Systems and methods for high-resolution inspection of semiconductors in back-end and wafer-level packaging

Abstract

An inspection system and operating method direct a light beam toward a sample on a stage. The sample is a wafer-level package wafer or a back-end wafer. Defect inspection is performed based on light reflected from the sample. The inspection system can use one or more of the following: a fluid supplied by an immersion subsystem comprising a fluid supply unit and a fluid removal unit; an illumination pattern for differential phase contrast; or ultraviolet or deep ultraviolet wavelengths.

Description

Technical Field

[0001] The present disclosure relates to wafer defect inspection. Background Art

[0002] The evolution of the semiconductor manufacturing industry places increasing demands on yield management. While critical dimensions continue to shrink, the industry needs to reduce the time it takes to achieve high-yield, high-value production. Minimizing the time from detecting a yield issue to resolving it determines the return on investment for semiconductor manufacturers.

[0003] Current inspection methods for back-end and wafer-level packaging (WLP) include the use of dry digital optical microscopes in the visible, ultraviolet (UV), or deep ultraviolet (DUV) wavelength bands. While the design rules for such packages are 5 μm or larger, defects of interest (DOIs) can be 2 μm or larger. Current systems with high numerical aperture (NA) may be able to provide images of sufficient quality for defect classification purposes.

[0004] As advanced WLP (aWLP) drives the industry's drive to continue Moore's Law, design rules are shrinking to 1μm, with a roadmap to 0.4μm. For example, defects in such design rules can be as small as 0.2μm. Due to the physical limitations of wavelength on the optical wavelength (NA), which is limited to less than or equal to 1.0, the previously mentioned inspection methods currently cannot provide the image quality required for detection and classification in such design rules. Furthermore, UV or DUV can damage the wafer, so the wavelength is limited to the visible range.

[0005] The inexpensive and slow scanning electron microscope (SEM) can be used to detect and classify defects when current inspection methods are insufficient. However, when certain materials in aWLP or back-end wafers are incompatible with vacuum due to outgassing or electrostatic chucks, SEM may not be used for these materials. Furthermore, some samples can be damaged by electron beam illumination in the SEM. Ultimately, current SEM capabilities are slower and more expensive than optical inspection.

[0006] Therefore, there is a need for improved optical inspection systems. Summary of the Invention

[0007] In a first embodiment, an inspection system is provided. The inspection system includes: a stage having a sample disposed thereon; a light source configured to emit a light beam toward the sample; a detector configured to detect a portion of the light beam reflected by the sample; a plurality of objective lenses; and a processor in electronic communication with the detector. The processor is configured to perform defect inspection on the sample. The sample is a wafer-level package wafer or a back-end wafer. Furthermore, the inspection system further includes: an immersion subsystem including a fluid supply unit and a fluid removal unit; the light source including a plurality of light-emitting diodes configured to form an illumination pattern for differential phase contrast; and / or the light source including a white light source emitting ultraviolet or deep ultraviolet wavelengths.

[0008] The light source may include the plurality of light emitting diodes. The light emitting diodes may be colored.

[0009] The light source may include a relay lens. The relay lens may be configured to image the light beam reflected by the sample onto the detector through at least one of the objective lenses. The detector may use a frame grabber module to convert the light beam from the relay lens into an image. The frame grabber module may be synchronized with the stage.

[0010] The light source may be the white light source. The light source may further include a color filter and a spatial filter.

[0011] The processor may be further configured to generate an intensity image and a phase image. The intensity image and the phase image may be generated based on altitude. The processor may be further configured to generate a composite image from the intensity image and the phase image.

[0012] In an example, the inspection system includes the immersion subsystem, the light source is the white light source, and the system includes the plurality of light emitting diodes.

[0013] The inspection system may include the inspection system of the first embodiment.

[0014] In a second embodiment, a method is provided. The method includes directing a light beam toward a sample on a stage. The sample is a wafer-level package wafer or a back-end wafer. The light beam reflected from the sample is received at a detector. A processor is used to perform defect inspection on the sample. One or more of the following are also performed: First, a fluid is supplied between the sample and an optical objective lens via an immersion subsystem including a fluid supply unit. Second, an illumination pattern is formed with the light beam for differential phase contrast. Third, the light beam is at an ultraviolet or deep ultraviolet wavelength.

[0015] The light beam may be generated by a plurality of light emitting diodes. The light emitting diodes may be colored.

[0016] The method may include imaging the light beam reflected by the sample onto the detector through at least one objective lens using a relay lens. The light beam from the relay lens may be converted into an image using a frame grabber module. The frame grabber module may be synchronized with the stage.

[0017] The light source may be the white light source. The light source may further include a color filter and a spatial filter.

[0018] The method may further include generating an intensity image and a phase image using the processor, generating the intensity image and the phase image based on altitude, and generating a composite image from the intensity image and the phase image.

[0019] In an example, the method includes supplying the fluid, forming the illumination pattern for the differential phase contrast, and the light beam is at the ultraviolet or deep ultraviolet wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a fuller understanding of the nature and purpose of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 Describe an embodiment of a system according to the present disclosure;

[0022] Figure 2 Describe further embodiments of the system according to the present disclosure; and

[0023] Figure 3 An embodiment of the method according to the present disclosure is described. DETAILED DESCRIPTION

[0024] Although the claimed subject matter will be described in terms of specific embodiments, other embodiments (including embodiments that do not provide all of the advantages and features set forth herein) are also within the scope of this disclosure. Various structural, logical, process step, and electrical changes may be made without departing from the scope of this disclosure. Accordingly, the scope of the present disclosure is defined solely by reference to the appended claims.

[0025] The systems and methods disclosed herein can provide inspection support for aWLP and BE applications. For samples of aWLP and BE wafers, embodiments can 1) inspect and classify defects using immersion techniques; 2) inspect and classify defects using differential phase contrast (DPC); 3) inspect and classify defects using focused scanning with DPC; 4) use quantitative modeling algorithms for DPC to polarize the illumination source and tube lens; or 5) inspect and classify defects using ultraviolet (UV) or deep ultraviolet (DUV) light using one or more of techniques 1) through 4). Systems can be configured for different applications. For example, a system can combine DUV and immersion with DPC for one application, visible wavelength with immersion and DPC for another application, and visible wavelength with DPC and focused scanning for another application. These different applications can be performed within the same inspection system.

[0026] The use of one or more of techniques 1) to 4) may depend on the size and material of the defect and / or may involve a trade-off between speed and performance. If the defect is large (e.g., 1 μm) and the material on the wafer is compatible with DUV, then DUV or immersion DUV can be used. If the defect size is large (e.g., 1 μm) and the material is not compatible with UV / DUV, then immersion visible imaging can be used. If higher resolution is required, DPC may be required, although this is slightly slower. For smaller defects (e.g., 0.4 μm), immersion DUV applied with focused scanning DPC can be used. Generally speaking, DUV and immersion may be more useful for finding broken / shorted Cu lines. For structural defects on Cu lines / surfaces, DPC and focused scanning can provide more value.

[0027] The semiconductor industry is moving toward 2μm. Previously, defect sizes were approximately 2μm to 5μm, and high-NA dry optical microscopes met the application requirements. More semiconductor manufacturers are beginning to adopt design rules for 2μm or less. Semiconductor manufacturers who need to improve yield or cannot afford multiple scanning electron microscope steps for such defects can use the embodiments disclosed herein.

[0028] The embodiments disclosed herein can be configured to suit the needs of semiconductor manufacturers, balancing performance, speed, and cost.

[0029] exist Figure 1. System 100 includes an optical-based subsystem 101 (i.e., an optical inspection tool). Generally speaking, optical-based subsystem 101 is configured to generate an optical-based output for sample 102 by directing light to (or scanning light across) and detecting light from sample 102. In one embodiment, sample 102 includes a wafer, a fabricated wafer, or a bonded wafer. The wafer may include any wafer known in the art, such as an aWLP or BE wafer.

[0030] exist Figure 1 In the embodiment of the system 100 shown in FIG, the optical-based subsystem 101 includes an illumination subsystem configured to direct light to the sample 102. The illumination subsystem includes at least one light source. For example, as in Figure 1 , the illumination subsystem includes a light source 103. In one embodiment, the illumination subsystem is configured to direct light to the sample 102 at one or more incident angles, which may include one or more oblique angles and / or one or more normal angles. For example, as shown in Figure 1 , light from light source 103 is directed at a normal angle of incidence through optical element 104 and then through lens 105 to sample 102. The oblique angle of incidence may include any suitable oblique angle of incidence, which may vary depending on characteristics of sample 102, for example.

[0031] The optical-based subsystem 101 can be configured to direct light at different angles of incidence at different times to the sample 102. For example, the optical-based subsystem 101 can be configured to modify one or more characteristics of one or more elements of the illumination subsystem so that light can be directed at different angles of incidence. Figure 1 1 and 2. In one such example, the optics-based subsystem 101 can be configured to move the light source 103, optical element 104, lens 105, and optical objective 110 so that light is directed to the sample 102 at different angles of incidence or oblique (or near-normal) angles of incidence.

[0032] An illumination beam with an oblique incident angle can also be achieved outside the objective lens 110 , as shown by the optional second light source 116 .

[0033] The scanning mechanism may vary the distance between the sample 102 and the objective lens 110. Various images or other data may be acquired at one or more predetermined positions.

[0034] In some examples, the optical-based subsystem 101 can be configured to direct light to the sample 102 at more than one incident angle simultaneously. For example, the illumination subsystem can include more than one illumination channel. One of the illumination channels can include, for example, Figure 1102 , and the other of the illumination channels (not shown) may include similar elements (or dissimilar lenses, such as illumination outside objective 110) that may be configured differently (e.g., wavelength polarization) or identically, or may include at least one light source and possibly one or more other components (such as those described further herein). If this light is directed to the sample at the same time as other light, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed to the sample 102 at different angles of incidence may differ, such that light originating from illumination of the sample 102 at different angles of incidence can be distinguished from one another at the detector(s).

[0035] In another example, the lighting subsystem may include only one light source (e.g., Figure 1 ) and the light from the light source can be separated into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. Light in each of the different optical paths can then be directed to sample 102. Multiple illumination channels can be configured to direct light to sample 102 at the same time or at different times (e.g., when different illumination channels are used to illuminate the sample sequentially). In another example, the same illumination channel can be configured to direct light with different characteristics to sample 102 at different times. For example, in some examples, optical element 104 can be configured as a spectral filter, and the properties of the spectral filter can be changed in a variety of different ways (e.g., by swapping out the spectral filter), so that light of different wavelengths can be directed to sample 102 at different times. The illumination subsystem can have any other suitable configuration known in the art for directing light with different or the same characteristics to sample 102, either sequentially or simultaneously, at different or the same angles of incidence.

[0036] The system 100 may also include an optional second light source 116 and light conditioning optics 117. The second light source 116 may provide an oblique illumination channel.

[0037] like Figure 1 , the detection channels are shown positioned in the plane of the paper and the illumination subsystem is also shown positioned in the plane of the paper. Thus, in this embodiment, the detection channels are positioned (e.g., centered) in the plane of incidence. However, one or more of the detection channels may be positioned outside the plane of incidence.

[0038] As further described above, each of the detection channels included in the optical-based subsystem 101 can be configured to detect scattered light. Figure 1The optical-based subsystem 101 shown in FIG may be configured for dark field (DF) output generation of the sample 102. However, the optical-based subsystem 101 may also or instead include (several) detection channels configured for bright field (BF) output generation of the sample 102. In other words, the optical-based subsystem 101 may include at least one detection channel configured to detect light specularly reflected from the sample 102. Thus, the optical-based subsystem 101 described herein may be configured for only DF imaging, only BF imaging, or both DF and BF imaging. Although each of the light collectors is Figure 1 1 and 2. Although shown as a single refractive optical element in FIG, it is understood that each of the light collectors may include one or more refractive optical dies and / or one or more reflective optical elements.

[0039] Detector 109 may include a charge-coupled device (CCD), a time-delay integration (TDI) camera, and any other suitable detector known in the art. Detectors may also include non-imaging detectors or imaging detectors. In this manner, if a detector having multiple detection channels is a non-imaging detector, each of the detectors may be configured to detect certain characteristics of scattered light (e.g., intensity) but not to detect such characteristics that vary depending on position within the imaging plane. Thus, the output generated by each of the detectors included in each of the detection channels of the optical-based subsystem may be a signal or data rather than an image signal or image data. In such examples, a processor (e.g., processor 114) may be configured to generate an image of sample 102 from the non-imaging output of the detector. However, in other examples, the detector may be configured as an imaging detector configured to generate an imaging signal or image data. Thus, the optical-based subsystem may be configured to generate the optical images or other optical-based outputs described herein in a number of ways.

[0040] Light source 103 can include any suitable light source. In one example, light source 103 includes a plurality of light-emitting diodes (LEDs) configured to form an illumination pattern for DPC. In one example, the LEDs are arranged in a 32x32 array with a discrete grid pattern. In another example, the LEDs are arranged in a 4-8 ring shape, with 16 LEDs in each ring. Each LED can be considered a coherent point source. For example, the LEDs can be activated within the radius of a semicircle. The radius of the LED array can vary.

[0041] In another example, light source 103 comprises a white light source that emits light from the visible to UV and DUV wavelengths, such as a Xe lamp. In this example, light source 103 may also be one or more LEDs. Light source 103 may further include a color filter and a spatial filter. The white light source may provide DUV wavelengths. The color filter may be fixed on a wheel or may be a variable filter. The spatial filter may be a programmable pinhole or a flash.

[0042] UV LEDs exist that provide a central wavelength of approximately 355 nm or approximately 388 nm. Visible light LEDs are available at 435 nm, 530 nm, and 635 nm. Other wavelengths are possible. Xe lamps with color filters can be used for DUV.

[0043] In yet another example, the light source 103 includes a plurality of LEDs. In this example, the LEDs are colored.

[0044] The light source 103 may further include a polarized light source and / or a tube lens.

[0045] The optical-based subsystem 101 may have multiple objectives. Some objectives operate dry, and others operate immersed with various NAs and fields of view (FoVs). Objectives may be changed or selected for a particular reception using, for example, a motorized turret that can be rotated or moved linearly.

[0046] Light from the optical element 104 can be focused onto the sample 102 by the lens 105. Figure 1 1 is shown as a single refractive optical element, but it is understood that in practice, lens 105 may include several refractive and / or reflective optical elements that combine to focus light from the optical element to the sample. Figure 1 The illumination subsystem shown in and described herein may include any other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarizing components, spectral filters, spatial filters, reflective optical elements, apodizers, beam splitters (e.g., beam splitter 113), apertures, and the like, which may include any such suitable optical elements known in the art. Additionally, the optical-based subsystem 101 may be configured to alter one or more of the elements of the illumination subsystem based on the type of illumination to be used to generate the optical-based output.

[0047] Light from the optical element 104 may be imaged on the back focal plane of the objective lens.

[0048] When DPC is desired, a pre-programmed illumination pattern may be utilized to obtain an image of light reflected from the sample 102 .

[0049] When focus scanning is required, images of light reflected from the sample 102 are obtained at different relative distances between the sample 102 and the objective lens 110 .

[0050] In an example, the light source 103 (or the lens 105 of the illumination subsystem) includes a relay lens (eg, a tube lens) configured to image a light beam reflected by the sample to the detector 109 through at least one objective lens (eg, objective lens 110 ).

[0051] The optical-based subsystem 101 may also include a scanning subsystem configured to scan light across the sample 102. For example, the optical-based subsystem 101 may include a stage 106 on which the sample 102 is positioned during generation of the optical-based output. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including the stage 106) that may be configured to move the sample 102 so that light may be scanned across the sample 102. Additionally or alternatively, the optical-based subsystem 101 may be configured such that one or more optical elements of the optical-based subsystem 101 perform some of the scanning of light across the sample 102. The light may be scanned across the sample 102 in any suitable manner, such as in a serpentine path or in a spiral path.

[0052] In one embodiment, the optical subsystem 101 includes an immersion subsystem 111, which may include a fluid supply unit and a fluid removal unit. A fluid is provided between the sample 102 and the optical objective 110. The fluid may have a refractive index higher than that of air. The fluid may be water with a refractive index of approximately 1.4, or another liquid compatible with the sample 102. For example, alcohol or oil may be used as the fluid. In one example, the fluid has a refractive index greater than 1.5. By using this fluid, the equivalent NA is greater than 1.0, which can prevent UV or DUV light from damaging the sample 102.

[0053] Very little liquid may be required to fill a gap of approximately 1 mm or less. After the measurement is completed, the liquid needs to be dried. Therefore, the system is configured with a one-side clean liquid supply 118 to the gap (e.g., a needle or nozzle) and a liquid remover 119 (e.g., a vacuum). Additional details are disclosed in U.S. Patent No. 7,436,527, the entire contents of which are incorporated herein by reference.

[0054] The gap may be the distance between the end face of the optical objective lens 110 and the surface of the sample 102. Figure 2 The separation distance h is depicted in FIG. The gap can be an air gap or a vacuum. Figure 2 In FIG, fluid 112 occupies the gap between optical objective 110 and sample 102. The gap between optical objective 110 and sample 102 may be completely filled with air or liquid.

[0055] In this example, the fluid is contained in a fluid supply unit of the immersion subsystem 111. The fluid can be pumped to the bottom surface of the optical objective 110. The fluid can be forced into the volume between the optical objective 110 and the sample 102 using a liquid supply 118. Residual liquid can be dried using a liquid remover 119. The liquid can be returned to the immersion subsystem 111. Thus, the system is configured to generate a flow of liquid between the optical objective 110 and the surface of the sample 102 during inspection. Additional details are disclosed in U.S. Patent No. 7,130,037, the entire contents of which are incorporated herein by reference.

[0056] The light source 103 may include a plurality of light emitting diodes using the immersion subsystem 111. The light source 103 may be a white light source.

[0057] It should be noted that this article provides Figure 1 The present invention generally illustrates configurations of an optical-based subsystem 101 that may be included in or used with the system embodiments described herein. As is typically performed when designing a commercial output acquisition system, the configurations of the optical-based subsystem 101 described herein may be modified to optimize the performance of the optical-based subsystem 101. Additionally, the systems described herein may be implemented using existing systems (e.g., by adding the functionality described herein to an existing system). For some such systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the systems described herein may be designed as entirely new systems.

[0058] Processor 114 can be coupled to components of system 100 in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) so that processor 114 can receive output. Processor 114 can be configured to perform a number of functions using the output. System 100 can receive instructions or other information from processor 114. Processor 114 and / or electronic data storage unit 115 can optionally electronically communicate with a wafer inspection tool, wafer metrology tool, or wafer review tool (not shown) to receive additional information or send instructions. For example, processor 114 and / or electronic data storage unit 115 can electronically communicate with a SEM. In another example, system 100 is part of an inspection system.

[0059] The processor 114 may be configured to generate an intensity image and a phase image. The intensity image and the phase image may be generated based on altitude.

[0060] To do this, we can obtain multiple images using different lighting conditions (e.g., LEDs in the right half of the ring, the left half, the top and bottom halves, only the inner ring, only the outer ring, etc.) The algorithm can use those images as input, and after processing all the data through the algorithm, it can produce intensity and phase images.

[0061] The processor 114 may be further configured to generate a composite image from the intensity image and the phase image. This may be performed using additional images at different relative distances between the sample and the objective lens.

[0062] Using processor 114, phase imaging can be performed using DPC using the intensity image. Phase images can use phase contrast and partially coherent illumination to improve image quality. Separate acquisition of phase and intensity images can be performed. Phase information can help inspect thin transparent materials such as photoresist, polybenzoxazole (PBO), or the like on metals (such as copper) used for aWLP or BE. Two images can be captured to implement DPC with an LED array: one image with half a circle of LEDs illuminated and one image with the other half a circle of LEDs illuminated. The array can be circular or have another pattern of two half-circle activation areas. The two images can be used to calculate a phase contrast image. Quantitative phase can be recovered by deconvolving the DPC image using the calculated transfer function. Due to the flexible patterning of the LED array, DPC measurements can be performed in real time and along any asymmetric axis using a minimal number of mechanical parts.

[0063] Focus scanning with a DPC configuration can provide height information of structures on the sample 102 being inspected. This height information improves image quality due to defocus, as the height of structures on the sample is typically higher than the depth of focus of a high-NA objective. This height information can also provide a method for measuring the height of features on the sample 102 using high NA, for example, through immersion and / or short wavelengths. 2D intensity is typically measured in a single image. The sample 102 can be scanned, and images can be captured at many focus planes to create a 3D intensity measurement.

[0064] DPC microscopy can use asymmetric illumination for phase contrast. For example, four images can be captured using a rotating semicircular source pattern. Dynamic source switching can be achieved using, for example, a programmable LED array.

[0065] Polarization control can be performed on the light source 102 and the tube lens. In high-NA systems (which improve spatial resolution), the focused light can no longer be considered as a proportional wave, but its vector properties may need to be considered according to electromagnetic wave theory. References to DPC do not consider the vector properties of light, and quantitative modeling of light propagation may be required in DPC. Therefore, it may be necessary to control the polarization of light in the system and / or model it in the DPC algorithm.

[0066] In an example where a relay lens is used, the detector 109 converts the light beam from the relay lens into an image using a frame grabber module, which may be part of or run on the processor 114. The frame grabber module may be synchronized with the movement of the stage 106 or the scan lens. The digitized image from the frame grabber may be stored in the electronic data storage unit 115. In an example, the detector 109 converts the light from the relay lens into a digitized image using a frame grabber.

[0067] The processor 114, other system(s), or other subsystem(s) described herein may be part of a variety of systems, including a personal computer system, a graphics computer, a mainframe computer system, a workstation, a network appliance, an Internet appliance, or other devices. The subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor, a CPU, or a GPU. In addition, the subsystem(s) or system(s) may include a platform with high-speed processing and software, either as a standalone or networked appliance.

[0068] The processor 114 and the electronic data storage unit 115 may be disposed in or otherwise be part of the system 100 or another device. In an example, the processor 114 and the electronic data storage unit 115 may be part of a separate control unit or in a centralized quality control unit. Multiple processors 114 or electronic data storage units 115 may be used.

[0069] In practice, processor 114 may be implemented by any combination of hardware, software, and firmware. Similarly, its functions as described herein may be performed by a single unit or divided among different components, each of which may be implemented by any combination of hardware, software, and firmware. Program code or instructions for processor 114 to implement various methods and functions may be stored in a readable storage medium, such as a memory in electronic data storage unit 115 or other storage.

[0070] If the system 100 includes more than one processor 114, the different subsystems may be coupled to each other so that images, data, information, instructions, etc. can be sent between the subsystems. For example, one subsystem may be coupled to (several) additional subsystems via any appropriate transmission medium, which may include any suitable wired and / or wireless transmission media known in the art. Two or more of such subsystems may also be operatively coupled via a shared computer-readable storage medium (not shown).

[0071] Processor 114 may be configured to perform a number of functions using the output or other output of system 100. For example, processor 114 may be configured to send the output to electronic data storage unit 115 or another storage medium. Processor 114 may be further configured as described herein.

[0072] If the system includes more than one subsystem, the different subsystems may be coupled to each other so that images, data, information, instructions, etc. can be transmitted between the subsystems. For example, one subsystem may be coupled to (several) additional subsystems via any appropriate transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more of such subsystems may also be operatively coupled via a shared computer-readable storage medium (not shown).

[0073] The processor 114 may be configured according to any of the embodiments described herein. The processor 114 may also be configured to perform other functions or additional steps using the output of the system 100 or using images or data from other sources.

[0074] Once all desired images have been generated, processor 114 may analyze the images. The output of the analysis may be an intensity image and a phase image, which may be height-dependent. The results may be further processed, for example, to form a composite image. The analysis results may be stored for documentation (e.g., in electronic data storage unit 115), fed into other algorithms for training (e.g., training a deep learning module for defect classification), and / or displayed to a user.

[0075] The various steps, functions, and / or operations of system 100 and the methods disclosed herein are performed by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls / switches, microcontrollers, or computing systems. Program instructions for implementing methods (such as those described herein) may be transmitted via or stored on a carrier medium. The carrier medium may include storage media such as read-only memory, random access memory, magnetic or optical disks, non-volatile memory, solid-state memory, tape, and the like. The carrier medium may include transmission media such as wires, cables, or wireless transmission links. For example, the various steps described throughout this disclosure may be performed by a single processor 114 or, alternatively, by multiple processors 114. Furthermore, the various subsystems of system 100 may include one or more computing or logic systems. Therefore, the above description should not be construed as limiting the present disclosure but is merely illustrative.

[0076] System 100 can provide sufficiently high resolution for aWLP and BE samples such as through-silicon vias (TSVs), copper microbumps, or contact pads. Other samples can be in redistribution layers (RDLs) on a substrate (e.g., glass, a blank Si wafer, or a wafer typically with functional dies). If multiple layers are formed, each layer has Cu for conduction and an isolation material such as PBO or polyimide (PI). System 100 is flexible for different samples. System 100 also mitigates UV / DUV damage to samples, is non-destructive, and avoids the complexity of vacuum compatibility.

[0077] Figure 3 An embodiment of method 200 is described. Method 200 includes, at 201, directing a light beam toward a sample on a stage. The sample is an aWLP wafer or a BE wafer. At 202, the light beam reflected from the sample is received at a detector. At 203, defect inspection is performed on the sample using information from the detector.

[0078] The method 200 includes at least one of: supplying a fluid between the sample and the optical objective by an immersion subsystem including a fluid supply unit; forming an illumination pattern with a light beam for differential phase contrast; or the light beam is at an ultraviolet or deep ultraviolet wavelength.

[0079] In the example of method 200, the light beam is generated by a plurality of LEDs. The LEDs may be colored.

[0080] In an example of method 200, a relay lens is used to image a light beam reflected from a sample through at least one objective lens onto a detector. The light beam from the relay lens can be converted into an image using a frame grabber module of the detector. The frame grabber module can be synchronized with the stage.

[0081] In the example of method 200, the light source is a white light source. The light source further includes a color filter and a spatial filter.

[0082] In an example, method 200 includes generating an intensity image and a phase image using a processor. The intensity image and the phase image are generated based on the height. Method 200 may further include generating a composite image from the intensity image and the phase image using the processor.

[0083] In an example, the method 200 includes supplying a fluid, a light beam forming the illumination pattern for differential phase contrast, and the light beam being at an ultraviolet or deep ultraviolet wavelength.

[0084] The embodiments described herein can be used to inspect and / or classify defects on samples in aWLP or BE. Immersion techniques for inspecting and classifying defects, DPC techniques for inspecting and classifying defects, focused scanning using DPC techniques for inspecting and classifying defects, polarization control of the illumination source and tube lens using quantitative modeling algorithms using DPC, or using one or more of these techniques in conjunction with UV or DUV for inspecting and classifying defects can improve the inspection and / or classification of defects on samples in aWLP or BE.

[0085] Although the present disclosure has been described with reference to one or more specific embodiments, it will be understood that other embodiments of the present disclosure can be made without departing from the scope of the present disclosure. Therefore, the present disclosure is considered to be limited only by the appended claims and a reasonable interpretation thereof.

Claims

1. An inspection system comprising: a carrier having a sample mounted thereon, wherein the sample is a wafer-level packaging wafer or a back-end wafer; a light source configured to emit a light beam toward the sample, wherein the light source comprises a white light source emitting at ultraviolet or deep ultraviolet wavelengths, and wherein the light source includes a relay lens; a detector configured to detect a portion of the light beam reflected by the sample; a plurality of objective lenses, wherein the relay lenses are configured to image the light beam reflected by the sample to the detector through at least one of the objective lenses, wherein the detector converts the light beam from the relay lenses into an image using a frame grabber module, and wherein the frame grabber module is synchronized with the stage; an immersion subsystem comprising a liquid supplier and a liquid remover, wherein the immersion subsystem is configured to provide liquid from the liquid supplier between one of the objective lenses and the sample; as well as A processor is in electronic communication with the detector, wherein the processor is configured to perform defect inspection on the sample.

2. The inspection system of claim 1, wherein the light source comprises a plurality of light emitting diodes configured to form an illumination pattern for differential phase contrast, and wherein the light emitting diodes are colored.

3. The inspection system of claim 1, wherein the light source further comprises a color filter and a spatial filter. 4 . The inspection system of claim 1 , wherein the processor is further configured to generate an intensity image and a phase image, wherein the intensity image and the phase image are generated according to height. 5 . The inspection system of claim 4 , wherein the processor is further configured to generate a composite image from the intensity image and the phase image.

6. The inspection system of claim 1, wherein the system comprises a plurality of light emitting diodes.

7. An inspection system comprising the inspection system according to claim 1.

8. A method comprising: directing a light beam toward a sample on a stage, wherein the sample is a wafer-level package wafer or a back-end wafer, and the light beam is of ultraviolet or deep ultraviolet wavelength; supplying a fluid between the sample and the optical objective via an immersion subsystem comprising a liquid supply; receiving the light beam reflected from the sample at a detector; Using a relay lens to image the light beam reflected by the sample to the detector through at least one objective lens; converting the light beam from the relay lens into an image using a frame grabber module, wherein the frame grabber module is synchronized with the stage; and A processor is used to perform defect inspection on the sample.

9. The method of claim 8, wherein the light beam is generated by a plurality of light emitting diodes, and wherein the light emitting diodes are colored.

10. The method of claim 8, wherein the light beam is generated by a light source, and the light source is a white light source, and wherein the light source further comprises a color filter and a spatial filter.

11. The method of claim 8, further comprising generating an intensity image and a phase image using the processor, wherein the intensity image and the phase image are generated as a function of altitude.

12. The method of claim 11, using the processor to generate a composite image from the intensity image and the phase image.

13. The method of claim 8, wherein the method comprises forming an illumination pattern with the light beam for differential phase contrast.

14. The method of claim 8, wherein the fluid has a refractive index equal to or greater than that of water.

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