A system for inspecting a peripheral edge of a substrate

Abstract

The invention concerns a system (OS) for inspecting a peripheral edge of a substrate (1) by projecting an inspection light wave on a portion of the peripheral edge and by imaging the reflected or scattered light. The system comprises an optical assembly (OA) collecting at least in part the reflected and / or scattered light and configured for directing the light reflected and / or scattered on a first region of the peripheral edge of the substrate, along a first light path (P1) toward a camera (2), and for directing the light reflected or scattered on a second region of the peripheral edge, distinct from the first region, along a second light path (P2) toward the camera (2), the second light path (P2) being longer than the first light path (P1). According to the invention, the optical assembly (OA) comprises at least one refractive optical element (OE1,OE2), at least one of which is positioned in the second light path (P2), configured to position the second region in the camera depth of field.

Description

[0001] A SYSTEM FOR INSPECTING A PERIPHERAL EDGE OF A SUBSTRATE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a system for the optical inspection of an edge of a substrate to detect the possible presence of defects such as particles , irregularities , cracks , or more generally to characteri ze its surface condition . The substrate can be a wafer for the manufacture of devices for instance in the field of microelectronics , optics , microsystems , or optoelectronics .

[0004] BACKGROUND OF THE INVENTION

[0005] Existing inspection systems generally direct a light beam on the surface of a substrate , for instance a semiconductor wafer . The light reflected and / or scattered from the surface is collected and analyzed to determine characteristics of the surface .

[0006] A wafer peripheral edge is more di f ficult to inspect , as it is composed of a plurality of non-coplanar regions . The geometry of such edge is defined and speci fied by international standards . For instance , as speci fied by SEMI Ml ( Semiconductor Equipment and Materials International - Polished Single Crystal Silicon Wafers ) and with reference to figure 1 , a wafer edge is composed of : front and back ring-shaped surfaces la, lb corresponding respectively to the periphery of the frontside FS and the backside BS of the wafer 1 ; top and bottom bevel s la' , lb' ; and edge apex 1c . Top and bottom bevels la' , lb' extend radially between the edge apex 1c and, respectively, the frontside and backside periphery of the wafer . The front and back ring-shaped surfaces la, lb may extend radially over a couple of millimeters over the front and backside of the wafer, while the apex 1c and the bevels la' , lb' together correspond to the thickness of the wafer, which can be in the order o f 775pm or less . Consequently, the unfolded width of the wafer edge may be typically within a few millimeters .

[0007] US7822260 discloses a system for inspecting a peripheral edge of a substrate using multiple cameras to inspect di f ferent areas of the edge independently of each other, making the whole optical setup rather cumbersome and bulky . Such a system requires lengthy integration and calibration procedures and is also very costly .

[0008] US20070127016A1 and US20200201011A1 are based on a rotating vision system with a radial motor to inspect all areas of the edge , but again the device is quite bulky and can have mechanical problems due to the radial motor .

[0009] US7280197B1 discloses a system for optical inspection of a substrate edge based on a single camera facing the edge apex . An optical assembly conveys images of multiple regions of the substrate edge onto a linear sensor array of a high pixel count line scan camera . The optical assembly is made of multiple lenses configured and arranged in the system so as to respectively position multiple obj ect planes at the multiple regions of the substrate edge , each obj ect plane being the optical conj ugate of the linear sensor array ( forming an image plane ) by the respective lenses . This approach requires to speci fically design and position several lenses in the system, which can be di f ficult to achieve with the necessary precision . In addition, positioning the camera to face the edge apex is not always a practical arrangement to achieve , notably because of ri sks o f breach of the wafer which is usually rotating at high speed .

[0010] OBJECT OF THE INVENTION

[0011] A purpose of the invention is to resolve , at least partially, the aforementioned problems . In particular, a purpose of the invention is to provide a system or device for optically inspecting the edge of a substrate , providing a sharp image of each region of the substrate edge , which is simple in constitution . Another purpose of the invention is to provide such device , which allows providing simultaneously a sharp image of each region of the substrate edge . Another purpose of the invention is to provide such device which is more compact . Another purpose of the invention is to provide such device where the camera is positioned so that it can be more easily protected in case of a breach of a wafer, in particular when rotating at high speed .

[0012] SUMMARY OF THE INVENTION

[0013] To this ef fect , the invention relates to a system for inspecting a peripheral edge of a substrate by proj ecting an inspection light wave on a portion of the peripheral edge and by imaging the reflected or scattered light , the system comprising :

[0014] • a support for positioning the substrate in a main plane in the system, such as to expose the peripheral edge of the substrate ;

[0015] • an illumination source configured to provide the inspection light wave ;

[0016] • a camera for imaging the light reflected and / or scattered by the peripheral edge o f the substrate , the camera comprising a camera obj ective and an image sensor associated with the camera obj ective , the image sensor presenting a sensing surface defining an image plane parallel to the main plane ;

[0017] • an optical assembly collecting at least in part the reflected and / or scattered light and configured for directing : i . the light reflected and / or scattered on a first region of the peripheral edge of the substrate , along a first light path toward the camera, and ii . the light reflected or scattered on a second region of the peripheral edge , distinct from the first region, along a second light path toward the camera, the second light path being longer than the first light path .

[0018] The camera is positioned with respect to the substrate such that the first region lies in the camera ' s depth of field, and the optical assembly comprises at least one refractive optical element , at least one of which is positioned in the second light path and is configured to position the second region in the camera depth of field .

[0019] According to further non limitative features of the invention, either taken alone or in any technically feasible combination :

[0020] - the at least one refractive optical element has a thickness and a refractive index along the second light path adj usted to shi ft an intermediate obj ect plane , optical conj ugate of the image plane by the camera obj ective , on the second region;

[0021] - the optical assembly comprises at least one light directing element to direct the light issued from, respectively, the first region and the second region towards the camera, the first region and the second region having a di f ferent angular orientation;

[0022] - the optical assembly is also configured to guide the light reflected or scattered on a third region of the peripheral edge , di f ferent from the first and second regions , along a third light path toward the camera, the third light path being longer than the first and second light path, and wherein the optical assembly comprises at least one further refractive optical element positioned in the third light path and configured to position the third region in the camera depth of field;

[0023] - the first region is arranged to be located on an annular surface on the frontside of the substrate , the second region is arranged to be located on an apex of an edge of the substrate and a third region is arranged to be located on an annular surface disposed on the backside of the substrate ;

[0024] - the system comprises a refractive optical element in the form of a glass plate ;

[0025] - the system a refractive optical element in the form of a prism;

[0026] - the optical assembly is arranged to respectively direct the light from the di f ferent regions of the peripheral edge of the substrate towards di f ferent parts of the image sensor ;

[0027] - the camera is a line or a TDI camera ;

[0028] - the camera comprises a single camera obj ective , and the optical assembly is arranged to direct the light reflected and / or scattered on the di f ferent regions of the peripheral edge of the substrate through said single camera obj ective ;

[0029] - the optical assembly is deprived of any focusing lens ;

[0030] - the camera obj ective comprises a bi-telecentric lens ;

[0031] - the illumination source comprises a plurality of LEDs positioned alongside the camera . DRAWINGS

[0032] Many other features and advantages of the present invention will become apparent from reading the following detailed description, when considered in conj unction with the accompanying drawings , in which :

[0033] Figure 1 represents an example of a portion of a peripheral edge of a substrate ;

[0034] - Figure 2a represents the image of an obj ect as seen through a refractive optical element ;

[0035] - Figure 2b illustrates the principle of the invention;

[0036] - Figures 3a and 3b represent di f ferent views of an optical system according to the invention .

[0037] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0038] Figure 2a illustrates an optical imaging arrangement comprising a camera obj ective or a lens 0 with an optical axis OAx and a refractive optical element OE formed by a plate made of a transparent , homogeneous medium, bounded by two flat , parallel faces . The faces of the refractive optical element OE as illustrated on the figure are perpendicular to the optical axis OAx . The refractive optical element OE is composed of a material ( for instance a glass ) having a refractive index n2 greater than the refractive index nl of its environment ( generally air ) . In the absence of the refractive optical element OE , an obj ect point Al ' of an obj ect would be imaged or conj ugated by the lens 0 into the image point AO of an image plane IP as illustrated . But by inserting the refractive optical element OE in the optical path between the camera obj ective and the obj ect , the obj ect point forming the optical conjugate of the image point AO by the lens 0 becomes Al. Using the paraxial approximation for simplicity, it can be demonstrated that the distance between the object point Al' , now virtual, and the actual object point Al is d = e(l-nl / n2) where e is the thickness of the optical element OE.

[0039] As a result, the refractive optical element OE allows shifting an intermediate object plane TOP which is the optical conjugate of an image plane IP by the lens 0 into an object plane OP which is further away from the intermediate object plane TOP. More specifically, that object plane OP is separated from the intermediate object plane TOP by a distance d which is determined by the thickness e of the refractive optical element OE and by the optical index ratio nl / n2. For illustrative purpose, when the refractive optical element is made of fused silica (n2=1.458) and the ambient is air (nl = 1.000) , the distance d is equal to 0.314 times the thickness e of the refractive optical element OE.

[0040] Figure 2b presents an optical set-up that illustrates how the refractive optical element OE of figure 2a may be used to image with sufficient sharpness two objects Al, Bl positioned at different distances from the camera. On this figure, a camera 2 comprises a camera objective 0 and an image sensor IS associated with the camera objective 0. The image sensor IS comprises a sensing surface defining an image plane IP. The camera objective 0 defines an intermediate object plane TOP, the intermediate object plane TOP being the plane conjugated, by the camera objective 0, of the image plane IP.

[0041] The image sensor IS can comprise a sensing surface with a plurality of pixels in a matrix configuration. It may also comprise a line of pixels, in case of a line sensor. In that case, the image plane is defined by a plane of the image sensor IS, or a plane comprising the line of pixels and being perpendicular to the optical axis OAx .

[0042] According to the invention, the camera 2 images a first object Bl positioned at a first distance from the camera 2 and a second object Al positioned at second distance from the camera 2, the second distance being greater than the first one.

[0043] In the illustrated embodiment, the camera 2 is positioned in the optical set-up such that the first object Bl lies in the camera depth of field, in or close to the intermediate object plane IOP, corresponding to the conjugate of the image plane IP by the objective 0. The second object Al, being further away from the camera 2, lies outside of its depth of field. To compensate for this greater distance and still provide a sharp image of object Al, a refractive optical element OE is positioned between the camera 2 and the second object Al. The refractive optical element OE is configured (through its thickness e and its optical index n2 ) in order to shift the intermediate object plane IOP by a distance d, to define a new object plan OP which is optically conjugate of the image plane IP by the camera objective 0 through the refractive optical element OE . So, the second object Al is "seen" by the image sensor IS as corresponding to the virtual object Al' located in the intermediate object plan IOP. And so, the second object Al is positioned in the camera depth of field and can be imaged properly.

[0044] The refractive optical element OE can be positioned in such a way to cover only a part of the field of view of the camera, which can be defined as the object plan(s) or points which can be imaged on the sensor IS, as shown in figure 2b. This allows to split the field of view, for instance to image a first field of view located at a first distance and a second field of view located at a second distance simultaneously with the same image sensor IS and the same objective 0. In the example illustrated, the refractive optical element OE is positioned in such a way to split the field of view of the camera in 2 hal f obj ect planes , TOP for the part of the field of view with the obj ect point Bl , and OP, shi fted along the optical axis of a distance d from TOP, for the other part of the field of view with the obj ect point Al .

[0045] Of course , the illustration of Figure 2b is only schematic . It is for instance preferable to control the light issued from the respective obj ect points (Al , Bl ) in such a way that the light from any obj ect point reaching the image sensor IS has either , not at all , or in totality, crossed the refractive optical element .

[0046] According to some embodiments :

[0047] - several optical refractive elements or a refractive element with several values of thicknesses can be used to split the field of view into several obj ect planes positioned at di f ferent distances from the obj ective 0.

[0048] - All parts of the field of view can be imaged through at least one refractive optical element .

[0049] The present invention exploits these principles to propose a system for the optical inspection of an edge of a substrate . The system proj ects an inspection light on a portion of the peripheral edge and images the reflected and / or scattered light to detect the possible presence of defects such as particles , irregularities or more generally to characteri ze its surface condition .

[0050] As already mentioned in the introduction of this disclosure , and as represented on figure 1 , the peripheral edge of a substrate is composed of several non-coplanar regions , including for instance front and back annular ( i . e ring-shaped) surfaces la, lb, top and bottom bevels la' , lb' and apex 1c . Figures 3a and 3b show an embodiment of a system OS according to the invention to image the peripheral edge of a substrate , in side view and top view, respectively . Generally speaking, the system OS comprises an illumination light source 3 configured to provide the inspection light wave . As shown on Figure 3b, the proj ection of the inspection light wave on the substrate 1 defines an inspection area I on the substrate , the inspection area I corresponding to an angular portion of the substrate peripheral edge . A camera 2 images the light reflected or scattered from the inspection area I . For instance , a defect ( scratch, particle... ) present on the illuminated portion of the substrate edge may cause the emission of scattered light radiations which are guided to , and imaged by, the camera 2 . And even in the absence of defects , the illumination light which is reflected by the surface of the substrate edge is collected and used to provide an image of the edge of the substrate .

[0051] An optical assembly OA is positioned between the substrate 1 and the camera 2 , to collect at least part of the light reflected and / or scattered on the inspection area I , and to position a plurality of regions ( and preferably all the regions ) of the substrate edge within the depth of field of the camera 2 .

[0052] Advantageously, the system comprises a single camera 2 . The optical assembly OA allows to image the non-coplanar regions forming the edge , unfolded, in the image plane of that single camera 2 , as this will be explained in greater details in a further passage of this description .

[0053] The camera 2 is facing the substrate frontside FS and comprises a camera obj ective 0 and an image sensor IS associated with the camera obj ective 0. According to some embodiments , the obj ective 0 is a bi-telecentric obj ective , which limits dimensional errors due to perspective and also reduces distortion . The image sensor IS defines an image plane IP parallel to a main plane (x, y) in which the substrate 1 resides , i . e parallel to the support 4 and to the substrate exposed fronts ide FS . In the illustrated embodiment , the sensing surface of the image sensor is configured as a line 2a, arranged radially with respect to the substrate 1 , as shown in the top view of the system in Figure 3b . The camera can then be a line camera, or a time delay integration ( TDI ) camera with a CCD or CMOS image sensor . The camera defines , in the system OS , an intermediate obj ect plane TOP that is the conj ugated plane of the image plane IP by the camera obj ective 0, in the absence of refractive elements in the optical path, usually in air or another gas . In the illustrated embodiment , the system is configured such that the intermediate obj ect plane TOP is made coplanar with the substrate front side FS . As this is well known, the camera 2 presents a depth of field extending on both sides of the intermediate obj ect plane TOP , that notably depends on its aperture and pixel resolution, and an obj ect disposed in the depth of field o f the camera 2 may be imaged sharply .

[0054] The illumination source 3 in the il lustrated embodiment is formed of a set of light emitting devices ( LEDs ) positioned alongside ( and all around) the camera 2 . The inspection light beam produced by the set of LEDs illuminates all regions of the substrate edge portion, guided by the optical elements composing the optical assembly OA. Note that this configuration does not form a necessary feature and the illumination source may be configured di f ferently, for instance by di sposing the individual LEDs within the optical system OS to directly expose the di f ferent regions of the portion of the peripheral edge under inspection to distinct inspection light beams , i . e . without the distinct inspection light beams being guided by the optical assembly OA.

[0055] In an alternative to the LEDs , the illumination source 3 may comprise a continuous or a pulsed laser . It may also comprise any other kind of light source such as thermal sources , supercontinuum, plasma light sources . The illumination source 3 may also comprise at least one optical fiber to guide the radiations generated the light source ( LED, laser, ... ) . The extremity of the fiber is emitting the inspection light wave and can be positioned within the system OS to proj ect the beam on the distinct regions of a peripheral edge portion . I f more than one beam is necessary to illuminate the distinct regions , the illumination source may comprise a splitter to propagate the radiation into a plurality of optical fibers .

[0056] The system OS also comprises a support 4 for positioning the substrate 1 with respect to the other elements , notably with respect to the illumination source 3 and with respect to the camera 2 . In the illustrated embodiment , the support 4 presents a receiving surface parallel to the main plane (x, y) and the substrate 1 is positioned on the support 4 such that a central region of the substrate 1 backside BS is contacting the receiving surface . This configuration allows exposing the frontside FS and all the distinct peripheral edge regions of the substrate 1 , including the front and back annular surfaces la, lb, top and bottom bevels la' , lb' and apex 1c . The substrate 1 is maintained on the support 4 for instance by vacuum suction . Of course , other kinds of supports may be used, such as a support with contacting points supporting the substrate only on a few points , each equipped with vacuum suction . In that case , the plan of the contacting points defines the receiving surface .

[0057] In the embodiment represented on f igure 3a, the support 2 may be translated in the main plane (x, y) in which the substrate 1 resides . Advantageously, the support may also be translated according to a direction z perpendicular to the main plane (x, y) . With such a configuration, it is possible to precisely calibrate the inspection area I on the substrate 1 and make sure that this area includes all the distinct edge regions . The support 4 may be rotated around an axis r, perpendicular to the main plane (x, y) and centered on the substrate 1 , so that , by rotating the support 4 , the complete peripheral edge of the substrate 1 may be scanned by the illumination light beam and imaged by the camera 2 .

[0058] The movement of the support is coordinated by a controller 6 that may comprise a microcontroller, data storage , input / output ports connected to actuators and motors for displacing and / or rotating the support 4 , and to other elements of the system OS , and further computing resources that are configured, in hardware or in software , to precisely control the scanning of the substrate peripheral edge . The substrate 1 being precisely positioned on the support 4 within the system OS , the controller 6 stores and controls the position ( for instance in linear or polar coordinates ) of the inspection area I in a referential linked to the substrate 3 . Consequently, the location of the inspection area I on the substrate 3 can be known at each moment .

[0059] The images provided by the camera 2 are provided to a processing unit 10 . Such processing unit comprises a computer or a microcontroller, with data storage and interface ports . That processing unit 10 is also connected to the controller 6 which provides the location of the inspection area I on the wafer at any time . The processing unit 10 is configured to provide an unfolded map of the substrate edge , including preferably all distinct regions of the peripheral edge , allowing to identi fy and locate defects present on this peripheral edge .

[0060] The optical assembly OA collects at least in part the light reflected and / or scattered by the peripheral edge of the substrate .

[0061] The optical assembly OA is notably configured for directing the light reflected and / or scattered by a first region of the peripheral edge of the substrate , along a first light path, toward the camera 2 . The camera 2 is then positioned with respect to the substrate 1 such that the f irst region lies in the camera depth of field, at or close to the intermediate obj ect plane TOP .

[0062] The optical assembly OA is also configured for directing the light reflected and / or scattered by a second region of the peripheral edge , distinct from the first region, along a second light path toward the camera 2 , the second light path being longer than the first light path .

[0063] The optical assembly OA comprises at least one refractive optical element inserted into the second light path and configured to position the second region in the camera depth of field, i . e . at or close to the intermediate obj ect plane TOP , using the principle exposed in relation to the description of figures 2a, 2b . By "refractive optical element" it is referred to an optical element made of a material transparent to the inspection light beam and which has a refractive index greater than the one of the ambient atmosphere ( generally air ) . This material may for example be fused silica or a glass .

[0064] In the embodiment of figures 3a, 3b, the camera 2 is positioned such that the intermediate obj ect plane IOP coincides or is close to the annular ( ring-shaped) front surface la and top bevel la' of the substrate peripheral edge . Since the camera 2 is positioned directly above these regions , the other regions of the peripheral edge ( apex 1c, bottom bevel lb' and annular back surface lb ) are positioned further away from the camera 2 .

[0065] In this embodiment , the light reflected and / or scattered by the annular front surface la and by the top bevel la' is not directed through a refractive element of the optical assembly OA. This light is directly directed toward the camera 2 along a relatively short first light path Pl .

[0066] Conversely, the light reflected and / or scattered by the apex 1c is intercepted by the optical assembly OA and guided by a mirror M toward the camera along a second light path P2 , longer than the first light path . The light reflected and / or scattered by the annular back surface lb and by the bottom bevel lb' is also intercepted by the optical assembly OA and guided by reflecting prims OE2 toward the camera 2 along a third light path P3 , longer than the second and first path .

[0067] To position the regions further away from the camera 2 ( apex 1c , annular back surface lb and by the bottom bevel lb' ) within the camera depth of field, the optical assembly OA comprises a plurality of refractive optical element 0E1 , 0E2 . The refractive optical elements are configured ( through their thickness and optical indices as this has been explained in a prior passage o f this description) to define new obj ect planes shi fted away from the intermediate obj ect plane TOP to coincide with respectively the apex 1c, the bottom bevel lb' and the annular back surface lb . And so , all parts of the edge of the substrate are " seen" by the camera 2 as being virtually positioned on or close to the intermediate obj ect plane TOP .

[0068] More precisely, the length of the second light path P2 is di f fering from the length of the first light path Pl by the distance separating the intermediate obj ect plane TOP to the edge apex 1c, through the directing mirror M . This di f ferential length may be in the order of several tens of millimeters . To compensate for this di f ferential length, the optical assembly OA represented on figure 3a comprises a plate 0E1 made of transparent material ( to the illumination beam) , for instance made of glass , optically disposed in the second light path P2 , but not in the first light path Pl . By selecting the thickness of the plate, for instance in the range between 20mm to 80mm depending on the differential length to compensate, it is possible to position the virtual image of the apex 1 at or close to the intermediate object plane TOP, within the depth of field of the camera 2.

[0069] A similar reasoning may be applied to compensate the differential length of the third light path P3, between the bottom bevel lb' , back annular surface lb and the camera 2, with respect to the first light path Pl. The third light path P3 is intersecting the plate 0E1, allowing to compensate part of this differential length. In addition, the optical assembly comprises a second refractive optical element 0E2, in the form of prims. In addition to guiding the reflected and / or diffracted light toward the camera 2, this second refractive optical element 0E2 also adds a thickness of refractive material that contribute to position the virtual image of the bottom bevel lb' and of the back annular surface lb, as viewed by the camera 2, at or close to the intermediate object plane IOP, within the depth of field of the camera 2.

[0070] So, the optical assembly allows compensating the difference of length of the various light paths towards the object planes, but also to accommodate for the different orientation and positions of these object planes. For instance, the apex 1c is perpendicular to the front annual surface la, and the back annular surface lb requires to be imaged from the opposite direction compared to the front annual surface la. In addition, thanks to the arrangement of light paths and of the refractive elements, the respective objects planes are "seen" by the camera to correspond to portions or series of points of the intermediate object plane (IOP) , which are in turn imaged into different portions of the image plane IP by the objective 0. As a result, the image plane IP provides an unfolded image of the peripheral edge, with for instance along the pixels of the line sensor: the front annual surface la, the top bevel la' , the apex 1c, the bottom bevel lb' and the back annular surface lb .

[0071] So , with the proposed optical assembly OA, it is possible to provide a sharp, unfolded image of the complete peripheral edge of the substrate , by imaging the illuminated portion while rotating the support 4 . The system OS is made particularly compact and simple by using a single camera facing the substrate frontside FS .

[0072] Other variations to the disclosed embodiment can be understood and ef fected by those skilled in the art in practicing the claimed invention, from a study of the drawings , the disclosure , and the appended claims .

[0073] In particular, it is not necessary that the camera 2 images the complete substrate peripheral edge , i . e . including all its distinct regions . In certain cases , only speci fic regions of the peripheral edge may be imaged, rather than all of them . The optical assembly may also have fewer refractive optical elements than described in relation to the embodiment of figures 3a and 3b .

[0074] Also , the optical assembly AO may also comprise a refractive element configured to also intercept the light propagating along the first path, for instance for guiding the light reflected and / or scattered on the first region toward the camera, or for positioning the intermediate obj ect plane away from the substrate frontside .

[0075] The optical assembly may comprise one or more light directing elements , such as the mirror M or the prism 0E2 of the illustrated embodiment , to direct the light issued from distinct regions toward the camera 2 , in particular when the distinct region presents di f fering angular orientations . In the described embodiment , the bottom bevel lb ' and back annular surface lb combine to form a single region of the substrate edge . Similarly, the top bevel la ' and front annular surface la also combine to form another region of the substrate edge . This is due to the negligible di f ference in elevation between them . In other instances , it may be beneficial to consider the respective bevels la' , lb' , the front and back annular surfaces la, lb as distinct regions . In such instances , the system may comprise more refractive optical elements than described in relation to the embodiment of figures 3a and 3b to compensate the di f ferential length separating each region to the camera .

[0076] In the same way, the substate edge may be defined di f ferently according to other standards , with other regions . In that case , the system may be adapted with other configurations of refractive elements to image these respective regions .

[0077] The optical assembly OA described includes optical directing elements , such as the mirror M and the prims 0E2 , along with optical refractive elements , plate 0E1 and prims 0E2 . But this should not be seen as limitative . In particular, the optical assembly OA may comprise further or di f ferent optical directing / refractive elements than the one described . The optical assembly may also comprise further optical elements , di f ferent from the directing optical element and refractive optical elements , for providing further function to the system . In certain embodiments , however, such as the one described with respect to figures 3a, 3b, the optical assembly is deprived of any focusing lens , which makes it simple to configure and calibrate .

Claims

CLAIMS1. A system (OS) for inspecting a peripheral edge of a substrate(1) by projecting an inspection light wave on a portion of the peripheral edge and by imaging the reflected or scattered light, the system comprising:• a support (4) for positioning the substrate in a main plane (x,y) in the system (OS) , such as to expose the peripheral edge of the substrate (1) ;• an illumination source (3) configured to provide the inspection light wave;• a camera (2) for imaging the light reflected and / or scattered by the peripheral edge of the substrate (1) , the camera comprising a camera objective (0) and an image sensor (IS) associated with the camera objective (0) , the image sensor (IS) presenting a sensing surface defining an image plane (IP) parallel to the main plane (x,y) ;• an optical assembly (OA) collecting at least in part the reflected and / or scattered light and configured for directing: i. the light reflected and / or scattered on a first region of the peripheral edge of the substrate, along a first light path (Pl) toward the camera ( 2 ) , and ii. the light reflected or scattered on a second region of the peripheral edge, distinct from the first region, along a second light path (P2) toward the camera (2) , the second light path (P2) being longer than the first light path (Pl) ; wherein the camera (2) is positioned with respect to the substrate (1) such that the first region lies in the camera's depth of field, and the optical assembly (OA) comprises at least one refractive optical element (OE1,OE2) , at least one of which is positioned in the second light path (P2) and isconfigured to position the second region in the camera depth of field.

2. A system (OS) according to claim 1, wherein the at least one refractive optical element (OE1,OE2) has a thickness and a refractive index along the second light path (P2) adjusted to shift an intermediate object plane (TOP) , optical conjugate of the image plane (IP) by the camera objective (0) , on the second region.

3. A system (OS) according to claim 1 or 2, wherein the optical assembly (OA) comprises at least one light directing element (M,0E2) to direct the light issued from, respectively, the first region and the second region towards the camera (2) , the first region and the second region having a different angular orientation.

4. A system (OS) according to any preceding claims, wherein the optical assembly (OA) is also configured to guide the light reflected or scattered on a third region of the peripheral edge, different from the first and second regions, along a third light path (P3) toward the camera (2) , the third light path (P3) being longer than the first (Pl) and second light path (P2) , and wherein the optical assembly (OA) comprises at least one further refractive optical element (0E2) positioned in the third light path (P3) and configured to position the third region in the camera depth of field.

5. A system (OS) according to claim 4, wherein the first region is arranged to be located on an annular surface (la) on the frontside of the substrate, the second region is arranged to be located on an apex (1c) of an edge of the substrate and a third region is arranged to be located on an annular surface (lb) disposed on the backside of the substrate.

6. A system (OS) according to any preceding claim, which comprises a refractive optical element (0E1, 0E2) in the form of a glass plate.

7. A system (OS) according to any preceding claim, which comprises a refractive optical element (0E1, 0E2) in the form of a prism.

8. A system (OS) according to any preceding claim, wherein the optical assembly (OA) is arranged to respectively direct the light from the different regions of the peripheral edge of the substrate towards different parts of the image sensor (IS) .

9. A system (OS ) according to any preceding claim, wherein the camera (2) is a line or a TDI camera.

10. A system (OS) according to any preceding claim, wherein the camera (2) comprises a single camera objective (0) , and the optical assembly (AO) is arranged to direct the light reflected and / or scattered on the different regions of the peripheral edge of the substrate through said single camera obj ective (0) .

11. A system (OS) according to any preceding claim, wherein the optical assembly (OA) is deprived of any focusing lens.

12. A system (OS ) according to any preceding claim, wherein the camera objective (0) comprises a bi-telecentric lens.

13. A system (OS) according to any preceding claim, wherein the illumination source (3) comprises a plurality of LEDs positioned alongside the camera (2) .

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