FOR DEFECTS AND LOCATING SUCH DEFECTS IN THREE DIMENSIONS

USING OPTICAL TECHNIQUES

CROSS-REFERENCE TO RELATED APPLICATIONS

[ 0001 ] This application claims the benefit of priority under 35 U.S .C. § 1 19 of U. S. Provisional Application Serial No. 62/181901 filed on June 19, 2015, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

[ 0002 ] The present disclosure relates to methods and apparatus for inspecting a substrate for defects and locating such defects in three dimensions using optical techniques.

[ 0003 ] In recent years the production of substrate materials, such as glass substrates, has evolved to include a requirement for highly refined surfaces, which are very smooth, lower in defects (e.g., fewer number of defects and/or smaller size of defects), etc. The higher quality surface of the substrate materials has resulted in many new products and applications and ever expanding commercial opportunities.

[ 0004 ] Although substrate manufacturing technologies, such as glass manufacturing technologies, have improved, the elimination of defects (e.g., surface defects) has not been achieved (at least at reasonable costs). Therefore, the detection of defects on or within substrates during manufacture is an important component of producing products that meet ever increasing requirements from customers. The ability to accurately detect the number and/or size of defects on or within a substrate (e.g. a glass substrate) at production rates provides the manufacturer with a valuable tool in ensuring that the customer obtains the required quality level without unnecessarily sacrificing production yields (and therefore profits).

[ 0005 ] A great advancement in the optical detection of defects during manufacture has been made using a non-imaging coherent line scanner system for performing optical inspection of transparent substrates. The details of such a system may be found in U. S. Patent Application No. 14/573,157, filed on December 17, 2014, entitled NON-IMAGING COHERENT LINE SCANNER SYSTEMS AND METHODS FOR OPTICAL INSPECTION (Attorney Docket SP13-396), the entire disclosure of which is hereby incorporated by reference. The aforementioned system provides the ability of rapidly determine the X-Y coordinates (and the size and shape) of a defect on or within a transparent substrate during production. The system is highly elegant in terms of providing a highly precise, low complexity, cost-effective detection solution, which exhibits a very large depth of field as compared with conventional detection systems having depths of field of only tens of microns. Therefore, the system permits use with substrates that are generally planar, but also somewhat domed or otherwise curved out of plane.

[ 0006 ] Some substrate applications, especially glass substrates, require that one side of the substrate (the so-called A-side) be much more pristine (fewer number and/or smaller size defects) than the opposite side (the so-called B side). For example, when a down-stream production process involves the use of a print head (or other object) to pass very close to the surface of the substrate (e.g., within 50 um), the existence of a protruding surface bump or foreign particle may cause a deflection of the print head from the intended position and a resultant flaw in production. In another example, a down stream process may require a further sheet of material to be laminated to the substrate, which may require that the surface of the substrate be free of defects and/or exhibit defects of only a certain number and/or size. Indeed, the existence of a protruding surface bump, a foreign particle, and/or a divot may cause voids during lamination and a resultant incomplete joining of the layers.

[ 0007 ] While the aforementioned optical system provides the ability of determining the X-Y coordinates of a defect, it does not permit the determination of a Z-dimension of the defect in a three-dimensional space. For example, that system does not permit the determination of which side of a substrate a surface defect may be located, and therefore does not provide a manner for determining whether a substrate having a surface defect would nevertheless exhibit one surface (i.e., an A-side surface) suitable for use in a downstream process.

[ 0008 ] Accordingly, there are needs in the art for new methods and apparatus for inspecting a substrate for defects and locating such defects in three dimensions using optical techniques. SUMMARY

[0009 ] For purposes of discussion, the disclosure herein may often refer to methodologies and apparatus involving substrates formed from glass; however, skilled artisans will realize that the methodologies and apparatus herein apply to substrates of numerous kinds, including glass substrates, crystalline substrates, single crystal substrates, glass ceramic substrates, polymer substrates, etc.

[0010 ] The methods and apparatus disclosed herein provide the ability to address three emerging requirements for defect detection during manufacturing: (i) highly precise measurement sensitivities enabling detection of smaller and smaller size foreign particles and/or defects; (ii) ability to scan very large areas and with high throughput; and (iii) ability to determine the location of a foreign particle and/or other defect in a Z-dimension at sufficient precision, for example, to ascertain on which side of the substrate a particle and/or other defect is located.

[0011 ] In accordance with one or more embodiments disclosed herein, methods and/or apparatus are provided for: supporting a substrate within a three-dimensional Cartesian coordinate system, such that: (i) the substrate has a width dimension in an X-axis, a height dimension in a Y-axis, and a thickness dimension in a Z-axis; (ii) the X-axis and Y- axis define an X-Y plane substantially parallel with respective first and second opposing major surfaces of the substrate; and (iii) the Z-axis is an axis of symmetry of the apparatus. The methods and/or apparatus further provide for orienting a first light source such that first light beam is directed from an angle of +A degrees from the axis of symmetry, and orienting a second light source such that second light beam is directed from an angle -A degrees from the axis of symmetry. The methods and/or apparatus further provide for at least one detector configured to detect the first and second light beams that have passed through, and have been affected by any defects of the substrate; and a processor configured to compute X, Y, and Z positions of the defects.

[0012 ] By way of example, the defects may include one or more surface defects on at least one of the first and second opposing major surfaces of the substrate. In such a case, the processor may be configured to compute X, Y, and Z positions of the surface defects with sufficient precision to ascertain on which of the first and second opposing major surfaces of the substrate each of the surface defects are disposed. [0013 ] Other aspects, features, and advantages will be apparent to one skilled in the art from the description herein taken in conjunction with the accompanying drawings. It is to be understood that various features disclosed in this specification and in the drawings can be used in any and all combinations. By way of non-limiting example the various features may be combined with one another as set forth in the following aspects:

[0014 ] According to a first aspect, there is provided an apparatus, comprising:

a transport mechanism configured to support a substrate within a three-dimensional Cartesian coordinate system, such that: (i) the substrate has a width dimension in an X-axis, a height dimension in a Y-axis, and a thickness dimension in a Z-axis, the thickness dimension being from 50 to 250 microns; (ii) the X-axis and Y-axis define an X-Y plane substantially parallel with respective first and second opposing major surfaces of the substrate; and (iii) the Z-axis is an axis of symmetry of the apparatus;

a first light source oriented such that a first light beam is directed from an angle of +A degrees from the axis of symmetry;

a second light source oriented such that a second light beam is directed from an angle of -A degrees from the axis of symmetry;

at least one detector configured to detect the first and second light beams that have passed through, and have been affected by any defects of the substrate, the defects having a dimension of from about 0.3 microns to about 50 microns; and

a processor configured to compute X, Y, and Z positions of the defects.

[0015 ] According to a second aspect, there is provided the apparatus of aspect 1, wherein:

the defects may include one or more surface defects on at least one of the first and second opposing major surfaces, of the substrate; and

the processor is configured to compute X, Y, and Z positions of the surface defects with sufficient precision to ascertain on which of the first and second opposing major surfaces of the substrate each of the surface defects are disposed.

[0016 ] According to a third aspect, there is provided the apparatus of aspect 1 or aspect 2, wherein:

the at least one detector includes an (N x n) array of light sensitive elements, with N substantially greater than n, oriented such that the N light sensitive elements extend substantially in the Y-axis; the transport mechanism is configured to cause relative movement between the substrate and the at least one detector along the X-axis at a speed of up to about 40 cm/s; and the at least one detector and the processor operate to detect and store a plurality of sets of (N x n) light measurements at successive relative positions of the substrate and the at least one detector along the X-axis, from which the X, Y, and Z positions of the defects are ascertained.

[0017 ] According to a fourth aspect, there is provided the apparatus of any one of aspects 1-3, wherein the first light beam and the second light beam are time-pulsed such that the at least one detector receives only one of the first and second light beams that has passed through the substrate at a time.

[0018 ] According to a fifth aspect, there is provided the apparatus of any one of aspects 1-3, wherein the first light beam and the second light beam are on at the same time such that the at least one detector receives both the first and second light beams that have passed through the substrate at the same time.

[0019 ] According to a sixth aspect, there is provided the apparatus of any one of aspects 1-5, wherein:

each of the defects causes a first interference of the first light beam passing through the substrate, and a second interference of the second light beam passing through the substrate;

the first light and the second light beams are of substantially different wavelengths; the at least one detector is separately sensitive to the substantially different wavelengths; and

the at least one detector and processor cooperate to measure a first fringe pattern resulting from the first interference and a second fringe pattern resulting from the second interference.

[0020 ] According to a seventh aspect, there is provided the apparatus of any one of aspects 1-6, further comprising:

a first polarizer disposed such that the first beam passes therethrough prior to passing through the substrate;

a second polarizer disposed such that the second light beam passes therethrough, and is polarized perpendicularly with respect to the first light beam, prior to passing through the substrate; and the at least one detector is separately sensitive to the substantially different polarizations.

[0021 ] According to an eighth aspect, there is provided the apparatus of any one of aspects 1-7, wherein:

each of the defects causes a first interference of the first light beam passing through the substrate, and a second interference of the second light beam passing through the substrate;

the at least one detector and processor cooperate to measure a first fringe pattern resulting from the first interference and a second fringe pattern resulting from the second interference; and

the processor is configured to: (i) compute at least X, Y, positions of the respective first and second fringe patterns of each defect, and (ii) compute a Z position of each defect based on the at least X, Y, positions of the respective first and second fringe patterns, where the Z position of each defect is a distance along the Z-axis between a reference position and the associated defect.

[0022 ] According to a ninth aspect, there is provided the apparatus of aspect 8, wherein:

the at least one detector is oriented in the X-Y plane; and

the Z position of each defect is computed using the following relationship: L = D/(2*tan(A)), where D is a distance between the at least X, Y, positions of the respective first and second fringe patterns.

[0023 ] According to a tenth aspect, there is provided the apparatus of aspect 8 or aspect 9, further comprising at least one collimating lens configured to direct the first and second light beams from the first and second sources, respectively, toward the substrate in collimated fashion.

[0024 ] According to an eleventh aspect, there is provided the apparatus of aspect 10, wherein:

the first and second light sources are configured to produce the first and second light beams, respectively, such that they exhibit fan characteristics in the Y-Z plane; and

the at least one collimating lens is a cylindrical lens, having an elongate dimension in the Y-axis as compared to the X-axis and shaped in the Y, Z axis to direct the first and second light beams, each having the fan characteristics, toward the substrate in collimated fashion. [0025 ] According to a twelfth aspect, there is provided the apparatus of aspect 11, wherein the first and second light sources are oriented such that the first and second light beams are directed from the +A and -A angles substantially in the Y-Z plane.

[0026 ] According to a thirteenth aspect, there is provided the apparatus of aspect 8, further comprising:

a first collimating lens having an input surface positioned in a substantially normal orientation with respect to the first light source, and being configured to direct the first light beam from the first light source toward the substrate in collimated fashion; and

a second collimating lens having an input surface positioned in a substantially normal orientation with respect to the second light source, and being configured to direct the second light beam from the second light source toward the substrate in collimated fashion.

[0027 ] According to a fourteenth aspect, there is provided the apparatus of aspect 13, wherein:

the first and second light sources are configured to produce the first and second light beams, respectively, such that they exhibit fan characteristics in the Y-Z plane; and

the first and second collimating lenses are respective cylindrical lens, each having an elongate dimension in the Y-axis as compared to the X-axis and being shaped in the Y, Z axis to direct the respective first and second light beam, each having the fan characteristics, toward the substrate in collimated fashion.

[0028 ] According to a fifteenth aspect, there is provided the apparatus of aspect 14, wherein:

the first light source and an input axis normal to the input surface of the first collimating lens lay in a first plane transverse to the axis of symmetry by an angle +a;

the second light source and an input axis normal to the input surface of the second collimating lens lay in a second plane transverse to the axis of symmetry by an angle -a; and each of the first light beam and the second light beam from the respective first and second collimating lenses is substantially co-planar with the respective first and second planes, and impinges substantially upon a single line parallel with the Y-axis on the at least one detector.

[0029 ] According to a sixteenth aspect, there is provided the apparatus of aspect 14, wherein the at least one detector includes: a first detector oriented such that an input surface thereof is directed normal to the collimated first light beam; and

a second detector oriented such that an input surface thereof is directed normal to the collimated second light beam.

[0030 ] According to a seventeenth aspect, there is provided the apparatus of aspect 16, wherein each of the first and second detectors includes an (N x n) array of light sensitive elements, with N substantially greater than n, oriented such that the N light sensitive elements extend substantially parallel with a respective one of the first and second collimating lenses.

[0031 ] According to an eighteenth aspect, there is provided the apparatus of aspect 16, wherein:

the Z position of each defect is computed using the following relationship: L = (S I - S2)/(2*cos (A)*tan(A));

51 is a representation of a distance, from a reference line and along the input surface of the first detector, to a position representing the first fringe pattern resulting from the first interference on the input surface of the first detector;

52 is a representation of a distance, from the reference line and along the input surface of the second detector, to a position representing the second fringe pattern resulting from the second interference on the input surface of the second detector;

the reference line is a representation of a line extending parallel to the X-axis at which respective input surfaces of the first and second detectors are co-planar;

and L is a perpendicular distance from a reference plane to each such defect, where the reference plane is parallel with the substrate.

[ 0032 ] According to a nineteenth aspect, there is provided a method, comprising: supporting a substrate within a three-dimensional Cartesian coordinate system, such that: (i) the substrate has a width dimension in an X-axis, a height dimension in a Y-axis, and a thickness dimension in a Z-axis, the thickness dimension being from 50 to 250 microns; (ii) the X-axis and Y-axis define an X-Y plane substantially parallel with respective first and second opposing major surfaces of the substrate; and (iii) the Z-axis is an axis of symmetry of the apparatus;

directing a first light beam from an angle of +A degrees from the axis of symmetry towards the substrate; directing a second light beam from an angle of -A degrees from the axis of symmetry towards the substrate;

detecting the first and second light beams that have passed through, and have been affected by any defects of the substrate, the defects having a dimension of from about 0.3 microns to about 50 microns; and

computing X, Y, and Z positions of the defects.

[ 0033 ] According to a twentieth aspect, there is provided the method of aspect 19, wherein:

the defects may include one or more surface defects on at least one of the first and second opposing major surfaces, of the substrate; and

the computation of the X, Y, and Z positions of the surface defects is with sufficient precision to ascertain on which of the first and second opposing major surfaces of the substrate each of the surface defects are disposed.

[ 0034 ] According to a twenty-first aspect, there is provided the method of aspect 19 or aspect 20, further comprising moving the substrate in the X direction at a speed of up to 40 cm/s.

DESCRIPTION OF THE DRAWINGS

[ 0035 ] For the purposes of illustration, there are forms shown in the drawings that are examples of embodiments of the claimed apparatus and methods, it being understood, however, that the embodiments disclosed and described herein are not limited to the precise arrangements and instrumentalities shown.

[ 0036 ] FIG. 1 provides two views of a generally planar substrate, the first view being of a visible major surface of the substrate (in an X-Y plane), and the second view being a side view, where the substrate exhibits a defect on one of the major surfaces thereof;

[ 0037 ] FIG. 2 is a side, schematic illustration of an embodiment of an optical system for inspecting the substrate for defects and locating such defects in three dimensions;

[ 0038 ] FIG. 3 is a visual image representing a detected optical interference pattern produced by the defect on the one major surface of the substrate;

[ 0039 ] FIG. 4 is a side, schematic illustration of a further embodiment of an optical system for inspecting the substrate for defects and locating such defects in three dimensions; [ 0040 ] FIG. 5 is a side, schematic illustration of a still further embodiment of an optical system for inspecting the substrate for defects and locating such defects in three dimensions;

[ 0041 ] FIG. 6 is a top view of the optical system of FIG. 5 ;

[ 0042 ] FIG. 7 is a side, schematic illustration of a still further embodiment of an optical system for inspecting the substrate for defects and locating such defects in three dimensions; and

[ 0043 ] FIG. 8 is a geometric representation of certain measured positions resulting from the defect on the one major surface of the substrate, and certain physical characteristics of the apparatus of the system of FIG. 7, which are used to determine the location of the defect in three dimensions.

DETAILED DESCRIPTION

[ 0044 ] For purposes of discussion, the embodiments discussed below refer to the testing of a substrate 10, such as a glass substrate. FIG. 1 provides two views of a generally planar substrate 10, the first view (at the left of the figure) is from a point of view perpendicular to a visible major surface 12 of the substrate, and the second view (at the right of the figure) is a side view of the substrate 10 showing first and second major surfaces 12, 14 thereof. The substrate 10 may be formed from a sheet of glass, having a width dimension in an X-axis, a height dimension in a Y-axis, and a thickness dimension in a Z-axis (within a Cartesian Coordinate System). Notably, the X-axis and Y-axis define an X-Y plane, which may be referred to herein as being in-plane and/or defining an in-plane reference for the substrate 10.

[ 0045 ] In general, the substrate 10 may be of any shape, such as rectangular, square, irregular, with straight and/or curved edges. Additionally, the substrate 10 may be substantially flat (i.e., planar as illustrated) or it may include some curvature and/or irregularities in its thickness. In one or more embodiments, the substrate 10 may be formed from any number of materials and have a thickness of from about 50 um (microns or micrometers) to about 250 um. In some embodiments, the substrate may have a thickness of from about 50 microns to about 150 microns. That is, the configuration of the system, is such that it can detect particles having a size of from about 0.3 microns to about 50 microns, and can discriminate on which side of the substrate they are located. In the past, for this thickness of substrate (50 to 250 microns), inspection equipment could not distinguish on which side of the substrate particles of this size (from about 0.3 microns to about 50 microns) were located. The substrate 10 may be formed from a material that is at least partially transparent to at least some wavelengths of light for measurement purposes (as will be discussed in greater detail later herein). In some embodiments, the substrate 10 is formed from a material that is substantially transparent to at least some wavelengths of light for measurement purposes. The disclosure herein may refer to methodologies and apparatus involving substrates 10 formed from glass (one example of a transparent material); however, skilled artisans will understand that the methodologies and apparatus herein apply to substrates of numerous materials, including glass substrates, crystalline substrates, single crystal substrates, glass ceramic substrates, polymer substrates, etc. Additionally, the methodologies and apparatus herein will apply to substrates formed from combinations of such materials, such as laminates of different glass substrates, laminates of glass and polymer substrates, and the like.

[0046 ] Notably, the substrate 10 may exhibit a defect 20, in this example a surface defect, on the first major surface 12 thereof. Although the surface defect 20 will be a focus of discussion herein, it is understood that any number and/or types of defects may be present, including other defects on or within the substrate 10. In general, defects may include bumps, depressions, indents, dimples, bubbles, inclusions, surface dirt, foreign particles on or in the substrate, etc.

[0047 ] FIG. 2 is a side, schematic illustration of an embodiment of an optical system 100-1 for inspecting the substrate 10 for defects and locating such defects in three dimensions. The system 100-1 includes a mechanism 102 for supporting the substrate 10 within the three-dimensional Cartesian coordinate system, such that the X-Y plane is substantially parallel with the respective first and second opposing major surfaces 12, 14 of the substrate 10. The Z-axis defines an axis of symmetry AS of the system 10 (shown in dotted line).

[0048 ] The system 100-1 also includes first and second light sources 104-1, 104-2, which are disposed in such a way as to direct respective first and second light beams 106-1 , 106-2 toward and through the substrate 10. In one or more embodiments, one or more of the first and second light sources 104-1, 104-2 may be implemented using a laser source (such as a diode laser) and one or more optical elements arranged downstream from the laser in such a way that the emitted first and second light beams 106-1 , 106-2 are each characterized by a narrow coherent laser-line beam that diverges from a central axis as the beam propagates away from the source. According to another example, each of the emitted first and second light beams 106- 1, 106-2 may be in the form of a fan-shaped beam substantially parallel to the Y-Z plane, and of a relatively narrow dimension in the X-axis. For example, each of the emitted first and second light beams 106-1 , 106-2 may have a beam width (in the X-axis) of about 0.25 inches (6.5 mm), about 0.5 inches ( 13 mm), or about 0.375 inches (9.5 mm). By way of example, the aforementioned first and second light beams 106- 1, 106-2 may be obtained by employing a point laser diode and a downstream optical fan generator.

[ 0049 ] The first and second light sources 104-1, 104-2 may be oriented in an advantageous way to improve the accuracy of detecting and measuring positions of any defects on or in the substrate 10. For example, the first light source 104- 1 may be oriented such that the first light beam 106-1 is directed from an angle of +A degrees from the axis of symmetry AS, while the second light source is oriented in a complimentary way; namely, such that the second light beam 106-2 is directed from an angle of -A degrees from the axis of symmetry AS. For purposes of illustration, the angles of +A, -A are shown as one arc, labeled 2A in FIG. 2. In this example, the first and second light sources 104-1, 104-2 are oriented in a substantially co -planar fashion in the Y-Z plane.

[ 0050 ] The system 100-1 may also include an optical element 110 to assist in modifying and/or directing the respective first and second light beams 106-1, 106-2 toward and through the substrate 10. For example, at least one collimating lens 1 10 may be employed to provide some collimation in the Y-Z plane, such that the first and second light beams 106- 1, 106-2 are substantially collimated when incident on the substrate 10. For example, the at least one collimating lens 1 10 may be implemented using a cylindrical lens, having an elongate dimension in the Y-axis (as compared to the X-axis) and being shaped in the Y-Z plane to produce collimated first and second light beams 108-1, 108-2 propagating toward the substrate 10. When only one collimating lens 1 10 is employed, which is aligned substantially parallel with the Y-axis as illustrated, the collimated first and second light beams 108- 1, 108-2 will be incident on the substrate 10 at respective angles, due to the first and second light sources 104-1 , 104-2 being oriented at angles of +A and -A, respectively. While such angles of incidence are not optimum, careful design may nevertheless result in acceptable precision in the measurements. [0051 ] The system 100-1 may also include at least one detector 1 12 configured to detect the first and second light beams 108-1, 108-2 that have passed through the substrate 10, and have been affected by any defects (such as defect 20). By way of example, the at least one detector 1 12 may include an array of light sensitive elements, which produce electrical signals having characteristics in proportion to the characteristics of incident light. In the illustrated embodiment, the at least one detector 112 may be implemented using an (N x n) array of light sensitive elements. In one or more embodiments, N and n may be of sufficient number to present an array large enough to respond to all the information carrying light from the substrate 10 at one time, such as yielding an array as large as, or larger than, the overall X-Y dimensions of the substrate 10. Under such an arrangement, a full measurement of the information carrying light incident on the detector 112 may be obtained in one data collecting scan. On the other hand, when N and/or n are not of sufficient number, producing an array too small to respond to all of the information carrying light from the substrate 10 in one scan, then multiple scans may be employed to collect all relevant information.

[0052 ] For example, in one or more embodiments, N may be substantially greater than n, such as n = 1 , yielding an N x 1 line array, oriented such that the N light sensitive elements extend in a line generally parallel to the Y-axis. By way of example, an N x 1 line array detector 112 may operate at a 90 kHz line rate and a one giga-pixel throughput (such as is available from Teledyne DALSA, Ontario, Canada). As noted above, a plurality of scans may be employed to respond to all of the information carrying light from the substrate 10 when the detector 112 is implemented as a line array. In this regard, the mechanism 102 may employ transport functionality, configured to cause relative movement between the substrate 10 and the detector 112 along the X-axis. For example, the mechanism 102 may operate to move the substrate 10 along the X-axis past the fixed, detector 112, such that at respective, sequential times (scans), the detector 1 12 may respond to respective N x 1 slices of information carrying light incident on the detector 112 that has passed through the substrate 10. For example, the mechanism 102 can move the substrate 10 along the X-axis at a speed of up to 40 cm/s; at this speed, the detector 1 12 can still operate to discriminate the position (in three dimensional space, particularly the Z direction, including whether the particle is on one side versus on the opposite side of the substrate) of particles having a size of from about 0.3 microns to about 50 microns on a substrate having a thickness of from about 50 to about 250 microns. [0053 ] The system 100-1 may also include a processor 114 configured to compute X, Y, and Z positions of the defects on and/or within the substrate 10 based on the information carrying light that has passed through the substrate 10 and has been received at the detector 112. In connection with the example discussed above, employing an N x 1 array of light sensitive elements, the processor 114, detector 112, mechanism 102, and light sources 104 may operate in synchronization to detect and store a plurality of sets (scans or frames) of (N x 1) measurements at successive relative X-axis positions of the substrate 10, from which the X, Y, and Z positions of any defects are ascertained. Further details as to the specific processes for ascertaining such X, Y, and Z positions of defects will be discussed later herein.

[0054 ] The processor 114 may be implemented using suitable hardware and/or software, such as using any of the known technologies available in the art. Such hardware may employ available digital circuitry, any of the known microprocessors that are operable to execute software and/or firmware programs, one or more programmable digital devices or systems, such as programmable read only memories (PROMs), programmable array logic devices (PALs), etc. Still further, the various functionality of the processor 114 may be implemented by way of software and/or firmware program(s) that may be stored on one or more suitable storage media, such as memory chips, etc.

[0055 ] In one or more embodiments, the processor 114 may include a frame grabber (such as the Xcelera-HS PX8 Teledyne frame grabber, also available from Teledyne DALSA) and a conventional desktop computer or a workstation, which executes a suitable software program. Such an arrangement causes the desktop computer to carry out the processing of a plurality of digital frames (sequential scans) from the frame grabber. As noted above, each such scan involves: (i) the mechanism 102 moving the substrate 10 to a specific position along the X-axis relative to the detector 112; (ii) obtaining a frame of information from the frame grabber (e.g., an N x 1 scan from the detector 1 12), which is a characterization of a slice of information carrying light that has passed through the substrate 10; (iii) storing the frame of information in the memory of the desktop computer; and (iv) repeating the above steps for successive incremental movements of the substrate 10 along the X-axis until the plurality of stored frames of information provide a complete set of the information carrying light characterizing the substrate 10. Thereafter, the desktop computer may be employed to execute a process for ascertaining the X, Y, and Z positions of any defects on and/or within the substrate 10. [0056 ] The procedure for ascertaining the X, Y, and Z positions of any defects on and/or within the substrate 10 may include producing a so-called interference image of the substrate 10. More specifically the processor 114 may be configured to assemble the interference image from the one or more frames (or scans) of information carrying light obtained by the detector 112 and collected by the processor 114. As explained below, the interference image is not a visual image of the substrate 10 in a conventional sense, but rather a representation of the substrate 10 as affected by any defects on and/or within the substrate 10.

[0057 ] The interference image of the substrate 10 results from the following characteristics and functionality of the system 100-1. The respective collimated first and second light beams 108-1, 108-2 approximately produce respective, substantially planar light wave fronts (approximate because of the respective angles of the respective incident first and second light beams 106-1, 106-2 and/or other influences). The respective, substantially planar light wave fronts then pass through, and are affected by the properties of the substrate 10, including any defects (such as the defect 20). Assuming a generally planar (or only modestly curved) substrate 10, without any defects, the light leaving the substrate 10 and impinging on the detector 10 will also be characterized by respective, substantially planar light wave fronts. Suitable data processing within the processor 114 may be calibrated to the characteristics of such substantially planar light wave fronts (without the influence of defects), yielding an interference image that is characterized by no information as to defects. The existence of the defect 20, however, produces respective interference wave fronts 109-1, 109-2 resulting from the planar light wave fronts passing through the substrate 10 and being redirected by the defect 20. The redirection of the planar light wave fronts (yielding the interference wave fronts 109-1, 109-2) is a function of the characteristics of the defect 20 and the angles +A, -A of the first and second light sources 104-1, 104-2.

[0058 ] FIG. 3 is a schematic representation of an interference image produced by the defect 20 on the first major surface 12 of the substrate 10. Notably, the single defect 20 produces a pair of interference wave fronts 109-1, 109-2, which in turn activate the light sensitive elements of the detector 112 in such a way as to produce respective first and second fringe patterns 116-1 , 116-2 (or signatures) shown in FIG. 3. The processor 114 may be configured to analyze the interference image in order to determine any number of characteristics of the defect 20, such as: (i) the size and/or shape of the defect 20; and/or (ii) the precise position of the defect 20 in three dimensional space (particularly the Z position).

[0059 ] As to the size and/or shape of a detected defect, the first and second fringe patterns 116-1, 116-2 may be characterized by a light center, and generally circular ripples diminishing in intensity with increasing radial distance from the center. Such a signature has been found to be indicative of a defect of a certain type, such as a bump, etc. Such a defect may act to concentrate light on the detector 112, thereby resulting in the light center. The generally circular center and ripples may indicate that the corresponding defect is of a generally circular shape and/or is so small that it produces a signature as if being an essentially point-like defect. Another example, not shown, may produce first and second fringe patterns that are characterized by a dark center, and generally circular ripples diminishing in intensity with increasing radial distance from the center. Such a signature has been found to be indicative of a depression, indentation, dimple, etc. Such a defect may act as a miniature negative lens that disperses light, thereby resulting in the dark center. The processor 1 14 may use a distance between the substrate 10 and the detector 112, and the wavelength(s) of the first and second light beams 106-1, 106-2, and/or other parameters to ascertain the size and shape of the measured defect to a reasonable degree of accuracy. For example, standard interference and diffraction methods known in the art of optics may be employed for such purposes.

[0060 ] As to the precise position of the defect 20 in three dimensions, the processor 114 may employ characteristics of the geometry of the system 100-1 and the substrate 10 (including the defect 20), as well as the X-Y positions of the first and second fringe patterns 116-1, 1 16-2 to compute the X, Y, Z positions of the defect 20 in three dimensional space. Since the signatures of the first and second fringe patterns 116-1, 116-2 may span respective areas of significant size, the processor 114 may utilize available mathematical algorithms to ascertain a center of each of the first and second fringe patterns 1 16-1, 116-2, and use the positions of such centers as the positions of the patterns 116 in later computations.

[0061 ] By way of example, the processor 114 may ascertain the X position of the defect 20 by determining the X position of the first and second fringe patterns 116-1, 116-2 in the interference image of FIG. 3. Indeed, in one or more embodiments, the first and second light sources 104-1 , 104-2 and detector 112 (implemented as a line array) may be generally co-planar in the Y-Z plane, yielding specific X positions of the first and second fringe patterns 116-1, 116-2 in the interference image of FIG. 3 that directly correspond to the X position of the defect 20 on the substrate 10.

[ 0062 ] By way of further example, the processor 114 may ascertain the Y position of the defect 20 by analyzing the respective Y positions of the first and second fringe patterns 116-1, 116-2 in the interference image of FIG. 3. Such analysis may employ certain geometric factors, such as the angles +A and -A, an offset in the Y direction of the defect 20 from the axis of symmetry AS of the system, etc.

[0063 ] By way of further example, the processor 114 may also ascertain the Z position of the defect 20 by further analysis of the respective X, Y positions of the first and second fringe patterns 1 16-1, 116-2. Employing principles of geometry to such analysis yields that the Z position the defect 20 is described by the following relationship: L = D/(2*tan(A)), where D is a distance between the respective first and second fringe patterns 116-1, 1 16-2 in FIG. 3. Notably, the techniques for ascertaining the X, Y, and Z positions of the defect 20 employed by the processor 114 may be of sufficient precision to ascertain on which of the first and second opposing major surfaces 12, 14 of the substrate 10 that the defect 20 is disposed. Indeed, the precision may also be sufficient to determine a specific depth within the substrate 10 at which a defect is located. Such information may be used to ascertain whether the substrate 10 exhibits sufficient quality as to establish an A-side and a B-side of the substrate 10 for downstream processes and/or applications.

[0064 ] It is noted that the processor 114 may be employed to reduce and/or eliminate undesirable artifacts in the interference image, such as artifacts resulting from bright/dark spots associated with implementations of the light sources 104-1, 104-2. For example, the processor 114 may be programmed to normalize the incoming data from a series of frames (or scans) of information carrying light obtained by the detector 112 and collected by the processor 114. One such normalizing algorithm involves averaging the incoming data (pixel by pixel) over a plurality of scans, for example 100 scans, and then multiplying the data of the incoming scans by the inverse of the average. Such a normalization algorithm will reduce and/or eliminate the effects of the aforementioned bright/dark spots and/or many other types of background noise in the interference image.

[0065 ] Among the alternative implementations of the system 100-1 (and indeed other embodiments disclosed herein and derived therefrom) are considerations of the interaction between the first and second light sources 104-1, 104-2 and the detector 112. For example, in one or more embodiments, the first and second light sources 104-1, 104-2 may be pulsed such that only one light source is ON at any one period of time, and therefore the detector 112 may only receive one of the first and second light beams 108-1, 108-2 that has passed through the substrate 10 at any one time. For example, the first and second light sources 104- 1, 104-2 may be pulsed ON and OFF in synchronization with odd and even scans, such as odd and even incremental X-position movements of the substrate 10 relative to the detector 112 (which may be the aforementioned line array). The resulting frames of data (scans) obtained from the detector 112 may be suitably stored and integrated by the processor 114 in order to compose the complete interference image of the substrate 10. Once the interference image of the substrate 10 is obtained, the aforementioned techniques may be employed to ascertain the Z position of any defects on and/or within the substrate 10.

[0066 ] Alternatively, in one or more embodiments, the first and second light sources 104-1, 104-2 may both be ON at the same time such that the detector 112 receives both the first and second light beams 108-1, 108-2 at the same time. In such an embodiment, the energy from each of the first and second light sources 104-1, 104-2 may be set to a half intensity and may be powered ON for every scan. The resultant scans may be stored and integrated by the processor 114 to produce one interference image containing both first and second fringe patterns 1 16-1, 116-2 and the software of the processor 114 may be employed to sort and find the fringe pattern pairs, calculate the centers of the first and second fringe patterns 116-1, 116-2, and then carry out the remaining analysis steps to determine the distance D and other quantities of interest.

[0067 ] In one or more alternative embodiments, a Time Delay Integration (TDI) camera may be employed in the detector 112 and the first and second light sources 104-1, 104-2 may again both be ON at the same time such that the TDI camera receives both the first and second light beams 108-1, 108-2 at the same time. In such an embodiment, the energy from each of the first and second light sources 104-1, 104-2 may be set to half intensity and may be powered ON for every scan. The resultant scans may be stored and integrated by the processor 114 to produce one interference image containing both first and second fringe patterns 116-1, 116-2 as discussed in previous embodiments.

[0068 ] Additionally and/or alternatively, in one or more embodiments, the first and second light sources 104-1, 104-2 may be implemented in such a way that the first light beam 106-1 and the second light beam 106-2 are of substantially different wavelengths. This may be accomplished using respective laser diodes of different spectral wavelengths. The detector 1 12 may be implemented in such a way as to be separately sensitive to the substantially different wavelengths, for example, by employing one or more color charge-coupled-device (CCD) sensors. Respective groups (such as respective lines) of CCD color sensitive elements may be employed to separate the respective first and second fringe patterns produced by the differing wavelengths of the first and second beams 106-1, 106-2. Each group (e.g., line) of the color sensitive elements of the detector 1 12 may be filtered by a suitable band-pass color filter (e.g., a first pass band for red light and a second pass band for blue light). Again, the resultant scans may be stored and integrated by the processor 1 14 to produce one interference image containing both first and second fringe patterns 1 16-1, 1 16-2 as discussed in previous embodiments.

[ 0069 ] Additionally and/or alternatively, in one or more embodiments, the first and second light sources 104-1 , 104-2 may include a respective first and second polarizers 1 18-1, 1 18-2 (see FIG. 2). The first polarizer 118-1 may be disposed such that a first light beam passes therethrough to produce a polarized first light beam 106-1. Similarly, the second polarizer 1 18-2 may be disposed such that a second light beam passes therethrough to produce a polarized second light beam 106-2. The first and second polarizers 118- 1, 1 18-2 may be designed such that the first light beam 106-1 is polarized at angle(s) perpendicularly with respect to the second light beam 106-2. The detector 1 12 may be designed to be separately sensitive to the substantially different polarizations. For example, the detector 1 12 may employ two separate line arrays, each with a respective polarizing filter 1 19-1, 1 19-2 that allows only the polarized light beam of corresponding polarization to pass. Again, the resultant scans may be stored and integrated by the processor 1 14 to produce one interference image containing both first and second fringe patterns 1 16-1, 1 16-2 as discussed in previous embodiments.

[ 0070 ] With reference to FIG. 4, a side, schematic illustration of a further embodiment of an optical system 100-2 for inspecting the substrate 10 for defects and locating such defects in three dimensions is shown. The system 100-2 is similar to the system 100-1 in many respects and therefore the details discussed above may be applied to the system of 100-2 with appropriate adjustments that will be apparent to the skilled artisan. The primary difference in the system 100-2 as compared with the system 100-1 is the fact that the optical element 1 10 is not employed. Thus, in the system 100-2, the respective first and second light beams 106-1, 106-2 are not collimated and propagate directly to, and through, the substrate 10. As in the system 100- 1, the resulting first and second fringe patterns 109-1 , 109-2 will again result; however, more complex algorithms will be required to find at least the Z position of any defects because the direction of the light wave front will vary with position across the detector 1 12. Skilled artisans, however, may readily adjust the disclosed algorithms to achieve suitable algorithms in the system 100-2 for ascertaining the Z position of any defects on and/or within the substrate 10.

[0071] With reference to FIG. 5, a side, schematic illustration of a still further embodiment of an optical system 100-3 for inspecting the substrate 10 for defects and locating such defects in three dimensions is shown. FIG. 6 is a top view of the optical system 100-3 of FIG. 5. The system 100-3 is similar to the system 100-1 in many respects and therefore the details discussed above may be applied to the system of 100-3 with appropriate adjustments that will be apparent to the skilled artisan. The primary difference in the system 100-3 as compared with the system 100-1 is the fact that the optics includes a first optical element 1 10- 1 and a second optical element 1 10-2. Each of the first and second optical elements 110-1 , 1 10-2 may be implemented using a respective collimating lens, which provides some collimation in the Y-Z plane, such that the first and second light beams 106-1 , 106-2 are substantially collimated when incident on the substrate 10. As in the system 100-1 , the respective collimating lenses may be implemented using a cylindrical lens, having an elongate dimension in the Y-axis (as compared to the X-axis) and being shaped in the Y-Z plane to produce collimated first and second light beams 108-1, 108-2 propagating toward the substrate 10. Each of the first and second collimating lenses 110-1, 1 10-2 may be oriented (at respective angles +/- A with respect to the axis of symmetry) such that the respective first and second light beams 106- 1, 106-2 are incident perpendicularly (normal) to the respective input surfaces thereof. It has been found that this implementation is more suitable for angles A of 20 degrees or more. Equation 1 (the relationship for L) above still applies to the Figure 5 concept. The aforementioned methodologies and variations as to ascertaining the size and/or shape of the defect 20, and/or the precise position of the defect 20 in three dimensional space may be applied by the skilled artisan to the system 100-3.

[0072] With reference to FIG. 6, when the detector 112 is implemented as a line array (and/or where multiple lines in the array are very close together in the X dimension), then some adjustments in the alignments of the first and second light sources 104-1 , 104-2 with the respective first and second collimating lenses 1 10-1 , 1 10-2 may be warranted. For example, the first light source 104-1 and an input axis normal to the input surface of the first collimating lens 1 10- 1 may be oriented such that they lay in a first plane transverse to the axis of symmetry by an angle +a. Similarly the second light source 104-2 and an input axis normal to the input surface of the second collimating lens 1 10-2 may be oriented in such a way that they lay in a second plane transverse to the axis of symmetry by an angle -a. By way of example, an angle +/- a of about 2 degrees may work quite well. When done properly, the first light beam 108-1 and the second light beam 108-2 from the respective first and second collimating lenses 1 10-1, 1 10-2 is substantially co-planar with the respective first and second planes, and impinge substantially upon a single line on the detector 1 12, parallel with the Y-axis.

[ 0073 ] With reference to FIG. 7, a side, schematic illustration of a still further embodiment of an optical system 100-4 for inspecting the substrate 10 for defects and locating such defects in three dimensions is shown. The system 100-4 is similar to the system 100-3 in many respects and therefore the details discussed above may be applied to the system of 100-4 with appropriate adjustments that will be apparent to the skilled artisan. The primary difference in the system 100-4 as compared with the system 100-3 is the fact that the detector 1 12 is implemented with two separate detectors 1 12-1, 1 12-2, each for detecting the respective first and second light beams 108- 1, 108-2. For example, the first detector 1 12-1 may be oriented such that an input surface thereof is directed normal to the collimated first light beam 108-1 ; and the second detector 112-1 may be oriented such that an input surface thereof is directed normal to the collimated second light beam 108-2. For example, in one or more embodiments, each of the first and second detectors 1 12-1, 1 12-2 may include an (N x n) array of light sensitive elements, with N substantially greater than n, oriented such that the N light sensitive elements extend substantially parallel with a respective one of the first and second collimating lenses 1 10-1 , 110-2.

[ 0074 ] With the arrangement of the system 100-4, the X, Y, and Z positions of each defect may be computed by the processor 114 using geometric computations as will be apparent to the skilled artisan. For example, FIG. 8 is a geometric representation of certain measured positions resulting from the defect 20 on the first major surface 12 of the substrate 10. It will be understood to the skilled artisan that the Z position of the defect 20 may be computed by the processor 1 14 using the following relationship: L = (SI - S2)/(2*cos (A)*tan(A)). S I is a representation of a distance, from a reference line PO and along the input surface of the first detector 1 12-1, to a position PI representing the first fringe pattern 1 16-1 (e.g., the center thereof). S2 is a representation of a distance, from the reference line PO and along the input surface of the second detector 1 12-2, to a position P2 representing the second fringe pattern 1 16-2 (e.g., the center thereof). The reference line PO is a representation of a line extending parallel to the X-axis at which respective input surfaces of the first and second detectors 1 12-1, 1 12-2 are co-planar. L is a perpendicular distance from a reference plane to the defect 20, where the reference plane is parallel with the substrate 10.

[ 0075 ] Although the disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the embodiments herein. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present application.