge area6a,6band6cof the wafer6. The illumination means50are arranged such that a bright field condition is met by their illumination and the arrangement of the cameras25,26and27.

FIG. 7shows a further embodiment of the arrangement of the cameras25,26and27and illumination means80. The illumination means80is a calotte81to which a plurality of light sources are attached. The calotte81is provided with a diffusely transparent screen or diffuser (not shown) thus contributing to a more homogeneous illumination. The calotte81has a shape corresponding to the cross-section of a cylinder. The cameras25,26and27and the calotte81are arranged on separate carriers, which are moved to the edge area of the wafer edge for capturing a defect. In the imaging position, the cameras25,26and27and the required illumination are thus opposite to the lower surface, the front surface or the upper surface of the wafer6. The calotte81comprises a recess82for imaging the edge of the wafer6in the interior of the calotte81. The calotte81is provided with several illumination elements84or light sources. The illumination elements84are designed as LEDs emitting white light. A specific different wavelength and/or wavelength composition may be used for illuminating the edge of the wafer6. The illumination elements84are arranged on the calotte81such that a bright field illumination of the edge of the wafer6is achieved.

In one embodiment, the cameras25,26and27are attached to the calotte81such that the objectives30of the cameras25,26and27are mounted in the calotte81. In this embodiment, the calotte81functions as a carrier for the cameras and the several illumination elements84. However, with this arrangement care must be taken that the bright field conditions are met to capture an area on the edge of the wafer6.

FIG. 8ashows a schematic representation of the illumination of the wafer6in side view. The screen (calotte)81provided with the LEDs as illumination elements surrounds part of the edge of the wafer6. The illumination of the edge of the wafer6has to meet predetermined requirements to provide adequate conditions for the bright field arrangement with the cameras. The illumination angle91from the edge80aof the screen81should be kept as large as possible. Likewise, the objective30of the cameras25,26and27should be constructed as slender as possible, so that at least most of a light tube93defined by the illumination, which originates, for example, from the front surface6bof the wafer6, enters the objective30, so that the conditions for bright field illumination are met.

FIG. 8bshows a schematic representation of the illumination of the upper or the lower edge area6aor6cof the wafer6, the view onto the front surface6bof the wafer being shown. From the calotte81or the illumination means80, part of the light reaches the upper edge area6aof the wafer6. In this illustration, the first camera25and the second camera26are shown schematically as filled circles. The incident light95at the upper edge area6aof the wafer6is designed such that the first camera25is in the bright field arrangement. The bright field arrangement is defined by the angle of incidence85of the light used for illumination being equal to the angle of reflection86. The angle of reflection86is identical to the detection angle at which the optical axes87of the cameras25,26or27are arranged for capturing the defects.

FIG. 8cshows a schematic top view of the illumination of the upper or lower surface of the edge of the wafer6. InFIG. 8cthe view onto the upper edge area6aof the wafer6is displayed. In this illustration, the position of the first camera25is illustrated by the rectangular shape of the CCD chip100of the first camera25. In this illustration, the second camera26is illustrated schematically as a filled circle. The position of the LEDs in the screen81is represented by plane96. The cameras25,26and27are also arranged in a plane97, which is at a symmetrical angle to the plane96of the LEDs (illumination elements84). The plane96of the LEDs and the plane97of the cameras25,26and27are both offset the same distance from the center line99, so that the bright field conditions are met for the cameras25,26and27. The CCD chips100of the cameras25,26and27have a long side length101and a short side length102. The long side length101is parallel to the center line99in this embodiment.

FIG. 9shows a top view of the upper surface of a wafer6. The wafer6has an edge area90where several defects88may be located. The wafer6also has a front surface6bwhich, as mentioned above, is opposite to the second camera26for capturing defects on the front surface6bof the wafer6.

As mentioned several times when describing the various embodiments of the arrangement of the cameras25,26and27, this arrangement allows viewing the front surface6bof the wafer6and viewing the upper edge area6aand the lower edge area6cof the wafer6. The wafer may be visually examined by the cameras25,26and27in any rotational positions within the defined edge area6aand6cof several millimeters on the upper surface and on the lower surface.

The wafer6is deposited on the prealigner10by a three-paddle handler14existing in the inspection system. The lateral run-out of the wafer6is determined by means of a measuring device of the prealigner10. The center offset may be corrected by briefly lifting and correcting the wafer6by means of the three-paddle handler14. If this value is not achieved by the first correction handling, a second handling must be performed, i.e. the wafer6is again deposited on the prealigner10. The device with the three cameras25,26and27moves in a radial direction with respect to the wafer6over the edge of the wafer6and into the focus of the camera opposite to the front surface6bof the wafer. With the help of image processing, the wafer6is moved into the image center of the field of view of the second camera26by raising the prealigner10. This ensures that both the upper edge area6aof the wafer6and the lower edge area6cof the wafer6are in the focus of the camera25and27, respectively. At the same time, the preselected position of the edge of the wafer6within the defined zone may be approached by rotating the prealigner10. In other words, this means that, by rotating the prealigner10, at least one defect gets into the field of view of one of the three cameras25,26or27. If, for example, a defect extends from the upper edge area6aof the wafer6across the front surface6bto the lower edge area6cof the wafer6, simultaneous imaging of this defect may be performed by all three cameras25,26,27.