System and method for die inspections

Abstract

There is a system for die inspections comprising an integrated optical arrangement having a first optical arrangement comprising a first brightfield illuminator, and a high and low angle darkfield illuminators for operating under a first operating mode. There is a second optical arrangement comprising a second brightfield illuminator and a collimator for operating under a second operating mode. The third optical arrangement comprises an infrared illuminator and an interferometry mechanism for operating under a third operating mode. An image capture device is configured to receive reflected illuminations from the first, second and third optical arrangements. A focusing mechanism is configured to direct the illuminations from the first, second and third optical arrangements to a die surface and their reflected illuminations to the image capture device. A processing unit is configured to analyze the captured images of the first, second and third operating modes to determine a visible and a non-visible defect, wherein the non-visible defect is determined by a combination of (i) analyzing color variations of the captured images under the first and second operating modes and (ii) confirmation of the non- visible defect by the third operating mode.

Description

[0001] SYSTEM AND METHOD FOR DIE INSPECTIONS

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a system and a method of die inspections to detect visible and non- visible defects on the surface of a package die. In particular, the system and method will enable detection of a full range of micro and macro sized surface defects down to sub-micron cracks with minimal false alarms in a single pass and at high production speeds.

[0004] BACKGROUND

[0005] Integrated Circuit (IC) packages such Integrated passive devices (IPDs) or passive components typically utilize a metallic lead frame. The die is electrically connected to the lead frame by means of bonding wires that have been pre-formed on the active surface of the package. The package and portions of the lead frame are encapsulated with a molding compound to protect the delicate electrical components on the active side of the package. In some applications, it is desirable to leave the back surface (opposite the active surface) of the package exposed; i.e., not to encapsulate the back surface of the package with molding compound and leaving the back surface of the die exposed to increase heat transfer out of the package.

[0006] In such exposed die packages, the back surface of the die may be pre-coated with a thin silver metallic layer to prevent electromagnetic interference (EMI) noises and at the same time to improve heat dissipation. During the manufacturing process, low profile grinding blades are also used to reduce the thickness of the over molded packages to expose the silicon die embedded inside. Package warpage can also cause grinding lines on the exposed die surface to crack. Cracks may also be due to distortions on the die surface caused by warpage of the assembled chip where the die is attached. Sometimes these cracks are very thin (<0.25pm width) with internal damage which cannot be easily seen externally.

[0007] A representative illustration of a package die surface under inspection is shown in FIG. 1. While existing Package Visual Inspection (PVI) solutions are able to effectively detect common defects, grinding lines and cracks of more than 0.5pm, cracks of less than 0.5pm are however difficult to address without overkilling due to confusion with the grinding lines. This is because existing systems are unable to differentiate between the grinding lines and submicron cracks smaller than 0.5pm. While microscope optics solutions can detect crack widths down to 0.3pm, these solutions produce defect contrasts which are not high enough. In addition, due to the shallow depth of focus of their lens objective, some cracks may not be visible. Grinding lines and sub-micron crack lines are also hard to distinguish resulting in an overkill of the rejection rate. Individual inspection of sub-micron cracks would be time consuming and reduce throughput of the package die inspection process.

[0008] There is therefore a need for a solution to enable detection of these sub-micron cracks of less than 0.5pm with minimum false alarms along with the other visible surface defects such as voids, balls, bumps, and pads at high production speeds during on-the-fly inspection of package dies.

[0009] SUMMARY

[0010] In an aspect, there is a system for die inspections comprising an integrated optical arrangement. The integrated optical arrangement comprises a first optical arrangement comprising a first brightfield illuminator, a high angle darkfield illuminator and a low angle darkfield illuminator for capturing images of a die surface under a first operating mode. The integrated optical arrangement further comprises a second optical arrangement comprising a second brightfield illuminator and a collimator for capturing images of a die surface under a second operating mode. The integrated optical arrangement comprises a third optical arrangement comprising an infrared illuminator and an interferometry mechanism for capturing images of a die surface under a third operating mode. The system comprises an image capture device configured to receive reflected illuminations from the first, second and third optical arrangements. The system further comprises a focusing mechanism for directing the illuminations from the first, second and third optical arrangements to a die surface and their reflected illuminations to the image capture device, and a processing unit configured to analyze the captured images of the first, second and third operating modes to determine a visible and a non- visible defect, wherein the non-visible defect is determined by a combination of (i) analyzing color variations and differentiation of the captured images under the first and second operating modes and (ii) further confirmation of the non-visible defect under the third operating mode.

[0011] In some embodiments, the focusing mechanism comprises one or more beam splitters, one or more reflective surfaces and a plurality of lenses.

[0012] In some embodiments, the focusing mechanism is configured to be activated individually or cooperatively during operation of each of the first, second and third optical arrangements. In some embodiments, the first optical arrangement comprises a first beam splitter arranged between the image capture device and the die, the first beam splitter being configured to direct illumination from the first brightfield illuminator and darkfield illuminators to a surface of the die under inspection and redirect reflected brightfield and darkfield illuminations from the die surface to the image capture device.

[0013] In some embodiments, the system comprises a telecentric lens positioned between the first beam splitter and the image capture device such that the reflected brightfield and the high angle and low angle darkfield illuminations are directed to the image capture device through the telecentric lens.

[0014] In some embodiments, illumination from each of the first brightfield illuminator and the high angle and low angle darkfield illuminators are configured to be emitted continuously or intermittently.

[0015] In some embodiments, each of the first brightfield illuminator and high angle and low angle darkfield illuminators is configured to supply illumination of varying intensities.

[0016] In some embodiments, the first brightfield illuminator is configured to emit co-axial illumination.

[0017] In some embodiments, the first brightfield illuminator is configured to emit broadband illumination with a wavelength between 380 to 700nm.

[0018] In some embodiments, each of the high angle and low angle darkfield illuminators is configured to emit broadband darkfield illumination with a wavelength between 380 to 700nm.

[0019] In some embodiments, the low angle darkfield illuminator is arranged at an angle of 3-30° with respect to a horizontal plane of the die in an inspection position.

[0020] In some embodiments, the high angle darkfield illuminator is arranged at an angle of 30-85° to the horizontal plane of the die in the inspection position. In some embodiments, the second optical arrangement comprises a second beam splitter arranged between the first beam splitter and the second brightfield illuminator, the second beam splitter being configured to direct illumination from the second brightfield illuminator through the first beam splitter to the surface of the die under inspection, wherein the first beam splitter is configured to redirect the reflected brightfield illumination from the die surface to the image capture device.

[0021] In some embodiments, illumination from the second brightfield illuminator is arranged to be supplied continuously or intermittently.

[0022] In some embodiments, the second brightfield illuminator is configured to emit broadband illumination with a wavelength between 380 to 700nm.

[0023] In some embodiments, the infrared illuminator has a wavelength of 780nm.

[0024] In some embodiments, the interferometry mechanism comprises a mirror positioned adjacent the first beam splitter such that illumination from the infrared illuminator is configured to pass through the second beam splitter and directed to the first beam splitter where the illumination is split into a reference beam which is directed to the mirror and reflected therefrom, and an object beam which is directed to the die surface and reflected therefrom. The reflected illumination from the die surface and mirror are directed to the image capture device through the telecentric lens.

[0025] In some embodiments, the system comprises a filter positioned between the mirror and the first beam splitter.

[0026] According to another aspect of the disclosure, there is a method for die inspections comprising providing an integrated optical arrangement comprising a first optical arrangement, a second optical arrangement and a third optical arrangement; capturing an image of a die surface under a first operating mode by the first optical arrangement comprising a first brightfield illuminator, a high angle darkfield illuminator and a low angle darkfield illuminator; capturing an image of a die surface under a second operating mode by the second optical arrangement comprising a second brightfield illuminator and a collimator; capturing an image of a die surface under a third operating mode by the third optical arrangement comprising an infrared illuminator and an interferometry mechanism; directing the illuminations from the first, second and third optical arrangements to the die surface and redirecting their reflected illuminations to an image capture device; and analyzing with a processing unit, the captured images of the first, second and third operating modes to determine a visible and a non-visible defect, wherein the non- visible defect is determined by a combination of (i) analyzing color variations and differentiation of the captured images under the first and second operating modes and (ii) confirmation of the non-visible defect by the third operating mode

[0027] In some embodiments, the first, second and third operating modes are configured to operate independently of one another or simultaneously.

[0028] In some embodiments, each of the first, second and third operating modes is configured to be performed individually or in any combination of two or three modes.

[0029] In some embodiments, the processing unit comprises an Al analyzer for identifying one or more defects.

[0030] In some embodiments, the Al analyzer comprises an inspection algorithm configured to manage the captured images and classify the defects.

[0031] In some embodiments, the processing unit further comprises an Al defect detection tool configured to recognise and differentiate the defects.

[0032] According to another aspect of the disclosure, there is a method for die inspections comprising the steps of capturing an image of the surface of a die under a first operating mode and performing image processing and measurements of the captured image for presence of visible surface defects and contaminants; capturing an image of the surface of a die under a second operating mode and performing image processing and measurements of the captured image for presence of grinding lines and crack lines; capturing an image of the surface of a die under a third operating mode and performing image processing and measurements of captured images for presence of sub-micron cracks; determining the types of defects by utilizing a combination of (i) color variations and differentiation of images under the first and second operating modes and (ii) images of non-visible defects under the third operating mode toidentify the non-visible defects; and classifying defects as visible defects or non-visible defects.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows top and section views illustrating the various defects and non-defects on a package die;

[0035] FIG. 2 is a schematic diagram illustrating the features of a system for inspecting defects in accordance with embodiments of the disclosure;

[0036] FIG. 3 is a schematic block diagram showing the features of the system for brightfield and darkfield inspection of surface defects in accordance with embodiments of the disclosure;

[0037] FIG. 4 is a schematic block diagram showing the features of the system for inspecting die cracks in accordance with an embodiment of the disclosure;

[0038] FIG. 5 is a schematic block diagram showing the features of the system for inspecting submicron die cracks in accordance with embodiments of the disclosure;

[0039] FIG. 6 is a flow diagram showing the different modes of the die defect inspection process in accordance with embodiments of the disclosure;

[0040] FIG. 7 is a flow diagram showing analysis of the defects to determine the presence of submicron cracks in accordance with embodiments of the disclosure.

[0041] DESCRIPTION

[0042] The disclosure was conceptualized to provide a system and a method of die inspections to detect visible and non-visible defects such as sub-micron cracks on the surface of a package die. In particular, the system and method will enable detection of a full range of micro and macro sized surface defects down to sub-micron cracks with minimal false alarms in a single pass and at high production speeds.

[0043] For purposes of brevity and clarity, the disclosure of the embodiments of the present invention is directed to a system and a method for detecting a range of defects such as surface defects to sub-micron cracks present on the surface of a package die. It will however be apparent by a person skilled in the art that this disclosure does not preclude the present invention from other inspection applications where fundamental principles prevalent among the various embodiments of the present invention such as operational, functional or performance characteristics are required. As used herein, the terms, “Cracks” or “crack lines” may be used interchangeably to describe the micro-cracks under different scenarios, as will be understood by one skilled in the art.

[0044] FIG. 1(a) is a representative illustration of the top view of a package die 20 under inspection with surface defects and contaminants. FIG.1(b) is a sectional view along a X-Y line showing typical profiles of the defects and contaminants including chips, fibres, grinding lines, and crack lines on the die surface 21. The dark colour formed in the crack lines are meant to indicate cavities as will be understood by one skilled in the art. FIG.1(c) is another sectional view showing a crack caused by a curvature of the mold resulting in a stress crack in the die surface 21. The crack may result in a ridge or fringe line formed separating the two sides of the crack line on the die surface. The two sides of the ridge or crack line may present a height difference of 0.2pm between them. Note that the grinding lines are shallow and do not create a height difference on both sides of the lines while the cracks are deep and may penetrate almost the entire thickness and width of the die and result in a height difference on either side of the crack lines.

[0045] FIG. 2 illustrates the features of a system 10 for inspecting semiconductor package dies 20. The system 10 may include a first set of brightfield illuminator 30 and darkfield illuminators 31; a second set of brightfield illuminator 32 provided with a collimator 33; and a third set of infrared (IR) laser illuminator 34 provided with a reference mirror 35 set-up. A plurality of beam splitters 43 and appropriate lenses 41 may be suitably arranged and used to direct the illuminations from the three sets of illuminators to the package die 20 and thereafter redirect the reflections from the package die 20 to an image capture device 40 via a pair of telecentric lens 41 to avoid distortions to the captured image. It will be well understood by a person skilled in the art that the set of darkfield illuminators 31 may include a low angle darkfield illuminator and a high angle darkfield illuminator. It should further be understood by a person skilled in the art that the first set of brightfield illuminator 30 and darkfield illuminators 31, the second set of brightfield illuminator 32, and the third set of IR laser illuminator 34 and the image capture device 40 may be flexibly positioned and configured as required to capture 2D (two- dimensional) images of the die surface 21. The beam splitters 43 and reference mirror 35, lenses 41 or other reflective surfaces can be positioned for directing the various illuminations to the package die surface 21 under inspection and further reflecting illuminations to the image capture device 40.

[0046] Each of the first set of brightfield illuminator 30 and darkfield illuminators 31; second set of brightfield illuminator 32 provided with collimator 33; and third set of IR laser illuminator 34 and reference mirror 35 may include focusing mechanisms for directing or focusing their illuminations onto the package die surface 21 positioned at the inspection position. Such focusing mechanisms may include a combination or arrangement of beam splitters, lens and reflective surfaces as will be well understood by those skilled in the art. The focusing mechanisms may be activated individually during operation of each of the sets of illuminators 30,32, 34 such that each set of illuminators may be configured and operated as a modular unit or operated cooperatively between them. In this way, the system 10 may be configured to operate under at least three different levels or modes of inspection or a combination of one, two or three different modes. Such an arrangement allows flexibility of machine modularity, utilisation and costs to meet package die types and sizes, budgets, and defect trends. Preferably, the inspection is performed while the package dies 20 are in motion. This means that the capture of images of the package dies 20 occurs as they are being displaced across the inspection position along a scan motion path. Alternatively, the package dies 20 may be momentarily stopped for capturing of the high-resolution images under an operating mode or a combination of operating modes as will be further explained. Operating Mode-1 Surface Defect inspection

[0047] FIG. 3 illustrates a first mode configuration for surface defect inspection of a package die surface 21. As shown in FIG. 3, the Mode-1 configuration includes a first set of brightfield illuminator 30 and darkfield illuminators 31. The Mode- 1 configuration may preferably include a plurality of shared and / or individually utilized focusing lens 41, beam splitters 43 and mirrors (not shown) or other reflective surfaces that are positioned and arranged for directing the brightfield and darkfield illuminations from their respective illuminators to the package die surface 21 under inspection and reflecting brightfield and darkfield illuminations from the die surface 21 to an image capture device 40. In the illustration shown in FIG. 3, beam splitter 43a is positioned between the image capture device 40 and the package die 20. A lens 41 is positioned between the brightfield illuminator 30 and the beam splitter 43a. Another lens 41 is positioned between the beam splitter 43a and the package die 20. A skilled person will understand that mirrors or other reflective surfaces may also be used in this configuration and are not limited to this illustration.

[0048] In operation, the first set of brightfield illuminator 30 and the low angle and high angle darkfield illuminators 31 may be controlled to emit illumination. The incident illumination from the brightfield illuminator 30 may be focused by lens 41 onto beam splitter 43a and then redirected by the beam splitter 43 a onto the package die surface 21, via another lens 41 as shown in FIG. 3. The incident illumination from the darkfield illuminators 31 may be directed to the package die surface 21. The illuminations from both the brightfield illuminator and darkfield illuminators are then reflected off the package die surface 21, focused onto the beam splitter 43a via lens 41 and received by the image capture device 40. The telecentric lens 42 may be positioned between the beam splitter 43a and the image capture device 40.

[0049] Illumination supplied by each of the brightfield illuminator 30, the low angle and high angle darkfield illuminators 31 can be controlled and can be either continuously supplied or intermittently supplied (pulsed). Such broadband illuminations enable identification of a wide range of micro and macro sized die surface defect types with varying surface reflectivity. In addition, the broadband wavelengths of both the brightfield illumination and the darkfield illuminations enable the inspection to be performed independently of the reflective characteristics of the die surface 21 under inspection. This means that the detection of defects on the package die surface 21 will not be undesirably influenced by different sensitivities or reflectiveness or polarization of the die surface 21 to different illumination wavelengths. Preferably, intensities of the brightfield and darkfield illuminations can be selected and varied as required based on the package die surface characteristics and for enhancing the quality of images captured. Such inspections can employ brightfield illumination, darkfield illumination, or a combination of both brightfield i llumination and darkfiekl illumination to detect the die surface defects.

[0050] Light reflectivity of a semiconductor wafer or package die typically has a significant effect on the quality of images obtained with brightfield and darkfield imaging. Both micro and macro structures present on the package die affect the light reflectivity of the package die. The amount of light reflected by the die surface 21 is a function of the direction or angle of incident light, the viewing direction, and the light reflectivity of the surface of the package die 20. The light reflectivity is in turn dependent on the wavelength of the incident light and material composition of the wafer or package die. Therefore, while the 380-700nm wavelengths of the brightfield and darkfield illuminations can detect a majority of micron sized defects on the surface of the dies, such as presence of surface particulates, imperfections, undulations and other irregularities, sub -micron cracks could not be readily detected without a lot of tedious analyses.

[0051] The first set of brightfield illuminator 30 may include an array of flash lamps or white light emitting diodes. Such an illuminator 30 supplies or emits co-axial brightfield illumination i.e., visible, or white light. Preferably, the illuminator 30 supplies broadband brightfield illumination with wavelengths of between 380-700nm. The low angle darkfield illuminator (not shown) and the high angle darkfield illuminator (not shown) may be flash lamps or white light emitting diodes in a ring light arrangement and emit or supply darkfield illuminations. Preferably, the darkfield illumination supplied by each of the darkfield illuminators 31 is a broadband darkfield illumination comprising wavelengths of between 380-700nm. The low angle darkfield illuminator is preferably positioned at an angle of 3-30° to the horizontal plane of the package die placed at the inspection position. The high angle darkfield illuminator is preferably positioned at an angle of 30-85° to the horizontal plane of the package die 20 placed at the inspection position. The image capture device 40 in this configuration receives brightfield and darkfield illumination or light from the package die 20 under inspection via a pair of telecentric lens 42. While the incident illuminations are preferably directed at a horizontal and planar die surface, it should be noted that in the event of a tilted die, the behavior of the brightfield and darkfield illuminators 30,31 can be variably interchanged such that the brightfield illuminator 30 can exhibit behavior from a brightfield illuminator to a darkfield illuminator depending on the tilt angle and vice versa for the darkfield illuminators 31. This reversal of roles relative to die tilt results in, for example, defects appearing in a dark coloration to a white coloration as the tilt angle is increased. This phenomenon is also useful to determine the presence of sub-micron cracks using machine learning or deep learning techniques by making use of color variations present on either side of a sub-micron crack line.

[0052] Operating Mode-2 Defect inspection (cracks)

[0053] FIG. 4 illustrates the second operating mode for detecting sub-micron cracks on the package die surface 21. As shown in FIG. 4, the Mode-2 configuration includes a second brightfield illuminator 32 to direct a beam of collimated white light onto the package die surface 21. In the illustration shown in FIG. 4, beam splitter 43b is positioned between beam splitter 43a and the second brightfield illuminator 32. A collimator 33 is positioned between the second brightfield illuminator 32 and the beam splitter 43b. A lens 41 is positioned between the second brightfield illuminator 32 and the beam splitter 43b.

[0054] In operation, the second brightfield illuminator 32 may be controlled to emit illumination. The incident collimated illumination from the second brightfield illuminator 32, together with the collimator 33 may be focused by lens 41 onto beam splitter 43b and then directed by the beam splitter 43b onto beam splitter 43a, and then subsequently, directed onto the package die surface 21, via lens 41. The illumination from the brightfield illuminator 32 is then reflected off the package die surface 21, focused onto the beam splitter 43a via lens 41 and received by the image capture device 40. The telecentric lens 42 may be positioned between the beam splitter 43a and the image capture device 40. Mode-2 configuration is directed to the detection of the sub-micron cracks which may not be easily detected by the Mode-1 defect inspection.

[0055] The second brightfield illuminator 32 may include a single flash lamp or a white light emitting diode and can be controlled to operate continuously or intermittently (pulsed). Preferably, the second brightfield illuminator 32 supplies broadband brightfield illumination comprising wavelengths of between 380-700nm. As will be understood by a person of ordinary skill in the art, Mode-1 illuminations supply scattered brightfield and darkfield illuminations and these uncollimated illuminations provide diffused light, and while able to detect the defects on the die surface 21, would not be able to clearly define any sub-micron cracks present on the die surface 21. As such, a collimator 33 is utilized in Mode-2 to align the light rays of the second brightfield illuminator 32 into a narrower or parallel beam with little or no parallax with the aim of producing a clearer image of the package die surface 21. Such a collimated illumination is better suited to detect sub-micron cracks that could not be seen in Mode-1. Collimators are well known in the art and may include a tube containing a convex lens at one end and an adjustable aperture at the other. Illumination entering the aperture leaves the collimator as a parallel beam, so that the image can be viewed without parallax.

[0056] Based on theoretical understanding of light behaviour, reflected illumination from the collimated brightfield illumination 32 serves to enhance the image of the sub-micron cracks, therefore the use of collimated illumination is possible in die crack inspections with requirements of 0.5pm or less. With macro lenses and coaxial illuminations via the beam splitters 43 used in the Mode-1 defect inspection configuration, sub-micron cracks were not as clear because light from the co-axial illuminations scatters the light in all directions with only some reaching the image capture device 40, making the crack less visible or smaller than it is. By using collimated light, if there is a sub-micron crack, light entering the crack is likely to reach the telecentric lens 42 because light parallel to the axis of the lens 42 will be received. This means that, if there is a crack line on the package die surface 21, it will appear black in the captured image.

[0057] Results from the configuration illustrated in FIG. 4 using a 4.5pm pixel resolution image capture device 40, show that cracks could be detected at 0.5 pm or less. However, with the image capture device 40 which typically is a CMOS 25-100MP camera, pixel resolution for this disclosure is 10pm while the crack detection goal is 0.5 pm or less. Therefore, if the image pixel resolution is smaller in size than the size of the crack, the crack will be sharply defined in the image. However, given a pixel resolution of 10pm, should any crack smaller than 10pm be detected, the image will still show the crack as 10pm. Further, the grinding lines and submicron crack lines presented similar images under this mode, i.e., the grinding lines and submicron crack lines could not be easily distinguished resulting in numerous false alarms being generated. A different approach to detect the sub-micron cracks with a good degree of clarity will therefore be needed if we are using a camera pixel resolution of 10pm to clearly define sub-micron cracks of 0.5pm or less.

[0058] Combining the collimated and standard brightfield & darkfield illuminations into one system using the same optical path was also problematic as the two modes’ illumination characteristics are very different. With the use of collimated light and telecentric lens, the alignment between illumination and the opto-mechanical packaging is critical and the surface 21 of the package die 20 must also be planar at the focal plane. While testing Mode-2 operations, it was found that the use of the collimated light was adversely affected by the placement of devices in warped trays. For example, the warped trays caused the package dies 20 to be non-planar at the focal plane and this causes the light falling on the package die 20 to reflect away from the telecentric lens 42 thus causing the Mode-2 sub-micron cracks detection to become problematic.

[0059] Operating Mode-3 Defect Inspection - To further refine detection of sub-micron cracks

[0060] The current state of the art uses interferometric solutions which are normally applied to measure 3D measurements such as planarity or other features of a surface by moving a reference mirror and capturing a series of pictures in the process. These types of optical setups are sensitive to vibrations, requiring a long time to capture multiple pictures (i.e., requiring more than 5 shots). They are also not capable of inspecting visible defects such as contaminations (having no changes in surface planes), voids, dimples, damages, discolorations, visible cracks (>0.5pm). Further, if a crack’s width is smaller than 0.5pm and there is a presence of strong grinding lines (grinding lines do not damage the components and thus are not classified as a defect), these current interferometric solutions are unable to detect the crack.

[0061] As shown in FIG. 1(c), the two sides of the ridge of a sub-micron crack line may present a height difference of about 0.2pm between each other. In Mode-3, this difference in height between the two sides of the sub-micron cracks are being utilized to identify the sub-micron cracks via a laser illuminator 34 and optical interferometry mechanism.

[0062] FIG. 5 shows a low coherence infrared (IR) laser illuminator 34 for illuminating the die surface 21 under inspection. This IR illuminator 34 has an optimal 780nm IR spectrum where silicon is non-transparent to provide an image contrast and sensitivity that is better than improving the optical pixel resolution of 4.5pm discussed in Mode-2. Further, by choosing the wavelength of 780nm, background signal and noise can be better suppressed to enhance the signal-to-noise ratio (SNR) of the captured image.

[0063] As illustrated in FIG. 5, illumination from the IR laser illuminator 34 passes through beam splitter 43c and beam splitter 43b and is split into a reference beam and an object (die surface) beam at beam splitter 43a. The reference beam is directed to the reference mirror 35 and reflected therefrom, while the object beam is directed to the die surface 21 and reflected therefrom. A filter 37 may be positioned between the reference mirror 35 and beam splitter 43a to filter out unwanted laser noise from getting through as is well known in the art. The returning beams are relayed by the beam splitter 43 a to the image capture device 40 via telecentric lens 42. As explained earlier, the sub-micron cracks may result in ridges (e.g., of 0.2pm height) formed separating the two sides of the sub-micron crack line on the die surface 21, i.e., the height variation of a sub-micron crack line will be different on both sides. In this way, the returning beams will form an interference pattern or image of the die surface 21 highlighting the sub-micron crack lines indirectly and clearly and thereby differentiating the sub-micron cracks from the grinding lines.

[0064] Defect Modes presentation

[0065] FIG. 6 is a schematic diagram illustrating the series of steps to capture and identify the micro and macro surface defects, and crack lines created by sub-micron cracks.

[0066] In a first step, Mode-1, brightfield, darkfield or a combination of brightfield / darkfield illuminations are provided to capture images of the package die surface. In Mode-2, a collimated brightfield illumination is provided to capture images of crack lines, grinding lines and other fibre-like contaminants. In Mode-3, an IR laser illumination is provided to clearly capture images of sub-micron crack lines via an interferometry mechanism to differentiate between sub-micron crack lines and grinding lines.

[0067] Individual modes or combinations of the three modes result in an integrated inspection solution for detecting all kinds of surface defects including the full range of macro and micro surface defects in addition to sub-micron cracks present on a package die surface.

[0068] In a second step, image capture device 40 captures images of each operating mode which can be performed individually or simultaneously while the inspection is conducted on-the-fly i.e., while the package die 20 is in motion. However, the movement of the package die 20 under inspection can also be stopped at any time during inspection if it is necessary to capture more images of the package die 20 at each mode. In a third step, images or a combination of images captured by the image capture device 40 are analysed. This is done by a processing unit utilising image processing methodologies (such as an Al analyser) for identifying the defects of interest. The Al analyser in principle includes an inspection algorithm to handle multiple images from the various modes of inspections to detect and classify micro and macro surface defects in addition to the sub-micron cracks. The software can be trained with a progression of images showing sub-micron cracks as well as image sets showing the standard defects and their classifications. For example, machine learning tools are trained to detect and classify sub-micron cracks using intelligent algorithms to learn the differences between normal grinding lines and sub-micron crack lines. Al defect detection tools thereafter learned the normal image patterns and develops a comprehensive understanding of the sub-micron cracks and other defects present on the die surface. For example, using machine learning, the sub-micron crack lines on the package dies can be differentiated from the grinding lines captured under Mode-2 and Mode -3 that would have otherwise passed inspection from traditional methods, only to prematurely fail in the field. At the same time, false alarms are also greatly reduced.

[0069] FIG. 7 is a representative flow diagram showing the sequence of steps processed by the processing unit to analyse the defects for determining the presence of sub-micron cracks. These sequences can be interchangeable or performed simultaneously with each other to reduce the turnaround time for the analysis in accordance with the defects mode or modes in operation at the inspection time.

[0070] (a) Perform image processing and measurements of captured images for presence of visible surface defects and contaminants under Mode- 1 ;

[0071] (b) Perform image processing and measurements of captured images for presence of grinding lines and crack lines under Mode-2;

[0072] (c) Perform image processing and measurements of captured images for presence of submicron cracks under Mode-3;

[0073] (d) Determine Mode-1, Mode-2 and Mode-3 defects such as surface defects, grinding lines (non-defect) or sub-micron crack lines (e.g., by analysing color variations of images caused by the crack lines under Mode-1, differentiating images of grinding lines and actual crack lines captured under Mode-2, accurately identify sub-micron cracks under Mode-3);

[0074] (e) Classify defects as visible defects such as surface defects or non- visible defects such as sub-micron cracks. This disclosure illustrates a novel system and method to detect visible and non-visible defects on the surface of a package die . The system and method will enable detection of a full range of micro and macro sized surface defects down to sub-micron cracks (typically of less than 0.5pm) with minimum false alarms in a single pass and at production speeds of at least 10,000 units per hour (UPH).

[0075] It will now be apparent that a system and method to detect visible and non-visible defects on the surface of a package die has been described in the specification with sufficient particularity to be understood by one of ordinary skill in the art. Moreover, it will be apparent to those skilled in the art that various modifications, variations, substitutions, and equivalents exist for features of the device which do not materially depart from the scope of the invention.

[0076] It should be further appreciated by the person skilled in the art that variations and combinations of features described above, not being alternatives or substitutes, may be combined to form yet further embodiments falling within the intended scope of the invention.

Claims

CLAIMS1. A system for die inspections comprising: an integrated optical arrangement comprising: a first optical arrangement comprising a first brightfield illuminator, a high angle darkfield illuminator and a low angle darkfield illuminator for capturing images of a die surface under a first operating mode; a second optical arrangement comprising a second brightfield illuminator and a collimator for capturing images of a die surface under a second operating mode; a third optical arrangement comprising an infrared illuminator and an interferometry mechanism for capturing images of a die surface under a third operating mode; an image capture device configured to receive reflected illuminations from the first, second and third optical arrangements; a focusing mechanism for directing the illuminations from the first, second and third optical arrangements to a die surface and their reflected illuminations to the image capture device; and a processing unit configured to analyze the captured images of the first, second and third operating modes to determine a visible and a non-visible defect, wherein the non-visible defect is determined by a combination of (i) analyzing color variations and differentiation of the captured images under the first and second operating modes and (ii) further confirmation of the non-visible defect under the third operating mode.

2. The system of claim 1, wherein the focusing mechanism comprises one or more beam splitters, one or more reflective surfaces and a plurality of lenses.

3. The system of claims 1 or 2, wherein the focusing mechanism is configured to be activated individually or cooperatively during operation of each of the first, second and third optical arrangements.

4. The system of any one of claims 2 to 3, wherein the first optical arrangement comprises a first beam splitter arranged between the image capture device and the die, the firstbeam splitter being configured to direct illumination from the first brightfield illuminator and darkfield illuminators to a surface of the die under inspection and redirect reflected brightfield and darkfield illuminations from the die surface to the image capture device.

5. The system of claim 4, further comprising a telecentric lens positioned between the first beam splitter and the image capture device such that the reflected brightfield and the high angle and low angle darkfield illuminations are directed to the image capture device through the telecentric lens.

6. The system of any of the preceding claims, wherein illumination from each of the first brightfield illuminator and the high angle and low angle darkfield illuminators are configured to be emitted continuously or intermittently.

7. The system of any of the preceding claims, wherein each of the first brightfield illuminator and high angle and low angle darkfield illuminators is configured to supply illumination of varying intensities.

8. The system of any of the preceding claims, wherein the first brightfield illuminator is configured to emit co-axial illumination.

9. The system of claim 8, wherein the first brightfield illuminator is configured to emit broadband illumination with a wavelength between 380 to 700nm.

10. The system of any of the preceding claims, wherein each of the high angle and low angle darkfield illuminators is configured to emit broadband darkfield illumination with a wavelength between 380 to 700nm.

11. The system of any of the preceding claims, wherein the low angle darkfield illuminator is arranged at an angle of 3-30° with respect to a horizontal plane of the die in an inspection position.

12. The system of any of the preceding claims, wherein the high angle darkfield illuminator is arranged at an angle of 30-85° to the horizontal plane of the die in the inspection position.

13. The system of any one of claims 2 to 12, wherein the second optical arrangement comprises a second beam splitter arranged between the first beam splitter and the second brightfield illuminator, the second beam splitter being configured to direct illumination from the second brightfield illuminator through the first beam splitter to the surface of the die under inspection, wherein the first beam splitter is configured to redirect the reflected brightfield illumination from the die surface to the image capture device.

14. The system of any of the preceding claims, wherein illumination from the second brightfield illuminator is arranged to be supplied continuously or intermittently.

15. The system of any of the preceding claims, wherein the second brightfield illuminator is configured to emit broadband illumination with a wavelength between 380 to 700nm.

16. The system of any one of claims 2 to 15, wherein the interferometry mechanism comprises a mirror positioned adjacent the first beam splitter such that illumination from the infrared illuminator is configured to pass through the second beam splitter and directed to the first beam splitter where the illumination is split into a reference beam which is directed to the mirror and reflected therefrom, and an object beam which is directed to the die surface and reflected therefrom, and wherein the reflected illumination from the die surface and mirror are directed to the image capture device through the telecentric lens.

17. The system of claim 16, further comprising a filter positioned between the mirror and the first beam splitter.

18. The system of any of the preceding claims, wherein the infrared illuminator has a wavelength of 780nm.

19. A method for die inspections comprising: providing an integrated optical arrangement comprising a first optical arrangement, a second optical arrangement and a third optical arrangement :capturing an image of a die surface under a first operating mode by the first optical arrangement comprising a first brightfield illuminator, a high angle darkfield illuminator and a low angle darkfield illuminator; capturing an image of a die surface under a second operating mode by the second optical arrangement comprising a second brightfield illuminator and a collimator; capturing an image of a die surface under a third operating mode by the third optical arrangement comprising an infrared illuminator and an interferometry mechanism; directing the illuminations from the first, second and third optical arrangements to the die surface and redirecting their reflected illuminations to an image capture device; and analyzing with a processing unit, the captured images of the first, second and third operating modes to determine a visible and a non- visible defect, wherein the non- visible defect is determined by a combination of (i) analyzing color variations and differentiation of the captured images under the first and second operating modes and (ii) confirmation of the non- visible defect by the third operating mode.

20. The method of claim 19, wherein the first, second and third operating modes are configured to operate independently of one another or simultaneously.

21. The method of claim 19, wherein each of the first, second and third operating modes is configured to be performed individually or in any combination of two or three modes.

22. The method of any one of claims 19 to 21, wherein the processing unit comprises an Al analyzer for identifying one or more defects.

23. The method of claim 22, wherein the Al analyzer comprises an inspection algorithm configured to manage the captured images and classify the defects.

24. The method of claim 23, wherein the processing unit further comprises an Al defect detection tool configured to recognise and differentiate the defects.

5. A method for die inspections comprising the steps of: capturing an image of the surface of a die under a first operating mode and performing image processing and measurements of the captured image for presence of visible surface defects and contaminants; capturing an image of the surface of a die under a second operating mode and performing image processing and measurements of the captured image for presence of grinding lines and crack lines; capturing an image of the surface of a die under a third operating mode and performing image processing and measurements of captured images for presence of sub-micron cracks; determining the types of defects by utilizing a combination of (i) color variations and differentiation of images under the first and second operating modes and (ii) images of non- visible defects under the third operating modes to identify the non- visible defects; and classifying defects as visible defects or non-visible defects.

Images