Patent Application
20210360140
The present invention relates generally to optical inspection systems and more particularly to multimodality multiplexed illumination useful in optical inspection systems.
Various types of optical inspection systems are known in the art.
The present invention seeks to provide an optical inspection system including spatially multiplexed multimodality illumination, for providing wide angle illumination having at least near full angular coverage.
There is thus provided in accordance with a preferred embodiment of the present invention an inspection system including an illumination subsystem and an image sensing subsystem, the illumination subsystem providing a plurality of illumination modalities, the system simultaneously illuminating at least two areas of an object with different ones of the plurality of illumination modalities, images of which are acquired by a single sensor forming part of the image sensing subsystem.
Preferably, the sensor includes an area sensor.
Preferably, the at least two areas of the object are mutually non-contiguous.
Preferably, the illumination subsystem includes at least two light modules respectively illuminating the at least two areas of the object with the different ones of the plurality of illumination modalities.
Preferably, the object and the inspection system are in at least near continuous relative motion along a scan direction.
Preferably, the illumination subsystem is strobed to illuminate the at least two areas of the object during the at least near continuous relative motion.
Preferably, the at least two light modules are mutually physically spaced apart by spaces along the scan direction and the plurality of illumination modalities include different angular modalities of illumination.
Preferably, the system also includes a beam splitter directing illumination from the at least two areas towards the sensor, the beam splitter being positioned such that edges thereof lie within the spaces.
Preferably, each of the at least two light modules provides at least two additional modalities of illumination in a cross-scan direction, generally orthogonal to the scan direction.
In accordance with a preferred embodiment of the present invention, the at least two additional modalities of illumination include different wavelength-encoded modalities.
Additionally or alternatively, the at least two additional modalities of illumination include different polarization-encoded modalities.
Further additionally or alternatively, the at least two additional modalities of illumination include different temporal modalities.
Preferably, the illumination subsystem includes a multiplicity of light sources directing light towards at least one transmissive concentrator element.
Alternatively, the illumination subsystem includes a multiplicity of light sources directing light towards at least one reflective concentrator element.
In accordance with a preferred embodiment of the present invention, the multiplicity of light sources includes an array of light sources outputting light to a corresponding array of light guides.
Preferably, the system also includes an array of light shaping elements, at least one light guide of the array of light guides outputting light to each light shaping element.
Preferably, the system also includes an image processing subsystem for processing the images.
Preferably, the processing includes co-registration of the images.
Additionally or alternatively, the processing includes demultiplexing of the images.
Preferably, the illumination provided by the illumination subsystem extends over an angular range of at least ±45°.
There is also provided in accordance with another preferred embodiment of the present invention a method for inspecting an object including simultaneously illuminating at least two areas of an object with different ones of a plurality of illumination modalities and acquiring images of the at least two areas by a single sensor.
Preferably, the sensor includes an area sensor.
Preferably, the at least two areas of the object are mutually non-contiguous.
Preferably, the illuminating is performed by at least two light modules respectively illuminating the at least two areas of the object with the different ones of the plurality of illumination modalities.
Preferably, the object and the at least two light modules are in at least near continuous relative motion along a scan direction.
Preferably, the illuminating includes strobing of the at least two light modules during the at least near continuous relative motion.
Preferably, the at least two light modules are mutually physically spaced apart by spaces along the scan direction and the plurality of illumination modalities include different angular modalities of illumination.
Preferably, the method also includes directing illumination from the at least two areas towards the sensor by a beam splitter, the beam splitter being positioned such that edges thereof lie within the spaces.
Preferably, the method also includes illuminating the at least two areas of the object with at least two additional modalities of illumination in a cross-scan direction, generally orthogonal to the scan direction.
In accordance with a preferred embodiment of the method of the present invention, the at least two additional modalities of illumination include different wavelength-encoded modalities.
Additionally or alternatively, the at least two additional modalities of illumination include different polarization-encoded modalities.
Further additionally or alternatively, the at least two additional modalities of illumination include different temporal modalities.
Preferably, the illuminating is performed by a multiplicity of light sources directing light towards at least one transmissive concentrator element.
Alternatively, the illuminating is performed by a multiplicity of light sources directing light towards at least one reflective concentrator element.
In accordance with a preferred embodiment of the method of the present invention, the multiplicity of light sources includes an array of light sources outputting light to a corresponding array of light guides.
Preferably, the method also includes providing an array of light shaping elements, at least one light guide of the array of light guides outputting light to each light shaping element.
Preferably, the method also includes processing the images following the acquiring.
Preferably, the processing includes co-registering the images.
Additionally or alternatively, the processing includes demultiplexing of the images.
Preferably, the illuminating includes illuminating over an angular range of at least 45°.
The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:
Reference is now made to
As seen in
Optical inspection system 100 preferably includes an illumination subsystem 120, preferably providing a plurality of illumination modalities, and an image sensing subsystem 122. Here, by way of example only, illumination subsystem 120 is seen to comprise an illuminator 124 and image sensing subsystem 122 is seen to comprise a camera 126, operation of which illuminator 124 and camera 126 is preferably controlled by image processing and control electronics 128, as seen in
It is particular feature of a preferred embodiment of the present invention that optical inspection system 100 preferably simultaneously illuminates at least two areas of object 106, such as first, second and third areas 130, 132, 134 seen in
Images acquired by image sensing subsystem 122, following image processing as carried out by processing and control electronics 128, preferably provide wide illumination angle coverage of object 106. Furthermore, such wide illumination angle coverage may, depending on the particular application, exhibit near full or full coverage over the angular range thereof, with negligible angular gaps therein, thereby advantageously providing both wide and at least almost gap-free angular coverage of object 106, as is further detailed henceforth with reference to
Optical inspection system 100 is preferably operative to perform continuous scanning of substrate 106. During scanning, substrate 106 is preferably in continuous motion relative to optical head 102 and illuminator 124 is preferably periodically strobed in order to illuminate substrate 106 at times corresponding to predetermined positions of substrate 106 with respect to illuminator 124, as is further detailed henceforth. Camera 126 is preferably operative to acquire images of substrate 106 as illuminated by the plurality of illumination modalities provided by illuminator 124.
Motion of optical head 102 and table 104 may be controlled by a motion subsystem 140. Precise timing of strobing of illuminator 124 and corresponding image acquisition by camera 126 may be controlled by a master computer 142 including various control and processing algorithms 144. Power may be supplied to both illuminator 124 and camera 126 by a power supply module 146 preferably included in optical head 102.
It is understood that the continuous relative motion of substrate 106 with respect to optical head 102 may be created by motion of optical head 102 along a scan direction 150 as substrate 106 remains stationary. Alternatively, such continuous relative motion may be by way of motion of substrate 106 with respect to a stationary optical head 102 or by way of motion of both substrate 106 and optical head 102 with respect to each other. It is appreciated that although the operation of system 100 is described hereinbelow with respect to motion of optical head 102 along scan direction 150 relative to stationary substrate 106, the principles of operation may be correspondingly applied to other modes of motion resulting in continuous relative motion of substrate 106 and optical head 102 along scan direction 150.
It is understood that the inspection system 100 of the present invention is thus preferably operated in a continuous scan mode, wherein illuminator 124 is strobed synchronously with respect to the motion of substrate 106 in relation to optical head 102, in order to acquire images of substrate 106 by area sensor 136. The operation of system 100 in a continuous scan mode facilitates a high scanning speed, which high scanning speed is particularly desirable in electronic substrate inspection.
Furthermore, the performance of continuous scanning in combination with the use of an area sensor for image acquisition, such as area sensor 136, rather than a line type image sensor improves the efficiency of light provision to camera 126, allowing camera 126 to perform image acquisition at a higher speed than would otherwise be the case should a line type image sensor be employed. Additionally or alternatively, the improved light efficiency arising from the use of area sensor 136 may be utilized towards a simpler and more reliable illuminator, as is further detailed below.
The improved light efficiency preferably achieved in the present invention by employing area type sensor 136 rather than a line type image sensor may be attributed to several factors. Firstly, the use of area type sensor 136 leads to a better area efficiency of corresponding illuminator 124, since the illuminated field of camera 126 may be substantially the same size as the effective camera field of view (FOV), thus reducing the amount of light wasted. In contrast, should a line sensor be employed, illuminator 124 may illuminate an area much wider than the line field of view sensed by the camera, thus resulting in wasted light.
The improved efficiency of illumination due to the use of an area rather than line type image sensor may be appreciated by considering the imaging of a 20 mm wide strip on an object such as object 106. In the case of a line sensor being used to perform such imaging, the instantaneous FOV imaged by the camera may typically be 10 μm ‘deep’ in the scan direction, meaning that the line camera ‘sees’ an area of 20 mm by 10 μm. In order to properly illuminate this FOV, the illuminator should uniformly illuminate a field that is larger by +0.5 mm in each dimension. The actual illuminated strip that would be uniformly illuminated, due to practical design and construction considerations, would be approximately 21 mm by 1 mm, resulting in an about 100 fold waste of light energy provided to object 106. In contrast, in the case of an area sensor being used to perform imaging of a 20 mm wide strip in accordance with preferred embodiments of the present invention, the camera FOV is comprised of several strip-like regions each measuring about 20 mm by 2 mm. Under similar practical design and construction considerations, each uniformly illuminated region would now be approximately 21 mm by 3 mm, resulting in only a 33 percent waste of light energy provided to object 106.
Additionally, the use of area type sensor 136 allows illuminator 124 to be operated with light strobes of a shorter duty cycle than would be feasible should a line type sensor be employed. The duty cycle typically is generally equal to the inverse of the sensor row count increment for each illumination modality along scan direction 150, which may be in the range 100-5000 in sensor 136. A reduced duty cycle may allow increased light levels while reducing cooling and electrical driving needs, thus achieving lower system complexity and cost.
Still further advantages will become apparent based on the detailed description provided hereinbelow.
Further details pertaining to the structure and operation of system 100 may be best understood with additional reference to
Turning now to
Each of first, second and third light modules 152, 154, 156 is preferably arranged to respectively illuminate first, second and third areas 130, 132 and 134 from mutually different angles, thus providing three mutually different angular modalities of illumination to FOV 160. The mutually different angular modalities are preferably provided simultaneously by illuminator 124 in a direction along scan direction 150. As seen most clearly in
Each of light modules 152, 154, 156 preferably comprises an astigmatic concentrator 162, projecting a strip of light onto the corresponding area of FOV 160 illuminated thereby. Astigmatic concentrator 162 may be of a type described in U.S. Pat. No. 7,6413,65, entitled ‘Linear Light Concentrator’, assigned to the same assignee as the present invention and incorporated herein by reference.
It is appreciated that it is the illumination of strip-like or elongate illumination fields 130, 132, 134 by multiple illumination modules 152, 154, 156 that allows the use of highly efficient non-imaging focused astigmatic concentrators 162. Such astigmatic concentrators may provide substantially uniform, shift invariant and non-vignetting light fields over wide angles in a cross-scan direction, thereby obviating the need for wasteful light diffusers or other types of homogenizing optical elements known in the art. Combining several such concentrating elements at various mutually different angles further preferably enables extending the overall angular coverage along scan direction 150. Still further advantages arising from the spatial multiplexing of illumination modules 152, 154, 156 of the present invention, such that each illuminates a separate strip on substrate 106, are detailed henceforth.
It is a particular feature of a preferred embodiment of the present invention that the illumination projected by light modules 152, 154, 156 is thus preferably substantially shift invariant and vignetting-free within the boundaries of the light strip projected by each light module, thus providing near full or full angular coverage over the angular range of each light module.
It is understood that the shift invariance and vignetting-free properties of the light strips projected by light modules 152, 154, 156 hold throughout most of the light strip projected by each module, with the exception of within finite regions at the strip edges in both lateral and longitudinal strip directions, as detailed hereinabove. As a result, the angular distribution of illumination remains substantially invariant irrespective of position within the illuminated strip.
It is appreciated that should optical vignetting be present in the illumination projected by light modules 152, 154, 156, this would create gradually widening angular gaps within the illumination numerical aperture (NA) as the point of observation deviates from the center of each light strip, thus limiting the performance capabilities of illuminator 124 and hence the inspection capabilities of system 100.
The provision of uniform, multi-modal, shift invariant, efficient and at least nearly gap free illumination by preferred embodiments of the present invention is highly advantageous. In contrast to somewhat seemingly comparable narrow angular coverage illumination systems known in the art employing imaging type light concentrators, the present invention preferably provides multi-modal, uniform and shift invariant illumination having wide angular coverage in both scan and cross-scan directions.
The provision by illuminator 124 of substantially uniform, substantially gap-free wide NA illumination over the region sensed by camera 126 is highly advantageous in improving the efficacy of substrate inspection performed by system 100. This is because inspection of electronic substrates typically involves image segmentation, wherein a pattern of one material is distinguished from patterns of other materials or from the underlying substrate material. Such segmentation often requires wide illumination angle, substantially gap-free coverage of the inspected object. By way of example, efficient segmentation of copper traces against the dielectric substrate of a PCB typically requires illumination angular coverage extending over an NA of approximately 0.7, corresponding to a total illumination angle of approximately +45°. Such wide angle substantially gap-free illumination is advantageously provided by preferred embodiments of the present invention.
Furthermore, the ability of each light module 152, 154 and 156 to provide substantially uniform angular coverage is advantageous even in cases where deliberate gaps between the angles covered by each individual module may be desirable. This is because, in embodiments of the present invention, such deliberate gaps may be precisely designed and implemented rather than being the result of uncontrolled vignetting within the illumination field projected by each module, as would typically be the case in conventional illumination systems.
It is understood that illumination of FOV 160 by three light modules 152, 154, 156 and the corresponding effective division of FOV 160 into three illuminated areas 130, 132, 134 as illustrated herein is exemplary only. FOV 160 may be divided into two or more areas and illuminator 124 correspondingly designed, in accordance with the design specification of system 100.
The at least two areas illuminated by illuminator 124 are preferably although not necessarily non-contiguous, as here illustrated to be the case with respect to illuminated strips 130, 132, 134 mutually separated by a series of gaps 164. As seen most clearly in
The effective width, henceforth also simply termed the width, of each illuminated strip may be defined as that region over which the illuminated field is substantially uniform and shift invariant. The effective width is related to both the physical size of the light sources, such as LEDs, and the optical properties of the light concentrator 162 employed within each of light modules 152, 154, 156. As noted hereinabove, the effective width is typically somewhat smaller than the overall spread of the illuminating light energy defining each illuminated strip.
It is understood that the effective width of the strip illuminated by each module 152, 154, 156 is a highly significant parameter, determining the light strobe duty cycle of each imaging modality. This may be appreciated by considering an example in which each pixel row of area sensor 136 included in camera 126 images a 5 μm region in FOV 160. As noted hereinabove, during scanning, substrate 106 is preferably in continuous motion relative to optical head 102. To avoid loss of imaging quality, illuminator 124 is preferably strobed for a period corresponding to a scanning distance substantially similar to the size of the region imaged by a single row of pixels, namely 5 μm in this example. In practice the strobing duration may correspond to a scan distance in the range of 1 μm or even less if allowed by the system light budget, up to about 10 μm without undue loss of imaging quality, depending on the particular application. Should the widths of strips 130, 132, 134 be 1 mm, each illumination modality would be strobed at 1 mm scanning increments, resulting in about a 1:200 strobing duty cycle. It should be noted that this result is irrespective of the number of illumination modalities projected into each of illuminated strips 130, 132, 134, as is detailed hereinbelow with reference to
Gaps 164 may have a width approximately equal to the widths of strips 130, 132, 134. Further details concerning the preferable placement of beam splitter 170 so as to minimize illumination non-uniformity arising therefrom are provided hereinbelow with reference to
Light incident on beam splitter 170 is preferably deflected towards a mirror 172, at which mirror 172 the light is preferably reflected towards camera 126. Light is preferably focused on camera 126 by a lens 174, preferably interfacing mirror 172 and camera 126. Sensor 136 within camera 126 preferably detects the incident light reflected from substrate 106. It is appreciated that a single sensor, namely area sensor 136, is thus operative to acquire an image of all of the areas 130, 132, 134 within the FOV 160 of camera 126, which areas are preferably simultaneously illuminated with mutually different angular illumination modalities by illuminator 124. Exemplary suitable sensors useful in preferred embodiments of the present invention include the CMV12000 by AMS Sensors, Belgium and the IMX253LLR by Sony. Cameras equipped with these sensors are available from such suppliers as Basler of Germany, Flir and EVT of BC, Canada.
Lens 174 is preferably a telecentric imaging lens having a magnification in the range 0.3×-3×. Since the optical path between FOV 160 and lens 174 is preferably entirely in air, lens 174 may be embodied as a commercially available lens having the desired magnification, resolution and FOV. Alternatively, for specialized applications a suitable lens may be custom designed and produced to specifications by such manufacturers as Qioptiq Photonics GmbH & Co KG and Jos. Schneider Optische Werke GmbH of Germany.
It is a particular feature of preferred embodiments of the present invention that in addition to the plurality of angular modalities of illumination provided by illuminator 124 in scan direction 150, illuminator 124 is preferably additionally configured and operative to provide additional sub-angular illumination modalities in a cross-scan direction 180, generally orthogonal to scan direction 150. Additional sub-angular illumination modalities provided in cross-scan direction 180 may include one or more of different polarization encoded modalities, different wavelength encoded modalities, different time multiplexed modalities, or any other variable modality of illumination for encoding the different angular illumination modalities, as may be known to one skilled in the art.
The wide illumination angular coverage provided by illuminator 124 is thus preferably split into multiple, individually switchable and sensed illumination modalities, each illumination modality preferably illuminating a single discrete segment of substrate 106, such as areas 130, 132, 134 arrayed along scan direction 150. Each scan-direction angular segment is preferably further split into a number of angular sub-segments arrayed along cross-scan direction 180. Each angular segment and sub-segment preferably constitutes an independently switchable illumination modality, wherein crosstalk between the various modalities may be minimized by employing one or more of temporal, wavelength and polarization encoding schemes.
Simultaneous activation of all of the angular segments leads to restoration of the full substantially uniform substantially gap free wide NA illumination, as may be required for efficient pattern distinguishing. The totality of illumination modalities incident on each portion of substrate 106 is subsequently demultiplexed computationally by computer 142, to produce a multi-modal imagery of the inspected substrate 106.
It is appreciated that the present invention thereby provides substantially uniform, substantially gap free and substantially shift invariant multi-modality illumination over a wide angle, compatible with area type image sensors operated in a continuous scanning mode.
The illumination of substrate 106 with multi-modality light oriented at variable and well-defined angles in both scan direction 150 and cross-scan direction 180 may be useful for aiding accurate characterization of possible defects on substrate 106. Particularly, the use of an increased number of illumination modalities improves identification of actual defects and reduces false positive identifications of benign substrate features. Furthermore, separating the illumination segments along scan direction 150 also facilitates the construction of the illuminator by avoiding physical obstructions, as is further detailed henceforth with reference to
Methods by which different cross-scan illumination angles may be multiplexed using different wavelengths or polarizations are further described below in relation to
Reference is now made to
As seen in
In the exemplary illumination regime charted in
At each time step or frame, illuminator 124 is strobed and areas 130, 132, 134 are preferably simultaneously illuminated by respective ones of groups of illumination angular modalities 310, 320, 330, each encoded by three wavelengths of illumination. Illuminated areas 130, 132, 134 are depicted in
Preferably, each illumination modality illustrated in
Each frame is preferably captured by camera 126. In this case, camera 126 preferably includes multiple ones of sensor 136 for sensing light at each wavelength and beam splitter 170 is preferably configured to partially transmit and reflect at all three wavelength channels.
During and following the strobing of illuminator 124, optical head 102 preferably continuously moves in scan direction 150. Illuminator 124 is preferably strobed at time intervals corresponding to optical head 102 having travelled across a full or almost full width of each of areas 130, 132, 134 in scan direction 150. Each point on substrate 106 included in a demarked region 350 is thus preferably sequentially imaged by camera 126 in each one of three areas 130, 132, 134 and as illuminated by each one of three wavelengths of illumination included in groups 310, 320, 330. Each point on substrate 106 included in demarked region 350 is thus illuminated by a total of nine illumination angular modalities corresponding to three wavelength encoded modalities illuminating each of three spatial regions on substrate 106. It is appreciated that the use of three wavelength modalities as described herein is exemplary only and that two or more than three wavelength encoded modalities may alternatively be used.
It is appreciated that should all three scan-direction angular modalities be incident on the same illuminated strip, as is typically the case in conventional illumination approaches wherein physically separate illumination modules are not employed, illuminator 124 would have be strobed at intervals corresponding to only approximately a third of the width of the illuminated strip between consecutive strobes and only three different modalities be activated at each strobe, in order to avoid cross-talk. This is contrast to the method of the present invention, in which the scan-direction angular modalities are incident on respective, separate strips, allowing nine modalities to be activated at each strobe. Employing an image sensor operating at a fixed frame rate within such a conventional system would thus result in a threefold loss of scanning speed relative to the preferred arrangement of
Furthermore, scanning speed would further be reduced in such a conventional system due to the increased number of image overlaps required between small strobing increments. The physically separate illumination modules employed in the present invention thus advantageously facilitate increased scanning speed in contrast to conventional illumination systems wherein such physically separate illumination modules are not employed.
Following the scanning of an entire length of substrate 106, substrate 106 may then be incrementally shifted in cross-scan direction 180 preferably by way of motion of table 104, depending on the width of substrate 106 in cross-scan direction 180. The above-described process may then be repeated until the entirety of substrate 106 has been scanned. It is appreciated that should substrate 106 be sufficiently narrow and/or light modules 152, 154, 156 be sufficiently extensive in cross-scan direction 180, system 100 may carry out single-pass scanning of substrate 106, such that no cross-scan direction motion of substrate 106 is required.
Wavelength encoding of illumination angle modalities as described herein may be particularly useful in cases for which the substrate under inspection is substantially wavelength agnostic within the wavelength range employed. For example, in PCB inspection copper reflectance is substantially invariant at wavelengths longer than about 600 nm. Thus wavelength encoding using a number of separate channels included in the range from about 600 nm to about 950 nm may be employed without giving rise to undue reflectance variation artifacts. In such a case, care should be taken to equalize the various modality images with respect to the camera sensor relative response at the respective wavelength. Wavelength encoding of illumination angle modalities may also be useful for color or multi-spectral image acquisition in the case of substrates that are substantially angle agnostic over the wavelength range employed. This may be the case with highly diffuse, quasi Lambertian reflecting surfaces.
Further details concerning the structure and operation of illuminator 124 used to produce such wavelength encoded multi-angular illumination are provided henceforth with reference to
Reference is now made to
As seen in
In the exemplary illumination regime charted in
At each time step or frame, illuminator 124 is strobed and areas 130, 132, 134 are preferably simultaneously illuminated by respective ones of groups of illumination angular modalities 410, 420, 430, each including two polarizations of illumination. Illuminated areas 130, 132, 134 are depicted in
Each frame is preferably captured by camera 126. In this case, camera 126 preferably includes a pair of sensors 136 for sensing light at each polarization and beam splitter 170 is preferably configured to partially transmit and partially reflect both polarizations.
During and following the strobing of illuminator 124, optical head 102 preferably continuously moves in scan direction 150. Illuminator 124 is preferably strobed at time intervals corresponding to optical head 102 having travelled across a full or almost full width of each of areas 130, 132, 134 in scan direction 150. Each point on substrate 106 included in a demarked region 450 is thus preferably sequentially imaged by camera 126 in each one of three areas 130, 132, 134 and as illuminated by each one of two polarization encoded illumination angular modalities included in groups 410, 420, 430. Each point on substrate 106 included in demarked region 450 is thus preferably illuminated by a total of six illumination angular modalities corresponding to two polarization modalities illuminating three spatial regions on substrate 106.
It is appreciated that should all six polarization encoded angular modalities be incident on a single strip, as would typically be the case in conventional illumination systems, optical head 102 would have to be incremented by only about a third of the width of the illuminated strip between strobes and only two angular modalities be activated with each strobe to avoid crosstalk.
Following the scanning of an entire length of substrate 106, substrate 106 may then be incrementally shifted in cross-scan direction 180 preferably by way of motion of table 104, depending on the width of substrate 106 in cross-scan direction 180. The above-described process may then be repeated until the entirety of substrate 106 has been scanned. It is appreciated that should substrate 106 be sufficiently narrow and/or light modules 152, 152, 156 be sufficiently extensive in cross-scan direction 180, system 100 may carry out single-pass scanning of substrate 106, such that no cross-scan direction motion of substrate 106 is required.
Polarization encoding of illumination angle modalities as described herein may be particularly useful in cases where the substrate 106 is substantially polarization agnostic within the wavelength range employed. For example, in PCB inspection, copper reflectance varies by only a few percent between mutually perpendicular polarizations at all incidence angles of interest and over visible wavelengths. The typically translucent dielectric substrate tends to depolarize the incident light upon reflection and is largely agnostic to angle of incidence.
Furthermore, in angle agnostic applications, polarization encoded illumination may be useful in analyzing the type of material at each location on substrate 106. For example, polarization encoded illumination as described herein may be useful in the inspection of patterned substrates comprising relatively thin and flat diffusely reflecting metal or dielectric films, as are typically created by the deposition of thin metal or dielectric films on optically rough ceramic, solar wafers or flexible plastic substrates.
Further details concerning the structure and operation of illuminator 124 used to produce such multi-polarized illumination are provided henceforth with reference to
Reference is now made to
As seen in
In the exemplary illumination regime charted in
First, second and third spatial regions 130, 132, 134 are preferably simultaneously illuminated by respective ones of the individual modalities of one of the three groups of illumination modalities 510, 520, 530, when illuminator 124 is strobed, sequentially with respect to the three groups 510, 520, 530.
Illuminated areas 130, 132, 134 are depicted in
During and following the strobing of illuminator 124, optical head 102 preferably continuously moves in scan direction 150. Illuminator 124 is preferably strobed at time intervals corresponding to optical head 102 having travelled a distance of approximately a third of a way across of each of areas 130, 132, 134 along scan direction 150, but with different groups of illumination modalities being delivered at each strobe. As appreciated from consideration of
It is understood that as a result of the different groups of illumination modalities 510, 520, 530 being delivered at different points in time with respect to each other, coupled with the continuous motion of illuminator 124 with respect to substrate 106, each group of illumination modalities preferably illuminates a progressively shifted region of each of areas 130, 132, 134. Preferably, there is a small spatial overlap between those regions of each of areas 130, 132, 134 illuminated by groups of illumination modalities 510, 520, 530, in order to allow for accurate subsequent image reconstruction.
Each point on substrate 106 included in a demarked region 550 is thus preferably imaged by camera 126 in each one of three areas 130, 132, 134 and as illuminated at three points in time within each area. Each point on substrate 106 included in demarked region 550 is thus illuminated by a total of nine illumination modalities corresponding to three temporal modalities illuminating three spatial regions on substrate 106. It is appreciated that the use of three time steps as described herein is exemplary only and that two or more than two time steps may alternatively be used.
Following the scanning of an entire length of substrate 106, substrate 106 may then be incrementally shifted in cross-scan direction 180 preferably by way of motion of table 104, depending on the width of substrate 106 in cross-scan direction 180. The above-described process may then be repeated until the entirety of substrate 106 has been scanned. It is appreciated that should substrate 106 be sufficiently narrow and/or light modules 152, 154, 156 be sufficiently extensive in cross-scan direction 180, system 100 may carry out single-pass scanning of substrate 106, such that no cross-scan direction motion of substrate 106 is required.
It is understood that the system throughput in the embodiment charted in
Further details concerning the structure and operation of illuminator 124 used to produce such time stepped illumination are provided henceforth with reference to
It is appreciated that various ones of the different illumination modalities charted in
In the exemplary illumination regime charted in
At each time step or frame, illuminator 124 is strobed and areas 130, 132, 134 are preferably simultaneously illuminated by respective ones of groups of illumination angle modalities 610, 620, 630, each including three wavelengths of illumination having two polarizations. Illuminated areas 130, 132, 134 are depicted in
The two orthogonal polarizations by which the various angular modality groups are encoded are respectively indicated by reference numbers 640 and 642 in
Each frame is preferably captured by camera 126. During and following the strobing of illuminator 124, optical head 102 preferably continuously moves in scan direction 150. Illuminator 124 is preferably strobed at time intervals corresponding to optical head 102 having travelled across a full or almost full width of each of areas 130, 132, 134 in scan direction 150. Each point on substrate 106 included in a demarked region 650 is thus preferably imaged by camera 126 in each one of three areas 130, 132, 134 and as illuminated by each one of six wavelength and polarization encoded angle modalities of illumination included in groups 610, 620, 630. Each point on substrate 106 included in demarked region 650 is thus illuminated by a total of eighteen illumination modalities corresponding to six wavelength and polarization encoded modalities illuminating each of three spatial regions on substrate 106.
It is appreciated that alternative combinations of different illumination modalities in addition to those charted in
It is understood that the greater the number of illumination modalities used to illuminate substrate 106, the greater the accuracy and resolution of inspection thereof, although in certain cases the system throughput may be slower as the number of modalities is increased.
Reference is now made to
As seen in
It is noted that beam 700 is preferably divided in cross-scan direction 180 into three spatially overlapping but angularly substantially distinct sub-beams, omitted from
It is appreciated that similar sub-beams would preferably comprise each of beams 700, 702, 704. It is additionally appreciated that each of beams 700, 702, 704 may be sub-divided into two or more sub-beams in cross-scan direction 180 in accordance with the number of illumination modalities provided in cross-scan direction 180. The formation of cross-scan sub-beams is further detailed in relation to
Preferably, although not necessarily, beams 700, 702 and 704 subtend slightly overlapping angles of incidence in scan direction 150, as seen in
Reference is now made to
As seen in
Multimodality illuminator 824 preferably includes at least two light modules, here embodied, by way of example, as a first light module 852, a second light module 854 and a third light module 856. It is appreciated that light modules 852, 854, 856 are a particularly preferred embodiment of light modules 152, 154, 156 comprising illuminator 124.
First, second and third light modules 852, 854, 856 are preferably although not necessarily mutually identical and are mutually aligned along scan direction 150. Preferably, although not necessarily, first, second and third light modules 852, 854, 856 are physically spaced apart in scan direction 150, as described hereinabove. Each one of light modules 852, 854, 856 preferably extends longitudinally in cross-scan direction 180.
Each light module preferably comprises an array of light sources, here embodied by way of examples as an array of LEDs 860. It is appreciated that other light sources may alternatively be suitable for inclusion in light modules 852, 854, 856, such as super luminescent diodes (SLDs), diode lasers, vertical-cavity surface-emitting lasers (VCSELs) or laser pumped phosphor lamps. The physical light sources may alternatively be coupled to optical fibers or other light guiding or homogenizing elements, where the output ends of those light guides function as effective light sources.
LEDs 860 may emit light at a single common wavelength, in order to produce monochrome illumination in accordance with an illumination regime such as that charted in
Each LED 860 is preferably coupled to a light guide 870. Light guide 870 preferably receives light emitted by the corresponding LED 860 mounted thereabove and randomizes the light in order to provide a spatially uniform light distribution. A group of three light guides 870 belonging to unit 862 of LEDs is preferably aligned with respect to a light shaping element 880. Light shaping element 880 preferably receives the uniform light output by the light guides 870 associated therewith and provides a light output of a predetermined shape.
The light output from each light shaping element 880 preferably propagates towards an elongate light concentrator element 890, at which elongate light concentrator element 890, light output from all of light shaping elements 880 is preferably concentrated. As described hereinabove, light concentrator element 890 may be a transmissive light concentrator element, preferably of a type described in U.S. Pat. No. 7,641,365, the entirety of which is incorporated herein by reference. Light concentrator element 890 preferably transmits concentrated light illuminating a corresponding one of areas 130, 132, 134 on substrate 106.
Transmissive light concentrator element 890 may alternatively be embodied as a reflective light concentrator element, as illustrated in
Turning now to
First, second and third light modules 952, 954, 956 are preferably although not necessarily not mutually identical. Each one of light modules 952, 954, 956 preferably extends longitudinally in cross-scan direction 180. Each light module preferably comprises an array of light sources, here embodied by way of examples as array of LEDs 860. It is appreciated that other light sources may alternatively be suitable for inclusion in light modules 952, 954, 956, such as super luminescent diodes (SLDs), diode lasers, vertical-cavity surface-emitting lasers (VCSELs) or laser pumped phosphor lamps. The physical light sources may alternatively be coupled to optical fibers or other light guiding or homogenizing elements, where the output ends of those light guides function as effective light sources.
LEDs 860 may emit light at a single common wavelength, in order to produce monochrome illumination in accordance with an illumination regime such as that charted in
Each LED 860 preferably is coupled to a light guide, such as light guide 870. Light guide 870 preferably receives light emitted by the corresponding LED 860 mounted thereabove and randomizes the light in order to provide a spatially uniform light distribution. A group of three light guides 870 belonging to unit 862 of LEDs is preferably aligned with respect to a light shaping element, such as light shaping element 880. Light shaping element 880 preferably receives the uniform light output by the light guides 870 associated therewith and provides a light output of a predetermined shape.
The light output from each light shaping element 880 preferably propagates towards a generally cylindrical light concentrator element 990, at which generally cylindrical light concentrator element 990, light output from all of light shaping elements 880 is preferably concentrated. Light concentrator element 990 may be a reflective light concentrator element, preferably of a type described in U.S. Pat. No. 5,058,982, entitled ‘Illumination system and inspection apparatus including same’, the entirety of which is hereby incorporated by reference. Light concentrator element 990 preferably reflects concentrated light towards a corresponding one of areas 130, 132, 134 on substrate 106.
For the sake of clarity,
It is appreciated that the light output of multimodality illuminators 824 and 924 may be of a single polarization. Alternatively, multimodality illuminators 824, 924 may be configured to provide light output at more than one polarization. For example, multimodality illuminator 824 may be modified to provide light output at multiple wavelengths and two polarizations, as shown in the case of a multimodality polarization-multiplexed illuminator 1024 shown in
As seen in
It is appreciated that although polarization multiplexed illuminator 1024 is shown for a multimodality illuminator of a type resembling multimodality illuminator 824, including transmissive concentrating elements 890, a polarization multiplexed illuminator of a type generally resembling multimodality illuminator 924, including reflective concentrating elements 990, may alternatively be provided in accordance with another preferred embodiment of the present invention.
Multiplexed illuminator 1024 is preferably capable of projecting 18 different angular illumination modalities. However, it is noted that in the case of angle agnostic applications, illuminator 1024 may be useful for multi-spectral imaging of substrate 106. In an exemplary case, the three LED wavelengths of one light module 1030 may be different than the three LED wavelengths of the other light module 1030 belonging to the same pair 1032. An illuminator 1024 designed in this way but not including polarizers may be used for multi-spectral scanning and imaging over up to 18 different wavelengths.
Reference is now made to
As seen in
Light shaping element 880 is preferably a freeform cylindrical refractive optical element. Element 880 may be fabricated of glass but is preferably made of injection molded plastic. Groups of elements 880 coupled to adjacent light guides 870 may preferably be fabricated as monolithic arrays of injection molded plastic elements. Elements 880 preferably provide uniform light of predetermined shape distribution to light concentrators, such as transmissive light concentrators 890 (
Light module 1100 preferably extends longitudinally in cross-scan direction 180. As described hereinabove, light module 1100 is preferably operative to provide a plurality of cross-scan direction illumination modalities, which cross-scan direction illumination modalities complement the different angular modalities of illumination provided in scan direction 150 by different ones of plurality of illuminators included in multimodality illuminator 824 or 924.
In one illumination regime, described hereinabove with reference to
In another illumination regime, described hereinabove with reference to
As seen at a first pane 1102 in
The sequential activation of a single group of three LEDs 864, 866, 868 coupled to three corresponding light guides 870 and a single light shaping element 880 is further illustrated for additional clarity in
The time gap between the points in time corresponding to the illumination represented in first, second and third panes 1102, 1104, 1106 is preferably that time gap during which optical head 102 has moved a distance of approximately a third of the way across each of illuminated areas 130, 132, 134.
In another illumination regime, described hereinabove with reference to
Reference is now made to
Angular coverage provided by a multimodality illuminator such as illuminator 124, 824 or 924, including three light modules such as light module 1100, is represented in
For the sake of completeness, angular coverage of FOV 160 in the case that only one set of LEDs is activated, such as only either LEDs 864 or LEDs 866 or LEDs 868, is shown in a third plot 1304. In this case, only three modalities of illumination out of the nine are provided, with a single cross-scan modality activated for each of the scan direction modalities. This corresponds to the light output by the activation of LEDs 868 in all three light modules such as 852, 854, 856 of
It should be noted that the angular coverage represented by plots 1300, 1302 and 1304 does not physically exist at one instant of time within the FOV 160. Rather, it is the angular coverage effectively obtained after suitably demultiplexing, processing and merging of the partially overlapping images obtained according to the scanning charts of
Further for the sake of completeness, angular coverage of FOV 160 in the case of only one light module being activated, such as only light module 852 or 854 or 856, is shown in a fourth plot 1306. In this case, only three modalities of illumination are provided in cross-scan direction 180.
As opposed to the three cross-scan modalities shown in plot 1304, all three modalities shown in plot 1306 may physically be activated simultaneously over one sub region such as 134 of FOV 160 under a wavelength multiplexed scheme such as
It is appreciated that all or part of the individual preferably partially overlapping images captured by camera 126, may be compiled by image processing and control electronics 128 (
Other image processing functions performed by control electronics 128 may include calibrating and compensating the individual modality images for differences in light intensity and camera response for the different wavelengths employed in the wavelength multiplexing scheme, and the relative attenuation of the light incident on sub region 132 by beam splitter 170.
In certain embodiments, image processing and control electronics 128 may perform high accuracy sub-pixel image registration in order to produce full angle images. The full angle images may then be used to detect defects in substrate 106 at a high detection rate with few false positives, due to the employment of the plurality of different illumination modalities as described hereinabove.
In certain embodiments, full angular coverage images may be obtained by adding the gray values corresponding to each separate modality at each substrate pixel, after suitable calibration and compensation as noted above. In such embodiments, it should be noted that the slight angular overlap between the various modalities may give rise to brighter contours appearing in images of very shiny and uneven metallic traces. However, the effect of such brighter contours is much less detrimental than would be the occurrence of dark contours resulting from angular gaps in the illumination and may be readily corrected for, by example through the use of non-linear image processing methods such as simple thresholding to even out the effect of brighter contours.
Reference is now made to
Turning to
Turning to
Turning to
It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly claimed hereinbelow. Rather, the scope of the invention includes various combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof as would occur to persons skilled in the art upon reading the forgoing description with reference to the drawings and which are not in the prior art.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IL2019/050958 | 8/27/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62727561 | Sep 2018 | US |
