Photoluminescence for semiconductor yield-related applications

Abstract

Methods and systems for determining information about a specimen are provided. Certain embodiments relate to detecting photoluminescence for applications such as inspection and / or metrology of electro-optically active devices or advanced packaging devices. One system embodiment includes an illumination subsystem configured to direct light having one or more illumination wavelengths toward the specimen and a detection subsystem configured to detect photoluminescence from the specimen. The system also includes a computer subsystem configured to determine information about the specimen from output generated by the detection subsystem in response to the detected photoluminescence.

Description

[Technical Field]

[0001] The present invention relates generally to methods and systems configured to determine information about a specimen. Particular embodiments relate to detecting photoluminescence for inspection or metrology applications. [Background technology]

[0002] The following descriptions and examples are included in this section and therefore are not admitted to be prior art.

[0003] Fabricating semiconductor devices, such as logic and memory devices, typically involves processing a substrate, such as a semiconductor wafer, using a number of semiconductor fabrication processes to form various features and multiple levels of semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist disposed on a semiconductor wafer. Further examples of semiconductor fabrication processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.

[0004] Inspection processes are used at various steps during the semiconductor manufacturing process to detect defects on wafers to promote higher yields and therefore higher profits in the manufacturing process. Inspection has always been an important part of fabricating semiconductor devices such as ICs. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful production of acceptable semiconductor devices, as smaller defects can cause the device to fail.

[0005] Defect review typically involves redetecting defects so detected by the inspection process and generating additional information about the defects at higher resolution using either high-magnification optics or a scanning electron microscope (SEM). Thus, defect review is performed at individual locations on the wafer where defects were detected by inspection. The high-resolution data about the defects generated by defect review is better suited to determining defect attributes, such as profile, roughness, and more precise size information.

[0006] Metrology processes are also used at various steps during semiconductor manufacturing processes to monitor and control the process. Metrology processes differ from inspection processes in that, unlike inspection processes in which defects are detected on wafers, metrology processes are used to measure one or more characteristics of wafers that cannot be determined using currently used inspection tools. For example, metrology processes are used to measure one or more characteristics of wafers, such as the dimensions (e.g., linewidth, thickness, etc.) of features formed on the wafer during the process, so that the performance of the process can be determined from the one or more characteristics. Additionally, if one or more characteristics of the wafer are unacceptable (e.g., outside a predetermined range for the characteristic), the measurements of the one or more characteristics of the wafer can be used to modify one or more parameters of the process so that additional wafers produced by the process have acceptable characteristics.

[0007] A metrology process also differs from a defect review process in that the metrology process may be performed at locations where no defects were detected, unlike a defect review process in which defects detected by inspection are revisited in the defect review. In other words, unlike a defect review, the locations on a wafer where the metrology process is performed may be independent of the results of an inspection process performed on the wafer. In particular, the locations where the metrology process is performed may be selected independently of the inspection results. Additionally, because the locations on a wafer where metrology is performed may be selected independently of the inspection results, the locations where the metrology process is performed may be determined before the inspection process is performed on the wafer, unlike a defect review in which the locations on a wafer where the defect review is performed cannot be determined until inspection results for the wafer are generated and available.

[0008] Different processes, such as those described above, may be selected based on information determined about the specimen, such as inspection, when defects are detected, review, when detected defects are redetected and further investigated, metrology, when properties of the specimen are measured, etc. Different processes may also be used for different specimens. For example, different inspection processes may be used or required for different types of semiconductor devices. Different inspection processes may also be used or required for the same type of semiconductor device at different points in the fabrication process.

[0009] In most cases, it is clear which processes are useful for semiconductor devices at any given time. One such example of an obvious process useful for examining electro-optically active devices is electrical testing, a traditional method used to determine whether such devices function properly. Electron beam inspection may also be used in voltage contrast (VC) mode to find, for example, shorts or opens. In addition, traditional optical or electrical beam inspection can be used to find many other defect types, such as bridges, falling particles, etc.

[0010] However, there are many other instances where the appropriate process for examining a semiconductor sample at a given point in the fabrication process is not necessarily clear. For example, certain defect types related to material band gap, color uniformity, luminous efficiency, etc., of electro-optically active devices are difficult to correlate with conventional defect types and therefore are not easily detected and measured using conventional inspection and metrology methods. Conventional techniques are also relatively slow, and in some cases, can be so slow that they become impractical. For example, many of the processes described above can adversely affect the semiconductor fabrication process if they take too long. Therefore, methods that can measure light at substantially high throughput are desirable and often needed. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent Application Publication No. 2016 / 0327485 [Patent Document 2] U.S. Patent Application Publication No. 2022 / 0113254 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, it would be advantageous to develop systems and methods for determining information about semiconductor-related specimens, such as electro-optically active devices and advanced packaging devices, that do not have one or more of the above-mentioned drawbacks. [Means for solving the problem]

[0013] The following description of various embodiments is not to be construed in any way as limiting the subject matter of the appended claims.

[0014] One embodiment relates to a system configured to determine information about a sample. The system includes an illumination subsystem configured to direct light having one or more illumination wavelengths toward the sample. The system also includes a detection subsystem configured to detect photoluminescence (PL) from the sample. In addition, the system includes a computer subsystem configured to determine information about the sample from output generated by the detection subsystem in response to the detected PL. The system may be further configured as described herein.

[0015] Another embodiment relates to a method for determining information about a sample. The method includes directing light having one or more illumination wavelengths to the sample. The method also includes detecting PL from the sample. In addition, the method includes determining information about the sample from an output in response to the detected PL. Each step of the method can be performed as described herein. The method can include any other step of any other method described herein. The method can be performed by any of the systems described herein.

[0016] Further advantages of the present invention will become apparent to those skilled in the art with the benefit of the following detailed description of the preferred embodiments, when read in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram illustrating a side view of one embodiment of a system configured as described herein. [Figure 2] 1A-1D are schematic diagrams illustrating different types of images that can be generated for samples described herein. [Figure 3] 3 is a schematic diagram illustrating an example of a more detailed image of one of the abnormal regions shown in one of the images of FIG. 2. FIG. [Figure 4] 1A-1C are schematic diagrams illustrating plan views of an example of different regions of a device on a sample and embodiments of composite images that may be generated for the different regions by embodiments described herein. [Figure 5] 1 is a plot of an example of the photoluminescence (PL) emission spectrum of a single micro light-emitting diode (LED), showing the difference between the spectra of a normal pixel and an abnormal pixel. [Figure 6] 1A-1C are schematic diagrams illustrating an example of images of a green light-emitting device with various color defects. [Figure 7] 1 is a schematic diagram illustrating an example image of a blue light-emitting device having regions of various sizes, brightnesses, and colors. [Figure 8] 1 is a plot of an example of PL emission spectra under different excitation wavelengths. [Figure 9] FIG. 1 is a block diagram illustrating one embodiment of a non-transitory computer-readable medium storing program instructions for causing one or more computer systems to perform the computer-implemented methods described herein. DETAILED DESCRIPTION OF THE INVENTION

[0018] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular forms disclosed; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0019] Referring now to the drawings, it should be noted that the figures are not drawn to scale. In particular, the scale of some of the elements in the figures has been greatly exaggerated to emphasize the characteristics of the elements. It should also be noted that the figures are not drawn to the same scale. Elements shown in multiple figures that may be similarly configured are indicated using the same reference numerals. Unless otherwise specified herein, any of the elements described and illustrated may include any suitable commercially available elements.

[0020] Generally, embodiments described herein relate to methods and systems for determining information about a sample using photoluminescence (PL) detected from the sample. The embodiments described herein may be configured to use various illumination and collection wavelength bands and modes of a multi-wavelength inspection system, which may be a commercially available system such as the Altair system commercially available from KLA Corp., Milpitas, Calif. This can be tuned as described herein to take advantage of the sample's material and device properties, perform substantially rapid inspection over a substantially large area (e.g., a full die or entire wafer), and analyze the PL signal to identify defects or regions of abnormal behavior. While such defects may be difficult to detect or invisible through traditional optical inspection, configuring the system to detect PL allows the system to reveal additional defect types with substantially higher throughput. Similarly, the embodiments described herein may be configured for metrology processes or systems configured to determine one or more metrology properties of the sample.

[0021] In some embodiments, the specimen is a wafer. The wafer can include any wafer known in the semiconductor arts. Although some embodiments may be described herein with respect to one or more wafers, the embodiments are not limited to the specimens with which they can be used. For example, the embodiments described herein can be used with specimens such as reticles, flat panels, personal computer (PC) boards, and other semiconductor specimens and / or specimens associated with the fabrication of semiconductor devices.

[0022] "Photoluminescence" or PL is defined herein as any form of light emission from a substance after absorption of a photon (electromagnetic radiation). In other words, PL is a phenomenon that can occur when light stimulates the emission of a photon. There are several types of PL, including fluorescence, phosphorescence, and chemiluminescence. Fluorescence occurs when a photon excites a molecule, placing it in an electronically excited state. The type of PL that the embodiments described herein are configured to detect will vary depending on the sample and the materials formed thereon.

[0023] Some molecules that may be present on the samples described herein may emit PL, such as fluorescence, in response to illumination according to the embodiments described herein. For example, for PL to occur, electrons from a lower energy level must be excited to a higher energy level via absorption of an excitation photon. The electrons then relax to a lower energy level via emission of a PL photon. Within the molecule, electronic transitions occur between distinct energy levels.

[0024] Such materials may include organic or non-device materials, such as photoresists, that are intentionally formed on the sample during some fabrication process steps, as well as other foreign matter, such as falling particles, that are not intentionally formed on the sample as described herein. The fluorescence of such materials is for the purposes described herein and is unrelated to the function of the material. For example, photoresists are designed to chemically change in response to exposure to some electromagnetic energy so that they can be patterned and then used to transfer that pattern to other materials on the sample. However, the materials themselves in their normal functioning do not emit light.

[0025] In one embodiment, the sample includes one or more packaging structures formed thereon. For example, in advanced semiconductor packaging fabrication processes, polymer-based materials such as polyimide (PI) and polybenzoxazole (PBO) are often used as intermetal dielectrics. In these materials, PL takes one of several forms, called fluorescence, in which molecules are excited by illuminating photons and then relax to a lower energy state through the emission of photons without a change in electron spin. Because polymers emit fluorescence and metals do not, PL inspection can be used to increase the capture rate of certain hard-to-find defects. As with the materials described above, the fluorescence or other PL emitted by such materials in response to illumination and detected by the systems described herein is independent of the material's normal functionality. For example, dielectric materials such as those described above in their normal functionality do not emit any type of light.

[0026] With respect to the embodiments described herein, an "advanced packaging device" means that some or all of the packaging of the device is performed while the device is still in wafer form or while attached / bonded to a device in wafer form. Additionally, an "advanced packaging process" typically involves processing techniques similar to those used in fabricating semiconductor devices on wafers (e.g., multilayer thin film processes, chemical mechanical polishing (CMP), etc.). While the embodiments described herein may be particularly well-suited for such devices, the embodiments are also well-suited for determining information about other types of packaging or packaged devices in addition to unpackaged semiconductor devices.

[0027] In contrast, the engineered functionality of some devices formed on the samples described herein may be what causes PL to be detected and used by the embodiments described herein. For example, in semiconductors, atoms may form periodic crystalline structures, and PL can occur when electrons from a low-energy band are excited to a high-energy band by absorption of an excitation photon, followed by relaxation to the low-energy band through the emission of a PL photon. The different energy bands may be, for example, a conduction band and a valence band. Thus, electronic transitions can occur between the valence and conduction bands. In this way, when some electro-optically active devices are illuminated with one or more carefully selected wavelengths, they can emit PL, much like the electro-optically active devices emit light when they are functioning properly. Such PL is therefore related to the electrical function for which the device is engineered.

[0028] In one embodiment, the sample comprises an electro-optically active device. In a further such embodiment, the electro-optically active device comprises a micro-light-emitting diode (LED), and the PL comprises PL emitted by the micro-LED. (As used herein, the term "micro-LED" is defined as an LED less than 100 microns in size.) For example, one important novel feature of the embodiments described herein is that they provide a system capable of exciting and analyzing the PL emission of micro-LEDs. For certain electro-optically active semiconductor devices, such as micro-LEDs, quantum dots, and integrated photonics, absorbed photons can excite quantum states dissimilar to those normally achieved by electron or hole currents during the device's designed operation. In one example, PL emitted by a blue-emitting device is blue, PL emitted by a green-emitting device is green, and so on. Thus, PL can be used to probe the electro-optical properties of a device. Such PL can also be observed, detected, and used as described herein, even when the device is not yet completed and therefore not functional in its intended final form.

[0029] As further described herein, one important advantage of the embodiments described herein is their flexibility. For example, in some embodiments, PL does not include fluorescence. In other embodiments, PL includes fluorescence. In other words, the type of PL detected and then used to determine information about the sample can include any of the PL types described above, including multiple types simultaneously. In one such example, due to the cost and complexity of the systems described herein, it would be highly advantageous if the same tool could be used for different samples and / or different types of information could be determined for the same or different types of samples. If the system could be used to detect fluorescence from materials such as the foreign particles described above and also detect PL from at least partially formed electro-optically active devices, this could be extremely beneficial to system owners.

[0030] The flexibility of the embodiments described herein is not limited to simply different types of PL. For example, the embodiments described herein can be flexibly configured to detect only PL, a combination of PL and non-PL light, scattered light, and / or reflected light, etc. One or more types of such light can be detected simultaneously or sequentially, as further described herein. Additionally, information about the sample can be determined from any one or more types of such detected light. In other words, the same system can be configured to determine multiple types of information from one or more types of detected light. Whether different types of light are detected from a sample depends on the sample characteristics and the information to be determined, and whether different types of light can be simultaneously detected from a sample can vary depending on factors including, but not limited to, differences in signal level between samples, the emission spectrum wavelength range of the emitted light, etc.

[0031] Another possible use for the embodiments described herein is to detect different PLs for the same purpose. For example, the systems described herein can be used to detect different types of defects on a sample, some of which emit PL at different wavelengths, and / or one or more of which emit PL while others do not (meaning that they must be detected at the same wavelength as the illumination). In such cases, the systems described herein can be configured to separately detect the different types of light, and therefore the different types of defects, simultaneously or sequentially in the same manner as described above.

[0032] Another important difference between the embodiments described herein and other currently available systems and methods for detecting PL from a sample is that the embodiments described herein can interrogate the samples described herein at throughputs that can compete with those of currently used semiconductor yield-related tools, such as wafer inspection tools designed for production-worthy throughput. In other words, the embodiments described herein are configured, or can be configured, to detect PL and determine information from PL as quickly as any other inspection tool currently commercially available for semiconductor applications. One reason achieving such throughput with the embodiments described herein may be particularly challenging and require careful selection of system configuration is that the amount of light available for detection is likely much less than with currently available systems. For example, the amount of PL light emitted from the samples described herein may be substantially less than the amount of non-PL light scattered or reflected from most of these samples. More specifically, the PL quantum yield is less than 1, and PL light emits isotopically and is therefore partially collected by objectives with limited numerical apertures (NA). Therefore, detecting as much PL as possible in as short a time as possible becomes even more important for configuring systems that can be used for PL-related applications without adversely affecting overall process throughput.

[0033] One embodiment of a system configured to determine information about a sample is shown in FIG. 1. The system includes an illumination subsystem configured to direct light having one or more illumination wavelengths toward the sample. The illumination subsystem includes at least one light source, such as light source 16 and / or light source 34. The illumination subsystem is configured to direct light toward the sample at one or more angles of incidence, which may include one or more oblique angles and / or one or more normal angles. For example, as shown in FIG. 1, light from light source 16 is directed toward sample 14 through optical element 18 and then lens 20 at an oblique angle of incidence. The oblique angle of incidence may include any suitable oblique angle of incidence, which may vary depending on, for example, the characteristics of the sample. Light from light source 34 may be directed toward sample 14 through optical elements 36, beam splitters 38 and 26, and then lens 24 at a normal (or substantially normal) angle of incidence. If the angle at which light from light source 34 is directed toward the sample is not exactly normal, a substantially normal angle of incidence can be selected based on the characteristics of the sample.

[0034] The illumination subsystem may be configured to direct light toward the sample at different angles of incidence at different times. For example, the illumination subsystem may be configured to direct light from one light source toward the sample, then direct light from another light source toward the sample. The illumination subsystem may also, or alternatively, be configured to simultaneously direct light toward the sample at multiple angles of incidence. For example, the illumination subsystem may include multiple illumination channels, one of which may include light source 16, optical element 18, and lens 20, and the other of which may include light source 34, optical element 36, and lens 24. When light from multiple illumination channels is simultaneously directed toward the sample, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed toward the sample at different angles of incidence may be different such that light resulting from illuminating the sample at different angles of incidence can be separated from one another and detected separately by a detector.

[0035] The same illumination channel may also be configured to direct light with different characteristics to the sample at different times. For example, in some cases, optical elements 18 and 36 may be configured as spectral filters, and the properties of the spectral filters can be changed in a variety of different ways (e.g., by swapping spectral filters) so that different wavelengths of light can be directed to the sample at different times. The illumination subsystem may have any other suitable configuration known in the art for sequentially or simultaneously directing light with different or the same characteristics to the sample at different or the same angles of incidence.

[0036] In one embodiment, light sources 16 and 34 each include a broadband plasma (BBP) light source. Thus, the light generated by the light sources and directed toward the sample can include broadband light. However, the light sources may include any other suitable light source known in the art, such as any suitable laser, arc lamp, polychromatic LED, or the like, configured to generate light of any suitable wavelength known in the art. The light sources may also be configured to generate monochromatic or nearly monochromatic light. Thus, the light sources may be narrowband light sources. The light sources may also include polychromatic light sources that generate light of multiple discrete wavelengths or wavelength bands. Light sources 16 and 34 may also be the same type of light source, possibly with one or more different emission characteristics (e.g., lasers emitting different wavelengths), or different types of light sources (e.g., one light source may be a BBP light source and the other a laser). Additionally, the illumination subsystem may include different numbers of light sources, e.g., one or more light sources, and the light source used to direct light toward the sample may vary depending on the sample and information determined therefor, as further described herein.

[0037] The optimal wavelength range for the illumination subsystem may depend on the achievable light budget versus throughput and sensitivity requirements. In one embodiment, the one or more illumination wavelengths include red (R), green (G), blue (B), and ultraviolet (UV) wavelengths. For example, UV illumination can be added to bright-field (BF) and / or dark-field (DF) modes in existing R / G / B BF and / or DF illumination subsystems to enable the functionality described herein. The UV wavelengths may range from about 360 nm to about 405 nm. In some embodiments, a broadband light source producing light with wavelengths between 360 nm and 720 nm can be used, with one or more filters positioned in front of the light source depending on the sample being interrogated. For example, if only UV light is used on the sample, optical element 18 may optionally be a bandpass filter configured at 385 nm ± 13 nm. An illumination bandpass filter may not always be used and may not be as essential to the configurations described herein as other possible filters, such as a longpass filter in the detection subsystem. However, it may be important to use a bandpass filter for illumination for some samples, regardless of the presence or absence of a longpass filter in the detection subsystem. For example, even with color LED light sources, there can be long tails at the illumination wavelength that can prevent light from being detected with a sufficient signal-to-noise ratio. Additionally, PL signals can be substantially weak even under the best conditions, so leakage of illumination light into the detection subsystem can overwhelm them.

[0038] In some embodiments, the sample includes an electro-optically active device, and one or more illumination wavelengths are selected to be absorbable by the electro-optically active device to emit PL. Experimental data generated by the inventors has shown that UV illumination is typically required to excite PL emission for blue-emitting devices. It may be possible to use either UV or blue illumination, or a combination thereof, to excite green-emitting devices. It may be possible to use UV, blue, or green illumination, or a combination thereof, to excite red-emitting devices. Providing options in this regard may be important to optimize sensitivity and light budget.

[0039] In one embodiment, the one or more illumination wavelengths include R, G, and B wavelengths. For example, data generated by the inventors indicates that blue or green illumination is sufficient to excite some green or red light-emitting devices, respectively. Therefore, one possible configuration of the system does not include UV illumination and relies on existing B, G, and R illumination in commercially available systems, such as the Altair. While such a system cannot, for example, inspect blue light-emitting devices in the same way using the PL emitted from the device, this may be an acceptable trade-off in some circumstances. Such a system is less complex and less costly than a complete R / G / B / UV PL system. Thus, one important novel feature of the embodiments described herein is that they can be configured as R / G / B or R / G / B / UV systems optimized for electro-optically active devices and / or advanced packaging devices.

[0040] Light from optical element 18 may be focused onto sample 14 by lens 20, and light from optical element 36 may be focused onto sample 14 by lens 24. Although lenses 20 and 24 are shown in FIG. 1 as single refractive optical elements, in reality, lenses 20 and 24 may each include several refractive and / or reflective optical elements that combine to focus light from the respective optical elements onto the sample. The illumination subsystem shown in FIG. 1 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, apertures, etc., and may include any such suitable optical elements known in the art. Additionally, the system may be configured to vary one or more of the elements of the illumination subsystem based on the type of illumination used to determine information about the sample.

[0041] The system may also include a scanning subsystem configured to scan the light over the sample. For example, the scanning subsystem may include a stage 22 on which the sample 14 is positioned during processing. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including the stage 22) that may be configured to move the sample so that the light can be scanned over the sample. Additionally or alternatively, the system may be configured such that one or more optical elements perform some scanning of the light over the sample. The light may be scanned over the sample in any suitable manner, such as a serpentine path or a spiral path.

[0042] In one embodiment, the scanning subsystem is configured to scan light from the illumination subsystem over the specimen while PL is detected from the specimen at an in-line inspection throughput. For example, one important novel feature of the embodiments described herein is that they are capable of performing PL inspection at a sufficiently high throughput suitable for in-line inspection, i.e., inspection performed during or between semiconductor fabrication process steps. In this manner, the throughput achievable by the embodiments described herein may be comparable to what is sometimes referred to in the art as "production-worthy throughput." The embodiments described herein may be capable of achieving different throughputs depending on the emitted light being detected from the specimen. The embodiments are advantageously capable of achieving an in-line inspection throughput for electro-optically active devices, such as micro-LEDs, of about several wafers (300 mm wafer equivalent) per hour. Thus, the term "in-line inspection throughput," as used herein with respect to the inspection of electro-optically active devices, may be defined as 2 to 10 300 mm wafer equivalents per hour.

[0043] The term "wafer equivalent" is used herein to easily compare the throughput of system embodiments to other types of wafer inspection. For example, currently, most micro LEDs are fabricated on 6-inch sapphire wafer substrates. Some manufacturers are experimenting with using 8-inch and 12-inch silicon wafers to fabricate micro LEDs. Therefore, the embodiments described herein can be used to inspect specimens of such different sizes, and throughput will vary accordingly. To provide PL inspection throughput estimates for the embodiments described herein, the qualifier "300 mm equivalent" is used. If the embodiments described herein were used to inspect 6-inch sapphire wafers, throughput estimates would be in the high teens (e.g., approaching 20 wafers per hour).

[0044] The system also includes a detection subsystem configured to detect PL from the sample. The detection subsystem can include one or more detection channels. Generally, each detection channel includes a detector configured to detect light from the sample resulting from illumination of the sample by the illumination subsystem and generate an output in response to the detected light. For example, the detection subsystem shown in FIG. 1 includes two detection channels: one formed by lens 24, beam splitter 26, lens 28, element 30, and detector 32, and the other formed by lens 24, beam splitter 38, lens 40, element 42, and detector 44. The two detection channels may be configured to collect and detect light at different or the same collection angles. In some cases, the detection channel including detector 32 is configured to detect light scattered from the sample due to illumination by light from light source 16, and the detection channel including detector 44 is configured to detect light specularly reflected from the sample due to illumination by light from light source 34. Thus, the detection channel including detector 32 may be configured as a dark-field (DF) channel, and the detection channel including detector 44 may be configured as a bright-field (BF) channel. In other cases, as described further herein, the detection subsystem may be configured to detect only DF light or only BF light.

[0045] 1 shows one embodiment of a detection subsystem including two detection channels, the detection subsystem may include a different number of detection channels (e.g., only one detection channel or two or more detection channels). In one such case, the detection subsystem may include one or more DF channels and / or one or more BF channels. Thus, the detection subsystems described herein may be configured for DF-only, BF-only, or both DF and BF imaging (simultaneous or sequential).

[0046] In one embodiment, the illumination and detection subsystem is configured for both BF and DF imaging, and a computer subsystem, e.g., computer subsystem 46, is configured to select BF imaging only, DL imaging only, or both BF and DF imaging to determine information based on one or more properties of the sample. Thus, the embodiments described herein provide a system with BF / DF flexibility in addition to the other important flexibilities described herein. Thus, one novel and important feature of the embodiments described herein is that they are flexible BF / DF systems with multiple illumination and collection bands and modes for PL inspection and / or metrology.

[0047] The one or more characteristics of the sample can include any known or expected characteristics of the sample, such as whether a defect of interest (DOI) scatters more light than it reflects, the angle at which an electro-optically activated device is expected to emit light, or the height or sidewall angle of a structure on the sample that may affect whether scattered or reflected light is better for imaging. Considerations for the type and other modes of imaging can also take into account both sample characteristics of interest, e.g., defects expected to scatter light, as well as sample characteristics that affect light from the sample but are not of interest, e.g., strong reflections from structure edges. In this way, the configurations of the systems described herein used to determine information about the sample can be chosen to selectively detect certain light while avoiding or at least reducing the detection of other light, which is why the flexibility described herein is substantially important.

[0048] Although lenses 28 and 40 are shown in FIG. 1 as single refractive optical elements, each of the lenses may include one or more refractive optical elements and / or one or more reflective optical elements. Beam splitters 26 and 38 may have any suitable configuration known in the art. As shown in FIG. 1, lens 24 may be configured to 1) direct light from light source 34 toward the sample and 2) collect a) light scattered from the sample due to illumination by light from light source 16 and b) light specularly reflected from the sample due to illumination by light from light source 34. Thus, the detection channels may share a common lens. However, the detection channels may not share any common elements or may share multiple common elements (not shown; e.g., a common spectral filter, etc.). Elements 30 and 42 may each include any one or more suitable elements known in the art, such as apertures, spatial filters, analyzers, other polarizing elements or filters, spectral filters, etc. Additionally, although only one element is shown positioned in the path of the light to each of the detectors, multiple such elements can be used in each detection channel (such as a combination of spectral and spatial filters). Furthermore, in one or both detection channels, the positions of lens 28 and element 30, and lens 40 and element 42, may be switched so that the light passes through the element and then the lens.

[0049] In one embodiment, the detection subsystem includes a long-pass filter, e.g., element 30 and / or element 42, positioned before the detector configured to detect PL. Because most PL phenomena involve light emitted at wavelengths longer than the excitation light, a long-pass wavelength filter can be included in the collection path to block shorter wavelengths and pass longer wavelengths. For example, the detection subsystem can include a UV-blocking filter that blocks essentially all UV illumination bands while passing essentially all B, G, and R bands. In one such example, the long-pass filter can be a 425 nm long-pass filter. The UV / B-blocking filter blocks essentially all UV and blue bands while passing essentially all green and red bands. And the UV / B / G-blocking filter blocks essentially all UV, blue, and green bands while passing essentially all red bands.

[0050] There may be multiple filters in the path of the collected / detected light. Additionally or alternatively, beam splitter 26 and / or beam splitter 38 may be configured to perform wavelength-based filtering of the light collected by lens 24. To generate a color PL image, the detection subsystem may also include wavelength filters in the collection path that pass only specific bands, i.e., UV, B, G, or R. In some cases, the illumination subsystem may include a bandpass filter in the illumination path to prevent illumination light from leaking into the collection path.

[0051] Configuring the system with a combination of filters and illumination wavelengths, as described further herein, allows the system great flexibility in covering a wide range of PL phenomena. In one embodiment, the illumination subsystem is configured to direct light having multiple illumination bands toward the sample, the detection subsystem is configured to detect light having multiple detection bands from the sample, and the computer subsystem is configured to select one or more of the multiple illumination bands and one or more of the multiple detection bands to be used to determine information based on one or more characteristics of the sample. The computer subsystem can be configured to select the illumination and detection bands as described further herein. During operation, the computer subsystem can generate a recipe specifying the particular PL bands and modes to be used for a particular sample. If necessary, multiple scans can be performed to collect the required image data.

[0052] The system embodiments described herein allow for several levels of hardware implementation, ranging from relatively simple with fewer features and capabilities to more complex with more capabilities. In one such example, a computer subsystem can generate a recipe for detecting PL resulting from blue illumination in an existing R / G / B system by adding a long-pass PL filter to the collection optics. This configuration likely cannot inspect blue-emitting devices, but can inspect green or red-emitting devices. In another example, a computer subsystem can add UV illumination in out-of-lens (OTL) DF mode coupled with a long-pass PL filter on the R / G / B collection optics. In this case, both blue and / or UV illumination can be used. In a further example, a system may be configured by adding UV through-the-lens (TTL) optics in addition to UV OTL illumination to an existing R / G / B BF / DF-enabled system coupled with a long-pass PL filter. This configuration is the most capable.

[0053] Lenses 20 and 24 are shown in FIG. 1 as distinct optical elements. In this case, the illumination channel including light source 34 and the detection channel that detects light in response to illumination by that illumination channel are configured as TTL optics. The illumination channel including light source 16 and the detection channel that detects light in response to illumination by that illumination channel are configured as OTL optics. However, in some configurations, lenses 20 and 24 may be one or more of the same optical elements (not shown). In such cases, all of the illumination and detection channels may be configured as TTL optics. However, the illumination subsystem may be further configured such that all of the illumination channels are configured for OTL illumination (not shown). In such cases, the illumination channel including light source 34 may include a lens that directs light toward the sample, which may be lens 20 or another separate lens (not shown) positioned outside the path of light collected and detected from the sample. In either case, the light from light sources 16 and 34 may be directed toward the sample at different angles of incidence.

[0054] Another potentially attractive configuration for some of the samples described herein is a DF configuration with UV and / or blue illumination. In such a configuration, the illumination may be symmetric with respect to the plane of incidence. For example, the embodiments described herein may use double-sided illumination, dual or full illumination, or ring illumination to eliminate edge shadows in sample images generated by the system. Such illumination may be most practical in an OTL configuration. Thus, as can be seen from the configuration description, due to the flexible illumination and flexible collection / detection subsystems described herein, there are a substantially large number of optical modes that can be used with the embodiments described herein. In another such example, asymmetric illumination may be more suitable for some samples than symmetric illumination, and the embodiments described herein can be configured for such illumination.

[0055] The one or more detection channels can include any suitable detector known in the art, such as a photomultiplier tube (PMT), a charge-coupled device (CCD), and a time-delay integration (TDI) camera. The detector may also be capable of detecting one or more wavelength ranges described herein, such as UV and / or visible. One example of a suitable detector is a color CCD camera. In one embodiment, one or more of the detection channels includes a spectrometer configured to measure the spectrum of the emitted light. The spectrometer may have any suitable configuration known in the art. Data collected by the inventors and further described herein indicates subtle spectral shifts between devices that can be used for diagnostics.

[0056] The detectors may also include non-imaging detectors or imaging detectors. When the detectors are non-imaging detectors, each detector may be configured to detect a particular characteristic of the scattered light, such as intensity, but may not be configured to detect such a characteristic as a function of position in the imaging plane. Thus, the output generated by each detector included in each detection channel may be a signal or data, but not an image signal or image data. In such cases, a computer subsystem, such as computer subsystem 46, may be configured to generate an image of the sample from the non-imaging output of the detector. However, in other cases, the detector may be configured as an imaging detector configured to generate an image signal or image data. Thus, the system may be configured to generate an image in several ways.

[0057] A computer subsystem, such as computer subsystem 46, may also include image acquisition software configured to collect images under various appropriate illumination and collection wavelength bands. Depending on the optical system configuration, multiple scans may be used to acquire all desired data.

[0058] FIG. 1 is provided herein to generally illustrate various configurations of illumination and detection subsystems that may be included in system embodiments described herein. Clearly, the system configurations described herein can be modified to optimize the performance of the system, as is typically done when designing commercial systems. Additionally, the systems described herein can be implemented using existing systems (e.g., by adding the functionality described herein to the existing system), such as the Altair and 29xx / 39xx series of tools commercially available from KLA. For some such systems, the embodiments 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 “from scratch” to provide an entirely new system.

[0059] In one such example, the embodiments described herein can be applied in a relatively straightforward manner to some tools that already provide a wide range of illumination wavelengths, for example, via a BBP light source. In such cases, a PL filter can be added to the tool in addition to any suitable image acquisition capabilities, for example, via software and / or algorithms implemented on a computer subsystem.

[0060] In another example, PL emission is isotropic regardless of illumination direction. Therefore, PL detection can be implemented on currently used platforms, including DF platforms, without disrupting the current architecture. In one such example, a small external near-ultraviolet (NUV) DF illuminator can be added to some architectures below the optics plate. Additionally, a long-pass filter can be easily added in front of the detector.

[0061] The embodiments described herein can also be implemented by augmenting blue LED-enabled inspection tools with the PL detection capabilities described herein. The embodiments may also be implemented by modifying existing systems to enable PL inspection of blue LED wafers and increase PL inspection throughput.

[0062] The illumination and detection subsystems may be further configured as described in U.S. Pat. No. 7,782,452, issued Aug. 24, 2010 to Mehanian et al., and U.S. Pat. No. 8,218,221, issued July 10, 2012 to Solarz, and U.S. Patent Application Publication No. 2009 / 0059215, published March 5, 2009, by Mehanian et al., which are incorporated by reference as if fully set forth herein. The embodiments described herein may be further configured as described in these references.

[0063] The computer subsystem 46 may be coupled in any suitable manner (e.g., via one or more transmission media, which may include "wired" and / or "wireless" transmission media) to the detectors of the detection subsystem so as to receive output generated by the detectors during illumination and possibly scanning of the sample. The computer subsystem 46 may be configured to use the detector output to perform several functions described further herein.

[0064] The computer subsystem shown in FIG. 1 (as well as other computer subsystems described herein) may also be referred to herein as a computer system. Each of the computer subsystems or systems described herein may take a variety of forms, including a personal computer system, an image computer, a mainframe computer system, a workstation, a network appliance, an Internet appliance, or other device. In general, the term "computer system" may be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium. A computer subsystem or system may also include any suitable processor known in the art, such as a parallel processor. In addition, a computer subsystem or system may include a computer platform with high-speed processing and software, either as a stand-alone or network tool.

[0065] When a system includes multiple computer subsystems, the different computer subsystems may be coupled to one another such that images, data, information, instructions, etc. may be transmitted between the computer subsystems. For example, computer subsystem 46 may be coupled to computer system 102, as shown by the dashed line in Figure 1, by any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more such computer subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

[0066] As described further herein, the illumination and detection subsystem may be configured to generate an output, e.g., an image, of the sample having multiple modes. Generally, a "mode" is defined by the values of the parameters of the illumination and detection subsystem used to generate the output for the sample. Thus, the modes may differ in the values of at least one of the parameters of the illumination and detection subsystem (other than the location on the sample where the output is generated). For example, in the optical subsystem, different modes may use different wavelengths of light for illumination. The modes may differ in illumination wavelength (e.g., by using different light sources, different spectral filters, etc. for the different modes), as described further herein. In another example, different modes may use different illumination channels of the illumination subsystem. For example, as described above, the illumination subsystem may include multiple illumination channels. Thus, different illumination channels may be used for different modes. The modes may also, or alternatively, differ in one or more collection / detection parameters of the detection subsystem. The modes may differ in any one or more modifiable parameters of the system (e.g., illumination polarization, angle, wavelength, etc., detection polarization, angle, wavelength, etc.). The illumination and detection subsystems may be configured to scan the sample in different modes in the same scan or in different scans, for example, depending on the ability to simultaneously scan the sample using multiple modes.

[0067] The systems described herein and illustrated in FIG. 1 can be modified in one or more parameters to provide different capabilities depending on the application for which they are used. In one embodiment, the system is configured as an inspection system. In another embodiment, the system is configured as a metrology system. For example, the illumination and detection subsystems illustrated in FIG. 1 may be configured to have higher resolution when used for metrology rather than inspection. In another example, the system may be configured to implement different scanning methods for inspection versus metrology. In other words, the system embodiment illustrated in FIG. 1 describes various configurations for the system that can be adjusted in several ways that will be apparent to those skilled in the art to produce systems with different capabilities that are more or less suitable for different applications.

[0068] In some embodiments where the system is configured as an inspection system, the inspection system is configured for macro inspection. As such, the systems described herein may be referred to as macro inspection tools. Macro inspection tools are particularly suited to inspecting relatively noisy back-end-of-line (BEOL) layers, such as redistribution wiring (RDL) and post-dice applications. Macro inspection tools are defined herein as systems having a spatial resolution of about 200 nm to about 2.0 microns or greater, not necessarily diffraction-limited. Such spatial resolution means that the smallest defect such a system can detect has dimensions greater than about 200 nm, which is much larger than the smallest defect that can be detected by today's commercially available state-of-the-art inspection tools, and thus the "macro" inspector designation. Such systems tend to utilize longer wavelengths of light (e.g., about 500 nm to about 700 nm) compared to today's commercially available state-of-the-art inspection tools. These systems may be used when the DOI has a relatively large size.

[0069] As described above, the system may be configured to scan light across a physical version of the sample, thereby generating an output about the physical version of the sample. In this manner, the system may be configured as a “real” system rather than a “virtual” system. However, the storage medium (not shown) and computer system 102 shown in FIG. 1 may be configured as a “virtual” system. In particular, the storage medium and computer system may be configured as a “virtual” inspection system such as those described in U.S. Pat. No. 8,126,255, issued February 28, 2012 to Bhaskar et al., and commonly assigned U.S. Pat. No. 9,222,895, issued December 29, 2015 to Duffy et al., both of which are incorporated by reference as if fully set forth herein. The embodiments described herein may be further configured as described in these patents.

[0070] A computer subsystem, such as computer subsystem 46 and / or computer system 102, is configured to determine information about the sample from output generated by the detection subsystem in response to the detected PL. Generally, the information determined by the computer subsystem based on the detection subsystem output may be information such as any test and / or measurement as described herein. Additionally, the information determined about the sample based on the detection subsystem output may be a combination of multiple types of information described herein.

[0071] The computer subsystem may be configured to analyze the PL response output and extract device and / or defect information from the image. Important PL information for both individual devices or sample regions containing multiple devices includes, but is not limited to, (1) absolute emission intensity, (2) intensity emitted into different wavelength bands, (3) relative changes in intensity emitted into different bands (i.e., color shift), (4) absolute or relative spectrum, (5) relative changes in intensity emitted into different cone angles, (6) intensity variation as a function of illumination light level (leakage effect), and (7) relative changes in intensity between different materials within the image.

[0072] In one such example, FIG. 5 is a plot of the PL emission spectra for one abnormal micro LED, i.e., a "dark pixel," and a normal micro LED, i.e., a "normal pixel." As illustrated by the emission spectra plotted in FIG. 5, the emission spectra of the abnormal and normal micro LEDs are sufficiently different from one another that they can be used to reveal differences in material and / or structure. In other words, by comparing the emission spectra of micro LEDs to one another, differences between micro LEDs can be detected. In addition, comparing the emission spectrum of a micro LED to the emission spectrum of a known "good" micro LED (a "reference" spectrum) can be used to detect abnormal micro LEDs. In either case, differences between only a portion of the spectra can be used for the applications described herein. For example, when there is a strong difference between the spectra at longer wavelengths, as is the case with the emission spectra shown in FIG. 5, that difference can be used by embodiments described herein even when there are other differences between the spectra (such as a shift in the wavelength of the peak emission intensity from 522.26 nm to 518.73 nm). Thus, by configuring the illumination and detection subsystems described herein to be capable of detecting and generating outputs in response to the emission spectra of the micro LEDs, and by configuring the computer subsystems described herein to compare the emission spectra with each other or with known good references, information about the micro LEDs, such as which micro LEDs are defective in material and / or construction, can be determined without the need to electrically test the completed micro LEDs.

[0073] The computer subsystem may also, or alternatively, be configured to analyze a PL macroscopic image (MOI) of the entire sample or wafer. The computer subsystem can generate the MOI by stitching together multiple PL images based on various spatial relationships between the individual images. Important PL information about the entire wafer that can be generated by the computer subsystem includes, but is not limited to, (1) intensity variation across the wafer, (2) emission spectrum variation across the wafer, (3) emission cone angle variation across the wafer, (4) intensity variation between different wafers, particularly between wafers from the same batch of epitaxy processes, (5) emission spectrum variation between different wafers, particularly between wafers from the same batch of epitaxy processes, and (6) emission cone angle variation between different wafers, particularly between wafers from the same batch of epitaxy processes.

[0074] In one embodiment, determining the information includes detecting defects on the specimen based on output generated by the detection subsystem in response to the detected PL. In this manner, embodiments described herein can be configured for defect detection using PL techniques. For example, defect detection may be performed using any of the information described above. Defect detection can be performed using either absolute values or relative comparisons (e.g., device-to-device, region-to-region, etc.). In one such example, the computer subsystem can compare the absolute emission intensity for each device to threshold(s), which can correspond to a range of absolute emission intensity below (or possibly above) the nominal or designed absolute emission intensity that is unacceptable for the device. If a device has an absolute emission intensity that is lower or higher than acceptable, this can be detected by the computer subsystem via such a comparison. Other algorithms and methods can also be used to determine which devices are defective (e.g., finding devices with outlying absolute emission intensities compared to other devices on the specimen). Additionally, the embodiments described herein may use any suitable defect detection algorithm known in the art that may be applied to the PL response output (image or otherwise) or that may be modified to operate on the PL response output and generate information such as a defect map, a heat map, or any other suitable defect-related information about the specimen.

[0075] In one such embodiment, determining the information includes determining a characteristic of the functionality of the electro-optically active device. The characteristic of functionality may simply be an indication of whether the device is fully functional, i.e., emits some light and thus appears to be functional, or whether it emits no light at all and therefore appears not to be functional. However, the characteristic of functionality may be qualitative or quantitative in one or more additional or other ways. One example of these qualitative characteristics may be whether the device emits the correct wavelength of light. Quantitatively, these characteristics may include how much the wavelength of the emitted light differs from the desired or expected wavelength of light, the brightness difference between the emitted light and the expected light, and other quantitative measures of emitted light as further described herein. The characteristic of functionality may be determined for any or all of the devices examined by the embodiments described herein and used as further described herein to determine which devices are defective.

[0076] 6 and 7 illustrate how color shifts detectable using PL response outputs generated as described herein can be used to detect color shifts and / or variations between devices. In particular, FIG. 6 shows an image of a sample 600 having multiple green light-emitting devices 602 formed thereon, which can be generated by embodiments described herein. More specifically, the image shown in FIG. 6 can be generated by illuminating the green light-emitting devices with one or more UV illumination wavelengths and detecting the PL (and possibly other light) emitted by the devices. A computer subsystem can then use this image to perform defect detection, for example, by detecting any areas in the image that emit light that differs from the expected wavelength of light. Defects 604 illustrate some exemplary defects that can be detected on such green light-emitting devices, which can include defects of various sizes and defects that emit yellow or dim green light (e.g., green light outside the expected or acceptable green wavelength range). Accordingly, embodiments described herein can detect defects of various characteristics on green light-emitting devices by illuminating the device with UV light and detecting the resulting color shift in the detected PL.

[0077] FIG. 7 shows an image of a sample 700 having multiple blue light-emitting devices 702 formed thereon that can be produced by embodiments described herein. More specifically, the image shown in FIG. 7 can be produced by illuminating the blue light-emitting devices with one or more UV illumination wavelengths and detecting PL (and possibly other light) emitted by the devices. The computer subsystem can then use this image to perform defect detection, for example, by detecting any areas in the image that emit light differently from the expected wavelength, any areas that have varying sizes, and / or any areas that emit light differently from the expected brightness for the expected wavelength of light. For example, the shading of most devices 702 indicates devices that have been determined to have a normal (or acceptable) size, brightness, and color. Devices with the same light shading as device 704 are devices that are normal size and color but not normal brightness, i.e., they are defective only because they are not as bright as they should be. Devices with the same dark shading as devices 706 and 708 are devices that are normal size and color but brighter than they should be. Devices with the same pattern filling as device 710 are normal size and brightness, but not normal color, e.g., they emit green light instead of blue light. Additionally, devices with the same pattern filling as device 712 are normal size, but not normal color or brightness, e.g., they emit green light instead of blue light, and are brighter than they should be.

[0078] The above-described functionality of an electro-optically active device can also be investigated at multiple illumination wavelength bands or wavelengths. For example, FIG. 8 is a plot of PL emission spectra under different excitation wavelengths, including 365 nm (at normal incidence), 385 nm, 405 nm (at normal incidence), and 415 nm (at normal incidence). The PL emission spectra can be normalized to the number of incident photons of the illumination light to more accurately compare and contrast emission spectra. As seen in plot 800, the same electro-optically active device can produce different PL emission spectra when illuminated with different excitation wavelengths. Each (or one or more) of these PL emission spectra can be generated by the embodiments described herein and used to determine information about the electro-optically active device, such as functionality, detected defects, and defect characteristics. Additionally, such PL emission spectra demonstrate how the flexibility of the optical systems of the embodiments described herein can be useful not only for detecting multiple PL emission spectra from the same device, but also for selecting from the various optical system setups and configurations described herein to determine as much or as little information as needed for any one device.

[0079] In another such embodiment, determining the information also includes identifying one or more of the electro-optically active devices that are anomalous based on the characteristics of their functionality. For example, one novel feature of the embodiments described herein is that the system can use PL emission to identify anomalous individual electro-optical devices or areas of the wafer containing anomalous devices. Figure 2 shows an example image of a micro-LED wafer showing anomalous regions. In particular, image 200 is a standard (i.e., non-PL) BF image of a micro-LED wafer that shows no features. In contrast, PL image 202 clearly shows anomalous regions of emission that are either less than or greater than acceptable.

[0080] Image 300 in Figure 3 is an image generated by zooming in on one of the anomalous regions shown in image 202. Each of the squares in this image may be an individual micro LED. When the computer subsystem zooms in on the anomalous region in the PL image, as shown in image 300, the computer subsystem can determine that the anomalous region actually corresponds to multiple devices on the wafer. In this way, the computer subsystem can obtain specific pixels in the image of the sample and then zoom in to reveal more detail, which may be useful in determining which pixels are actually emitting light.

[0081] FIG. 4 illustrates how a computer subsystem can generate a composite image from portions of multiple devices to enhance abnormal regions, thereby making them easier to detect and analyze. For example, the computer subsystem can generate a composite image 406 using only pixels in raw image 400 that are near the center of each device (active area 402, but not edge area 404) and assign an average to that device. Each pixel in the composite image represents one device. Darker regions are clearly visible. In another example, the computer subsystem can generate a composite image 410 using only pixels in raw image 408 that are near the edge of each device (edge area 404, but not active area 402) and assign an average to that device. Each pixel in composite image 410 also represents one device, with brighter regions clearly visible. In this way, the computer subsystem can analyze the functionality of different portions of the devices described herein, as well as how functionality differs between devices or between regions on a sample.

[0082] In some such embodiments, the electro-optically active devices are unfinished devices that cannot be electrically tested. For example, one major advantage of the embodiments described herein is that they provide PL capabilities that can be used to detect subtle material variations between devices or across wafers that affect PL emission. These variations may indicate local defects or process variations that may not be detected until electrical testing once the wafer is fully processed. By detecting these deviations early, users can take corrective action quickly, saving time and money. Additionally, the embodiments described herein use PL to sort or screen all micro LEDs on a wafer at production-worthy throughput before mass-transferring them to final display devices, at which point they can be electrically probed.

[0083] In one embodiment, the sample includes one or more packaging structures formed thereon, and the PL includes PL emitted by the one or more packaging structures. Accordingly, one important novel feature of the embodiments described herein is that they generally provide systems configured to excite and analyze the PL (or fluorescence) emission of advanced packaging devices. Recent years have seen an acceleration of advanced packaging techniques that make mass production of complex mobile devices and high-performance computing processors feasible. Once these devices are produced, they need to be inspected. Therefore, inspection of advanced packaging structures is a growing and important application area. The embodiments described herein offer significant advantages for such applications, as they can provide all of the advantages described herein for inspecting these packaging structures.

[0084] In one such embodiment, determining the information includes determining whether any of the one or more packaging structures are abnormal based on the detected PL. For example, one novel feature of the embodiments described herein is that the system can use PL emission to identify abnormal advanced packaging devices or areas of a wafer containing abnormal devices. For example, some advanced semiconductor packaging materials, such as PI and PBO, emit fluorescence, while metals do not. Therefore, PL inspection can be used to increase the capture rate of certain hard-to-find defects. In the embodiments described herein, the system can be configured to selectively detect fluorescence from illuminated samples for illumination wavelengths that can induce fluorescence from such materials and from illuminated samples having such advanced packaging structures formed thereon. The computer subsystem can then detect defects on the sample based on the output responsive to the fluorescence. For example, the detected fluorescence can be used to determine information about the fluorescing structures and / or materials, such as location, size, and shape. The computer subsystem can then apply a defect detection method to the information, e.g., applying a threshold to the size of the fluorescent structure to determine whether the fluorescent structure is large enough to be considered a defect. Instead of applying the defect detection method to information determined from the fluorescence response output, the defect detection method can be applied to the fluorescence output itself. Such defect detection may include applying one or more thresholds to the characteristics of the fluorescent response output, which may include any of the PL response output characteristics described further herein.

[0085] In another embodiment, determining the information includes determining metrology information about one or more structures formed on the sample based on output generated by the detection subsystem in response to the detected PL. For example, the computer subsystem may be configured to analyze the PL response output and extract critical dimension (CD) information from the image. CD information may include, but is not limited to, (1) size and shape of the micro-LED light extraction window, (2) size and shape of the micro-LED mesa, (3) micro-LED pitch, (4) RDL width and pitch, (5) via dimensions, (6) photoresist opening dimensions, and (7) overlay. The computer subsystem may be configured to determine such metrology information about the sample using any suitable method and / or algorithm known in the art.

[0086] In further embodiments, the illumination subsystem, the detection subsystem, and the computer subsystem are configured to simultaneously determine information and perform non-PL inspection of the specimen. As used herein, the term "non-PL inspection" is defined as inspection performed by detecting light from the specimen having the same wavelength as the illumination wavelength and detecting defects on the specimen based on an output in response to the detected light. For example, the system may be configured to perform any of the PL-related functions described above simultaneously with conventional optical inspection. The system may be configured to perform non-PL or conventional inspection of the specimen in any suitable manner known in the art.

[0087] In one such case, as further described herein, light from the sample having the same wavelength as the illumination and PL from the sample can be separately detected. The computer subsystem can be configured to separately use the different outputs to determine information about the sample. For example, the computer subsystem can apply a first defect detection algorithm to the PL response output and a second defect detection algorithm to the non-PL response output. The first and second defect detection algorithms can be the same or different in any one or more parameters, and the computer subsystem can apply the first and second defect detection algorithms to the different outputs simultaneously or at different times.

[0088] In some cases, determining information from PL and non-PL inspections may be performed using the same method or algorithm (e.g., when one defect detection method can be used to detect defects on a specimen using both PL and non-PL response outputs). However, in many cases, the information determined using PL and non-PL is likely to be different, so the computer subsystem may use different methods or algorithms to determine information using PL and non-PL response signals, even if it simply means detecting different types of defects on a specimen using PL and non-PL outputs.

[0089] The computer subsystem may also be configured to simultaneously process images (PL and / or non-PL) in a more conventional manner to detect traditional optical inspection defects such as bridges, opens, residues, overetching, underetching, fallen particles, etc. Thus, PL capability may be an add-on feature that can be enabled or disabled depending on the application and does not adversely affect throughput or sensitivity if not used.

[0090] While different inspections may typically be performed to detect different types of defects on the same specimen, in some cases, different inspections may be performed to detect the same type of defect on a specimen. For example, conventional defect inspection can be used to detect as many defects as possible on a specimen, which may include some defects that do not emit PL under all circumstances, and possibly some defects. PL inspection may also be performed on a specimen (possibly simultaneously, as described herein) for several reasons, including to detect defects on the specimen that emit PL and may be missed by conventional inspection, and / or to separate detected defects into those that do and do not emit PL. In this way, the results of PL inspection performed in combination with conventional inspection can be used as a type of additional defect attribute that can be used to separate different defect types from each other. The same is true for conventional inspection defect attributes used as a supplement to PL-based defect attributes. In this way, PL inspection and non-PL inspection can be used as different modes in the inspection process, and can be performed similarly to any other multi-mode inspection process currently being implemented.

[0091] Similarly, the systems described herein may be configured to perform inspection with PL while performing conventional metrology, or vice versa. In some cases, performing inspection and metrology simultaneously may not make sense due to the different measurement times typically required for such processes; however, if the metrology can be performed substantially quickly, e.g., at the same or approximately the same throughput as the inspection, such a system configuration becomes more practical. Another possibility is to perform PL measurements while simultaneously or otherwise performing non-PL measurements on the same sample. For example, it may make sense to determine a first metrology characteristic of a patterned feature on the sample using non-PL measurements and a second metrology characteristic of the same feature using PL measurements. In another example, a system may be configured to determine a metrology characteristic of a first patterned feature on the sample using non-PL measurements and a second patterned feature on the sample using PL measurements. In a further example, a system may be configured to determine the same metrology characteristic of a patterned feature on the sample using a combination of PL and non-PL response outputs. In this way, the flexibility of the systems described herein allows the embodiments described herein to provide the ability to determine more metrology information about a sample, which may be better (e.g., more accurate, more detailed, etc.) than currently available metrology tools.

[0092] The computer subsystem can be configured to generate results for the sample that can include any of the information described herein, such as information about any of the devices determined to be defective, any of the defects or metrology information described herein, a map of defects or metrology information for the entire sample, etc. The results for the defective devices can include, but are not limited to, information about the location of the defective devices, a detection score, a defective device classification such as a class label or ID, or any such suitable information known in the art. The results for the sample can be generated by the computer subsystem in any suitable manner.

[0093] All of the embodiments described herein may be configured to store the results of one or more steps of the embodiment on a computer-readable storage medium. The results may include any of the results described herein and may be stored in any manner known in the art. The results for a sample may have any suitable form or format, such as a standard file type. The storage medium may include any storage medium described herein or any other suitable storage medium known in the art. After the results are stored, they may be accessed from the storage medium, used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, system, or the like to perform one or more functions on the sample or another sample of the same type.

[0094] Such functions include, but are not limited to, modifying a process, such as a fabrication process or step, that has been performed or will be performed on the specimen, such as in a feedback or feedforward manner. For example, the computer subsystem may be configured to determine one or more modifications to a process that has been performed on the specimen and / or that will be performed on the specimen based on the defective devices. The modifications to the process may include any suitable modifications to one or more parameters of the process. The computer subsystem preferably determines the modifications such that they can reduce or prevent defective devices on other specimens on which the revised process is performed, can correct or eliminate defective devices on the specimen in another process performed on the specimen, can compensate for the defective devices in another process performed on the specimen, etc. The computer subsystem may determine such modifications in any suitable manner known in the art.

[0095] These changes can then be transmitted to a semiconductor fabrication system (not shown) or a storage medium (not shown) accessible to both the computer subsystem and the semiconductor fabrication system. The semiconductor fabrication system may or may not be part of the system embodiments described herein. For example, the imaging hardware and / or computer subsystems described herein may be coupled to the semiconductor fabrication system via one or more common elements, such as, for example, a housing, a power supply, a sample processing device or mechanism, etc. The semiconductor fabrication system may include any semiconductor fabrication system known in the art, such as a lithography tool, an etch tool, a chemical-mechanical polishing (CMP) tool, a deposition tool, etc.

[0096] Each of the embodiments of each of the systems described above may be combined into one single embodiment.

[0097] Another embodiment relates to a method for determining information about a sample. The method includes directing light having one or more illumination wavelengths toward the sample, e.g., using an illumination subsystem configured as described herein. The method also includes detecting PL from the sample, e.g., using a detection subsystem configured as described herein. Additionally, the method includes determining information about the sample from an output in response to the detected PL, e.g., using a computer subsystem configured as described herein.

[0098] Each of the method steps can be performed as further described herein. The method can also include any other steps that can be performed by the system, computer subsystem, and / or illumination and detection subsystems described herein. The computer subsystem, illumination subsystem, and detection subsystem can be configured according to any of the embodiments described herein, such as computer subsystem 46, the illumination subsystem shown in FIG. 1, and the detection subsystem shown in FIG. 1, respectively. In addition, the above-described method can be performed by any of the system embodiments described herein.

[0099] An additional embodiment relates to a non-transitory computer-readable medium storing program instructions executable on one or more computer systems to perform a computer-implemented method for determining information about a sample. One such embodiment is shown in Figure 9. In particular, as shown in Figure 9, a non-transitory computer-readable medium 900 includes program instructions 902 executable on a computer system 904. The computer-implemented method can include any step of any of the methods described herein.

[0100] Program instructions 902 implementing the methods as described herein may be stored on a computer-readable medium 900. The computer-readable medium may be a storage medium such as a magnetic or optical disk, magnetic tape, or any other suitable non-transitory computer-readable medium known in the art.

[0101] The program instructions may be implemented in any of a variety of ways, including procedure-based techniques, component-based techniques, and / or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes (“MFC”), SSE (Streaming SIMD Extensions), or other technologies or methodologies, as appropriate.

[0102] The computer system 904 may be configured according to any of the embodiments described herein.

[0103] Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. For example, methods and systems for determining information about a sample are provided. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those shown and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, as would be apparent to all skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention, as set forth in the following claims.

Claims

1. A system configured to determine information about a sample, An illumination subsystem comprising a bright-field (BF) illumination channel and a dark-field (DF) illumination channel, configured to direct light having one or more illumination wavelengths onto a sample, wherein the BF illumination channel is further configured to direct the light onto a first region on the sample, while the DF illumination channel is further configured to direct the light onto a second region on the sample spatially separated from the first region, the BF illumination channel is further configured to direct the light onto the sample through a lens, and the DF illumination channel is further configured to direct the light onto the sample at an inclined incidence angle without passing through the lens, and one or more parameters of the illumination subsystem are selected to cause the sample to emit photoluminescence. A detection subsystem configured to simultaneously and separately detect photoluminescent and non-photoluminescent light from the sample, A computer subsystem configured to determine information about a sample by detecting a first type of defect on the sample only from the output generated by the detection subsystem in response to the detected photoluminescence, and by detecting a second type of defect on the sample only from the output generated by the detection subsystem in response to the detected non-photoluminescent light. A system equipped with these features.

2. The system according to claim 1, wherein the one or more illumination wavelengths include red, green, and blue wavelengths.

3. The system according to claim 1, wherein the one or more illumination wavelengths include red, green, blue, and ultraviolet wavelengths.

4. The system according to claim 1, wherein the sample comprises an electro-optically active device, and one or more illumination wavelengths are selected to be absorbable by the electro-optically active device, thereby causing the electro-optically active device to emit the photoluminescence.

5. The system according to claim 4, wherein determining the information includes determining the functional characteristics of the electro-optically active device from the output generated by the detection subsystem in response to the detected photoluminescence.

6. The system according to claim 5, wherein determining the information further comprises identifying one or more of the electro-optically active devices that are abnormal based on the characteristics of the functionality.

7. The system according to claim 4, wherein the electro-optically active device is an unfinished device that cannot be electrically tested.

8. The system according to claim 4, wherein the electro-optically active device comprises a microlight-emitting diode, and the detected photoluminescence includes photoluminescence emitted by the microlight-emitting diode.

9. The system according to claim 1, wherein the photoluminescence does not contain fluorescence.

10. The system according to claim 1, wherein the photoluminescence includes fluorescence.

11. The system according to claim 1, wherein the sample comprises one or more packaging structures formed thereon, and the photoluminescence comprises photoluminescence emitted by the one or more packaging structures.

12. The system according to claim 11, wherein determining the information includes determining whether any of the one or more packaging structures is abnormal based on the detected first type of defect.

13. The system according to claim 1, wherein the detection subsystem is further configured for both bright-field and dark-field imaging, and the computer subsystem is further configured to select bright-field imaging only, dark-field imaging only, or both bright-field and dark-field imaging in order to determine the information based on one or more characteristics of the sample.

14. The system according to claim 1, wherein the illumination subsystem is further configured to direct light having a plurality of illumination bands onto the sample, the detection subsystem is further configured to detect light having a plurality of detection bands from the sample, and the computer subsystem is further configured to select one or more of the plurality of illumination bands and one or more of the plurality of detection bands used to determine the information based on one or more characteristics of the sample.

15. The system according to claim 1, wherein determining the information includes determining measurement information about one or more structures formed on the sample based on the output generated by the detection subsystem in response to the detected photoluminescence.

16. The system according to claim 1, further comprising a scanning subsystem configured to scan the light from the illumination subsystem over the sample while the photoluminescent and non-photoluminescent light are being detected from the sample at in-line inspection throughput.

17. The system according to claim 1, wherein the detection subsystem comprises a long-pass filter positioned in front of a detector configured to detect photoluminescence.

18. A method for determining information about a sample, The method involves directing light having one or more illumination wavelengths onto a sample using a BF illumination channel and a DF illumination channel, wherein the BF illumination channel is configured to direct the light onto a first region on the sample, while the DF illumination channel directs the light onto a second region on the sample spatially separated from the first region, the BF illumination channel is further configured to direct the light onto the sample through a lens, and the DF illumination channel is further configured to direct the light onto the sample at an inclined incidence angle without passing through the lens, and one or more parameters of the light are selected to cause the sample to emit photoluminescence. To simultaneously and separately detect photoluminescent and non-photoluminescent light from the aforementioned sample, To determine information about the sample by detecting a first type of defect on the sample only from the output in response to the detected photoluminescence, and detecting a second type of defect on the sample only from the output in response to the detected non-photoluminescent light. Methods that include...

19. The system according to claim 1, wherein the detection subsystem is further configured for both bright-field and dark-field imaging of the non-photoluminescent light from the sample, and the output in response to the detected non-photoluminescent light, used solely for detecting the second type of defect, includes an output in response to the non-photoluminescent light detected by the bright-field imaging alone, the dark-field imaging alone, or both the bright-field imaging and the dark-field imaging.

20. The system according to claim 1, wherein the detection of the non-photoluminescent light separately and simultaneously includes bright-field imaging, the detected photoluminescence includes fluorescence, the one or more illumination wavelengths include one or more ultraviolet wavelengths, and the detection subsystem comprises a dichroic beam splitter configured to direct the fluorescence to a first detector and the non-photoluminescent light to a second detector.

21. The system according to claim 1, wherein the detection of the non-photoluminescent light separately and simultaneously includes bright-field imaging, the detected photoluminescence includes fluorescence, the one or more illumination wavelengths include one or more blue wavelengths, and the detection subsystem comprises a dichroic beam splitter configured to direct the fluorescence to a first detector and the non-photoluminescent light to a second detector.

22. The system according to claim 1, wherein the detection of the non-photoluminescent light separately and simultaneously includes dark-field imaging, the detected photoluminescence includes fluorescence, the one or more illumination wavelengths include one or more ultraviolet wavelengths, and the detection subsystem comprises a dichroic beam splitter configured to direct the fluorescence to a first detector and the non-photoluminescent light to a second detector.

23. The system according to claim 1, wherein the detection of the non-photoluminescent light separately and simultaneously includes dark-field imaging, the detected photoluminescence includes fluorescence, the one or more illumination wavelengths include one or more blue wavelengths, and the detection subsystem comprises a dichroic beam splitter configured to direct the fluorescence to a first detector and the non-photoluminescent light to a second detector.

24. The system according to claim 1, wherein the BF illumination channel and the DF illumination channel each comprise a plurality of light sources configured to illuminate different channels of the system, and the detection subsystem comprises a plurality of detectors in the different channels each configured to be coupled to the BF illumination channel and the DF illumination channel and to acquire an image of the sample, the different channels being spatially separated on the sample.

25. The system according to claim 24, wherein a first channel of the different channels is configured for bright-field imaging, a second channel of the different channels is configured for dark-field imaging, and the first and second channels of the different channels are further configured to perform the bright-field imaging and the dark-field imaging simultaneously.

26. The system according to claim 25, wherein one of the plurality of light sources configured to illuminate the second channel and the third channel of the different channels comprises an ultraviolet light source, the third channel of the different channels is configured to detect the photoluminescence, and the detection subsystem further comprises a dichroic beam splitter configured to direct the non-photoluminescent light scattered from the sample to the second channel of the different channels and the photoluminescence to the third channel of the different channels.

27. ​​The system according to claim 25, wherein one of the plurality of light sources configured to illuminate the second channel and the third channel of the different channels comprises a blue light source, the third channel of the different channels is configured to detect the photoluminescence, and the detection subsystem further comprises a dichroic beam splitter configured to direct the non-photoluminescent light scattered from the sample to the second channel of the different channels and the photoluminescence to the third channel of the different channels.

28. The system according to claim 25, wherein one of the plurality of light sources configured to illuminate the first channel and the third channel of the different channels comprises an ultraviolet light source, the third channel of the different channels is configured to detect the photoluminescence, and the detection subsystem further comprises a dichroic beam splitter configured to direct the non-photoluminescent light specularly reflected from the sample to the first channel of the different channels and the photoluminescence to the third channel of the different channels.

29. The system according to claim 25, wherein one of the plurality of light sources configured to illuminate the first channel and the third channel of the different channels comprises a blue light source, the third channel of the different channels is configured to detect the photoluminescence, and the detection subsystem further comprises a dichroic beam splitter configured to direct the non-photoluminescent light specularly reflected from the sample to the first channel of the different channels and the photoluminescence to the third channel of the different channels.

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